Contents
Is Stainless Steel Corrosion Resistant?
- John
Yes, but stainless steel does not possess absolute corrosion resistance. It is affected by many factors, including alloy composition, use environment and surface condition. We answer a series of questions about the corrosion resistance of stainless steel, including the source of stainless steel’s corrosion resistance, the corrosion resistance of different grades and the causes of stainless steel rust, and provide you with some rust prevention and rust removal methods.
Why Is Stainless Steel Corrosion Resistant?
Stainless steel is a corrosion-resistant alloy material, and its corrosion resistance mainly comes from the chromium (Cr) element in its alloy composition.
Protective Film
Stainless steel’s corrosion resistance comes from an extremely thin passive oxide layer that forms on its surface, mainly composed of chromium oxide. This oxidized layer is produced when chromium in stainless steel and oxygen in air or water react, which effectively avoids the metal coming into contact with corrosive substances.
Although this protective film is only a few nanometers thick, it is very strong and self-healing. If the surface is damaged, the oxide layer will automatically regenerate as long as there is enough oxygen in the environment. This feature makes stainless steel very suitable for use in harsh, wear-prone environments.
Stainless Steel Composition
The addition of other alloying elements affects the corrosion resistance of stainless steel. Some key elements include:
Chromium (Cr): Cr is a crucial element for imparting corrosion resistance to stainless steel, with a minimum content of 10.5% required to facilitate the formation of a protective oxide layer.
Nickel (Ni): Stabilizes the austenitic structure, improving toughness and corrosion resistance, especially in sour environments.
Molybdenum (Mo): Increases resistance to pitting and crevice corrosion, specifically in chloride-rich environments such as marine applications.
Nitrogen (N): Improves strength and resistance to localized corrosion. Often added to duplex and austenitic stainless steels.
Carbon (C): Improves hardness, but can cause intergranular corrosion. Use of lower carbon grades (e.g. 304L, 316L) avoids this problem.
Silicon (Si): Enhances oxidation resistance, especially at high temperatures, and improves resistance to sour environments.
Titanium (Ti): Prevents intergranular corrosion in welded stainless steels by stabilizing carbon and preventing the formation of chromium carbides.
Copper (Cu): It also increases the resistance to sulfuric acid and further enhances the steel’s ability to withstand stress corrosion cracking in chloride-containing environments.
Niobium (Cb/Nb): Prevents intergranular corrosion, similar to titanium, used in high temperature stainless steel grades (such as 347).
The exact composition of these elements can vary depending on the grade of stainless steel, affecting its resistance to different types of corrosion.
Structural Conditions
The microstructure of stainless steel is instrumental in determining its corrosion resistance capabilities. Classified based on their microstructural characteristics, there are three primary types of stainless steel:
Austenitic stainless steels: Face-centered cubic (FCC) crystal structure, non-magnetic, contains high amounts of chromium and nickel, and is the most corrosion-resistant of the stainless steel families.
Ferritic stainless steels: They are magnetic and have a body-centered cubic (BCC) crystal structure. They have a high chromium content and low nickel content, making them less corrosion resistant than austenitic stainless steels and more susceptible to corrosion in environments containing chlorides.
Martensitic stainless steels: Martensitic stainless steels (such as 410, 420) are a body-centered tetragonal (BCT) structure and are known for their hardness and strength, but have lower corrosion resistance than austenitic types.
Does Stainless Steel Rust?
Yes. Despite its name, stainless steel is not entirely immune to rust. In some environments and under specific conditions, stainless steel can indeed corrode.
Related reading:
Does stainless steel rust?
Does stainless steel turn green?
Why Does Stainless Steel Rust?
Rust on stainless steel occurs when the passive oxide layer is compromised or damaged. This breakdown can be caused by:
- Mechanical Damage: Scratches, dents, or impacts can disturb the protective layer, leaving the underlying metal exposed to the environment.
- Exposure to Chlorides: Chlorides, commonly found in saltwater, road de-icing salts, and even certain cleaning products, can breach the passive layer and lead to pitting corrosion.
