CF8 stainless steel is one of the most widely specified stainless steel casting alloys in industries ranging from water treatment to food processing. Thanks to its excellent balance of corrosion resistance, castability, and cost-effectiveness, it has become the standard material for producing complex stainless steel cast components.
What is CF8 Stainless Steel?
CF8 is an austenitic stainless steel casting grade specified under ASTM A351 for corrosion-resistant castings. It shares similar chromium and nickel contents with AISI 304 stainless steel. So, many engineers recognize CF8 as the cast equivalent of 304 stainless steel. But the two materials are not identical. CF8 is specifically developed for casting applications, with a chemical composition and microstructure optimized to improve molten metal flow, reduce casting defects, and produce reliable components with complex geometries.
What does “CF8” mean?
Unlike wrought stainless steels that use AISI designations such as 304 or 316, cast stainless steels follow the ASTM alloy designation system. Each letter and number in the name “CF8” conveys specific information about the alloy.
- C indicates a corrosion-resistant alloy intended for service in corrosive environments.
- F identifies the alloy family within the iron-chromium-nickel (Fe-Cr-Ni) stainless steel system.
- 8 represents a maximum carbon content of 0.08%.
This naming system also explains related casting grades such as CF3, CF8M, and CF3M, which differ primarily in carbon content and alloying elements to meet different corrosion resistance and welding requirements.
Chemical Composition of CF8 Stainless Steel
The chemistry of CF8 is tightly controlled under ASTM A351 to ensure consistent corrosion resistance and mechanical performance:
| Element | Content (%) |
|---|---|
| Chromium (Cr) | 18.0 – 21.0% |
| Nickel (Ni) | 8.0 – 11.0% |
| Carbon (C) | ≤ 0.08% |
| Manganese (Mn) | ≤ 1.50% |
| Silicon (Si) | ≤ 2.00% |
| Phosphorus (P) | ≤ 0.04% |
| Sulfur (S) | ≤ 0.04% |
| Iron (Fe) | Balance |
The combination of these elements gives CF8 an excellent balance of corrosion resistance, mechanical performance, and manufacturing reliability, making it suitable for both investment casting and sand casting applications. This also earned CF8 the industry nickname “18/8 cast stainless steel”, reflecting its approximate chromium and nickel content.
Mechanical Properties of CF8 Stainless Steel
ASTM A351 specifies the minimum mechanical requirements that CF8 castings must achieve after proper heat treatment.
| Property | Typical Value |
| Tensile Strength | ≥ 485 MPa (70 ksi) |
| Yield Strength | ≥ 205 MPa (30 ksi) |
| Elongation | ≥ 35% |
| Hardness | 134–196 HB |
In addition to its mechanical strength, CF8 offers several physical characteristics that make it suitable for demanding industrial environments.
| Property | Typical Value |
|---|---|
| Chromium (Cr) | 18.0 – 21.0% |
| Nickel (Ni) | 8.0 – 11.0% |
| Carbon (C) | ≤ 0.08% |
| Manganese (Mn) | ≤ 1.50% |
| Silicon (Si) | ≤ 2.00% |
| Phosphorus (P) | ≤ 0.04% |
| Sulfur (S) | ≤ 0.04% |
| Iron (Fe) | Balance |
Another characteristic worth noting is the slight magnetism of CF8. Although austenitic stainless steels are generally considered non-magnetic, cast CF8 intentionally contains a small amount of delta ferrite (typically 5–15%), which helps to reduce the risk of hot cracking during solidification but also imparts slight magnetism.
Material Equivalents and Standards
Because stainless steel designations vary among international standards, engineers frequently need to identify equivalent materials during product design or supplier qualification.
The following table summarizes the most commonly recognized equivalents for CF8 stainless steel.
| Standard | Equivalent |
| ASTM (Cast) | A351 CF8 |
| UNS | J92600 |
| Wrought Equivalent | AISI 304 |
| DIN (Germany) | 1.4308 |
| JIS (Japan) | SCS13A |
Although these materials are considered equivalent for many engineering applications, they are not always interchangeable. Differences in manufacturing methods, heat treatment, casting quality, and dimensional requirements should always be considered when selecting a material for a specific application.
Comparison with Other Materials
CF8 vs. SS 304
CF8 and 304 stainless steel share approximately 98% of their alloy composition. The key difference lies not in chemistry, but in form and microstructure:
- 304 is a wrought grade—produced by rolling, forging, or extruding. It is available as sheets, plates, bars, and pipes.
- CF8 is a cast grade—produced by pouring molten metal into a mold. It only exists as cast components.
To aid castability, CF8 has slightly higher silicon (max. 2.0% vs. 0.75%). Its microstructure contains 5-15% delta ferrite to prevent hot cracking—this also gives CF8 weak magnetism, while 304 is fully austenitic and non-magnetic.
