Abstract: As one of the most promising candidates for the 3rd generation advanced high-strength automotive steel, quenching and partitioning (Q&P) steels have attracted wide attention due to their low cost and superior comprehensive mechanical performance. Compared with the 1st and 2nd generation of advanced high strength steel, Q&P steel is more consistent with modern automobile development idea of light weight, environmental friendliness and safety, which is applicable to manufacturing high-strength and complex stamping parts like bumpers, collision beams and A/B/C columns. In particular, alloying elements are fundamental for research and development of Q&P steel. In recent years, by exerting the role of alloy elements in steel and following microstructure control concept of “multiphase”, “metastable” and “multiscale”, Q&P steel has achieved considerable progress in comprehensive performance. Nevertheless, the prohibitive strength of Q&P steel (800—1 500 mPa) has kept manufacturers away, only a few domestic steel enterprises (Baosteel, Ansteel and Tangsteel) possess production capacity. Inspired by the development of mn-Si TRIP steel and high-Si C-free air-cooled bainite steel, J.G.Speer revealed basic concept of Q&P steel comprehensively based on the experimental results of high carbon or medium carbon Si-contained steel and relative thermodynamics and kinetics simulations analysis. The key procedure lies in the selection of quenching temperature and partitioning time, namely, maximizing C partitioning on the premise of ensuring strength, for the sake of acquiring the optimal martensite/austenite multiphase structure ratio. Thereby numerous researchers are devoted to continuously explore the process parameters of Q&P steel. It has been found that carbides precipitation and austenite decomposition as a competition with C partitioning are inevitable during partitioning process, and it is impossible for C to completely diffuse into austenite, resulting in retained austenite content being only about 10%, which restricts the further increase of elongation. While continue to raise C content will deteriorate welding performance. In order to solve this contradiction, researchers at home and abroad have proposed the idea of stabilizing austenite by co-partitioning of alloying elements like C, mn, etc. Specifically, partitioning behaviors of alloy elements and the way to promote their partitioning in Q&P steel have become the focus of current research on austenite stabilization. 3D-APT or EPmA techniques are employed to characterize the partitioning of diverse alloy elements in ferrite, austenite and cementite and fruitful results have been achieved. As the main alloy elements in steel, C, mn, Si/Al and Cu/Ni diffuses under the drive of chemical potential gradient among phases, in which C, mn and Cu/Ni atoms diffuse toward the austenite side and play the role of stabilizing austenite, while Si/Al is partitioned into ferrite to inhibit cementite precipitation. Besides, a large number of experiments have also confirmed that intercritical heating and deformation can strengthen the partitioning behavior of alloy elements. This article briefly introduces the characteristics of the quenching and partitioning process, expound the plasticizing mechanism of Q&P steel. Through analysis of the role of various alloy elements in Q&P steel, the partitioning behavior of various alloy elements are discussed with emphasis. meanwhile, according to the partitioning characteristics of alloy elements in different phases, two main ways to promote partitioning behavior of alloy elements are proposed. Finally, the application prospect of alloying elements in Q&P steel is pointed out, which lays an important foundation for the application and industrialization of Q&P steel.
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