Nitrogen-induced nanotwinning of bainitic ferrite in low-alloy steel

International audienceThe isothermal decomposition of austenite between BS and MS was investigated after carburizing and carbonitriding in low-alloy steel 23MnCrMo5. The microstructure of the products differed significantly between carburizing and carbonitriding. The carburized alloy produced an expected bainitic microstructure consisting mainly of bainitic ferrite with some cementite and retained austenite. In contrast, the microstructure of the nitrogen-containing sample showed finer, entangled ferrite plates, retained austenite and nitrides. The ferrite plates contain numerous transformation twins, which can be as thin as only a few nanometers. This original result proves that abundant twinning can be found in bainite as well as in martensite