Abstract

The electrochemical behavior of low alloyed Fe-Cr steels with 3 and 5% wt. of Cr in neutral Na2SO4 electrolyte combined with a detailed chemical and morphological characterization of these alloys performed by Auger electron spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy are presented here. The corrosion of low alloyed Fe-Cr steels proceeds in the prepassive range, with the formation of corrosion surface films having a duplex structure with outer iron oxide/hydroxide layer and inner Cr oxide-rich layer. The thickness, composition, and the morphology of the surface films vary as a function of chromium content in the alloy as well as conditions of electrochemical tests (temperature). Even a low chromium content shows a beneficial effect on the corrosion performances of the Fe-Cr steels. The chromium as a more active component than iron of ferrite increases the anodic activity of this phase, which results in a rapid saturation of the surface with the anodic reaction products forming a fine crystalline-like and compact layer of corrosion products. In this way, the chromium acts as a modifier of formation/crystallization of the iron-rich surface film (mainly magnetite) in the prepassive range.

Highlights

  • Published: 18 October 2021Low- and medium-chromium steels are materials, which are commonly used in building constructions and industrial equipment

  • The aim of this work is to present the influence of chromium on the corrosion resistance, morphology, and chemical composition of the corrosion products formed on low chromium (1, 3, and 5% of Cr) binary ferritic Fe-Cr alloys in Na2 SO4 electrolyte as a function of temperature

  • The electrochemical properties of iron were studied by cyclic voltammetry (CV) in deaerated 0.1M Na2 SO4 solution

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Summary

Introduction

Low- and medium-chromium steels are materials, which are commonly used in building constructions and industrial equipment. The application of these steels is related to their relatively good corrosion resistance in atmospheric conditions (weathering steels), in water and in steam at elevated temperatures [1,2,3]. The electrochemical laboratory tests, as well as the field tests, ruled out the possibility of passivation of low- and medium-chromium steel in thermal water at high temperatures (up to 150 ◦ C) [5,7,8]. The mechanism of the positive influence of chromium on the corrosion resistance of the low-alloyed steel has not been sufficiently investigated according to our knowledge.

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