Low-Temperature Pack Aluminizing of X80 Pipeline Steel through Addition of Zinc and Surface Self-Nanocrystallization

Rapid low-temperature pack aluminizing was achieved on pipeline steel X80 through combined effect of surface refinement treatment and modification of pack powder. Self-nanocrystallization surface of pipeline steel X80 was obtained by surface mechanical attrition treatment (SMAT). In addition, zinc (Zn), which has lower melting point than that of Al, was added in the pack powder, to enhance the concentration of active aluminum (Al) atom. The mechanism of the low- temperature pack aluminizing was analyzed by examining the distribution of atoms and coating thickness using EDS and SEM. The study shows that aluminizing rate of as-SMATed pipeline steel with self-nanocrystallization surface is higher than that of non-SMATed pipeline steel under the same pack condition. The addition of Zn can increase the activity of diffusion atoms and accelerate the aluminizing by changing the state of pack powder from a single solid phase to a mixture of solid phase and liquid phase. The diffusion of atoms in this low-temperature pack aluminizing is considered as bulk diffusion which is driven by the activity of diffusion atoms in an unstable state following Fick law.