1. Memo Report No. III College of Engineering and Computer Science at California State
University, Northridge
Group # 4, Tuesday, Heat Treatment and Hardenability of Steel
To: Lisa R. Reiner
From: Stephanie Ha
Date: November 4, 2008
ABSTRACT
The effect of heat treating six SAE1045 type steel specimens was examined by taking hardness
measurements before and after heat treating each specimen
DESCRIPTION OF WORK
Initial hardness measurements using the Rockwell A scale were taken before and after the heat
treatment of six SAE1045 type steel. Four specimens were heated in one furnace at 870 ± 15°C
for 30 minutes and later quenched while the other two specimens were heated in a separate
furnace at the same temperature for 30 minutes.
One specimen from the separate furnace was taken out and air-cooled for one hour and the other
left in the furnace to furnace cool for an hour. Air-cooling on a brick and furnace-cooling (in a
furnace) these specimens illustrate how cooling affects hardness and allows for other phases.
Hardness measurements were taken for the air-cooled, furnace-cooled, and quenched samples
before tempering. Three of the quenched samples were then re-heated (tempered) at: 315°C,
430°C, and 540°C for 30 minutes. The purpose of quenching and tempering these samples is to
enhance the toughness and ductility of a material.
After tempering, hardness measurements were taken using the Brinell (3000kg) and Rockwell A
scales. The diameter of impression, d for each specimen was measured using dial calipers.
Brinell numbers were then computed using the following formula: HB = 2P / πD|D-(D2
– d2
)1/2
|
where P = 3000kg, D (diameter of ball) = 10mm, d = diameter of indent.
Based on a conversion chart for Rockwell A or C, the computed values were compared with the
converted values. From the averaged BHN, the ultimate tensile strength (uts) was calculated
using: σult = 500 x B.H.N. Graphs were then constructed for B.H.N vs. Rockwell numbers
(Figure3) and Rockwell A or C vs. annealing temperature (°C, Figure2).
Two steels: type1045 and type4143 were stamped for identification. Initial hardness using the
Rockwell A scale was then measured. Specimens were then placed in a furnace at 870 ± 45°C for
45 minutes. (While waiting for the specimens, the microstructure of the alloy steel and carbon
steel specimens were examined).
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2. After 45 minutes, one specimen was removed and placed in a holder with water for 10 minutes
before quenching. After cooling, a flat surface 0.025 inches is ground along the length of the bar.
Rockwell A hardness measurements were taken 1/16 inch for the first inch, then 1/8 the next, and
¼ for the next 2 inches. A graph of distance vs. hardness (Figure1) was constructed based on this
date. Results for type4143 were then compared with another group’s.
RESULTS AND DISCUSSION
Initially, it was found that each specimen shared roughly the same hardness (from Table1):
SAE1045 I with 56.5, 54.7, 53.5, SAE1045 II with 56.6, 56.1; SAE1045 III with 54.3, 56.0;
SAE1045 IV with 55.3, 53.1; SAE1045 V with 53.1, 54.4; SAE1045 VI with 55.3, 54.9. Heat
treating (Table2), however, showed that the quenched samples increased in hardness: Quenched I
with 81.1, 80.5; Quenched II with 79.5, 80.4; Quenched III with 78.0, 77.7, 78.1; Quenched IV
with 79.2, 80.4 in comparison with the initial readings.
Results (table2) indicated that the air-cooled and furnace-cooled samples showed a great
decrease in strength with measurements being: 1) air-cooled with 46.7, 46.3, 46.6; 2) furnace-
cooled with 46.5, 47.4.
Table3 illustrates hardness testing results after testing for each specimen. Brinell measurements
were found to be 514, 388, and 352, respectively for temperatures: 315°C, 430°C, and 540°C.
Calculated values were found to be precise and accurate within the Brinell measurements with:
516, 390, and 354. Meanwhile, converted HRA values were found to be imprecise and
inaccurate. Results are as follows: 1) 443, 469, and 443 for T = 315°C compared with 514 HB;
2) 253, 294, and 294 for T = 430°C compared with 388 HB; 3) 294, 311, and 294 for T = 540°C
compared with 352 HB.
