Report and Analysis of experiment which tested the mechanical properties and resulting microconstituents of carbon steel under various cooling conditions

1. Lab # IV:
Heat Treatment of Steels
Submitted By
DeAndria L. Hardy
Laboratory Instructor: A Samant
Date of Experiment: March 22, 2007

2. I. Introduction
The purpose of this lab was to illustrate the cooling effects of plain carbon steel.
To observe this, plain carbon steel was cooled from austenite using four methods. The
methods were furnace cooling, air cooling, water or oil quenching. Also during this lab
the effects of additional tempering after quenching on the steel’s microstructure and
hardness were observed.
II. Procedure
For this lab six samples of each of the three carbon steel compositions-1018
(.18% C, .39% Mn), 1045 (.45% C, .88% Mn), 1095 (.95% C, .39% Mn) - were
austenitized for two hours at 870oC. After the steels were austenitized they were given
various heat treatments. Micrographs provided by the TA were used for comparison of
the various heat treated samples.
Hardness measurements were taken of the heat treated samples and converted
from Scales B and C to DPH. Also a Jominy End Quench Test was performed and the
hardness recorded and converted to the DPH scale.
III. Results and Discussion
All data, results, tables, graphs and micrographs can be found in supplement sheets.
When steel is heat treated to reduce its heated temperature down to room
temperature, continuous cooling is required. On the Continuous Cooling Transformation
(CCT) diagram provided by the TA, a sketch of the approximate cooling curves for the
specimens tested can be found. The CCT not only approximates cooling curves but also
when transformation occurs within the steel. A transformation in the material begins after
a time period corresponding to the intersection of the cooling curve with the start of the
reaction curve, and ends after crossing the completion transformation curve. As observed,
each sample has a different cooling curve and rate so different microconstituents will be
present.
The cooling rate of each cooling type (anneal, air, oil, and water) is calculated by
dividing the change in temperature by the cooling time. As the cooling rate of the
samples increased, their hardness also increased. This is evident even without a hardness
being performed. The convention of cooling rate and hardness increasing simultaneously
can be made by comparing cooling rates with corresponding microconstituents. For
instance, the rate of the annealed sample is a negligible amount, and it forms coarse
Pearlite, while the water quenched sample has a high cooling rate and forms Martensite.
Martensite is substantially harder than Pearlite so it’s concluded that a higher cooling rate
yields an increase in hardness.
From the data recorded in Table 5 and the corresponding graph of Temperature vs.
Hardness, the correlation between the hardness and the percent weight of carbon in each
steel sample is seen. The higher the percent carbon, the higher the hardness value of the
steel. Also it’s evident that the hardness value decreases as the tempering temperature
increases. There is a slight inconsistency of the 1045 steel tempered at 370 oC. This can
mostly likely be attributed to the fact that the 1045 steel sample is 0.88% Mn compared
to the other steel samples having only 0.39% Mn.

3. The Jominy End Quench Test was used to observe the relationship between the
hardness of the steel and its cooling rate. The Jominy End Quench Test exposes the lower
end of the steel specimen to a jet of water at a specified flow rate and temperature. As a
result, the cooling rate is at its max at the quenched end of the specimen and diminishes
with position along the length of the specimen. Due to this diminishing cooling rate along
the vertical axis, the hardness decreases as the distance from the end of the specimen
increases. A direct correlation can be seen to Table 5 and its corresponding graph where
the hardness decreased as the temperature increased.
IV. Conclusion
It was observed that hardness increased as the cooling rate increased. The
formulation of microconstituents depended on the method of cooling and the rate of the
cooling curve. As the tempering temperature of a sample increased, the hardness of that
sample decreased. In the Jominy End Quench Test, the hardness decreased as the
distance from the sample’s end increased.

4. Table 1: Hardness Data for Heat Treated Sample
Sample
Rockwell Hardness
DPH
1018A
86.3 (Scale B)
175
1045A
89.8 (Scale B)
192
1095A
98.5 (Scale B)
247
1018N
91.7 (Scale B)
203
1045N
94.6 (Scale B)
220
1095N
23.1 (Scale C)
254
1018O
98.4 (Scale B)
240
1045O
35.5 (Scale C)
353
1095O
47.5 (Scale C)
485
1018WQ
45 (Scale C)
446
1045WQ
47 (Scale C)
471
1095WQ
57 (Scale C)
636
1018WT(370)
32.7 (Scale C)
327
1045WT(370)
37.8 (Scale C)
373
1095WT(370)
47.5 (Scale C)
485
1018WT(705)
95.6 (Scale B)
225
1045WT(705)
96.5 (Scale B)
230
1095WT(705)
21.7 (Scale C)
246
Table 2: Avg Cooling Rate for each Cooling Type
Material
Avg. Cooling Rate (oC/s)
Annealed
0.009
Normalized
0.47
Oil quenched
28.17

5. Water quenched
422.50
Table 3: Microconstituents Present According to CCT Graph
Material
I. Annealed
II. Normalized
III. Oil quenched
Microconstituents
Coarse Pearlite
Fine Pearlite
Bainite, Fine Pearlite,
Martensite
IV. Water quenched
Martensite
Table 4: Hardness Data for Jominy Bar
Distance from the quenched end (in)
Rockwell Hardness
DPH
0.129
55.7 (Scale C)
617
0.182
35.5 (Scale C)
353
0.461
24.9 (Scale C)
268
0.802
21.4 (Scale C)
243
1.113
96 (Scale B)
225
1.372
95.3 (Scale B)
220
1.603
91.7 (Scale B)
203
1.872
91.7 (Scale B)
203
2.31
90.7 (Scale B)
198
2.514
94 (Scale B)
214
2.852
93 (Scale B)
209
3.137
92.7 (Scale B)
209

6. Jominy Hardness Data
700
600
Hardness
500
400
Series1
300
200
100
0
0
0.25 0.5 0.75
1
1.25 1.5 1.75
2
2.25 2.5 2.75
3
3.25
Distance From End (in)
Table 5: Hardness Data for Tempering Temperatures
Carbon
WQ+Tempering WQ+ Tempering at WQ+ Tempering
Content
at 25 oC
370 oC
at 705 oC
(Wt. %)
(DPH)
(DPH)
(DPH)
0.18
528
279
232
0.45
562
271
274
0.95
613
353
312
Steel
1018
1045
1095
Temperature vs. Hardness
Hardness (DPH)
700
600
500
1018
400
1045
300
1095
200
100
0
0
100
200
300
400
Temperature
500
600
700
800

7. Jominy Hardness Data
700
600
Hardness
500
400
Series1
300
200
100
0
0
0.25 0.5 0.75
1
1.25 1.5 1.75
2
2.25 2.5 2.75
3
3.25
Distance From End (in)
Table 5: Hardness Data for Tempering Temperatures
Carbon
WQ+Tempering WQ+ Tempering at WQ+ Tempering
Content
at 25 oC
370 oC
at 705 oC
(Wt. %)
(DPH)
(DPH)
(DPH)
0.18
528
279
232
0.45
562
271
274
0.95
613
353
312
Steel
1018
1045
1095
Temperature vs. Hardness
Hardness (DPH)
700
600
500
1018
400
1045
300
1095
200
100
0
0
100
200
300
400
Temperature
500
600
700
800