Oxide Reduction Processes, Microstructure and Properties of Sintered Chromium Pre-Alloyed Steel

The reduction processes during the sintering of Fe-3Cr-0.5Mo+0.5C pre-alloyed powder using continuous monitoring of exhaust gas composition (CO, CO2, 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) and type of sintering atmosphere (10%H-2-N-2, N-2), respectively. The progress in reduction processes was evaluated by changes in C and O contents and fracture strength values as well. The results were compared with metallographic study of microstructure and fractographic observations of fracture surfaces. The sintering temperature of 1200 degrees C and density <7.0 g/cm(3) resulted in a relative decrease in oxygen content by more than 80%. Higher cooling rate (50 degrees C/min) eliminates re-oxidation during cooling. Higher oxygen content causes weakening of interfaces with residual oxides.