Microstructure evolution and enhanced performance of a novel Nb-Mo microalloyed medium Mn alloy fabricated by low-temperature rolling and warm stamping

摘要

A combined low-temperature rolling and warm stamping process was proposed for a Fe-5.6Mn-0.19C-1.2Al-0.05Nb-0.22Mo alloy to improve the tensile ductility and surface quality of the stamped parts. The results show that the present warm-stamped U-shaped parts exhibited the relatively uniform ultrafine multiphase microstructure and desirable mechanical properties, e.g. the average products of ultimate tensile strength and total elongation (PSE) values reached 27.5-31.3 GPa.%, which are more than double or triple times higher than those of the hot-stamped boron steels with similar strength level. As the stamping temperature decreased from 760 to 700 degrees C, both the fractions of ferrite and austenite increased, resulting in the enhanced tensile ductility (up to 24.5%) with sacrificing tensile strength from 1717 +/- 117 to 1424 +/- 53 MPa. The difference in stamping temperature greatly affected the tensile deformation behavior of the stamped parts: at 700 degrees C, the tensile curves exhibited Luders band propagation (LBP) behavior, and both Portevin-Le Chatelier (PLC) and transformation induced plasticity (TRIP) effects happened, while at 760 degrees C, the tensile curves exhibited continuous yielding behavior, and only TRIP effect happened over the entire plastic deformation. (C) 2017 Elsevier Ltd. All rights reserved.