Chances and limits of High silicon ductile iron
Dr.-Ing. Claudia Dommaschk
TU Bergakademie Freiberg, Foundry Department
Metal Casting Conference – South Africa 2017
TU Bergakademie Freiberg | Foundry Department | Bernhard-von-Cotta-Str. 4 | 09599 Freiberg |
Tel.: 03731 / 39-4000 | www.gi.tu-freiberg.de | Dr.-Ing. Claudia Dommaschk | South Africa 2017
Introduction
In Ductile Iron the strength increases with the increase of the pearlite
content, promoted by Mn,Cu,Sn
pearlitic
EN GJS-600-3
EN GJS-600-10
high silicon
By using Si-contents between 3 and 4.3 % and a ferritic structure, the
strength increases by solid-solution hardening of the ferrite
2
Basics
 Ductile Iron with homogenous ferritic Matrix
 The radii of the Si- and Fe- Atoms are different
 Stress in the lattice
 solid-solution hardening of the ferrite
rSi = 117 pm
rFe = 124 pm
body-centered cubic
lattice
3
Basics
„conventional“ Ductile iron: control of properties by
GJS – 400 – 18
GJS – 500 – 7
„high Si-“ Ductile iron: control of properties by
GJS – 450 – 18
Si~3.2%
GJS – 500 – 14
Si~3.8%
Ferrite – Pearlite – ratio
GJS – 600 – 3
Si-Content
GJS – 600 – 10
Si~4,3%
4
The effects of Silicon
2,4 % Si
4,8 % Si
• Movement of the eutectic point to lower Carbon-contents
• Increase of the eutectoid temperature
The formation of ferrite is promoted
• Increase of the eutectoid interval
• Decrease of the austenite area
5
In 2011 the DIN EN 1563 was modified.
Three high silicon materials were registered:
EN-GJS-450-18
EN-GJS-500-14
EN-GJS-600-10
EN-GJS
450-10
450-18
500-7
500-14
600-3
600-10
min. Rm
[N/mm²]
450
450
500
500
600
600
min. Rp0,2
[N/mm²]
310
350
320
400
370
470
min. A
[%]
10
18
7
14
3
10
6
Comparison of the properties –
0.2 % Yield Strength [MPa]
„Conventional“ Ductile Iron – High silicon Ductile iron
Elongation [%]
7
Results
4,3 %Si
The Influence of the silicon content
Tensile Strength [MPa]
700
[M
Y-2 samples
Y-4 samples
600
500
400
300
200
100
0
2
3
4
5
6
% Si
The tensile strength has the maximum at 4.3 % silicon
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
8
0.2 % yield strength [MPa]
4,3 %Si
The Influence of the silicon content
[M
700
Y-2 samples
Y-4 samples
600
500
400
300
200
100
0
2
3
4
5
6
% Si
The 0.2 % yield strength has the maximum later than the tensile strength
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
9
4,3 %Si
The Influence of the silicon content
Elongation [%]
Y-2 samples
Y-4 samples
[M
2
3
4
5
6
% Si
With silicon contents higher than 4.3 % the elongation is dramatically reduced
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
10
Brinell Hardness
4,3 %Si
The Influence of the silicon content
% Si
With increasing the Si content, the hardness increases continuously
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
11
The mechanical properties depends on
the temperature.
The difference of the Tensile strength
and Yield Strength between „new“ and
„conventionel“ Dutile Iron is minimal at
temperatures above 400 °C
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
12
Tensile strength [MPa]
4,3%Si
The influence of pearlitic and carbidic elements
The tensile strength is not influenced by different alloying or trace elements
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
13
[MPa]
4,3%Si
The influence of pearlitic and carbidic elements
The Yield stress is not influenced by different alloying or trace elements
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
14
Elongation [%]
4,3%Si
The influence of pearlitic and carbidic elements
The elongation is not influenced by different alloying or trace elements
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
15
Structure
Y2-sample
4,03% Si; 3,01 %C; 1,0 % Mn; 0,003 % Cr
4,16% Si; 3,04 %C; 1,0 % Mn; 0,3 % Cr
Rm: 581 MPa; Rp0,2: 486 MPa; A: 19,8 %
Rm: 618 MPa; Rp0,2: 481 MPa; A: 18,6 %
0 % Pearlite
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
0,5 % Pearlite
16
Fibrous Fracture
Fibrous Fracture
Impact strength (J)
Brittle Fracture
120
Fibrous and Brittle Fracture
100
80
60
Brittle Fracture
40
20
0
GJS 400-18
(ferritic)
GJS 500-7
(ferritic/pearlitic)
GJS 450-18
GJS 500-14
GJS 600-10
(ferritic, Si: 3.08%) (ferritic, Si: 3.62%) (ferritic, Si: 4.12%)
RT
Quelle: Knothe, Vortrag VDI Konferenz 2016
-20°C
- 17 -
18
Notched bar impact strength (J)
Influence of the Silicon content to the Notched bar impact strength
ferritic
ferritic (Si: 3,2%)
ferritic (Si: 3,8%)
ferritic/pearlitic
Temperature (°C)
• Conventional ferritic Ductile iron has the best impact strength.
