Revision 3
Material Science
Student Guide
Approved by:
_
Chairperson, Industry OGF Working Group
Approved by:
5/17/2017
Date
5/17/2017
Manager, INPO Learning Development
Date
NOTE: Signature also satisfies approval of PowerPoint presentation and overview sheet.
GENERAL DISTRIBUTION
GENERAL DISTRIBUTION: Copyright © 2017 by the National Academy for Nuclear Training. Not for sale or
for commercial use. This document may be used or reproduced by Academy members and participants. Not
for public distribution, delivery to, or reproduction by any third party without the prior agreement of the Academy.
All other rights reserved.
NOTICE: This information was prepared in connection with work sponsored by the Institute of Nuclear Power
Operations (INPO). Neither INPO, INPO members, INPO participants, nor any person acting on behalf of them
(a) makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or
usefulness of the information contained in this document, or that the use of any information, apparatus, method,
or process disclosed in this document may not infringe on privately owned rights, or (b) assumes any liabilities
with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or
process disclosed in this document.
ii
Table of Contents
INTRODUCTION ..................................................................................................................... 2
TLO 1 METALLIC BONDING AND STRUCTURES FLUIDS ........................................................ 2
Overview .......................................................................................................................... 2
ELO 1.1 Metallic Bonding ............................................................................................... 3
ELO 1.2 Solid Material Properties................................................................................... 6
ELO 1.3 Metallic Lattice Structures .............................................................................. 10
ELO 1.4 Metallic Imperfections .................................................................................... 12
TLO 1 Summary ............................................................................................................ 16
TLO 2 METALLIC ALLOYS.................................................................................................. 18
Overview ........................................................................................................................ 18
ELO 2.1 Characteristics of Alloys ................................................................................. 18
TLO 2 Summary ............................................................................................................ 22
TLO 3 PHYSICAL AND CHEMICAL PROPERTIES OF METALS ................................................ 22
Overview ........................................................................................................................ 22
ELO 3.1 Physical and Chemical Properties of Metals ................................................... 23
ELO 3.2 Metal Treatments ............................................................................................ 31
TLO 3 Summary ............................................................................................................ 34
TLO 4 METAL CORROSION ................................................................................................. 35
Overview ........................................................................................................................ 35
ELO 4.1 General and Galvanic Corrosion ..................................................................... 36
ELO 4.2 Characteristics of Localized Corrosion ........................................................... 38
ELO 4.3 Hydrogen Embrittlement ................................................................................. 40
TLO 4 Summary ............................................................................................................ 43
TLO 5 DESCRIBE COMMON MATERIAL FAILURE MECHANISMS ......................................... 45
Overview ........................................................................................................................ 45
ELO 5.1 Material Failure Mechanisms .......................................................................... 45
TLO 5 Summary ............................................................................................................ 50
MATERIAL SCIENCE MODULE SUMMARY ........................................................................... 51
Knowledge Check Answer Key ....................................................................................... 1
ELO 1.1 Metallic Bonding ............................................................................................... 1
ELO 1.2 Solid Material Properties................................................................................... 1
ELO 1.3 Metallic Lattice Structures ................................................................................ 2
ELO 1.4 Metallic Imperfections ...................................................................................... 2
ELO 2.1 Characteristics of Alloys ................................................................................... 3
ELO 2.2 Stainless Steel.................................................................................................... 3
ELO 3.1 Physical and Chemical Properties of Metals ..................................................... 4
ELO 3.2 Metal Treatments .............................................................................................. 4
ELO 4.1 General and Galvanic Corrosion ....................................................................... 5
ELO 4.2 Characteristics of Localized Corrosion ............................................................. 5
ELO 4.3 Hydrogen Embrittlement ................................................................................... 6
ELO 5.1 Common Material Failure Mechanisms ............................................................ 6
iii
This page is intentionally blank.
iv
Material Science
Revision History
Revision
Date
Version
Number
Purpose for Revision
Performed
By
7/18/2016
0
New Module
OGF Team
5/17/2017
3
No changes made. Updated
revision number for
consistency – skipped
numbers 1 and 2.
OGF Team
Rev 3
1
Introduction
This module provides the student with basic concepts in material science.
Some of the topics include the following:









Bonding arrangement of atoms
Metal crystalline structures and lattices
Alloying
Stress and strain
Brittle and ductile properties
Metal working
Corrosion
Thermal stress and shock
Industrial material selection and failure mechanisms
Objectives
At the completion of this training session, the trainee will demonstrate
mastery of this topic by passing a written exam with a grade of 80 percent
or higher on the following Terminal Learning Objectives (TLOs):
1. Describe the bonding, structures, and imperfections found in solid
materials.
2. Describe the basic microstructure and characteristics of metallic
alloys.
3. Describe physical and chemical properties of metals and methods
used to modify these properties.
4. Describe the considerations commonly used when selecting material
for use in an industrial facility and common material failure
mechanisms.
5. Describe common material failure mechanisms.
TLO 1 Metallic Bonding and Structures Fluids
Overview
The bonding arrangement of atoms determines a material’s behavior and
properties. In this module, the term material specifically describes metals,
the chief construction material in reactor plants.
Metals consist of crystalline structures, arranged in three-dimensional arrays
called lattices on a molecular level. Crystalline structures appear as grains
in the metal under a microscope. The characteristics of these lattice
structures, grains, and boundaries between grains determine the metal's
characteristics.
Rev 3
2
Objectives
Upon completion of this lesson, you will be able to do the following:
1. Describe the types of bonding that occur in materials.
2. Describe the following types and features of solids:
a. Amorphous
b. Crystalline solids
c. Grain structures
3. Describe the following lattice-type structures that occur in metals:
a. Body-Centered Cubic (BCC)
b. Face-Centered Cubic (FCC)
c. Hexagonal Close-Packed (HCP)
4. Describe the various imperfections that occur in solid materials.
ELO 1.1 Metallic Bonding
Introduction
Matter exists primarily in three states: solid, liquid, and gas. Atomic and
molecular bonding and structures occurring within a substance determine its
state. The focus of this lesson focuses on the solid state of materials
because metallic solids are of greatest concern for our purposes.
Metallic Bonding
Forces between neighboring atoms or molecules bond atoms or molecules
together to form solid matter. These forces exist from differences in the
electron clouds of atoms. Valence electrons, those in the atom’s outer shell,
determine an atom's attraction to its neighboring atom.
When the physical attraction between the molecules or atoms of a material
is great, these tight bonds create solid materials. Weaker attractions
produce liquids; gases exist when there are virtually no attractive forces
between the atoms or molecules.
Types of Bonds
The way atomic forces hold matter together determines the type of bond.
The following list includes examples of several types of bonds and their
characteristics:

Rev 3
Ionic bond: where one or more electrons completely transfers from
an atom of one element to the atom of another. The force of attraction
due to the opposite polarity of the charge holds the element together.
An example of an ionic bond is shown in the following figure.
3
Figure: Ionic Bond for Sodium Chloride

Covalent bond: the bond formed by shared electrons, shown below
in the graphic. In this instance, when an atom needs electrons to
complete its outer shell it shares those electrons with its neighboring
atom. The electrons become a part of both atoms, filling both atoms'
electron shells.
Figure: Covalent Bond for Methane

Metallic bond: the atoms do not share or exchange electrons to bond
together. Many electrons, roughly one for each atom, are more or less
free to move throughout the metal; each electron can interact with
many of the fixed atoms. The graphic below shows an example of a
metallic bond.
Figure: Metallic Bond for Sodium

Rev 3
Molecular bond: a temporary weak charge exists when electrons of
neutral atoms spend more time in one region of their orbit than in
another region. The molecule weakly attracts other molecules. This
molecular bond also called a van der Waals bond, shown in the
following graphic.
4
Figure: Van Der Waals Forces

