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Abstract
This paper investigated the oxidation behavior of iron powder. Iron powder with different oxygen content was prepared by various ways, the microstructure and mechanical properties of sintered steels made from oxidized iron powder was studied. The results showed that iron powder with different oxygen content exerted an influence on compressibility and green strength of blended powder, the mechanical properties of sintered steels declined. Furthermore, with the increasing of oxygen content of iron powder, the pearlite content in sintered steels decreased, and pearlite content of core was lower than that of surface.
Iron powder with low oxygen content is favorable in powder metallurgy application in order to improve compressibility and avoid consumption of carbon in the sintering process.1,2 In fact, because of its high specific surface area, chemical activity and nonmetallic impurities, combined with ocean traffic, long-term storage and high humidity storage environment, iron powder is easily oxidized. The oxidized iron powder is harmful to sintering. Therefore, effect of oxidation of iron powder on properties of PM parts is studied in this paper.
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1. Experimental
The iron powder of 100 mesh particle size having a low oxygen content of 600 ppm was used in this research work (Fig.1). Iron powder was oxidated at 100°C~200°C in dry air and high humidity air respectively in order to obtain different oxygen content, as shown in Fig. 2. The effect of oxidized iron powder on its physical properties was studied. The oxidized iron powder was mixed with Cu, Ni and C according to composition listed in Table 1. Testing samples were compacted at 600MPa, sintered at 1120°C in 90/10 N2/H2 for 20 minutes. Hardness and transverse rupture strength were measured respectively.
2. Results and Discussion
2.1 Oxidation of pure iron powder
When heated in baking oven at 100-200°C in dry air, the surface of iron powder would be oxidated by oxygen slowly and oxide layer forms on the surface of iron powder. On this condition, the governing factor of oxidation rate is diffusion.3 Therefore, after long-time oxidation the oxygen content slowly increased to only 0.13%.
When heated in high humidity air at 100-200°C,a very thin...