1. Field of the Invention
The present invention relates to a sintered carbonitride alloy with Ti as main component and a cobalt binder phase, which has improved properties particularly when used as tool material for steel and cast iron cutting. More particularly, the present invention relates to a carbonitride-based alloy of specific composition and controlled relative saturation magnetization and coercivity for optimal combination of abrasive wear resistance, toughness and resistance to plastic deformation.
2. Description of the Related Art
Titanium-based carbonitride alloys, so called cermets, are widely used for metal cutting purposes. Compared to WC—Co based materials, cermets have excellent chemical stability when in contact with hot steel, even if it is uncoated, but have substantially lower toughness. This makes them most suited for finishing operations, which generally are characterized by limited mechanical loads on the cutting edge and a high surface finish requirement on the finished component.
Cermets comprise carbonitride hard constituents embedded in a metallic binder phase generally of Co and/or Ni. The hard constituent grains generally have a complex structure with a core, most often surrounded by one or more rims of other composition. In addition to Ti, group VIa elements, normally both Mo and W, are added to facilitate wetting between binder and hard constituents and to strengthen the binder phase by means of solution hardening. One or more of group IVa and/or Va elements, e.g. Zr, Hf, V, Nb and Ta, are also added in all commercial alloys available today. Cermets are produced using powder metallurgical methods. Powders forming binder phase and powders forming hard constituents are mixed, pressed and sintered.
During recent years many attempts have been made to control the main properties of cermets in cutting tool applications, namely toughness, wear resistance and plastic deformation resistance. Much work has been done especially regarding the chemistry of the binder phase
U.S. Pat. No. 6,344,170, U.S. Pat. No. 6,344,445 and U.S. Pat. No. 6,325,838 relate to a sintered body of a carbonitride alloy with titanium as main component with improved properties when used as cutting tool material. This has been achieved by combining a carbonitride based hard phase of specific chemical composition with an extremely solution hardened Co binder phase. By optimizing composition and sintering process in the Ti—Ta—W—C—N—Co system improved toughness and resistance to plastic deformation are accomplished. The two parameters that are used to optimize toughness and resistance to plastic deformation are the Ta- and Co-contents. The use of pure Co-based binder is a major advantage over mixed Co—Ni-based binders with respect to the toughness behavior due to the differences in solution hardening between Co and Ni.
U.S. Pat. No. 7,332,122, and U.S. Pat. No. 7,157,044 are similar. They relate to a titanium based carbonitride alloy containing Ti, Nb, W, C, N and Co. By replacing Ta in U.S. Pat. No. 6,344,170 by Nb and carefully controlling the amount of undissolved Ti(C,N) cores a further optimization of technological properties has been achieved. More particularly, said patents relate to a carbonitride-based hard phase of specific composition, for which the amount of undissolved Ti(C,N) cores is optimized for maximal abrasive wear resistance, while the Co and Nb contents are simultaneously optimized to give the desired toughness and resistance to plastic deformation.