用Monte Carlo模拟方法研究了超低温用9Ni钢焊接热影响区(HAZ)的晶粒长大。结合焊接试验,建立了9Ni钢焊接HAZ晶粒长大模型,模拟了晶粒生长过程。模拟结果表明,HAZ奥氏体晶粒尺寸平均为70~85μm,与实际对应焊接工艺参数条件下的晶粒尺寸测量结果相吻合。并给出了HAZ存在很陡的温度梯度对晶粒长大起阻碍作用的“热钉扎”效应。研究了焊接工艺参数(焊接热输入和预热温度)对HAZ晶粒尺寸的影响,得出热输入是影响HAZ晶粒尺寸的主要因素。为获得优良的HAZ韧性,在焊接实际生产中需采用较小的热输入。 The grain growth of the weld heat affected zone (HAZ) of 9Ni steel for ultra-low temperature was studied by Monte Carlo simulation. Combined with the welding test, the HAZ grain growth model of 9Ni steel was established and the grain growth process was simulated. The simulation results show that the average grain size of HAZ austenite is 70 ~ 85μm, which is in good agreement with the actual grain size measurement under the corresponding welding process parameters. The “pinning” effect of the steep temperature gradient in the HAZ hinders the growth of the grains. The effect of welding parameters (heat input of welding and preheating temperature) on the grain size of HAZ was studied. It was found that heat input was the main factor affecting the grain size of HAZ. In order to obtain excellent HAZ toughness, a smaller heat input is required in the actual welding production.