Friction Stir Welded AISI 304 Metal Sheets for Application in Food Implants

Abstract

Stainless steels are indispensable materials in many industrial fields. They can be easily shaped and joined by traditional welding methods. Some problematics such as possible decrease in corrosion resistance at the welding bead and in the heat-effected zone, residual stress, crack formation and distortions may take place after welding. Friction Stir Welding (FSW) may be used for joining stainless steels in a single pass and for optimising microstructure and mechanical properties of the processed region. The application of FSW to the widely used AISI304 stainless steel is investigated in food implants. The mechanical properties together with corrosion resistance and surface finishing are characterized. A high energy input is chosen for the welding (2000 rpm tool rotational speed and 50 mm/min advancing speed). The stirred zone (SZ) is characterized by optical microscopy. Vickers microhardness in the SZ results 37% higher than in the base material. Tensile tests highlight elongations up to 40% keeping maximum stress values at 600 MPa. All samples pass accelerated corrosion tests that simulate 20 years of cleaning cycles in a typical food implant.