Abstract
Plates of SUS 304 up to 4.8 mm in thickness were quenched in an oil after having been annealed at temperatures from 1173 to 1473 K for 1.8 ks in 5.33 Pa. Surface brightness was measured by an optical microscope equipped with a silicon photocell. The carburization occurred on the plate surface oil-quenched from temperatures above about 1300 K. The case depth increased with increasing quenching temperature and increasing thickness of plate. The carburization brought about deterioration in corrosion resistance (in boiling 65% nitric acid) and in brightness which was caused by the formation of carbides (M23C6, M7C3) and/or by sooting. The two-stage cooling, that is, oil-quenching subsequent to the gas-cooling to about 1200 K is proposed as a method to prevent the carburization. No carburization was observed on the two-stage cooled plates. This cooling method extremely improved the brightness and corrosion resistance of SUS 304 plates. A comparison in the calculated cooling rate between the oil-quenching and the two-stage cooling showed little difference. A practical application of the two-stage cooling method was made. All the results showed that it was possible to prevent the carburization during oil-quenching by the two-stage cooling.
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More From: Journal of the Japan Institute of Metals and Materials
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