Effects of Alloying Elements (Cr, Mn) on Corrosion Properties of the High-Strength Steel in 3.5% NaCl Solution

Bomi Kim,Soojin Kim,Heesan Kim

doi:10.1155/2018/7638274

Abstract

Effects of chromium and manganese as alloying elements on corrosion resistance of carbon steel were examined using evaluation of corrosion resistance in 60°C NaCl solution with a weight loss test, polarization test, analysis of rust with X-ray diffractometer, Raman spectroscopy, transmission electron microscopy, energy dispersive spectroscopy, and electron energy loss spectroscopy. The weight loss behavior conformed to a typical parabolic law, and the oxidation state of iron in rust was higher along the fast pathway but was disproportionate to the distance from the alloy/AR interface. It suggests that the corrosion process of the alloys was controlled by transport of oxygen to the rust layer. The improvements in corrosion resistance of 18Mn and 18Mn5Cr resulted from both the refinement of grain in adherent rust (AR) and the increase of the amounts of goethite in nonadherent rust (NAR) by chromium and manganese. Especially, the effectiveness of chromium on corrosion resistance was also related to the refinements of grain in AR and the amounts of goethite in NAR. The Tafel extrapolation method was inadequate to measure the instantaneous corrosion rate of steels with various alloying elements and immersion periods because of the difference in electrochemical reduction rates of rust, depending on its constituent.

Highlights

High manganese steels with high strength and toughness were developed to satiate the need for a material with superb physical properties in response to energy crisis and carbon dioxide release restriction [1]
Compared to the rust on the REF, both chromium and manganese accelerate the formation of goethite in nonadherent rust (NAR) and finegrained magnetite in adherent rust (AR), though the chromium is more effective than manganese as shown in Figures 10(b) and 10 (c). e higher effectiveness of chromium on corrosion resistance of steels is because both the formation rate and refinement of goethite are enhanced in NARs [4, 36, 50] as well as AR grain sizes are more refined [36]. e higher
Unlike previous studies [15, 16, 18], which state that magnetite is related to a decrease in corrosion resistance of steel, the ARs formed on the alloy steels with higher corrosion resistances contained fine magnetite as a main component. e discrepancy is due to the difference in the location of rust from the alloy/rust interface

Summary

Introduction

High manganese steels with high strength and toughness were developed to satiate the need for a material with superb physical properties in response to energy crisis and carbon dioxide release restriction [1]. Even recently, relevant studies on the effects of manganese on corrosion resistance of steel have been comparatively minimal [2,3,4,5]. The effects of manganese on corrosion resistance of steel during the exposure to chloride-containing environments have been reported inconsistently [4, 6,7,8,9,10,11,12]. Melchers [13, 14] proposed a model on the corrosion process of carbon steel. Because the model remains in the second stage for the most of the total exposure period, we believe that corrosion resistance of carbon steels during a long-term exposure greatly depends on the rust as it serves as a medium for oxygen penetration. Because the model remains in the second stage for the most of the total exposure period, we believe that corrosion resistance of carbon steels during a long-term exposure greatly depends on the rust as it serves as a medium for oxygen penetration. e long-term exposure test has shown that the corrosion rates for the rust components are less than 0.01 mm/yr, as shown in (1) [15, 16]:

Methods

Results

Discussion

Conclusion