Cemented carbide with improved toughness
A cemented carbide comprises particles including a tungsten carbide (WC) as a main component; a binder phase including cobalt (Co) as a main component; and particles including a carbide or a carbonitride of at least one selected from the group consisting of Group 4a, 5a, and 6a elements, or a solid solution thereof, wherein a cubic phase free layer (CFL), in which the carbide or the carbonitride is not formed, is formed from a surface of the cemented carbide to a depth of 5 μm to 50 μm.
1. A cemented carbide comprising:
1.5 wt % to 20 wt % of carbide or carbonitride including at least one of tantalum (Ta), niobium (Nb), and titanium (Ti);
4 wt % to 10 wt % of cobalt (Co); and
a tungsten carbide (WC) as well as unavoidable impurities as a remainder,
wherein a cubic phase free layer (CFL), in which the carbide or the carbonitride is not formed, is formed from a surface of the cemented carbide to a depth of 5 μm to 50 μm,
wherein,
an upper portion of the CFL is defined from a center of the CFL to a surface of the CFL,
a lower portion of the CFL is defined from the center of the CFL to a boundary of a bottom of a base material,
a size of the Co structure is defined as a length of a major axis of a Co structure, in which a ratio of the length of the major axis of the Co structure formed in the CFL to a length of a minor axis thereof is 5 or less, and
a size of the largest Co structure in the lower portion of the CFL is 1.3 times or less a size of the largest Co structure in the upper portion of the CFL.
2. The cemented carbide of claim 1 , wherein a thickness of the CFL is in a range of 10 μm to 30 μm.