Hybrid Materials Technical Publications
200. The Effect of Sintering Conditions and Composition on the Mechanical Property Response of Cr Containing PM Steels: The desire for advanced ferrous PM materials has led to the development of alloys that more closely simulate wrought steel compositions. Traditional wrought steel alloying elements, such as Cr, are used to improve mechanical properties, hardenability and are cost effective. Chromium has historically been avoided in PM due to oxygen related issues, but newer PM alloy systems now contain this element. While providing good mechanical properties and overall product cost, proper sintering of these alloys is the critical challenge. This paper presents the role of sintering and composition on the mechanical properties and microstructure of a chromium containing PM steel.
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.
194. Effect of Post Sintering Thermal Treatments on Dimensional Precision and Mechanical Properties in Sinter-Hardening PM Steels: Dimensional precision is a critical parameter in net shape processing of ferrous PM components. PM parts producers continue to pursue larger parts, but absolute tolerances dictated by the end user generally do not scale with part size. Therefore, in larger parts, the variation in percentage change in size, or dimensional change, must be reduced. Beyond the dimensional changes associated with pressing and sintering of typical low alloy PM steels, sinter-hardenable alloys present some unique challenges and opportunities for PM part manufacturing. The ability to harden a part in the sintering furnace eliminates the need for a secondary quenching operation. The resulting microstructure of untempered martensite is, however, not ideal for dimensional stability and mechanical properties. Tempering hardened steels results in improved mechanical properties and dimensional shrinkage, as the martensite converts to a more stable ferrite and carbide microstructure of higher density. In addition, many sinter-hardening grades contain high Cu and C contents that result in relatively high amounts of retained austenite. Retained austenite can improve impact and ductility properties, but contributes to dimensional instability as it can transform to lower density bainite and/or martensite with thermal fluctuations. Proper thermal treatments of sinter-hardened steels are necessary to obtain the best combination of mechanical properties and dimensional control. This paper reviews the effects of different post-sintering thermal treatments on the dimensional, microstructural and mechanical property changes of sinter-hardened PM steels.
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.
188. Surface Densification Coupled with Higher Density ProcessesTargeting High-Performance Gearing: This paper will describe a powder and processing method that facilitates single press-single sintered densities approaching 7.5 g/cm³. At this sintered density, mechanical properties of the powder metal (PM) component are significantly improved over current PM technologies and begin to approach the performance of wrought steels. High performance gears have the added requirement of rolling contact fatigue durability that is dependent upon localized density and thermal processing. Combining high density processing of engineered PM materials with selective surface densification enables powder metal components to achieve rolling contact fatigue durability and mechanical property performance that satisfy the performance requirements of many high strength automotive transmission gears. Data will be presented that document PM part performance in comparison to conventional wrought steel grades.
187. Enhanced Machinability of Sinter-Hardenable PM Steels: Machining of sinter-hardened PM steels provides a challenge for part makers. The machinability of PM steel already differs from that of wrought steel due to the presence of porosity and the often heterogeneous microstructure. In addition, hardened wrought steels are generally machined prior to hardening, whereas in sinter-hardened PM steels, the only options are green or pre-sintered machining and machining in the hardened condition. To facilitate machining of sinter-hardened materials, a new additive (MA) has been developed to increase tool life during the machining process. Hard turning tests were performed to evaluate the effect of this new additive. Sintered compacts with the MA additive were compared to compacts without a machining aid and to compacts that contained the MnS additive. This paper discusses the improvement in machinability with this new additive in sinter-hardenable PM steels.
186. Dimensional Precision in Sinter-Hardening PM Steels: Dimensional precision is a critical parameter in net shape processing of ferrous PM components. Beyond the dimensional changes associated with pressing and sintering of typical low alloy PM steels, sinter-hardening alloys undergo a transformation from austenite to martensite. The formation of martensite results in a large expansion during cooling, as martensite is the lowest density phase in steels. Tempering hardened steels results in shrinkage, as the martensite converts to a ferrite and carbide microstructure of higher density. Both of these transformations have a large impact on the dimensional change. In addition, martensitic regions with high Cu and C contents may contain large amounts of retained austenite. As austenite is the highest density phase, retained austenite results in less growth of the compact. The presence of martensite and retained austenite, in addition to the tempering step, all play a role in the final dimensions of a component. This paper reviews two sinter-hardening grades and investigates the dimensional and microstructural changes of those grades through different post-sintering thermal treatments.
