Effect of Aluminum on Thermally Induced ε-Martensite for Fe-Mn-C TWIP Steels

Abstract

Cold-rolling of hot-rolled plate of Fe-18.7Mn-0.61C-1.4Al (Al-TWIP) steel was identified with an austenite single phase through the entire thickness, and that of Fe-17.8Mn-0.57C (TWIP) steel was composed of ε-martensite and austenite phases from the surface to a thickness of ~45 ㎛. Electron back-scattered diffraction (EBSD), glow discharge spectrometry (GDS), and transmission electron microscopy (TEM) were conducted to investigate the ε-martensite transformation of TWIP steel. In TWIP steel, thermally induced ε-martensite transformation was produced since the surface austenite stability decreased due to surface decarburization. The thickness of ε-martensite (~45 ㎛) was coincident with the depth at which 0.45 wt% C of TWIP steel was achieved. However, the TWIP steel with added Al increased the austenite stability of the surface layer and suppressed ε-martensite transformation.