ICAME 2005 (PDF)

"Influence of Cu and Ni on the morphology and composition of the rust layer of steels exposed to industrial environment (p. 739-740)

Abstract

Four samples of steels with alloying elements were exposed to an industrial environment during 1,955 days, aiming to elucidate the effect of the alloying elements Cu and Ni on the resistance of weathering steels to corrosion processes. The samples were characterized with optical microscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), saturation magnetization measurements and with energy dispersive (EDS), infrared, Mossbauer and Raman spectroscopies. All the steels originated orange and dark corrosion layers; their thicknesses were determined from the SEM images.

EDS data of such rust layers showed that the alloying element content decreases from the steel core towards the outer part of the rust layer. Moreover, in the dark rust layer some light-gray regions were identified in the Wand Cu-alloy steel, where relatively higher Cr and Cu contents were found. XRD patterns, infrared, Raman and Mossbauer spectra (298, 110 and 4 K) indicated that the corrosion products are qualitatively the same, containing lepidocrocite (yFeOOH; hereinafter, it may be referred to as simply L), goethite (aFeOOH; G), feroxyhite (bFeOOH; F), hematite (aFeZ03; H) and magnetite (Fe304; M) in all samples; this composition does not depend upon the steel type, but their relative concentrations is related to the alloying element. Mossbauer data reveal the presence of (super)paramagnetic iron oxides in the corrosion products. Saturation magnetization measurements suggest that feroxyhite may be an occurring ferrimagnetic phase in the rust layer.

Key words low alloy steels iron oxides -corrosion

1 Introduction

The knowledge of the resistance of steels to corrosion is very important for metallurgy industries. The weathering steel, also known as low