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.
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.
182. Lower Molybdenum Steels for High Performance Powder Metallurgy Applications: Molybdenum has long been known to be a useful alloying element in powder metallurgy steels because of its enhancement of hardenability at relatively modest alloying levels. Since their introduction to the industry two decades ago, hybrid alloys based on prealloyed Mo steels such as FLN2-4405 have often been used in the heat-treated state to provide high performance properties. However, as raw material prices have become increasingly unstable in the last few years, the economic benefit to such alloys has reduced, forcing parts manufacturers to seek alternative materials systems. The current work provides a comparative analysis of a recently developed 0.3 wt.% Mo steel with more conventional 0.85 wt.% Mo and Mo-free steels. Property data and metallography are presented for crankshaft sprockets processed in the as-sintered, oil quenched & tempered, and induction hardened conditions.
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.
179. The Effect of Post Sintering Cooling Rate on Microstructure and Machinability of a PM Sinter Hardened Steel: The effect of post sintering cooling rate on the microstructure of a PM sintered steel was investigated by assigning three different cooling conditions to the same alloy. The various microstructures produced by these different cooling conditions were evaluated and quantitatively analyzed for volume fraction of bainite, martensite, and retained austenite. Machinability tests were also performed on samples from all three cooling conditions to determine how these microstructures affected tool life. This was done using a turning operation and the tool life machinability criteria. It was found that the volume fraction of martensite was the most important factor in determining machinability. Lower martensite contents produced much higher machinability and vice versa. Lower martensite contents also resulted in decreased hardness. Bainite was found to be a much more favorable phase from a machinability standpoint. It was also observed that the trajectory of the chips during the turning operation was an indicator of the condition of the tool edge.
178. Effects of Residual Surface Stress and Tempering on the Fatigue Behavior of Ancorsteel® 4300: In this study, the microstructure, residual stress and fatigue behavior of Hoeganaes' Ancorsteel 4300 sintered steel were characterized. Samples were tempered at either 205°C or 315°C and then machined by low-stress grinding. The effects of residual surface stress (measured by XRD) on the fatigue behavior were studied by either application of a stress-relieving heat-treatment after machining or by polishing away the machined surface. Based on this study, samples tempered at 315°C had slightly higher fatigue strengths than samples tempered at 205°C. Although significant compressive stresses were induced by machining on the surface of samples, these residual stresses did not affect the fatigue behavior. Rather, the fatigue behavior was controlled by porosity inherent to these sintered 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/cm3 at 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.
175. Surface Densified PM Steel - Comparison With Wrought Steel Grades: The next major opportunity of PM steels is in automotive transmission gears. The stress levels in these types of gears arise from rolling contact of gear teeth with certain amount of sliding. RCF studies have been undertaken to study the fatigue properties of powder metal gears using ZF test rig. AISI 8620 grade steel was also tested. Results of these investigations suggest that P/M gears are competitive with wrought steel grades.
173. Higher Green Strength Materials for Green Handling: Proper handling of green components is of great importance to parts manufacturers. Damage to fragile compacts has the potential of being economically catastrophic in a production setting. To counteract this problem, a newly engineered lubricant system was developed that provides enhanced green strengths compared to traditional lubricants. AncorMix™ HGS, which is applicable to all iron-based compositions, is most effective when tooling temperatures are between 60 and 75 °C (140 and 165 °F) and requires no powder heating or curing. This manuscript reviews the enhancements in green strengths that are obtained using HGS compared to ethylene bisstearamide. Laboratory as well as production data are presented.
170. Processing P/M Components to High Density Using an Advanced Lubricant/Binder System: The recent introduction of a high-density lubricant system enables the processing of ferrous PM components to up to 98% of pore-free density when using a heated compaction tool. This system, AncorMax® D, uses proprietary lubricants that enable the total organic content of a PM premix to be reduced while maintaining comparable ejection characteristics. This results in the ability to compact components to higher green densities (up to 7.40 g/cm3) using higher compaction pressures. This paper outlines production experience using this advanced system.