- Lack of Oxygen: In environments where oxygen is limited, such as crevices or under deposits, the passive oxide layer may not regenerate, making the metal more vulnerable to corrosion.
Will Stainless Steel Rust Outside?
Sometimes. Stainless steel can perform well in outdoor environments, especially if high-quality grades like 316 or 2205 duplex stainless steel are used. However, in coastal regions where salt is present in the air, even grades like 304 can rust if not properly maintained. Regular cleaning and appropriate maintenance can prevent rust in these conditions.
Does Stainless Steel Rust in Water?
Yes. Stainless steel exhibits inherent resistance to water, though the constituents of the water can be pivotal in determining its lifespan. Specifically, hard water contains large amounts of minerals such as calcium and magnesium, which deposit residues on the surface of the steel, eventually damaging its corrosion-resistant passivation layer. Conversely, stainless steel can remain rust-free for a longer duration when exposed to soft or pure water environments.
Does Stainless Steel Rust in Salt Water?
Yes. Saltwater environments are particularly aggressive toward stainless steel. Chlorides in the saltwater accelerate the breakdown of the passive oxide layer, especially in lower grades like 304 stainless steel.
For marine applications, higher molybdenum content 316 stainless steel is typically used because of its high resistance to pitting and crevice corrosion. However, even 316 may corrode over time without proper maintenance.
How Long Does It Take for Stainless Steel to Rust?
The rate at which stainless steel rusts depends on several factors, including the grade of steel, the environment, and the presence of corrosive agents like chlorides. In mild environments, such as indoors, stainless steel may last indefinitely without rusting. In more aggressive environments, such as near the ocean, rust can appear within a few months if the steel is not properly maintained.
Does Surgical Steel Rust?
No. Surgical steel is designed to be corrosion-resistant, making it highly unlikely to rust under normal conditions. It typically contains a higher percentage of chromium, which forms a protective layer on the surface. However, if exposed to harsh conditions or improper care, it can develop corrosion over time. Regular cleaning and avoiding prolonged exposure to moisture can help maintain its integrity.
Types of Corrosion in Stainless Steel
There are many types of stainless steel corrosion due to different environmental and material exposure conditions.
Uniform Corrosion
Uniform corrosion affects the entire surface of stainless steel evenly, leading to a consistent loss of material. This type is common in highly corrosive environments like strong acids. To prevent it, select the appropriate stainless steel grade and use protective coatings.
Localized Corrosion
Localized corrosion affects specific areas of stainless steel, often causing more severe damage due to its hidden nature.
- Pitting Corrosion: Pitting corrosion is caused by the breakdown of the passive layer in localized areas, usually initiated by chlorides, resulting in the formation of small pits or holes in the metal surface. Pitting is common in marine environments and can quickly lead to material failure if not addressed.
- Crevice Corrosion: Crevice corrosion typically takes place in confined areas where oxygen cannot adequately enter, such as under gaskets, seals or deposits. Without enough oxygen, the passive layer cannot regenerate, leading to localized corrosion within the crevice.
Galvanic Corrosion
Galvanic corrosion occurs when stainless steel comes in contact with a more reactive metal, such as carbon steel, and an electrolyte, such as water, is present. In this case, the more reactive metal acts as the anode, accelerating dissolution, while the stainless steel acts as the cathode, with little or no corrosion.
Intergranular Corrosion
This is a particularly dangerous form of corrosion in stainless steel. It occurs along the edges of metal grains and does not cause any changes in the metal’s appearance, but it can dramatically reduce the mechanical properties of structures and parts, leading to sudden damage to equipment. Intergranular corrosion can be seen in both austenitic and ferritic stainless steels.
Stress Corrosion Cracking (SCC)
SCC occurs when stainless steel is subjected to tensile stress in corrosive environments, particularly those containing chlorides. The result is cracking, which can lead to sudden failure of the material.
How Can You Prevent Stainless Steel From Rusting?
Preventing rust on stainless steel requires a combination of choosing the right grade, maintaining the material, and treating it appropriately for the environment in which it will be used.
- Choose the Right Grade: For harsh environments, such as marine settings or industrial applications with high chloride exposure, use 316 or duplex stainless steel, which offer better resistance to pitting and crevice corrosion.
