Deformation of a weldment is governed by the mechanical properties of its base metals and fusion zone. In a weldment, the base metals and fusion zone exhibit changing microstructural features with various phases present along the weldment. Specifically, the heat affected zone of a base metal exhibits a heterogeneous microstructure generated during weld thermal cycles and by post‐weld heat treatment. As a result, the mechanical properties in a weldment are often non‐uniformly distributed. In this study, tensile tests combined with digital image correlation were performed to obtain the non‐uniform distributions of the mechanical properties of a weldment composed of P91 and 347H steels. From the experimental tensile tests, it was found that the 347H base metal had significantly distinct mechanical properties compared to the other zones of the weldment. Furthermore, the 347H base metal had the lowest yield stress but the highest strain hardening exponent. Because of its lowest yield stress, the 347H base metal had the highest plastic strain accumulation at any stage of global deformation. However, the strain hardening rate of the P91 base metal enabled it to accumulate the necessary plastic strain to activate its necking first. Therefore, the failure location of the P91‐347H weldment was expected to occur at the P91 base metal. A 3D finite element simulation of the tensile deformation of P91‐347H weldment also suggested the same. However, from the present experimental observations, one weldment out of three was found to fail unexpectedly at the heat affected zone of the P91 base metal. The reason for this unexpected failure was determined by microscopic analysis to be the presence of a large defect.

中文翻译：

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P91和347H钢的异种金属焊件的拉伸变形行为

焊件的变形受其基础金属和熔合区的机械性能支配。在焊件中，贱金属和熔合区表现出变化的微观结构特征，沿焊件存在各种相。具体而言，母材的热影响区表现出在焊接热循环和焊后热处理过程中产生的异质微观结构。结果，焊件的机械性能通常不均匀地分布。在这项研究中，拉伸测试与数字图像相关性相结合，获得了由P91和347H钢组成的焊件的力学性能的非均匀分布。根据实验拉伸试验，结果发现，与焊件的其他区域相比，347H母材具有明显不同的机械性能。此外，347H基本金属的屈服应力最低，但应变硬化指数最高。由于其最低的屈服应力，因此347H基本金属在整体变形的任何阶段都具有最高的塑性应变累积。但是，P91基体金属的应变硬化速率使其能够积累必要的塑性应变，以首先激活其颈缩。因此，预计P91-347H焊件的失效位置会在P91母材处发生。P91-347H焊件拉伸变形的3D有限元模拟也表明相同。但是，从目前的实验观察来看，发现三分之二的焊件在P91母材的热影响区意外失效。通过显微镜分析确定该意外故障的原因是存在大缺陷。