Characteristics of undissolved and re-precipitated MC-type carbides in H13 steel

An investigation is conducted using TEM and EDS to characterize the MC-type carbides in H13 steel, including the undissolved MC during austenitization and the re-precipitated MC from austenite during pre-cooling treatment. The results show that the undissolved MC exhibit spherical or elliptical morphology (∼200 nm), in contrast to the rhombic morphology and smaller size (∼100 nm) of the re-precipitated one. An orientation relationship of (020) MC // ( 10) M , [10 ] MC // [11 ] M is identified between the re-precipitated MC and the martensitic matrix (M). During quenching from 1100 °C to room temperature, the partitioning of Mo from austenite to MC causes its segregation at the periphery of undissolved MC particle. Pre-cooling treatment at 950 °C promotes the re-precipitation of MC from austenite and provides adequate time for the diffusion of Mo, thereby achieving a homogeneous distribution of Mo within the MC.