High Pressure Sintering

High Temperature Sintering 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.

193. Chromium Steels for High Performance PM Applications Chromium steels have long dominated the landscape of the wrought industry because of their high performance capabilities at modest cost levels. Historically, chromium steels have had difficulty penetrating the powder metallurgy market because of oxidation issues. Recent powder manufacturing advances, however, have resulted in low-oxygen chromium steels such as Ancorsteel 4300, which enables the production of high performance parts with conventional processing techniques. The current work reviews the capabilities of this Cr-Si-Ni-Mo alloy and its derivatives. Static properties, dynamic properties, and dimensional stability data are reviewed with an emphasis on a sintering temperature of 1120 ºC (2050 ºF). Comparisons are made to traditional powder metallurgy materials in both the as-sintered and heat-treated conditions as well as to heat-treated wrought alloys.

183. Performance Capabilities of High Strength Powder Metallurgy Chromium Steels with Two Different Molybdenum Contents The desire for advanced ferrous powder metallurgy materials has led to the development of alloys that simulate wrought steel compositions. A recently commercialized Cr-Si-Ni-Mo steel can be effectively sintered at conventional temperatures and provides good compressibility, high hardenability, and excellent dimensional stability while maintaining oxygen contents below 500 ppm. This alloy has demonstrated 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 to offer complimentary performance levels at a lower Mo content, while still providing excellent sinter-hardenability. The current work reviews static and dynamic properties of the two Cr steels with an emphasis on accelerated cooling rates after sintering at 1120 ºC (2050 ºF). Comparisons are made to traditional powder metallurgy materials processed in both the sinter-hardened and heat-treated conditions as well as to heat-treated wrought alloys.

162. Effect of Case Carburizing on Mechanical Properties And Fatigue Endurance Limits of P/M Steel Case carburizing has long been a basic technique for the improvement of the wear and fatigue resistance and of PM steel components. The key to the successful improvement in carburizing, however, is understanding, and interpreting the microstructure of the carburized case. The main area for growth in the PM industry is in the high performance gearing applications. The success of penetrating this area depends upon the ability to understand the key components that effect the fatigue endurance limits of PM materials. This paper will examine and illustrate how tensile properties and the fatigue endurance limits of a P/M hybrid alloy are affected by alloying additions and carburizing.

160. Surface Densification Approach to High Density Gears High performance components for automotive gearing applications have requirements incorporating high static strength, high bending fatigue, and lastly rolling contact fatigue durability. Advances in P/M alloys and processing can produce as-sintered densities approaching 7.4 g/cm³ in complex helical gearing geometries. This high sintered density results in high static and fatigue resistance. However, to achieve the rolling contact fatigue properties required in high performance gears, fully dense surface and sub-surface conditions are necessary. This paper will investigate the effects of part processing and surface densification on the rolling contact fatigue properties of a high density FLN2-4405 material. Variable studied include depth of densification, sintering conditions, surface microstructure, and post densification heat treatment practices. The results will demonstrate the effects of residual porosity, carburizing practice, and the effects of soft-nickel rich regions (as influenced by the sintering practice) on the rolling contact fatigue properties. Metallographic analysis will examine the cause of the failures leading to future improvements.

156. Development of a High Performance Nickel-Free PM Steel A developmental nickel-free P/M steel containing Cr, Mn, Si and Mo is being evaluated as a new high performance material. Bonded premixes with varying carbon contents were made with the AncorMax^®D system and pressed to densities of 7.2 g/cm³. Sintering studies were performed at 1177°C and 1260°C. Higher strengths were achieved in the CrMnSiMo steel as compared to a Ni containing steel with a higher total alloy content. Ultimate tensile strengths over 1200 MPa and hardnesses of 70 HRA can be achieved in the sinter + temper condition. The effect of sintering temperature, cooling profile and carbon content on mechanical properties and microstructure will be discussed.

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.

