Understand the basic composition of stainless steel
The corrosion resistance of stainless steel mainly comes from its alloy composition, especially the content of chromium and nickel. Generally speaking, the higher the chromium content, the better the corrosion resistance of stainless steel. Common types of stainless steel include 304, 316, etc. Among them, 316, due to the presence of molybdenum, has better corrosion resistance, especially in chloride environments.
Observe the surface treatment
The surface treatment method of stainless steel coils will also affect their corrosion resistance. Polishing, brushing and other surface treatments can enhance the corrosion resistance of stainless steel, as these treatments can remove impurities and oxide layers on the surface, making the protective film more uniform.
Conduct salt spray tests
Salt spray testing is a common accelerated corrosion testing method. It involves conducting spray tests on stainless steel by simulating salt spray in Marine environments to observe its corrosion resistance. This method can quickly assess the performance of stainless steel in harsh environments.
Chemical reagent testing
The corrosion resistance of stainless steel can be tested quickly by using specific chemical reagents. For example, the nitric acid titration method can be used to test the pitting corrosion resistance of stainless steel. Drop nitric acid on the surface of stainless steel and observe its reaction. If there is no obvious change, it indicates that the corrosion resistance is good.
Reference standards and certifications
Choosing stainless steel products that have been certified by authoritative institutions can provide greater security. Commonly used international standards for stainless steel include ASTM, EN, JIS, etc. These standards have clear regulations on the composition and properties of stainless steel.
Investigation of the actual application environment
Finally, the corrosion resistance of stainless steel coils also needs to be evaluated in combination with the actual application environment. For instance, in environments with high temperatures, high humidity or containing chemical substances, stainless steel types with stronger corrosion resistance should be selected.
1.Material grade (key indicator)
The corrosion resistance of different stainless steel components varies significantly. Comparison of common grades:
304 (A2 stainless steel) : It is basically corrosion-resistant and suitable for general environments (such as interior decoration, food equipment).
316 (A4 stainless steel) : Contains molybdenum (Mo), and has stronger resistance to chloride corrosion (preferred for coastal, chemical, and medical industries).
430/201: Low cost but poor corrosion resistance, only suitable for dry environments or short-term use.
Identification method: Request the supplier to provide the material report (Mill Test Certificate, MTC) to confirm whether the composition complies with the standards (such as ASTM, EN, JIS).
2. Surface treatment process
The surface condition directly affects the corrosion resistance:
2B (Cold-rolled bright annealed) : Standard industrial use, medium corrosion resistance.
BA (Bright Annealed) : Smoother, reduces dirt adhesion, suitable for food grade.
No.4 (Brushed) : Aesthetically pleasing but requires regular maintenance.
Passivation treatment: Acid washing is used to remove surface iron particles to enhance corrosion resistance.
Identification method: Observe whether the surface is uniform and free of defects, or simulate the corrosive environment with salt spray tests (such as ASTM B117).
3. Industry standard testing
Salt Spray Test
304 stainless steel: Usually no red rust for ≥48 hours.
316 stainless steel: Usually no red rust for ≥96 hours.
Intergranular corrosion test (ASTM A262) : To detect the corrosion resistance after welding or high-temperature processing.
Pitting equivalent (PREN value) :
PREN = %Cr + 3.3×%Mo + 16×%N
304: PREN≈19; 316: PREN≈25 (The higher the value, the more corrosion-resistant it is).
Identification method: Request the supplier to provide a third-party test report (such as SGS, TUV)
4.Actual application environment assessment
Choose the appropriate stainless steel coil according to the use scenario:
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Environment
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Recommended material
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Reason
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Coastal/high humidity
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316L
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Resistant to chloride ion corrosion
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Food/medicine
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304/316L
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Non-toxic, easy to clean
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Chemical/acidic environment
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317L/2205
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High molybdenum/duplex steel acid resistant
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High temperature environment
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310S
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Strong oxidation resistance
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Identification method: Provide the use environment details (such as temperature, contact with chemicals) to the supplier to match the material.
5. Simple Self-Check Methods (for Non-professional Reference)
Magnet test
Austenitic stainless steel (304/316) is usually non-magnetic or weakly magnetic (it may have slight magnetism after processing).
High magnetism may be 430 or inferior materials (with poor corrosion resistance).
Chemical reagent testing
Use stainless steel identification solution (such as Ni8 reagent) to distinguish 304/316 through color change reaction