Continuing with table3, averaged BHN values of 452, 280, and 300 still indicate that the values
are still inaccurate and imprecise when compared with the Brinell measurements. Consequently,
from the averaged values, σult was found to be 226kpsi, 140kpsi, and 150kpsi.
Thus, the hardness test that appears to be the most accurate and most consistent is the Brinell
(3000kg). The machine is restricted to sphere shaped materials but is most consistent within a
millimeter of impression and is not as versatile as Rockwell A.
Possible sources of error for the Rockwell A tester lies in calibrating the tester as well as the
shape of the material. It can be used for many shapes, sizes, and tips can be changed accordingly
to a material. However, it is noted that readings tend to differ whenever a different area of the
same material is tested.
Accordingly, it is found that figure 1 and table5 illustrate the scattering of hardness (HRA).
Factor(s) that probably contributed to the scattering of data is the uneven uniform water flow of
the quenched end of the bar which can possibly lead to an uneven distribution of heat throughout
the bar.
2
3. From table5, it is evident that values fluctuated as measurements were made along the length of
the bar. The general trend between the two 4143 columns is that values increased and decreased
periodically throughout the hardness testing of the bar. Instead of a linear decrease in hardness
(along the bar) as measurements were made from the quenched end before reaching the bar, the
data was heavily scattered.
However, there are slight discrepancies between the data. To further illustrate this point, the 1st
column of 4143 begins at 48.9 then increasing to 53.5 as the length increased while the 2nd
column decreases for the first two measurements: beginning at 61.7 then decreasing to 52. It was
stated previously that the uneven water flow distribution for the quenched end is a possible
source of error for this experiment.
Using the inverse lever rule, the amount of carbide present at 733°C for SAE1045 was .
However, heating a sample at 1600 ± 25°F (870 ± 15°C) for ½ hour and then rapidly quenching
it yields the microstructure: marsenite (brittle and hard). The finer the microstructure and the
more transformations and heat treatment a material undergoes: the greater the strength the
material has but with the cost of low ductility.
Tempering, however, enhances the strength but decreases the ductility of the remaining three
specimens. A material undergoes a phase transformation whenever a material is heated at a high
temperature and later re-heated to an intermediate temperature to achieve a different
microstructure. Re-heating the remaining specimens with one each at: 600°C (315°C), 800°C
(430°C), and 1000°C (540°C) yielded tempered marsenite, respectively. Tempered marsenite has
a strength lower than marsenite but a greater ductility as well.
Alloying an element enhances the hardness (strength) of a material. Figure 1 illustrates hardness
vs. distance for 4143 and 1045 steel. Noting the curve, it is noted that type4143, a low alloy has
an enhanced hardness than the 1045.
Alloying shifts the nose of the TTT curve to longer times and results in an increase in the Ms
temperature which allows for a slower cooling rate to reach the marsenite phase. A slower
cooling rate permits a thicker part to be heat-treated.
