고규소 구상흑연주철의 박육화 및 고온산화특성에 관한 연구

Abstract

This paper was studied on microstructure, mechanical properties and high temperature oxidation characteristics of Hi-Si-Mo and Hi-Si-Mo-M ductile cast iron for exhaust manifold. Hi-Si-Mo-M was developed by optimum alloy design and casting design. Exhaust manifold prototype was fabricated from Hi-Si-Mo-M and was obtained to effect of 0.77kg weight reduction. The microstructural characteristics of Hi-Si-Mo and Hi-Si-Mo-M were similar and graphite nodularity was 83%, 92% respectively. Tensile strength of Hi-Si-Mo and Hi-Si-Mo-M were 663.5, 674.4Mpa and brinell hardness(HB) of them was 235.3, 243.9 respectively. Hi-Si-Mo and Hi-Si-Mo-M had a parabolic weight gain behavior in high temperature oxidation. Weight gain of Hi-Si-Mo and Hi-Si-Mo-M after isothermal oxidation test in air at 800℃ for 72hours were 11.7mg/cm2, 11.4mg/cm2 respectively. Weight gain of Hi-Si-Mo and Hi-Si-Mo-M after isothermal oxidation test in air at 900℃ for 72hours were 3.8mg/cm2, 3.2mg/cm2 respectively. Kp(Parabolic growth rate) values of Hi-Si-Mo-M were 5.8×10-3mg2cm-4sec-1 lower than Hi-Si-Mo at 800℃ Kp values of Hi-Si-Mo-M were 2.7×10-3mg2cm-4sec-1 lower than Hi-Si-Mo at 900℃. Oxidation layers of Hi-Si-Mo and Hi-Si-Mo-M were divided into external and internal layer. Fe concentration showed higher in external layer than internal layer. Si concentration showed high in interface of matrix and internal layer.