146. Sintering of Water Atomized PIM Fe-2Ni-0.8C The use of water atomized powders in powder injection molding processes has long been an area of interest because of the cost savings afforded by the water atomization process over gas atomization and chemical methods. In this study, water atomized Fe-2Ni powder is investigated for sintering response in the milled and as-received conditions. Variations in particle size, carbon content, heating rate, sintering temperature, and atmosphere were studied. The findings indicate that, aside from sintering temperature, the most important factors influencing the sintered density are the particle size, heating rate, and surface chemistry. Milling alters the surface chemistry and decreases the particles size, both of which serve to increase sintered density.

144. Unique Stainless Steel Materials and Processing for High Strength with Reduced Magnetic Performance A new automotive part was designed having property requirements incorporating high yield and tensile strengths with good ductility, while at the same time requiring reduced magnetic performance. This combination of properties precludes the use of iron and low alloy materials because of their intrinsic magnetic response. In an effort to satisfy both requirements, type 200 stainless steel powders were prepared and processed into both mechanical property test specimens and magnetic toroids. Processing of the compacted samples was optimized to give the required strength characteristics with required minimal magnetic response. This paper will detail the types of stainless materials utilized and unique processing developed to accomplish these conflicting requirements. The mechanical and magnetic properties will be presented.

143. Development of a High Performance Nickel-Free P/M Steel Chromium and manganese are used frequently in the wrought steel industry to improve mechanical properties and hardenability. However, these elements have been difficult to incorporate into P/M steels due to their high affinity for oxygen. A new nickel-free P/M steel containing Cr, Mn, Si and Mo is being developed for high performance applications. Sintering studies performed over a range of temperatures have shown that reasonable oxygen contents along with superior mechanical properties can be achieved with this new steel. The effect of sintering temperature and density on mechanical properties will be discussed.

142. Chromium Containing Materials for High Performance Components Recently developed silicon-bearing alloys were engineered to replace malleable and ductile cast irons, and have shown excellent property combinations at high sintering temperatures. A modification to these alloys merges the power of silicon and chromium in one system, and allows for extraordinary performance. The presence of chromium improves both static and dynamic properties with the added benefit of being close to die-size after sintering. The current work details extensive laboratory data that show the effects of compaction pressure on this modified alloy processed at high sintering temperatures. Also presented is a field experience on a heat-treated production component that combined the high performance alloy system with warm compaction technology. Static and dynamic properties are presented for samples sintered in both laboratory and production scale furnaces.

141. Effects of Cooling Rate on the Hardenability of Chromium Containing P/M Steels Two chromium containing grades, Cr-modified Ancorloy^®MDC and a developmental CrMnSiMo steel, have been investigated to develop an understanding of the phase transformation behavior of these steels during cooling. The cooling rates studied are in the range typically found in sintering furnaces. A quantitative study to assess the hardenability of these materials has been undertaken and the results of dilatometric, metallographic and hardness evaluations to determine the effects of cooling rate on the various Cr containing steels are presented.

137. Rollong Contact Fatigue of Surface Densified Material: Microstructural Aspects (Surface Densification Approach to High Density Gears) Automotive gearing applications have material requirements combining static strength, bending fatigue, and rolling contact fatigue durability. Advances in P/M alloys and processing can produce as-sintered densities greater than 7.4 g/cm³ in complex gearing geometries. This high sintered density results in high static and fatigue resistance. However, at less than full density rolling contact fatigue performance is compromised. For high duty cycle gearing, pore free density is needed in the tooth contact region and in the area where the tooth flank intersects with the gear tooth root radius. This paper will investigate the effects of part processing and surface densification on the rolling contact fatigue properties of a high density FLN2-4405 material. Variables studied include: depth of densification, sintering conditions, surface microstructure, and post densification heat treatment practices. The results will demonstrate effects of residual porosity, case microstructure, and soft-nickel rich regions on rolling contact fatigue. Metallographic analysis will illustrated the cause of the failures associated with these variables.

134. Ancorloy Hardenability The Continuous Sinter Cooling Transformation diagrams of five proprietary admix compositions including Ancorloy^® 2 and Ancorloy^® 4 at sintered carbon contents of 0.50 w/o and Ancorloy^®MDB, Ancorloy^® MDC and Ancorloy^® MDCL at sintered carbon contents of 0.60 w/o are presented for sintered densities in the neighborhood of 7.10 g/cm³.

