Effects of heat treatment on the surface of a die steel STD11 machined by W-EDM

Wire-cut electro-discharge-machining (W-EDM) has been widely adopted as a manufacturing process for new die materials with high strength and hardness. Some inherent defects on the die surface machined by W-EDM, however, cause overall deterioration of the product and will limit its service life. In order to investigate the effects of heat treatments on the surface machined by W-EDM, four different machining methods are considered. Those are (A) milling and then grinding, (B) W-EDM, and (C) low temperature heat treatment or (D) high temperature heat treatment after W-EDM. The resulting surface roughness is measured and the changes of surface microstructures are investigated using a scanning electron microscope (SEM) with an energy dispersive X-ray spectrometer (EDS). In general, heat treatments after W-EDM improve the quality in terms of microstructures and surface roughness. In particular, high temperature tempering can remove almost the entire defects in the thermally affected zone. In order to examine the service life of a press, on-line experiments with a chain product are carried out. It can be concluded that the quality of a press die prepared by the method (D) could be as good as that by traditional manufacturing processes of the method (A).