Abstract
The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.
Highlights
The quenching and partitioning (Q-P) process has been applied to advanced high-strength steels to obtain austenite (γ) + martensite (α) multiphase microstructures, which exhibit high strength and excellent ductility [1,2,3,4]
The microstructural evolution and carbon redistribution in the one-stage Q-P process and two-stage Q-P process were assessed by modeling
The interface migration, uniformity of carbon in austenite and retained austenite after the final quenching were considered in the simulation
Summary
The quenching and partitioning (Q-P) process has been applied to advanced high-strength steels to obtain austenite (γ) + martensite (α) multiphase microstructures, which exhibit high strength and excellent ductility [1,2,3,4]. In the Q-P process, the quenching of austenite between the martensite start temperature (Ms ) and the martensite finish temperature (Mf ) results in martensite laths and untransformed austenite. In the partitioning step, the steel is held at the same or higher temperature to promote carbon diffusion from supersaturated martensite to untransformed austenite. The process improves the carbon concentration in austenite, and the austenite retains greater stability at room temperature. The quenching, partitioning and tempering (Q-P-T) process emphasizes the effects of alloy carbides, and results in higher strength and elongation for some alloy steels [10,11].
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