Abstract: This study optimized the ultrafine grain forging process of 18Ni （250） martensitic aging steel for specific application requirements in deep and low temperature environments， aiming to improve the plasticity and toughness of the material under deep and low temperature conditions. The study analyzed the behavior of materials during hot deformation process and the influence of deformation process on microstructure through hot deformation method， observed the microstructure after hot deformation， and established the constitutive equation and hot working diagram between material rheological stress， deformation temperature， and strain rate. Finally， the optimal heat treatment process area was determined， which is the range of deformation temperature and deformation rate. Research has shown that when the deformation temperature is higher than 1050 ℃ and the deformation is 30 percent， the material exhibits austenite grain recrystallization phenomenon. When the deformation temperature is 1150 ℃， the grain structure tends to refine. Based on the thermal deformation equation and thermal processing diagram with deformation temperature between 850 ℃-1 150 ℃ and strain rate within the range of 0.01 s^-1-10 s^-1， the ideal thermal processing zone of the material was obtained， which is the deformation temperature range of 1050 ℃-1150 ℃ and the strain rate range of 0.01 s^-1-10 s^-1.

Key words: Hot Deformation, 18Ni（250） Steel, Recrystallization, Grain Refinement, Intrinsic Equation

摘要： 本研究针对深低温环境中的特定应用需求，优化了18Ni（250）马氏体时效钢的超细晶化锻造工艺，旨在提升该材料在深低温条件下的塑韧性。通过热变形方法，分析了材料在热变形过程中的行为以及变形工艺对显微组织的影响，观察热变形后的显微组织，并建立了材料流变应力、变形温度和应变速率之间的本构方程和热加工图。最终，确定了最佳的热处理工艺区域，即变形温度和变形速率的范围。研究表明，当变形温度高于1050 ℃，且变形量为30%时，材料出现奥氏体晶粒再结晶现象，当变形温度为1150 ℃时，晶粒组织趋向细化。根据变形温度在850~1150 ℃，应变速率在0.01~10 s^-1的热变形方程和热加工图，得到了材料理想的热加工工艺区，即变形温度为1050~1150 ℃，应变速率为0.01~10 s^-1。

关键词: 热变形, 18Ni（250）钢, 再结晶, 晶粒细化, 本构方程