Tool Steels. Influence of Ni Content on the Property of Heat Checking in Maraging Steel.

Effect of Ni content, range of 6% to 24%, on the heat checking resistance of 4%Mo -8%Co maraging steel were studied. The experimental results are as follows. (1) The heat-checking resistance for the total number, mean length and maximum length of heat checks, were improved with decreasing Ni content. In order to improve heat-checking resistance quantitatively, Ni content must be lowering to 18% at 873K, 12% at 923 and 973K, respectively. But crack length was significant level at 973K heat-checking test. (2) The effect of Ni was quantitatively converted to the HC value. HC= (Heat checking temp.) / (As temp.) Heat checking temp.:Heat checking temperature (K) As temp.:Austenite transformation temperature gained by 150K/s heating rate(K) ,which is equal to heat checking test . The heat-checking resistance were decreased drastically the HC value, above 1.0, whereas improved gradually with decreasing the HC value, below 1.0. (3) Austenite retransformation has occurred the HC value, above 1.0