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MATERIALS LABORATORY
EXPERIMENT 5
HEAT TREATMENT OF STEELS
OBJECTIVE: The structural changes that occur during the heat treatment of plain carbon steels can be related closely to the iron-carbon phase diagram and to the time-temperature (TTT) diagram for these steels.
The different response of alloy steels to heat treatment can be related to the effects of the alloying elements on the phase diagram and the TTT diagram. The object of this experiment is to study the effects of alloy content and of heat treatment on the hardness and microstructure of steels
Introduction: The experiment is divided into four parts:
A.
Effect of Carbon on Strength
B.
Effect of Cooling Rate on Austenite Transformation
C.
Tempering
D.
Hardenability
Two different steels will be evaluated, AISI 1040 and AISI 4340, with composition range specifications:
Element
C
AISI 1040 AISI 4340
0.37-0.44 0.38-0.43
Mn
Ni
Cr
Mo
P
S
0.60-0.90 0.60-0.80
--
--
--
1.65-2.00
0.70-0.90
0.20-0.30
0.04 max 0.04 max
0.05 max 0.04 max

A. Effect of Carbon on Steel
Perform Rockwell Hardness tests on 1018, 1040, and 1090 plain carbon steels impact bars. Plot hardness vs. carbon content. Discuss results thoroughly .
READING
Test 1
Test 2
Test 3
1018 Steel 1040 Steel 1090 Steel
B. Cooling Rate from the Austenizing Temperature
Austenitize the proper number of 1040 & 4340 samples at 850° C for about two hours. After which one sample is to be quenched in water, one in oil, those from a third cooled in air (normalized), and those from a fourth allowed to cool in the furnace (annealed). Obtain hardness values for each of the materials. Determine expected microstructure for each quench condition. Compare the various quench methods to each material and compare the differences in 1040 and 4340. Use TTT curves to support results.
Water Quenched
1040:
4340:
Oil Quenched Normalized Annealed
C. Tempering
The purpose of this phase is to determine the effect of both time and temperature on the tempering of steel.
Austenitize 18 samples of either 1040 and/or 4340 at 850°C for 2 hours and water quenched. Record the
Rockwell hardness values. A sufficient number of samples should then be prepared to do the following tempering at temperatures of 300°C, 400 C, and 500 C: for 5, 10, and 20 minutes, 1, 1.5, and 48 hours and/or any additional times that may be appropriate. The sample should be air cooled after the tempering operation.
Hardness readings should then be recorded. Plots of Hardness vs time for each temperature should be created. Discuss Results.
300

C
5 min:
400

C 500

C
10 min:
20 min:
60 min:
90 min:
2880 min:
NOTE: Indicate Rockwell Scales when reporting values

D. Jominy End-Quench Hardenability
Austenitize a bar of each steel at 850 C for one hour. Prior to placing the bar in the fixture, adjust the flow rate so that a 2 ½” stream flows above the outlet. Close the valve. Remove the bar from the furnace and place into the Jominy apparatus. Open the water valve and allow the sample to cool for 10 to 15 minutes.
Grind flats on opposite sides of the bar. Take hardness readings every 1/16” for the first inch, then in 1/8” intervals for the second inch, and ¼” for the rest of the bar.
Plot hardness vs. distance from the quenched end. DISCUSS RESULTS.
Reading (distance from quenched end) [in]
0
1/16
1/8
3/16
1040 Steel
Rockwell C
4340 Steel
Rockwell C
1/4
5/16
3/8
7/16
½
9/16
5/8
11/16
¾
13/16
7/8
1
1 1/8
1 ¼
1 3/8
1 ½
REPORT MATERIAL:
Hardness vs. Carbon Content
Hardness results for the various quenches
Hardness results for the tempering
Hardenability curves
Differences between 1040 & 4340
Discuss the microstructure present and whether the mechanical data supports this. Correlate the microstructure with TTT curves (when appropriate) and hardness values. Discuss all plots and graphs and report sources of error if any.