Performance analysis of 700 MPa grade ultrafine grained steel friction welding for sucker rod

Key words:  ultrafine grained steel  friction welding  joint structure  performance

Abstract:

Friction welding was used in the welding of sucker rod of 700 MPa grade ultrafine grained steel. Experimental results show that ultrafine grained steel has good weldability of friction welding when the friction welding process parameters are strictly controlled. It indicates that the grain growth can be inhibited effectively when selecting the following experimental parameters:friction pressure of 60 MPa, friction time of 3 s, upset pressure of 120 MPa, upset time of 1 s. Friction time is the most important factor affecting the axial expansion allowance. Ultrafine grained steel friction welding joints are mainly composed of welding seam, thermal-mechanically affected zone (TMAZ) and heat affected zone (HAZ). There is a slight grain growth with the maximum grain diameter of 9-11 μm in the heat affected zone. The performance analysis of welding joint shows that micro-hardness of friction welding joints is lower than that of the base metal of 4.13%. The tensile strength of the ultrafine grained steel friction welding joint is up to 715 MPa, with the cross section elongation percentage of 22%, the cross section contraction ratio of 68% and the impact toughness of 98 J, which shows a typical ductile fracture.