Microstructures and Mechanical Properties of Friction Tapered Stud Overlap Welding for X65 Pipeline Steel Under Wet Conditions

Abstract

This paper exhibits a novel in situ remediation technique named friction tapered stud overlap welding (FTSOW) to repair a through crack in structures and components in extremely harsh environments. Furthermore, this paper presents variations in process data, including rotational speed, stud displacement, welding force, and torque for a typical FTSOW weld. In the present study, the effects of welding parameters on the microstructures and mechanical properties of the welding joints were investigated. Inapposite welding parameters consisted of low rotational speeds and welding forces, and when utilized, they increased the occurrence of a lack of bonding and unfilled defects within the weld. The microstructures with a welding zone and heat-affected zone mainly consisted of upper bainite. The hardness value was highest in the welding zone and lowest in the base material. During the pull-out tests, all the welds failed in the stud. Moreover, the defect-free welds broke at the interface of the lap plate and substrate during the cruciform uniaxial tensile test. The best tensile test results at different depths and shear tests were 721.6 MPa and 581.9 MPa, respectively. The favorable Charpy impact-absorbed energy was 68.64 J at 0 °C. The Charpy impact tests revealed a brittle fracture characteristic with a large area of cleavage.