Diffusion Alloy

Diffusion Alloy - Materials Technical Publications

196. Sintering of Powder Premixes - A Brief Overview Advances in the understanding of the sintering of powder premixes have contributed significantly to the growth of the ferrous powder metallurgy industry. This includes sintering both in the solid state and in the presence of a liquid phase. In this article, the sintering of iron powder premixes containing: 1) graphite; 2) nickel and graphite; 3) copper and graphite; 4) Phosphorus as ferrophosphorus; and, 5) boron as ferroboron are discussed. The evolution of microstructure and mechanical properties are discussed as well.

189. Capabilities of Two Chromium Powder Metallurgy Steel for High Performance Applications at Conventional Sintering Temperatures Ancorsteel 4300, a high performance Cr-Si-Ni-Mo steel, was unveiled two years ago as the first in a series of powder metallurgy alloys that will simulate wrought steel compositions. Advantages of this alloy include good compressibility, high hardenability, and excellent dimensional stability. More important, however, is that this alloy has the ability to be effectively sintered at 1120 °C and maintain oxygen contents below 500 ppm. This unique blend of performance and processing capabilities provides static and dynamic properties that exceed those of conventional powder metallurgy alloys and approach wrought gearing materials. A second Cr-Si-Ni-Mo alloy has now been developed that offers complimentary performance levels at a lower Mo content. This manuscript reviews properties of the two chromium steels with comparisons to traditional sinter-hardened and heat-treated powder metallurgy alloys.

184. Dimensional Control in Cu-Ni Containing Ferrous PM Alloys Elemental additives, such as copper and nickel, modify the dimensional change in sintered parts. Typically, Cu causes growth and Ni causes shrinkage. Interactions between Cu, Ni and C complicate these simple trends leading to more complex behavior. With the use of prealloyed Mo base materials, these alloy systems can be used for sinter-hardening applications. This paper investigates the dimensional and microstructural changes of Cu-Ni containing PM alloys during the sintering process.

181. Machinability Additives for Improved Hard Turning of PM Steel Alloys The machining of ferrous PM alloys differs considerably from wrought materials. The role of porosity and heterogeneous microstructures complicates the machining process, often making it more challenging. In addition, the presence of martensite in the microstructure of more highly alloyed and/or sinter-hardened PM components increases tool wear. One advantage of PM is that machinability additives can be easily admixed into the powder and therefore into the final part. Manganese sulfide is a well known additive for improving machinability. A new machining additive, designated MA, has been developed to compliment MnS in PM steels. Hard turning tests were performed to evaluate the effect of both additives on tool wear in different material systems. The MA additive was found to improve machinability beyond that of MnS in sintered compacts containing martensite. It additionally reduced rusting on the part surface. This paper discusses the improvement in machinability with these additives, with an emphasis on sinter-hardenable PM steels.

177. High Density Processing of Cr-Si-Ni-Mo Containing Steel Ancorsteel 4300, an iron alloy containing Cr-Si-Ni-Mo, was recently introduced and is capable of achieving high mechanical strength with exceptional dimensional stability. With the ability to be sintered at conventional temperatures, this alloy offers a unique blend of performance capabilities that can provide an economic advantage over alloy systems requiring high temperature sintering or secondary quench hardening. The current work discusses the performance of the new chromium steel at densities above 7.2 g/cm³at various cooling rates using an advanced lubricant/binder system. Comparisons to a hybrid Ni-Mo steel and a diffusion alloyed Ni-Cu-Mo steel are presented.

166. A New CR-Bearing Alloy for High Performance Applications Ancorsteel 4300 was recently introduced to the marketplace and is the first in a series that will simulate wrought steel compositions. This new alloy represents a technological breakthrough with low sintered oxygen contents in a system that employs both chromium and silicon. Its main advantages include the ability to be effectively sintered at 1120 °C (2050 °F), good compressibility, high hardenability, and exceptional dimensional stability across a variety of processing conditions. These characteristics make this material an attractive cost-effective alternative to alloys that require secondary quench hardening treatments and enable the penetration of P/M into higher performance applications. The current work reviews the effects of density, cooling rate, and carbon content on the static and dynamic properties of this new product, along with comparisons to Q&T properties for wrought AISI grades 4340 and 8620.

165. High Density Processing of a New CR-Bearing Steel The application of P/M steels in highly stressed applications requires both high density processing and high performance alloys. Ancorsteel 4300, a new high performance alloy that contains Cr, Si, Mo, and Ni, utilizes the hardenability and mechanical property enhancement of chromium while maintaining low sintered oxygen contents. The elevated mechanical properties compliment the high compressibility of the powder allowing for use in high density applications. When combined with high density processing techniques such as the advanced lubricant/binder system AncorMax D, high densities and excellent properties can be achieved. This paper presents the effects of processing on density and mechanical properties with this new material, with a comparison to FLN2-4405 and FD-0405.

