Evolution of surface morphology and mechanical characterization of GTAW welded SDSS thin sheets

Abstract

Super duplex stainless steel (SDSS) is becoming a growing trend because of its superior mechanical qualities and high corrosion resistance. This study examines the changes in surface morphology and mechanical properties of SDSS thin (2 mm) sheets welded using the Gas Tungsten Arc Welding (GTAW) process. The optimized GTAW parameters have a welding current of 70 A, arc voltage of 12 V, torch speed of 200 mm/min, with shielding gas at a rate of 12 L/min. The surface morphology of the welds revealed the presence of coarse particles in both the weld zone (WZ) and the heat affected zone (HAZ). It is made through several grain-boundaries, intragranular, and Widmanstätten austenite, produced due to the fast cooling and high temperature gradients of the GTAW. The scanning electron microscopy analysis revealed distinct phase boundaries and areas with needle-like structures in the austenite phase of the WZ. Elemental mapping revealed that Chromium decreases from 25.50% in the base metal to 23.40% in the area of WZ as a result of the GTAW heating cycle. Vickers hardness testing for surface hardness profiling revealed that the WZ displayed a greater hardness of 305 HV in contrast to the HAZ at 282 HV and the base metal at 260 HV. This localised surface hardening effect shows resistance to plastic deformation and wear, crucial for high-stress situations. The mechanical performance was assessed by a Flexural surface analysis, revealing that the welded joint attained a maximum flexural strength of 800 MPa demonstrating excellent ductility along with strength.

Keywords

• Super duplex stainless steel
• GTAW
• Microstructure
• Microhardness
• Three-point bending