Toughening effect of delta-ferrite in a modified PH13-8Mo steel

Abstract The presence of the delta-ferrite phase in steel is often considered detrimental, as it reduces both ductility and toughness. However, this study reports that in a B2-NiAl precipitation-reinforced modified PH13-8Mo steel, delta-ferrite can impart a toughening effect similar to that of retained austenite, exhibiting a three-fold increase in ductility without sacrificing material strength. Using several analysis techniques, the toughening effect was attributed to strain accommodation between delta-ferrite and martensite. This was owing to multiple strengthening mechanisms in delta-ferrite, including precipitation, orientation, solid solution, fine grain, and the elimination of grain boundary brittleness. These findings provide an innovative method for improving the toughness of maraging steels.