INTRODUCTION
Steel specimens of different heat treatments were tested in this laboratory investigation. The
three types of treated 4140 steel were as-received, fully annealed and quenched and tempered. The
fully annealed and quenched and tempered specimens were conditioned by heating them in a furnace
and cooling them at different rates. Material properties’ response to heat treatment is an essential
knowledge of the design process of components of any system. Properties of materials may be tailored
to the design application to achieve optimum performance while ensuring safety.
PROCEDURE
First, four of the 4140 0.505in steel specimens were heat treated. Two specimens were fully
annealed by heating them in a furnace to 1600oF and then furnace cooling them down to below the
eutectic temperature of 727oC. The other two specimens were quenched and tempered by heating
them in a furnace to 1600oF and immediately quenching them in oil. Once clean at room temperature,
they were placed back in the furnace and heated to 1000oF and kept at that temperature for an hour.
Once the heat treated samples were created, their diameters were measured with a digital
caliper. 2in gage marks were impressed with a mallet and 2in indenter. After marking the steel
specimens, their hardness was measured with the Rockwell Hardness Tester as described below.
Separately, their tensile strengths were tested by the universal testing machine, the steps also described
below. The broken steel specimens were then clamped back into their pre-fracture position. With a
digital caliper, the distance between the 2in gage marks and the diameter of the slimmest portion of the
neck were measured.
UNIVERSAL TESTING MACHINE
Testing the specimens’ tensile strength in the UTM was done in the following manner:
1. The specimen was placed securely in the universal testing machine’s knurled gripping nuts.
2. An electronic extensometer was properly mounted on the specimen before a load was applied.
The extensometer measured and plotted load against strain in real-time.
3. The specimen was loaded by turning the ‘Load’ valve counter-clockwise. The strain rate was kept
steady at around 0.2/min.
4. Once the strain reached 0.1 for as-received and quenched and tempered, and 0.2 for fully
annealed the extensometer was removed to avoid damage during fracture.
5. The loading was resumed until the sample necked and fractured.
ROCKWELL HARDNESS TESTER
The B Scale was used for the as-received and fully annealed samples, and the C Scale was used
for the quenched and tempered sample. Testing the specimens’ hardness in the Rockwell Hardness
Tester was completed in the following manner:
1. The specimen was placed horizontally on the stand underneath the indenter.
2. The indenter control wheel was turned clockwise until the indenter made contact with the
specimen. The wheel was then turned slowly until the shortest pointer on the dial gage pointed
directly over the designation dot.
3. By rotating the dial at the base of the machine, the longer pointer was adjusted to match its
corresponding indicator arrow.
4. The pedal at the lower front of the machine was pressed to engage the load.
5. After the load settled and the lever at the bottom right of the machine stopped self-rotating
clockwise, the lever was pulled counter-clockwise. The reading on the dial was recorded.
6. The sample was re-positioned to where the indenter could punch a fresh indent. The test was
repeated twice more, both in different locations along the specimen.
RESULTS
Two 4140 steel specimens of the as-received, fully annealed and quenched and tempered
conditions were tested in hardness and tensile strength.
