Laboratory heats of SAE 4135 steel modified with 0.75 percent Mo and 0.035 percent Cb were tested for the effect of rolling temperature, cooling rate after austenitizing and after tempering, and tempering time and temperature on mechanical properties and sulfide stress cracking (SSC) resistance. The SSC resistance of unworked heat-treated material was also determined. Tests were performed on bent beam specimens and double cantilever beam specimens. Hot working temperature in the range of 815 – 1205°C (1500–2200° F) has practically no effect on SSC resistance. Cast modified SAE 4135 steel in the quenched-and-tempered conditon has lower SSC resistance than wrought material, but the SSC resistance of the unworked material is nevertheless about equal to that of wrought SAE 4130 steel in the quenched-and-tempered condition having the same yield strength. Optimum SSC resistance of modified SAE 4135 steel is obtained in quenched-and-tempered material with a uniform structure of tempered martensite. The SSC resistance is reduced with increasing amounts of bainite in the microstructure. SSC resistance increases with increasing tempering time and temperature. Rapid cooling after tempering reduces SSC resistance only insofar as it increases the hardness of the steels. SSC resistance of the modified steel is distinctly higher than that of unmodified SAE 4130 steel. This advantage increases with increasing strength level of the steel.

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