Hydrogen bond: shown below in the graphic and similar to the
molecular bond, a hydrogen bond occurs because of the ease with
which hydrogen atoms are willing to give up an electron to atoms of
oxygen, fluorine, or nitrogen.
Figure: Hydrogen Bond for Ice
Examples of Materials and Bonds
The following table shows examples of both materials and their bonds.
Graphics showing each of these types of bonds are on the previous two
pages.
Examples of Materials and Their Bonds
Material
Bond
Sodium Chloride (Table Salt)
Ionic
Diamond
Covalent
Sodium
Metallic
Solid Hydrogen
Molecular
Ice (Frozen Water)
Hydrogen
The type of bond determines both the tightness as well as the microscopic
properties of the metal material. For example, properties such as the ability
to conduct heat or electrical current relate to the freedom of electron
Rev 3
5
movement in the material. Understanding a material’s microscopic
structure helps predict how that material behaves under specific conditions.
Additionally, synthetically fabricated materials with a given microscopic
structure yield certain desirable properties for specific applications.
Metallic bonds affect the physical properties of metals including factors
such as luster, strength, ductility, electrical conductivity, thermal
conductivity, and opacity.
Knowledge Check (Answer Key)
This type of bond is characterized by the transference
of one or more electrons from one atom to another.
A.
Covalent
B.
Ionic
C.
Molecular
D.
Electronic
ELO 1.2 Solid Material Properties
Introduction
Solids have greater bonding attractions through their bonding arrangements
than do liquids and gases. However, there are many other property
variations of solid materials. These material properties depend on interatomic bonding. These bonds also dictate spacing and physical
arrangement between atoms in solids. Amorphous or crystalline are
classifications used for these physical arrangements for solids.
Amorphous Materials
Amorphous materials have an irregular arrangement of atoms or molecules;
they exhibit properties of solids. Amorphous solids do not have a repeating
crystalline structure. These materials have definite shape and volume and
diffuse slowly; however, they lack sharply defined melting points. As
solids, they resemble liquids that flow slowly at room temperature. Glass
and paraffin are examples of amorphous materials. Other examples of
amorphous materials include thin gels and thin films.
Crystalline Solids
Arrays of atoms in regular patterns create crystal structures in metals and
other solids. Crystalline structures have repeating units of atoms, ions, and
molecules. A crystal structure has atoms arranged in a pattern that repeats
Rev 3
6
periodically in a three-dimensional geometric lattice. Forces associated
with chemical bonding result in this repetition and produce properties such
as strength, ductility, density, conductivity, and shape. Ductility is the
metal’s ability to bend.
Grain Structure and Boundary
Examining a thin section of a common metal under a microscope illustrates
the molecular structure similar to that shown below in the figure. Each of
the light areas is a grain, or crystal, which is the region of space occupied by
a continuous crystal lattice. Grain boundaries are the dark lines surrounding
the grains. The term grain structure refers to the arrangement of the grains
in a metal. Each grain has a particular crystal structure determined by the
type of metal and its composition.
Figure: Grain Structure
Grain Boundary
The grain boundary is the outside area of a grain separating it from the other
grains. The grain boundary is a region of misfit or interface between grains
and is usually one-to-three atom diameters wide. Grain boundaries
arbitrarily separate oriented crystal regions (polycrystalline) where the
crystal structures are identical. The figure on the next page represents four
grains of different orientation and the grain boundaries that develop at the
interfaces between the grains.
Rev 3
7
Figure: Grain Boundaries
Grain Size
The average size of the grain is important to a metal's characteristics
because it determines the properties of the metal. Smaller grain size
increases tensile strength and tends to increase ductility. A larger grain size
is preferred for improved high-temperature creep properties. Creep is the
permanent deformation of a metal that increases with time under constant
load or stress, accelerated normally with increasing temperature. More
information about the mechanisms of creep is provided later in this module
in TLO 9.
Grain Orientation
Another important property of the grains found in metals is their
orientation. One example is the random arrangement of the grains such that
no one direction within the grains aligns with the external boundaries of the
metal sample. Cross rolling the metal material during its manufacturing
process results in this grain orientation, shown in the figure below.
Figure: Grain Random Arrangement
Rev 3
8
The figure below shows a grain-oriented structure developed from over
rolling a metal sample in one direction when processing the metal. Rolling
a metal in this manner results in a metal where the grains have a preferred
orientation. In many cases, preferred orientation is desirable, but in other
instances, it can be undesirable. The choice depends on the metal's
application or the way it is used.
Figure: Grain Preferred Arrangement
Grain preferred arrangement is another configuration of the properties
found in metals. A grain preferred arrangement or orientation shows the
texture of the metal and its crystals. The metal’s texture includes materials
properties such as strength, chemical reactivity, stress corrosion cracking
resistance, deformation behavior, weldability (whether the metal can be
welded), resistance to radiation damage, and magnetic susceptibility.
Knowledge Check (Answer Key)
The outside area of a grain that separates it from other
grains in a metal is known as _______________.
A. grain structure
B.
crystal boundary
C.
grain boundary
D. crystal structure
Rev 3
9
ELO 1.3 Metallic Lattice Structures
Introduction
Metals have lattice structures to show or hold their crystals. While there are
seven crystal shapes, there are 14 different crystal lattices for metals. The
three basic crystal patterns associated with metals discussed in this lesson
are:



Body-Centered Cubic (BCC)
Face-Centered Cubic (FCC)
Hexagonal Close-Packed (HCP)
Body-Centered Cubic
The unit cell consists of eight atoms at the corners of a cube and one atom
at the body center of the cube in a body-centered cubic (BCC) arrangement
of atoms.
Metals such as α-iron (Fe) (ferrite), chromium (Cr), vanadium (V),
molybdenum (Mo), and tungsten (W) possess BCC structures. These BCC
metals have two properties in common, high-strength and low-ductility.
Figure: Body-Centered Cubic Unit Cell
Face-Centered Cubic
In a face-centered cubic (FCC) arrangement of atoms, the unit cell consists
of eight atoms at the corners of a cube and one atom at the center of each of
the faces of the cube.
Some FCC metals include γ-iron (Fe) (austenite), aluminum (Al), copper
(Cu), lead (Pb), silver (Ag), gold (Au), nickel (Ni), platinum (Pt), and
thorium (Th). These FCC metals generally have lower strength and higher
ductility than BCC metals.
Figure: Face-Centered Cubic Unit Cell
Rev 3
10
BCC and FCC Iron Structures Differ
Note
Although drawn similarly in size, most diagrams
of the structural cells for the BCC and FCC forms
of iron are not equal in size.
In the BCC arrangement, the structural cell, which
uses only nine atoms, is smaller than the structure
found in the FCC arrangement using fourteen
atoms.
Hexagonal Close-Packed
The unit cell consists of three layers of atoms in a hexagonal close-packed
(HCP) arrangement of atoms. The top and bottom layers each contain six
atoms at the corners of a hexagon and one atom at the center of each
hexagon. The middle layer contains three atoms nestled between the atoms
of the top and bottom layers, therefore, the name close-packed.
Metals with HCP structures include beryllium (Be), magnesium (Mg), zinc
(Zn), cadmium (Cd), cobalt (Co), thallium (Tl), and zirconium (Zr). HCP
metals are not as ductile as FCC metals.
Figure: Hexagonal Close-Packed Unit Cell
Rev 3
11
Knowledge Check (Answer Key)
Which of the following basic crystal patterns has the
greatest number of atoms per unit cell?
A.
BCC
B.
FCC
C.
HCP
D.
HCC
ELO 1.4 Metallic Imperfections
Introduction
Materials such as metals do not have perfectly formed crystal structures, nor
are they free of impurities that alter their properties. Even amorphous solids
have imperfections and impurities within their crystal structure.
Imperfections and impurities, known as crystallographic defects, interrupt
the regular patterns of crystal structures.
Uranium is an example of a metal that exhibits polymorphism. Depending
on temperature, metallic uranium exists with three different crystalline
structures: orthorhombic, tetragonal, or body centered cubic.
Imperfections exist within the crystal structures of minerals and metals.
Three types of crystallographic defects are point imperfections, line
imperfections or dislocations, and interfacial imperfections.

Point imperfections have atomic dimensions. For example, an atom
of a different element replaces an atom of a metal in that specific
metal's crystalline lattice. Point defects are found only at or near a
single lattice point and do not extend in any direction or dimension.
 Line imperfections or dislocations are generally many atoms in length
and occur where the some of the atoms in the crystal are misaligned.
 Interfacial imperfections are larger than line defects, and they occur
over a two-dimensional area.
Point Imperfections
Point imperfections within the crystalline structure include the following
three defects:



Rev 3
Vacancy defects
Substitutional defects
Interstitial defects
12
The presence of point defects either enhances or decreases the usefulness of
a material for construction, depending on the intended use of the material.
The figure below illustrates these three types of defects.
Figure: Point Defects
Vacancy Defects
Vacancy defects, the simplest defect, result from a missing atom in a lattice
position. This defect results from imperfect packing during the
crystallization process, or may be due to increased thermal vibrations of the
atoms from elevated temperatures.
Substitutional Defects
Substitutional defects result from an impurity present at a lattice position.
An alloying material added to the metal, such as carbon (carbon steel)
creates an impurity at a lattice position. Alloys are discussed in more detail
later in this module.
Interstitial Defects
Interstitial refers to locations between atoms in a lattice structure. They
result from an impurity located at an interstitial site or one of the lattice
atoms being in an interstitial position instead of its lattice position.
Interstitial impurities called network modifiers act as point defects in
amorphous solids.
Line Imperfections
Line imperfections, also called dislocations, occur only in crystalline
materials. There are three types of line imperfections. These include edge,
screw, or mixed, depending on the way they distort the lattice. Dislocations
cannot end inside a crystal; they must end at a crystal edge or other
dislocation, or close back on itself. The ease with which the line
imperfections move through crystals determines their importance.
Rev 3
13
Edge Dislocations
Edge dislocations consist of an extra row or plane of atoms in the crystal
structure, shown below in the figure. The imperfection may extend in a
straight line all the way through the crystal, or it may follow an irregular
path. The edge dislocation may be short, extending only a small distance
into the crystal causing a slip of one atomic distance along the glide plane
(direction the edge imperfection is moving).
Figure: Edge Dislocation
The slip occurs when stress acts on the crystal, and the dislocation moves
through the crystal until it reaches the edge or becomes arrested by another
dislocation. The figure below shows a series of edge dislocations as a
crystal deforms. Position 1 shows a normal crystal structure. Position 2
shows a force applied from the left side and a counterforce applied from the
right side. Positions 3 to 5 show the structure slipping. Position 6 shows
the final deformed crystal structure. The slip of one active plane ordinarily
extends 1,000 atomic distances. Slip on many planes produces yielding,
leading to separation of the material.
Figure: Slips Along Edge Dislocations
Rev 3
14
Screw Dislocations
Screw dislocations develop by a tearing of the crystal parallel to the slip
direction. A screw dislocation makes a complete circuit, shows a slip
pattern similar in shape to that of a screw thread, whether left- or righthanded. It is necessary for some of the atomic bonds to re-form
continuously such that after yielding to this location, the crystal returns to
the original form in order for another screw dislocation to occur.
Figure: Screw Dislocation
Mixed Dislocations
The orientation of dislocations varies from pure edge to pure screw, and at
some intermediate point, dislocations may possess characteristics of each.
Macroscopic (Bulk) Material Defects
Bulk defects are three-dimensional macroscopic material defects. They
generally occur on a much larger scale than microscopic defects, usually
introduced into a material during refinement from its raw state or during the
material's fabrication processes.
The most common bulk defect arises from inclusion of foreign particles in
the prime material. Called inclusions, they undesirably alter the material's
structural properties. Examples of inclusions include oxide particles in a
pure metal or a bit of clay in a glass structure.
Other bulk defects include gas pockets or shrinking cavities generally found
in castings. These defects weaken the material and fabrication techniques.
If possible, minimize these.
Working and forging of metals can cause cracks that act as stress
concentrators resulting in material weakening. Welding or joining defects
also classify as bulk defects.
Rev 3
15
Knowledge Check (Answer Key)
Vacancy defects, substitutional defects, and interstitial
defects are examples of _______________.
A.
line imperfections
B.
point imperfections
C.
interfacial imperfections
D.
bulk defects
TLO 1 Summary
 Ionic bond: an atom with one or more electrons wholly transferred
from one element to another. Elements hold together by the force of
attraction due to the opposite polarity of the charge.
 Covalent bond: an atom that needs more electrons to complete its
outer shell also and which shares those electrons with its neighbor.
 Metallic bond: atoms do not share or exchange electrons to bond
together. Instead, many electrons (roughly one for each atom) are
more or less free to move throughout the metal, so that each electron
can interact with many of the fixed atoms.
 Molecular bond: when neutral atoms undergo shifting in the centers
of their charge, they can weakly attract other atoms with displaced
charges. A molecular bond is also a van der Waals bond.
 Hydrogen bond: similar to the molecular bond, this occurs due to the
ease with which hydrogen atoms displace their charge.
 Amorphous microstructures: lack sharply defined melting points
and do not have an orderly arrangement of particles. Solids act as
liquids.
 Lattices: crystalline microstructures arranged in three-dimensional
arrays.
 Crystal structure: consists of atoms arranged in a periodically
repeating pattern in a three-dimensional geometric lattice.
— Body-Centered Cubic structure (BCC): an arrangement of
atoms where the unit cell consists of eight atoms at the corners
of a cube and one atom at the body center of the cube.
o Metals with BCC structures include ferrite, chromium,
vanadium, molybdenum, and tungsten.
o BCC metals possess high strength and low ductility.
— Face-Centered Cubic structure (FCC): an arrangement of
atoms where the unit cell consists of eight atoms at the corners
of a cube and one atom at the center of each of the six faces of
the cube.
o Metals with FCC structures include austenite, aluminum,
copper, lead, silver, gold, nickel, platinum, and thorium.
Rev 3
16