133. Advanced Performance Alloys Processed by High Temperature Sintering Technique As the demand for improved performance of P/M components increases, requirements for selection of proper alloy composition as well as its processing routine continue to climb. Major areas of process improvement include utilization of high performance alloy systems, high temperature sintering to create more homogeneous diffusion throughout the alloy matrix, and higher final densities of the processed components. This paper demonstrates the benefits gained by combining all of these factors. Specifically, the properties of recently developed MD compositions compacted to high initial green densities by using an advanced binder system and subsequently subjected to high temperature sintering in a pusher furnace at full-scale production conditions are investigated.

132. High Density Processing of Ancorloy MDC Materials Previous experimental work has shown that silicon containing steels exhibit high tensile properties and impact strength at relatively low densities ranging from 7.0 to 7.1 g/cm3. Higher densities via AncorMax D^® processing has shown that sintered densities in excess of 7.3 g/cm3 are possible at compaction pressures ranging from 550 to 760 MPa. (40 to 55 tsi) This paper will examine the metallurgical and mechanical enhancements achieved through the AncorMax D process and high temperature sintering of the Ancorloy^® MDC and Ancorloy^® MDCL materials at densities ranging from 7.0 to in excess of 7.3 g/cm³.

131. Methods to Improve the Fatigue Life of Sinter-Hardened Components Previous experimental work showed that fatigue performance is affected by the alloy system, heat treatment method, and microstructural features of test specimens. The present study will present information concerning the effects of varying the sinter-hardening cooling rate (and subsequent microstructure features) on the mechanical properties sinter-harden steels and the Ancorloy MDCL™ material system. Emphasis will be given to the rotating bending fatigue performance of these systems and how this experimental data correlates with the fatigue performance of the actual component in accelerated life testing.

128. Chromium Additions to the Ancorloy MD Series Ancorsteel 41AB, introduced several years back, demonstrated the benefits of chromium and manganese additions to molybdenum steels. The more recently developed Ancorloy MD series provides enhanced ductility and strengths in P/M steels. This paper examines the mechanical properties achieved through the combination of high performance materials with chromium additions and high temperature sintering. Two chromium-modified materials were developed by replacing a portion of admixed nickel with a high carbon ferroalloy to improve dimensional properties and hardenability. Reviews of properties such as tensile, impact, transverse rupture, rotating bending fatigue, hardenability, and compressibility are presented.

127. Powder Metallurgy of High Density Helical Gears Powder Metallurgy is a proven technology to produce high strength gears for the automotive industry. Advances in powder production, compaction, and sintering combined with double pressing have enabled overall part densities up to 7.5 g/cm³ in spur gears. However, helical gears are more difficult to produce to these same densities because the geometry does not lend itself to the DP/DS process. Described in this paper is a P/M parts making technology capable of producing single pressed and sintered helical gears with core densities approaching 7.4 g/cm³. Description of a prototype run will be presented with the resulting sintered part densities and part-to-part variability. To further enhance the performance and geometry of these helical gears, they were subsequently surface densified via rolling. Improvements in the surface density and gear quality will be described.

124. Properties and Applications of High Density Sinter-Hardening Materials Sinter-hardening materials are characterized by their high hardenability which enables the formation of >80% martensite during accelerated cooling. However, these moderately alloyed materials often exhibit lower compressibility and the resulting lower density limits their use in potential high strength applications.

What is needed is a method to improve the green and sintered density of current sinter-hardening materials that will enable these materials to be utilized in new high strength applications. This paper describes how the green and sintered density of standard sinter-hardening alloys can be improved using new alloy systems coupled with advanced binder technology. The resulting improvements in mechanical properties will be presented as well as the potential use of high density

116. Advanced Sinter-Hardening Materials and Practices Sinter hardening is a well-established production technique utilized in the manufacture of P/M components with hardness and tensile strengths that approach the values of quench and tempered materials. The potential drawback of the sinter hardening process is the uniform carbon content of the case and core. This uniformity of carbon content does not promote a desirable compressive stress condition on the surface of the component leading to less than optimum fatigue strength. Experimental work was performed in which several sinter-hardening materials were produced with lower core carbons and subsequently carburized after the sintering process to produce a carburized case. Mechanical properties including tensile and fatigue of the non-carburized and carburized material will be presented plus the effect of the carburizing cycle on the carbon gradient of the new sinter hardening materials.

