Effect of welding current on the organization and properties of welded joints of Q690D high-strength steel

Abstract

In this study, the effects of various welding currents used in the CO2 gas shielded welding process on the microstructure, EBSD, texture and mechanical properties of Q690D steel were investigated. The results show that the number of ferrite in the welded joints increases with the increase of welding current; the EBSD analysis results show that the welded core area shows a coarse columnar organization with a long stripe distribution, a high average value of KAM, a high density of dislocations, and a large number of dynamic recrystallisation of GOS in the tempering area; the welded joints have both a rolled weave and a recrystallized weave; The XRD diffraction peaks show a sharp shape, with the main peaks pointing to the α-Fe phase, and the grains are orientated in the (110) direction. The ideal mechanical properties were obtained at a welding current of 170 A. The tensile residual stress was a compressive stress of 117 MPa, and the tensile strength and elongation were 680.7 MPa and 10.13 %, respectively, which showed ductile fracture; the microhardness of the welded joints was the lowest in the incompletely recrystallized zone, which was about 250 HV.