o FCC metals possess low strength and high ductility.
— Hexagonal Close-Packed structure (HCP): an arrangement of
atoms where the unit cell consists of three layers of atoms. The
top and bottom layers contain six atoms at the corners of
hexagon and one atom at the center of each hexagon. The
middle layer contains three atoms nestled between the atoms of
the top and bottom layers.
o Metals with HCP structures include beryllium,
magnesium, zinc, cadmium, cobalt, thallium, and
zirconium.
o HCP metals are not as ductile as FCC metals.
Body-Centered Cubic structure (BCC): an arrangement of atoms
where the unit cell consists of eight atoms at the corners of a cube and
one atom at the body center of the cube.
Grain structure: the arrangement of grains in a metal. The grains
composing a specific metal have a particular crystalline structure.
Grain boundary: outside area of a grain that separates it from other
grains.
Face-Centered Cubic structure (FCC): an arrangement of atoms in
which the unit cell consists of eight atoms at the corners of a cube and
one atom at the center of each of the six faces of the cube.
Microscopic imperfections:
— Point imperfections are in the size range of individual atoms.
— Line (dislocation) imperfections are generally many atoms in
length.
o Line imperfections can be of the edge type, screw type,
or mixed type, depending on lattice distortion.
o Line imperfections cannot end inside a crystal; they must
end at crystal edge or other dislocation, or close back on
themselves.
— Interfacial imperfections are larger than line imperfections and
occur over a two dimensional area.
o Interfacial imperfections exist at free surfaces, domain
boundaries, grain boundaries, or interphase boundaries.
Slip transpires when stress occurs to the crystal, and the dislocation
moves through the crystal until it reaches the edge or arrested by
another dislocation.
Bulk (Macroscopic) defects are three-dimensional defects.
— Foreign particles included in the prime material (inclusions) are
most common bulk defect.
— Gas pockets
— Shrinking cavities
— Welding or joining defects
Objectives
Now that you have completed this lesson, you should be able to do the
following:
1. Describe the types of bonding that occur in materials.
Rev 3
17
2. Describe the following types and features of solids:
a. Amorphous
b. Crystalline solids
c. Grain structures
3. Describe the following lattice-type structures that occur in metals:
a. Body-Centered Cubic (BCC)
b. Face-Centered Cubic (FCC)
c. Hexagonal Close-Packed (HCP)
4. Describe the various imperfections that occur in solid materials.
TLO 2 Metallic Alloys
Overview
Most of the materials used in power plant construction are metals. Alloying
is a common practice of obtaining metals with more preferable properties
for use in certain applications than pure unalloyed materials. The alloying
process has been available and used for thousands of years. For example,
the creation of bronze alloyed from copper and tin started about 2,500 BC.
Some other metallic alloys include brass, phosphor bronze, pewter, brass,
solder, or steel.
Objectives
Upon completion of this lesson, you will be able to do the following:
1. Describe the common characteristics of alloys.
2. Identify the desirable properties of type 304 stainless steel.
ELO 2.1 Characteristics of Alloys
Introduction
An alloy is a mixture of two or more materials, of which at least one is a
metal. Alloy microstructures consist of solid solutions, where secondary
atoms combine as substitutionals or interstitials in a crystal lattice. An alloy
might also be a crystal with a metallic compound at each lattice point.
Alloys may also be composed of secondary crystals imbedded in a
primary polycrystalline matrix, called a composite. The term composite
does not necessarily imply that the component materials are metals.
Metallic bonds are also present in alloys.
Characteristics of Alloys
Alloys are usually stronger than pure metals, although generally with
reduced electrical and thermal conductivity. Strength is one of the most
important criteria for judging many structural materials. Therefore, for
industrial construction normally the preferred choice is alloy over pure
metals. Steel, a common structural metal, is an example of an alloy. Steel
alloy consists of iron and carbon, and other elements combined to produce
Rev 3
18
structurally desirable properties. Another interesting example of an alloy is
aluminum and copper, both are soft and ductile, but when alloyed the result
is much harder and stronger.
It is sometimes possible for a material to be composed of several solid
phases. Creating a solid structure composed of two interspersed phases
enhances the strengths of each.
When a material is an alloy, it is possible to quench the metal from its
molten state in order to form the interspersed phases. We discuss
quenching in more detail later in this module; however, the type and rate of
quenching determines the material’s final solid structure as well as its
properties.
Composition of Common Engineering Materials
The variety of structures, systems, and components found in industrial
applications require many different types of materials. A large percentage
of these materials are alloys using a base metal of iron or nickel and other
metals. Selection of a material for a specific application requires
consideration of many factors including where and how the metal will
function. Some of the more common considerations include:






Temperature and pressure
Resistance to specific types of corrosion
Radiation influence
Toughness and hardness (load and/or creep)
Weight
Other applicable material properties
Knowledge Check (Answer Key)
Which one of the following is NOT a characteristic of
an alloy?
Rev 3
A.
Usually stronger than pure metals.
B.
Generally have reduced electrical and thermal
conductivity.
C.
Usually have better ductility than pure metals.
D.
Usually preferred for industrial construction over pure
metals.
19
ELO 2.2 Stainless Steel
Introduction
One material that has wide application in nuclear power plants is stainless
steel. There are nearly 40 standard types of stainless steel and many other
specialized types under various trade names Through the variations of
alloying elements, steel, whether stainless another types, can be adapted to
specific applications.
Stainless Steel Details
Based on lattice structure, stainless steel's primary classifications are
austenitic or ferritic.

