镍基合金焊接过渡区微观结构及应力腐蚀行为研究

来源期刊：金属学报2010年第10期

论文作者：侯娟 彭群家 庄子哲雄 王俭秋 柯伟 韩恩厚

文章页码：1258 - 1266

关键词：镍基合金； 同种/异种金属焊接； 微观结构； 残余应变； 应力腐蚀开裂

Key words：Ni-based alloy； similar/dissimilar metal weld； microstructure； residual strain； stress corrosion cracking

摘    要：利用微观分析手段深入分析了镍基合金690-52同种金属焊接和镍基182合金-A533B低合金钢异种金属焊接的焊接过渡区微观结构,定量测量了同种金属焊接热影响区(HAZ)残余应变分布,用带缝隙的弯曲横梁样品模拟了异种金属焊接过渡区在高温含氧水中的应力腐蚀开裂(SCC)行为.结果表明,同种金属焊接过渡区的HAZ具有残余应变峰值、敏感的晶界微观结构,因而导致最高的SCC敏感性;异种金属焊接过渡区具有复杂的微观结构和成分分布,典型特征是靠近熔接线(FB)的熔合区(FZ)内形成平行于FB的type-Ⅱ和连接FB与type-Ⅱ的type-Ⅰ晶界,type-Ⅱ具有高的SCC敏感性和裂纹扩展速率,type-Ⅰ引导裂纹向FB扩展,裂纹到达FB后发生点蚀钝化停止扩展,FB起阻碍裂纹进一步向低合金钢扩展的作用.

Abstract: Welding technique is generally used in nuclear power plant for manufacturing and machining important components such as steam generator.The similar metal weld and dissimilar metal weld were commonly involved to connect and fixup tubings in steam generators.However,in recent years large amounts of cracking accidents have been observed in the welded joints.A concern has been raised about the integrity and reliability in the joint transition zone due to the high susceptibility of heat affected zone (HAZ) and fusion zone (FZ) to stress corrosion cracking(SCC).In this study,the similar metal and dissimilar metal joints were investigated and compared,focusing on the correlation between microstructure,residual strain and SCC behavior.The microstructures of transition zone in Ni-based Alloys 690 and 52 similar metal joint and Alloys 182 and A533B low alloy steel dissimilar metal joint were investigated comprehensively by SEM,EBSD,TEM.The residual strain distribution in the HAZ of 690-52 similar metal joint was quantitatively measured.The SCC behavior of 182-A533B dissimilar metal joint in high temperature oxygenated water were simulated by creviced bent beam specimen.The HAZ in the similar joint exhibits higher residual strain,sensitive microstructure and high susceptibility to SCC,therefore,the HAZ region deserve more attention during the inspection and examination of components.The FZ of the dissimilar metal joint exhibits complicated microstructure and chemical composition.The type-Ⅱ which parallels the fusion boundary (FB) and type-Ⅰ linking the FB and type-Ⅱ was typical in the FZ of the dissimilar weld.The SCC susceptibility and cracking growth rate are higher at type-Ⅱ boundary in the FZ.The role of type-Ⅰ boundary is to lead the crack growth to the FB.After reaching the FB,the crack growth is blunted by pitting.The FB plays a barrier role to the crack growth in the low alloy steel.The FZ in dissimilar metal joint is weak and high susceptible to SCC.