Evaluations of tensile properties as a function of austenitizing temperature and springback by V-bending testing in medium-Mn steels

In the present study, tensile and springback properties of medium (3-7 wt%) Mn steels for warm stamping were investigated as functions of Mn content, austenitizing temperature (T-aus), V-bending temperature (T-b) and time (t(b)). For comparison, the tensile and springback properties of 22MnB5 steel used for hot stamping were also evaluated. Whereas medium-Mn steels were air-cooled to room temperature after austenitizing at various T-aus, the 22MnB5 steel was water-quenched. The 5Mn steel exhibited the highest tensile properties due to the martensitic matrix with inactive auto-tempering and negligible amount of retained austenite. The springback of medium-Mn specimens was increased by the addition of Mn at a given Tb when tb was 0 s. At the T-b of 300-500 degrees C, the fraction of martensitic transformation was raised by increasing the Mn content, resulting in high springback. At the T-b of 600. C, the rise in transformation strain by the addition of Mn raised springback. When T-b was fixed to be 600 degrees C, the springback of medium-Mn specimens was increased by the addition of Mn due to the increases in transformation strain at the t(b) of 0 s and the fraction of martensitic transformation during air cooling at the t(b) of 2 s and over.