Double Press Double Sinter

Double Press / Double Sinter Technical Publications

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 P/M 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.

164. Full Density Properties of Low Alloy Steels Full density produces the best mechanical properties in a P/M 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.

153. Fatigue Crack Growth of Sintered Steels with A Heterogeneous Microstructure 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/cm^3,7.36 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 ∆K_th. 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, contributed to toughening and crack deflection. These findings are supported by quantitative measurements of crack growth rate, through the various microconstituents.

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.

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 (P/M) 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 P/M steels is discussed.

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.

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.

95. Conventional Powder Metal Is Still A Technology Leader Recent advancements in powder metal technology have made it possible to achieve physical properties rivaling many competitive technologies. Improvements in raw materials have made powder metal a viable replacement for several malleable and ductile cast irons. The combination of raw material and processing improvements continues to push powder metal technology performance into the wrought steel arena. Nevertheless, in the midst of all of these technological advancements, conventional powder metallurgy is still providing innovation in torque transfer systems. At BorgWarner’s TorqTransfer Systems division, conventional powder metallurgy has found application in six separate components of the newly created interactive torque management system dubbed ITM. This patented torque transfer device provides the all-wheel drive technology for MotorTrends SUV of the year – the Honda Acura MDX.[4] This paper describes how conventional powder metal technology provided the perfect solution for this highly innovative torque transfer technology.

94. Silicon Containing High Performance Alloys - Machinability and Mechanical Properties With the introduction of several silicon-containing materials, the potential for replacing ductile and malleable cast irons with P/M alloys has never been greater. These materials exhibit extremely competitive property combinations when conventionally compacted and sintered at 1260 °C (2300 °F). However, additional opportunities exist if advanced densification processes such as double press / double sinter or warm compaction are employed. This paper investigates several important manufacturing processes including advanced densification techniques, vacuum sintering, and machinability.

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.

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.

27. Recent Developments in Ferrous Powder Metallurgy Alloys A systems approach to engineered ferrous powder metallurgy (P/M) materials is described. The approach encompasses the use of high compressible, high performance powders in premixes produced using proprietary mixing technology that employs patented binders. To ensure that an appropriate microstructure is achieved to suit the functional requirements of a particular application, alloys are formulated based on knowledge of the compaction and sintering cycle that will be used to make the P/M parts. These premixes have improved flow and die filling characteristics that result in greater consistency throughout the entire P/M part manufacturing process. In addition, the use of binder treated premixes leads to reduced dusting and segregation of alloy additions. Binder treated premixes produced using high compressible, prealloyed molybdenum steel powders are shown to be particularly well suited for quench-hardening, sinter-hardening, and high temperature sintering. They also form the basis for a series of chromium, manganese, and chrome-manganese P/M 'Steels. The systems approach will be augmented during 1994 by the introduction of new material and process technology that enables part densities of 7.3 to 7.5 g/cm3 to be achieved through single compaction processing.

26. High Performance Ferrous P/M Materials For Automotive Applications The majority of automotive components (transmission, chassis, suspension, and engine) for which parts with densities up to about 7.0 g/cm3 are suitable have already been converted to P/M and there are few opportunities for growth in this density range. In order to meet the requirements of more demanding applications there has been a trend toward higher densities through the use of infiltration, double pressing/double sintering, or powder forging (l - 4) to produce parts such as synchronizer hubs, crankshaft sprockets, chain sprockets, gerotors, steering column tilt levers, planetary gear carriers, parking gears shift levers, and connecting rods. While powder forging has been shown capable of producing parts, which are superior to wrought, or cast products process economics have limited market penetration by this technology (5). The double press and sinter route also adds process costs and is probably too expensive for other than premium applications. There is a real need for a systems approach that will permit double pressed and sintered or infiltrated performance characteristics to be achieved by means of single compaction processing. The mechanical properties of P/M materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final product (6).

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

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

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

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

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

13. Performance Characteristics of a New Sinter-Hardening Low-Alloy Steel A martensitic microstructure can be developed in some powder metallurgy materials without the need for a secondary heat treatment operation provided the material is cooled sufficiently rapidly from the sintering temperature. These P/M materials are termed "sinter-hardening" steels. The partially alloyed powder, Distaloy 4800A, and nickel-molybdenum prealloyed steels such as Ancorsteel ® 4600V with copper additions are capable of being sinter-hardened. Ancorsteel 85 HP, a new highly compressible low-alloy powder employing molybdenum as the primary alloying element, is also capable of being sintered-hardened when copper and graphite additions are made to it. Ancorsteel 85 HP has a higher compressibility than nickel-molybdenum prealloyed powders. The effect of cooling rate has been studied on the microstructure and mechanical properties of Ancorsteel 85 HP + 2% copper + 0.9% graphite. Tensile and impact properties have been evaluated for a range of material densities and compared with those obtained with samples based on Ancorsteel 4600V.

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.

11. Tensile, Impact and Fatigue Performance of New Water ATomized Low-Alloy Powder - Ancorsteel 85 HP A new water atomized, prealloyed powder has been developed containing 0.85% molybdenum as the alloying addition. The as-sintered and heat treated tensile, impact and fatigue performance have been determined for a range of graphite additions using both single and double pressing techniques. Results indicate that the new powder, Ancorsteel 85 HP, has a unique ability to be compacted and repressed to densities not attainable with existing prealloyed nickel-molybdenum powders. The higher densities achieved produce performance equivalent to or better than Ancorstee12000 or Ancorstee14600V using conventional single compaction techniques. However, the additional density increment achieved during repressing results in mechanical properties in excess of what is possible with the existing low-alloy steels. It is expected that the new prealloyed powder will be used in high-density applications requiring good hardenability. It will also provide a base for our high performance ferrous material development program.

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

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

4. Ferrous Powders - How Alloying Method Influences Sintering The mechanical properties of P/M materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final sintered product (1,2).

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

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

1001 Taylors Lane • Cinnaminson, NJ 08077-2017 • USA • 856-829-2220