- Regular Cleaning: Keep stainless steel surfaces clean by regularly removing deposits of dirt, salt, and chemicals. Use non-abrasive cleaning tools and avoid cleaners that contain chlorides.
- Passivation: Passivation is the strengthening of the passive oxide layer on stainless steel through a chemical process. This treatment can be applied after fabrication to improve corrosion resistance.
- Protective Coatings: Using a protective coating such as powder coating can provide an additional barrier against corrosion.
How to Remove Rust from Stainless Steel?
If rust does form on stainless steel, there are several methods for removing it:
Mechanical Cleaning: Use a soft cloth or non-abrasive scrubbers to gently remove rust spots. It is recommended to refrain from using steel wool or metal brushes, as they have the potential to harm the surface and accelerate the process of rusting.
Chemical Rust Removers: There are rust removers specifically designed for stainless steel. These products dissolve the rust without damaging the surface or affecting the passive layer.
Passivation: After rust removal, consider passivating the surface to restore the oxide layer and prevent future rust.
Related reading:
How to Clean and Polish Stainless Steel: Rust Removal & Others
How to Remove Scratches from Stainless Steel?
What Is the Most Corrosion-Resistant Stainless Steel?
Among the common grades of stainless steel, 316 and 2205 duplex stainless steel are often considered the most corrosion-resistant. The heightened molybdenum content in 316 stainless steel imparts exceptional resistance against pitting and crevice corrosion, making it an ideal choice for applications in chloride-rich environments.
Stainless Steel Corrosion Resistance Chart
Below is a comparison of various stainless steel grades and their corrosion resistance in different environments:
| Grade | Cr (%) | Ni(%) | Mo (%) | Acidic Environment | Alkaline Environment | Saltwater/Chlorides | Applications |
| 304 (18-8) | 18 | 8 | 0 | Good (resistant to weak acids like nitric) | Moderate (resistant to weak alkalis) | Fair (can suffer pitting corrosion) | Food processing, kitchenware |
| 316 | 16 | 10 | 2-3 | Excellent (resistant to sulfuric, hydrochloric) | Good (resistant to alkaline environments) | Excellent (good resistance to chlorides) | Marine, chemical, medical devices |
| 410 | 12-13 | 0 | 0 | Moderate (resistant to mild acids) | Poor (limited alkaline resistance) | Poor (prone to rust in saltwater) | Cutlery, tools, valves |
| 430 | 16-18 | 0 | 0 | Fair (resistant to weak acids) | Moderate (resistant to weak alkalis) | Fair (prone to pitting in chlorides) | Automotive trim, kitchen equipment |
| 2205 (Duplex) | 22-23 | 4-6 | 3-5 | Excellent (resistant to strong acids) | Good (resistant to alkalis) | Excellent (resistant to chlorides) | Oil & gas, petrochemical |
| 17-4 PH | 15-17 | 3-5 | 0 | Good (resistant to weak acids) | Moderate (resistant to weak alkalis) | Fair (moderate chloride resistance) | Aerospace, valves, pump parts |
| 303 | 17-19 | 8-10 | 0 | Fair (not recommended for acidic environments) | Moderate (resistant to alkalis) | Poor (low resistance to chlorides) | Machined parts, fasteners |
| 316L | 16 | 10 | 2-3 | Excellent (similar to 316, with better welding) | Good (resistant to alkaline environments) | Excellent (superior chloride resistance) | Biomedical, chemical processing |
| 17-7 | 16-18 | 6-8 | 0 | Good (resistant to weak acids) | Fair (limited alkaline resistance) | Fair (moderate resistance to chlorides) | Springs, high-strength parts |
Does 304 Stainless Steel Rust?
No. 304 stainless steel is highly resistant to rust due to its chromium content, but it can still corrode under certain conditions, especially if exposed to saltwater, harsh chemicals, or inadequate cleaning. Regular maintenance and care can help prevent rusting.
Does Stainless Steel Corrode Regular Steel?
