| 摘要 |
PURPOSE:To generate a desired ferrite structure without the needs for separate ferrite heat treatment by a method in which a spherical graphite cast iron pipe containing a specific amount of Si is molded and then subjected to a heat treatment involving heating and cooling under specific conditions. CONSTITUTION:A spherical graphite cast iron pipe containing 2.3-2.8% Si is cast by a casting method, removed from the casting mold as it is in high-temperature state, cooled to 700-750 deg.C, right below the transformation point Ar1, and then charged into a heat treatment furnace, where the pipe is heated to about 850 deg.C, right above the transformation point Ac1 to convert its pearlite structure into austenite. Then, the pipe is gradually cooled at 700-650 deg.C at a cooling rate of about 10 deg.C (+ or -2.5 deg.C)/min or less and then air-cooled. Thus, the retention time of the pipe at a maximum holding temperature of 850 deg.C can be greatly shortened. |
