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

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\ub0C), heating and cooling rates (10 and50\ub0C/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\ub0C) and low density (6.5 g·cm-3) result in a relative decrease of oxygen content by more than 80%. Higher cooling rate (50\ub0C/min) eliminates re-oxidation during cooling. The reducing ability of the nitrogen atmosphere can be improved by sintering in a graphitecontainer. 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 behigher than ~0.45%