APPENDIX
Table1. Initial Hardness of SAE1045 (before heating)
Specimen RA (Rockwell A Hardness)
SAE1045 I 56.3, 54.7, 53.5
SAE1045 II 56.6, 56.1
SAE1045 III 54.3, 56.0
SAE1045 IV 55.3, 53.1
SAE1045 V 53.1, 54.4
SAE1045 VI 55.3, 54.9
Table2. Hardness of SAE1045 after heating
Specimen RA (Rockwell A Hardness)
Air-Cooled 46.7, 46.3, 46.6
Furnace-Cooled 46.5, 47.4
Quenched I 81.1, 80.5
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6. Basis: HB = 2P / πD|D-(D2
– d2
)1/2
| where P = 3000kg, D (diameter of ball) = 10mm, d =
diameter of indent
1. HB for d = 3.232mm for T = 540°C
HB = 2(3000kg) / π10mm|10mm-(10mm2
– 3.232mm2
)1/2
|
= (6000kg) / π10mm|10mm-(100mm2
– 10.445824mm2
)1/2
|
= (6000kg) / π10mm|10mm-(89.554176mm2
)1/2
|
= (6000kg) / π10mm|10mm-9.46mm|
= (6000kg) / π10mm|0.54mm|
= 353.677 ≈ 354
2. HB for d = 3.094mm for T = 430°C
HB = 2(3000kg) / π10mm|10mm-(10mm2
– 3.094mm2
)1/2
|
= (6000kg) / π10mm|10mm-(100mm2
– 9.572836mm2
)1/2
|
= (6000kg) / π10mm|10mm-(90.427164mm2
)1/2
|
= (6000kg) / π10mm|10mm-9.51mm|
= (6000kg) / π10mm|0.49mm|
= 389.767 ≈ 390
3. HB for d = 2.692mm for T = 315°C
HB = 2(3000kg) / π10mm|10mm-(10mm2
– 2.692mm2
)1/2
|
= (6000kg) / π10mm|10mm-(100mm2
– 7.246864mm2
)1/2
|
= (6000kg) / π10mm|10mm-(92.753136mm2
)1/2
|
= (6000kg) / π10mm|10mm-9.63mm|
= (6000kg) / π10mm|0.37mm|
= 516.18 ≈ 516
B. Converted Rockwell A to Brinell (based on hardness conversion tables from Gordon)
*Note: Values are rounded up or down depending on its decimal digit!
1. HB for T = 315°C
a. 74.4 HRA = ≈ 74 HRA = 443 HB
b. 75.3 HRA ≈ 75 HRA = 469 HB
c. 73.9 HRA ≈ 74 HRA = 443 HB
2. HB for T = 430°C
a. 62.7 HRA ≈ 63 HRA = 253 HB
b. 65.5 HRA ≈ 66 HRA = 294 HB
c. 65.8 HRA ≈ 66 HRA = 294 HB
3 HB for T = 540°C
a. 65.7 HRA ≈ 66 HRA = 294 HB
b. 66.6 HRA ≈ 67 HRA = 311 HB
c. 66.2 HRA ≈ 66 HRA = 294 HB
C. Averaged B.H.N
1. HB for T = 315°C
HB(avg) = (443 + 469 + 443)HB / 3 = 1355HB/3 ≈ 452HB
2. HB for T = 430°C
HB(avg) = (253+294+294)HB/3 = 841HB/3 ≈ 280HB
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7. 3. HB for T = 540°C
HB(avg) = (294+311+294)HB/3 = 899HB/3 ≈ 300HB
D. σult from Averaged B.H.N for each specimen
Basis: σult = 500 x B.H.N
1. σult for T = 315°C
σult = 500 (452) = 226000psi = 226 kpsi
2. σult for T = 430°C
σult = 500 (280) = 140000psi = 140 kpsi
3. σult for T = 540°C
σult = 500 (300) = 150000psi = 150 kpsi
E. Amount of Carbide (Fe3C) present at 1338°F (733°C) for SAE1045 (based on FeC diagram)
Basis: Inverse Lever Rule
o Wt% = Cm - Cα
-------------- x 100, where Cm = unknown, Wt = 6.67, Cα = 0.022, C0 = 0.008
Cα – C0
o Wt%(Cα-C0) = 100(Cm – Cα)
o Wt%(Cα-C0)/100 = Cm-Cα
o Cm = [Wt%(Cα-C0)/100] + Cα
o Cm ≈ 8.93E-3%
REFERENCES
1. D. Callister Jr, Fundamentals of Materials Science and Engineering, J. Wiley & Sons, NY,
2nd
Ed. 2005, Chapter 5.
2. Flinn and Trojan, Engineering materials and Their Applications, Chapter 6.
3. ASM Vol 1, Properties of Iron and Steel, 1977.
4. Hardness Conversion Chart. Cabride Depot.com. 21 Oct 2008. <
http://www.carbidedepot.com/formulas-hardness.htm>
5. Equivalent Hardness Conversion Table. Gordon England. 24 Oct 2008.
http://www.gordonengland.co.uk/hardness/hardness_conversion_1m.htm
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