158. Chromium Containing Materials for High Strength-High Fatigue Applications As the use of P/M in advanced applications continues to grow, the industry continues to encounter increasing demands for high strength-high fatigue alloys. Ancorsteel 4300, a developmental alloy, has been engineered for high performance applications and employs the use of silicon, chromium, and molybdenum. This alloy will be the first in a new line of engineered high performance binder-treated products that simulate wrought steel compositions and can be processed at conventional sintering temperatures. Advanced fabrication techniques prevent the alloy from being susceptible to the common oxygen-related problems that are often seen with chromium-containing P/M materials. The presence of chromium and silicon with a low oxygen content serves to increase hardenability, strength, and fatigue life. This manuscript presents the effects of compaction pressure, cooling rate, and sintering temperature on the performance of the developmental alloy.

151. Properties of High Density Diffusion Bonded Alloys For P/M components, overall mechanical properties can be improved by increasing the density coupled with alloy additions. This can be seen by the excellent properties achieved for high performance applications with material compositions based on 1.75% Ni and 4% Ni diffusion bonded steel powders processed to high densities. Through the use of an advanced binder system, higher densities with subsequent increases in mechanical properties can be achieved in a single compaction step. Further densification can be achieved through the use of the double press, double sinter process coupled with the warm compaction process. The static and dynamic mechanical properties of warm compacted and double pressed, double sintered FD-0205 and FD-0405 with densities up to 7.5 g/cm³are presented.

103. The Development of Engineered Binder-Treated Alternatives to Duffusion-Alloyed Powders Engineered binder-treated premixes have been developed as alternatives to diffusion alloyed powders. The binder-treated materials meet the chemical composition limits for the diffusion alloyed materials listed in MPIF Standard 35, Materials Standard for P/M Structural Parts.

At an equivalent combined carbon content the binder-treated materials exhibit higher strength than the diffusion alloyed materials. When the combined carbon content of the binder-treated materials is reduced, to provide an equivalent strength level, the binder-treated materials match the tensile ductility and impact energy of the diffusion alloyed products.

The as-sintered and the quench-hardened and tempered performance of the new materials is reviewed and compared with diffusion alloyed materials of similar chemistry. These recently developed materials represent the first in a new family of high performance ferrous P/M materials.

88. Advances in High Performance PM Alloys For Automotive Applications The as-sintered and the sintered and tempered transverse rupture and tensile properties of seven recently developed high performance PM compositions are reviewed. Two are improved versions of the well known diffusion alloyed grades according to MPIF Standard 35. Two others are likewise improved versions of more highly alloyed analogs of the latter that have only recently been introduced. The remaining three are all new compositions that take advantage of the powerful alloying effects of silicon. The silicon is added by a proprietary method that greatly reduces its susceptibility to oxidation during sintering, an effect that has heretofore limited its use.

86. The Development of Binder-Treated Alternatives to Diffusion Alloyed Powders Engineered binder-treated premixes have been developed as alternatives to diffusion-alloyed powders. One family of binder-treated materials meets the chemical composition limits for diffusion-alloyed materials listed in MPIF Standard 35, Materials Standards for P/M Structural Parts. A second family of engineered binder-treated premixes has been developed as an alternative to high performance diffusion-alloyed materials that are based on prealloyed low-alloy steels containing 1.5 weight percent molybdenum. The as-sintered and the quench-hardened and tempered performance of the new materials will be reviewed and compared with diffusion-alloyed materials of similar chemistry.

83. New High Performance Ferrous P/M Materials for Demanding Automotive Applications Diffusion-alloyed powders have been used for many years in automotive applications such as synchronizer hubs where there is a need for a combination of tensile strength, ductility, and impact energy. Recently, engineered binder-treated premixes have been developed as alternatives to diffusion-alloyed powders including those based on a prealloyed powder (1.5 w/o molybdenum). The engineered binder-treated materials will be compared with their diffusion-alloyed counterparts.

78. Binder-treated Analogs of Diffusion Alloyed Compositions Based On Ancorsteel 150 HP The powder, green and sintered properties of binder-treated analogs of two diffusion alloyed steels based on Ancorsteel 150 HP are presented. These new additions to the binder-treated family of compositions are made according to a proprietary practice that does not include diffusion alloying. It is shown by direct comparison that these new premixes offer significantly improved compressibility and otherwise generally similar powder, green and sintered properties to compositionally similar premixes of the diffusion alloyed steels. The sintered property comparisons presented include the TRS, tensile, and impact properties of the subject compositions in the as-sintered and sintered and tempered conditions.

