Weathering steel refers to a type of low-alloy, high-strength steel that exhibits excellent corrosion resistance in the atmosphere due to the addition of small amounts of alloying elements. Weathering steel offers 2 to 8 times the atmospheric corrosion resistance of ordinary carbon steel, and its corrosion resistance becomes more pronounced the longer it is used. In addition to its excellent weather resistance, weathering steel also possesses superior mechanical and welding properties, making it widely used in railway rolling stock, bridges, and shipping containers.

Principle of Weathering Steel

The addition of trace elements such as phosphorus, copper, chromium, and nickel to the steel causes a dense and highly adherent protective film to form on the steel surface. This film prevents rust from diffusing inward and developing further, thereby protecting the substrate beneath the rust layer and slowing down the corrosion rate. The amorphous spinel-type oxide layer, approximately 50 μm to 100 μm thick, formed between the rust layer and the substrate is dense and exhibits excellent adhesion to the base metal. The presence of this dense oxide film prevents oxygen and water in the atmosphere from penetrating the steel substrate, thereby slowing the progression of corrosion into the steel material and significantly enhancing its resistance to atmospheric corrosion. Weathering steel is a steel grade that allows for thinner sections, exposed use, or simplified coating, thereby extending the service life of products, saving labor and reducing consumption, and facilitating product upgrades. It is also a steel grade capable of incorporating new mechanisms, technologies, and processes in modern metallurgy to ensure its continuous development and innovation.

Weathering Steel Manufacturing Process

Weathering steel generally follows a process route involving the charging of high-quality raw materials into the furnace—smelting (converter or electric furnace)—microalloying treatment—argon blowing—LF refining—low-superheat continuous casting (with rare earth wire feeding)—controlled rolling and controlled cooling. During smelting, scrap steel is charged into the furnace along with the raw materials and smelted according to conventional processes. After tapping, deoxidizers and alloying elements are added. The molten steel undergoes argon blowing treatment and is immediately cast; the molten steel, whose temperature has been adjusted by argon blowing, is cast into slabs using a continuous casting machine. Due to the addition of rare earth elements, the weathering steel is purified, and the content of inclusions is significantly reduced. (Rare earth elements are highly reactive and act as potent deoxidizers and desulfurizers, primarily serving to purify the steel. They refine the grain structure, alter the state of inclusions in the steel, reduce the number of harmful inclusions, and minimize corrosion initiation sites, thereby enhancing the steel’s resistance to atmospheric corrosion.)

Different weathering elements have varying effects on corrosion in different environments. For example, molybdenum is effective in reducing the corrosion rate in industrial atmospheres but has no significant effect on corrosion resistance in marine atmospheres. Therefore, depending on the corrosion environment, weathering steel is evolving toward specialized and specific applications, and its chemical composition is changing accordingly to improve the effectiveness and application efficiency of the added weathering elements. Specialized steel grades such as seawater-resistant steel, marine climate-resistant steel, acid climate-resistant steel, and tropical climate-resistant steel are representative examples of this category. Consequently, weathering steel should also evolve toward greater diversification.