Stainless steel is often known as ‘corrosion-resistant steel’ because it doesn’t corrode, stain or rust as much as typical carbon steel. This is largely due to the large amounts of chromium present. Stainless steel is an obvious choice for applications in which corrosion resistance is important, and it is used in a wide variety of applications including in architectural cladding, in railways and in food hygiene.
Stainless Steel and Chloride Corrosion
Stainless steel is often used in reinforced concrete structures, as despite being one of the most affordable structures, reinforced steel has poor durability. This lack of durability is exacerbated in severe conditions such as those in contact with oceans, de-icing or other chloride-contaminated environments. On the surface of steel, a thin oxide layer forms following exposure to an alkaline medium. When this layer is exposed to a large concentration of chloride ions it can be destroyed.
Because there are so many corrosion-related issues in standard steel, stainless-steel can be a viable alternative to increase the durability of reinforced concrete structures which are in chloride-rich environment. Stainless steel can be alloyed with elements of chromium, nickel and molybdenum to create a more stable oxide layer that is able to protect the metal beneath from chloride corrosion.
Despite this, the combination of tensile stress and a high-chloride environment can cause stainless steels to crack, in a process known as stress corrosion cracking. No stainless steel grade can be totally immune to chloride stress corrosion cracking, however the resistance does vary between the grades. Environmental factors such as increased temperatures can also increase the susceptibility of stainless streel grades to stress corrosion cracking.
Stainless Steel Use in the Railway Industry
Steel is one of the most commonly used materials in the railway sector due to its strength, versatility and economy. However, steel must be protected or it will corrode or rust, particularly in environments where evaporation can result in a local build-up of corrosive substances such as chlorides.
Generally speaking, the stainless steel used in railways must be of a high quality which is not susceptible to corrosion as railway materials are subject to high levels of dynamic stress.
In coastal areas, railway tracks are in regular contact with air containing chloride and in colder climates, salt is place on the tracks to stop them from freezing over. Over time, this chloride builds up on the tracks, causing them to corrode or be subject to stress corrosion cracking under the pressure of railway vehicles.
Corrosion Resistant Stainless Steel from Masteel
Masteel produces corrosion-resistant stainless steel grades such as grade 316, which is recommended for use in severe applications. 316 stainless steel can be used in coastal regions or areas where de-icing salts are frequently used because of its resistance to chloride.