Stainless steel is one of the most widely used materials in multiple industrial and commercial sectors, mainly due to its excellent mechanical properties and corrosion resistance. Its extraordinary ability to resist the harmful action of corrosive agents makes it a preferred choice in many contexts, both for use in the home and use in decidedly different contexts.
In this article, we will try to learn more about the characteristics of stainless steel and why it is one of the most used materials to fight corrosion. Along with this, titanium, aluminum, nickel, tantalum, phosphor bronze, and fluorine-based polymers are other materials resistant to corrosive phenomena.
But to better understand what we are talking about and the importance of the presence of these materials in the creation of objects that are part of our daily life or in construction, first we need to understand what the corrosion of a material is.
What is the corrosion of a material and how to fight it
Corrosion is a natural process involving the degradation of a material due to interaction with its surrounding environment. Stainless steel is specifically engineered to withstand this process, providing long-lasting, reliable protection for a variety of uses. But what are the factors that give the stainless steel corrosion resistance?
Corrosion of steel is a chemical process in which steel, a type of metal alloy mainly composed of iron, reacts with its surroundings causing its gradual deterioration. This phenomenon is mainly caused by the oxidation of the iron present in the steel in the presence of water and oxygen.
Corrosion of steel can be influenced by many factors, including humidity, temperature, the presence of aggressive chemicals, and the degree of exposure to air. Water is a fundamental element for the corrosion process, as it acts as a transport medium for the metal ions. Oxygen, on the other hand, promotes the formation of iron oxides on the steel surface.
It is during the corrosion process that a patina composed of iron oxides forms on the affected surface: rust. This can cause the steel to lose its structural strength, compromising its integrity. That depends on the strength of the stainless steel.
The corrosion resistance of stainless steel comes mainly from the presence of a thin layer of oxide on its surface, known as the “passive film”. This protective film forms spontaneously when stainless steel is exposed to oxygen in the air or water. It is mainly composed of chromium oxide, but also contains other elements such as nickel and molybdenum, which help improve its corrosion resistance properties.
The chromium oxide in the passive film is highly stable and insoluble in water, which prevents the metal ions from diffusing and consequently damaging the steel surface. This film plays a vital role in protecting stainless steel from oxidation and corrosion by providing a physical barrier between the metal and its surroundings.
Features of stainless steel
In addition to the passive film, stainless steel can benefit from other characteristics that contribute to its corrosion resistance. For example, the addition of nickel improves the steel’s resistance to corrosive attack by acids. Molybdenum, on the other hand, offers greater resistance to corrosion by substances such as chlorides and saline solutions. These alloying elements, together with chromium, create a synergistic combination that makes stainless steel highly resistant to a wide range of corrosive agents.
It should be emphasized that the corrosion resistance of stainless steel can vary based on its chemical composition and crystalline structure. There are several grades of stainless steel, each of which is designed to meet specific requirements in terms of corrosion resistance, mechanical strength, and physical properties. For example, austenitic stainless steel, which contains high levels of nickel and chromium, is particularly suitable for applications requiring higher strength.