Study on Sulfurizing Treatment of Mild Steel (A Study on the Nitriding Process in Molten Salt, 1st Report)

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  • 塩浴による軟鋼の浸硫窒化処理について
  • エンヨク ニ ヨル ナンコウ ノ シンリュウチッカ ショリ ニ ツイテ

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In order to obtain some information about sulfurizing process, specimens of mild steel (0.13%C) were treated in salt bath containing sodium cyanide, sodium thiosulfate, sodium chloride and sodium carbonate, and then were investigated by means of metallography, X-ray or electron diffraction method and X-ray probe microanalysis. The results obtained can be summarized as follows: (1) The sulfurizing process is only a sort of nitriding process and thiosulfate added has an effect to oxidize and decompose sodium cyanide and to promote, in consequence, the nitriding reaction. (2) The rate of reaction of α-iron with nitrogen was found to follow the parabolic law at temperatures between 500°C and 600°C. (3) It was also found that the rate constant of nitriding reaction was not in linear relation with the reciprocal of the absolute temperature. This fact indicates that the nitrogen concentration at interface varies with temperature. (4) Iron sulfides constituted the compound layer with cementite and iron nitrides such as Fe4N, Fe2N, etc., but the greater part of them were distributed near the surface. (5) In respect of the nitriding reaction, a similar effect is expected to be obtained if sodium cyanate (NaCNO) or potassium cyanate (KCNO) is used as a primary constituent.

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