169. Rolling Contact Fatigue Performance Contrasting Surface Densified, Powder Forged, and Wrought Material: Previous experimental work demonstrated that rolling contact fatigue durability of high-density powder metallurgy samples was influenced by depth of surface densification (achieved via roll densification), sintering temperature, and heat treat practice. One observation of the previous work was reduced rolling contact fatigue life at high Hertz stress levels relative to wrought machined steel samples. There were also some questions regards the influence of nickel rich regions and how they affected rolling contact fatigue performance. In an effort to understand the influence of elemental nickel additions, FLN2-4405 samples were sintered at 2050 °F (1120 °C) and 2300 °F (1260 °C) and subsequently powder forged to full density. This experimental work was designed to clarify the effects of elemental nickel additions on rolling contact fatigue durability. Additionally, wrought AISI 8620 carburizing steel was machined into rolling contact fatigue samples, carburized and tested. Additionally, the AISI 8620 was evaluated for tensile, impact and fatigue characteristics in the quench and tempered condition.
168. Effect of Composition and Cooling Rate on Physical Properties and Microstructure of Prealloyed PM Steel: The composition of PM steels plays an important role on the microstructure and physical properties of sintered parts. The different levels of alloying elements prealloyed into base powders change the hardenability of the material. In addition, copper and graphite additives also play an important role. Further, different cooling rates will have a profound effect on the microstructure. Three base alloys with different levels of copper and graphite were sintered at 1120°C and cooled at either conventional rates or under sinter-hardening conditions. The effect of these variables on microstructure and mechanical properties will be discussed, with an emphasis on dimensional change.
167. High Performance Applications of Chromium Steels Sintered at Conventional Temperatures: To meet the rigorous demands of automotive gearing, sprocket and other power transmission applications, double-press / double-sinter (DP/DS) techniques are often used to achieve the desired level of static and fatigue performance. Ancorsteel® 4300, a new Cr-bearing material, has shown improved strength levels compared to traditional PM steels. By employing such an alloy, core property requirements can be met at densities around 7.0 g/cm3. Replacing the pre-sinter and secondary press operations with selective densification, which will ensure sufficient contact fatigue resistance, can provide an economic benefit. The current work demonstrates the viability of processing a sprocket for a power transmission application with this high performance alloy system sintered at 1120 °C (2050 °F) in a production furnace. Subsequent selective densification and surface carburization provides a wear resistant and durable case layer. The results are compared with those achieved using FLN2-4405 processed through the traditional route of DP/DS, heat-treat.
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 PM 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 PM 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.
164. Full Density Properties of Low Alloy Steels: Full density produces the best mechanical properties in a PM or P/F component. Full density properties are available for traditional P/F materials, which are based on unalloyed base iron or low alloys with Ni and Mo additions. Additional base alloys have been developed which may be suitable for full density processing. This paper outlines the full density properties of these steels. Mechanical properties and microstructure will be presented.
163. Effect of Heat Treatment and Case Carburizing High-Density PM Steels: Recent advancements in high-density lubricants enable PM steels to be processed to densities approaching 7.40 g/cm3 in a single compaction step using heated compaction tools via the AncorMax D® process. This broadens the number of suitable applications for PM steels, including high performance gears. However, in addition to high-density, the microstructural and mechanical property requirements vary depending on the application. This objective of this paper is to quantify and understand the mechanical property differences obtained by subjecting high-density PM steels to various heat-treatments. Mechanical properties, fatigue properties, and microstructural analysis will be presented in the as sintered, quenched and tempered, and carburized states.
162. Effect of Case Carburizing on Mechanical Properties And Fatigue Endurance Limits of 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 PM 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 PM 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.
158. Chromium Containing Materials for High Strength-High Fatigue Applications: As the use of PM 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 PM 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.
156. Development of a High Performance Nickel-Free PM Steel: A developmental nickel-free PM 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.
155. Single Pressed Single Sintered PM Products for High Density, High Performance Applications: Further improvements are being developed in binder and lubricant technology that makes it possible to reach green densities approaching 7.4 g/cm3 in some applications, without the need to heat the iron powder or to double press and double sinter. This paper outlines the progress of this research. The effect of die temperature and part length on ejection behavior and final properties has been studied. In addition, optimal processing parameters as well as mechanical data are presented.
154. A Review of Current Sinter-Hardening Technology: Sinter-hardening has developed into a highly cost effective production method for the production of through hardened PM parts without the need for additional heat-treatments. Over the last several years advances have been made in sinter-hardening material systems and furnace technology. This paper reviews these advances as well as some key processing parameters required to produce high quality sinter-hardened components. Specific topics included are proper alloy selection, mechanical and fatigue properties, microstructural development, optimization of furnace cooling rates, and proper tempering practices.