65. Ancorloy Premixes: Binder Treated Analogs of the Diffusion Alloyed Steels The properties at two carbon levels of binder treated analogs of the diffusion alloyed steels are presented. These Ancorloy premixes are made according to a proprietary practice that does not include diffusion alloying. It is shown by direct comparison with compositionally similar premixes of the diffusion alloyed steels that the Ancorloys generally exhibit similar powder, green and dimensional change properties and significantly enhanced mechanical properties. Tensile, impact and fatigue property data in the sintered, sintered and tempered and quenched and tempered conditions are presented.

53. The Application of Warm Compaction to High Density Powder Metallurgy Parts The warm compaction process (ANCORDENSE^®) has been shown to provide increased density in ferrous powder metallurgy parts. This improvement in density contributes significantly to mechanical properties and thus the overall performance of the part. The combination of increased density with high performance material selections, provides parts that can exceed the performance of forged or cast material counterparts while taking advantage of powder metallurgy's net shape forming capabilities.

Turbine hubs for automatic transmission torque converters have proven to be ideal candidates for the powder metallurgy (P/M) process. The complex shape of turbine hubs is costly to produce via conventional forging and machining operations. However, increases in engine size and torque requirements in several automotive designs have required that turbine hubs possess higher levels of mechanical properties. High density P/M manufacturing techniques, in combination with high performance ferrous materials produces components capable of replacing a forged and machined turbine hub.

This paper will review the conversion of a conventionally forged and machined turbine hub used in a high torque automatic transmission to a single pressed and single sintered P/M turbine hub. The material used for the P/M hub was an FD-0405. This diffusion alloyed material was evaluated in the laboratory and mechanical properties are reported at several density levels. Warm compaction processing achieved high overall sintered densities in the highly stressed internal spline region. Extensive mechanical and part specific testing was conducted to verify the suitability of the P/M part.

42. The Effect of Microstructure on Fatigue Properties of High Density Ferrous Materials Fatigue testing (rotating bending fatigue) has been performed on several high performance ferrous P/M material systems. Detailed metallographic analysis was performed to determine differences in the failure mechanisms for various material and process combinations. A variety of material compositions were single compacted to high density via the ANCORDENSE™ compaction system. This was followed by conventional and high temperature sintering and testing in the as-sintered and heat treated conditions. The analysis provides information as to the relationships between density, structure and composition with fatigue life.

41. Properties of Several ANCORDENSE Processed High Performance Materials The effect of powder and compaction temperature on the ANCORDENSE™ warm compaction system is evaluated. Detailed property analysis is presented on several warm compacted high performance materials systems. Properties evaluated include density, tensile, and impact performance. A detailed assessment of the microstructure resulting from various alloy compositions and processing techniques is performed. The materials involved in the tests were conventional and high temperature sintered and tested in the as sintered and heat treated condition.

38. Powder Metallurgy Gears - Expanding Opportunities Powder metallurgy (P/M) is a precision metal forming technology for the manufacturing of parts to net, or near net shape. The powder metallurgy process is illustrated schematically in Figure 11. There are three basic steps to producing parts; mixing, compacting, and sintering. Variations to these basic steps such as infiltration, double pressing/double sintering, and powder forging may be used to achieve higher density parts. A sizing operation may be used to qualify critical part dimensions. Alternatively, a machining step may be added for the same purpose or to achieve a geometric feature not possible during rigid die compaction. P/M parts may be through hardened or surface hardened as required by the intended application.

33. An Investigation Into the Effects of Processing Methods on the Mechanical Characteristics of High Performance Ferrous P/M Materials The mechanical properties of high performance ferrous P/M materials are influenced by the material composition and processing method. This paper investigates the effects of the ANCORDENSE™ process, a new, high density, single compaction method, on the mechanical properties of Distaloy® 4800A based materials. The results of this study are discussed with a comparison to the mechanical properties for the same materials developed through single-pressed and double-pressed, doublesintered processing methods. In addition, a case study is performed on a component produced via the ANCORDENSE method.

32. Properties of Diffusion Bonded Alloys Processed to High Densities Diffusion bonded alloys have been shown to exhibit excellent properties. Recent advancements in compaction technology have allowed these materials to reach green density levels of over 7.3 g/cm³ in a single compaction process. Various capabilities of this new compaction system will be demonstrated utilizing diffusion bonded alloys. Properties of several diffusion bonded materials will be investigated at these high density levels. A variety of processing techniques will be utilized including high temperature sintering and heat treatment to demonstrate the flexibility of these materials.

26. High Performance Ferrous P/M 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 P/M 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 P/M 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).

