In general, stainless steel does not rust, but if it is used or maintained improperly, or in a harsh environment, it will rust or tarnish, for example, the photo above shows a stainless steel shackle on a cruise ship corrodes due to long-term exposure to the marine environment, the surface appears brown rust and spots.
The reason why stainless steel does not rust is because it contains chromium (Cr) and nickel (Ni). These two metal elements will form a dense oxide film with oxygen, this layer of oxide is also called a passivation film, which enhances the corrosion resistance.
When the surface of stainless steel is scratched, it will instantly form a new oxide film, thus preventing it from further rusting and corrosion.
What is Stainless Steel?
Stainless steel is an alloy of iron, chromium, and nickel. It is a popular choice for many industries due to its durability and corrosion resistance.
Here are some of the benefits of stainless steel:
- It is durable and strong – Stainless steel is one of the most durable metals available. It does not rust or corrode easily. This makes it ideal for projects that require long-lasting materials.
- It is easy to clean – Stainless steel is easy to clean and maintain. This makes it ideal for applications where hygiene is important, such as in food preparation or medical facilities.
- It has a high resistance to heat – Stainless steel can withstand high temperatures without losing its strength or shape. This makes it ideal for projects that require heat-resistant materials, and stainless steel is suitable for welding.
- It is low maintenance – Once installed, stainless steel requires little maintenance. This makes it ideal for projects where maintenance costs are a concern.
Stainless steel is a versatile material that offers many benefits over other common types of steel. It is durable, easy to clean, and resistant to heat and corrosion. Its many benefits is why it’s one of the most commonly used metals across various industries.
Does Stainless Steel Rust?
The simple answer is yes, stainless steel does rust. It is much more resistant to corrosion than other types of steel, but not 100% rustproof. There are certain conditions—such as exposure to salt water or high temperatures—which can cause stainless steel to corrode.
However, with proper care and maintenance, stainless steel can last for many years without rusting. The reason stainless steel is so resistant to corrosion is because it contains chromium. Chromium forms a passive film on the surface of the stainless steel which protects it from oxidation.
However, there are a few conditions that need to be met for this to be true. Firstly, the stainless steel must have at least 12% chromium. Secondly, the steel underneath must be sheltered from exposure and protected from an oxygen-rich environment.
If stainless steel has its integrity compromised or is subject to long-term exposure, it can still suffer from rust.
While all several conditions need to be met for rusting to occur, the compromised chromium layer is by far the most important factor. This is because chromium creates a thin layer of oxide on the surface of the stainless steel that prevents further corrosion from happening.
This means that the rust-proof properties of stainless steel can be compromised when engraving stainless steel if precautions aren’t taken.
As you can see, while stainless steel doesn’t easily rust, there are certain circumstances where it can become corroded. If you want to avoid this from happening, it is important to choose a high-quality stainless steel that contains a high percentage of chromium.
Why Does Stainless Steel Rust or Tarnish?
When the passive layer is destroyed and the iron is exposed, it reacts with water and oxygen in the air to form iron oxide (rust).
The causes of passive layer destruction are various, including but not limited to mechanical wear, chemical corrosion, and contamination by iron particles.
Mechanical Abrasion
Scratches and physical damage to the stainless steel surface can break the protective chromium oxide layer. This can occur during fabrication, installation, or regular use.
Tools like steel wool, wire brushes, or any abrasive materials can damage the passive layer, exposing the underlying metal to the environment.
Chemical Exposure
Certain chemicals can react with stainless steel, compromising its protective layer. For example, acids and alkaline solutions, particularly those containing chlorides, can lead to localized corrosion.
Chloride-containing cleaners commonly found in homes and industries are particularly dangerous, as they can damage stainless steel by triggering localized corrosion, such as pitting and crevice corrosion.
Environmental Conditions
Harsh environmental conditions, such as long-term high humidity, salty air, and extreme temperature changes, challenge the chromium oxide layer on the surface of stainless steel and reduce its protective effectiveness.
Stainless steel structures near coastal areas or in industrial environments are especially susceptible due to the presence of salt and pollutants in the air.
Contamination with Iron Particles
During the production process, stainless steel may be accidentally contaminated with iron particles from tools, machinery, or other steel products.
