Enhancing Mechanical Properties of Medium Mn Advanced High-Strength Steel by Inter-Critical Annealing: Elimination of Austenizing and Quenching Steps

Here, hardenability was enhanced by choosing two different chemical compositions, i.e. the addition of boron (0.12 wt-%) and chromium (2.5 wt-%) to the ordinary composition of the medium Mn advanced high-strength steels (AHSSs). Carbo-boride precipitates were formed in the samples having both boron and carbon in their compositions. Martensite was tempered after intercritical annealing at 700 degrees C. In the alloy with both boron and carbon (A2 alloy), austenite was formed by 2.8 vol.-% after 10-min annealing. Primarily, the annealing process led to the austenite stabilization in the structure of the cold-rolled A2 alloy due to the dissolution of carbo-boride precipitates. For the carbon-free alloy (A1 alloy), on the other, the annealing process and subsequent dissolution of precipitates failed to create austenite stabilization. The resulting mechanical properties for the cold-rolled A2 alloy are ultimate tensile stress of 1029 MPa, total elongation per cent of 19.5 and formability index of 20 GPa%.