Microstructure and Tensile Deformation Behavior of a Hot-rolled Directly Quenched and Dynamically Partitioned Steel Containing Proeutectoid Ferrite

摘要

Hot-rolling direct quenching and dynamical partitioning (HDQ&DP) processes were applied to a low-carbon steel containing silicon and manganese based on thermo-mechanical control process (TMCP) technology and ultra-fast cooling (UFC) technology. The microstructures and phase compositions were characterized and analyzed using SEM, EBSD, TEM and XRD. The mechanical properties and tensile deformation behaviors were investigated by means of uniaxial tensile test. The microstructures and tensile deformation behaviors of both HDQ&DP steel with and without proeutectoid ferrite were comprehensively expounded by comparing with each other. Results show that the amount of retained austenite in the HDQ&DP steel with proeutectoid ferrite can reach up to 17.3%, which is higher than that in the HDQ&DP steel without proeutectoid ferrite (15.7%). The HDQ&DP steel without proeutectoid ferrite possesses extremely high ultimate tensile strength (UTS) up to 1700 MPa with yield ratio about 0.73 and elongation about 11.5%. The introduction of proeutectoid ferrite can result in a moderate decrease of UTS to 1240-1400 MPa, a drastic decrease of yield ratio to 0.51-0.69 and a certain increase of elongation to 13.0-13.7%. The existence of the proeutectoid ferrite can partly enhance the work hardening ability of the steel and may improve its formability. It is concluded that the HDQ&DP steel with relatively large amount of proeutectoid ferrite and certain amount of bainite has extensive application prospects.