Influence of Silicon Contents on the Microstructure and Tensile Properties of Quenching and Partitioning (Q&P) Processed Low Carbon Steel

Abstract

The microstructure and corresponding tensile properties were examined in quenching and partitioning (Q&P) processed low carbon steels, depending on the silicon content ranging from 0.1–2.0 wt.%. The silicon content and process temperature generated a highly interactive influence on the evolution of final microstructure, including the fraction of constituent phases and their characteristics such as solute carbon content in each phase. The yield strength was nearly unchanged or slightly decreased even with the silicon addition for a given Q&P condition. The change of yield strength showed a reasonable correlation with the loss of solute carbon in martensite or bainite caused by the carbide precipitation and the carbon partitioning into austenite, which depended on the silicon content. High partitioning temperature enhanced the yield strength for a given silicon content and quenching condition, because of the tempering effect on the martensite matrix. Although the fraction and stability of retained austenite were still critical for improving ductility, the intrinsic properties of the martensite matrix, such as the occurrence of tempered martensite embrittlement, governed the ductility of Q&P steels in situations where the role of retained austenite was limited due to low fraction or poor mechanical stability.