Effect of Atmosphere Composition on the Surface Interactions during Sintering of Chromium-alloyed PM Steels

Paper in proceeding, 2011

Chromium is extensively used today in PM steels, nevertheless its high affinity to oxygen requires strict atmosphere control during the sintering process. Nitrogen-based atmospheres with different hydrogen contents (0, 3 and 10%H2) were used during sintering of chromium-alloyed water atomized steel powders with continuous atmosphere monitoring in the sintering furnace. Fracture surface of pressed and sintered specimens were studied using high resolution scanning electron microscopy (HR SEM) equipped with EDX in order to investigate the development and characteristics of the reaction products formed. The investigation was complemented with thermal analysis using DTA/TG. The formation of particulate reaction products containing strong-oxide forming elements such as Cr, Si and Mn was detected for all conditions. Enhanced oxide reduction was observed in samples processed in hydrogen containing atmospheres independently of the actual content. Obtained results show that significant reduction of the oxygen content can be achieved by adjusting the atmosphere purity/composition.