What is CF8C Stainless Steel Casting?
Definition
CF8C is a niobium-stabilized austenitic stainless steel casting grade per ASTM A351. It is the cast equivalent of wrought AISI 347 stainless steel – meaning you get similar performance, but with the design freedom of casting.
This material is specifically engineered for cast components used in high-temperature services. It offers excellent resistance to intergranular corrosion – particularly in welded castings or applications exposed to the sensitization temperature range (450–850°C).
What Does “CF8C” Mean?
The designation “CF8C” follows the ASTM standard naming system for cast stainless steels. Each character carries specific meaning:
- C (first letter) stands for “corrosion-resistant,” indicating this is a stainless steel grade intended for corrosive service environments.
- F denotes the alloy’s nominal location on the Fe-Cr-Ni ternary system—specifically representing the 19% Cr / 9% Ni austenitic family.
- 8 indicates the maximum carbon content of 0.08%, a limit set to balance strength and corrosion resistance while complementing the stabilizing effect of niobium in this grade.
- C (final letter) stands for “Columbium,” now more commonly known as Niobium (Nb). Columbium is a stabilizing element added to this grade to combine with carbon and prevent chromium depletion at grain boundaries.
Chemical Composition & Mechanical Properties of CF8C Stainless Steel
CF8C Chemical Composition
The table below shows the ASTM A351 composition. Pay special attention to the niobium content.
| Element | Content (%) |
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 1.50 |
| Silicon (Si) | ≤ 1.50 |
| Chromium (Cr) | 18.0 – 21.0 |
| Nickel (Ni) | 9.0 – 12.0 |
| Molybdenum (Mo) | ≤ 0.50 |
| Niobium (Nb) | ≥ 8 × C%, ≤ 1.00 |
| Phosphorus (P) | ≤ 0.040 |
| Sulfur (S) | ≤ 0.040 |
| Iron (Fe) | Balance |
CF8C Mechanical Properties
Use these values to confirm the material can handle your service conditions.
| Properties | Value |
| Tensile Strength (min) | ≥ 485 MPa (70 ksi) |
| Yield Strength (min) | ≥ 205 MPa (30 ksi) |
| Elongation (min) | ≥ 30% |
| Hardness (Brinell) | ~156 – 170 HB (Typical) |
CF8C Equivalent Materials – International Standards Cross-Reference
Matching CF8C to your local standard? This table gives you the equivalents.
| Standard | Grade |
| ASTM | CF8C |
| UNS | J92710 |
| Wrought Equivalent | 347 / S34700 |
| EN / DIN | 1.4552 / GX5CrNiNb18-9 |
| JIS | SCS21 |
| BS | 347C17 |
Key Advantages: Why Choose CF8C Castings?
CF8C offers three critical advantages for demanding high-temperature applications, and as a casting grade, it brings additional value to component manufacturing.
- Niobium stabilization prevents intergranular corrosion by forming stable NbC carbides. For cast components that require welding during fabrication or repair, this ensures your castings maintain corrosion resistance without the risk of weld decay.
- CF8C maintains excellent high-temperature strength under prolonged thermal exposure. As a casting grade, this allows you to produce complex, near-net-shape components that perform reliably in high-temperature services – at a lower cost than wrought alternatives.
- CF8C delivers good weldability without requiring post-weld heat treatment. This streamlines your production workflow, eliminates a time-consuming step, and gets your castings from mold to installation faster. This is what makes CF8C particularly valuable for large fabricated components.
How Does CF8C Compare to Other Materials?
CF8C vs. CF8
CF8 is cheaper and works for low-temperature service, but it lacks niobium stabilization. CF8C resists intergranular corrosion at high temperatures and after welding – making it the better choice for demanding conditions.
CF8C vs. CF8M
CF8M fights pitting in chloride-rich environments with its molybdenum addition. But if you’re dealing with high-temperature, hydrogen-rich services, CF8C’s niobium stabilization gives you the edge against carbide precipitation.
CF8C vs. 347 Stainless Steel (Wrought)
347 is CF8C’s wrought equivalent – chemically they’re nearly the same. The difference is in the process: if you need complex, large components, CF8C casting gives you the same performance with far more design freedom than wrought forms can offer.
What Can YTD Casting Do for Your CF8C Castings?
Understanding the material is only half the picture. The other half is finding a casting partner who can deliver on these technical requirements. At YTD Casting, we turn CF8C’s material advantages into finished components you can install with confidence.
Niobium Chemistry Verification
We verify every heat to ensure niobium meets the 8× carbon minimum per ASTM A351. If the chemistry isn’t right, we don’t pour. This is the first step – and we never skip it.
Heat Treatment Capability
As-cast CF8C contains non-uniform carbides and residual stresses. We heat-treat all castings to 1040°C–1120°C, holding until carbides dissolve completely, followed by rapid water quenching. This optimizes ductility, toughness, and corrosion resistance.
Process Flexibility: Sand or Investment Casting
- Silica Sol Investment Casting: Ideal for small-to-medium, thin-walled, intricate parts (e.g., turbocharger components, EGR valves) requiring tight tolerances (ISO 8062 CT4–CT6) and smooth surfaces.
- Resin Sand Casting: Best suited for heavy, thick-walled components (e.g., high-pressure petrochemical valve bodies, manifold housings) up to 2,000 kg.
Conclusion
To sum up, CF8C is more than a material grade – it’s a solution for high-temperature, corrosive, and hydrogen-rich environments where reliability matters. Specifying the right alloy is only half the job. The real difference comes from working with a casting partner who understands the nuances of this stabilized stainless steel. At YTD Casting, we combine material expertise with process control to deliver CF8C castings you can trust. Contact us today to discuss your CF8C project.
FAQs
Is CF8C magnetic?
Yes, slightly. While austenite is non-magnetic, quality CF8C castings contain 5% to 12% delta ferrite to prevent solidification cracking. This small ferrite percentage imparts a slight magnetic attraction, which is completely normal.
CF8C vs. Inconel – which one should I choose?
CF8C handles high-temperature services up to ~650°C for mechanical strength, but its corrosion resistance is most reliable below 490°C. For extreme heat beyond 650°C or aggressive oxidation, Inconel is the better choice – at a significantly higher cost.
Can CF8C be machined easily?
Yes, but it work-hardens during cutting. Use sharp tooling, proper speeds, and cooling for best results.
Does CF8C require post-weld heat treatment?
Generally no – thanks to niobium stabilization. However, major weld repairs (>20% wall thickness) may require solution annealing to restore corrosion resistance.
What is the maximum service temperature for CF8C?
Typically 480°C to 650°C. Extended exposure above 540°C may lead to sigma phase embrittlement over time, which can reduce toughness.
What is CF8C-Plus?
An enhanced version developed by ORNL, with Mn and N added for creep resistance. It offers higher high-temperature strength than standard CF8C but is not a direct substitute.
Is CF8C readily available?
Yes, through most stainless steel foundries. Custom or high-integrity castings may need extra time for verification and inspection.
