Prealloy Materials Publications
199. Alloy Development of Sinter-Hardenable Compositions: Market forces in the PM industry are challenging the traditional compositions typically used in PM alloys. Mo, Ni and Cu are the predominant alloying elements used in ferrous PM due to their low affinity for oxygen. In addition, Mo has little effect on compressibility and copper rapidly alloys by way of a liquid phase at sintering temperatures. All three elements also increase the hardenability of steels, allowing for sinterhardening of parts produced with a combination of the elements. Price pressures are causing a reevaluation of powder chemistries utilizing these elements, and the challenge of alloy development is to advance alloy systems that optimize the balance between mechanical properties and overall production cost. Sinter-hardenable compositions play a key role in this regard. This paper will evaluate and discuss alternative alloys to those primarily used in the European market.
174. Fatigue Crack Growth of Prealloy Fe-0.85Mo-2Ni-0.6C Steels with a Homogeneous Microstructure: The fatigue crack growth behavior of powder metallurgy steels (PM steels) is strongly affected by the nature of porosity and microstructure of steel matrix. Our previous work has focused on a premix PM steel prepared from Fe-0.85Mo prealloy mixed and binder-treated with 2%Ni and 0.6% graphite. In this study, we have studied the fatigue crack growth behavior of a prealloy steel of similar composition. Use of the prealloy powder resulted in more homogenous microstructure than the premix steel. The alloys were tested at three different densities: 7.0 g/cm3 , 7.3 g/cm3, and 7.5 g/cm3. Microstructure characterization was conducted by optical and scanning electron microscopy (SEM). 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. The degree of crack closure was measured for both premix and prealloy steels at different R-ratios, and is discussed.
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.
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) PM steels based on prealloyed Ancorsteel® 85 HP was evaluated. In phase two we assess crack propagation response. The base powder and additions were mixed with 0.75 w/o Lonza Acrawax in 227 kg (500 lb) batches. A density of 7.4 g/cm3 was obtained by double pressing (550/550 MPa). Sintering temperatures of 2050 °F(1120 °C) and 2300 °F (1260 °C ) were utilized. A group of sintered compacts of each alloy was heat treated by quenching from 1650 °F (900 °C) into warm oil at 160 °F (70 °C) followed by tempering at 375 °F (190 °C) for 1 h. Two groups of sintered compacts of the FLC2-4405 and FLN2-4405 alloys were sinter hardened and tempered at 375 °F (190 °C) for 1 h. Experimental data showed that the P/M steels exhibit comparable fatigue crack growth rates (1.1207E-4 to 3.0185E-4 mm/cycle) at a stress intensity range of 1000 MPa (mm)1/2. Quenched and tempered microstructures resulted in the highest fatigue crack growth rate. Sinter hardening of FLC2-4405 and FLN2-4405 lowered the fatigue crack growth rate. High temperature sintering reduced the fatigue crack growth rate in FL-4405 but increased it in FLC2-4405 and FLN2-4405.
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.
68. Performance Characteristics of a New Water-Atomized Prealloyed Powder (0.5 weight % Molybdenum): A new prealloy material containing 0.50 w/o Mo was introduced recently. This medium hardenability material can be admixed with a variety of alloying ingredients to produce superior tensile properties. Results of admixing this prealloyed powder with nickel, copper, manganese, and graphite will be presented. In addition, quench and temper properties will also be discussed.
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.
38. Powder Metallurgy Gears - Expanding Opportunities: Powder metallurgy (PM) is a precision metal forming technology for the manufacturing of parts to net, or near net shape. The powder metallurgy process is illustrated schematically in Figure 11. There are three basic steps to producing parts; mixing, compacting, and sintering. Variations to these basic steps such as infiltration, double pressing/double sintering, and powder forging may be used to achieve higher density parts. A sizing operation may be used to qualify critical part dimensions. Alternatively, a machining step may be added for the same purpose or to achieve a geometric feature not possible during rigid die compaction. PM parts may be through hardened or surface hardened as required by the intended application.
31. Advanced Properties of High Density Ferrous Powder Metallurgy Materials: The introduction of the ANCORDENSE™ system has provided significantly higher density levels than previously possible in a single press/single sinter operation. This paper will explore the role that higher density has on mechanical properties. Various properties will be evaluated, including transverse rupture strength, tensile strength, and impact. Additionally, the effect of other processes, such as high temperature sintering and heat treatment, will be addressed.
27. Recent Developments in Ferrous Powder Metallurgy Alloys: A systems approach to engineered ferrous powder metallurgy (PM) materials is described. The approach encompasses the use of high compressible, high performance powders in premixes produced using proprietary mixing technology that employs patented binders. To ensure that an appropriate microstructure is achieved to suit the functional requirements of a particular application, alloys are formulated based on knowledge of the compaction and sintering cycle that will be used to make the PM parts. These premixes have improved flow and die filling characteristics that result in greater consistency throughout the entire PM part manufacturing process. In addition, the use of binder treated premixes leads to reduced dusting and segregation of alloy additions. Binder treated premixes produced using high compressible, prealloyed molybdenum steel powders are shown to be particularly well suited for quench-hardening, sinter-hardening, and high temperature sintering. They also form the basis for a series of chromium, manganese, and chrome-manganese PM 'Steels. The systems approach will be augmented during 1994 by the introduction of new material and process technology that enables part densities of 7.3 to 7.5 g/cm3 to be achieved through single compaction processing.
