Sinter hardening of steel powders in furnaces equipped with fast cooling units represents a cost effective way to manufacture components with high strength and high apparent hardness without the need for secondary operations. However, due to microstructural transformations allowing achievement of high hardness after sintering, the dimensional control of components is of paramount importance. For this reason, Rio Tinto Metal Powders and Metaldyne, a powder producer and a part manufacturer respectively, have worked together over the last few years in order to better understand the behavior during sintering of ATOMET 4601 and ATOMET 4701, two widely used sinter-hardening powders. Extensive studies were carried out under production conditions with the ultimate goal to improve the dimensional accuracy of components and to reduce as much as possible the cost related to quality issues resulting from dimensional variation. Some of the key factors related to the materials and to the sintering process, as well as their impact on dimensional change, are discussed in this paper. In the first part, the effect of mix formulation and type of additives on dimensional change occurring during sintering is evaluated. In addition, the optimized mix formulations obtained at the end of the first part and their properties are summarized. In the second part, the effect of sintering conditions on dimensional consistency is presented. In particular, the improvement in dimensional consistency achieved through optimization of sintering conditions in mass production is discussed in detail. In conclusion, it was found that both materials and processing conditions must be optimized in order to maximize the benefits offered by the sinter hardening technology.
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