Microcracking Behaviour and Mechanism in Multipass Weld Metal of Alloy 690
Microcracking Behaviour and Mechanism in Multipass Weld Metal of Alloy 690
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690合金多道焊缝金属微裂纹行为及机理
DOI：
10.2207/qjjws.28.61
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
K. Nishimoto
中科院分区：
文献类型：
--
作者：
K. Saida;Y. Nomoto;A. Taniguchi;M. Sakamoto;K. Nishimoto
研究了690合金多道焊过程中的微裂纹行为。采用点Varestraint试验研究了P、S等杂质元素对重加热焊缝金属塑性-浸裂敏感性的影响。随着焊缝中杂质元素含量的减少，塑性-浸裂敏感性降低，为防止多道焊金属微裂纹，焊缝金属中(P+1.2S)的含量应控制在30ppm以内。微观偏析的数值计算和分子轨道分析表明，塑性浸入裂纹是由于P和S晶界偏析引起的晶界脆化。热应变有限元分析预测，当塑性应变-温度曲线与塑性浸入温度区间(DTR)相交时，多道焊过程中会出现塑性浸入裂纹。采用含La或Ce的焊料，研究了在焊缝金属中添加稀土金属(REM)对微裂纹敏感性的影响。在焊缝金属中加入质量分数为0.01-0.025%的REM可显著改善塑性-浸入裂纹敏感性。显微组织分析表明，由于REM的清除作用，降低了晶界偏析P和S，从而降低了塑性-倾角裂纹敏感性。多道焊试验证实，采用含约690%的焊料，可完全防止690合金多道焊产生微裂纹。0.03质量%REM。
Microcracking behaviours in the multipass welds of alloy 690 were investigated. The effect of impurity elements such as P and S on ductility-dip cracking susceptibility in the reheated weld metal was evaluated by the spot-Varestraint test using different filler metals varying the contents of P and S. The ductility-dip cracking susceptibility was reduced with a decrease in the content of impurity elements in the filler metal, and the amount of (P+1.2S) in the weld metal should be limited to 30ppm in order to prevent the microcracking in the multipass weld metal. Numerical calculation of microsegregation and molecular orbital analysis have suggested that ductility-dip cracking was attributed to the grain boundary embrittlement due to the grain boundary segregation of P and S. FEM analysis of thermal strain predicted that ductility-dip cracks would occur during multipass welding when the plastic strain-temperature curve intersected the ductility-dip temperature range (DTR). The effect of the addition of rare earth metals (REM) to the weld metal on the microcracking susceptibility was examined by using the La or Ce containing filler metals. The ductility-dip cracking susceptibility could be significantly improved by adding 0.01-0.025mass%REM to the weld metal. Microstructural analyses revealed that the ductility-dip cracking susceptibility decreased as a result of lowering the grain boundary segregation P and S due to the scavenging effect of REM. The multipass welding test confirmed that microcracks in the multipass welds of alloy 690 were completely prevented by using the filler metals containing approx. 0.03mass%REM.