The twice softening of martensitic matrix in Q–P–T steels and its effect on ductility

Abstract

ABSTRACTWhen a Si-containing steel is subjected to quenching-partitioning-tempering (Q–P–T) process, it will become a martensitic steel with considerable volume of retained austenite, which is attributed to the partitioning of carbon from martensite to retained austenite leading to carbon-depletion in martensitic matrix and carbon-enrichment in the retained austenite. The softening of the martensitic matrix caused by carbon-depletion markedly enhances its deformation ability and raises the ductility of Q–P–T steels. During deformation dislocation absorption by retained austenite (DARA) effect will occur, that is, the dislocations in martensitic matrix will move into nearby retained austenite through the martensite-austenite interface and be absorbed by the retained austenite. This second softening of the martensitic matrix also enhances its deformation ability and effectively raises the ductility. The effect of DARA on ductility during deformation is more effective than the transformation-induced plasticity (TRIP) effect caused by martensitic transformation of retained austenite, because during the TRIP effect the twin-type martensite produced by strain-induced martensitic transformation of retained austenite is very detrimental to ductility.