In this work, a new equation to evaluate the yield strength change caused by grain refinement was proposed in low-carbon martensitic steel, based on the Hall-Petch formula. MATLAB analysis showed that martensite and the prior austenite grain (parent phase) were more consistent with the Kurdjumov and Sachs orientation relationship in the martensitic transformation process. The martensite variant selectivity became significant and was dominated by the CP group, among which the V1, V3, V4, V7, V11, and V12 variants were higher in content. Using OM, SEM, EBSD, and TEM characterized the sample at different quenching temperatures. Then, the relationship between the refined hierarchical microstructure and both yield strength (YS) and impact toughness (IT) was carefully analyzed. Researched results found that with grain refinement, the YS first increased rapidly and then slowly increased. It indicated the Hall-Petch relationship was a discontinuous formula. Utilizing the new equation, we concluded that martensite laths and prior austenite grains were the microscopic units that determined the YS of the steel. Martensite packets and blocks contributed nearly same to the strength of the steel, while the growth of martensite packets into square shapes would led to a decline in the strength of the steel. Additionally, the IT of the steel was determined by the overall grain boundary length of high strain gradient plastic zone and martensite laths width, in which high-angle grain boundaries contributed more to IT than low-angle grain boundaries.

中文翻译：

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不同淬火温度低碳马氏体钢细化分级组织与屈服强度和冲击韧性关系研究

在这项工作中，基于 Hall-Petch 公式，提出了一个新的方程来评估低碳马氏体钢中晶粒细化引起的屈服强度变化。MATLAB分析表明，马氏体相变过程中马氏体和原奥氏体晶粒（母相）更符合Kurdjumov和Sachs取向关系。马氏体变体选择性变得显着，以CP组为主，其中V1、V3、V4、V7、V11和V12变体含量较高。使用 OM、SEM、EBSD 和 TEM 对不同淬火温度下的样品进行表征。然后，仔细分析了细化的分级微观结构与屈服强度（YS）和冲击韧性（IT）之间的关系。研究结果发现，随着晶粒细化，YS先快速增加，然后缓慢增加。这表明霍尔-佩奇关系是一个不连续的公式。利用新方程，我们得出结论，马氏体板条和原奥氏体晶粒是决定钢的 YS 的微观单元。马氏体块和马氏体块对钢的强度贡献几乎相同，而马氏体块生长成方形会导致钢的强度下降。此外，钢的IT由高应变梯度塑性区的总晶界长度和马氏体板条宽度决定，其中大角度晶界对IT的贡献大于小角度晶界。