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Las Vegas Papers 2009
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A Comparison of FC-0208 to a 0.3 % Molybdenum Prealloyed Low-Alloy Powder with 0.8 % Graphite
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PDF (170 KB)
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Iron copper steels are the most widely used structural PM materials. Although the elemental copper addition melts during initial sintering, complete homogenization of the copper is not achieved at conventional sintering temperatures and sintering times. This lack of microstructural homogeneity coupled with the potential for large pores can often lead to reduced strength and greater dimensional variability during sintering and subsequent heat treatments, if required. A proposed alternative to the FC-02XX materials is a 0.3% molybdenum prealloyed material. This material has nearly identical compressibility compared with the iron copper materials but has the added benefit of a homogeneous microstructure. This paper will focus on a comparison of FC0208 to a 0.3% molybdenum material with 0.8% added graphite. The materials will be compared in both the as-sintered and heat-treated conditions. Additional testing will evaluate the dimensional stability and variability of these two materials in both the as-sintered and heat-treated conditions.
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Sinter-Hardening Response of Leaner Alloy Systems
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PDF (816.2 KB)
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With the recent volatility in raw material prices, powder producers have responded by introducing leaner alloy systems into the marketplace. Examples of these new developments include Ancorsteel® 721 SH and Ancorsteel® 4300L. While leaner alloys are cost effective, the reduced alloy content suggests that hardenability will be reduced. It is important to understand how these leaner alloy systems behave under conditions typically found in sintering furnaces. A quantitative study to assess the hardenability of these alloy systems has been undertaken and a comparison made with more traditional Mo-Ni-Cu alloys. Continuous sinter cooling transformation curves are presented along with apparent hardness and metallographic analysis of various phase fractions.
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Surface Modifications of PM Stainless Steels for Enhanced Corrosion Resistance
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PDF (682.7 KB)
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In general, PM stainless steel parts have inferior corrosion resistance to their wrought counterparts. Furthermore, the variation in surface porosity and oxide layers exhibited by sintered PM parts can lead to a considerable amount of uncertainty in corrosion resistance. In the present study addition of elements, which may modify or segregate to the surface of the powder, leading to enhanced corrosion resistance, are added prior to sintering. The effect of these elements on mechanical properties and corrosion resistance will be studied and compared to grades of stainless steel powder commercially available. The effect of processing variables such as sintering atmosphere and density will also be considered.
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Influence of Chemical Composition and Austenitizing Temperature on Hardenability of PM Steels
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PDF (1 MB)
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The hardenability of powder metallurgy (PM) steels is an important measure of how well certain alloy systems can be used for sinter hardening. Several options are now available for sinter-hardening applications as new alloys have been developed over the last few years. Alloy composition has been optimized to take advantage of rapid cooling in sinter-hardening furnaces while addressing the cost of alloying elements. One of the most widely used tests for hardenability is the Jominy end-quench, where samples are heated into the austenite range and water quenched on one end of the sample, producing a wide range in cooling rate within one sample. The hardenability of different alloy systems was examined by way of Jominy tests and sintering studies. Austenitizing temperature has an important effect on the measured Jominy hardenability of higher molybdenum containing steels. Selection of the austenitizing temperature for these alloy grades therefore has a profound effect on the predicted hardenability of different alloy systems.
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