Investigation of microstructure and mechanical property evolution in a novel low-cost Ni-free maraging steel based on Mn and C through cold rolling followed by aging

Abstract

In this work, we investigate the microstructures and mechanical properties evolution on a novel carbon-based maraging steel with the compositions of Fe–10Mn-0.25C–1Cr–2Mo wt%, through hot and cold rolling following by heat treatment. The composition was designed through thermodynamic modelling to achieve a combination of high strength and high tensile elongation through the development of fine tempered martensite with carbide strengthening, and the transformation induced plasticity (TRIP) from the reverted austenite. After hot and cold deformation, a solution treatment at 870 °C followed by quenching gave a martensitic structure with 5% retained austenite. The microstructure and tensile properties were then investigated in detail as a function of ageing time at 510 °C. The kinetics of austenite reversion were much more rapid, with a peak in austenite content after only 5h, giving a maximum volume fraction of ∼26%, with a sharp reduction for longer ageing times. The best tensile properties were obtained after an 8 h age with only ∼16.5% of reverted austenite, which provided a UTS of 1560 MPa (220 MPa contributed by TRIP) and an elongation of 14.5%. While the smallest grain size was attained after 16 h of aging, accompanied by an exceedingly low volume fraction of reverted austenite (∼2.1%) for the TRIP effect, the UTS decreased to 1356 MPa, with a slightly improved elongation of 15.7%. The results show that achieving the optimal mechanical properties requires balancing the volume fraction of reverted austenite for the TRIP effect with the grain size to enhance both strength and ductility.

Keywords

• Medium Mn steel
• Cold rolling
• Austenite reversion
• TRIP
• Grain refinement