The influence of holding time on the microstructure and properties of TLP joints of Q355 steel

Using BNi as the interlayer material, transient liquid phase diffusion welding experiments were conducted on Q355 steel at a welding temperature of 1050 degrees C under different holding times (10, 15, 20, 25 min). The welded joint microstructure, element diffusion migration, and phase composition were analyzed by using modern analytical testing instruments such as optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The mechanical properties of the joint were tested and analyzed by using a microhardness tester, universal testing machine, and impact testing machine. The electrochemical corrosion property of the welded joint was analyzed and studied by using an electrochemical workstation. The results showed that under the conditions of 1050 degrees C and 6 MPa pressure, the Q355 steel TLP welded joint with better property could be obtained with a 20-min holding time. With the increase of holding time, the width of the bonding interface layer increased first and then decreased, and the microstructure tended to be more uniform. The shear strength gradually increased, reaching a maximum of 496.7 MPa (25 min), but the impact toughness increased first and then decreased, with a maximum of 250.61 J/cm2 (20 min). The corrosion resistance of the joint also improved first and then weakened.