ER90S-G低合金钢焊丝作为第三代压水堆核电机组AP1000钢制安全壳拼装焊材，对其质量需要严格控制。某批次ER90S-G焊丝在入厂验收过程中，检测发现焊接试样在室温条件下的抗拉强度为740 MPa，超过ASME Ⅱ SFA 5.28：2013要求的上限值（735 MPa），而在后续复验时测得抗拉强度分别为650 MPa和640 MPa。通过力学性能试验、化学成分分析、金相检验和焊接参数对比分析等方法，对造成力学性能前后测试结果存在差异的原因进行了分析。结果表明：焊接过程中层间温度偏低是造成性能差异的主要原因，其造成接头的晶粒尺寸变小，最终导致抗拉强度和屈服强度升高，断后伸长率降低。

ER90S-G, a low alloy steel welding wire, is the welding material for the assembly of AP1000 steel containment of the third generation PWR nuclear power plant group, which requires high quality. During the acceptance process of a batch of ER90S-G welding wire, it was found that the tensile strength of the welding sample at room temperature was 740 MPa, which exceeded the upper limit of the requirement of ASME Ⅱ SFA 5.28:2013 (735 MPa). In the subsequent retesting process, the tensile strength values were 650 MPa and 640 MPa respectively. The causes of the difference of mechanical property test results were analyzed by means of mechanical property test, chemical composition analysis, metallographic examination and comparative analysis of welding parameters. The results show that the low temperature between layers during welding process was an important cause for performance difference, which made the grain size of the joint to be smaller, and finally led to the high tensile strength and yield strength, and the low elongation after fracture.