Microstructure Stabilities of Newly Developed Hot-Working Die Steel and H13 Steel at Elevated Temperature

Herein, the microstructure stability of a newly developed hot-working die (HWD700) steel at elevated temperatures up to 700 degrees C is investigated using transmission electron microscopy (TEM), selected-area electron diffraction, energy-dispersive spectrometer, and high-resolution transmission electron microscope. It is showed in the results that the HWD700 steel exhibits a higher thermal stability than the commercial H13 steel when the temperature is up to 700 degrees C. After quenching and tempering, high densities of intra-lath rodlike and inter-lath spherical MC nano-carbides and inter-lath strip-like M7C3 nano-carbides are observed in the HWD700 steel. These carbides remain nanoscale at temperatures up to 700 degrees C. For comparison, rod-shaped MC nano-carbides in the tempered H13 steel tend to coarsen and transform into larger M23C6 carbides at temperatures up to 650 degrees C. The TEM observation further reveals that the interface misfit between the MC nano-carbide and matrix in the HWD700 steel is as low as 0.88%, lower than that of 14.8% in the H13 steel. This can be the main reason for the improved stability of the HWD700 steel by pinning dislocations and grain boundaries and thereby hindering the recrystallization process at an elevated temperature.