Austenitic stainless steels, including types 304 and 316, have a facecentered cubic structure of iron atoms with the carbon in interstitial
solid solution. Type 304 stainless steel is an alloy of chromium and
nickel that resists oxidation as well as corrosion. Type 316 stainless
steel is composed of chromium, nickel, and molybdenum, which
results in greater resistance to chemical corrosive factors.
 Ferritic stainless steels, including type 405, have a body-centered
cubic iron lattice and contain no nickel. Ferritic steel is easier to
weld and fabricate and less susceptible to stress corrosion and
cracking than austenitic stainless steels. Ferritic steel only has
moderate resistance to other types of chemical attack.
Another durable metal that has specific applications in some industrial
facilities is INCONEL®, a family of austenitic nickel and chromium based
alloys trademarked by the Hartford, New York-based Special Metals
Corporation. Inconel alloys resist oxidation and corrosion in extreme
environmental service conditions. Inconel is well suited in hightemperature applications. The table on the following page shows the
composition of Inconel and stainless steel variants.
Rev 3
20
Alloy Composition of Common Stainless Steels and INCONEL®
Alloy
Percent
Iron
(Fe)
Percent
Carbon
(C)
Percent
Chromium
(Cr)
Percent
Nickel
(Ni)
Percent
Molybdenum
(Mo)
Percent
Manganese
(Mn)
Percent
Silicon
(Si)
304
Stainless
Steel
Balanced
0.08
19.0
10.0
N/A*
2.0
1.0
304 L
Stainless
Steel
Balanced
0.03
18.0
8.0
N/A
2.0
1.0
316
Stainless
Steel
Balanced
0.08
17.0
12.0
2.5
2.0
1.0
316 L
Stainless
Steel
Balanced
0.03
17.0
12.0
2.5
2.0
N/A
405
Stainless
Steel
Balanced
0.08
13.0
N/A
N/A
1.0
1.0
INCONEL
8
N/A
15.0
Balanced
N/A
1.0
0.5
®
*N/A means not applicable.
Type 304 Stainless Steel
Type 304 stainless steel, which contains 18 to 20 percent chromium and 8
to 10.5 percent nickel, is extremely tough and corrosion resistant. Used
extensively in applications where corrosion is a concern, Type 304 Stainless
Steel resists most, but not all, types of corrosion.
Knowledge Check (Answer Key)
What are the two desirable characteristics of Type 304
Stainless Steel? ___________ and ___________
Rev 3
A.
high temperature tolerant; toughness
B.
corrosion resistance; toughness
C.
cubic iron lattice; corrosion resistance
D.
corrosion resistance; contains no nickel
21
TLO 2 Summary
 An alloy is a mixture of two or more materials, at least one of which
is a metal.
 Alloy microstructures include some of the following characteristics:
— Solid solutions: introduces secondary atoms as substitutional or
interstitials in a crystal lattice.
— Crystal: metallic bonds
— Composites: where secondary crystals are embedded in a
primary polycrystalline matrix.
 Alloys are usually stronger than pure metals although alloys generally
have reduced electrical and thermal conductivities.
 The two desirable properties of type 304 stainless steel are corrosion
resistance and high toughness.
Objectives
Now that you have completed this lesson, you should be able to do the
following:
1. Describe the common characteristics of alloys.
2. Identify the desirable properties of type 304 stainless steel.
TLO 3 Physical and Chemical Properties of Metals
Overview
Material selection for various applications in power plants depends on the
physical and chemical properties associated with those materials. It is
possible to change the properties of metals by metallurgical processes such
as heat treatment and the hot and cold working of metal. Personnel need to
understand the effects of these processes on metals to recognize the
selection of materials used in industrial systems and facilities.
Objectives
Upon completion of this lesson, you will be able to do the following:
1. Describe the following terms:
a. Strength
2. Ultimate tensile strength
3. Yield strength
b. Ductility
c. Malleability
d. Toughness
e. Hardness
4. Describe the following types of treatments used on metals:
5. Heat treatment
a. Cooling (Quenching)
b. Annealing
6. Cold working
7. Hot working
Rev 3
22
ELO 3.1 Physical and Chemical Properties of Metals
Introduction
Metal properties use many terms to describe and quantify their strengths
and weakness. Previous lessons in this module gave a basic overview of
some of these. This lesson adds to that knowledge.
Strength
Strength is the ability of a material to resist deformation. The strength
requirements of a structure equal the maximum load that can be borne
before failure occurs.
Determining a Material's Strength
Permanent deformation or plastic strain generally takes place in a
component before failure when under tension. The load-carrying capacity
of the material at the instant of failure is probably less than the maximum
load the material can support at a lower strain. This failure occurs because
the load spreads over a significantly smaller cross-section of the metal as
the deformation of the material takes place.
Conversely, under compression, the load at fracture is the maximum
applicable over a significantly enlarged area due to compression of the
material compared to the cross-sectional area without a load.
This nominal stress is included in quoting the strength of a material and
qualified by the type of stress applied, such as tensile strength, compressive
strength, or shear strength. Compressive strength equals the tensile strength
for most structural materials. This is a safe assumption because the nominal
compression strength is always greater than the nominal tensile strength
because of the increase in effective cross sectioning during compression.
Strength and Slip
Grain boundaries in metals prevent slip. The smaller the grain sizes yield,
the larger the grain boundary areas. Decreasing the grain size through cold
or hot working of the metal tends to retard slip, and thereby increases the
strength of the metal.
Ultimate Tensile Strength
The ultimate tensile strength (UTS) is the maximum resistance a material
presents to fracture. It is equivalent to the maximum load capability of one
square inch of cross-sectional area with the load applied as simple tension.
𝑈𝑇𝑆 =
Rev 3
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑙𝑜𝑎𝑑
𝑃𝑚𝑎𝑥
=
= 𝑝𝑠𝑖
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
𝐴𝑜
23
The ultimate tensile strength appears as the stress coordinate value of the
highest point on the curve on a stress-strain curve shown below in the
figure.
Figure: Stress-Strain Curve
Materials that elongate greatly before breaking undergo a large reduction of
cross-sectional area so that the material carries less of the load in the final
stages of the tensile test, which accounts for the stress decrease shown on
the curve between points 4 and 5. The stress decreases since we use the
original cross-sectional area in stress calculations and the cross-sectional
area decreases.
Necking appears when large amounts of strain or instability happen in a
local cross-section of a material and the material hardens during the
deformation prior to its failure. This creates the basis for the name necking
because stress creates a narrowed part in a material, similar to a person’s
neck .
Yield Strength
Yield strength is the term for identifying the stress where plastic
deformation starts. The yield strength is the stress where a predetermined
amount of permanent deformation occurs.
Determining Yield Strength
The graphic below shows a portion of the early stages of a tension test
evaluating yield strength. The predetermined amount of permanent strain is
set along the strain axis of the graph, to the right of the origin zero (0) on
the axis, shown as Point D in the figure on the next page, to find yield
strength.
Rev 3
24
Figure: Brittle Material Stress-Strain Curve
Draw a straight line through Point D at the same slope as the initial portion
of the stress-strain curve, and extend it to meet the stress-strain curve. The
intersection of the new line and the stress-strain curve is the yield strength,
shown as Point 3 of the above figure. This method allows us to subtract the
elastic strain from the total strain, leaving the predetermined permanent
offset as a remainder. Stated yield strength includes the amount of offset.
For example, Yield strength (at 0.2 percent offset) = 51,200 psi.
Examples of Yield Strength
Yield strength varies according to the material or the metal. The below list
shows example of the yield strengths for some metals:



Aluminum: 3.5 x 104 to 4.5 x 104 psi
Stainless steel: 4.0 x 104 to 5.0 x 104 psi
Carbon steel: 3.0 x 104 to 4.0 x 104 psi
Yield Point
Yield point is the identified position in the stress-strain curve when visible
stretch and plastic deformation first occur.
Rev 3
25
Proportional Limit
The proportional limit is the stress at which the stress-strain curve first
deviates from a straight line. The ratio of stress to strain is constant, and the
material follows Hooke's Law, stress is proportional to strain, below this
limiting value of stress. Proportional limits often are not utilized in
specifications because the deviation begins so gradually that controversies
appear concerning the exact stress where the line begins to curve.
Elastic Limit
The elastic limit, previously defined, is the stress at which plastic
deformation starts. This limit cannot be accurately determined from the
stress-strain curve.
Maximum Shear Stress
Yield strength identifies the maximum allowable stress a material can
withstand. However, for components that have to withstand high pressures,
such as those used in pressurized steam generating facilities, this criterion is
not adequate. The American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code incorporates these measures.
Ductility
Glossary
Ductility is the ability of a material to deform easily on
the application of a tensile force, or the ability of a
material to withstand plastic deformation without
rupturing. Ductility also considers factors such as
bendability and crushability.
Ductile materials demonstrate great deformation before
fracturing. Usually if two materials have the same
strength and hardness, the one with the higher ductility
is more desirable for engineering applications.
Rev 3
26
Ductility Determination
The percent elongation reported in a tensile test is the maximum elongation
of the gauge length divided by the original gauge length.
Figure: Elongation after Failure
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑒𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 =
=
𝑓𝑖𝑛𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ − 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ
𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ
𝐿𝑥 − 𝐿𝑜
= 𝑖𝑛𝑐ℎ𝑒𝑠 𝑝𝑒𝑟 𝑖𝑛𝑐ℎ × 100
𝐿𝑜
Reduction of area is the proportional reduction of the cross-sectional area of
a tensile test piece at the plane of fracture measured after fracture.
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑎𝑟𝑒𝑎 (𝑅𝐴)
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 − 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑓𝑖𝑛𝑎𝑙 𝑎𝑟𝑒𝑎
=
𝑎𝑟𝑒𝑎 𝑜𝑓 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛
=
𝐴𝑜 − 𝐴𝑚𝑖𝑛 𝑑𝑒𝑐𝑟𝑒𝑎𝑠𝑒 𝑖𝑛 𝑎𝑟𝑒𝑎 𝑠𝑞𝑢𝑎𝑟𝑒 𝑖𝑛𝑐ℎ𝑒𝑠
=
=
× 100
𝐴𝑜
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑎𝑟𝑒𝑎
𝑠𝑞𝑢𝑎𝑟𝑒 𝑖𝑛𝑐ℎ𝑒𝑠
The reduction of area is additional information to the percent elongation for
the deformational characteristics of the material. These two characteristics
indicate ductility, the ability of a material to elongate in tension. Because
the elongation is not uniform over the entire gauge length and is greatest at
the center of the neck, the percent elongation is not an absolute measure of
ductility. The reduction of area, measured at the minimum diameter of the
neck, is a better indicator of ductility.
Rev 3
27
Changes in Ductility
The ductility of many metals changes with altering conditions. Increasing
temperature increases ductility. Decreasing temperature decreases ductility
and potentially changes the material to brittle behavior from ductile
behavior. Radiation, also known as neutron radiation, changes ductility.
Materials become more brittle with greater amounts of radiation exposure.
Cold working makes metals less ductile. Cold working occurs at a
particular temperature region over a particular time interval to obtain plastic
deformation without relieving strain hardening. Strain hardening, another
term for work hardening, also strengthens metal by plastic deformation.
Annealing is heating a cold worked metal to or above the temperature at
which metal atoms return to their equilibrium positions, increasing the
ductility of that metal.
Minor additions of impurities to metals markedly influence the change to
brittle behavior from ductile behavior.
Advantages of Ductile Material
Ductility is a desirable factor in high-temperature and high-pressure
industrial applications because of increased stresses on the metals. High
ductility in these applications helps prevent failure by brittle fracture.
Malleability
Where ductility is a material's ability to deform easily on the application of
a tensile force, malleability is a metal’s ability to exhibit large deformation
or plastic response when subjected to compressive force. Uniform
compressive force causes deformation by compressive force as shown in the
figure below.
Figure: Malleable Deformation of a Cylinder under Uniform Axial
Compression
Rev 3
28
Deformation by Compression
Applying compressive force causes the material’s contraction axially with
the force and laterally as compression increases. Restraint due to friction at
the contact faces induces axial tension on the outside of the material.
Tensile forces operate around the circumference concurrent with lateral
expansion or increasing girth. Plastic flow at the center of the material also
induces tension. Because of these factors and the criterion of fracture, the
limit of plastic deformation for a ductile material depends on tensile rather
than compressive stress.
Changes In Malleability
Temperature change may modify both the plastic flow mode and the
fracture mode of a material, changing a material's malleability.
Toughness
Toughness describes the way a material reacts under sudden impacts.
Toughness is the work required to deform one cubic inch of metal until it
fractures.
Material Toughness Tests
The Charpy test and the Izod impact strength test measure toughness. Both
tests use a notched sample. The location and V-shaped notch are standard.
The points of support of the sample and the impact of the hammer must
bear a constant relationship to the location of the notch.
These tests mount metal samples in a device like the one shown below in
the figure. A pendulum of a known weight falls freely from a set height and
strikes the sample.
Figure: Charpy V-Notch Test
Rev 3
29
The maximum energy developed by the hammer is 120 ft/lb in the Izod Test
and 240 ft/lb in the Charpy Test. The energy absorbed by the specimen
limits the upward swing of the pendulum after fracturing the material
specimen. The greater the amount of energy absorbed by the specimen, the
smaller the upward swing of the pendulum and the tougher the material.
Toughness Test Results
Toughness is relative and applies only to instances involving exactly this
type of sample and method of loading. A sample of a different shape yields
an entirely different result. Notches confine the deformation to a small
volume of metal that reduces toughness. In effect, the shape of the metal
and the material composition determine the toughness of the material.
Hardness
Hardness is the property of a material enabling its resistance to plastic
deformation, penetration, indentation, and scratching. Hardness is
important from an engineering standpoint because resistance to wear by
friction or erosion from steam, oil, water flow, and so forth, generally
increases with hardness.
Hardness Test
Hardness tests serve an important need in industry even though they do not
measure a unique quality that can be termed hardness. Several methods
exist for hardness testing. Those most often used include the following:






