Processing Conditions And Reduction Of Oxides During Sintering Of Chromium Pre-Alloyed Steel

Artikel i vetenskaplig tidskrift, 2012

Oxide reduction processes and their temperature intervals during sintering of Fe-3Cr-0.5Mo pre-alloyed powder have been identified using continuous monitoring of processing gas composition (CO, CO2, H2O). Their interpretation is in relation to density (6.5-7.4 g·cm-3), sintering temperature (1120 and 1200°C), heating and cooling rates (10 and 50°C/min), carbon addition (0.5/0.6/0.8%), and type of sintering atmosphere (10%H2-N2, N2), respectively. The progress in reduction processes was evaluated by the relative change in oxygen and carbon contents and related to resultant fracture strength. Higher sintering temperature (1200°C) and low density (6.5 g·cm-3) result in a relative decrease of oxygen content by more than 80%. Higher cooling rate (50°C/min) eliminates re-oxidation during cooling. The reducing ability of the nitrogen atmosphere can be improved by sintering in a graphite container. High density of 7.4 g·cm-3, achieved by a pressing/re-pressing method, causes a slowing down of the reduction processes. In terms of optimizing strength, the carbon content in this sintered steel should not be higher than ~0.45%.