113. Effect of Small Additions of Boron on Mechanical Properties & Hardenability of Sintered P/M Steels Low levels of boron (0.01-0.15w/o) may induce sufficient hardenability and strength in powder metallurgy steels to permit a decrease in the level of the alloying elements, increase powder compressibility and reduce the as-sintered hardness. These lean alloys may be sufficiently ductile to coin and be hardened by subsequent heat treatment. The goal of this study was to identify the boron level in FLN2-4400 (Fe + 0.85w/oMo, 2.0w/oNi, 0.3w/oC) which yields the optimal combination of strength, ductility, and hardenability. Tensile, transverse rupture, hardness, and Jominy end quench tests were performed on this alloy with six different levels of boron added Sintered strength and ductility increase up to 0.05w/oB, but decrease beyond this level, even though sintered density increases significantly. Jominy hardness traces show that the hardenability is not increased substantially until the concentration of boron reaches 0.05w/o. The microstructures of the Jominy bars show that with an increase in boron level, the depth to which martensite is retained increases, but that grain boundary segregation occurs. A level of boron ~ 0.05w/o gives the optimum combination of strength, ductility, and hardenability in FLN2-4400.

112. Processing of Hybrid Alloys to High Densities Premixes containing prealloy molybdenum, such as Ancorsteel 85HP, nickel and graphite have exceptional mechanical properties. This presentation will highlight the properties of these materials processed to densities of 7.25 to 7.45 g/cm³ by single press, single sinter techniques. The exceptional green strength of these materials in combination with density provides a unique opportunity to convert more automotive components to P/M.

111. Economics and Benefits of High Temperature Sintering of High Performance Alloys Today’s global economy has produced an extremely competitive marketplace. Design engineers constantly compare the economics and benefits of powder metallurgy (P/M) with those of stamping, casting and wrought machining. While parts manufacturers have traditionally exploited the near net shape cost savings of conventional P/M compositions, many have turned to higher performance alloys and elevated temperature sintering in an effort to optimize the metallurgical and mechanical properties of their products. Powder producers and furnace manufacturers have continued to support these endeavors through new product and process development.

This study will examine the metallurgical and mechanical enhancements achieved through the combination of high performance alloy systems and high temperature sintering. In addition, it will show how these benefits can be exploited to produce superior parts economically. High performance silicon-containing P/M steels sintered at 1150 to 1343 °C (2100 to 2450 °F) will be used to explore these property enhancements. These silicon-containing P/M steels yield excellent properties when sintered above 1260 °C (2300 °F) and are capable of attaining high apparent hardnesses .

110. Enhanced Processing of Silicon-Containing High Performance Materials In 2001, an extensive program was initiated to evaluate new silicon-containing materials designed to compete with various grades of ductile and malleable cast irons. These bindertreated, press-ready premixes were compared to a standard FLN4-4405 in a production environment on a complicated, high volume application. This year’s work investigates both double pressed / double sintered and heat-treated performance of the new silicon-containing materials. Mechanical properties and dimensional stability information are presented and compared to several standard material candidates containing no silicon.