Brinell Test
Rockwell Test
Vickers Test
Tukon Test
Sclerscope Test
Files Test
The first four tests employ indentations in the material. The Sclerscope
Test uses the rebound height of a diamond-tipped metallic hammer. The
Files Test establishes the harness of a material by determining how well a
new file of a proven hardness abrades the material’s surface.
Nickel
Nickel is an important alloying element because it increases the toughness
and ductility of steel without increasing its hardness when used in
concentration of less than 5 percent. Nickel will not increase the hardness
when added in small quantities because it does not form solid carbon
compounds (carbides).
Rev 3
30
Chromium
Chromium alloyed in steel creates carbide that hardens the metal. The
chromium atoms may also occupy locations in the metal's crystalline lattice,
increasing the metal’s hardness without affecting its ductility. A nickel and
chromium alloy intensifies the effects of chromium, resulting in steel with
increased hardness and ductility.
Stainless steels, characteristically resistant to many corrosive conditions, are
alloyed steels containing at least 12 percent chromium.
Copper
Copper’s effect on steel is similar to that of nickel. Copper does not form a
carbide; however, it increases hardness by retarding dislocation movement
within the metal's crystalline lattice.
Molybdenum
When added to steel, molybdenum forms a complex carbide. Because of
the structure of the carbide, molybdenum hardens steel substantially and
minimizes grain enlargement. Molybdenum augments the desirable
properties of both nickel and chromium when alloyed in steel.
Knowledge Check (Answer Key)
_______________ is a material's maximum resistance
to fracture.
A.
Strength
B.
Yield Strength
C.
Ductility
D.
Ultimate tensile strength
ELO 3.2 Metal Treatments
Introduction
Heat treatment and the working of metal are metallurgical processes used to
change the properties of metals. A basic understanding of these methods
helps with understanding how metal treatments modify the properties of
some metals necessary for nuclear plant applications.
Rev 3
31
Heat Treatment
Large carbon steel components undergo heat treatment that takes advantage
of metallic crystalline structures and their effects on the metal to gain
certain desirable properties. Toughness and ductility decrease as hardness
and tensile strength increase in heat-treated steel. Heat treatment is
unsuitable for increasing the hardness and strength of type 304 stainless
steel because of its crystalline structure.
Quenching (Cooling)
Varying the rate of quenching or cooling the metal, allows control of the
grain size and grain patterns in the metal material during manufacture.
Grain characteristics produce different levels of hardness and tensile
strength. Generally, the faster a metal cools, the smaller the grain size.
Smaller grain size yields a harder metal.
The cooling rate used in quenching depends on the method of cooling and
the size of the metal. Uniform cooling is important because it prevents
distortion. Steel components typically use oil or water for quenching.
Annealing
Annealing is another common heat-treating process for carbon steel
components. The annealing process is where component heating occurs
slowly to an elevated temperature then held there for a long time and
cooled. Annealing results in the following effects:


Softens the steel and improves ductility.
Relieves internal stresses caused by previous processes such as heat
treatment, welding, or machining.
 Refines the metal’s grain structure.
Cold Working
Cold working is plastic deformation in a particular temperature region and
over a specific time interval such that the strain, or work hardening, is not
relieved.
Cold working a metal decreases the metal's ductility. The decreased
ductility results from the cold working process, which repeatedly deforms
the metal. Slip occurs essentially on primary glide planes and the resulting
dislocations form coplanar arrays in the early stages of plastic deformation.
Cross slip takes place as deformation proceeds. The cold worked structure
forms high dislocation density regions that eventually develop into
networks. The grain size decreases with strain at low deformation; however
as deformation continues, the grains reach a fixed size. Altering the metal's
grain size during the cold working process causes the decrease in ductility.
Rev 3
32
Hot Working
Hot working refers to the process where metal deformation happens above
the re-crystallization temperature and prevents strain hardening from
occurring.
Hot working metals usually takes place at elevated temperatures. The
resistance of metals to plastic deformation generally becomes lower with
increasing temperature. Metals display distinctly viscous characteristics at
sufficiently high temperatures, and their resistance to flow increases at high
deforming rates. This deforming is a characteristic of viscous substances
and the slowed rate of recrystallization. Hot working larger sections of
metal by forging, rolling, or extrusion are preferred in this temperature
region.
Despite this, lead is hot-worked at room temperature because of its low
melting temperature. At the other extreme, molybdenum cold working
occurs when deformed at red-hot temperatures because of its high
recrystallization temperature.
Welding
Welding induces internal stresses that remain in the material. The crystal
lattice is face-centered cubic in austenite stainless steels, such as type 304.
Some surrounding metals may be elevated to between 260 °C and 538 °C
(500 °F and 1,000 °F) during high-temperature welding. In this temperature
region, austenite transforms into a body-centered cubic lattice structure
known as bainite.
Regions surrounding the weld contain some original austenite and some of
the newly formed bainite once the metal has cooled. A problem arises
because the packing factor (PF = volume of atoms per volume of unit cell)
is not the same for FCC crystals as for BCC crystals. Bainite’s longer
crystalline structure occupies more space than the original austenite lattice.
Elongation of the material causes residual compressive and tensile stresses.
Heat sink welding minimizes welding stresses from lower metal
temperatures. Annealing also reduces welding stress.
Rev 3
33
Knowledge Check (Answer Key)
Varying the rate of cooling of a metal in order to
control grain size and grain patterns is
_______________.
A.
heat treating
B.
annealing
C.
cold working
D.
quenching
TLO 3 Summary
 Strength is the ability of a material to resist deformation.
— An increase in slip decreases the strength of a material.
— Ultimate tensile strength (UTS) is the maximum resistance to
fracture.
— Yield strength: the stress at which a predetermined amount of
plastic deformation occurs.
 Ductility is the ability of a material to deform easily on application of
a tensile force, or the ability of a material to withstand plastic
deformation without rupture.
— Increasing temperature increases ductility.
— Ductility decreases with lower temperatures, cold working, and
irradiation.
— Ductility is desirable in high-temperature and high-pressure
applications.
 Malleability is the ability of a metal to exhibit large deformation or
plastic response when compressed.
 Toughness describes impact and is the work required to deform one
cubic inch of metal until it fractures.
 Hardness is the property of a material that enables it to resist plastic
deformation, penetration, indentation, and scratching.
 Quenching is varying the rate of cooling the metal that helps control
both grain size and grain patterns.
— Controlling grain characteristics produces different levels of
hardness and tensile strength
 Heat treating: hardness and tensile strength increase in heat-treated
steel; however, toughness and ductility decrease.
 Annealing: slowly heating a component to an elevated temperature
and holding it there for a specified time, then cooling:
— Softens steel and improves ductility
— Relieves internal stresses caused by previous processes
— Refines grain structure
Rev 3
34

