Study of microstructural evolution, microstructure-mechanical properties correlation and collaborative deformation-transformation behavior of quenching and partitioning (Q&P) steel

This paper presents a detailed characterization of the microstructural evolution of quenching and partitioning (Q&P) steel by dilatometer, X-ray diffraction and scanning electron microscopy. Influence of partitioning time on mechanical properties was investigated and the relationship between microstructures and mechanical properties was established. The results indicate that bainite transformation occurs at the preliminary stage of partitioning and the amount is proportional to quenching temperature. Martensite softening, bainite transformation kinetics, amount and stability of retained austenite collaboratively have effects on mechanical properties. The purpose of the EBSD investigation is to study the changes in the microstructure of the Q&P steel during deformation and obtain a better understanding of collaborative deformation-transformation behavior. During deformation, plastic deformation preferentially occurred in the vicinity of ferrite-martensite interfaces and spread to the interior of ferrite grain with strain increasing. Plastic deformation started to occur in martensite after large strain. Furthermore, grain rotation occurred in some austenite grains or divided into subgrains during deformation.