26. High Performance Ferrous PM Materials For Automotive Applications: The majority of automotive components (transmission, chassis, suspension, and engine) for which parts with densities up to about 7.0 g/cm3 are suitable have already been converted to PM and there are few opportunities for growth in this density range. In order to meet the requirements of more demanding applications there has been a trend toward higher densities through the use of infiltration, double pressing/double sintering, or powder forging (l - 4) to produce parts such as synchronizer hubs, crankshaft sprockets, chain sprockets, gerotors, steering column tilt levers, planetary gear carriers, parking gears shift levers, and connecting rods. While powder forging has been shown capable of producing parts, which are superior to wrought, or cast products process economics have limited market penetration by this technology (5). The double press and sinter route also adds process costs and is probably too expensive for other than premium applications. There is a real need for a systems approach that will permit double pressed and sintered or infiltrated performance characteristics to be achieved by means of single compaction processing. The mechanical properties of PM materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final product (6).
24. Properties of High Density Ferrous PM Materials, A Study of Various Processes: Several methods of achieving higher density in ferrous PM 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.
18. Properties of Heat Treated PM Alloy Steels: Further development of ferrous PM technology into highly stressed applications will require the development of PM steels with mechanical properties approaching those of cast or wrought products. The PM process offers many routes to improve mechanical properties through alloy design, increased density and high temperature sintering. The paper will present the results of a study into the effects of density and composition upon the microstructure and properties of quenched and tempered PM alloy steels.
17. Sinter-Hardening Low-Alloy Steels: The availability of prealloyed steel powders employing molybdenum as the major alloying element offers new levels of compressibility and mechanical properties. When the prealloyed powders are combined with conventional PM additives such as copper, nickel and graphite, it is possible to develop high strength martensitic microstructures directly from the sintering cycle. The impact and tensile properties of copper, nickel, graphite premixes based upon the prealloyed molybdenum steels are compared under controlled cooled conditions. The ability to balance tensile strength, toughness and hardness by control of alloy chemistry is illustrated.
16. High Performance Ferrous PM Materials Utilizing High Temperature Sintering: Several new and more challenging PM applications require materials that exhibit higher strength along with improved dynamic property characteristics. To meet these requirements, development efforts focused on material grades capable of achieving high performance properties when sintered at elevated temperature. Several elements, specifically nickel and copper, were admixed to the water atomized, prealloyed low-alloy steel powders Ancorsteel® 85 HP and 150 HP using the patented ANCORBOND® process. Tensile and impact performance of the resulting materials have been reviewed along with quantitative metallography of selected as-sintered samples. The results indicate the type and amount of each admixed element plays an important role in achieving specific characteristics. In addition, the overall performance values are greater for the single press and sinter technique used in this investigation than could previously be achieved using a double press - double sinter process.
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 PM 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.
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 Ancorsteel® 2000 or Ancorsteel® 4600V 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.
8. Powder Forging: is a process in which unsintered, presintered, or sintered powder metal preforms are hot formed in confined dies. The process is sometimes called PM (powder metallurgy) forging, PM hot forming, or is simply referred to by the acronym P/F. When the preform has been sintered, the process is often referred to as "sinter forging."
6. Microcleanliness Studies of Low Alloy and Carbon Steel Powders Intended for Powder Forging Applications: The results of ten years of experience aimed at continuously improving the quality of powders for forging applications are reviewed. An automated image analysis procedure for inclusion assessment is described which evaluates the inclusion content of samples and defines fragmented inclusion clusters on the basis of a concept of near neighbor separation. A task group approach was used for cause-and-effect analysis to determine the source of different inclusion types and eliminate and/or reduce their incidence. The benefits of this approach are demonstrated by the significant reduction effected in inclusion levels.
4. Ferrous Powders - How Alloying Method Influences Sintering: The mechanical properties of PM materials are directly related to their microstructure and the size, distribution, and morphology of the porosity they contain. Alloying additions are made to develop specific material performance characteristics. However, the manner in which the alloys are constituted has a significant effect on the porosity and microstructure of the final sintered product (1,2).
3. Fatigue Properties of PM Materials: The tensile properties and fatigue endurance limits of several widely used PM 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 PM Materials: Dynamic property data on pressed and sintered ferrous powder metallurgy materials have come under increasing demand as the PM 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 PM alloy development. Un-notched Gharpy impact energy and rotating bending fatigue tests have been used to characterize commonly used PM 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.