Cold working is plastic deformation in a particular temperature
region and over a specific time interval such that the strain, or work
hardening, is not relieved.
 Hot working refers to the process where metal deformation happens
above the re-crystallization temperature and prevents strain hardening
from occurring.
 Welding - Welding induces internal stresses that remain in the
material.
— Heat sink welding and annealing minimize stresses
Objectives
Now that you have completed this lesson, you should be able to do the
following:
1. Describe the following terms:
a. Strength
b. Ultimate tensile strength
c. Yield strength
d. Ductility
e. Malleability
f. Toughness
g. Hardness
2. Describe the following types of treatments used on metals:
3. Heat treatment
a. Cooling (Quenching)
b. Annealing
4. Cold working
5. Hot working
TLO 4 Metal Corrosion
Overview
Corrosion is deterioration of a material because of interaction with its
environment. Corrosion is the process where atoms leave the metal or form
compounds in the presence of water and gases. As corrosion continues,
metal atoms leave a structural element until it fails or oxides build up and
plug a pipe. All metals and alloys can corrode, including noble metals, such
as gold, in some environments.
Corrosion of metals is a natural process. Most metals are not
thermodynamically stable in their metallic form. Corrosion allows
reversion to more stable forms, such as oxides that exist in ores. Corrosion
occurs continuously, and is a primary concern in nuclear facilities.
Corrosion control methods exist; however, it is impossible to stop.
Rev 3
35
Objectives
Upon completion of this lesson, you will be able to do the following:
1. Describe the following types of corrosion and methods for
controlling:
a. General corrosion
b. Galvanic corrosion
2. Describe the following types of localized corrosion including
prevention/control methods:
a. Stress corrosion cracking
b. Chloride stress corrosion
c. Caustic stress corrosion
3. Describe hydrogen embrittlement
ELO 4.1 General and Galvanic Corrosion
Introduction
Corrosion is a major factor when selecting material for use in industrial
systems and facilities. The material selected must resist the various types of
corrosion caused by the environment, other materials, and conditions that
the specific material undergoes at the facility.
General Corrosion
General corrosion caused by water, steel, or iron often results from a
chemical reaction where the steel surface oxidizes, forming iron oxide, or
rust. Many systems and components in industrial nuclear plants use
materials constructed from iron alloys. Standard material selection methods
to protect against general corrosion include the following:

Using materials with corrosion-resistant composition, such as
stainless steel, nickel, chromium, and molybdenum alloys
 Using protective coatings, such as paints and epoxies prevents
corrosion:
— Corrosion is electrochemical by nature, and the corrosion
resistance of stainless steel results from surface oxide films that
interfere with the electrochemical process.
 Applying surface metallic and nonmetallic coatings or linings protects
against corrosion and allows the material to retain its structural
strength.
— For example, a carbon steel pressure vessel lined with stainless
steel cladding.
Galvanic Corrosion
Galvanic corrosion occurs when two dissimilar metals with different
electrical potentials are in electrical contact in an electrolyte. It may also
take place within one metal with heterogeneities (dissimilarities such as
Rev 3
36
impurity inclusions, grains of different sizes, differences in grain
composition, or differences in mechanical stress).
Galvanic Corrosion Mechanism
Different electrical potential exists for each metal and serve as the driving
force for electrical current flowing through the electrolyte in galvanic
corrosion. This electrical current results in corrosion of one of the metals.
The larger the potential difference, the greater the rate of galvanic
corrosion.
Galvanic corrosion only results in deterioration of one of the metals. The
less resistant, more active metal becomes the anodic or negative corrosion
site. The stronger, nobler metal is cathodic or positive and protected. The
two metals are uniformly attacked by the corrosive medium as if there was
no electrical contact and therefore no current flow.
For any particular medium, a sequential list arranging metal from most
active, or those with the least amount of noble metals, to passive or those
with the largest amount of noble metals identifies the galvanic series. The
Chemistry Fundamentals module discusses the galvanic series for seawater.
Minimizing Galvanic Corrosion
Galvanic corrosion is a concern in both design and material selection.
Material selection is important because different metals may contact each
other and form galvanic cells. Design is important to minimize system low
flow conditions and resultant areas of corrosion buildup. Loose corrosion
products transport through systems and deposit in low-flow areas, causing
additional flow restrictions. Substances formed by corrosion and exposed
to radiation become highly radioactive, further increasing radiation levels
and contamination issues in nuclear plants.
Cathodic Protection
There are methods of reducing galvanic corrosion. For example, when
pieces of zinc are attached to the bottom of a steel water tank, the zinc
become the anode, and corrodes. The steel in the tank becomes the cathode,
remaining unaffected by the corrosion. This electrical current between the
anode and cathode causing the anode to corrode is passive galvanic cathodic
protection. The corroding anode is the sacrificial anode. The more active
metal becomes the anode or negative and the more noble metal is the
cathode or positive and protected. An external direct current (DC) electrical
power source provides sufficient current to negate the corrosion in certain
large systems in industrial applications.
Rev 3
37
Knowledge Check (Answer Key)
_______________ is an attack on the entire surface of
a metal, where the surface of the metal oxidizes to form
rust.
A.
Chloride stress corrosion
B.
General corrosion
C.
Caustic stress corrosion
D.
Galvanic corrosion
ELO 4.2 Characteristics of Localized Corrosion
Introduction
This lesson covers various types of localized corrosions: stress corrosion
cracking, chloride stress corrosion, and caustic stress corrosion.
Localized Corrosion
Localized corrosion is the selective removal of metal by corrosion in small
areas or zones on a metal surface in contact with a corrosive environment,
usually a liquid. Corrosion attacks small local sites at a higher rate than the
rest of the metal’s surface. Localized corrosion can be especially damaging
when combined with corrosion and other destructive processes such as
stress, fatigue, erosion, and other forms of chemical attack. Localized
corrosion mechanisms often cause more damage than any individual one of
the destructive processes.
Pitting, stress corrosion cracking, chloride stress corrosion, caustic stress
corrosion, heat exchanger tube denting, wastage, and intergranular attack
corrosion are examples of localized corrosions.
Stress Corrosion Cracking
Stress corrosion cracking (SCC), a form of intergranular attack corrosion
occurring at the grain boundaries of a metal under tensile stress, is one of
the most serious metallurgical problems.
SCC propagates as stress opens cracks in metal, increasing the area subject
to corrosion. The cracks continue corroding, weakening the metal, followed
by further cracking. The cracks follow intergranular or transgranular paths,
and tendencies exist for crack branching.
Rev 3
38
The cracks form and propagate at approximately right angles to the
direction of the tensile stresses at lower stress levels than required to
fracture the material in the absence of the corrosive environment. These
cracks reduce the material’s cross-sectional area to absorb tensile stresses.
As cracking penetrates further into the material, it eventually reduces the
supporting cross section to the point of structural failure from overload.
Causes of Stress Corrosion Cracking
Stresses that cause cracking in metals happen because of residual stresses of
cold work, welding, grinding, or thermal treatment. Externally applied
stress during service is also possible. These stresses must be tensile (as
opposed to compressive) for them to propagate SCC.
SCC occurs in metals exposed to environments where if stress was not
present or was at a much lower level, no damage would result. If the same
stress was in a different environment non-corrosive to that material, there
would be no failure if the structure was subjected to the same stress. Some
examples of SCC in industry are cracks in stainless steel piping systems and
in stainless steel valve stems.
Preventing Stress Corrosion Cracking
The most effective means of preventing SCC include the following:



Designing proper systems and components
Reducing stress
Removing critical environmental factors such as hydroxides,
chlorides, and oxygen
 Avoiding stagnant areas and crevices in heat exchangers where
chloride and hydroxide might become concentrated
Lower alloy steels are less susceptible than higher alloy steels and are
subject to SCC in water containing chloride ions. Chloride or hydroxide
ions do not affect nickel-based alloys. Inconel is an example of a nickelbased alloy resistant to stress-corrosion cracking. Inconel is composed of
72 percent nickel, 14 to 17 percent chromium, 6 to 10 percent iron, as well
as small amounts of manganese, carbon, and copper.
Chloride Stress Corrosion
Chloride stress corrosion, an intergranular type of corrosion in austenitic
stainless steel under tensile stress in the presence of oxygen, chloride ions,
and high temperature, is of tremendous concern to the nuclear industry.
Chloride stress corrosion starts when chromium carbide deposits along
grain boundaries allow corrosion of the original metal. Controlling chloride
stress corrosion requires low chloride ion and oxygen content in the
environment and the use of low-carbon steels.
Rev 3
39
Caustic Stress Corrosion
Carbon steels are susceptible to caustic stress corrosion. Similarly to other
types of localized corrosion, caustic steel corrosion begins when cracks
form and grow along the grain boundaries combined with extensive crack
branching. High-tensile stress external to the steel or within the steel’s
fabrication cause caustic stress corrosion.
Despite the qualification of Inconel for specific applications, some caustic
stress corrosion also occurred in Inconel tubing. Depending on prior
solution treatment temperature, heat-treating Inconel at 620 °C to 705 °C
improves its resistance to caustic stress corrosion cracking. Other possible
problems found with Inconel include wastage, tube denting, pitting, and
intergranular attack.
Knowledge Check (Answer Key)
_______________ is a type of corrosion generally
associated with Inconel.
A.
Chloride stress corrosion
B.
Caustic stress corrosion
C.
Galvanic corrosion
D.
General corrosion
ELO 4.3 Hydrogen Embrittlement
Introduction
Personnel should be aware of conditions that cause hydrogen embrittlement
and its formation. This lesson discusses the sources of hydrogen and the
properties and causes of hydrogen embrittlement.
Hydrogen Embrittlement Details
Hydrogen embrittlement is another form of stress-corrosion cracking.
Although embrittlement of materials takes many forms, hydrogen
embrittlement in high-strength steels has the most devastating effect
because of the often-catastrophic nature of these types of fractures.
Hydrogen embrittlement is the process whereby steel loses its ductility and
strength due to tiny cracks resulting from the internal pressure of hydrogen
(H2) or methane gas (CH4) that form at the grain boundaries. Hydrogen
embrittlement is a particular concern in the nuclear industry because of the
susceptibility of zirconium alloys to this type of corrosion. Zirconium
Rev 3
40
alloys are widely used as nuclear reactor fuel cladding for compatibility,
corrosion resistance, and nuclear properties.
Sources of Hydrogen
Sources of hydrogen causing embrittlement include the following:





