Impact of local forging parameters on the microstructural evolution and mechanical properties of hot forging steel dies

An original multi-scale approach is proposed to understand how local forging parameters influence the evolution of the topography, microstructure and mechanical properties near the tool surface during its service life. To this end, the study is based on observing the geometric elements constituting the tool surface in 3 life states. The mechanical and thermal tribological conditions encountered during forming differ according to the local geometry. Near-surface mechanical properties are determined from nanoindentation tests for the different geometric conditions and wear states. The mechanical property measurements and the microstructure analysis correlate quite well. A significant decrease in hardness and elastic modulus was observed depending on the geometric area studied. Analysis of the microstructure revealed a transition from martensite to a ferrite matrix with globular cementite and fine metal carbonitride precipitates.