Effects of Nitrogen Uptake during Sintering on the Properties of PM Steels prealloyed with Chromium
EURO PM2001, in Nice, France. Author: Ola Bergman. Powders prealloyed with chromium have recently been introduced on the market for sintered steels. Due to chromium’s high affinity for oxygen, sintering is performed in nitrogen/hydrogen-based atmospheres with low oxygen partial pressures. However, chromium also has a high nitrogen affinity, which will lead to nitrogen uptake by the steel during the sintering process. The effects of nitrogen uptake during sintering have been studied for a water atomised iron powder fully prealloyed with 3% chromium and 0.5% molybdenum. Test specimens with varying graphite additions and green densities were sintered for 30 minutes at 1120°C in a mixture of nitrogen and hydrogen (90%N2/10%H2). Different cooling rates after sintering were applied. Evaluation of the sintered specimens included metallography, phase analysis, chemical analysis, and mechanical testing. Based on the evaluation results, conclusions are drawn regarding how nitrogen uptake and nitride formation during sintering affect the material properties.