Admixed

Admixed - Materials Technical Publications

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

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.

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.

140. A Metallographic Investigation Into the Effect of Sintering on a FC-0205 Premix The properties of ferrous P/M materials are developed during the sintering process where metallurgical bonds are formed at particle-to-particle contacts and alloying of mixed and bonded additives occurs. Increasing either the sintering temperature or time can produce improvements in the microstructure and, consequently, the ensuing properties. In this paper, an FC-0205 premix, sintered for various times at 1120 °C (2050 °F), will be used to study the microstructural changes resulting from increases in sintering time. Features of interest include, changes to the surface-to-volume ratios at the particle boundary and pore surface areas, diffusion of the copper in the solid state and as a liquid component, and the homogenization of the microstructrue with increasing sintering times. Stereological techniques, using light optical microscopy, will be employed to examine the diffusion of the added alloying materials and to quantify the improvement in the degree-of-sinter. Additionally, electron microscopy (SEM) will be used to examine Charpy impact fracture surfaces from specimens sintered at the various times.

114. Role of Additives in P/M Machining Many P/M parts are machined before final assembly. The increasing use of dedicated lines, or cells, in which many sequential operations are conducted on an assembly means that the time required to machine a P/M component will need to be reduced if it is the bottleneck in the assembly process. This paper examines the effects of three freemachining additives: boron nitride, manganese sulfide and pre-alloyed, or resulfurized, sulfur, upon the machining response of an FC-0205 P/M steel in a turning operation. The effects of the additives on tool wear, cutting forces, chip form and surface finish are compared.

100. Higher Green Strength Enhancements to Increase Process Robustness The use of binder-treated premixes has grown dramatically since the introduction of the technology in the late 1980’s. Decreased levels of respirable dust coupled with reduced segregation and significantly improved powder flow have helped to stimulate this growth. More recently, binder-treated premixes that significantly enhance the green strength of P/M parts have been developed. The higher green strength results in more robust handling of green parts prior to the sintering operation and reduced levels of green scrap. In addition, the significantly higher green strength provides an opportunity for “green” machining of the P/M parts prior to sintering. This paper will discuss recent advances in binder-treatment technology and will review production experience with binder-treated premixes.

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.

87. Advances in Binder-Treatment Technology The use of binder-treated premixes has grown dramatically since the introduction of the technology in the late 1980’s. Decreased levels of respirable dust coupled with reduced amounts of alloy addition segregation and significantly improved powder flow have helped to stimulate this growth. More recently, binder-treated premixes have been developed that significantly enhance the green strength of P/M parts. The higher green strength results in more robust green parts for handling prior to the sintering operation and reduced levels of green scrap. In addition, the significantly higher green strength provides the opportunity for “green” machining of the P/M parts prior to sintering. This paper will discuss recent advances in binder-treatment technology and will review production experience with binder-treated premixes.

72. Advances in Binder - Treatment Technology Statistical Data on ANCORBOND Plus Binder treatment technology has been well accepted in the marketplace to provide reduced segregation and better powder flowability. However, there is a need to increase the green strength of some parts for better handling of intricate shapes and also a need to improve the bonding of nickel and copper. ANCORBOND Plus is an engineered bonding technology that can produce very high green strength and green density based on conventional compaction processing. The system, which uses a zincless lubricant, is based on the optimization of the bonding mechanism and binder chemistry. This paper will present statistical data collected on parts processed in a production press.

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

· mean particle size of 4 mm

· mean particle size of 50 mm

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

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

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

51. Processing Experience of Green Strength Enhanced Material Systems Green strength enhanced material systems have been developed for iron and Low alloy as well as stainless powder metallurgy applications. Relative to normal processing, the increase in green strength is 50-100%. The nature of green strength with respect to both materials and processing conditions is reviewed. The processing variations designed to meet target properties such as apparent density, flow and compressibility are compared with conventional material systems. Manufacturing experience with a mechanical press is presented.

45. The Development of High Performance P/M 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 P/M parts.

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.

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

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.

9. Properties of Parts Made from ANCORBOND Processed Carbon-Nickel-Steel Powder Mix(FN-0208) Studies were conducted to determine the effects on property variability of parts made from a bonded Ancorsteel 1000 mix containing 0.95% graphite, 2.0% nickel, 0.6% Acrawax and 0.3% zinc stearate. The part geometry studied was that of a cylindrical bushing. The treatment effects on powder properties and on several parts properties were determined. The powder properties included the traditional green and sintered properties and the graphite and nickel dusting resistance’s. The parts properties surveyed included both green and sintered properties and sintered carbon and nickel contents. Similar studies of a companion regular mix of nominally the same composition were conducted for purposes of comparison.

Compared with the regular mix, the bonded mix exhibited marked improvements in graphite and nickel dusting resistance and in powder flow properties. In the parts-making study, the bonded mix showed significant differences in mean dimensional change characteristics but was otherwise reasonably similar to the regular mix in terms of mean property values. In the case of variability, the bonded mix was statistically equivalent in green and sintered dimensional change characteristics and sintered nickel content but otherwise significantly improved relative to the regular mix in all of the other properties of interest. The latter included green weight and density and sintered density, hardness, crush strength and carbon content.

The variability improvements in the parts from the bonded mix were attributed both to the effects of the binder treatment in improving powder flow properties and reducing carbon segregation. The difference in mean dimensional change characteristics between the parts from the bonded mix and those from the regular mix were also attributed to the effect of the binder treatment in improving alloy admix uniformity.

The fact that the parts variability improvements of the bonded mix did not extend to the dimensional change characteristics was suspected to be due largely to a purely statistical effect arising from the dissimilarity in the mean dimensional change values relative to those of the regular mix. A limited laboratory-scale study was subsequently conducted to examine this possibility. In general, the findings supported the idea. In addition, they also presented a strong indication that it may be possible by virtue of the ANCORBOND process to effect significant reductions in the nickel contents of graphite-nickel mixes without sacrificing either mechanical 2 properties or dimensional change characteristics.

5. Statistical Process Control in Iron Powder Production and New Product Development SPC is discussed with a view to indicating its implications not only to manufacturing and quality but to research and product development as well. In the manufacturing/quality area, the efforts and methods attending full-scale implementation of SPC are briefly reviewed with special reference to the differences inherent in powder making versus manufacturing of parts. SPC charting techniques suitable for powder making are described and discussed. In the product development area, it is shown how SPC influenced a major research program. The objective of the program was to improve premixed products with a view to reducing variability in parts manufacturing. ANOVA studies of production mixes generally showed that the main sources of premix variability were mix to mix differences and within mix differences arising from demixing subsequent to premix manufacture. It was recognized that SPC is especially applicable to dealing with the first of these and subsequent efforts to implement it to premixes are described. In the case of demixing, the developments of a new premixing process is reported in which the alloy admix ingredients are bonded to the iron.

The general findings of extensive studies, which show the benefits of the new process in terms of reduced variability in parts manufacturing, are reviewed and the results of a study of a FC-0208 premix are presented as an example. SPC theory and concepts are used to indicate the significance of the results and their potential applicability to the production of parts.

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

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

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

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