Effect of Austenite Grain Size on Sulfide Stress Cracking Resistance of Low Alloy Martensitic Steels.

Abstract

Effect of grain size on sulfide stress cracking (SSC) resistance, thought to be an important metallurgical factor, is not clearly understood. There are some conflicting experimental results about grain size effect on SSC resistance. In this paper, effect of austenite grain size of low alloy tempered martensite steel was investigated using a constant load SSC test, considering their correlation with chemical compositions. An Rs value (SSC threshold stress/yield strength) begins to decrease with increase in yield strength at the yield strength equal to σc85. Fractographic study reveals that σc85 corresponds to the minimum yield strength for the occurrence of intergranular fracture. σc85 rises with refinement in austenite grains, Rs is not affected by austenite grain size at yield strengths below σc85. σc85 at a constant grain size is influenced also by chemical compositions. When Rs is plotted against its tensile strength, no effect of austenite grain size, however, appears. The proposed model shows that grain refinement strengthening apparently increases σc85.