Abstract
The effect of ferrite-pearlite and ferrite-martensite phase combinations on the passive layer properties of low carbon steel is investigated in a 0.1 M NaOH solution. Heat treatments were designed to obtain ferrite-pearlite and ferrite-martensite microstructures with similar ferrite volume fractions. Potentiostatic polarisation and electrochemical impedance spectroscopy (EIS) results demonstrated the lower barrier properties of passive films on ferrite-martensite microstructure compared to the ones formed on ferrite-pearlite microstructure. This was attributed to the higher donor density of the passive layer on ferrite-martensite samples, measured with Mott–Schottky analysis. This behaviour was explained by the complex microstructure morphology of the martensite phase that led to the formation of a more defective passive film.
Highlights
A wide range of industries such as aerospace, automotive, oil and gas employ highstrength steels due to their mechanical properties in efforts to reduce weight in structures and save energy in transportation applications
The role of phase constituents on the passivity behaviour of two-phase low alloy steels is investigated in a 0.1 martensite start (Ms) NaOH environment
The effect of phases on the passivity behaviour of two-phase steels is analysed with potentiostatic polarisation, electrochemical impedance spectroscopy, and Mott–Schottky analysis
Summary
A wide range of industries such as aerospace, automotive, oil and gas employ highstrength steels due to their mechanical properties in efforts to reduce weight in structures and save energy in transportation applications. The exceptional mechanical properties of these steels (an advantageous combination of strength, ductility and plasticity) often result from a multi-phase microstructure created through a precise balance between kinetic processes and thermodynamics [1]. In combination with ferrite, are widely used in two-phase steels. The role of pearlite and martensite in combination with ferrite in two-phase steels on mechanical properties is understood relatively well [2,3]. Their corrosion and passivity behaviour is not yet well understood [4,5]. This is mainly due to the complex interaction of the microstructural features—grain sizes, phase fractions, dislocation densities, crystallographic orientations, phase morphologies—
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