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The Ac1 (lower transformation temperature) for 4140 steel in degrees C. QUESTION 2 The AC3 (upper transformation temperature), at which the iron is transformed to
The Ac1 (lower transformation temperature) for 4140 steel in degrees C. QUESTION 2 The AC3 (upper transformation temperature), at which the iron is transformed to austenite, is degrees C. QUESTION 3 What is the quickest cooling rate per second according to the 4140 steel CCT diagram? A. 0.040C/sec B. 8C/sec C. 37.7C/sec D. 1.07C/sec For a cooling rate of 27.7C/sec, the expected hardness would be HV. QUESTION 5 What type of microstructure can I expect if I have a cooling rate of 8C/sec ? A. Bainite and martensite B. Ferrite and bainite C. Austenite and pealite D. Coarse pearlite (large grain) QUESTION 6 True or False: For a cooling rate of 27.7C/sec., the time it takes to cool from the upper critical temperature to 100C is approximately 90 seconds. True False What cooling rate will yield the softest part with the lowest hardness reading? A. 37.7C/sec B. 1.07C/sec C. 0.040C/sec D. Any rate will provide the same hardness reading QUESTION 8 True or False: Martensite begins to form at 500C. True False QUESTION 9 What is the best cooling rate to achieve a hardness of 308HV ? A. 27.7C/sec B. 0.079C/sec C. 0.48C/sec D. 2.35C/sec
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