b'Seco ToolsToughness represents tool resistance to pressure and impact, which is required when performing interrupted cutting.Cutting Tool MaterialsA fine balance exists between hardness and toughness in carbide inserts.By Aaron Eller Hardness represents wear resistance, which translates to the ability of a tool to withstand heat A t first blush, hardness and toughness mayduring metalcutting. The Rockwell A scale mea-seem like interchangeable concepts, but theysures the hardness of tungsten carbide, though exist at opposite ends of a continuum that de- some specifications translate HRA values to the fines indexable insert and solid cutting tool per- more familiar HRC scale used to measure the hard-formance, particularly when it comes to carbide in- ness of steel and other alloys. The temperature re-serts. Hard inserts offer greater wear resistance forsistance that correlates with hardness plays a huge enhanced performance and tool life in hot cuttingrole in cutting tool behavior and selection.environments than somewhat softer inserts do, yetIn the cutting zone, temperatures can rise above tough inserts can withstand impacts and stressors760 C (1,400 F). Hard carbide withstands and dis-to achieve high feed rates and DOCs. For any givensipates those high temperature levels and there-application, there is an optimal balance of hardnessfore handles the high heat generated in continuous and toughnessand toolmakers have worked dil- cutting. High hardness levels can make metal brit-igently to establish metallurgical principles andtle, however, which explains why heat-resistant car-provide a range of tools that can meet the diversebide tools tend to chip in situations that produce needs of part manufacturers. large amounts of pressure or vibration.36MAY 2020 CuttingMaterial.indd 36 4/16/20 5:30 PM'