108. Effect of Microstructural Inhomogeneties on the Fatigue Properties of a Prealloyed & Two Hybrid P/M Steels In the first phase of this study, the effect of microstructural inhomogeneities on the tensile and impact response of a prealloyed (FL-4405) and two hybrid (FLC2-4405 and FLN2-4405) P/M steels based on prealloyed Ancorsteel 85 HP was evaluated. In phase two we assess crack propagation response. The base powder and additions were mixed with 0.75 w/o Lonza Acrawax in 227 kg (500 lb) batches. A density of 7.4 g/cm³ was obtained by double pressing (550/550 MPa). Sintering temperatures of 2050 °F(1120 °C) and 2300 °F (1260 °C ) were utilized. A group of sintered compacts of each alloy was heat treated by quenching from 1650 °F (900 °C) into warm oil at 160 °F (70 °C) followed by tempering at 375 °F (190 °C) for 1 h. Two groups of sintered compacts of the FLC2-4405 and FLN2-4405 alloys were sinter hardened and tempered at 375 °F (190 °C) for 1 h. Experimental data showed that the P/M steels exhibit comparable fatigue crack growth rates (1.1207E-4 to 3.0185E-4 mm/cycle) at a stress intensity range of 1000 MPa (mm)^1/2. Quenched and tempered microstructures resulted in the highest fatigue crack growth rate. Sinter hardening of FLC2-4405 and FLN2-4405 lowered the fatigue crack growth rate. High temperature sintering reduced the fatigue crack growth rate in FL-4405 but increased it in FLC2-4405 and FLN2-4405.

106. Materials Solutions for Converting Cast Iron Applications to Powder Metal In the last several years, powder metallurgy (P/M) materials have been developed to rival the properties of cast iron and screw machined grades utilized in both automotive and non-automotive applications. These materials offer the P/M industry a momentous opportunity to dramatically increase its market by replacing some of the cast iron volume utilized today. While the inherent net shape capabilities of P/M and the potential cost savings of conversion to P/M offer customers distinct advantages, previous materials have not offered property combinations comparable to many cast iron grades. This work will explore the common grades of cast iron and propose P/M materials as possible replacements for each.

105. Advances in P/M Gear Materials Powder Metallurgy is an efficient manufacturing process for the production of gearing and similar net shape components. Because of limitations arising from the inherent porosity and limited alloy systems available, the traditional uses for P/M gearing was in relatively low stress applications. The recent introduction of new compaction techniques and new alloy materials has produced P/M components with significantly higher yield and tensile strengths approaching the strength levels of wrought gearing materials. This paper will review the new P/M processes and materials and their suitability for gear type applications. Mechanical property comparisons will be made to the common automotive gearing materials including ductile and malleable cast irons and wrought low alloy steels.

104. Application of Sinter-Hardenable Materials for Advanced Automotive Applications Such as Gears, Cams, and Sprockets Recent demands within the automotive industry have been for applications requiring high apparent hardness, high hardenability, and increased mechanical performance. These often-conflicting requirements necessitated the development of new materials that offer high as-sintered apparent hardness and good static/dynamic mechanical properties without the added expense of a secondary heat treatment. Traditionally, sinter-hardening materials have offered acceptable apparent hardness but at the expense of mechanical properties and sintered density. This paper will document the mechanical properties of a series of sinter hardening materials that offer good compressibility, high apparent hardness and enhanced mechanical properties. The discussion will focus on utilization of these materials in automotive applications (within both the engine and transmission) such as gears, cams and sprockets that are currently produced by either the press, sinter, and heat treat process or by conventional machining of a casting or wrought material. Enhanced processing through high temperature sintering also will be discussed.

99. Effect of Microstructural InHomogeneities on The Mechanical Properties of Hybrid P/M Steels The effect of microstructural inhomogeneities on the tensile and impact response of a prealloyed (FL-4405) and two hybrid (FLC2-4405 and FLN2-4405) P/M steels was investigated. Tensile and impact response, microstructures, pore characteristics and fracture modes were determined in the sintered, quenched + tempered and sinterhardened conditions. Sintering temperatures of 1120°C (2050°F) and at 1260°C (2300°F) were utilized anddensities in the range 7.0 - 7.4 g/cm3 were achieved by single and double pressing and sintering. Over this sintered density range, tensile strength increases by >30%. In the quenched + tempered condition tensile strength exceeds 1000 MPa. Tensile properties are rationalized in terms of the attendant microstructures and modes of fracture.

