Effect of microstructure on mechanical properties in weld-repaired high strength low alloy steel

Abstract

To understand the effect of microstructure on mechanical properties of weld-repaired high strength low alloy (HSLA), as-received and weld-repaired HSLA with and without buffer layers (BLs) were prepared. Microstructure analysis was carried out using optical microscope and SEM, and mechanical properties were measured by Vickers hardness test and fatigue test.The fatigue resistance of weld-repaired HSLA without BL was deteriorated with comparing to parent metal (PM). Meanwhile, Vickers hardness (VH) showed an obviously reduction in the melted parent metal (MPM), which was due to formation of predominately block ferrite. For the weld-repaired HSLA with BL, the VH and fatigue resistance increased with the incorporation of 4mm BL, which was mainly due to formation of lath ferrite and fine-grained pearlite and bainite. When BL thickness increased to 10mm, the VH and fatigue resistance decreased, which was because the thick BL diluted the MPM. VH number from low temperature (below melting point) heat affected zone (HAZ) fluctuated, but had a little scatter. However, the fatigue crack growth rate from HAZ was not obviously affected by the welding as comparison with the PM.