The Study of Carbon Tool Steel Chromized in Salt Bath
Date Issued
2010
Date
2010
Author(s)
Hsieh, Shao-Tsung
Abstract
In order to enhance the wear-resistance of carbon tool steel and improve the anti-oxidation and anti-corrosion in high temperature atmosphere, the feasibility of chromizing on the surface of carbon tool steel was investigated. This research was divided into two parts. First, the specimen was chromized in a high temperature(above 820℃) borax bath in order to ascertain the relationship between carbide thickness and treatment parameters. Second, the specimen was chromized in a lower temperature (between 600~700℃) chloride salt bath for long time periods. After the above treatments, the properties of chromized specimen were studied through measuring the thickness of carbide layer and the surface hardness distribution, identifying the type of chromium carbide, comparing the ability of anti-oxidation and anti-corrosion of specimens, and examining the chromizing depth. The results obtained were shown as follows:
1. No matter the specimen was treated in a high temperature borax bath or in a lower temperature chloride salt bath, the forming carbide layer was almost the same type, Cr7C3 and Cr23C6. The thickness of carbide layer was related to the proportion of Cr7C3 and Cr23C6 compounds. The thicker the carbide layer was, the more Cr7C3 compound it contained.
2. Between borax bath chromization and chloride salt bath chromization, the chromizing depth of latter would be deeper than the former for the same thickness of carbide layer.
3. The hardenability of chromized specimen would be better than untreated one, so the surface hardness of specimen would be improved.
4. The anti-oxidation of specimen in high temperature atmosphere was dependent on the thickness of carbide layer. There was no direct relationship between the anti-oxidation and the chromizing depth. When the specimen had a thicker carbide layer, it would be provided with a better anti-oxidation ability.
5. The chromized specimen had better resistance to the corrosion caused by nitric acid and sulfuric acid at 40 degrees centigrade, but it could not sustain the corrosion caused by hydrochloric acid. The ability against corrosion by hydrochloric acid; however, could be improved when the specimen had a thicker carbide layer. As the result of no. 4, the anti-corrosion of specimen was dependent on the thickness of carbide layer but independent on the chromizing depth.
Subjects
Chromizing
Chromium carbide
Anti-oxidation
Anti-corrosion
Chromizing depth
Hardenability
Type
thesis
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