• With increasing Si content, the notched impact strength decreases.
• The steep front of the impact strength is displaced to higher temperatures.
Quelle: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012
19
Results – Fracture mechanics
KIC (Mpa*m1/2)
120
100
80
60
40
20
0
1
1,5
2
2,5
3
3,5
4
Si (%)
The Fracture toughness decreases dramatically with increasing Si content.
Quellen: [4] Wolfensberger, S. u. a.: Teil II: Gusseisen mit Kugelgraphit, Giessereiforschung 39 (1987) 2, S. 71-80
[5] Komatsu, S. u. a: AFS Transactions, 102, 1994, pp 121-125
[6] Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012
20
KIC (Mpa*m1/2)
Results – Fracture mechanics
GJS 400-18 GJS 450-18 GJS 700-2
(ferritic)
(ferritic, high-Si) (pearlitic)
The Fracture toughness of the ferritic High Si- Ductile Iron and the pearlitic
Ductile Iron are similarly low.
Quelle: Pusch, G. u.a.: CAEF, Continuous Casting Section, Prüfbericht: TU Bergakademie Freiberg, Januar 2012
21
Content of Nodular graphite particels (shape V and VI)
Inoculation technology
%
Inoculants
Wall Thickness (mm)
The degree of nodularity depends on the type of inoculant
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
21
Example Inoculant 1:
The content of nodular graphite particels with shape V and VI decreases
Content of Nodular graphite particels (shape V and VI)
with increasing the Si-content
%
Inoculant 1
(73-78 % Si; max 0,1 % Ca; 0,6-1
% Sr; max. 0,5 % Al)
Wall Thickness (mm)
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
22
Example Inoculant 2:
The content of nodular graphite particels with shape V and VI increases
with increasing the Si-content to ~4.4%
Content of Nodular graphite particels
(shape V and VI)
Inoculant 2
%
(62-38 % Si; 1 % Al; 1,8-2,4%
Ca; 0,8-1,2% Re; 0,8-1,2 % Bi)
Wall Thickness (mm)
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
23
Structure and inoculation technology
Content of Nodular graphite particels
(shape V and VI)
%
Low Si
Good inoculation
Different
inoculants
High Si
Poor inoculation
Wall Thickness (mm)
Quelle:
Projekt „SIRON“;AiF-Nr.: 41 EN
24
Results on a real casting
GJS-600-3
GJS-600-10
1
1
2
Material
Pos.
2
do
Rm
Rp0.2
A
[mm]
[Mpa]
[Mpa]
[%]
1
GJS-600-3
6
675
372
7.9
2
GJS-600-3
12
646
375
4.4
1
GJS-600-10
6
638
503
18.0
2
GJS-600-10
12
633
508
14.7
25
25
Summary
Benefits of HighSi- ferritic Ductil Iron
against ferritic/pearlitic Ductile Iron
Because of the combination of a high tensile strength, high 0.2 yield
strength and good elongation it is possible to decrease the wall thickness
(Light weight construction)
The hardness and tensile strength is homogenous over the wall thickness
It is not necessary to chance the pattern
Higher contents of carbidic elements in the charge materials are not a problem.
26
Summary
Problems
-
An optimal process technology is absolutly necessary.
-
The Si-content is limited to 4.3 %.
-
The solid solution hardening leads to a massive embrittlement of the ferrite.
The properties are not comparable to the conventional α- ferrite.
-
The fracture behavior changes from the fibrous fracture to the brittle fracture
-
With Increasing the Si- content will decrease the impact strength will decrease
-
The Fracture toughness of the ferritic High Si- Ductile Iron and the pearlitic
Ductile Iron are similarly low.
27