149. An Investigation Into the Effect of Copper and Graphite Additions to Sinter Hardening Steels: Sinter-hardenable powders have been used as replacements for traditional quench-hardened and tempered materials due to their ability to transform to a martensitic microstructure upon cooling during a typical sintering operation. In the manufacture of the base sinter-hardenable powders, alloying additions are made to the melt (prealloyed), with graphite added to the base powder as the carbon source. However, additions of copper to further improve the hardenability of the mix are commonplace. The combined admixed additions of graphite and copper to the prealloyed powder can conceivably lead to increased retained austenite contents. In the present study, metallographic techniques have been developed to resolve retained austenite in a predominately martensitic material. Etching and staining techniques, automated image analysis, and scanning electron microscopy were the metallographic tools used in this study.
148. Higher Density and Higher Performance by Single Pressing and Single Sintering: Further improvements were made in binder and lubricant technology that makes it possible to reach green densities approaching 7.4 g/cm3 in some applications, without the need to heat the iron powder or to double press and double sinter. The effect of die temperature and part length on ejection behavior and final properties will be studied. In addition, optimal processing parameters as well as mechanical data will be presented.
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.
139. Effect of Microstructure on the Rotating Bend Fatigue Response of a Prealloyed and Two Hybrid PM Steels: The effect of microstructural inhomogeneities on the rotating bend fatigue response of a prealloyed (FL-4405) and two hybrid (FLC2-4405 and FLN2-4405) steels was evaluated. Different microstructures at a nominal density of 7.4 g/cm3 were developed by conventional sintering, high temperature sintering, quenching and tempering and sinter hardening followed by tempering. In previous studies on these steels, tensile and impact properties, hardenability, fatigue crack growth rates, pore characteristics and residual stress distributions were quantified. For each steel, the highest fatigue limit but the lowest fatigue ratio is obtained in the quenched + tempered condition. Sinter hardening of the steels containing copper and nickel increases the fatigue limit relative to the as-sintered condition. High temperature sintering reduces the fatigue limit relative to conventional sintering. The fatigue ratio is a function of microstructure and is lowest in the three steels in the quenched + tempered condition. The inferior fatigue behavior of the copper-containing steel is attributed to the large pores resulting from the coarse copper powder.
138. Fatigue Crack Growth of Fe-0.85Mo-2Ni-0.6C Steels with a Heterogenous Microstructure (Experiments and Microstructure-Based Simulations of the Axial Fatigue Behavior of PM Alloys): Powder metallurgy processing of steel alloys typically results in a material with heterogeneous microstructure and residual porosity. The fatigue crack growth behavior of these materials is strongly affected by the nature of porosity and heterogeneous microstructure. Notched fatigue specimens were prepared from a Fe-0.85Mo prealloy mixed and binder-treated with 2%Ni and 0.6%C. The alloys were tested at three different densities: 6.98 g/cm3, 7.36 g/cm3, and 7.53 g/cm3. The microstructure at each density was characterized to determine the porosity, microconstituents, and phase fractions. Fatigue testing was performed at various R-ratios, ranging from –2 to 0.8. Increasing porosity and increasing R-ratio resulted in a decrease in ∆Kth. In situ observation of crack growth showed that the cracks propagated through Ni-rich regions. It appears that pearlite regions, and, to some extent bainite regions, however, contributed to toughening and crack deflection.
137. Rolling 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 PM 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.
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.
129. Effect of Cooling Rates During Sinter-Hardening: Sinter-hardening is becoming a more widely used process for the production of high strength PM parts. The ability to produce martensite directly from the sintering furnace enables the process to produce parts, with properties close to those of quenched and tempered steels, more efficiently by omitting a separate heat treatment operation. The success of sinter-hardening depends upon the ability to produce microstructures of high martensite content consistently during accelerated cooling after sintering. This paper will examine and illustrate the effects of changes in cooling rate from sintering temperature upon the microstructure, hardness and properties of a hybrid PM steel. It will show how comparison of cooling curves of instrumented Jominy and sintering furnace can be used to improve the sinter-hardening process.
128. Chromium Additions to the Ancorlo®y 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 PM 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 PM 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.