Table 1 - AR
Property
Elastic Modulus
Experimental
Literature
% Difference
23553579.17 psi
29700000 psi
23.1%
73066.32 psi
97900 psi
29.1%
103272.60 psi
148000 psi
35.6%
% Elongation
16.63%
17.8%
6.8%
% Reduction in Area
34.82%
48.2%
32.2%
96.4
99
2.7%
Property
Elastic Modulus
Yield Strength
Tensile Strength
% Elongation
% Reduction in Area
Hardness, Rockwell B
Table 2 - O
Experimental
Literature
28270774.68 psi
29700000 psi
54102.60 psi
60200 psi
99216.20 psi
95000 psi
27.74%
25.7%
44.97%
56.9%
86.3
92
% Difference
4.9%
10.7%
4.3%
7.6%
23.4%
6.4%
Property
Elastic Modulus
Yield Strength
Tensile Strength
% Elongation
% Reduction in Area
Hardness, Rockwell C
Table 3 – Q&T
Experimental
Literature
30382893.20 psi
29700000 psi
174700.45 psi
161000 psi
186135.80 psi
171900 psi
13.25%
15.4%
36.75%
55.7%
32.65
37
% Difference
2.3%
8.2%
8.0%
15.0%
41.0%
12.5%
Yield Strength
Tensile Strength
Hardness, Rockwell B
Figure 1. Complete stress-strain curves
Figure 2. Cropped stress-strain curves for as-received 4140 steel with 0.2% offset line
Figure 3. Cropped stress-strain curves for fully annealed 4140 steel with 0.2% offset line
Figure 4. Cropped stress-strain curves for quenched and tempered 4140 steel with 0.2% offset line
DISCUSSION
Figure 5. Properties of Q&T 4140 steel against tempering temperature
CONCLUSION
The as-received, fully annealed and quenched and tempered specimens created and tested in
this experiment exhibited expected macroscopic characteristics. The fully annealed sample showed a
greater ductility and lower strength while the quenched and tempered sample presented a much
greater strength but lower ductility in comparison to the sample in its as-received condition.
REFERENCES
“AISI 4140 Steel, normalized at 870°C (1600°F), air cooled, 13 mm (0.5 in.) round,” MatWeb: Material
Property Data, MatWeb LLC.2011,
http://www.matweb.com/search/DataSheet.aspx?MatGUID=42f0179c4d5d4d49b20feb5ad9370f08
“AISI 4140 Steel, oil quenched, 13 mm (0.5 in.) round [845°C (1550°F) quench, 540°C (1000°F) temper,”
MatWeb: Material Property Data, MatWeb LLC. 2011,
http://www.matweb.com/search/DataSheet.aspx?MatGUID=423b97220479413cbecf2143727e8b3b
“AISI 4140H Steel, annealed at 815°C (1500°F) furnace cooled 11°C (20°F)/hour to 665°C (1230°F), air
cooled, 25 mm (1 in.) round,” MatWeb: Material Property Data, MatWeb LLC. 2011,
http://www.matweb.com/search/DataSheet.aspx?MatGUID=c7710cd98dc6450885e73d3b6db9b2f3
APPENDIX
Table 4. Hand Data
4140 AR (a)
Lo
Lf
Do
Df
HRb
2.005
2.315
0.507
0.411
96.0
4140 AR (b)
Lo
Lf
Do
Df
HRb
2.000
2.356
0.505
0.406
96.0
%EL
Ductility
17.80%
%RA
35.36%
4140 O (a)
Lo
Lf
Do
Df
HRb
1.980
2.544
0.505
0.375
85.9
% EL
Ductility
28.48%
% RA
44.86%
87.1
85.0
4140 O (b)
Lo
Lf
Do
Df
HRb
2.002
2.543
0.508
0.377
89.3
% EL
Ductility
27.00%
% RA
45.07%
4140 QT (a)
Lo
Lf
Do
Df
AQ HRc
Tempered HRC
1.986
2.211
0.502
0.402
47.0
35.5
4140 QT (b)
Lo
Lf
Do
Df
AQ HRc
Tempered HRC
1.982
2.283
0.502
0.397
46.0
32.1
% EL
Ductility
15.46%
% RA
34.28%
97.5
96.0
96.0
97.0
84.2
86.4
% EL
Ductility
11.30%
% RA
36.03%
46.5
28.0
49.5
32.2
% EL
Ductility
15.19%
% RA
37.46%
48.0
34.5
48.0
33.5
avg
96.5
avg
96.3
avg
86.0
avg
86.6
avg
47.7
31.9
avg
47.3
33.4
Table 5. Properties and Tempering Temperature
o
Temp ( F)
400
600
800
1000
1200
UTS(ksi)
257
225
181
138
110
1000
186.9396
YS(ksi)
238
208
165
121
95
%EL
8
9
13
18
22
%RA
38
43
49
58
63
Bhn
510
445
370
285
230
HRc
51.6
47
40.4
29.9
20.2
175.8562
15.19
37.46
310.9
33.4
(experimental
data)