Microstructural evolution in P91 (modified 9Cr–1Mo) steel and 316LN Stainless Steel (SS) bi-metallic weld joints fabricated by arc welding technique using Inconel-182 electrode has been studied in as-welded and post weld heat treated (PWHT) conditions. The PWHT brought about significant changes in the microstructure which altered the strength gradient especially in the ferritic steel side. The differences in weld thermal cycling which occurred in various regions of the P91 steel side caused M₂₃C₆ precipitates to evolve in varying sizes. The size variation in these precipitates was the paramount cause for the variation in strength in this region which could be probed by miniature specimen testing. Using this testing it could be established that PWHT resulted in offsetting the strength variation in the HAZ of the ferritic steel side. It could also be understood that PWHT generates a weak region in the P91 side making it most susceptible to damage.

在焊接和焊后热处理（PWHT）条件下，已经研究了使用Inconel-182电极通过电弧焊技术制造的P91（改性9Cr-1Mo）钢和316LN不锈钢（SS）双金属焊接接头的组织演变。PWHT引起了显微组织的重大变化，从而改变了强度梯度，特别是在铁素体钢侧。在P91钢侧面的各个区域中发生的焊接热循环差异导致M ₂₃ C ₆沉淀物以不同大小演化。这些沉淀物的尺寸变化是该区域强度变化的最重要原因，可以通过微型试样测试来探测。使用该测试可以确定，PWHT可以抵消铁素体钢侧面热影响区的强度变化。还可以理解，PWHT在P91侧产生一个弱区，使其最容易受到损坏。