Effects of WC grain size, Co content and Cr3C2 addition of WC-Co based cemented carbides on tensile fatigue property were investigated because tensile repetitive stress often causes fracture of impact punches. To determine loads of repetitive stress for measuring fatigue property, tensile strength of each cemented carbide was measured. Fatigue property was evaluated by number of times of repetitive stress until fatigue fracture of the cemented carbides for several repetitive stress at each grade of cemented carbide. The specimens were broken into two in a small number of times for high repetitive stress. The specimens were not broken until numbers of times of 107 by decreasing the repetitive stress to 30-50 % of the tensile strength. Fining grain size of WC, optimized Co content and adopting Cr3C2 increased number of times for a same repetitive stress.
