| 摘要 |
PURPOSE:To make spheroidal graphite cast iron suitable for use as a material for machine structural parts having high strength and toughness by remarkably increasing the number of graphite grains in the cast iron. CONSTITUTION:Molten metal having the composition of spheroidal graphite cast iron contg. graphite spheroidized by combinedly adding Mg or Mg and Ca and a rare earth element is charged into a casting mold for rapid cooling or a casting mold provided partially with a chilling block. The whole casting is solidified, or white pig iron or mottled pig iron is partially formed by solidification, and when the casting is at a prescribed temp. above the A1 transformation point, the mold is disjointed. After the casting is held for the time required to decompose cementite, it is rapidly cooled at a cooling rate at which pearlite transformation is not caused, and the cooling is stopped once at a temp. above the Ms point. The casting is held at a prescribed temp., or the temp. is slowly lowered, and after the lapse of a prescribed time, the casting is allowed to cool or cooled rapidly to carry out direct austempering.
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