Study on Microstructures and Properties of Low-Carbon-Steel Heavy Plate Treated by Quenching and Dynamic Partitioning

As a modification of quenching and partitioning processing for martensitic steels to obtain mixed microstructures of martensite and austenite aiming at improving strength plasticity, the process of quenching and dynamic partitioning is much simple in practical, especially suitable for components with larger cross-sections. In this paper, a kind of air-quenched low-carbon steel was designed and prepared. The martensitic transformation behaviors at different cooling rates, the structure–property relationship and the strengthening–toughening mechanisms of testing steel under a different processing were explored. The results show that the testing steel exhibits good hardenability that fairly martensitic transformation occurs while it is cooled at the rate of 0.1~1.0°C.s^-1. The microstructures of plate samples with 25~40 mm in thickness after air quenching are composed of lath martensite and strip-like retained austenite of about 5 vol.%. Once the air-quenched samples are tempered at 450°C, the volume fraction and thermal stability of retained austenite are further reinforced, and good comprehensive properties are obtained with R_p0.2≈1200 MPa, R_m≈1400 MPa, A≈18% and KV≈1000 kJ.m^-2.