The CF8 gate valve, CF8M gate valve, CF3M gate valve are the core austenitic stainless steel materials for industrial settings, which directly determine the corrosion resistance life and safety level.
This guide compares the three most common stainless steel casting grades for gate valves, including their chemical composition and global certifications. Selecting the right material ensures a long service life and prevents system failure.
Decoding Brand Alphanumeric Codes
- The first letter “C”: Casting process identification (that is different from forging “AISI 304”).
- The second letter “F”: Austenitic iron-based alloy (Fe-Cr-Ni system).
- The numbers “8” or “3”: “8” → Standard carbon (≤0.08%) → Basic corrosion resistance. Meanwhile, “3” → Ultra-low carbon (≤0.03%) → Intergranular corrosion resistance.
- The suffix “M”: Added molybdenum element, which is an upgraded version of chloride ion corrosion resistance.
Equivalent Forging Grades (Key Reference for Purchasers)
| Casting Grades | Forgings Equivalent Grade | International Standards | Key Differences |
| CF8 | ASTM 304 | ASTM A351 | The casting structure is coarser and the pressure resistance is less than 10%. |
| CF8M | ASTM 316 | EN 1.4408 | Molybdenum content is 2–3%, improving seawater resistance. |
| CF3M | ASTM 316L | ISO 4991 | Low carbon with molybdenum for strong corrosion resistance and good weldability. |
A Comparison of Core Element Contents (ASTM A351 Standard)
| Elements | CF8 | CF8M | CF3M | Function & Impact | Critical Red Line & Performance Impact |
| Carbon (C) | ≤0.08% | ≤0.08% | ≤0.03% | Higher carbon increases strength but reduces resistance to intergranular corrosion. | Above 0.03%: Higher risk of intergranular corrosion in weld areas. |
| Chromium (Cr) | 18.0-21.0% | 18.0-21.0% | 17.0-21.0% | Core elements for resistant oxidation media. | Below 17%: Nitric and acetic acid corrosion rate increases about three times. |
| Nickel (Ni) | 8.0-11.0% | 9.0-12.0% | 9.0-13.0% | Stable austenite structure with improved acid resistance. | Below 8%: Higher probability of cold bending cracks. |
| Molybdenum (Mo) | Not added | 2.0-3.0% | 2.0-3.0% | Key to pitting resistance (particularly chloride ion). | No molybdenum: Seawater pitting life may be less than one year |
| Manganese (Mn) | ≤1.50% | ≤1.50% | ≤1.50% | Enhances deoxidation efficiency and strength. | Above 2%: Impact toughness decreases about 30%. |
| Silicon (Si) | ≤2.00% | ≤1.50% | ≤1.50% | Improves sealing and corrosion resistance. | Above 1.5%: Higher risk of casting porosity. |
Note:
- The ultra-low carbon (C≤0.03%) of CF3M is the core of its anti-welding corrosion
- The molybdenum content of CF8M/CF3M (Mo = 2-3%) determines the chloride ion resistance.
Helpful Rules of Purchasing
| Media Types | Mandatory Elements | Recommended Grades | Prohibited Grades |
| Dilute sulfuric acid or acetic acid | Cr≥18% | CF8 | – |
| Chloride ion solution | Mo≥2.0% | CF8M/CF3M | CF8 |
| High temperature welding pipeline | C≤0.03% | CF3M | CF8/CF8M |
| Concentrated nitric acid (＞65%) | Cr≥20% | Special high chrome steel | All CF series |
Note: Element deviations can cause failures. Therefore, selecting the right stainless steel for the environment ensures pipeline safety.
Detailed Comparison of Performance
Corrosion Resistance: Chloride ions vs Acidic media
The decisive role of molybdenum (Mo), such as seawater working conditions.
| Material | Pitting Corrosion Index (PRE) | Allowable chloride ion concentration | Typical Lifespan |
| CF8 | 18.5 | ≤200 ppm | 1-2 years (risk of perforation) |
| CF8M | 25.5 | ≤5000 ppm | 15+ years |
| CF3M | 25.5 | ≤5000 ppm | 15+ years |
Mechanical Strength: High Temperature vs Room Temperature
| Material | Room temperature tensile strength (MPa) | 538℃ strength retention rate | Critical warning temperature |
| CF8 | 485 | 58% | ≥425℃ need to be derated |
| CF8M | 485 | 55% | Same as CF8 |
| CF3M | 450 | 60% | Low carbon improves high temperature plasticity. |
Temperature Limit: Material Safety Boundary
| Performance Dimension | CF8/CF8M | CF3M | Breakthrough Solution |
| Low temperature limit | -196℃ | -254℃ | CF3M for Liquid Oxygen Rocket Valve |
| High temperature oxidation | 870℃ (continuous) | 870℃ (continuous) | >870℃ needs HK40 |
| Creep rupture | 425℃ | 425℃ | Inconel 625 for overlimit |
A Summary Table of Performance
| Material | Seawater Corrosion Resistance | Weldability | High Temperature Strength | Cost-Effectiveness | Recommended Scenarios |
| CF8 | 1/5 stars | 2/5 stars | 3/5 stars | 5/5 stars | Ordinary medium at normal temperature, chlorine-free |
| CF8M | 5/5 stars | 2/5 stars | 3/5 stars | 3/5 stars | Seawater or chlorinated process fluids |
| CF3M | 5/5 stars | 5/5 stars | 4/5 stars | 3/5 stars | Versatile choice for demanding conditions |
Global Certifications
| ASTM | EN | ISO | JIS | GB |
| CF8 | GX5CrNi19-10 | – | SCS13 | 022Cr19Ni10 |
| CF8M | GX5CrNiMo19-11-2 | CF-8M | SCS14A | 022Cr17Ni12Mo2 |
| CF3M | GX2CrNiMo19-11-2 | – | SCS16A | 022Cr17Ni12Mo2 |
Conclusion
Selecting between CF8, CF8M, and CF3M heavily depends on chemical exposure and welding needs. The CF8 gate valve is ideal for general water and food applications, while CF8M and CF3M resist acid and salt environments. Matching the specific stainless steel gate valve material to the application prevents expensive repairs and ensures safety.
YKY manufactures a variety of gate valves in multiple stainless steel grades. Our solutions are built to ensure zero-leak performance in different applications, including deep-sea pipelines and oilfield equipment, therefore providing long-term energy security. Moreover, we provide ready-to-ship valves with neutral packaging and flexible MOQ for easy scaling.
Partner with YKY for stable supply, fast quotes, and made-to-order valve solutions.