125. Effect of Density on the Microstructure and Mechanical Behavior of Powder Metallurgy FE-MO-NI Steels: The microstructure and mechanical properties of Fe-0.85Mo-Ni powder metallurgy (PM) steels were investigated as a function of sintered density. A quantitative analysis of microstructure was correlated with tensile and fatigue behavior to understand the influence of pore size, shape, and distribution on mechanical behavior. Tensile strength, Young's modulus, strain-to-failure, and fatigue strength all increased with a decrease in porosity. The decrease in Young's modulus with increasing porosity was predicted by analytical modeling. Two-dimensional microstructure based finite element modeling showed that the enhanced tensile and fatigue behavior of the denser steels could be attributed to smaller, more homogeneous, and more spherical porosity which resulted in more homogeneous deformation and decreased strain localization in the material. The implications of pore size, morphology, and distribution on the mechanical behavior and fracture of PM steels is discussed.
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.
123. Effect of Porosity on the Thermal Response, Hardness, Hardenability and Microstructure of PM Steels: The pores present in sintered steels affect their thermal characteristics. In the present study the role of porosity was examined in two hybrid PM steels in relation to cooling rate, hardness, hardenability, and microstructure utilizing an instrumented Jominy test. To establish a base line for thermal response in the absence of pores, Jominy bars were hot isostaticlly pressed after sintering. Pores enhance slightly the measured cooling rate near the water quenched end of the Jominy bar. This behavior is predicted on the basis of a recent simple heat transfer model in which a decrease in thermal diffusivity results in faster cooling near the water quenched surface. Alternatively, simulation of penetration of water into the pores by capillary action predicts that this is a viable mechanism to enhance cooling rate.
120. Statistical Approach to a Leaner Sinter Hardening Alloy: A popular sinter-hardening alloy is based on pre-alloyed Fe-Ni-Mo-Mn powder to which 2% copper and 0.9% graphite is added. Data in the literature suggests that reduced copper and graphite contents may provide equal hardenability and higher tensile properties. Experimental results demonstrate that a fully martensitic microstructure and higher tensile properties may be obtained with leaner alloy chemistry. Reduced additive (copper and graphite) content improves pore free density. Response Surface Methodology (RSM) is used to illustrate the results of the statistically based experimental design.
119. Cooling Rate Effects on the Metallurgical Response of a Recently Developed Sinter Hardening Grade: The results of dilatometric, metallographic and hardness determinations to characterize the effects of cooling rates in the low to moderate sinter hardening range on the response of various Ancorsteel® 737 SH compositions are presented.
117. Properties of High Density Sinter Hardening PM Steels Processed Using an Advanced Binder System: Sinter-hardening PM alloys offer an excellent opportunity for a part manufacturer to produce hardened components in an economical fashion by eliminating secondary heat-treatments. Unfortunately, sinter-hardening PM base iron grades are prealloyed with substantial levels of Ni, Mn, and Mo which increase hardenability but reduce compressibility. Furthermore, Cu and graphite are added to further increase strength and hardness. These alloying additions all reduce compressibility limiting the maximum attainable green and sintered densities. This paper explores how processing sinter-hardening alloys with a new proprietary binder system can improve compressibility and lead to higher densities and mechanical properties. The data show green density increases of 0.05-0.15 g/cm3 and be achieved and can result in tensile strength and hardness improvements.
116. Advanced Sinter-Hardening Materials and Practices: Sinter hardening is a well-established production technique utilized in the manufacture of PM 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 PM 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 PM.
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 Inhomogeneities on the Fatigue Properties of a Prealloyed & Two Hybrid PM 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 PM 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.
107. Effect of Copper and Nickel Alloying Additions in the Tensile and Fatigue Behavior of Sintered Steels (Axial Fatigue Behavior of Sintered Ferrous PM Alloys: Experiments and Modeling): The influence of Cu and Ni on tensile and fatigue behavior of Fe-0.85Mo prealloy with 0.6% graphite addition was investigated. The transient liquid phase formed by the presence of Cu resulted in more rounded pores in the Fe-Ni-Cu alloy compared to Fe-Ni. While the total porosity was similar in both alloys, a larger fraction of secondary pores was present in the Fe-Ni-Cu. The addition of Cu resulted in an increase in proportional limit stress, ultimate tensile strength, and fatigue strength over the Cu-free alloy. The higher fatigue resistance was attributed to the enhanced solid solution strengthening provided by Cu in Fe, and the higher proportional limit in the Fe-Ni-Cu alloy, caused by the more rounded nature of the pores, and stronger Fe-Ni-Cu matrix surrounding the pores. The proportional limit stress appears to be a good indicator of fatigue strength, since it quantifies the onset of localized plasticity in these materials.
