Abstract: The simulation on circulation process of heat of low temperature steel 9Ni (/% : 0.049C, 0.22Si, 0.58Mn, 0.0006S, 0.0029P, 9.16Ni, 0.020Al, 0.003Ti, 0.0030N, 0.0006O) with different cooling time (6-100 s) from 800 °C cooling to 500 ℃(t_8/5) has been carried out by using Gleeble-3500 simulator, and combined with metallography the simulated heat affected zone continuous cooling transformation (SHCCT) curves of tested steel are established. The structure in tested specimen with different cooling time of t_8/5 is observed by optical and scanning electron microscope to study the effect of cooling time on original austenite grain size, M-A group area, size, number and shape factor (ratio of massive M-A). Results show that the structure of simulated heat affected zone of continuous cooling specimen consists of bainite (B) and martensite (M) , the relative content of M depends on cooling time of t_8/5 ； with increasing cooling time from 800 °C to 500℃ (t_8/5 ) the original austenite grain size, particle bainite content and M-A group size increase while the M-A group content and ratio of massive M-A decrease, it is available to improve the low temperature toughness of coarse grain heat affected zone of steel 9Ni.

Key words: Simulated Heat Affected Zone Continuous Cooling Transformation ( SHCCT), Low Temperature Steel 9Ni, Phase Transition from 800°C to 500°C, M-A Group, Bainite

摘要： 利用Gleeble-3500热模拟试验机对9Ni低温钢（/%:0.049C，0.22Si，0.58Mn，0.0006S，0.0029P，9.16Ni，0.020Al，0.003Ti，0.0030N，0.0009O）在800℃冷却至500℃时间-t_8/5（6~100s）的热循环过程进行了模拟,结合金相法建立了试验钢的SHCCT（模拟热影响区连续冷却转变）曲线。采用光学显微镜和扫描电镜对不同t8/5试样的显微组织进行了观察,研究了冷却时间对原奥氏体晶粒尺寸、M-A组元含量、尺寸、数量和形状因子（M-A组元面密度）的影响。结果表明,模拟热影响区连续冷却试样的显微组织由贝氏体（B）和马氏体（M）组成,其相对含量取决于冷却时间t_8/5;随800℃至500℃(t_8/5)冷却时间的增加原奥氏体晶粒尺寸,粒状贝氏体含量、M-A组元尺寸增加,同时M-A组元含量和面密度降低,有利于改进9Ni钢粗晶热影响区的低温韧性。

关键词: 热模拟影响区连续冷却转变(SHCCT), 9Ni低温钢, 800℃-500°C相变, M-A组元, 贝氏体