The reheat cracking susceptibility of welded joints has been evaluated by 900°C high-temperature constant load test and 750°C–900°C high-temperature slow strain rate tensile (SSRT) test on welded joints of TP347 steel, and the influencing factors and mechanism of reheat cracking in welded joints have been further investigated by microcosmic characterization techniques of SEM and EDS, etc. The result shows the critical fracture stress of TP347 steel welded joints at 900°C is 24 MPa, which is much lower than 80% of the high-temperature yield strength of base material, indicating that the reheat crack of the welded joint is highly sensitive at this temperature; the average reduction of area (RoA) of welded joints obtained by 750°C–900°C SSRT test at each temperature is below 20%, which means all welded joints have a reheat cracking susceptibility in this temperature range, and the reheat cracking susceptibility increases with the rising of temperature. Based on study and analysis using microcosmic methods of optical microscope, scanning electron microscope, and energy spectrum analysis, it is found that welded joints of TP347 steel have a high reheat cracking susceptibility because the high temperature accelerates the diffusion of Cr, Nb, and impurity elements to the grain boundary, and a large quantity of carbides and low-melting-point eutectics are collected and precipitated at the grain boundary to reduce the plasticity of the grain boundary. Since there is a high welding residual stress in welded joints, cavities are formed under the action of the stress at a high temperature, and the merging of cavities causes the formation of cracks which extend along the grain boundary.

中文翻译：

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347型奥氏体不锈钢焊接接头再热裂纹敏感性及机理研究

采用TP347钢焊接接头900℃高温恒载试验和750℃～900℃高温慢应变速率拉伸（SSRT）试验评价了焊接接头的再热裂纹敏感性，以及影响因素通过SEM、EDS等微观表征技术进一步研究了焊接接头再热开裂的机理和机理，结果表明TP347钢焊接接头在900℃时的临界断裂应力为24 MPa，远低于80%。母材高温屈服强度的变化，说明该温度下焊接接头的再热裂纹高度敏感；750°C–900°C SSRT试验在每个温度下获得的焊接接头平均面积减少量（RoA）低于20%，这意味着所有的焊接接头在这个温度范围内都有再热裂纹敏感性，并且再热裂纹敏感性随着温度的升高而增加。通过光学显微镜、扫描电镜、能谱分析等微观方法研究分析发现，TP347钢焊接接头由于高温加速了Cr、Nb和杂质的扩散，具有较高的再热裂纹敏感性。元素进入晶界，大量碳化物和低熔点共晶在晶界处聚集析出，降低晶界的塑性。由于焊接接头存在较高的焊接残余应力，在高温应力的作用下会形成空洞，