Effects of axial force on microstructures and mechanical properties of underwater friction taper plug welding for dissimilar steel

In this study, friction taper plug welding (FTPW) experiments were performed using X52 pipeline steel as base material and Q345 steel as plug. The effects of axial force on microstructures and mechanical properties for FTPW weld were discussed. The results showed that lack of bonding defect formed in the weld at the bottom corner under the conditions of 7 000 r/min rotating speed and 30 kN axial force. With the axial force increasing to 35 kN, the weld defect was avoided, and the width of forged zone and HAZ at the corner near bottom hole expanded. Due to the effect of quick water cooling, the microstructure of the FTPW weld was complex, which consisted of lath martensite and lath bainite. The hardening tendency of FTPW weld was obvious, and the hardness value reached 450 HV1. The V-notch impact absorbed energy at 0 °C in the center of the weld continuously increased as the axial force increase, which reached up to 62 J and was much lower than that of the base material (267 J).