Some Properties of Sintered Chromium Steel

In order to find the best way of adding Cr to sintered ferrous material, the authors investigated the fundamentals of the manufacturing process and the properties of the sintered chromium steel of the system Fe-Cr-C. Three kinds of chromium containing powders, metallic chromium, ferro-chromium and σ (sigma)-phase Fe-Cr powders, were used as a source of chromium for Fe-Cr-C alloys. The mixtures of iron powder, chromium-containing powder and carbon were compacted at 5t/cm2, pre-sintered for lhr at 750°C and sintered for lhr from 1100 to 1320°C. The results obtained are as follows.(1) Sintered chromium steels made from the σ-phase powder have the best properties of those from three kinds of chromium-containing powders. For example, the Fe-5% Cr-0.5%C alloy from σ-phase powder which was sintered at 1300°C has sintered density of 7.45g/cm3, tensile strength of 95kg/mm2, hardness of 110 HRB and elongation of 1.0%. The metallographical investigation showed that this alloy has a homogenized martensitic microstructure.(2) The properties of sintered chromium steel made from σ-phase powders, containing 1.5-10.5% chromium and 0-1.0% carbon are as follows: the sintered densities range from 7.36 to 7.50g/cm3, the tensile strength varies from 50 to 110kg/mm2, and the elongation from 0.6 to 120%.Microstructures of the as-sintered alloys depend on the Cr-content. The martensitic structures are found for more than 5% Cr. This phenomenon can be attributed to the self-hardenability of the Cr element. The properties the above mentioned alloys are in good agreement with those of ordinary cast wrought chromium steel.