Machinery's Handbook, 31st Edition
Cemented Carbides and Other Hard Materials 861 Table 1. Typical Properties of Tungsten Carbide-Based Cutting Tool Hard Metals ISO Application Code Composition (%) Density (g/cm 3 ) Hardness (Vickers) Transverse Rupture Strength (N/mm 2 ) WC TiC TaC Co
P01 P05 P10 P15 P20 P25 P30 P40 P50 M10 M20 M30 M40 K01 K05 K10 K20 K30 K40
50 78 69 78 79 82 84 85 78 85 82 86 84 97 95 92 94 91 89
35 16 15 12
7
6 6 8 7 8 8 9
8.5 11.4 11.5 11.7 12.1 12.9 13.3 13.4 13.1 13.4 13.3 13.6 14.0 15.2 15.0 14.9 14.8 14.4 14.1
1900 1820 1740 1660 1580 1530 1490 1420 1250 1590 1540 1440 1380 1850 1790 1730 1650 1400 1320
1100 1300 1400 1500 1600 1700 1850 1950 2300 1800 1900 2000 2100 1450 1550 1700 1950 2250
8 3 5 4 2 3 4 5
8 6 5 5 3 5 5 4 4
10 16
6 8
10 10
2
3 4 6 6 9
1 2
11 2500 A complementary development was the introduction of ever more complex chipbreak ers derived from computer-aided design and pressed and sintered to precise shapes and dimensions. Another advance was the application of hot isostatic pressing (HIP), which has moved hardmetals into applications that were formerly uneconomical. This method allows virtually all residual porosity to be squeezed out of the carbide by means of inert gas at high pressure applied at about the sintering temperature. Toughness, rupture strength, and shock resistance can be doubled or tripled by this method, and the reject rates of very large sintered components are reduced to a fraction of their previous levels. Further research has produced a substantial number of excellent cutting-tool materials based on titanium carbonitride. Generally called “cermets,” as noted previously, carboni tride-based cutting inserts offer excellent performance and considerable prospects for the future. Compositions and Structures: Properties of hardmetals are profoundly influenced by microstructure. The microstructure, in turn, depends on many factors, including basic chemical composition of the carbide and matrix phases; size, shape, and distribution of carbide particles; relative proportions of carbide and matrix phases; degree of intersolubility of carbides; excess or deficiency of carbon; variations in composition and structure caused by diffusion or segregation; production methods generally, but especially milling, carburizing, and sintering methods, and the types of raw materials; post sintering treatments such as hot isostatic pressing; and coatings or diffusion layers applied after initial sintering. Tungsten Carbide/Cobalt (WC/Co): The first commercially available cemented car bides consisted of fine angular particles of tungsten carbide bonded with metallic cobalt. Intended initially for wire-drawing dies, this composition type is still considered to have the greatest resistance to simple abrasive wear and, therefore, to have many applications in machining. For maximum hardness to be obtained from closeness of packing, the tungsten carbide grains should be as small as possible, preferably below 1 m m (0.00004 inch) and consider ably less for special purposes. Hardness and abrasion resistance increase as the cobalt content is lowered, provided that a minimum of cobalt is present (2 percent can be enough,
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