To achieve the objective of enhancing the yield strength (YS) of quenching and partitioning (Q&P) steel without compromising tensile strength and ductility, a stepped partitioning (SP) strategy was proposed for Q&P treatment on medium carbon silicon-rich steel. The optimized partitioning strategy involves a two-stage partitioning, the first stage is conducted at temperatures above the martensite start () temperature, followed by the second stage carried out at a lower temperature for an extended period, involving isothermal partitioning. Experimental results demonstrate that the SP strategy yields a significant quantity of small carbides, with an average size of 59.02 nm, along with 15.71 vol% of retained austenite (RA) and a carbon concentration of 1.01 wt% in RA. Furthermore, the SP-treated specimen exhibits a remarkable balance of strength and ductility, showcasing YS, ultimate tensile strength (UTS), and total elongation (TE) values reaching 1732 MPa, 2263 MPa, and 14.9%, respectively. The microstructure evolution during tensile deformation demonstrates that RA in short-duration conventional partitioning specimens underwent premature martensitic transformation during tensile deformation due to early deformation, whereas RA in long time conventional partitioning specimens was overstabilized due to highest C concentration, which resulted in poor enhancement of strengthening and ductility by TRIP effect. In contrast, the SP strategy achieved a reasonable stability of RA, resulting in a simultaneous increase of tensile strength and ductility. Simultaneously, an analysis of precipitation strengthening indicates that the abundance of fine carbides in martensite contributes to an increase in YS due to precipitation strengthening.

中文翻译：

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优化中碳富硅钢中奥氏体和碳化物含量：阶梯式分配策略及强化和延性增强机制分析

为了在不影响抗拉强度和塑性的情况下提高淬火分配（Q&P）钢的屈服强度（YS），提出了一种中碳富硅钢Q&P处理的阶梯分配（SP）策略。优化的分配策略涉及两阶段分配，第一阶段在高于马氏体起始温度（）的温度下进行，然后第二阶段在较低温度下进行较长时间，涉及等温分配。实验结果表明，SP 策略产生了大量的小碳化物，平均尺寸为 59.02 nm，以及 15.71 vol% 的残余奥氏体 (RA)，RA 中的碳浓度为 1.01 wt%。此外，SP处理的样品表现出强度和延展性的显着平衡，YS、极限拉伸强度（UTS）和总伸长率（TE）值分别达到1732 MPa、2263 MPa和14.9%。拉伸变形过程中的微观组织演变表明，短时常规分配试样中的RA由于早期变形而在拉伸变形过程中发生了过早马氏体转变，而长时间常规分配试样中的RA由于C浓度最高而过度稳定，导致了拉伸变形的增强效果较差。通过 TRIP 效应增强强度和延展性。相比之下，SP策略实现了RA的合理稳定性，导致拉伸强度和延展性同时增加。同时，对沉淀强化的分析表明，马氏体中大量的细小碳化物由于沉淀强化而有助于YS的增加。