Effects of Strengthening Mechanisms on Sulfide Stress Cracking Resistance of Low Strength Steels

抄録

Sulfide stress cracking (SSC) of low strength steels are often thought as being related to non-metallic inclusions. However, effects of intrinsic metallurgical factors such as chemical composition and micro structure have not yet been clarified. In this paper, effects of strengthening due to grain refining, precipitation, solid solution and dislocation were studied using tensile type SSC tests. Threshold stress (σ_th) is in proportion to intragrain hardness irrespective of strengthening mechanism and grain size. Further analysis shows that σ_th is related to σ_o defined in the Hall-Petch relationship. The ratio of σ_th to yield strength therefore increases with an increase in grain size, which is contrary to the case of high strength steel. The difference originates from the fact that SSC of low strength steels is transgranular whereas SSC of high strength steel contains integranular fractures.