| Summary: | 碩士 === 國立中正大學 === 機械工程研究所 === 86 === In this work, study was carried out to evaluate the wear characteristics of different hardfacing alloys deposited by using PTA or spray and fusion process. Pin - on - disk wear test was carried out on 5 different alloys including Co - based Stellite 6, Stellite 6 + 30wt% chromiun carbide, Co - based Stellite 21, Ni - based Colmonoy 88 and 420 stainless steel and base metal S45C under different temperatures, loads and speeds. Comparison was also made between Stellite 6 deposited by PTA and by spray and fusion process. The wear volume was measured based on surface profile. The wear mechanism on the hardfacing surface was analysed by using optical and scanning electron microscopy. Oxidation resistance test by using thermogravimetry analysis (TGA) and were test after oxidation was carried out on PTA cladded specimens to evaluate the post - oxidation wear behavior.
The results showed that the clad layers deposited by PTA process are superior to that by the spray and fusion process. The wear resistance of hardfacing alloys being tested can be ranked in the following sequence: Stellite 6 + CrC, Stellite 6, Stellite 21, Colmonoy 88, 420 stainless steel. The base metal S45C possessed the lowest wear resistance among the tested alloy. In general, the wear volume increased with increasing test temperature, applied load and sliding speed. However, the 420 stainless steel was the only one exception in which the wear resistance was signifcantly improved at 450℃.
The result of oxidation test showed that Co - based hardfacing alloys were superior to Ni - based Colmonoy 88 and 420 stainless steel in oxidation resistance. The 420 stainless steel was the worst among all. The sequence of oxidation resistance of cobalt based alloys was: Stellite 6, Stellite 6 + CrC and Stellite 21. In addition, the results of post - oxidation wear test showed that oxidation was beneficial to the subsequent Colmonoy 88. However, the wear resistance of Stellite 6, Stellite 6 + CrC, and Stellite 21 and 420 stainless steel was deteriorated after oxidation.
Accroding to the properties of wear resistance and oxidation resistance under different test conditions at elevate temperature, obtained from the hardfacing alloys, suggestions could be made in the proper selection of hardfacing alloys for the wear resistance cladding application on rollers at different locations of rolling mills.
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