24. Properties of High Density Ferrous P/M Materials, A Study of Various Processes Several methods of achieving higher density in ferrous P/M parts are possible. Double press/double sinter allows densities in excess of 7.3 g/cm3 but is limited by cost and geometry considerations. A new method of single processing high performance materials is evaluated and compared to other methods of processing. The comparison is performed utilizing Ancorsteel 85HP and Distaloy 4800A base materials. Various green and sintered properties are evaluated including; green strength, transverse rupture strength, tensile properties and impact values.

The data clearly demonstrates that the patented (1) ANCORDENSE™* process offers performance comparable to double press/double sinter processing. Green density values of approximately 98.5% of the pore free density limit are achieved with a single compaction step.

23. High Density Processing of High Performance Ferrous Materials Density is an predominant factor in the performance of powder metallurgy components. Methods such as double press/double sinter, copper infiltration and powder forging have been employed to provide higher densities than traditional single press and sinter operations; however, their widespread use is constrained by cost and geometry considerations.

A commercially proven method for obtaining single compaction/single sinter densities in the 7.25 to 7.55 g/cm³ range by means of the patented ANCORDENSE™ technology is introduced. Conventional compaction pressures and sintering temperatures, typically not exceeding 50 tsi or 2300°F, respectively, are utilized. Resulting properties for several high performance materials are presented.

Test results indicate that the ANCORDENSE process is a cost effective method of providing high density parts with outstanding physical properties. The process is shown to be applicable to a wide variety of high performance materials. Additionally, significant improvements in green strength and ejection forces are realized.

12. Improved Dimensional Control and Elimination of Heat Treatment for Automotive Parts The automotive industry has expressed concern about the general quality of heat treatment (austenization and quenching) and the desire to reduce or eliminate dependence upon this process whenever possible. Therefore, in a continuing effort for improvement during the past year, a process has been developed that eliminates the conventional heat treating operation for some applications. Some of these finished parts require both a high impact strength and a hardened wear resistant surface. The Charpy impact, tensile and TRS properties of a binder treated premix based on a partially alloyed powder have been evaluated utilizing a variety of processing conditions. These include various carbon contents, sintering temperatures and sintering times. Quantitative metallography was used to evaluate the pore size, pore shape and microstructural constituents present as a result of the various materials and processes. These factors were then correlated with the measured properties.

10. Steering Column Tilit Lever - P/M Material Development Automotive steering columns use a variety of levers to lock the flit mechanism in position. A new P/M material has been developed to withstand the impact and hardness performance requirements of this application. The new material is currently subjected to a brief surface carburizing and tempering treatment to impart wear resistance. The P/M part only requires honing of the pivot hole to meet the specified tolerance.

Long term plans are to achieve the desired performance requirements using a modified version of the new P/M material, with a higher graphite addition, which can be used after tempering the" as-sintered" product. The Charpy impact properties of three P/M materials, each based on a partially alloyed powder (Distaloy 4800A) but with different percentages of added graphite, have been tested for a variety of processing conditions. Neutral hardening, carburizing, and sinter-hardening treatments have been compared. The influence of tempering temperature and the incorporation of a cryogenic treatment in the process cycle have been reviewed. Quantitative metallography has been used to compare the pore size, pore shape, and percentage of microstructural constituents present in the different P/M materials. The measured impact properties are discussed in relation to these factors.

4. Ferrous Powders - How Alloying Method Influences Sintering The mechanical properties of P/M 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).

3. Fatigue Properties of P/M Materials The tensile properties and fatigue endurance limits of several widely used P/M steels have been tested. Statistical estimates of the 99.9% survival stress have shown that fatigue endurance ratios can vary from 0.16 to 0.47. Thus the use of 0.38 as a rule of thumb for estimating the fatigue endurance limit from static tensile property data can result in large errors. The single most effective method of improving fatigue properties is to increase the part density. Fractographic observations were made on some of the fatigue failures, including stable and unstable crack growth.

1. Impact and Fatigue Characterization of Selected Ferrous P/M Materials Dynamic property data on pressed and sintered ferrous powder metallurgy materials have come under increasing demand as the P/M industry has grown into areas of application involving more highly stressed components. Data collected from relatively simple dynamic property tests will provide new avenues for P/M alloy development. Un-notched Gharpy impact energy and rotating bending fatigue tests have been used to characterize commonly used P/M steels. The endurance ratios of porous steels have been found to be relatively insensitive to processing, with higher strength materials giving proportionally higher endurance limits. Since impact energy was not strongly affected by varying the carbon content up to the eutectoid composition, increasing the carbon content of low alloy steels is a viable way of increasing endurance limit. Impact energy transition temperature has been found to be a factor in carbon-free phosphorus steels, but not in conventional low alloy steels. As has been indicated in the literature, sintered density is crucial to both impact energy and fatigue endurance limit. Metallographic examination of the fatigue cracks has provided some insight into the nature of the R.B.F. test.

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