Influence of Powder Type and Density on Pore Closure and Surface Hardness Changes Resulting from Steam Treatment of Sintered Iron

Abstract

Two types of Höganäs iron powder – sponge, and atomized with very high compressibility (ASC), after compaction to densities of 6·0, 6·4, and 6·8 Mg m⁻³ and sintering under standard conditions were subjected to steam oxidation at 450, 525, and 600°C. The progress of oxidation was studied by measurement of weight gain and hardness. X-ray methods were used to determine the type of oxide present after treatment. During steam oxidation the type of powder has an important influence on the extent of pore closure and on the morphology of the oxide produced. The kinetics of oxidation were always faster for sponge iron than for atomized iron and there was a corresponding increase in the rate of pore closure and in surface hardness. For effective sealing of surface pores components should be of high density and be steam treated at 600°C but for attainment of maximum hardness components should be of low density and be steam treated at 525°C.