厚壁异种钢脉冲UNGW熔合过渡区微观组织调控与演变及其对接头高温蠕变性能的影响

Based on the idea of regulating the distribution gradient of Ni and microstructure of the transition region of fusion of dissimilar steel welding for improving high temperature creep properties of dissimilar steel joint, and ultra-narrow-gap welding(UNGW) has the advantages of high welding efficiency, low heat input, low residual stress and so on, this subject will carry on the UNGW of 15CrMo-1Cr18Ni9Ti thick-walled dissimilar steel with the constricted impulse arc by fine granular flux. This subject will study the key scientific problems, such as formation mechanism of type-Ⅱ boundary of dissimilar steel joint welded by impulse UNGW with the wire of FA solidification model, regulation of the distribution gradient of Ni in the transition region of fusion of dissimilar steel with impulse UNGW and its effects on the solidification model of welding pool and microstructure evolution, and improving mechanism of high temperature creep properties of dissimilar steel joint with impulse UNGW. The research of this subject will benefit to optimize the welding technology of dissimilar steel, supply the weldability theory of dissimilar steel, and ultimately provide theory evidence and basis of experiment for early realizing industrial application of dissimilar steel with ultra-narrow-gap welding.

基于调控异种钢焊接熔合过渡区Ni分布梯度和微观组织以改善异种钢接头高温蠕变性能的思路，以及超窄间隙焊接(UNGW)厚壁件所具有的焊接效率高、热输入低、残余应力小等优点，本课题将采用细颗粒焊剂约束的脉冲电弧进行15CrMo-1Cr18Ni9Ti厚壁异种钢的UNGW。本课题将主要对填充FA凝固模式焊丝的异种钢脉冲UNGW接头“Ⅱ型边界”形成机理，异种钢脉冲UNGW熔合过渡区Ni分布梯度的调控及其对熔池凝固模式和微观组织演变的影响，异种钢脉冲UNGW接头高温蠕变性能的改善机制等关键科学问题开展研究。该研究将为优化异种钢焊接工艺，补充异种钢焊接性理论，并最终实现异种钢UNGW的工业化应用提供理论依据与实验基础。

基于调控异种钢焊接熔合过渡区Ni分布和微观组织以改善异种钢接头高温蠕变性能的思路，以及超窄间隙焊接(UNGW)厚壁件所具有的焊接效率高、热输入低、残余应力小等优点，本课题将细颗粒焊剂约束的脉冲电弧用于厚壁异种钢的UNGW。通过对填充FA凝固模式焊丝的异种钢脉冲UNGW接头“Ⅱ型边界”形成机理，异种钢脉冲UNGW熔合过渡区Ni分布的调控及其对熔池凝固模式和微观组织演变的影响等关键科学问题的研究，证明了二型边界是由晶界迁移所形成的客观事实，提出并阐明了填充FA凝固模式焊丝的异种钢脉冲UNGW接头在四种情况下的“Ⅱ型边界”形成机理，从而对Nelson二型边界理论所不能解释的异种钢焊接问题给出了圆满解释。研究发现平行于异种钢接头“ 岛状区”(ISZ)边缘的晶界可能是迁移晶界，也可能是凝固晶界，并阐明了该迁移晶界的形成机理。采用预置镍基合金片的方法对熔合过渡区的Ni分布进行了调控，明确了预置镍基合金片对异种钢UNGW接头微观组织及高温下碳扩散的影响。此外，提出了“TIG冷焊+UNGW”的组合焊接工艺，有效解决了1Cr17/1Cr18Ni9Ti异种不锈钢的焊接HAZ晶粒易粗化问题。该研究将为优化异种钢焊接工艺，补充异种钢焊接性理论，并最终实现异种钢UNGW的工业化应用提供理论依据与实验基础。