20th International Forgemasters Meeting - IFM 2017

High Carbon Forged White Cast Iron Rolls are manufactured using a hot stage of as cast ingot till final forging shapes in order to avoid a brittle fracture of this material. The Forgings should be cooled for the first time to RT through a spheroidal heat treatment. During a continuous forging process carbides grow alone grain boundary and inside of grains. The special carbides are formed rod or disc and grow to bigger size as the Widmanstätten Carbide. The structure with grown disc like cementite indicates the weakness on impact properties. Therefore, rolls with over 2.2%C are not manufactured depending on existence of the uncontrolled this structure. In order to achieve a good wear resistance of high carbon level forged roll, the method how to erase this carbide structure was investigated in the 2.2%C NT roll and others. The Widmanstätten cementite grows only in the special thermal gradient that carbide embryo should be located in austenite matrix alone grain boundary or beside of ledeburite in the forging process. If the generating condition and growth condition of carbide nucleus are removed, the Widmanstätten cementite will be disappeared. The heat treatment for this purpose is pearlite treatment. In this treatment, cementite embryos are located of great number in grain. Forging and re-heating of forging process, return to austenite always remains the cluster of carbon, then in case of cooling cementite grain will be grown always. Pearlite transformation is the key technology to disappear the Widmanstätten carbide. Adopting the internal heat treatment, we are succeeded in making the large size of high C% NT rolls in manufacturing process and in applications. 　　　　　　　　　　　　　　　　　　　　　　　　　　　 　　　END