Yes, when stainless steel comes into contact with regular steel in the presence of moisture, galvanic corrosion can occur. The stainless steel becomes the cathode and does not corrode, but the regular steel, acting as the anode, will corrode more quickly. To prevent this, ensure the two metals are not in direct contact or use isolation techniques such as washers or coatings.
Which Is More Corrosion-Resistant: Austenitic or Martensitic Stainless Steel?
Like 304 and 316, austenitic stainless steels are more corrosion-resistant than martensitic stainless steels like 410. Austenitic steels have higher chromium and nickel content, which gives them better resistance to corrosion, especially in environments containing chlorides.
Does Stainless Steel Jewelry Rust?
Generally no. Stainless steel jewelry is typically made from 304 or 316 stainless steel, which provides excellent corrosion resistance. Despite their inherent rust resistance, prolonged exposure to harsh chemicals or saltwater can gradually lead to discoloration or tarnishing of these materials. To mitigate this, regular cleaning and proper maintenance practices are essential in preserving their original appearance and extending their lifespan.
Other Metals vs Stainless Steel
| Material | Acidic Environment | Alkaline Environment | Saltwater/Chlorides | General Corrosion Resistance | Common Applications |
| Titanium | Excellent (resistant to most acids) | Excellent (resistant to alkalis) | Excellent (outstanding in seawater) | Excellent | Aerospace, marine, medical implants |
| Aluminum | Fair (resistant to weak acids, but can pit) | Moderate (good in mild alkalis) | Fair (pitting in saltwater) | Good | Packaging, transportation, construction |
| Nickel | Excellent (high resistance to acids) | Excellent (very resistant to alkalis) | Excellent (resistant to seawater) | Excellent | Chemical industry, batteries, electronics |
| Brass | Good (resistant to mild acids) | Fair (can suffer corrosion in strong alkalis) | Poor (prone to dezincification in seawater) | Moderate | Plumbing, decorative fittings, musical instruments |
| Bronze | Good (resistant to mild acids) | Fair (resistant to weak alkalis) | Good (better than brass in saltwater) | Good | Marine hardware, bearings, sculptures |
| Galvanized Steel | Fair (zinc layer provides limited protection) | Poor (can corrode in strong alkalis) | Poor (zinc layer breaks down in saltwater) | Moderate (limited to environments without chloride exposure) | Construction, outdoor structures, fences |
| 304 Stainless Steel | Good (resistant to weak acids) | Good (moderate resistance to alkalis) | Fair (pitting in high chloride environments) | Good | Food processing, kitchenware |
| 316 Stainless Steel | Excellent (resistant to strong acids) | Good (resistant to alkalis) | Excellent (resistant to chlorides and seawater) | Excellent | Marine, chemical processing, medical equipment |
| Duplex Stainless Steel | Excellent (resistant to harsh acids) | Good (resistant to alkalis) | Excellent (superior chloride resistance) | Excellent | Oil & gas, marine, chemical applications |
Does Stainless Steel Oxidize?
Yes, stainless steel can oxidize. While it forms a protective oxide layer that helps prevent corrosion, exposure to certain conditions, like high temperatures or aggressive chemicals, can lead to oxidation and potential deterioration over time.
Does Stainless Steel Tarnish?
Stainless steel can tarnish over time, especially if exposed to harsh chemicals, pollutants, or high-salinity environments. Tarnishing usually appears as a surface discoloration but can be removed with proper cleaning. Regular maintenance and cleaning can prevent tarnishing and keep stainless steel looking pristine.
Related reading:
Will Stainless Steel Tarnish or Fade?
How to Buff & Polish Stainless Steel?
Does Steel Rust?
Yes, steel can rust. Rusting occurs when iron in steel reacts with moisture and oxygen, leading to corrosion. This is more common in carbon steel, which lacks the corrosion-resistant properties found in stainless steel.
Get Satisfactory Stainless Steel！
By understanding the types of corrosion that can affect stainless steel and how to prevent it, you can ensure the longevity and durability of your stainless steel products. Whether you are choosing stainless steel for marine environments, industrial applications, or jewelry, please contact us. As a professional stainless steel supplier and manufacturer, we are more than happy to help you choose the most suitable product!