106. Materials Solutions for Converting Cast Iron Applications to Powder Metal: In the last several years, powder metallurgy (PM) 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 PM 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 PM and the potential cost savings of conversion to PM 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 PM materials as possible replacements for each.
105. Advances in PM 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 PM gearing was in relatively low stress applications. The recent introduction of new compaction techniques and new alloy materials has produced PM components with significantly higher yield and tensile strengths approaching the strength levels of wrought gearing materials. This paper will review the new PM 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.
101. Fatigue Crack Initiation and Propagation in Ferrous Powder Metallurgy Alloys: Many of the targeted applications for powder metallurgy materials, particularly in the automotive industry, undergo cyclic loading. It is, therefore, essential to examine the fatigue mechanisms in these materials. The mechanisms of fatigue crack initiation and propagation in ferrous powder metallurgy components have been investigated. The fatigue mechanisms are controlled primarily by the inherent porosity present in these materials. Since most, if not all, fatigue cracks initiate and propagate at the specimen surface, surface replication was used to determine the role of surface porosity in relation to fatigue behavior. Surface replication provides detailed information on both initiation sites, and propagation path of fatigue cracks. The effect of microstructural features such as pore size, mean pore spacing, as well as the heterogeneous microstructure on crack deflection was examined and is discussed. Fracture surfaces were examined to elucidate a mechanistic understanding of fatigue processes in these materials.
99. Effect of Microstructural InHomogeneities on The Mechanical Properties of Hybrid PM 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) PM 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.
98. Effect of Porosity on the Hardenability of PM Steel: Pores in sintered PM steels influence their thermal response and thus hardenability. Porosity decreases thermal conductivity and attendant cooling rates, and it reduces the mass of the steel from which heat is removed during quenching. The latter effect is quantified by a factor (1-), where e is the fraction of porosity; in contrast, the influence of e on thermal conductivity is more complex. In the present study, the hardenability of three sintered steels (Fl-4405, FLC2-4405 and FLN2-4405) with levels of porosity in the range 7v/o-16v/o has been determined experimentally using an instrumented Jominy test in which thermocouples gave direct readings of cooling rate as a function of distance from the water-quenched end of the bar. The cooling of the Jominy bars was also simulated by means of a three – dimensional model using the finite difference method. Cooling curves are given for the three steels as a function of the level of porosity at distances in the range 5 mm to 65 mm from the water-quenched end of the Jominy bars; the corresponding hardness traces define the 50% martensite distance. The model predicts a decrease in cooling rate with an increase in porosity, hence hardenability should decrease whereas the experimental data show clearly that the PM steels with a level of porosity > 12v/o cool faster than a baseline pore-free wrought steel. This is attributed to penetration of the water via the interconnected pores in the sintered steels.
96. PM High Strength Magnetic Alloys: Sintered PM 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 PM magnetic materials. Described in this paper are PM 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 PM 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.
91. Engineered Approach to High Density Forming using Internal and External Lubricants: The drive to obtain higher densities, strength and dynamic properties in PM has prompted the development of methods, including Double Press / Double Sinter, Copper Infiltration, Warm Compaction etc., to achieve these goals. One of the contributing factors influencing higher densities is the addition of lubricant to the premix. With advances in lubricant technology and binder-treated premixes it is possible to achieve higher density parts, with reduction of internal lubricant and die wall lubrication This study combines the effects of using a balance of internal and external lubrication to improve the properties of PM materials.
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.
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 PM 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 PM 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.
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 (PM) 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 PM material systems and processing parameters. This property discussion will demonstrate the suitability of the PM process in replacing these cast and machined components. Examples of specific parts will be cited and discussed.
80. 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 hardness, high hardenability, and increased mechanical performance. These often conflicting requirements necessitated the development of new materials that offer high as-sintered hardness and good static/dynamic mechanical properties without the added expense of a secondary heat treatment. Traditionally, sinter-hardening materials have offered acceptable hardness but at the expense of mechanical properties and sintered density. This paper will document a series of sinter hardening materials that offer good compressibility, high 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.
78. Binder-treated Analogs of Diffusion Alloyed Compositions Based On Ancorstee®l 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.
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.
