核电焊接低压转子用25Cr2Ni2MoV钢晶粒细化工艺研究

Study on Grain Refinement Process of 25Cr2Ni2MoV Steel Useful for Welded Low-Pressure Rotor of Nuclear Power Generator

基本成分为0.22%C、2.32%Cr、2.27%Ni、0.69%Mo和0.05%V(质量分数)的25Cr2Ni2MoV钢,适用于焊接的核动力发电机低压转子。但低压转子的组件轴头和圆盘锻件由于尺寸大、形状复杂,锻造变形不均匀,导致其晶粒粗大且不均匀。为细化25Cr2Ni2MoV钢锻件的晶粒,通过有限元数值模拟研究了正火温度、一次和多次正火工艺、奥氏体化后于620~690等温30 h、50 h、90 h、120 h和150 h对25Cr2Ni2MoV钢锻件晶粒尺寸的影响。结果表明,25Cr2Ni2MoV钢锻件可通过多次正火或奥氏体化后于620~690℃等温90 h消除组织遗传,使其晶粒细化、均匀化,确保锻件用超声波检测的晶粒尺寸和均匀性符合要求。已采用该热处理工艺成功试制了低压转子的轴头和圆盘锻件。

25Cr2Ni2 MoV steel containing essential compositions such as 0.22% C,2.32% Cr,2.27% Ni,0.69%Mo,and 0.05% V by mass is useful for welded low-pressure rotor of nuclear power generator.The large-sized and intricate stub and disc that are assembly of the low-pressure rotor,however,will offer coarse and non-uniform grains after forging because of non-uniform deformation.Effects of normalizing temperatures,single and multiple normalizing practices,and austenitizing then holding at 620℃to 690℃for 30 h,50 h,90 h,120 h and 150 h on grain size of the 25 Cr2 Ni2 MoV steel forging were investigated by finite element numerical simulation,for the purpose of refining its grains.The results showed that the multiple normalizing or austenitizing then holding at620℃to 690℃for 90 h was enabled to eliminate structure inheritance of the 25Cr2Ni2 MoV steel forging,and to cause its grains to become finer and more uniform,thus making certain that the forging exhibits desired size and uniformity of grains which are discovered by ultra-sonic testing.Such heat treatment processes have been successfully used in trial-producing the stub and disc forgings of low-pressure rotor.