Alloying and Processing of Medium Manganese Steels for Forging Applications

Abstract

The processability of medium Mn-containing steels (MMnS) with 4–10% Mn is discussed in light of their continuous casting behavior. Precipitation, phase transformation, extension, or shift of solidification intervals induced by various alloying concepts are decisive in controlling the hot ductility. It turns out that the formation of complex AlN and MnS precipitates as well as δ‑ferrite solidification deteriorates the high temperature ductility. The concept of MMnS has been used to develop air-hardening forging steels with 4% Mn. The alloy design and the heat treatment parameters have been varied with a focus on the prevention of Mn embrittlement as well as the formation of fine austenite grains during intercritical annealing. It is shown that the addition of B and Mo increases the impact toughness, although the effectiveness of each element varies depending on the heat treatment conditions. The impact toughness can be significantly improved by the introduction of a globular metastable austenitic phase. Compared to conventional quenched+tempered steels, an improved cyclic strength for an ultimate tensile strength level of more than 1300 MPa can be achieved.