The main alloying element in stainless steel is chromium. Generally speaking, stainless steel with a chromium content of at least 10.5% has good corrosion resistance. Different types of stainless steel (such as 304, 316, etc.) have different corrosion resistance, and 316 is more corrosion resistant than 304 due to the molybdenum content. Stainless steel will also rust if not correctly maintained.
Stainless steel is generally not easy to rust but is only partially rust-proof. Its corrosion resistance mainly depends on alloy composition, treatment, and environmental conditions.
Even in non-harsh environments (high chlorine and high-temperature environments), slight corrosion may still occur in some cases.
Stainless steel can rust due to high air humidity or the adsorption of moisture on the surface by pollutants and dust accumulation, mechanical damage to the stainless steel surface that destroys the surface passivation film, and electrochemical corrosion of other metals entering and exiting.
Corrosion morphologies of 304 stainless steel after exposed in South Sea atmospheric for different time: (a)controlled samples, (b)1 month, (c) 3 months, (d)6 months.
Reasons for Stainless Steel Rust Prevention
The main reason for stainless steel rust prevention is that a dense and stable passivation film is formed on its surface, which can effectively isolate the metal from the external environment, thereby preventing corrosion.
Stainless steel contains at least 10.5% chromium. Chromium reacts with oxygen to form a very thin chromium oxide (Cr₂O₃) passivation film that covers the steel’s surface.
In addition to chromium, stainless steel may contain other alloying elements, such as nickel, molybdenum, and titanium. These elements can further enhance the steel’s corrosion resistance.
The surface of stainless steel is usually smooth, reducing the possibility of dirt and impurities accumulating. The smooth surface also allows the chromium oxide film to be evenly distributed and tightly covered, enhancing the rust-prevention effect.
Now that we know the reasons for stainless steel rust prevention, we should avoid the occurrence of factors that damage stainless steel rust prevention during use.
Why does Stainless Steel Rust?
Stainless steel rust is mainly caused by damage to the protective film on its surface. While stainless steel is highly resistant to corrosion, it can still rust under certain conditions. The following are the main reasons for stainless steel rust:
Passivation film damage: Stainless steel’s corrosion resistance comes from a thin and stable oxide passivation film, primarily composed of chromium oxide, on its surface. If this film is scratched, mechanically damaged, or affected by chemicals, the local area loses protection, allowing oxygen and moisture to come into contact with the steel, leading to rust.
Environmental factors: High humidity, high salt content (e.g., seaside locations), acidic or basic environments, and severe air pollution can make the passivation film on stainless steel more susceptible to corrosion. Environments containing chloride ions (e.g., seawater, bleach) can accelerate the degradation of the passivation film, leading to rust.
Chemical pollution: Exposure to corrosive chemicals (e.g., hydrochloric acid, sulfuric acid) over a prolonged period, or contact with other types of steel, can trigger an electrochemical reaction, damaging the passivation film and causing rust.
Improper welding or processing: Inadequate treatment of the stainless steel surface during processing or welding, such as failure to clean the weld spot promptly after welding or improper heat treatment, can lead to local damage to the passivation film and subsequent rust formation.
Improper maintenance: Failure to clean or maintain stainless steel for an extended period can result in the accumulation of dirt, grease, metal chips, etc. These substances can create local corrosion cells under wet conditions, leading to the gradual destruction of the passivation film and rust formation.
How to Prevent Steel from Rusting
In order to prevent stainless steel from rusting, we need to avoid damage to the passive film, chemical contamination, improper welding, and inadequate maintenance. In addition to these measures, there are additional steps that can be taken:
1. Apply paint, powder coating, galvanizing oil, or grease to the surface of stainless steel to create a protective layer.
2. Use cathodic protection by attaching a more easily corroded metal such as magnesium or zinc to the steel as a sacrificial anode, which corrodes first and protects the steel from rusting.
Other preventive measures include:
– Regular maintenance
– Inspection and cleaning: Regularly inspect the steel structure to remove any dirt, salt, or contaminants that may cause rust.
– Repair: Promptly address any damage to the protective coating or surface to prevent rust from occurring.
By utilizing these methods, steel can be effectively prevented from rusting, thereby extending its service life and maintaining its structural integrity.
How to Remove Rust from Stainless Steel
When removing rust from stainless steel, it’s important to proceed carefully to avoid causing damage to the metal surface. Materials such as baking soda, vinegar, and lemon juice have gentle cleaning properties and can effectively eliminate surface rust without harming the stainless steel. These substances work by chemically reacting with the rust, primarily composed of iron oxide, and transforming it into a substance that is easier to remove.
Methods For Cleaning Rusty Stainless Steel
Helpful Tips:
Always use non-abrasive tools like a soft brush, cloth, or sponge.
Avoid using steel wool, as it can scratch the surface and lead to further rusting.
Regularly clean and maintain stainless steel to prevent the reformation of rust.
Why SSM is Your Trusted Supplier of Speical Metal Products
Selecting the right stainless steel products for your project is a critical decision, and at SSM, we understand that it shouldn’t be left to chance. We go beyond being just a supplier – we are your reliable partner in providing stainless steel products.
Get in touch with us today for a free quote and experience the difference of partnering with true experts in metal excellence.
