STP979

    Effects of Residual Elements in Heavy Forgings: Past, Present, and Future

    Published: Jan 1988


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    Abstract

    In the past, steelmakers of heavy forgings had considerable flexibility with regard to materials specifications. Today there is increasing emphasis on clean steels with extremely low residual element content, particularly with respect to heavy forgings for high-temperature applications. The clean steels are of interest primarily due to their improved ductility, toughness and uniform mechanical properties. Future materials specifications can be expected to reflect the current interest in “superclean” steels. However, the shift to clean steel specifications has greatly reduced the steelmaker's processing options for producing such steels. In addition, in some cases the clean steels have created new problems for the forgemaster (e.g., machining and meeting mechanical property and NDE specifications).

    This paper provides a steelmaker's perspective on the role of residual elements in heavy forgings. The paper also contains a summary of some of the historical events which led to the need for reduction in residual element levels. Innovations which have allowed the steelmakers to meet the challenge for lower residual levels are also discussed. The forging grades which are given focus include: Ni-Mo-V, Ni-Cr-Mo-V, Cr-Mo-V, and 12Cr-Mo-V-Cb-N turbine rotor steels and 2¼Cr-1Mo, A508 Class 2, and A508 Class 4 pressure vessel steels. The role of traditional residual elements, such as P, S, Cu, Sb, As, Sn, Ca, Al, H, O, N, B, and rare earths, as well as the current interest in maintaining very low Mn and Si, are discussed as they relate to steelmaking, forging, heat treatment, machining, and service life. Residual elements as they relate to segregation, inclusion type, overheating, hardenability, temperability, temper embrittlement, creep embrittlement, hydrogen flaking, and stress corrosion cracking are also discussed.

    Keywords:

    heavy forgings, residual elements, clean steel, inclusions, hardenability, segregation, temper embrittlement, creep embrittlement, reheat cracking, hydrogen flaking, stress corrosion cracking, turbine rotors, pressure vessels, steelmaking, ladle refining furnace, electroslag refining


    Author Information:

    Bodnar, RL
    Senior Research Engineer, Research Department, and Director of Technology and New Product Development, BethForge, a division of Bethlehem Steel Corporation, Bethlehem Steel Corporation, Bethlehem, PA

    Cappellini, RF
    Senior Research Engineer, Research Department, and Director of Technology and New Product Development, BethForge, a division of Bethlehem Steel Corporation, Bethlehem Steel Corporation, Bethlehem, PA


    Paper ID: STP29124S

    Committee/Subcommittee: E04.05

    DOI: 10.1520/STP29124S


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