These iron particles will oxidize and rust on their own, which will trigger a chain reaction of corrosion on the surface of the stainless steel. It’s crucial to use dedicated tools and clean workspaces to prevent cross-contamination.
Improper Maintenance
Failure to properly clean and maintain stainless steel can lead to the accumulation of dirt, grease, and other contaminants. These substances can trap moisture and promote rust formation.
Taking proper cleaning measures to maintain the integrity of the passivation layer on the surface of stainless steel is an important part of ensuring its long-term durability.
Heat Treatment and Welding
Heat treatment and welding can cause changes in the microstructure of stainless steel, leading to the formation of chromium carbides at the grain boundaries. This process, known as sensitization, depletes the chromium content in these areas, making them more susceptible to intergranular corrosion.
Does Stainless Steel Corrode?
There are many different types of corrosion that can affect all types of metals, including stainless steel. The four most common types of corrosion are general corrosion, pitting corrosion, crevice corrosion, and Stress Corrosion Cracking (SCC).
General Corrosion
General corrosion is the most common type of corrosion that affects all metals, including steel. General corrosion occurs when metal is exposed to oxygen and moisture, causing it to break down over time.
The best way to prevent general corrosion is to regularly inspect your equipment for signs of rust or other forms or deterioration and perform routine maintenance as needed.
Pitting Corrosion
Pitting corrosion occurs when small holes or pits form in the surface of the metal due to exposure to oxygen and moisture. This type of corrosion can be difficult to detect because it often happens below the surface where it cannot be seen with the naked eye.
Pitting corrosion can be prevented by regularly inspecting your equipment for signs of pits or other irregularities in the surface of the metal
Crevice Corrosion
Crevice corrosion occurs when there is a build-up of stagnant water or other liquids in small cracks or spaces on the surface of the metal exposed to oxygen and moisture.
In order for crevice corrosion to occur, there must be two conditions present: an anodic area and a cathodic area. The anodic area is where the oxidation reaction occurs, while the cathodic reacts as a base from which electrons are transferred.
Crevice corrosion affects stoves, pipes, cars, bridges, boats, water treatment plants, food processing equipment, and any other metal structures or surfaces that may have tiny cracks or spaces where water or other liquids can pool.
Crevice corrosion can be combined with pit formations to cause even more extensive damage. It is important to regularly inspect your equipment for signs of anomalies or deformations that may indicate possible crevices in which corrosive liquids can accumulate.
Prevention of crevice corrosion can be achieved by design modifications, regular cleaning and maintenance of equipment surfaces, and proper storage of corrosive materials.
Stress Corrosion Cracking
Stress corrosion cracking (SCC) is a corrosion process that occurs when there is a failure to relieve internal stresses in a metal. SCC can be prevented by maintaining low levels of tensile stress in the metal during service exposure to corrosive conditions.
It is important to consult with a metal fabrication professional before attempting to prevent SCC in service materials because some methods for relieving internal stresses may in fact increase the risk for SCC.
In order for stainless steel to maintain its resistance to corrosion, it must be cleaned and maintained on a regular basis. In addition, it is important to pick the right type of stainless steel for the specific application in order to prevent widespread damage from occurring.
How to Prevent Stainless Steel from Rusting?
Preventing rust on stainless steel involves several strategies that can be implemented during the design, fabrication, and maintenance stages:
1. Design
Proper design can minimize water penetration and reduce potential damage. Ensure good drainage and air circulation to avoid crevices and moisture accumulation.
Designs that avoid sharp corners, crevices, and areas where water can accumulate will help prevent corrosion. Including drainage holes and ensuring that surfaces are easily cleanable can also reduce the risk of corrosion.
To prevent stainless steel corrosion, our factory optimizes the structure when designing to reduce moisture retention.
2. Fabrication
During the manufacturing process, ensure that stainless steel is completely isolated from carbon steel to prevent any form of direct contact, use stainless steel-specific tools and equipment, and maintain a highly clean working environment to prevent carbon steel particles from contaminating the stainless steel surface and affecting its corrosion resistance.
3. Maintenance
Regular maintenance of stainless steel is essential. Cleaning is carried out using non-abrasive tools and mild detergents, avoiding the use of hard materials that may damage the surface.
