Corrosion Product Film of a Medium-Mn Steel Exposed to Simulated Marine Splash Zone Environment.

Xinyong Yan,Pengyu Li,Shumei Kang,Meiling Xu

doi:10.3390/ma14195652

Abstract

The corrosion behavior of a medium-Mn steel in a simulated marine splash zone was studied by a dry–wet cyclic corrosion experiment and electrochemical experiment. The corrosion products were characterized by corrosion rate calculation, composition detection, morphology observation, element distribution detection, valence analysis, polarization curve, and electrochemical impedance test. The results show that the corrosion products of the sample mainly include γ-FeOOH, FexOy, MnxOy, and a small amount of (Fe,Mn)xOy, and the valence state of iron compounds and manganese compounds in different corrosion stages changed obviously. In the initial corrosion products, Mn is enriched significantly and facilitates the electrochemical reaction of corrosion process. The content of Ni in the inner rust layer is high. The semi-quantitative analysis of the corrosion product elements shows that the atomic concentrations of Cr and Mo increase significantly in later corrosion products, indicating that the dense isolation layer formed by alloy element compounds in the corroded layer is the main factor to improve the protection ability of the rust layer at the end corrosion stage of the sample. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.

Highlights

IntroductionWith the global over-exploitation of terrestrial resources and the continuous depletion of energy sources, the move to marine resources has become a new development trend [1,2,3]
The results show that the corrosion rate of medium-Mn steel in the test is low in the early corrosion stage, and the corrosion rate in the middle/late stage of corrosion is significantly lower than that in the early stage of corrosion
At the initial stage of corrosion, the cathodic process includes oxygen reduction and the reduction of rust layer components; the strong or weak change of these two effects is the main reason for the increase in initial corrosion rate, and the turning of velocity is caused by the compactness or physicochemical properties of the rust layer

Summary

Introduction

With the global over-exploitation of terrestrial resources and the continuous depletion of energy sources, the move to marine resources has become a new development trend [1,2,3]. Considering the economy and reliability of offshore platform equipment, a medium-Mn steel with composition specifications of 0.267C-4.390Mn-0.020Cu-0.385Cr0.345Mo-3.270Ni mass% is newly developed for offshore industrial platforms [4,5]. On the one hand, increasing Mn and other alloy elements to a certain extent will damage the casting properties of steels [6,7], but replacing Ni, Mo, and other elements with relatively cheap alloying element Mn can greatly reduce the casting cost of steel [8,9]. Its superior mechanical properties, high strength, and good low-temperature toughness can meet the comprehensive mechanical properties of marine equipment structures [10,11].

Methods

Discussion

Conclusion