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Fine rounded powders preferable for metal injection moulding (MIM) are expensive. This forces MIM makers to recycle green scraps, for example, the runner system and defected green parts. This is particularly necessary for injection moulded small parts where parts are only a small portion of the injection short size. There is very little published data, although recycling feedstock has been practise throughout the industry. This work aims at investigating the effects of recycled stainless steel 630 feedstock content on the density, mechanical properties, dimensional changes and microstructure. Five batches of compounded virgin and recycled feedstock were studies from 0% to 100% recycled feedstock with the increment of 25%. Homogenously compounded feedstock was injected using the same injection condition. Subsequently, green parts were debinded and sintered at 1325°C for 2 hours in argon atmosphere. The results suggest that the green density increases linearly with increasing percentage of recycled feedstock because the polymeric binder was broken down during previous process. However, the sintered density remains nominally constant. As a result, the mechanical properties and microstructure of sintered parts are independent of recycled feedstock content. However, the volumetric and linear shrinkage decreases linearly with the increase in percentage of recycled feedstock. The difference in shrinkage is vital to dimensional control during commercial production. For example, only 4.5% of recycled feedstock can be added to virgin feedstock if a tolerance of ±0.3 mm is required for a 25 mm MIM part.

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As a fundamental study of the Warner process, phase relations in the Cu2S-ZnS-FeS and Cu2S-ZnS-PbS pseudo ternary systems and the Cu-Zn-S and Cu-Zn-X-S (X: Fe, Pb) systems were determined at 1,473 K. In the Cu2S-ZnS-FeS system, the solubility of ZnS in the liquid phase is considerably small at less than Nzns= 0.1 in the high Cu2S and FeS composition ranges. The solubility of Cu2S in the solid solution of sphalerite (Zn; Fe, Cu) S is also considerably small when conjugated with the high Cu2S melt. In the Cu2S-ZnS-PbS system, the solubility of ZnS in the liquid phase is around Nzns= 0.1 in the low composition range of PbS. The Raoultian activity coefficients of ZnS in these pseudo ternary systems at 1,473 K, which were determined from the obtained phase relation data, are very large at about 10. In the Cu-Zn-S ternary system, a two-phase region consisting of the L1 alloy phase rich in copper and the L2 matte phase exists in a considerably wide composition range from Nzn = 0 to about 0.2. When 3.4, 4.3 or 5.5 mole % Fe is added to the Cu-Zn-S ternary system, the range of the two-phase region of (L1 + L2) in the quaternary system is wider than that in the Cu-Zn-S ternary system. While, when 0.8, 1.5 or 2.4 mole % Pb is added to the Cu-Zn-S ternary system, the range of the two-liquid region does not change with the lead content. The distribution ratios of iron, lead, arsenic, antimony and silver in the matte (L2) against the alloy (L1) in