96. P/M High Strength Magnetic Alloys Sintered P/M magnetic materials are characterized by good DC magnetic performance with relatively low yield and tensile strengths, typically the tensile strengths are less than 50,000 psi. This inherently low strength of the common magnetic alloys results from the use of pure iron or iron phosphorus alloys. This low strength often limits the potential applications for sintered P/M magnetic materials. Described in this paper are P/M alloys that have tensile strengths approaching 70,000 psi (480 MPa) in the as sintered condition with tensile ductility approaching 10% and having magnetic properties equal to the pure iron and / or iron phosphorus alloys. These alloys are intended for higher strength, magnetic applications. A comparison to the standard P/M magnetic alloys will be made.

93. High Performance Materials - Ancorloy MD Series New silicon-containing materials were recently introduced to compete with various grades of ductile and malleable cast irons. These binder-treated, press-ready premixes offer extremely good physical and mechanical property combinations. This work focuses on the evaluation of these materials in a production environment. Properties such as impact energy, tensile strength, elongation, dimensional change and apparent hardness are presented.

90. Advanced Processing of Sinter-Hardening Materials The sinter-hardening process has been shown to provide excellent mechanical properties and part-to-part size control. Previous work has indicated that exceptional mechanical properties and high apparent hardness values can be achieved by sinter hardening in a high temperature furnace with standard cooling. This work focuses on combinations of advanced techniques intended to optimize mechanical properties for stringent applications. While warm compaction is utilized to increase density, various material alloy combinations are blended together in an effort to study green density variables. Where applicable, specific market opportunities are identified.

89. Newly Developed P/M Materials to Replace Malleable and Ductile Cast Irons Malleable and ductile cast irons are used extensively in automotive applications such as clutches, gears, carriers, shafts, bearings, cam, racers, hubs, etc. Recently developed P/M materials can be processed cost efficiently to replace malleable and ductile iron castings. An UTS in excess of 1240 MPa and a YS in excess of 825 MPa can be achieved with one of these new materials. These tensile properties can be coupled with elongations over 2% and impact energies over 25 Joules. This presentation will cover processing routes for these new materials and will identify parts that may benefit from this new technological advancement.

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.

85. New High Performance P/M Alloy Substitutes for Malleable and Ductile Cast Irons Ferrous P/M alloys generally do not exhibit a good combination of strength, ductility, and impact toughness. A series of new P/M alloy systems has been developed to match the performance characteristics of malleable and ductile cast irons. The new materials maintain excellent tensile ductility at high strength levels while possessing good impact resistance. The performance characteristics and benefits of the new P/M materials will be presented.

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.

82. New Higher Performance Materials Through the use of enhanced atomization, annealing, and binder treatment technologies, several new silicon-containing alloy grades have been introduced for high performance automotive applications. This presentation will include data on compacts produced from these new grades using conventional compaction, warm compaction, and double press / double sinter processing. With these new material systems, single compaction can achieve ultimate and yield strengths in excess of 1200 MPa and 800 MPa with elongation over 2%. Such tensile properties can be developed in conjunction with apparent hardness values over 65 HRA and impact energies exceeding 25 Joules.

81. Opportunities for Conversion of Powertrain Components from Malleable/Ductile Cast Irons to Powder Metallurgy Malleable and ductile cast irons are used extensively in gearing and high strength applications within automotive power train applications. Advantages of malleable and ductile cast irons are low material cost with mechanical properties that meet or exceed the requirements of the intended application(s). One disadvantage of the malleable cast iron is the extensive heat treating required to obtain the proper microstructure and mechanical properties. Both malleable and ductile iron components require extensive machining to produce the finished component. The combination of heat treating and extensive machining often results in a component that is costly to manufacture. Recent advances in the Powder Metallurgy (P/M) process including high strength material systems and high density processing have achieved mechanical properties that meet or exceed the level achieved with the current malleable and ductile cast iron materials. This paper will present an evaluation and comparison of the mechanical properties of malleable cast iron with selected P/M material systems and processing parameters. This property discussion will demonstrate the suitability of the P/M process in replacing these cast and machined components. Examples of specific parts will be cited and discussed.