Steel manufacturing process
Welding
Hydrogen gas in vessels
Byproducts of general corrosion
Corrosion reactions such as rusting, cathodic protection, and
electroplating
 Byproduct from industrial chemicals
Hydrogen Embrittlement of Stainless Steel
As shown below in the following figure, hydrogen diffuses along the grain
boundaries where it combines with carbon (C) alloyed with the iron, and
forms methane gas. The methane gas is not mobile and collects in small
voids along the grain boundaries where it builds up pressures that start
cracks. Hydrogen embrittlement leads to brittle fracture, a failure
mechanism, or mode with little or no plastic deformation when a high
tensile stress exists in the metal.
Figure: Hydrogen Embrittlement
The hydrogen atoms are absorbed into the metal’s lattice and diffused
through the grains, gathering at inclusions or other lattice defects at normal
room temperatures. The path is transgranular if stress induces cracking
under these conditions. Transgranular fractures, shown in the graphic on
the following page, follow the edges of the lattices and ignore the grains.
Rev 3
41
Figure: Transgranular Cracking
Intergranular stress-induced cracking, shown below in the graphic, results
from absorbed hydrogen gathering in the grain boundaries at high
temperatures and resulting in fractures.
Stress-induced intergranular cracking follows the grain of the material. In
material with multiple lattices, when one lattice ends and other begins, the
crack changes direction to follow the new grain, resulting in a jagged
looking fracture with bumpy edges.
Figure: Intergranular Cracking
The cracking of martensitic and precipitation of hardened steel alloys is
believed to be a form of hydrogen-stress corrosion cracking that results
from the entry into the metal of a portion of the atomic hydrogen produced
in the following corrosion reaction:
3𝐹𝑒 + 4𝐻2 𝑂 → 𝐹𝑒3 𝑂4 + 4𝐻2
Rev 3
42
Hydrogen embrittlement is not a permanent condition. The hydrogen rediffuses from the steel, restoring the metal's ductility if cracking does not
occur and the environmental conditions change so that no hydrogen
generates on the metal’s surface.
Minimizing Occurrences of Hydrogen Embrittlement
The following measures address the problem of hydrogen embrittlement:



Controlling the amount of residual hydrogen in steel
Controlling the amount of hydrogen in processing
Developing alloys with improved resistance to hydrogen
embrittlement
 Developing low or no embrittlement plating or coating processes
 Restricting the amount of in-situ, or in position, hydrogen introduced
during a part’s service life
Knowledge Check (Answer Key)
What two conditions are necessary for hydrogen
embrittlement to occur? ____________ and
___________
A.
Hydrogen
B.
Oxygen
C.
Carbon
D.
Elevated temperature
TLO 4 Summary
 Corrosion is the natural deterioration of a metal in which metallic
atoms leave the metal or form compounds in the presence of water or
gases.
 General corrosion: minimized by the use of corrosion-resistant
materials and the addition of protective coatings and liners.
 Galvanic corrosion occurs when dissimilar metals exist at different
electrical potentials in the presence of an electrolyte.
— Careful design and selection of materials regarding dissimilar
metals and the use of sacrificial anodes reduce galvanic
corrosion.
• Localized corrosion can be especially damaging when combined with
corrosion and other destructive processes such as stress, fatigue,
erosion, and other forms of chemical attack.
— Localized corrosion mechanisms often cause more damage than
any individual one of the destructive processes.
Rev 3
43








