Cause on Mechanical Properties Difference of ER90S-G Welding Wire Joint

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.