Beneficial role of Sn in rapid rust stabilization of weathering steel in marine environments

Abstract

Weathering steel exhibits excellent corrosion resistance and is widely used in bridges, towers, railways, highways, and other engineering projects that are exposed to the atmosphere for long periods of time. However, before the formation of stable rust layers, weathering steel is prone to liquid rust sagging and spattering, leading to environmental pollution and city appearance concerns. These factors limit the application and development of weathering steel. In this study, a rapid and environmentally friendly method was developed by introducing alloying elements, specifically investigating the role of Sn in the rapid stabilization of rust layers in marine atmospheric environments. The rust layer formed on weathering low-alloy steel exposed to prolonged outdoor conditions and laboratory immersion experiments was explored using electron probe micro-analyzer (EPMA), micro-Raman, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. Results showed an optimal synergistic effect between Sn and Cr, which facilitated the accelerated densification of the rust layer. This beneficial effect enhanced the capability of the rust layer to resist Cl− erosion and improved the protection performance of the rust layer.

1. Introduction

Weathering steel forms a dense rust layer on its surface under natural atmospheric conditions by incorporating small amounts of alloying elements such as Cu, P, Cr, Nb, Mn, Ni, and Al, thereby preventing further penetration by corrosive ions and exhibiting excellent resistance to atmospheric corrosion [1–2]. However, the formation of a stable, protective rust layer on weathered steel typically requires several years in natural environments [3]. In marine atmospheric environments, developing a dense rust layer is difficult for weathering steel due to factors such as high humidity, salinity, and climatic variability [4–5]. The difficulty in forming a protective rust layer facilitates the easy penetration of Cl− into the rust layer, leading to further corrosion of the steel substrate. Stabilization treatment technology involves a special surface treatment of weathering steel before its use to form a protective film on its surface [6–7].

Kamimura et al. [8] developed a rust layer stabilization treatment solution using phosphates and molybdates as primary salts. Weathering steel treated with this solution could be exposed to coastal atmospheric conditions and could rapidly form a stable rust layer on the surface. However, the addition of chemical agents to stabilizers may contribute to environmental pollution. Hu et al. [9] introduced a pre-corroded rust layer containing Cu to mimic the enrichment of alloying elements, thus providing an accelerated pathway for the formation of a protective rust layer on weathering steel. The introduction of alloying elements is a fast and environmentally friendly method to address the issues of the long formation time of the protective rust layer on bare weathering steel and environmental pollution [10].

Sn has traditionally been considered a harmful element [11–12]. However, recent research has indicated that the addition of appropriate amounts of Sn may play a beneficial role in promoting the stabilization of the rust layer on weathering steel [13–14]. Sun et al. [15] reported that the presence of Sn enhances the transformation of Cr and Mo into stable compounds, particularly Cr(OH)3 and molybdate. The results also revealed a positive correlation between Sn content and the density and stability of the resulting rust layer. Feng et al. [16] investigated the effect of adding Sn to alloys on the corrosion resistance and properties of passive films in stainless steel. The results show that Sn accelerated the heterogeneous nucleation of passive films. Yang et al. [17] observed under rural atmospheric conditions that Sn can promote corrosion. Therefore, the addition of Sn could reduce the time required for weathering steel to reach a protective state [18]. However, current research was insufficient to draw a definitive conclusion on whether Sn could be considered an effective element for stabilizing rust films on weathering steel.