The nanostructure and microstructure of steels: Electrochemical Tafel behaviour and atomic force microscopy

Abstract

The influence of chemical composition and heat treatment on a low-carbon steel, chromium steel and high speed steel has been examined by polarisation curves and electrochemical parameters deduced from the Tafel plots. The electrochemical corrosion resistance, which is small between the as-received steels become greater after heat treatment, following the order: carbon steel < chromium steel $ high speed steel. To explain these differences, the nano-and microstructure of the steels has been characterized by the ex situ techniques of atomic force microscopy and optical microscopy, before and after surface etching with Nital (a solution of 5% HNO 3 in ethanol). This causes preferential attack of the ferrite phases showing the carbide phases more clearly. From these nanostructural studies it was possible to better understand why the passive films formed on chromium steel and high speed steel have superior protective properties to those formed on carbon steel.

Long term localised corrosion of marine steel piling welds

“…More generally, the use of filler metals with compositions different from the base material may produce electrochemical potential differences. 23,24,25 Furthermore, the electrochemical rest potential experimental result show that the PMZ is slightly more noble compared to the HAZ and WZ (Fig. 7).…”

Pitting susceptibility of induction-quenched pipeline with microstructural heterogeneity

“…It should be mentioned that the decarburization would alter the steel composition of surface layer. Alves et al [9] studied the localized corrosion behavior of AISI 1015 steel that possessed classic ferrite ? pearlite structure under hot-rolled condition.…”

“…Fig. 16 Effect of chloride on anodic polarization behavior and the band structure of passive film that is an n-type semiconductor Recently, the local activity of metallic surface in situ and evolution of surface morphology in corroding environments in nano-scale has been investigated with local probe techniques, such as scanning tunneling microscopy [41], atomic force microscopy [9], and scanning Kelvin probe [42]. The application of these techniques offers alternative approaches to explore the mechanism of localized breakdown.…”

“…For instance, the non-metallic inclusions decrease the pitting resistance of low alloy steels [6][7][8][9]. In NaCl solutions, furnace-cooled 9 %Cr-1Mo steel is less resistant to localized corrosion than the water-quenched one, as indicated by higher passive current density and lower pitting potential [10].…”

“…When the carbon steels possess microstructure of ferrite ? pearlite, pits preferably form in ferrite phase [2,9,11,12]. An increase of ferrite content in microstructure can also increase the pitting susceptibility [12] and environmentally assisted cracking [13].…”