Heat treatment inside the HIP unit

The possibility of combining densification or compaction of steel parts with a heat treatment has recently evolved due to the production of HIP units with a rapid quenching device. Several studies have already been performed to assess the cooling speed and show possibilities for heat-treating steels. It has already been shown that several alloyed steel grades could be hardened by quenching inside a HIP unit. This study aims to characterize the impact of high isostatic pressure during austenitization and quenching on the transformation behavior and resulting microstructure of hardenable steels. The effect of pressure during quenching was studied using two methods. The first method is to measure the latent heat inside the transforming steel during isothermal holding. The release or uptake of energy reveals information about the transformation sequence taking place. The second method is to use the electrical resistivity of a steel as a sensitive indicator for the existing phases and solution state of the steel during continuous cooling after austenitization. Both experimental methods reveal that an isostatic pressure of 170 MPa is sufficient to shift the transformations to longer times and lower temperatures and hence increase the hardenability of hardenable martensitic steel.