Effect Of Surface Mechanical Attrition Treatment On The Aluminizing X80Pipeline Steel At Low Temperature

Since pipeline steel is usually used in the complex oil and gas transportation condition with some corrosion medium, corrosion resistance of pipeline steel is key to decide the whole life of pipeline steel. In order to improve corrosion resistance of pipeline steel, a low-temperature alumetizing technology is carried out on the surface of X80pipeline steel.In this process, first, a nanostructure is made by Surface Mechanical Attrition Treatment (SMAT),then Zinc (Zn) is added in the pack powder so as to decrease its melting-point and improve its wettability,finally aluminizing can be proceeded.Under600℃, the analysis of stability on the X80pipeline steel micro-surface is conducted by OM, the effect of the pre-treatment of SMAT on the morphological features, the element distribution,and diffusion depth of the low-temperature pack aluminizing is analysed by SEM、EDS,the study is carried out on the corrosion resistance of the original sample and the alumetized sample of X80pipeline steel by the electrochemical corrosion method, whether the medium compositions can have an effect on the antioxidation properties is analysed by testing the quanlity change of the aluminized sample of X80pipeline steel before and after high-temperature oxidation; phase of X80pipeline steel aluminized layer surface composition is studied after the pre-treatment of SMAT by XRD,the low-temperature pack alumetizing technology is identified.Experiment shows:the surface nano-structures is stability when the temperature is lower than600℃.Compared with the direct pack aluminizing processing, an uniformer, denser and thicker aluminizing layer of X80pipeline steel can be achieved by SMAT and the addition of Zn in the pack powder which can provide a better corrosion protection for X80pipeline steel, From weak to strong corrosion resistance as follows:the original X80pipeline steel sample, SMATed X80pipeline steel is not aluminized, the original X80pipeline steel is aluminized, SMATed X80pipeline steel is aluminized;Aluminized layer antioxidant capacity increase with the Zn content decreased;As the pack aluminizing temperature was ranged from400℃to530℃, The main phase composition of low-temperature pack aluminizing layer is Fe2Al5when the addition content of Zn in the pack powder was lower than84.4wt.%. The main phase composition of low-temperature pack aluminizing layer is Fe2Al5besides some peaks of FeAl identified by XRD as the addition content of Zn in the pack powder was over84.4wt.%. As the addition content of Zn is lower than9.5wt.%, the surface microhardness of as-aluminized X80pipeline steel is about800HV0.1. The surface microhardness of as-aluminized X80pipeline steel decrease to770HV0.1as addition content of Zn is in the range from9.5wt.%to84.4wt.%.Once the addition content of Zn is higher than84.4wt.%, the surface microhardness of as-aluminized X80pipeline steel is only about750HV0.1.