Formability of austenitic stainless steels under warm hydroforming conditions

Use of stainless steel has been increasing in HVAC., sanitary and medical devices, as well as several structural and transportation applications, due to their high strength-to-weight ratio, corrosion resistance and aesthetic appearance. Austenitic stainless steels are the most common type used in the metal industry. Due to the limitations of forming these alloys into complex shapes at room temperature conditions, forming at elevated temperature has been considered as an enabling technique. Formability of these stainless steels is affected by strain rate and temperature due to martensitic transformation of meta-stable austenite microstructure. In this study, deformation characteristics of three common austenitic stainless steels (AISI 201, 301, and 304) were investigated using hydraulic bulge testing at cold and warm conditions. Material behavior of these alloys was determined based on continuous pressure and dome height measurements using several calculation approaches. These curves were then incorporated into finite element models (FEA) to be compared and validated with additional closed-die warm hydroforming experiments. Results suggest that material model and FEA results are in good agreement with experimental findings, and hence, they can be used for further predictions of complex and different parts with confidence.