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Abstract
Micro-Melt Maxamet Alloy is a highly-alloyed powder metallurgy (P/M) high speed steel (HSS) that was originally designed to have heat treated properties between conventional high speed steels and cemented carbides. These properties are obtained through the formation of a high volume fraction of uniformly distributed fine carbides in a fine-grain matrix. This microstructure provides excellent wear resistance while maintaining good toughness. This presentation will review the processing used to produce Maxamet powder and P/M millforms, such as round and flat bar. The chemical, physical, mechanical, and metallurgical properties of the annealed and heat-treated alloy will also be described. Information will also be provided on the alloy's recent performance in specific commercial tooling applications.
Introduction:
Currently there are essentially two types of materials that are available for the more demanding tooling applications such as metal cutting and shaping tools such as hobs, forming tools, and rolls: high speed tool steels and cemented carbide materials. High speed tool steels, such as AISI Types M2, M3, and M4, can be produced either by cast/wrought or powder metallurgy processing; however, tools made from these alloys, as well as high hardness (67- 68 HRC) super high speed steels such as AISI Types T15, M42 and M48, are not adequate for today's most demanding tooling requirements or longer production runs because of insufficient wear resistance, room temperature hardness and hot hardness. There is presently a trend in industry toward use of dry machining as opposed to the use of cutting fluids because of the potential environmental hazard associated with conventional cutting fluids. Metal cutting tools are likely to be subjected to significantly higher operating temperatures when used in dry machining operations. Most of the known high speed steel alloys are not suitable for use in dry cutting operations because their wear resistance and hardness degrades very rapidly under the extreme temperature conditions.
To avoid the limitations of the known high speed tool steels, one approach has been to produce high speed steel cutting tools with a very hard surface coating to improve the service life of these cutting tools. Such a coating is typically applied by either physical vapor deposition (PVD) or chemical vapor deposition (CVD). Such coatings are typically harder than about 70 HRC, which is harder...