Effect of fusion and friction stir welding techniques on the microstructure, crystallographic texture and mechanical properties of mild steel

Abstract

The present investigation aims at studying the effect of different welding techniques on the microstructure and mechanical properties of the welds. Weld zone (WZ) in the metal inert gas (MIG) welding, contains higher martensite fraction compared to arc and tungsten inert gas (TIG) welding. The micro-hardness of the WZ was found to be maximum after MIG welding (220 ± 14 HV) in comparison to arc welding (190 ± 12 HV), TIG welding (142 ± 10 HV) and friction stir welding (FSW) (202 ± 10 HV) as well as the base metal (BM) (108 ± 14 HV). The joints fabricated via MIG welding exhibited higher tensile strength (371 ± 10 MPa) as compared to other welding techniques (arc and FSW). The ductility of the parent metal was 42 ± 2% whereas the ductility of the MIG and arc joints were lower (13 ± 2% and 17 ± 3% respectively) due to the presence of martensite during fusion welding. The FSW joint shows higher yield and tensile strengths (356 ± 8 MPa) along with higher elongation (22 ± 4%) compared to fusion-welded joints due to the presence of fine, equiaxed recrystallized grains in the WZ. Fracture occurs at the HAZ/base metal interface, where the hardness is lower compared to the WZ. Compressive and tensile residual stress is obtained in the WZ upon fusion and FSW, respectively. In this paper, analytical tools are used to calculate the orientation of prior austenite (γ) in the MIG weld joint. The texture of high temperature γ phase is simulated for the different welding techniques. The occurrence of the Kurdjumov–Sachs (KS) orientation relationship (OR) is determined from the martensite grains in MIG weld. The texture investigation showed the occurrence of texture memory effect of ferrite in the HAZ after MIG welding.