2010 Full-Line Drill Catalog - Desanto

Guhring tool materialsBasic characteristics of carbide fordrilling applicationsCarbideCarbide, similar to steel, is a less than precise and indeeda very general term for an entire material group. Carbidecan be produced in an infinite number of variations withdifferent characteristics through the combination of at leasttwo basic constituents.Carbide productionCarbide consists of a hardness carrier – tungsten carbideplus maybe one or more carbides – and an extremelytough component: Cobalt (Co). Cobalt basically serves as acementing or binding agent in which the carbide particlesare distributed.In order to satisfy the diverse demands that, dependenton the individual application task, are placed on carbide,Guhring offers a choice of more than 20 different standardcarbide types. Some are especially hard, others possess avery high toughness, some are ultra fine grain and othersare coarse. Furthermore, on the request of the customer,any conceivable carbide grade can be developed andproduced as a special carbide, so-to-speak.Our carbide division has a state-of-the-art laboratory atits disposal to ensure our carbide always correspondswith customer requirements. From the raw material to thefinished product, samples are continuously examined inorder to guarantee and document the highest quality andprocess reliability in accordance with the certification.For drilling applications the following characteristics are ofimportance:RigidityRigidity is a measure of the energy that is required to forcea material to deform. With carbide it is determined by thecobalt content. The higher the cobalt content, the lower therigidity of the material.The rigidity of conventional carbide is more than doublecompared to that of steel. Subsequently, holes ofconsiderably greater straightness can be produced withcarbide drills than with steel drills. However, this positiveeffect of the rigidity is limited because of deformation forcedupon the drill – for example through offset or imbalance –result in a heavy increase in load on the material. Therefore,more rigid materials are also more prone to breakage.HardnessHardness is described as the resistance of a material againstpenetration of another. It is clear, that the tool material mustbe considerably harder than that of the workpiece, in orderto not be exposed to excessive wear.There are several possibilities to adjust the hardness ofcarbide: on the one hand by modifying the cobalt contentand on the other hand by varying the carbide grain size. Ifthe cobalt content is increased whilst retaining the samegrain size, the hardness of the carbide is reduced. However,if the grain size is reduced whilst retaining the same cobaltcontent, the hardness is increased.Hardness K ICGrain size in μm175013TechnicalHardness HV501700165016001550150014501211109Toughness KIC MPam 0,5140080.2 0,2 0.4 0,4 0.6 0,6 0.8 0,8 1.0 1,0 1.2 1,2 1.4 1,4333