Effects of the Gas Composition on Internal Oxidation Characteristics of Low Carbon Alloy Steel during Carburizing in Nitrogen-Propane-Air Atmospheres

질소-프로판-공기분위기에서 저탄소 합금강의 침탄시 내부산화 특성에 미치는 가스조성의 영향

This study has been performed to investigate into the internal oxidation characteristics of low carbon steel with respect to the added amount of air in nitrogen-propane atmosphere after gas carburizing for various times at $930^{\circ}C$. The results obtained from the experiment are as follows ; (1) Optical micrographs have shown that the internal oxidation is unlikely to occur in the gas atmosphere without air and that oxidized zone in the outer surface layer is formed in the gas atmosphere with air revealing that the depth of oxidized zone increases with increasing the added amount of air. (2) The formation of internally oxidized zone in the outer surface layer has been found to be inhibited as Ni content increases, i. e, the amount of alloying element increases. (3) The depth of oxidation has been measured to increase with almost parabolically gas carburizing time of up to 6 hours.