矫顽力在叶片残余应力评估中的应用研究

Research on the Application of Coercivity in Residual Stress Evaluation of Blades

马氏体不锈钢水轮机叶片需进行焊后热处理以减少叶片焊接残余应力,但缺乏快捷无损的方式评估消应力热处理工艺。通过预制对比试件,采用磁矫顽力和钻孔残余应力检测方法分析焊后叶片的残余应力分布情况。结果表明,在比对试件中,钻孔法测得热处理后焊缝热影响区最大主应力下降55%,远低于材料的屈服强度550 MPa,矫顽力检测值下降20%;待评估试件热处理后热影响区矫顽力下降46%,矫顽力降至母材矫顽力同等水平,表明试件焊缝位置残余应力得到有效控制。验证了基于矫顽力无损评估马氏体不锈钢焊后热处理工艺和焊接接头应力分布的可行性。

The martensitic stainless steel turbine blades required post welding heat treatment(PWHT)to reduce residual stresses during welding,but there was a lack of a fast and non-destructive(NDT)way to evaluate the stress relief heat treatment process.The distribution of residual stresses in welded blades was analyzed by using magnetic coercivity and drilling residual stress detection methods through prefabricating comparative specimens.The results showed that in the comparison specimens,the maximum principal stress in the heat affected zone(HAZ)of the weld seam measured by the drilling method decreased by 55%after heat treatment,which was lower than the material yield strength of 550 MPa,and the coercive force detection value decreased by 20%.After heat treatment,the coercivity in the HAZ of the evaluated specimen decreased by 46%,and the coercivity decreased to the same level as that of the base metal,indicatimg that the residual stress at the weld position of the specimen was effectively controlled.The feasibility of NDT assessment of PWHT process and stress distribution in welded joints of martensitic stainless steel based on coercivity was verified.