Abstract: Apparatus and a method for evaluating the plane strain stretch formability for thin steel sheets used in automotive bodies to provide easy evaluation of the plane strain stretch formability. The apparatus includes: a lower die and an upper die with a lock bead installed thereon. A rectangularly shaped test specimen is inserted between the upper and lower dies and, and is clamped by means of the lock bead along the circumferential edge of the test specimen, so that the material of the test specimen can be moved into the upper die. A punch is elevated to apply a stretch forming force on the test specimen, and then, the plane strain stretch formability is evaluated based on the fracture limit punch height at the instant of the fracture. The punch has a saddle-like, semi-cylindrical shape.

Abstract: An austenitic high manganese steel having superior formability, strengths and weldability, and a process for manufacturing the steel, are disclosed. The superior formability of the steel is suitable for use on automobiles and electronic panel. The steel has a composition of (in weight %) less than 1.5% of C, 15.0-35.0% of Mn, 0.1-6.0% of Al, and the balance of Fe and other indispensable impurities. The size of the austenite grains is less than 40.0 .mu.m, and, one or more elements are added by selecting them from a group consisting of less than 0.60% of Si, less than 5.0% of Cu, less than 1.0% of Nb, less than 0.5% of V, less than 0.5% of Ti, less than 9.0% of Cr, less than 4.0% of Ni, and less than 0.2% of N, thereby providing an austenitic high manganese steel having superior formability, strengths and weldability.