Diffusion-alloying sintering of Cr–Mo pre-alloyed iron powders with carbon: The effect of the carbon introduction method on the sinter’s properties

The influence of the carbon introduction method on the microstructure and the mechanical properties of sinters produced from iron-based powders by diffusion-alloying sintering has been studied. Two methods of carbon introduction were tested: (1) Premixing of the base powder with graphite, and (2) Coating of the base powder with a carbon-containing substance. The results obtained could be summarized as (1) The microstructure and the mechanical properties depend on the method of carbon introduction; (2) The sinters produced from coated powders possess finer micro-structure, improved homogeneity, and in two out of three of the studied compositions, better mechanical properties. Based on the results obtained, a reasonable assumption was made that the method of carbon introduction affects the dissolution rate of the carbon additive, thus affecting the micro-structure and the mechanical properties of the sinter.

The Effect of Powder Ball Milling on the Microstructure and Mechanical Properties of Sintered Fe-Cr-Mo-Mn-(Cu) Steel

The effect of ball milling powder mixtures of Höganäs pre-alloyed iron Astaloy CrM, low-carbon ferromanganese Elkem, elemental electrolytic Cu and C-UF graphite on the sintered structure and mechanical properties was evaluated. The mixing was conducted using Turbula mixer for 30 minutes and CDI-EM60 frequency inverter for 1 and 2 hours. Milling was performed on 150 g mixtures with (in weight %) CrM + 1% Mn, CrM + 2% Mn, CrM + 1% Mn + 1% Cu and CrM + 2% Mn + 1% Cu, all with 0.6%C. The green compacts were single pressed at 660 MPa according to PN-EN ISO 2740. Sintering was carried out in a laboratory horizontal furnace Carbolite STF 15/450 at 1250°C for 60 minutes in 5%H2 – 95%N2 atmosphere with a heating rate of 75°C/min, followed by sintering hardening at 60°C/min cooling rate. All the steels were characterized by martensitic structures. Mechanical testing revealed that steels based on milled powders have slightly higher mechanical properties compared to those only mixed and sintered. The best combination of mechanical properties, for ball milled CrM + 1% Mn + 1% Cu was UTS 1046 MPa, TRS 1336 MPa and A 1.94%.