Effect of Austenite Reversion Treatment and Partitioning on the Phase Transformation Behavior and Mechanical Properties of Martensitic–Austenitic CrMnNi‐Cast Steel

The grain size of austenitic‐stainless‐cast steels is usually coarse and may be several hundred microns to millimeters, depending on solidification conditions and ingot geometry. During solidification, dendritic crystals grow into the supercooled melt and stop growing when they touch each other, which is accompanied by the formation of high‐angle grain boundaries. Further cooling of metastable austenitic steels with a martensite start temperature above room temperature can partially transform them into martensite. During subsequent heating above the austenite start temperature, also known as austenite reversion treatment (ART), the martensite transforms back into austenite. The resulting austenitic microstructure is thus significantly refined, leading to an even finer martensitic microstructure during subsequent cooling. To reduce the martensite formation capability, partitioning is carried out to enrich the austenite with C and N and thus improve the formability. In the present work, the temperature‐dependent phase transformation behavior of the martensitic–austenitic stainless X16CrNiMnN15‐3‐1 transformation‐induced‐plasticity‐cast steel is determined by means of dilatometry. The influence of a single or multiple ART on the resulting austenite grain size, the microstructure and the tensile properties are described. It is demonstrated that ultrahigh‐strength steels with good ductility can be achieved by using partitioning after ART.