Rev 3
Stress-corrosion cracking occurs at grain boundaries under tensile
stress and propagates as stress opens cracks, increasing the area
subject to corrosion, ultimately weakening the metal until failure.
— Effective ways of reducing SCC include the following:
o Designing proper systems and components
o Reducing stress
o Removing corrosive agents - such as hydroxides, chlorides,
and oxygen
o Avoiding areas of chloride and hydroxide ion concentration
Chloride stress corrosion occurs in austenitic stainless steels under
tensile stress in the presence of oxygen, chloride ions, and hightemperature.
— Controlling chloride stress corrosion requires low chloride ion
and oxygen content in the environment and the use of lowcarbon steels.
Possible problems with Inconel include some caustic stress corrosion
cracking, wastage, tube denting, pitting and intergranular attack.
— Inconel's resistance to caustic stress corrosion cracking is
improved by heat-treating
Hydrogen embrittlement is the process whereby steel loses its
ductility and strength due to tiny cracks resulting from the internal
pressure of hydrogen (H2) or methane gas (CH4), that form at the
grain boundaries.
Conditions required for hydrogen embrittlement in steel include some
of the following:
— The presence of hydrogen dissolved in the water
— Carbon in the steel
Hydrogen dissolved in the water comes from:
— Steel manufacturing process
— Processing parts
— Welding
— Storage or containment of hydrogen gas
— Related to hydrogen as an environmental contaminant that is
often a by-product of general corrosion
— A by-product of the chemicals used in processing
Hydrogen embrittlement in stainless steel results from hydrogen that
diffuses along the grain boundaries and combines with the carbon to
form methane gas.
— The methane gas collects in small voids along the grain
boundaries where it builds up enormous pressures that initiate
cracks and decreases the ductility.
— If the metal is under a high tensile stress, brittle fracture can
occur.
The occurrence of hydrogen embrittlement is minimized by:
— Controlling the amount of residual hydrogen in steel
— Controlling the amount of hydrogen pickup in processing
— Developing alloys with improved resistance to hydrogen
embrittlement
44
— Developing low or no embrittlement plating or coating processes
for metals
— Restricting the amount of in-situ, or in position, hydrogen
introduced during the service life of a part.
Objectives
Now that you have completed this lesson, you should be able to do the
following:
4. Describe the following types of corrosion and methods for
controlling:
a. General corrosion
b. Galvanic corrosion
5. Describe the following types of localized corrosion including
prevention/control methods:
a. Stress corrosion cracking
b. Chloride stress corrosion
c. Caustic stress corrosion
6. Describe hydrogen embrittlement
TLO 5 Describe Common Material Failure Mechanisms
Overview
Constructing an industrial facility requires many different kinds of
materials. Once constructed, exposure of these materials to different
environments and operating conditions may lead to material problems. This
lesson discusses common failure mechanisms of industrial plant materials.
Objectives
Upon completion of this lesson, you will be able to do the following:
1. Describe the following material failure mechanisms:
a. Fatigue failure
b. Work hardening
c. Creep
ELO 5.1 Material Failure Mechanisms
Introduction
Material failures in industrial facilities are not limited only to ductile
fracture or to brittle fracture. Other failure mechanisms exist, such as
fatigue failure, work hardening, and creep, which in time lead to mechanical
component failures.
Rev 3
45
Fatigue Failure
Fatigue causes the majority of engineering failures. Fatigue failure is a
material’s the tendency of a material to fracture by means of progressive
brittle cracking under repeated alternating or cyclic stresses at levels
considerably below the normal strength. Although characterized as brittle,
this type of failure may take some time for a fracture to propagate,
depending on both the intensity and frequency of the stress cycles.
Unfortunately, there is little, if any, warning before the failure occurs.
The number of cycles required to cause fatigue failure at a particular peak
stress is generally quite large; however, it decreases as the stress levels
increase. For some mild steels, an infinite number of cyclical stresses may
continue provided the peak stress, sometimes called fatigue strength, is
below the endurance limit value.
Breaking a paper clip with your hands after bending it back and forth a
number of times in the same place is an example of fatigue failure. Another
example is an unbalanced pump impeller resulting in vibrations that can
cause fatigue failure.
The most common type of fatigue in industrial facilities is thermal fatigue.
Thermal fatigue arises from thermal stresses produced by cyclic changes in
temperature. Large thick-walled components, such as steam piping, are
subject to cyclic stresses caused by temperature variations during facility
startup, normal operation, and shutdown.
Fatigue Failure Mechanism
The primary cause of the phenomenon of fatigue failure is unknown.
Fatigue failure apparently arises from the initial formation of a small crack
resulting from a defect or microscopic slip in the metal grains. The crack
propagates slowly at first and then more rapidly when the local stress
increases due to a decrease in the load-bearing cross section. The metal
fractures when the local stress in the intact cross-section exceeds the
fracture strength.
Microscopic cracks and notches in the metal’s surface indicate fatigue
failure; these include factors such as grinding and machining marks on the
surface. As a result, avoid materials that display defects subjected to cyclic
stresses (or strains). These types of defects also favor brittle fracture.
Avoiding Fatigue Failure
Fundamental requirements during the design and manufacturing stage for
avoiding fatigue failure vary for different components, depending on the
types of subjected stresses. For components with low load variations and a
high cycle frequency, steel of high-fatigue strength and high-ultimate
tensile strength is desirable. High ductility is the main requirement for the
Rev 3
46
steel used in components with large load variations and low cycle
frequencies.
Plant operations performed in a controlled manner mitigate the effects of
cyclic stress by minimizing it by using heatup and cooldown limitations,
pressure limitations, and pump operating curves. Proper record keeping
includes maintaining cycle logs on equipment. Keeping cycle log records
on equipment allows identification of the need for replacement prior to
fatigue failure. Installed thermal sleeves minimize thermal stresses in high
thermal-stress piping systems.
Work (Strain) Hardening
Work hardening occurs when straining a metal beyond the yield point in the
ductile region. Increasing stress produces additional plastic deformation
and causes the metal to become stronger and more difficult to deform. True
stress plotted against true strain shows that the rate of strain hardening
(illustrated by the slope of the true stress line) becomes almost a straight
line as shown below in the figure below. The slope of the true stress line
reflects the strain (or work) hardening coefficient or work hardening
coefficient.
Figure: Nominal versus True Stress-Strain Curve
Factors Affecting Work Hardening
The slope of the straight part of the line above the nominal maximum stress
line shown in the previous figure is the strain-hardening coefficient or
work-hardening coefficient, and closely relates to the shear modulus
(approximately proportional). Therefore, a metal with a high shear modulus
has a high strain or work hardening coefficient (for example, molybdenum).
Rev 3
47
Grain size also influences strain hardening. A material with small grain size
strain hardens more rapidly than the same material with a larger grain size.
However, the effect only applies in the early stages of plastic deformation,
and the influence disappears as the structure deforms and grain structure
breaks down.
Work Hardening Mechanism
Work hardening closely relates to fatigue. Bending the thin steel rod
becomes more difficult the more the rod is bent, shown in the previous
example. This is the result of work or strain hardening. Work hardening
reduces ductility, which further increases the chances of brittle failure.
Work Hardening as a Material Treatment
Work hardening is useful for treating metal. Prior work hardening by cold
working causes the treated metal to have an apparently higher yield stress,
yielding strengthened metal.
Creep
Structural materials develop the full strain they will exhibit as soon as a
load is applied at room temperature. This is not necessarily the case at high
temperatures (for example, stainless steel above 1,000 °F). Many materials
continue to deform at a slow rate at elevated temperatures and constant
stress or load, which demonstrates creep behavior.
The Mechanism of Creep
The rate of creep is approximately constant for a long period at a constant
stress and temperature. After this time and after a certain amount of
deformation, the rate of creep increases, and fracture soon follows, as
shown in the following figure.
Initially, primary or transient creep occurs in Stage I. The creep rate, slope
of the curve, is high at first, but it soon decreases. Secondary or steady state
creep in Stage II follows this, when the creep rate is small and the strain
increases linearly and slowly with time. Eventually, in Stage III, known as
tertiary or accelerating creep, the creep rate increases more rapidly and the
strain may become so large that it results in failure.
Rev 3
48
Figure: Successive Stages of Creep with Increasing Time
The rate of creep depends on both stress and temperature. With most of the
industrial alloys used in construction at room temperature or lower, ignoring
the small amount of creep strain is permissible. Creep does not become
significant until the stress intensity approaches the fracture failure strength.
However, as temperature rises, creep becomes progressively more important
and eventually supersedes fatigue as the likely criterion for failure. The
temperature where creep becomes important varies with the material
involved.
Limiting Creep
The total deformation due to creep must be well below the strain where
failure occurs for safe operation, which can be done by staying well below
the creep limit.
Creep Limit
Glossary
The stress to which a material can be subjected without
the creep exceeding a specified amount after a given
time at the operating temperature (for example, a creep
rate of 0.01 in 100,000 hours at operating temperature).
The creep limit generally does not pose a limitation at the temperature at
which high-pressure vessels and piping operate in most industrial
applications; however, creep may become a concern when extremely high
temperatures and pressures are involved in the industrial process.
Rev 3
49
Knowledge Check (Answer Key)
Work hardening __________ the ductility of a metal.
A.
raises
B.
has no effect on
C.
lowers
D.
insufficient information to answer
TLO 5 Summary
 Fatigue failure is the tendency of a material to fracture by means of
progressive brittle cracking under repeated alternating or cyclic
stresses considerably below the normal strength.
— Thermal fatigue is the fatigue type of the most concern because
of cyclic changes in temperature.
— Fundamental requirements during design and manufacturing
help avoid fatigue failure.
— Controlling plant operations reduces cyclic stress.
— Heatup and cooldown limitations, pressure limitations, and
pump operating curves help curb fatigue failure.
 Work hardening takes place when strain in a metal goes beyond the
yield point.
— Work hardening reduces ductility, increasing the chances of
brittle fracture.
— Prior work hardening causes the treated material to have an
apparently higher yield stress; therefore, strengthening the metal.
 Creep refers to materials deforming at elevated temperatures and
constant stress over time.
— Creep becomes a problem if the stress intensity approaches
fracture failure strength.
— If creep rate increases rapidly, the strain becomes so large it
could result in failure.
— Minimizing the stress and temperature of a material controls the
creep rate.
Objectives
Now that you have completed this lesson, you should be able to do the
following:
1. Describe the following material failure mechanisms:
a. Fatigue failure
b. Work hardening
c. Creep
Rev 3
50
Material Science Module Summary
The bonding arrangement of atoms determines a material’s behavior and
properties. In this module, you learned that metals consist of crystalline
structures, arranged in three-dimensional arrays called lattices on a
molecular level. Crystalline structures appear as grains in the metal under a
microscope. The characteristics of these lattice structures, grains, and
boundaries between grains determine the metal's characteristics such as its
strength, ductility/malleability, and resistance and susceptibility to different
types of corrosion. All of these are taken into consideration when selecting
materials for specific applications in a nuclear power plant.
Now that you have completed this module, you should be able to
demonstrate mastery of this topic by passing a written exam with a grade of
80 percent or higher on the following TLOs:
1. Describe the bonding, structures, and imperfections found in solid
materials.
2. Describe the basic microstructure and characteristics of metallic
alloys.
3. Describe physical and chemical properties of metals and methods
used to modify these properties.
4. Describe the considerations commonly used when selecting material
for use in an industrial facility and common material failure
mechanisms.
5. Describe common material failure mechanisms.
Rev 3
51
Material Science Knowledge Check Answer Key
Knowledge Check Answer Key
ELO 1.1 Metallic Bonding
Knowledge Check
This type of bond is characterized by the transference
of one or more electrons from one atom to another.
A.
Covalent
B.
Ionic
C.
Molecular
D.
Electronic
ELO 1.2 Solid Material Properties
Knowledge Check
The outside area of a grain that separates it from other
grains in a metal is known as _______________.
A. grain structure
B.
crystal boundary
C.
grain boundary
D. crystal structure
Rev 3
1
Material Science Knowledge Check Answer Key
ELO 1.3 Metallic Lattice Structures
Knowledge Check
Which of the following basic crystal patterns has the
greatest number of atoms per unit cell?
A.
BCC
B.
FCC
C.
HCP
D.
HCC
ELO 1.4 Metallic Imperfections
Knowledge Check
Vacancy defects, substitutional defects, and interstitial
defects are examples of _______________.
Rev 3
A.
line imperfections
B.
point imperfections
C.
interfacial imperfections
D.
bulk defects
2
Material Science Knowledge Check Answer Key
ELO 2.1 Characteristics of Alloys
Knowledge Check
Which one of the following is NOT a characteristic of
an alloy?
A.
Usually stronger than pure metals.
B.
Generally have reduced electrical and thermal
conductivity.
C.
Usually have better ductility than pure metals.
D.
Usually preferred for industrial construction over pure
metals.
ELO 2.2 Stainless Steel
Knowledge Check
What are the two desirable characteristics of Type 304
Stainless Steel? ___________ and ___________
Rev 3
A.
high temperature tolerant; toughness
B.
corrosion resistance; toughness
C.
cubic iron lattice; corrosion resistance
D.
corrosion resistance; contains no nickel
3
Material Science Knowledge Check Answer Key
ELO 3.1 Physical and Chemical Properties of Metals
Knowledge Check
_______________ is a material's maximum resistance
to fracture.
A.
Strength
B.
Yield Strength
C.
Ductility
D.
Ultimate tensile strength
ELO 3.2 Metal Treatments
Knowledge Check
Varying the rate of cooling of a metal in order to
control grain size and grain patterns is
_______________.
Rev 3
A.
heat treating
B.
annealing
C.
cold working
D.
quenching
4
Material Science Knowledge Check Answer Key
ELO 4.1 General and Galvanic Corrosion
Knowledge Check
_______________ is an attack on the entire surface of
a metal, where the surface of the metal oxidizes to form
rust.
A.
Chloride stress corrosion
B.
General corrosion
C.
Caustic stress corrosion
D.
Galvanic corrosion
ELO 4.2 Characteristics of Localized Corrosion
Knowledge Check
_______________ is a type of corrosion generally
associated with Inconel.
Rev 3
A.
Chloride stress corrosion
B.
Caustic stress corrosion
C.
Galvanic corrosion
D.
General corrosion
5
Material Science Knowledge Check Answer Key
ELO 4.3 Hydrogen Embrittlement
Knowledge Check
What two conditions are necessary for hydrogen
embrittlement to occur? ____________ and
___________
A.
Hydrogen
B.
Oxygen
C.
Carbon
D.
Elevated temperature
ELO 5.1 Common Material Failure Mechanisms
Knowledge Check
Work hardening __________ the ductility of a metal.
Rev 3
A.
raises
B.
has no effect on
C.
lowers
D.
insufficient information to answer
6