ASTM B390-92 pdf free.Standard Practice for Evaluating Apparent Grain Size and Distribution of Cemented Tungsten Carbides.
This procedure for the visual comparison and classifi-cation of the apparent grain size and distribution of cementedtungsten carbides is limited to cemented tungsten carbides thatcontain approximately 6, 10, and 18 % cobalt.This standard does not purport to address all of thesafety concerns，if any, associated with its use. lt is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
ASTM Standards:B 657Test Method for Metallographic Determination ofMicrostructure in Cemented Carbides2.B665 Practice for Metallographic Sample Preparation ofCemented Tungsten Carbides2. apparent grain sizethe average diameter of a tung-sten carbide particle as measured on an etched metallographi-cally polished surface of a specimen of sintered cementedcarbide. The apparent grain size is expressed in micrometresand is generally reported as a range.The apparent size and distribution of tungsten carbidegrains in cemented carbides affects the material’s wear resis-tance and fracture. For a given chemical composition,anincrease in the average grain size will result in increasedtoughness and decreased wear resistance. This practice illus-trates representative micro-structures for a wide range oftungsten carbide-cobalt grades.This is not intended to be usedas a specification for carbide grades; producers and users mayuse the micrographs and the grain size chart as a guide indeveloping their own specifications.
The grain size rating of a cemented tungsten carbidespecimen is accomplished by selecting the photomicrographsin Fig. 1，Fig. 2,or Fig. 3 that most nearly match the fieldobserved on the specimen being evaluated (see Appendix Xl).7.2 A range of numerical values for various concentrationsof tungsten carbide particles，even though arbitrary，is sug-gested in Table 1.After visual comparison of a specimen with the photo-micrographs contained in this practice, the apparent grain sizeof a particular specimen shall be rated relative to one or moreof the photomicrographs. Cobalt contents should always bespecified.For example, a cemented tungsten carbide specimencontaining approximately 6 % cobalt, having a fine grain sizeand a grain size distribution similar to the one shown in Fig.1(a) would be reported as Type 6-F. The”F”indicates a finegrain size and the”6″identifies the cobalt content.ASTM B390 pdf download.