Dilatometry

Dilatometry Technical Publications

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.

146. Sintering of Water Atomized PIM Fe-2Ni-0.8C The use of water atomized powders in powder injection molding processes has long been an area of interest because of the cost savings afforded by the water atomization process over gas atomization and chemical methods. In this study, water atomized Fe-2Ni powder is investigated for sintering response in the milled and as-received conditions. Variations in particle size, carbon content, heating rate, sintering temperature, and atmosphere were studied. The findings indicate that, aside from sintering temperature, the most important factors influencing the sintered density are the particle size, heating rate, and surface chemistry. Milling alters the surface chemistry and decreases the particles size, both of which serve to increase sintered density.

141. Effects of Cooling Rate on the Hardenability of Chromium Containing P/M Steels Two chromium containing grades, Cr-modified Ancorloy^®MDC and a developmental CrMnSiMo steel, have been investigated to develop an understanding of the phase transformation behavior of these steels during cooling. The cooling rates studied are in the range typically found in sintering furnaces. A quantitative study to assess the hardenability of these materials has been undertaken and the results of dilatometric, metallographic and hardness evaluations to determine the effects of cooling rate on the various Cr containing steels are presented.

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.

97. Processes Determining The Dimensional Change Of PM Steels The dimensional change characteristics of PM steels are generally not determined by the effects of the processes that occur at the sintering temperature. Instead, dilatometry shows that the largest contributions are typically due to the combined effects of various lower temperature processes. The present report both illustrates and discusses these effects in various common PM steels.

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