The use of Metal Injection Moulding (MIM) continues to expand to cover an increasingly varied range of components across a multitude of advanced applications. One of the most versatile alloys currently used in MIM is 440C martensitic stainless steel as it offers a combination of high hardness and good corrosion resistance. These characteristics make the alloy suitable for applications including automotive engine parts, medical instruments and a range of machine tool components. Achieving reproducible properties and consistent hardness requires close control of carbon levels in particular.
There are a number of variants on 440C in use today: some with enhanced carbon levels to achieve higher hardness and some with additions of niobium (Nb), which is claimed to increase the sintering process window for the alloy. In this study, we examine the sintering behaviour at different temperatures of 440C and 440C + Nb made by prealloy and master alloy routes. Differences in hardness and mechanical properties are discussed with reference to chemistry and microstructures of sintered parts.