CF8 vs. CF3 vs. CF8M
Here is a comparison of three casting grades—CF8, CF3, and CF8M—focusing on their key chemical and casting differences:
| Grade | CF8 (Standard Austenitic) | CF3 (Low-Carbon Version) | CF8M (Molybdenum-Enhanced Version) |
| Equivalent Wrought Grade | 304 Stainless Steel | 304L Stainless Steel | 316 Stainless Steel |
| Key Chemical Differences | Carbon content ≤ 0.08%, molybdenum-free | Ultra-low carbon (≤ 0.03%), molybdenum-free | Carbon content ≤ 0.08%, containing 2%–3% molybdenum (Mo) |
| Corrosion Resistance | Good(in oxidizing environments and mild media) | Excellent (to intergranular corrosion /sensitization-free due to ultra-low carbon) | Superior pitting and crevice corrosion resistance in chloride-containing environments (PREN ≥ 26) |
| Casting Fluidity | Good (Si 1.5-2.0%) | Slightly poor; higher viscosity risks incomplete fill in thin sections | Excellent. Molybdenum improves molten metal flow |
| Risk of Hot Cracking in casting | Low (ferrite 3-20%) | Moderate (ultra-low carbon makes ferrite control harder) | Low (Mo stabilizes microstructure) |
| Post-Weld Heat Treatment | Mandatory (1040°C solution treatment) | Generally not required | Recommended (optional for non-critical areas) |
| Cost | Baseline | Slightly more expensive than CF8 | 15%–25% more expensive than CF8 |
Common Application of CF8 Stainless Steel
CF8 stainless steel is widely used in industries where moderate corrosion resistance, mechanical strength, and cost efficiency are required. It performs well in water-based environments, mild chemicals, and general industrial service conditions, making it a versatile material for both standard and custom cast components.
Water Treatment and Fluid Handling
CF8 is commonly used in water treatment systems and fluid handling equipment due to its reliable performance in fresh water, steam, and non-aggressive media.
Typical components include valve bodies, pump casings, impellers, pipe fittings, and strainers. For more aggressive environments such as seawater or chloride-rich fluids, CF8M is generally preferred.
Food and Beverage Equipment
Thanks to its clean surface finish and corrosion resistance, CF8 is suitable for food processing and sanitary applications after proper polishing and passivation.
It is often used for food processing housings, sanitary valves, grinder components, and fluid transfer equipment where hygiene and durability are important.
General Industrial Equipment
In mild chemical environments and general machinery applications, CF8 offers a good balance between performance and cost. It is commonly found in pump and valve components, structural parts, brackets, housings, and flow control systems.
Note: For parts permanently submerged in salt water (like deep-sea propellers), we highly recommend upgrading to molybdenum-enhanced CF8M.
Crucial Casting Process Considerations for CF8
Linear Shrinkage
CF8 shrinks approximately 1.8–2.2% during solidification. Poor compensation leads to shrinkage porosity, cavities, or cracks.
Thus, we will compensate for this in mold design. For critical components, we typically use numerical simulation to optimize gating and riser design for your custom castings.
Solution Annealing
CF8 requires solution annealing at 1040–1065°C to deliver full corrosion resistance. The cycle: heat, hold to dissolve chromium carbides, then water quench.
Skipping this step leads to intergranular corrosion—chromium depletion at grain boundaries.
At YTD Casting, we fully anneal every CF8 casting and offer re-annealing after welding per your specifications.
Conclusion
As the cast equivalent of 304 stainless steel, CF8 is a highly versatile and cost-effective alloy offering excellent corrosion resistance and mechanical properties across industries. However, achieving consistent performance requires more than just the right alloy; it demands expert mold design, heat treatment, and quality control. Working with an experienced investment casting manufacturer ensures every stage of production is optimized for long-term reliability.
If your project requires custom CF8 stainless steel castings, our engineering team can assist with material selection, design optimization, prototype development, and full-scale production. From precision investment casting to CNC machining and surface finishing, we provide complete manufacturing solutions tailored to your application.
FAQs
Is CF8 magnetic?
Slightly. Unlike wrought 304 stainless steel, CF8 typically contains 5–15% delta ferrite, resulting in weak magnetic properties. This is normal and does not indicate poor material quality.
Can CF8 rust?
Like all stainless steels, CF8 is not completely immune to corrosion. Under normal atmospheric conditions and in fresh water or mild chemical environments, it provides excellent corrosion resistance. However, prolonged exposure to chlorides or seawater may cause pitting corrosion, in which case CF8M is usually a better choice.
Can CF8 stainless steel be used for high-temperature applications?
CF8 is suitable for continuous service up to about 538°C (1000°F). Above this range, oxidation increases, and higher-temperature alloys are recommended.
What is the difference between CF8 and CF8M? Is the upgrade worth it?
The primary difference is the addition of 2–3% molybdenum in CF8M. This significantly improves resistance to pitting and crevice corrosion, especially in chloride-containing environments such as seawater and chemical processing plants. It is worth upgrading to CF8M if you need parts that serve seawater/chemical applications.
What is the machinability rating of CF8 castings?
CF8 stainless steel has a machinability rating of approximately 50–60% relative to B1112 free-machining carbon steel. While it is not considered a free-machining material, it can still be machined effectively using appropriate tooling and cutting parameters.
What casting methods are best for CF8 stainless steel?
The answer depends on the component size and complexity. Investment casting is ideal for complex parts requiring high dimensional accuracy, tight tolerances, and excellent surface finish. Sand casting is generally more suitable for large components with relatively simple geometries and lower tooling costs.
What inspections and certificates should I demand for CF8 castings?
MTC, PMI, dimensional report, and NDT (PT/RT) per ASTM A351 and your specifications.
Does every CF8 casting require heat treatment?
Most corrosion-resistant CF8 castings are solution annealed after casting to achieve the required corrosion resistance and mechanical properties. Unless otherwise specified, solution annealing is considered standard practice for high-quality CF8 components.
