The effects of intercritical annealing, before and after cold rolling, on retained austenite volume fractions, austenite stability, and tensile properties of a 7.39Mn-0.14C-1.55Al-0.2Si (wt pct) medium Mn sheet steel were evaluated. The extent of hot band annealing at 650 °C prior to cold rolling is shown to be an important parameter to consider in the development of processing histories leading to high strength–ductility combinations required for third-generation advanced high-strength steels.

This paper highlights some recent efforts to extend the use of medium-Mn steels for applications other than intercritically batch-annealed steels with exceptional ductility (and strengths in the range of about 1000 MPa). These steels are shown to enable a range of promising properties. In hot-stamping application concepts, elevated Mn concentration helps to stabilize austenite and to provide a range of attractive property combinations, and also reduces the processing temperatures and likely eliminates the need for press quenching. The “double soaking” concept also provides a wide range of attractive mechanical property combinations that may be applicable in cold-forming applications, and could be implemented in continuous annealing and/or continuous galvanizing processes where Zn-coating would typically represent an additional austempering step. Quenching and partitioning of steels with elevated Mn concentrations have exhibited very high strengths, with attractive tensile ductility; and medium-Mn steels have been successfully designed for quenching and partitioning using room temperature as the quench temperature, thereby effectively decoupling the quenching and partitioning steps.

Nitrogen-annealed tensile specimens of a cold rolled medium Mn (9.76 wt%) steel exhibited significantly reduced ductility due to a two-zone embrittled surface layer, imparted during annealing in a nitrogen atmosphere. The embrittlement was associated with high nitrogen contents at the surface.

The effects of adiabatic heating during deformation of a medium-manganese transformation-induced plasticity steel containing 10.1Mn-1.68Al-0.14C-0.2Si (wt.%) processed with initially 57 vol.% retained austenite were investigated over the temperature range from − 60°C to 100°C at strain rates from 0.002 s⁻¹ to 0.2 s⁻¹. Tensile tests were performed on specimens immersed in isothermal baths, which reduced but did not completely eliminate adiabatic heating. The specimen temperature depended on the extent of adiabatic heating, which increased with strain and strain rate. The measured properties primarily reflected the effects of temperature on austenite stability and the corresponding resistance of austenite transformation to martensite with strain. Changes in austenite stability were monitored by measurements of austenite fractions at a specific strain and observation of microstructures after deformation. The results of this study provide a basis to identify input material parameters required for numerical models applicable to sheet metal forming of medium-Mn steels.