The paper presents the detailed microstructure study and mechanical behavior of P91 welded joint produced by gas tungsten arc welding process (GTAW) using the dissimilar nickel grade superalloy Inconel 718 filler (ERNiFeCr2). The microstructural changes in the weld fusion zone (WFZ) and heat-affected zone (HAZ) were also studied for varying heat treatment conditions. The effect of the Inconel 718 filler on the tensile properties, hardness and Charpy impact toughness (CIT) of the welded joint was also studied for as-welded and heat-treated conditions. The post-weld heat treatment (PWHT) was performed in a temperature range of 650–1060 °C. The microstructure study showed the formation of an unmixed zone at the interface of the HAZ and weld metal and remain unaffected during the PWHT. The region of weld metal near the boat fusion line showed the cellular and columnar dendrites. The center region of the bulk weld metal was solidified as the columnar dendrites and cellular dendrites along with segregation of the elements at inter-dendritic boundaries. The dendrite core showed the segregation of the Ni, and Cr; however, at dendrite boundaries, major segregation was observed for the elements Nb, Mo and Ti. The heat treatment up to a temperature of 810 °C has observed a negligible effect on the WFZ microstructure; however, a significant change in microstructure was observed for the P91 HAZ region. A significant change in the microstructure of the WFZ was measured after the normalizing at 1060 °C, followed by tempering at 760 °C for 2 h (complex heat treatment). The tensile strength of the welded joint was measured 817 MPa with a joint efficiency of 146 %for as-welded condition and a maximum of 901 MPa with a joint efficiency of 161% for complex heat treatment. The welded joint CIT was measured a maximum of 48 J in as-welded condition and get reduced after the PWHT and measured a minimum of 35 J after complex heat treatment. A hardness variation was observed along the welded joint for as-welded and PWHT condition. In the as-welded condition, the hardness of the WFZ was measured about 417 ± 21 HV and showed a minute change with an increase in tempering temperature. The minimum hardness was measured in the inter-critical HAZ region for the as-welded joint and produce a significant level of heterogeneity in hardness variation along the P91 HAZ. PWHT has observed a considerable reduction in the hardness value of the P91 HAZs except for ICHAZ. A negligible level of hardness variation along P91 HAZ was measured after PW 4.

本文介绍了使用异种镍级超合金Inconel 718填料（ERNiFeCr2）进行的钨极氩弧焊（GTAW）生产的P91焊接接头的详细组织结构和力学性能。对于不同的热处理条件，还研究了熔合区（WFZ）和热影响区（HAZ）的微观结构变化。在焊接和热处理条件下，还研究了Inconel 718填料对焊接接头的拉伸性能，硬度和夏比冲击韧性（CIT）的影响。焊后热处理（PWHT）在650-1060°C的温度范围内进行。显微组织研究表明，在热影响区和焊缝金属的界面处形成了一个非混合区，并且在PWHT期间不受影响。船形熔合线附近的焊缝金属区域显示出蜂窝状和柱状树突。大块焊缝金属的中心区域被固化为柱状树枝状和蜂窝状树枝状，以及元素在树枝状晶界之间的偏析。树枝状核显示出Ni和Cr的偏析。然而，在枝晶边界，观察到Nb，Mo和Ti元素的主要偏析。最高温度为810°C的热处理对WFZ显微组织的影响可忽略不计。然而，在P91 HAZ区域观察到微观结构的重大变化。在1060°C下进行正火，然后在760°C下回火2 h（复杂的热处理）后，测得WFZ的微观结构发生了显着变化。焊接接头的抗拉强度为817 MPa，焊接条件下的接头效率为146％，对于复杂热处理，最大值为901 MPa，接头效率为161％。焊接接头CIT在焊接状态下的最大测量值为48 J，在PWHT之后降低，在复杂热处理后的最小测量值为35J。在焊接状态和PWHT条件下，沿焊接接头观察到了硬度变化。在焊接状态下，测得的WFZ硬度约为417±21 HV，并随回火温度的升高而发生微小变化。在焊缝的临界HAZ区域内测量了最小硬度，并且沿P91 HAZ产生了很大程度的硬度变化异质性。PWHT观察到，除ICHAZ外，P91 HAZ的硬度值已大大降低。PW 4后测得的沿P91 HAZ的硬度变化可忽略不计。