STP1042

    Production of Super Clean Steels—Deoxidation Mechanism During Ladle Refining

    Published: Jan 1989


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    Abstract

    Investigations carried out by several institutions under Projects RP559, RP2060, RP1403, RP2741 for the Electric Power Research Institute, Palo Alto, CA, resulted in a 3.5% NiCrMoV steel completely free from temper embrittlement as a material for low pressure rotors but also for combination proberty rotors, for example, integral high-pressure low-pressure (HILP) rotors for future steam plants. This steel contains very low percentages of residual elements including sulfur and phosphorus, and its contents of aluminum, silicon, and manganese are also very low.

    The main problem in producing such a steel on an industrial scale is gaining a sufficiently low oxygen content as a precondition for successful desulfurization and high cleanliness. This situation is only possible by applying ladle refining techniques. Two model rotors of this “super clean steel” were produced and tested. The tests proved complete resistance to temper embrittlement.

    As an approach for further process development and for the economic production of “super clean steels,” the mechanism governing the deoxidation was investigated in detail by means of trial heats. The influences of the composition of process slags and the influence of the ladle linings were examined. The deoxidation was found mainly to be based on steel-slag reactions. The minimum oxygen content achievable in the steel is limited by interactions between ladle linings and melt, which create a dissociation of the linings and an oxygen supply to the liquid steel.

    Keywords:

    forging, steam turbine, melting, temper embrittlement, 3,5% NiCrMoV steel, turbine rotor forging, ladle refining, slags, ladle linings, desulfurization, deoxidation


    Author Information:

    Meyer, W
    Head, Vereinigte Edelstahlwerke AG, Kapfenberg,

    Kucharz, A
    Manager, Melting Shop, Vereinigte Edelstahlwerke AG, Kapfenberg,

    Hochörtler, G
    Head, Vereinigte Edelstahlwerke AG, Kapfenberg,


    Paper ID: STP24569S

    Committee/Subcommittee: A01.06

    DOI: 10.1520/STP24569S


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