To prevent crack propagation to a pipe even though cracks or the like generate in a cast steel product main body by casting-in a cooling double pipe, having an aluminum diffusion coated layer applied a calorizing treatment to the inner surface of the inner pipe and the outer surface of the outer pipe, in the non-fused state.
The cooling double pipe 2 is composed of the concentric inner pipe 3 and outer pipe 4 and a cooling water is made to flow through the inner pipe 3. The aluminum diffused layer 5, 5' by the calorizing treatment are formed in the inner surface of the inner pipe 3 and the outer surface of the outer pipe 4, whereby the excellent high temperature oxidation resistance and corrosion resistance are provided in the cooling double pipe 2. Since the alumina coating by oxidation is formed on the outer surface of the aluminum diffusion coated layers 5, 5' to prevent the invasion of an oxygen atom, high temperature oxidation resistance is obtained. Since the alumina film has a high melting point and bad wettability with molten metal, it is not brought into contact with molten metal and cast-in in the non-fused state. By this way, even though cracks generate in the cast steel product, crack propagation to the double pipe 2 is prevented, and water leakage and corrosion of the cast-in cooling double pipe 2 are prevented.
OGURO MITSURU
YOMO KEIICHI
KOBAYASHI TATSUHIKO
KANENAGA MASAAKI
MAEZATO MASAO
SINTOKOGIO LTD