79. New High Performance P/M Alloy Substitutes for Malleable and Ductile Cast Irons To advance applications of powder metallurgy (P/M) into areas where current products do not have the desired performance characteristics, a series of new alloys has been developed. These new materials exhibit mechanical properties comparable to those of malleable and ductile cast irons. Some possible applications include ring gears, pinion gears, and carriers. The tensile and impact properties of the new materials are presented for compaction pressures of 415, 550, and 690 MPa and comparisons are made with current high performance P/M materials as well as with various cast irons.

77. Field Experience on a New Sinter-Hardening Material Traditionally, the processing of sinter-hardening materials has been limited to conventional sintering temperatures. Hence, very little sinter-hardening research has been conducted at higher sintering temperatures. However, the superior hardenability of Ancorsteel^® 737 SH allows for sinter-hardening at temperatures in excess of 1180 ºC (2150 ºF) without the need for accelerated cooling.

This paper will both present field experience on conventional sinter-hardening processes and investigate the effect of copper, nickel, and graphite additions on the properties of Ancorsteel 737 SH sintered at 1260 ºC (2300 ºF) utilizing conventional cooling. Particular attention will be paid to dimensional change characteristics, mechanical properties, apparent hardness values, and martensite content in sintered parts.

76. New High Performance P/M Alloys for Replacing Ductile Cast Irons Improvements in atomizing technology and binder treatment technology have allowed Hoeganaes to develop unique alloy systems with high strength, ductility, and impact energy. These systems, material MDD (currently experimental) and AncorloyÒ MDA (commercial product), have been shown to be extremely competitive with numerous ductile cast iron grades. This paper presents the powder, green, and sintered properties of the new materials and compares their performance with existing material systems.

68. Performance Characteristics of a New Water-Atomized Prealloyed Powder (0.5 weight % Molybdenum A new prealloy material containing 0.50 w/o Mo was introduced recently. This medium hardenability material can be admixed with a variety of alloying ingredients to produce superior tensile properties. Results of admixing this prealloyed powder with nickel, copper, manganese, and graphite will be presented. In addition, quench and temper properties will also be discussed.

67. A Comparison of ANCORDENSE Processed Materials with Malleable Cast Iron A study was conducted that compared the mechanical properties of a series of ANCORDENSE prepared materials with malleable cast iron. This paper will present the mechanical properties (TRS, tensile, impact, and fatigue) of various ANCORDENSE prepared premixes in the as sintered condition compared with a malleable cast iron. The objective of this investigation was to demonstrate that an engineered P/M material coupled with ANCORDENSE processing can replace a malleable cast iron component giving equivalent mechanical property performance and potentially equivalent gear performance.

59. The Effect of Microstructure and Pore Morphology on Mechanical and Dynamic Properties of Ferrous P/M Materials Fatigue testing was performed on FN-0205 premixes in order to evaluate the effect of pore structure and processing method on the fatigue properties. The premixes were made with two nickel sources:

· mean particle size of 4 mm

· mean particle size of 50 mm

Metallographic analysis was performed to quantify the pore structure. The following parameters were examined: pore size, pore shape, mean pore spacing and average pore size. Previous work, which examined a variety of materials, indicated that predicting the fatigue strength of a material is a complex relationship between the type and strength of the microstructural constituents, as well as stereological parameters such as mean pore spacing and pore size. This paper attempts to determine to what extent each of the above parameters influences the fatigue strength of P/M materials.

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.

52. The Effect of Microstructure on Fatigue Properties of Ferrous P/M Materials Fatigue testing (rotating bending fatigue) was performed on several materials in order to evaluate the effect of several microstructural elements. Metallographic analysis was performed to characterize the microstructures of the materials and attempt to identify failure mechanisms.

Previous work indicated that predicting the fatigue strength of P/M materials is a complex relationship between the grain size of the material, the type and strength of the microstructural constituents present and, primarily, the mean pore spacing. [1,2] This study examines these relationships in more depth.

