Structure and Properties of High-Manganese TWIP, TRIP and TRIPLEX Steels

Abstract

The aim of this paper is to determine the high-manganese austenite propensity to twinning induced by the cold working and its effect on structure and mechanical properties, and especially the strain energy per unit volume of newly-developed high-manganese Fe-Mn-(Al, Si) investigated steels. Newly-developed steels achieve profitable connection of mechanical properties. The newly-developed high-manganese steels provide an extensive potential for automotive industries through exhibiting the twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) mechanisms. TWIP steels not only show excellent strength, but also have excellent formability due to twinning, thereby leading to excellent combination of strength, ductility, and formability over conventional dual phase steels or TRIP steels. Conditions applied to high-manganese TWIP/TRIP/TRIPLEX steels sheets during deep drawing are different from those applied during tensile testing; the formability cannot be evaluated by mechanical properties obtained from the tensile test. The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light, scanning and electron microscopies as well as x-ray diffractometry. Results obtained for newly-developed high-manganese austenitic steels with the properly formed structure and properties in the heat treatment- or thermo-mechanical processes indicate the possibility and purposefulness of their employment for constructional elements of vehicles, especially of the passenger cars to take advantage of the significant growth of their strain energy per unit volume.