| Summary: | 碩士 === 長庚大學 === 機械工程研究所 === 92 === In this study we investigated the microstructure and electrochemical behavior of the oxides developed on high carbon tool steel specimens (SK3), which were heated at 700, 800, 900 and 1000℃ and then cooled in air to obtained different structures of oxides on their surfaces. The oxides were prepared for electrochemical tests in NH4HF2 and HCl solutions and then examined with scanning electron microscope.
Experimental results show that a compact oxide could be achieved as the steel was heated at 800℃ then cooled in air. Heating above 900℃, the oxide separated from the steel substrate; furthermore, few oxide can be found as the steel heated at 1000℃. The weight of the oxide increased with increasing heating periods as the steel was heated at 800℃. Interestingly an amorphous oxide can be found on the steel when heating at 800℃longer than 1h. From the results of electrochemical tests, the corrosion potential, Ecorr, of the oxide heated at 800℃ is obvious higher than the other oxides. The behavior of the oxide dissolution in the NH4HF2 solution is obviously different to the HCl solution. In the former solution dissolution of the oxide was resulted from cracking of the oxide and in the latter solution the scale was corroded uniformly.
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