| 摘要 |
PURPOSE: An austemper thermal treatment method of ductile graphite cast iron is provided to improve the quality of a product and to degrade defect ratio by transforming a seam structure of a workpiece to a bainite structure as a surface as well as to simplify treatment processes. CONSTITUTION: A workpiece of ductile graphite cast iron is heated until the temperature of the seam portion approaches 850-950°C. The workpiece is quenched in a first salt bath of 200-300°C for 10sec-5min to have the quenching path of the seam portion step away from a pearlite precipitation area. The workpiece is isothermal-transformed in a second salt bath of 300-450°C for 60-90min. Finally, the workpiece is cooled at a normal temperature. Thereby, the seam portion of the workpiece is transformed to a bainite structure the same as the surface structure.
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