Aluminizing Coating Prepared on Oil Casing Steel N80 by Low-Temperature Pack Cementation

摘要

Aluminizing has been verified to be an effective way to improve the corrosion resistance of steel due to the formation of continuous Al_2O_3 layer, but traditional aluminizing processing carried out at high temperature can not be used to prepare aluminide layer on the surface of oil casing steel. In this paper, an aluminide coating was prepared on oil casing steel N80 by a low-temperature pack cementation only at 803 K for 2 hours by adding zinc in the pack powder and pre-treatment of N80 substrate by surface mechanical attrition. The phase composition, microstructure, element distribution and properties of as-aluminized oil casing steel N80 were characterized by means of XRD, SEM, EDS, micro-hardness test and electrochemical corrosion measurements. The results indicate that aluminide coating mainly consists of FeAl_3, Fe_2Al_5 and FeAl. The continuous aluminide coating with an average thickness around 50 ìm could be successfully formed on the surface of oil casing steel N80 which shows a good coherence with as-packed substrate. After preparation of aluminide coating, oil casing steel N80 shows a higher microhardness in the range of aluminizing coating than that of the virgin material because of the formation of iron aluminide. The exception noted is that the proposed low-temperature aluminizing processing does not have any damaging impact on the mechanical properties of steel substrates. Moreover, it is concluded that oil casing steel N80 with aluminizing coating shows a better corrosion resistance than that of original N80 by analyzing of electrochemical test results.