The evolution of microstructure and micro-mechanical properties in the repeatedly renovated QHZ punch in fine-blanking

Abstract As a kind of high speed steel, QHZ has been widely used in industry for fine-blanking punches. However, because of complicated working conditions of fine-blanking, the service life of punches decreases as the number of repair increases. In this paper, the evolution of QHZ punches with different numbers of renovations was studied at the micro-scale level to investigate the influence of impact accumulation on their service life. The force condition and life of the punch during fine-blanking process were studied through finite element method. Electron backscatter diffraction was applied to investigate the microstructural evolution with the assistance of a scanning electron microscope. And the punch’s micro-mechanical properties such as hardness and Young’s modules were characterized by nano-indentation technique. It was found that the service life is closely related to the micro-evolution of QHZ during punching process. The deterioration of microstructure paralleling to the punching direction, such as the increase of grain size, the decrease of ∑3 grain boundary fraction, and the transformation of crystallographic orientation, usually results in life reduction. Therefore, it is highly anticipated that this study can offer guidance for further research on life improvement.