Alloying Methods Technical Publications
28. Dust and Segregation-Free Powders For Flexible PM Processing: During the past few years, there has been increasing demand placed on PM parts producers to improve density uniformity, weight variation, alloy homogeneity and dimensional control. Enhanced flow and die fill characteristics are also required to improve productivity and reduce the percentage of green scrap. The ANCORBOND™ process developed by Hoeganaes has satisfied many of these requirements by bonding the alloy additives and fines to the base iron particles. Increased concerns regarding the inability to retrofit higher apparent density premixes to existing tool sets, a slight loss of compressibility and the desire to reduce the total organic content for improved burnout response led to further improvements in the bonding process. Several factors that contribute to the performance and greater flexibility of binder-treated mixes compared with regular mixes will be discussed in this paper.
27. Recent Developments in Ferrous Powder Metallurgy Alloys: A systems approach to engineered ferrous powder metallurgy (PM) materials is described. The approach encompasses the use of high compressible, high performance powders in premixes produced using proprietary mixing technology that employs patented binders. To ensure that an appropriate microstructure is achieved to suit the functional requirements of a particular application, alloys are formulated based on knowledge of the compaction and sintering cycle that will be used to make the PM parts. These premixes have improved flow and die filling characteristics that result in greater consistency throughout the entire PM part manufacturing process. In addition, the use of binder treated premixes leads to reduced dusting and segregation of alloy additions. Binder treated premixes produced using high compressible, prealloyed molybdenum steel powders are shown to be particularly well suited for quench-hardening, sinter-hardening, and high temperature sintering. They also form the basis for a series of chromium, manganese, and chrome-manganese PM 'Steels. The systems approach will be augmented during 1994 by the introduction of new material and process technology that enables part densities of 7.3 to 7.5 g/cm3 to be achieved through single compaction processing.
26. High Performance Ferrous PM Materials For Automotive Applications: The majority of automotive components (transmission, chassis, suspension, and engine) for which parts with densities up to about 7.0 g/cm3 are suitable have already been converted to PM and there are few opportunities for growth in this density range. In order to meet the requirements of more demanding applications there has been a trend toward higher densities through the use of infiltration, double pressing/double sintering, or powder forging (l - 4) to produce parts such as synchronizer hubs, crankshaft sprockets, chain sprockets, gerotors, steering column tilt levers, planetary gear carriers, parking gears shift levers, and connecting rods. While powder forging has been shown capable of producing parts, which are superior to wrought, or cast products process economics have limited market penetration by this technology (5). The double press and sinter route also adds process costs and is probably too expensive for other than premium applications. There is a real need for a systems approach that will permit double pressed and sintered or infiltrated performance characteristics to be achieved by means of single compaction processing. The mechanical properties of PM materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final product (6).
7. High Performance Ferrous PM Materials: The Effect of Alloying Method on Dynamic Properties: A comparison has been made between fully prealloyed, partially prealloyed, and elementally admixed alloys in the "as sintered" condition in order to assess the influence of microstructural and chemical homogeneity on the tensile, impact, and fatigue properties. Elementally admixed and completely prealloyed powders were prepared with chemistry similar to that of the diffusion bonded Distaloy® 4600A (nominally 1.8 wt. % Ni, 1.6 wt. % Cu, and 0.55 wt. % Ho). An addition of 0.6% graphite was made to each of these materials. In one series of experiments, test pieces were prepared from each of the materi`1als pressed to a green density of 6.9 g/cm3. Sintering was carried out at 2050°F for 30 minutes at temperature in a dissociated ammonia atmosphere. A second series of experiments was carried out in which a fixed compaction pressure of 45 tsi was applied to each of the materials. Sintering was carried out in a similar manner to the first series. An additional prealloyed material, Sumiron 4100S, was included in this second series of experiments. However, this material was sintered at 2300°F to reduce the tendency for oxidation of this chromium and manganese steel alloy. For the samples pressed to a fixed green density of 6.9 g/cm3, the tensile strength of the partially prealloyed material was significantly higher than the other materials. The impact energy of the partially prealloyed material was also higher. A similar trend was found for the samples pressed at a fixed compaction pressure of 45 tsi. The partially prealloyed product, sintered at 2050OF, was even superior to the Sumiron 4100S; sintered at 2300°F. The differences in the tensile and impact properties were significant at the one percent level. The rotating bending fatigue performance of the partially prealloyed material was superior to that of the Sumiron 4100S.
4. Ferrous Powders - How Alloying Method Influences Sintering: The mechanical properties of PM materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final sintered product (1,2).