Surface Interactions During Sintering of Chromium-alloyed PM Steels in Different Atmospheres

摘要

Chromium is the one of the most attractive alloying elements in PM steels, nevertheless its high affinity to oxygen during sintering, especially during the heating stage, have to be considered. The type, morphology and distribution of the reaction products on the fracture surface of the pressed and sintered specimens of chromium-alloyed water atomized steel powders were studied by means of high resolution scanning electron microscopy (SEM including EDX). Specimens were sintered in three different atmospheres - nitrogen, nitrogen/10% hydrogen and vacuum. In all materials formation of particulate reaction products containing strong-oxide forming elements such as Cr, Si and Mn was detected. Positive effect of hydrogen on the oxides reduction during heating stage was observed. Preferred location of the inclusions inside the dimples of inter-particle ductile fracture indicates that they originate from fine particulates on the original powder surface that were enclosed during heating stage. Obtained results indicate that oxygen content can be significantly reduced by adjustment proper atmosphere purity/composition or high-temperature sintering.