オーステンパー処理球状黒鉛鋳鉄のべイナイト変態における炭素の挙動

抄録

  With a view of investigating the bainitic transformation of spheroidal graphite cast irons and a high silicon steel especially the behavior of carbon in transformation, the simultaneous detections of the differential thermo-analysis and dilatometric measurement of specimens on the first stage of isothermal holding after quenching into metallic bath were performed by using a specially designed quenching and holding apparatus for austempering. The change of volume of retained austenite during holding various time at given temperatures for various time after quenching was investigated. The expansion caused by bainitic transformation consisted of two different stage of transformation both in spheroidal graphite cast iron and high sillicon steel. Moreover, the difference in the carbon content in each retained austenite matrices exists in these two irons and steel. Besides, the potentio-static electrolytic etching with chromic acid shows the distinct difference in microstructure of the bainitic ferrite, martensite and retained austenite. Also it has been recognized that the close relation exists between peak value in thermal transformation and carbon content in high sillicon steel.