The Influence of fine Microstructures on Mechanical Properties and Formability of Ultra High Strength DP Steel

摘要

The influence of fine microstructures on mechanical property and formability of ultra high strength DP steel was researched.It was showed that if grain size of ferrite and martensite of DP980 steel increase,the demanded volume percentage of martensite increase for obtaining the same tension strength 1000MPa,at the same time,the elongation and yield strength of DP980 steel decrease.There is an obvious rule that Rp0.2 and Rm increase with volume percent of martensite increasing,and Rp0.2 and Rm of DP 980 steel with fine microstructure are higher than that of DP980 steel with coarse grain at the same martensite percentage,and Yield strength ratio Rp0.2/Rm correlates to phase size ratio Fsize/Msize,if phase size ratio Fsize/Msize increase,the yield strength ratio Rp0.2/Rm will decrease.The research also showed that decreasing the grain size of ferrite and martensite could enhance initial work-hardening rate,yield strength ratio,So DP980 steel with refined grain Ferrite and martensite has flexure properties.