Patent ID: 8621757

Claim:
A blade member in which a surface of a base plate forming a cutting edge is coated with a coating layer, wherein the coating layer includes a non-nitrided layer coating the surface of the base plate and a nitrified layer coating a surface of the non-nitrided layer, and the non-nitrided layer and the nitrided layer have structures and compositions enhancing cutting performance of the cutting edge and improving durability of the cutting edge as defined below; wherein the non-nitrified layer has a thickness of 30 to 70 nm and contains Ti, Al and Cr, wherein relative proportions of Ti, Al and Cr of the non-nitrided layer vary along a direction of a thickness of the non-nitrided layer, the Ti, Al and Cr are contained in the non-nitrided layer respectively by atomic ratios a, b and c, where a+b+c=1, and the atomic ratios a, b and c respectively for the Ti, Al and Cr contained in the non-nitrified layer satisfy the relationships: 0.25≦a≦015, 0.25≦b≦0.75 and c=0 in the range from the surface of the base plate to a point corresponding to the thickness of 5 to 20 nm, and the atomic ratios a, b and c respectively for Ti, Al and Cr contained in the non-nitrided layer satisfy the relationships: 0.2≦a≦0.30, 0.55≦b≦0.765 and 0.06≦c in the range corresponding to the thickness of 30 to 70 nm, wherein the nitride layer has a thickness of 50 to 90 nm and contains Ti, Al, Cr and N, wherein the relative proportion of Ti, Al, Cr and N is set constant at a predetermined depth from the surface of the nitrided layer, and the Ti, Al, Cr and N are contained in the nitrided layer respectively by atomic ratios a, b, c and d, where a+b+c=1, and the atomic ratios a, b, c and d respectively for Ti, Al, Cr and N contained in the nitrided layer satisfy the relationships: 0.2≦a≦0.30, 0.55≦b≦0.765, 0.06≦c and 0.5≦d≦1, wherein the ratio between the thickness of the nitrided layer and the thickness of the non-nitrided layer is in the range from 1:1 to 2:1 and the hardness of the nitrided layer is greater than the hardness of the non-nitrided layer.