Abstract
The decarburization behaviour during the sintering of metal-injection-moulded 420 stainless steel was investigated. Particular attention has been paid to the decarburization mechanisms and carbon distribution of parts sintered at different temperatures. The results indicate that the loss of carbon content occurs mainly through the reduction of surface oxides of powder particles or reaction with the atmosphere. Depending on the densification level, the sintering decarburization is separated into two stages. Below 1200 °C, decarburization occurs at the powder particle surface. The surface oxides react with the amorphous carbon or residual organics to pose the metal surface. At this time, the carbon content distribution of the sintered body is similar to that of the as-debound sample. The reduction of surface oxides promotes sintering. At 1200 °C, the densification speed is higher in the centre region of the sample, where the interconnected pores close and the second stage of decarburization takes place. At temperatures above 1200 °C, carbon atoms in the inner layers must migrate to the surface to react with the atmosphere. The decarburization speed is reduced and the carbon content distribution of the as-sintered part is similar to that of the dense decarburized part.
Highlights
Metal injection moulding (MIM) is a novel net shape method for producing stainless steel parts with high performance and complex shapes [1,2]
The carbon content may deviate from the standard composition, which is attributed to the decomposition of the residual organic and chemical reaction of carbon with the oxygen in the metal and atmosphere [3,4]
3 shows oxygen and carbon content of samples sintered at different temperatures
Summary
Metal injection moulding (MIM) is a novel net shape method for producing stainless steel parts with high performance and complex shapes [1,2]. Metals 2020, 10, 211 surface regions; the surface exhibits a higher carbon content than the inner region These compositions react with the oxygen or moisture in the atmosphere and escape through pores. Proper carbon content could enlarge the sintering temperature range (within the γ + MC + L phase); a sample with a high density and low grain size could be obtained. In order to overcome the drawbacks of heterogenous carbon content, a further understanding on the decarburization mechanism under different temperature ranges is required. The decarburization mechanism under different temperatures and the carbon distribution in the sintered parts were analysed. On the basis of the experimental work, theoretical models were proposed to disclose the effects of sintering temperatures on the decarburization rate and carbon distribution. The findings of this work could provide a theoretical base for the large-scale production of MIM stainless steel
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