Surface Densification

Surface Densification Technical Publications

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 (P/M) component are significantly improved over current P/M 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 P/M 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 P/M part performance in comparison to conventional wrought steel grades.

175. Surface Densified P/M Steel - Comparison With Wrought Steel Grades The next major opportunity of P/M 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.

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.

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.

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

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

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

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