49. The Effect of Nickel Content, Sintering Temperature, and Density on the Properties of a 0.85 w/o Molybdenum Prealloy The combination of molybdenum prealloyed steel powders and admixed nickel provides sintered steels that are used in structural parts requiring strength, wear resistance, and impact toughness. The properties of these materials, like all P/M steels, are dependent on density, microstructure and composition. This work discusses the effect of admixed nickel content, sintering temperature, and density on the properties of a 0.85 w/o molybdenum prealloy. Samples were prepared with 0, 2, 4 and 6 w/o nickel additions. The materials were warm compacted at 30, 40, 45, and 50 tsi (415, 550, 620 and 690 MPa) and sintered at 1900°F, 2100°F and 2300°F (1040°C, 1150°C, and 1260°C). Mechanical properties were determined and related to the density, microstructure, and composition.

43. Single Compaction to Achieve High Density in Ferrous P/M Materials in Automotive Applications The continued growth of ferrous powder metallurgy in automotive applications is dependent on the development of higher density and improved dynamic properties. New powder metallurgy applications also must be cost effective through the continued use of the process's, net shape forming capabilities and a reduced number of manufacturing steps. The processes utilized to manufacture some of these new parts also must provide the ability to produce thin walled parts with complex geometries.

The use of the warm compaction process (ANCORDENSE™) will be shown to develop high density levels with a single compaction process. The process also provides increased green strength and reduced ejection forces. The dependence of mechanical properties on density will be demonstrated.

An example of a potential application of the warm compaction technology is an output shaft. The capability of manufacturing this part with the warm compaction process is outlined and compared with the same part made by the double press/double sinter (DPDS) process. Part density and performance from both processes are compared.

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.

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.

31. Advanced Properties of High Density Ferrous Powder Metallurgy Materials The introduction of the ANCORDENSE™ system has provided significantly higher density levels than previously possible in a single press/single sinter operation. This paper will explore the role that higher density has on mechanical properties. Various properties will be evaluated, including transverse rupture strength, tensile strength, and impact. Additionally, the effect of other processes, such as high temperature sintering and heat treatment, will be addressed.

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.

22. High Density Processing of CR-Mn P/M Steels The use of chromium and manganese as alloying elements in P/M steels offers several potential advantages over copper and nickel that are used in conventional P/M alloy steels. The paper will illustrate how the principles used to improve the hardenability and performance of wrought steels can be applied to P/M chromium and manganese alloy steels using a systems approach. The use of chromium-manganese for P/M applications was made possible by binder-treated premix technology of a highly compressible prealloyed low alloy base material. The flexibility of alloy design will be illustrated by examples of through hardening, high strength low alloy steels.

16. High Performance Ferrous P/M Materials Utilizing High Temperature Sintering Several new and more challenging P/M applications require materials that exhibit higher strength along with improved dynamic property characteristics. To meet these requirements, development efforts focused on material grades capable of achieving high performance properties when sintered at elevated temperature. Several elements, specifically nickel and copper, were admixed to the water atomized, prealloyed low-alloy steel powders Ancorsteel® 85 HP and 150 HP using the patented ANCORBOND® process. Tensile and impact performance of the resulting materials have been reviewed along with quantitative metallography of selected as-sintered samples. The results indicate the type and amount of each admixed element plays an important role in achieving specific characteristics. In addition, the overall performance values are greater for the single press and sinter technique used in this investigation than could previously be achieved using a double press - double sinter process.

15. Surface-Hardenable Heat Treated P/M Steels The addition of fine particles (< 20µm) of high-carbon ferroalloys to the high compressible prealloy powders, Ancorsteel® 85 HP and Ancorsteel 150 HP, has been shown to be a practical way of producing ferrous low-alloy steels containing chromium and manganese. Increased sintering temperatures improved the mechanical properties of the materials and the effect was particularly noticeable at 2350°F.

The ferroalloy additions significantly enhanced the hardenability of the base low-alloys. Materials based on the low-alloy powder containing 1.5% molybdenum were more hardenable than those based on the 0.85% molybdenum alloy. These materials are well suited for plasma nitriding and should find use in gears and cams that require a hard wear-resistant surface coupled with a strong, tough core.

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.

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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