Cost Effective High Performance Parts

So called "mid-range" parts are not generally considered exceptionally low in cost, but rather as parts for which a cost reduction and improved behavior can both be obtained. There are many parts in this category that are the subject of current production programs. They generally fall into three categories of parts: billet materials, P/M near-net shapes, and clad composite materials.

Billet Materials. A good example of billet materials are high-speed steel billets made by hot isostatic pressing (HIP) of gas-atomized powders. This material is current bill-of-material for about 8000 tons/year of high-speed steels manufactured in both the United States and Europe (Ref 13). It is typically competitively priced with cast and wrought material and has a strong advantage for the larger size products due to its fine, uniform carbide size. This gives it manufacturing advantages (especially grindability) and performance advantages over conventional cast and wrought material. Other widely used P/M billet materials include sputtering targets for applying the coatings used in data storage applications. Important materials are powders such as chromium, chromium alloys, and cobalt alloys. Important characteristics are 100% density, high purity, and uniformity of chemical composition, traits that are the trademark of HIP P/M materials.

Powder metallurgy near-net shapes have made their mark for production applications in several industries. Power turbines for instance have used rotors, rings, and disks (Ref 14) HIP densified from steel alloys such as 12% Cr (X 20 CrMo V 12 1) and 9% Cr 1% Mo (Grade 91). The P/M alloys are superior to their wrought counterparts in that the properties developed are isotropic and are equivalent to the maximum wrought properties in the forging direction. Powder metallurgy near-net shape manifolds and valve bodies have become standard production items in the North Sea oil fields in alloys such as austenitic and duplex (ferritic-austenitic) stainless steels (Ref 15). Manifold sections can be made as net shapes with no machining except for the mating surfaces on connecting flanges. Individual parts are then welded into sections for use in underwater applications. Also, P/M near-net shapes are finding acceptance for pump and valve components in hostile environments.

The advantage these parts have compared to closed-die forgings is that they have the same properties as the maximum forged properties in all directions (isotropic), but with inside detail that is not possible with forgings. Also, the delivery time is much shorter for first deliveries for the P/M parts due to much more simplified tooling.

HIP cladding of powder materials on solid substrates has become an important engineering technique in a number of applications involving improving corrosion, erosion, and wear properties. The advantage of the technique is that the P/M alloy can be engineered precisely for the environmental factors and then applied in sparing quantities in such a way that a metallurgical bond is created with a low-cost substrate that will withstand the rigors of the application. A good example is tooling for plastic extrusion. Corrosion resistance can be provided, for example, by selecting a gas-atomized nickel-chromium alloy as a base and blending in tungsten carbides for wear resistance. This powder can be HIP bonded to the inside surface of relatively inexpensive steel barrels to provide a duplex material capable of giving long life in extruder service.

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