Microstructure and mechanical properties of T-joints in mid-thick Q345 steel plates welded using deep penetration tungsten inert gas welding

•Used deep penetration tungsten inert gas welding to make mid-thick plate T-joints.•Thoroughly studied the microstructure and mechanical properties of the T-joint.•The distribution of brittle BG is a fundamental influence on crack propagation. The deep penetration tungsten inert gas welding process was first used to realize efficient manufacturing of T-joints. The macroscopic morphology, microstructure, microhardness, and mechanical properties of T-joints were investigated. The welding parameters are a welding current of 465 A, a welding speed of 4 mm/s, and the distance between the tungsten electrode tip and the web plate and flange plate is 2 mm. The one-side welding both sides formation of T-joint was realized under these welding parameters. The Widmanstätten austenite in the web plate's overheated zone hinders the crack’s propagation. The failure crack in the flange plate first propagates in the brittle fusion zone and then propagates in the weld metal. The fracture mode of DP-TIG joints of Q345 steel is mainly brittle fracture. The maximum tensile strength of the joint welded using DP-TIG is 302.15 MPa.