Parameters Controlling the Oxide Reduction during Sintering of Chromium Prealloyed Steel

Artikel i vetenskaplig tidskrift, 2013

Temperature intervals of oxide reduction processes during sintering of the Fe-3%Cr-0.5% Mo prealloyed powder using continuous monitoring of processing-exhaust gas composition (CO, CO2, and H2O) were identified and interpreted in relation to density (6.5-7.4 g/cm(3)), sintering temperature (1120 and 1200 degrees C), heating and cooling rates (10 and 50 degrees C/min), carbon addition (0.5/0.6/0.8%), type (10% H-2-N-2, N-2), and purity (5.0 and 6.0) of the sintering atmosphere. The progress in reduction processes was evaluated by oxygen and carbon contents in sintered material and fracture strength values as well. Higher sintering temperature (1200 degrees C) and density <7.0 g/cm(3) resulted in a relative decrease of oxygen content by more than 80%. The deterioration of microclimate purity of inner microvolumes of compacts shifted the thermodynamic equilibrium towards oxidation. It resulted in a closing of residual oxides inside interparticle necks. The reducing ability of the N-2 atmosphere can be improved by sintering in a graphite container. High density of 7.4 g/cm(3) achieved by double pressing indicated a negative effect on reduction processes due to restricted replenishment of the microclimate atmosphere with the processing gas. In terms of strength properties, carbon content should not be higher than similar to 0.45%.