초미세 결정립 이상 조직강의 가공경화거동

Abstract

Strain hardening behavior of ultrafine grained (UFG) dual-phase (DP) steels via equal-channel angular pressing and subsequent intercritical annealing followed by water quenching was investigated at ambient temperature. The formation of UFG martensite islands of ~1㎛ was not confined to the prior pearlite colonies, but uniformly distributed throughout UFG ferrite matrix. Their room temperature tensile properties were examined and compared to those of coarse grained DP steels. Although uniform and total elongations were not degraded, the strengths of UFG-DP steels were much higher than that of coarse grained DP steels. In contrast to conventional UFG steels fabricated by equal-channel angular pressings, UFG-DP steels exhibited significant strain hardening rate, which was attributed to uniform distribution of island-typed martensite as well as grain refinement of each constituent phase throughout the microstructure. Such strain hardening behavior was discussed in relation to modified C-J analysis based on Swift relationship.