| 摘要 |
PURPOSE:To easily improve the machinability of the products in which a cast iron-type difficult-to cut material is used, by regulating the thickness in the required part of a cast iron-type difficult-to-cut material to a proper value, applying the internal chill casting of a steel member with superior machinability to the above-mentioned part and then subjecting the above to austempering treatment. CONSTITUTION:In a product prepared by using a cast iron-type difficult-to-cut material such as austemper spheroidal graphite cast iron, etc., a steel member with superior machinability is cast, as a part of the product, integrally with the part requiring machining by means of a internal chill casting method. At this time, the thickness in the part, requiring machining, of the above steel member is regulated to >=1/5 the thickness in the cast-iron part adjacent to it, and then the above-mentioned internal chill casting is applied. Subsequently, the above product is heat-treated by means of austempering treatment. By this method, the above steel member is integrated with the cast-iron part into one and the same structure but it maintains easy-to-cut characteristic without being carburized at the time of casting and heat treatment, so that machinability of the above-mentioned product can be effectively improved.
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