The tempering behavior of granular structure in a Mn-series low carbon steel

The granular structure in a Mn-series low carbon steel composed of ferrite matrix and martensite–austenite islands does not exhibit temper brittleness which is quite different from common microstructures in steels. This characteristic facilitates the performance optimization through adjusting tempering temperature. A good combination of tensile strength (750–1000 MPa) and impact toughness (Aku, 138–154 J) can be obtained after quenching and tempering at 400 °C for a round billet with 250 mm in diameter.