Objective To analyze the welding materials and welding parameters used in the actual frame repair welding process, it is necessary to investigate the influence of different process parameters on the welding mechanical properties of the high-strength low-alloy steel Q620M.

Method Taking the butt joints of high-strength low-alloy steel Q620M welded by MAG (metal active gas arc welding) as an example, metallographic tests, tensile tests, and pulsating tensile fatigue tests are conducted on the MAG-welded butt joints of high-strength low-alloy steel Q620M under different process parameters, and their mechanical properties are characterized.

Result & Conclusion  The results of the metallographic tests show that with the decrease of welding heat input and the increase of the number of weld passes, the bainite content in the weld zone gradually increase, the content of proeutectoid ferrite decrease, and the grain sizes of ferrite and bainite also increase. The results of the tensile tests indicate that under the conditions of high welding heat input parameters (welding heat input of 0.997 kJ/mm with 1 weld pass, and welding heat input of 1.050 kJ/mm with 2 weld passes), the tensile fracture of the specimens all occurs in the base metal zone. This shows that under the same welding heat input, the number of weld passes has little effect on the tensile strength. When the welding heat input is reduced to 0.660 kJ/mm with 3 weld passes, the tensile strength decreases significantly and fracture occurs in the heat-affected zone (coarse-grained zone), indicating that low welding heat input and multiple weld passes will reduce the tensile strength of the welded joint. The results of the pulsating tensile fatigue tests show that when the welding heat input is 0.997 kJ/mm with 1 weld pass, the MAG welded butt joint of high-strength low-alloy steel Q620M exhibits excellent fatigue performance.