Why Is My Stainless Steel Rusting or Magnetic? Let’s Clear That Up
At Selectlok, we often get asked about two stainless steel phenomena that seem to defy what people know about this highly durable and corrosion-resistant metal: tea staining and magnetism.
In this blog, we’ll explore why these seemingly contradictory characteristics appear in stainless steel and explain what’s actually going on behind the scenes.
What Is Stainless Steel, Really?
Stainless steel is a family of iron-based alloys known for their corrosion resistance, primarily due to the presence of chromium. Chromium forms a passive film on the surface that protects the metal underneath.
There are several types of stainless steel, distinguished by their crystal structure, alloying elements, and atomic arrangements. Among the most common are austenitic, ferritic, and martensitic grades.
Tea Staining: What It Is and Why It Happens
Tea staining is the appearance of a reddish-brown discoloration on the surface of stainless steel. It most commonly affects stainless steel in outdoor or coastal environments and is especially prevalent on rougher surfaces that trap contaminants.
While it’s often mistaken for rust or deep corrosion, tea staining is typically superficial and does not indicate that the stainless steel has failed or is of poor quality.
What Causes Tea Staining?
Several factors contribute to tea staining:
- Salt-rich environments (e.g. coastal areas with high chloride levels).
- Rough surface finishes that trap pollutants.
- Contact with iron-rich materials, causing iron particle contamination.
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Prolonged exposure to moisture or stagnant water.
How to Clean and Prevent Tea Staining
Cleaning Tips:
- Mild detergent and warm water: Use a soft cloth to gently remove stains.
- Baking soda paste: Effective for tougher stains when scrubbed with a soft cloth or brush.
- White vinegar solution: Equal parts water and vinegar can dissolve staining; rinse thoroughly after use.
- Commercial cleaners: Stainless steel-specific products can help remove staining; always follow the manufacturer’s instructions.
📝 Tip: Always clean with the grain of the stainless steel to avoid scratching the surface.
Prevention Tips:
- Choose the correct grade of stainless steel for your environment.
- Opt for smooth, polished finishes that resist buildup.
- Avoid contact with iron or other iron-rich materials.
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In high-risk environments (e.g. marine areas), clean regularly and consider applying a protective coating.
Magnetism in Stainless Steel: Myth vs. Reality
Is Stainless Steel Magnetic?
The answer is: it depends.
Stainless steel is primarily made of iron, so it can be magnetic — but its magnetic properties vary significantly based on its microstructure and chemical composition.
- Austenitic grades (like 304 and 316): Generally non-magnetic, due to added nickel and higher chromium levels.
- Ferritic grades: More magnetic, due to their iron-rich composition.
However, even austenitic stainless steel can become slightly magnetic depending on how it’s processed or finished.
Why Can Stainless Steel Become Magnetic?
Some Selectlok products may show mild magnetic attraction — and here’s why:
- Cold working: Bending, stamping, or forming at room temperature can partially shift the structure toward iron-rich, making it magnetic.
- Mechanical deformation: Manufacturing stresses can change the microstructure.
- Surface finishing: Processes like sandblasting or brushing may introduce ferrous (iron-rich metal) contaminants that cause magnetic responses.
- Lack of annealing: Forged or cold-worked components that aren’t annealed may retain magnetic traits.
304 vs 316 Stainless Steel
These are the two most common grades found in Selectlok products:
- SS-304: General-purpose, non-magnetic under normal conditions. Widely used in architecture, domestic products, and food processing.
- SS-316: Contains molybdenum for added strength and corrosion resistance, making it ideal for marine environments. Slightly more expensive, but more robust in harsh conditions.
While both can become mildly magnetic during manufacturing, they remain non-ferritic in most applications.
Both tea staining and magnetism in stainless steel are often misunderstood. These phenomena don't mean the material is defective — they’re natural outcomes of environmental exposure or manufacturing processes.
At Selectlok, we ensure that our stainless steel products, whether 304 or 316 grade, meet the highest standards for quality and durability.
If you’re ever unsure about what stainless steel solution is right for your needs, we’re here to help.