74. Improved Efficiency by Use of Sinter-Hardened PM Automotive Components: Sinter-hardening, accelerated cooling, of PM components directly from the sintering furnace is an increasingly popular production process. Sinterhardened PM steels possess similar macrohardness and strength to heat treated PM steels processed by quenching and tempering. Where design permits, sinter-hardening enables PM fabricators to improve process efficiencies by omitting a separate heat treatment operation. This paper examines the interaction of material selection and process conditions required to develop a sinterhardened PM component for an automotive application.
73. Hardenability of Sintered Fe-B-C Alloys: The objective of this study was to evaluate and interpret the effect of small additions of boron (<0.09 w/o) on the hardenability of sintered Fe-B-0.3 w/o C alloys. For comparison, in terms of hardness response, binary Fe-B alloys were also evaluated. The alloys were prepared by mixing gas atomized Fe-12 w/o B with Ancorsteel 85 HP powder; carbon was added in the form of graphite. Jominy bars were fabricated from the alloy powder by cold isostatic pressing (414 MPa) in a polyurethane bag and sintering at 1120 °C or 1230 °C (30 min) in dry hydrogen (dewpoint – 40 °C). Hardenability was quantified by means of the standard Jominy end quench test. Small additions of boron enhance both the hardness and hardenability of the base Fe-C alloy, particularly at the higher sintering temperature. This effect is attributed to inhibition of the nucleation of ferrite by the boron which retards the formation of pearlite.
69. The Effect of Microstructure and Pore Morephology on Mechanical and Dynamic Properties of Ferrous PM Materials: The objective of this study was to quantify and understand the combined role of microstructure and pore characteristics on the transverse rupture strength (TRS), tensile properties and rotating bend fatigue response of conventional and ANCORDENSE™ processed FLN2-4405 premixes. To this end, the premixes were made with samples using fine (4µm) and coarse (50µm) nickel powder to promote differences in pore size and diffusion characteristics. Compacts were sintered in synthetic DA (75 v/o H2 / 25 v/o N2) at 2050°F (1120°C) or 2300°F (1260°C) to densities in the range of 6.8 g/cm³ - 7.2 g/cm³. Pore size and spacing, cumulative pore size and number of pores per unit area were determined by stereological analysis, and the crack path was monitored by means of optical microscopy. The static and dynamic properties of the materials made from the two premixes are interpreted in terms of the attendant microstructures and pore characteristics, as dictated by the premix type, sintering temperature and sintered density.
59. The Effect of Microstructure and Pore Morphology on Mechanical and Dynamic Properties of Ferrous PM 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 PM materials.
54. Sinter-Hardening PM Steels: The use of PM structural parts is growing in part due to the use of the sinter-hardening process which utilizes high performance materials in combination with an accelerated post sintering cooling rate. The sinter-hardening process offers improved mechanical properties over conventional sintering without a separate heat treatment operation. Thus, where the part design permits, sinter-hardening offers considerable economic benefits to the part producer. Sinter-hardening typically requires that the PM steel substantially transform to martensite during cooling. A variety of microstructures and properties can be obtained by varying the post sintering cooling rate. By controlling this rate, the microstructure can be manipulated to produce the required amount of martensite to obtain the desired mechanical properties. Alloying elements such as molybdenum, nickel, and copper promote hardenability in PM parts. By increasing the hardenability of the material, the parts can be cooled at slower rates and still produce large amounts of martensite. The ability to increase the amount of martensite, leading to increased strength and hardness, through the use of proper alloy selection and accelerated cooling rate will be discussed.
50. Effect of Process Conditions Upon Sinter-Hardening Response of FLC-4608 Materials: Sinter-hardening provides for improved efficiency and competitiveness by eliminating a separate, secondary heat treatment operation. Materials options, process flexibility, and application requirements demand a better understanding of process, microstructure, and mechanical property relationships in order to fully capitalize on the opportunity afforded by sinter-hardening. This study investigates the effect of cooling rate on the material properties of an FLC-4608 material processed under production conditions. Variables used to control accelerated cooling are related to componet microstructure and mechanical properties. Production cooling rates and microstructural comparisons are made with a laboratory developed Continuous Cooling Curve (CCT) for the FLC-4608 alloy.
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 PM 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.
45. The Development of High Performance PM Steels: Ferrous powder metallurgy has continued to displace competing cast or wrought technologies in automotive applications. This required the development of materials systems with higher, more consistent performance than those available previously. However, competing technologies are not static. The paper examines the materials development and microstructural control required to meet the challenges and opportunities offered by the development of new PM parts.
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 PM 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.