Pay special attention to choosing chlorine-free or low-chlorine detergents to reduce the risk of pitting.
Regularly inspecting the surface of stainless steel to detect and treat any signs of corrosion in a timely manner can effectively extend its service life.
4. Water Treatment
Use treated water to reduce mineral deposits and corrosion risk. Softened water helps prevent deposits that can break down the passive layer.
Water treatment systems can remove harmful minerals and impurities, ensuring that the stainless steel remains protected. In areas with hard water, regular maintenance and cleaning are particularly important to prevent the build-up of deposits.
5. Protective Coatings
To further enhance the corrosion resistance and aesthetics of stainless steel, high-quality protective coatings such as polyurethane and epoxy resin can be applied. These coatings can effectively block corrosive elements in the environment and protect the stainless steel substrate from damage. Also, periodically check the integrity and adhesion of the coating and, if necessary, paint or recoat it to ensure its continued effectiveness.
As a manufacturer specializing in stainless steel products, our factory has implemented careful measures in the production process. We strictly classify, operate with special tools, and use advanced water treatment technology to ensure pure production. Regularly maintain the coating to protect the durable quality.
Choose us, you choose high-quality, easy-to-maintain, and durable stainless steel products!
Stainless Steel Grades with Better Corrosion Resistance
Choosing the right Grade of stainless steel is crucial, as not all stainless steel grades are created equal in terms of corrosion resistance. Choose the right grade for your specific application:
- Grade 304 stainless steel, a type of stainless steel that is widely used in the market, has excellent corrosion resistance under various environmental conditions due to its ratio of 18% Cr to 8% Ni.
- Grade 316: Contains 16% Cr, 10% Ni, and 2-3% Mo. The addition of molybdenum improves resistance to chlorides and other corrosive substances, making it suitable for marine and industrial applications.
- Grade 317: Similar to 316 but with higher Mo content for even greater resistance to chemical attack.
- Grade 321: Contains Ti, which stabilizes the structure against chromium carbide formation, making it ideal for high-temperature environments.
- 2205 Duplex: Contains 22% Cr, 5% Ni, and 3% Mo, which further enhances its protection against stress corrosion cracking, pitting, and even crevice corrosion.
- 2507 Super Duplex: Contains 25%Cr, 7%Ni, and 4%Mo, providing excellent corrosion resistance, especially in highly corrosive environments such as offshore and chemical processing.
- Grade 439: It not only performs better in stress corrosion cracking resistance but also significantly improves weldability and broadens its application areas.
- Grade 17-4 PH: Contains 17% Cr, 4% Ni, and Cu, offering a combination of high strength, hardness, and corrosion resistance. Used in aerospace, chemical, and petrochemical industries.
How to Remove Rust from Stainless Steel?
When you encounter rust on stainless steel, you can also use a special rust remover to remove the rust.
DIY——Lemon, Lime, and Salt
Mix lemon/lime juice and salt to make a scrubbing paste. The citric acid breaks down the rust, and the salt helps abrasive removal. It works well on small rust spots and is suitable for daily maintenance.
Store-Bought Rust Removers
For severe rust, using a commercially available professional rust remover is an effective method. These products can dissolve stubborn rust and restore the shine of stainless steel.
When using, follow the manufacturer’s instructions carefully to ensure effectiveness and safety. Provide ventilation when operating to protect your personal health.
Industrial Methods
Large or severely rusted items can be treated with sandblasting or chemical soaking. Sandblasting uses high-speed abrasives to remove rust, while chemical soaking immerses the item in a rust-dissolving solution. These methods are often used in industrial environments.
Why Choose Stainless Steel for Metal Fabrication?
Despite its susceptibility to corrosion in some cases, stainless steel remains one of the most popular materials used in metal fabrication due to its durability, aesthetic appeal, and resistance to staining and rusting. When properly cared for, stainless steel can last for many years without losing its lustre.
While it’s true that stainless steel does rust under certain conditions, with proper care and maintenance, it can last for many years without corroding. So if you’re looking for a material that will stand the test of time, stainless steel may be the right choice for your next project.
If you are considering using stainless steel for your next project, be sure to contact a reputable metal fabrication company in Australia to get started.