Abstract

The optimal process parameters of grade 250 maraging steel for hot forging were investigated with a process map and microstructure analysis. To generate the process map, hot compression tests were performed at 800–1200 °C and strain rates of 0.01–5 s⁻¹. The flow stress–strain curves were calibrated by Bayesian artificial neural network (ANN) modeling to compensate the heat generated by dynamic deformation. The Ni and Mo segregation during the solidification of the ingot caused alternating layers of Ni- and Mo-rich and -lean bands, which affected the recrystallization behavior during hot compression. According to the calculated process map, 1100–1200 °C × 0.01–0.7 s⁻¹ and 1000–1200 °C × 0.01–0.2 s⁻¹ are favorable process conditions that ensure wide process windows in terms of strain rate and temperature, respectively. The common features of the microstructure deformed under both conditions were relatively coarse martensite blocks and low values in the electron backscattered diffraction (EBSD) kernel average misorientation (KAM) results (i.e., low residual stresses), which were attributed to a low fraction of fine martensite block region.

Graphic Abstract

中文翻译：

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偏析对250级马氏体时效钢组织和热加工性能的影响

摘要

通过工艺图和组织分析，研究了用于热锻的250级马氏体时效钢的最佳工艺参数。为了生成过程图，在800–1200°C和0.01–5 s ^-1的应变速率下进行了热压缩测试。通过贝叶斯人工神经网络（ANN）建模对流动应力-应变曲线进行校准，以补偿动态变形产生的热量。铸锭凝固过程中的镍和钼偏析导致富镍和富钼带和贫带交替出现，从而影响了热压缩过程中的再结晶行为。根据计算出的过程图，1100–1200°C×0.01–0.7 s ^-1和1000–1200°C×0.01–0.2 s ^-1有利的工艺条件可确保在应变率和温度方面分别具有宽广的工艺窗口。在两种情况下变形的微观结构的共同特征是马氏体块相对较粗，电子背散射衍射（EBSD）核平均取向差（KAM）结果的值较低（即残余应力低），这归因于细粉的比例低马氏体区。

图形摘要