Ni基超合金のアーク炉溶解技術

概要

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Daido Steel Shibukawa Plant has developed the melting process for Ni-based alloys, such as permalloys and heat-resisting superalloys, by Electric Arc Furnace (EAF) combined with Vacuum Ladle refining Furnace (VLF) and/or AOD.Results obtained in the running operation are summarized as follows:(1) DecarburizationThe rate of decarburizing from liquid Ni-based superalloys in AOD process is proportional to fc (carbon activity coefficient in Fe-based low alloy steel) as well as Fe-based steel.In case of Ni-Cr-C alloys, [C] can be removed to about 0.03% by O2 blowing in EAF in spite of high [Cr] content as 20%Cr.(2) Nitrogen removalThe behavior of nitrogen removal in AOD process can be calculated by the sum of Ar gas volume and CO gas volume generated in decarburization as well as stainless steel. The rate of nitrogen removal increases with the increase of fN (nitrogen activity coefficient) in Ni-based superalloys.It is also effective for nitrogen removal in EAF or VLF to use CO boiling caused by the decarburizing reaction.(3) Merits of EAF melting processCompared with VIF melting process, the production cost is reduced and the productivity is increased because of the high flexibility of this process.The superalloys melted by this process are supplied as the electrodes for Electro-Slag Remelting or Vacuum Arc Remelting, and the ingots for forging and/or rolling.
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