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 σ_c⁸⁵. Fractographic study reveals that σ_c⁸⁵ corresponds to the minimum yield strength for the occurrence of intergranular fracture. σ_c⁸⁵ rises with refinement in austenite grains, Rs is not affected by austenite grain size at yield strengths below σ_c⁸⁵. σ_c⁸⁵ 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 σ_c⁸⁵.