Martensite Transformation of Carbon Steel Powders Produced by Electro-Spark Machining

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  • 放電加工の際に生じた炭素鋼粉末のマルテンサイト変態
  • ホウデン カコウ ノ サイ ニ ショウジタ タンソ コウフンマツ ノ マルテンサイト ヘンタイ

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Abstract

Fine particles of carbon steel containing 0.9 and 1.4% carbon were made by electro-spark machining, in which a simple R-C resonance circuit was used, the voltage being 100 volts, R 100 Ω and C 2 or 16 μF. The insulating liquid was transformer oil or ethanol. The size and structures of the produced particles were examined by means of electron microscopy and X-ray diffraction with the following results: The size was about 0.01 μ in diameter, which was independent of the condition of machining and of the carbon content. In the Debye-Scherrer photographs, a stronger but somewhat diffused pattern of austenite was seen while that of martensite was weaker compared with the case of bulk steels. This fact indicates a suppression of martensite transformation, which is interpreted to be due to the following two effects: The surface effect coming from the small particle size of about 0.01 μ, and the effect of the cooling with an extremely rapid cooling rate probably from a very high temperature as approximating boiling point of steel.

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