Effect of tempered martensite micro structure on strength and SSC resistance of the HSLA steel with varying carbon content

摘要

The effect of microstructure of high strength low alloy steel (HSLA) on strength and sulfide stress cracking (SSC) resistance is investigated for achieving superior sour resistance to the existing sour grade materials. Modified AISI 4130 (1.0wt%Cr-0.7wt%Mo-0.1wt%V) steel with varying carbon content from 0.15wt% to 0.58wt% quenched and tempered were analyzed with respect to martensite sub-structure (such as block size), precipitation of carbide, dislocation density and hydrogen absorption behavior. By increasing carbon content, the sizes of martensite blocks were refined (become smaller). It resulted in increasing strength of the steel even after high temperature tempering. The high temperature tempering leaded to reducing dislocation density and spheroidizing carbides. Hydrogen absorption in the steel with higher carbon content was reduced in a sour environment due to the reduction in dislocation density. SSC resistance was evaluated using tensile tests according to NACE Standard TM0177 Method A. The steel with higher carbon content had higher threshold strength of SSC resistance, which is likely to be due to the above mentioned microstructural improvements.