Zinc stearate (ZnSt) and N,N'-ethylene bis (stearamide) (EBS) are conventional lubricants for powder metallurgy. While an iron powder mixture containing ZnSt exhibits excellent flowability, its ejection property was found to be inferior to that of a mixture containing EBS. The main purpose of this study was to identify the reason why EBS is superior to ZnSt in the ejection property. To achieve this objective, we attempted to evaluate the "lubricity" and "extrusive property" of the two lubricants separately, as these properties appear to determine their ejection properties. Lubricity was investigated by sliding tests on a uniform lubricant film. The friction coefficient of EBS obtained in this test was larger than that of ZnSt. The extrusive property, which means the ability to fill the gap between the compact and the die wall, was evaluated by an X-ray analysis of the compact surfaces. The results of those measurements indicated that the extrusive property of EBS was greater than that of ZnSt, resulting in the better ejection property.

A new segregation-free iron-based powder mixture with excellent lubricity was developed. The most notable feature of this new powder mixture is superior lubricity compared with mixtures containing conventional lubricants such as zinc stearate. In addition, clean sintered surfaces can be obtained because the new mixture does not contain zinc stearate. These features will contribute to improvement of product quality and the yield rate of sintered parts. The mechanism of the excellent lubricity of this powder mixture was investigated by SEM/EDX analysis of green compact surfaces. The analysis indicated that the ejection force of the compacts made of this powder mixture was reduced by concentration of the lubricant between the compact and the die wall surface during the compaction process.

This study aims to obtain the superior mechanical properties of Mo diffusion-bonded alloyed steel by the optimum combination of processes: primary-sintering (PS), cold-forging (CF), heat treatment (HT) and shotblast. In our previous research, it was found that the fracture of sintering connections, namely, micro-cracks occurred on the surface layer of high-density specimens in addition to the work hardening on materials, which decreased both the impact energy and the bending strength. Also, since the optimum heat treatment leads the diffusion bonding of the pressurized cracks in the surface layer, the microstructure could be reformed. In this study, it was found that the 0.4 mass%Mo-steel powder had both the highest densification and deformability among the powders of 0.4, 1, 2 and 4 mass%Mo without precipitation of the unneeded ternary molybdenum carbide Fe3Mo3C. Also, when sintered specimens were cold-forged, the impact waveform of those showed clearly effects of both the work hardening and the damage of the microstructure. Finally, both the superior fatigue strength and the wear resistance were implemented with the proper processes to 0.4 mass%Mo sintered steel such as a second sintering, vacuum carbonitriding heat treatment and shotblast. Obtained properties were equal to or more than those of wrought steel SCr420H.

Iron-based powder mixtures for the powder metallurgy process commonly contain solid lubricants. Both zinc stearate (ZnSt) and N,N'- ethylenebis(stearamide) (EBS), which are conventional lubricants in this field, exhibit similarly adequate lubrication performance. However, their effects on powder mixture flowability are different; that is, powder mixtures containing ZnSt exhibit better flowability than ones containing EBS. In this study, the adhesive and frictional properties of five surface combinations (iron -iron, iron-EBS, iron-ZnSt, EBS-EBS, and ZnSt- ZnSt) were investigated using surface force and resonance shear measurements. The adhesive forces obtained for all combinations were almost the same. On the other hand, the frictional forces for the iron-EBS and EBS-EBS combinations obtained from resonance shear measurement were larger than the others under low applied loads (<ca. 1.0 mN). This result suggests that the frictional properties of lubricants under low applied loads determine the powder mixture flowability.

Iron powder is one of the “long-seller” material because it has been used since B. C. 300. Iron powder is mainly used for powder metallurgy in recent years. On the other hands, it is also used for the functional applications by using chemical reaction, such as body warmer, deoxidant and agricultural application. There are the several methods to produce iron powder, and reduced and water atomized iron powders are mainly used for the powder metallurgy due to their good compactibilities. In this paper, the details of production process of iron powders containing alloyed steel powders in JFE steel, which produces both reduced and water atomized iron powders, are described. In addition, the powder characteristics of these two kinds of iron powders are also described. The expansion of functional applications such as additive manufacturing process or magnetic cores is expected in the future, thus additional improvement of iron powders quality will be required.

Effects of graphite additive contents and processing parameters on the mechanical properties of sintered and case-hardened compacts made of molybdenum hybrid-alloyed steel powder have been investigated.High tensile strength and impact value were obtained in the conditions of the medium internal carbon content, higher sintering temperature, lower carbon potential or shorter carburizing time.The mechanical properties are deteriorated due to increasing hard martensite phases with high carbon content.It is believed that the reduction of these mechanical properties are mainly caused by increasing of brittle fracture by an internal notch effect of the pores, because the hard martensite phase have a high notch sensitivity.

A newly developed Ni-free pre-alloyed steel powder, Fe-0.5 %Cr-0.2 %Mn-0.2 %Mo (JIP® 5CRA) shows a rotating bending fatigue limit of 510 MPa after compacting, sintering and case-hardening process. This is approximately 40 % higher than that of a case-hardened sintered steel based on a conventional diffusion bonded steel powder, Fe-4 %Ni-1.5 %Cu-0.5 %Mo (4Ni). This is attributed to the higher compressive residual stress of the 5CRA based material. In spite of the higher fatigue limit, its tensile strength is lower than that of the 4Ni based material. The difference in the microstructural transformation behavior is a possible cause of this reverse phenomenon.

Effects of graphite additive contents and processing parameters on the mechanical properties of sintered and case-hardened compacts made of molybdenum hybrid-alloyed steel powder have been investigated. High tensile strength and impact value were obtained in the conditions of the medium internal carbon content, higher sintering temperature, lower carbon potential or shorter carburizing time. The mechanical properties are deteriorated due to increasing hard martensite phases with high carbon content. It is believed that the reduction of these mechanical properties are mainly caused by increasing of brittle fracture by an internal notch effect of the pores, because the hard martensite phase have a high notch sensitivity.