NEWS&CASES
Time：2026-04-24
Class：Blog
What is the corrosion resistance of 304 and 316 stainless steel plates, and how significant is the difference between the two?
1. Corrosion Resistance of 304 Stainless Steel Plates
304 stainless steel plates (UNS S30400, EN 1.4301) are composed of 18-20% chromium, 8-10.5% nickel, and no molybdenum, which forms the foundation of their corrosion resistance. Its corrosion resistance performance is mainly reflected in mild environments, making it the most cost-effective choice for general scenarios.
In daily and general industrial environments, 304 stainless steel plates perform excellently: they can resist corrosion from clean air, fresh water, and most household chemicals (such as common detergents and weak acids like acetic acid). They are widely used in kitchen equipment, architectural handrails, food processing equipment (non-corrosive media), and indoor decorative panels because they do not rust or degrade under normal use conditions.
However, 304 has obvious limitations in harsh environments: it is prone to pitting and crevice corrosion when exposed to chloride ions (Cl⁻) above ~150 ppm. For example, in coastal areas with high salt spray, marine environments, or applications involving salt water, 304 plates may start to rust within months. At temperatures above 60°C, its resistance to chloride corrosion further decreases, and it may even suffer stress corrosion cracking under long-term stress.
Additionally, 304 stainless steel is sensitive to thiosulfate anions released by pyrite oxidation (such as in acid mine drainage), which can lead to severe pitting corrosion when in contact with sulfide-rich materials. For welded components, 304’s carbon content (max 0.08%) may cause intergranular corrosion if not properly treated, so 304L (low carbon) is often preferred for corrosive welding scenarios.
2. Corrosion Resistance of 316 Stainless Steel Plates
316 stainless steel plates (UNS S31600, EN 1.4401) are upgraded based on 304, with the key addition of 2-3% molybdenum (Mo), plus a higher nickel content (10-14%) and slightly lower chromium content (16-18%). Molybdenum is the "game-changer" for its corrosion resistance, making it far superior to 304 in harsh corrosive environments.
The core advantage of 316 lies in its strong resistance to chloride-induced corrosion: molybdenum cooperates with chromium to form a denser and more stable Cr₂O₃-MoO₃ composite passivation film on the surface, which effectively blocks the penetration of chloride ions and inhibits pitting and crevice corrosion—the most common corrosion forms in salt-rich environments. In standard seawater (about 3.5% salinity), 316 can be used for years or even decades without rusting, while 304 may corrode in months.
316 also performs well in acidic and high-temperature environments: it can resist corrosion from most weak acids and some strong acids (such as sulfuric acid and phosphoric acid), and is more resistant to vulcanization corrosion in high-temperature sulfur-containing environments (e.g., refinery heat exchangers). The low-carbon variant 316L (carbon content ≤0.03%) further avoids intergranular corrosion caused by carbide precipitation during welding, making it suitable for welded components in corrosive environments.
It should be noted that 316 is not completely rust-free: long-term immersion in high-concentration saturated salt water or high-temperature salt water (above 60°C), surface scratches, welding residues, or long-term high stress may still damage its passivation film, leading to local corrosion, though the probability is much lower than that of 304.
3. How Significant Is the Difference in Corrosion Resistance Between 304 and 316?
The difference in corrosion resistance between 304 and 316 is not subtle—it is a qualitative gap determined by their chemical composition, especially the presence of molybdenum in 316. We can quantify and summarize the differences through key indicators and practical scenarios:
3.1 Quantitative Comparison of Corrosion Resistance
- Chloride ion resistance: 304 can only withstand chloride ion concentrations up to about 150-400 ppm (depending on temperature), while 316 can resist concentrations above 2000 ppm—its pitting resistance is more than 5 times that of 304.
- Salt spray test performance: 304 starts to rust within 72 hours under ASTM B 117 salt spray test conditions, while 316 shows no visible corrosion even after 1000 hours.
- Acid resistance: 304 is only suitable for weak acid environments, while 316 can resist most acidic media, including some strong还原性 acids.
3.2 Practical Scenario Differences (Critical for Selection)
The significance of the corrosion resistance difference is most obvious in practical applications—choosing the wrong grade can lead to premature failure and high maintenance costs:
- Indoor/non-corrosive environments: The difference is negligible. 304 is sufficient, and its lower cost (316 is 20-30% more expensive than 304) makes it more cost-effective.
- Coastal/marine environments: The difference is decisive. 304 will corrode quickly, while 316 can maintain long-term stability, making it the only reliable choice for ship accessories, marine engineering, and seawater desalination equipment.
- Chemical/medical industries: The difference is critical. 316’s resistance to corrosive chemicals and sterilizing agents makes it suitable for chemical processing equipment, medical implants, and pharmaceutical production tools—304 will fail quickly in these scenarios due to corrosion.
- High-temperature/high-stress environments: 316 is more stable. 304 is prone to stress corrosion cracking in high-temperature salt water, while 316’s risk is significantly lower, making it suitable for heat exchangers and high-stress components.
4. Key Takeaways for Practical Selection
To help you avoid wrong choices, here is a concise selection guide based on corrosion resistance differences:
- Choose 304 stainless steel plates if: Your application is in indoor, dry, or mild environments (e.g., kitchen sinks, indoor handrails, non-corrosive food processing equipment), and cost control is a priority.
- Choose 316 stainless steel plates if: Your application involves salt water, salt spray, corrosive chemicals, high temperatures, or high stress (e.g., marine equipment, chemical tanks, coastal buildings, medical devices)—the extra cost is worthwhile to avoid premature corrosion and replacement.
In summary, 304 and 316 stainless steel plates have distinct corrosion resistance characteristics: 304 is a cost-effective choice for mild environments, while 316 is a high-performance option for harsh corrosive scenarios. The difference between them is not just a "slight improvement" but a fundamental upgrade in corrosion resistance, which directly determines whether the product can meet long-term use requirements. Choosing the right grade based on your specific environment will maximize the value of your investment.