抄録
Nine commercial stainless steels were heated at temperatures from 900 to 1150°C for times up to 250 min in vacuums of 5.33 and/or 1.33 Pa. The steels heated were die cooled in the vacuums to prevent their surfaces from being stained with quenchants. Brightness of the surfaces was measured by use of an optical microscope equipped with a silicon photocell. The effects of temperature, heating time, and vacuum were investigated. An observation of the surfaces showed that an oxide film once formed during heating disappeared again with increasing temperature and/or heating time, resulting in the marked increase in surface brightness. A mechanism of the disappearance, that is, a reduction of the oxide film by solute carbon in the steels, is presented on the basis of a thermodynamical analysis and of experimental evidence, by which the results obtained through the experiments on several stainless steels can be fully interpreted.
