微观组织对临界折射纵波横向焊接残余应力测量结果的影响

Influence of microstructure on the measurement result of transverse welding residual stress by LCR wave

焊接过程中较高的热输入容易引起较高的焊接残余应力,而较高的残余应力有可能降低工件疲劳寿命,促进裂纹萌生扩展,增加应力腐蚀敏感性。表面和内部的焊接残余应力的无损检测对服役可靠性的评估具有重要意义。临界折射纵波(LCR波)残余应力的测量原理是基于声波传播速度的改变和应力之间的线性关系。当使用LCR波测量横向焊接残余应力时,收发换能器可能同时覆盖焊缝(MZ)、热影响区(HAZ)以及母材(PM)中的两个甚至三个区域,然而这些区域微观组织的差异性都可能影响应力常数K,当测量距离焊缝中心不同距离的残余应力时,有必要对应力常数K进行修正,提高LCR波对横向焊接残余应力的测量精度。

Heat input in welding process leads to greater welding residual stresses,and large residual stress is likely to reduce the work piece＇s fatigue life,as well as promote crack extension and sensibility of stress corrosion. Nondestructive testing of surface and internal welding residual stress is very significant for the assessment of service reliability. The measurement theory of residual stress with the LCR wave is based on the linear relationship between the stress and the change of sound wave velocity. When using the LCR wave to measure transverse residual stress, the transmit-receive transducer may cover two or three zones of melting zone（ MZ ）, heat affect zone （ HAZ ） and parent material（ PM ）, but the differences between the micrnstructures of these zones may effect the stress constant K. When measuring the residual stresses which has different distance from the weld center, it is necessary to correct the stress constant K to improve the measurement accuracy of transverse welding residual stress by LCR wave.