b'For any given application, there is an optimal balance of hardness and toughness.Juggling Act ness and toughness while carbon boosts hardness, and the combina-tion of the two yields tungsten-car-Tough Enough? bide molecules. Meanwhile, cobalt, At the other end of the contin- which has a lower melting point uum, toughness represents pres- than tungsten and carbon, contrib-sure and impact resistance, whichutes to toughness and intensifies correlate with the ability of a toolthe performance characteristics of to withstand high feed rates, heavyother elements. In tungsten car-DOCs and the repetitive impactsbide, cobalt serves as a binder, es-associated with interrupted cut- sentially glue that holds carbide ting. But in exchange for durability,grains together.tough carbide becomes vulnerableGrain size also can determine the to heat, making tough carbide lesslevel of hardness and toughness. than ideal for high-speed, continu- Hard carbide grades have smaller ous cutting. grains,andtoughgradeshave Both attributes tie directly tolarger ones. Hard grades need less the primary elements that makecobalt binding to hold their grainsduring continuous cutting than with up carbide: tungsten, carbon andtogether, which promotes bettersofter grades. Tough grades in-cobalt. Tungsten promotes hard- heat resistance for longer tool lifeclude more cobalt binding, which [email protected] 2020CuttingMaterial.indd 38 4/16/20 5:30 PM'