Failure Analysis on Fatigue Crack of Continuous Extrusion Die for Copper Alloy

H13 steel extrusion wheel of copper alloy continuous extrusion die has fatigue crack in the middle of service life, which leads to the early failure of the die. The chemical composition, nonmetal inclusion, crack morphology,microstructure and grain size of the failed die were detected and analyzed by direct reading spectrometer, digital display Rockwell hardness tester and optical microscope. The results show that both sides of the extrusion wheel groove have obvious cracks, and one side of the wheel groove is adhered off by copper alloy, and the average crack depth is up to 1 mm. The main cause of failure is that there are coarse grains in the material, which greatly reduces the strength and toughness of the material,and the thermal fatigue cracks occur in the die under the action of alternating thermal stress.