b'Cutting Tool MaterialsA variety of attributes determine the grade of tungsten carbide.By Alan Richter grain sizes over the years, Dep- Mets grades ranges from 3% to tola said. As a result, nanograin car- 25%. According to Deptola, the low S electingatungsten-carbidebide, which provides a higher levelend of that range is found in tools grade for an application is similarof hardness compared with gradesfor cutting wood and composite to putting together a jigsaw puzzle.with larger grains, is easier to manu- materials while grades for parts that You cant just look at one attributefacture than in the past. To minimizeexperience a lot of impact, such as and determine the quality is goinggrain growth during the sinteringcold heading dies, have the high-to be good based on that, saidprocess, he added that refractoryest amount.Rich Deptola, quality and continu- carbides, such as vanadium carbideAs you increase the cobalt, you ous improvement director for Tech- and chromium carbide, are added. increase the toughness, he said. Met Carbides Inc. There are quiteCarbide hardness is measuredIn other words, its more resistant a few things that fit together thatin the HRA scale. At TechMet, theto breaking.give you a full picture of the grade. hardness of grades ranges fromWhen selecting a grade for cut-Founded more than 20 years ago,81.5 to 94 HRA. At the high end is the Hickory, North Carolina-baseda grade made with ultrafine grain. company provides tungsten-car- Although some grades have a va-bide technology and products toriety of grain sizes, such as ones for fabricators and OEMs. producing mining bits, Deptola said Those puzzle pieces include thegrain size is typically uniform in cut-size of the tungsten-carbide grains,ting tools. The goal is to have a the percentage of binder content,nice, homogenous microstructure.the quantity of lesser alloying ele-mentsor refractory carbides Held Tightin the mix and the level of wear re- A binder is also added to the mix sistance. to hold the grains together. For cut-ting tools, cobalt is essentially al-Against the Grain ways used as the binding material, The classifications for grain sizebut nickel is one option for suitable at TechMet include nanograin, ul- applications, such as a wear part in trafine, submicron, fine, medium,an aggressive environment, Dep-coarseandextracoarse,Dep- tola said. That might see a lot of tola noted. A nanograin measureschemical attack on the part itself, around 0.2 m (0.000008") whileso it would have a nickel binder in-an extra-coarse grain is larger thanstead of cobalt.6 m (0.000236"). Between thoseThe amount of cobalt in Tech-two are ultrafine at 0.2 m to 0.5 m (0.00002"), submicron at 0.5 m toabout the author 0.8 m (0.000031"), fine at 0.8 m to 1.3 m (0.000051"), medium atAlan Richter is 1.3 m to 2.5 m (0.000098") andeditor at large of coarse at 2.5 m to 6 m. CTE. Contact him The technologies that have beenat 847-714-0175 developed have been pushing theor alanr@boundaries of smaller and smallerctemedia.com.TechMet Carbides42MAY 2020 CTMFeaturette.indd 42 4/16/20 5:40 PM'