Prediction Of Superplasticity Of Austenitic Stainless Steel -304 At Hot Working Temperatures

Abstract

Abstract Austenitic stainless steels are widely used in many industrial, medical, marine and nuclear applications. The use of stainless steel is growing due to the ease of maintenance, excellent corrosion resistance, attractive appearance, ductility, fire resistance and toughness. Anisotropy is usually described with two parameters: as planar anisotropy and as a normal anisotropy. The strain rate sensitivity index plays an important role in characterizing superplastic deformation. In the present work experiments are conducted from room temperature 700°C to 900°C in intervals of 50°C in rolling [R0], perpendicular [R90] and transverse directions [R45] at strain rate in the range of [0.01S to 0.0001s-1]. Using tensile test experimental data anisotropy and strain rate sensitivity index is calculated. Strain rate sensitivity calculated is positive. The positive rate sensitivity shows improvement in forming and has a similar effect on strain hardening. It is shown that with the increase in strain rate sensitivity the amount of elongation in the tensile test piece increases after maximum load, necking and before failure. The normal anisotropy ratio, r - value, is a very important parameter of cold rolled thin sheet metals. It is a constant numeric value which has been used as an indicator of formability of sheet metals by deep drawing and used as property of materials in software for numeric simulation of a plastic forming process. This paper investigates the behavior of austenite stainless steel sheet, based on a sophisticated experiment show significant variations of the r value during the forming process.