알루미나이징처리한 12Cr 내열강의 내산화성에 미치는 미세조직의 영향

Abstract

The effects of aluminizing and diffusion treatment on the formation of alloy layer in 12Cr heat resisting steel were examined and then oxidation properties were investigated. The conclusions are as follows: With increase of aluminizing treatment temperature and time, thickness of alloy layer increased. When diffusion treatment was carried out after aluminizing treatment, thickness of alloy layer was increased. Moreover, it was increased as well with increasing the diffusion temperature and time. The Thickness of heat resisting steel with the microstructure of martensite is thicker than that of heat resisting steel with the microstructure of martensite and ferrite. When either aluminizing treatment or diffusion treatment after aluminizing treatment is carried out, alloy layer with over Hv 850 which was consisted of Al13Fe4 chemical compound was obtained. As substituted Al for Cr in accordance of aluminizing and diffusion treatment, Al concentration increased in alloy layer while Cr concentration decreased. Al concentration in alloy layer of aluminized specimen increased as location goes inner part. In contrast, Al concentration decreased in alloy layer of aluminized and diffusion-treated specimen. A degree to increase the thickness of alloy layer induced aluminizing treatment time and diffusion treatment time after aluminizing increased with increasing the temperature of aluminizing and diffusion treatment. When diffusion treatment after aluminizing treatment is carried out, according to the boundary between alloy layer and matrix cracks layer were formed in alloy. Besides, more cracks were formed with increasing the diffusion temperature and time. When alloy layer is formed due to either aluminizing treatment or diffusion treatment after aluminizing treatment, oxidation resistance showed the increase of over 35% in air atmosphere and over 30% in water vapor compared with untreated specimen. However there was no difference in oxidation resistance of both specimens.