Optimization of austenitic and ferritic steels for deep drawing. Part 1: metallurgical and mechanical analyses.

Abstract

Deep drawing of stainless steels thin sheets is a cold forming process used to produce components with complex geometries at limited costs. Although it seems a simple shaping technique, this technology requires a high level of know-how, essential to optimize parameters and limit production scraps. The choice of stainless steel type also plays a fundamental role, since there are austenitic and ferritic grades with improved chemical composition which should be characterized by a superior deformability when compared to the more common ones. This study investigates the formability of two austenitic and two ferritic stainless steels, AISI 304, 304 mod., AISI 430 and AISI 441, using tensile tests and Erichsen tests. From the former, the mechanical properties and anisotropy coefficients were determined along three sampling directions in respect to the rolling direction. Since the deep drawing is influenced also by some technological parameters such as the lubrication, the punch speed, and the blank-holder pressure, Erichsen tests were performed varying the deformation conditions and an Erichsen index (IE) was determined. The Erichsen samples were also subjected to metallographic and HV0.2 microhardness analyses to study the modification of the microstructure and the consequent impact on the local mechanical properties.