Effect of Cr Element in Gas-Shielded Solid Wire for Oil and Gas Long-Distance Pipeline on Microstructure and Low Temperature Toughness of Weld

Abstract

In this paper, the influence of Cr element on the mechanical properties of welded joints of gas-shielded solid wire used in oil and gas long-distance pipelines was studied by means of tensile test, impact test, and hardness test, and the microstructure and crack propagation path of weld were characterized by means of an optical microscope, scanning electron microscope, and electron backscattering diffraction. The results show that with the addition of Cr, the strength and toughness of the weld are significantly improved, in which the tensile strength is increased from 607 MPa to 656 MPa, and the impact toughness is increased from 126.37 J to 223.79 J. The proportion of the ferrite side plate in the weld structure is reduced by about 20%, and the effective grain size of acicular ferrite is reduced by about 15%. The reason is that the addition of the Cr element improves the hardenability of the weld structure, inhibits the formation of the ferrite side plate, and promotes the effective refinement of acicular ferrite, which increases the proportion of high-angle grain boundaries in the weld, effectively hindering the crack propagation, improves the crack propagation work, and thus improves the strength and toughness of the weld.