1. Introduction
CF8 stainless steel, often referred to as cast CF8, represents the cast equivalent of wrought 304 stainless steel.
With a balanced chemistry—up to 0.08 % carbon, 18–20 % chromium, and 8–10.5 % nickel—CF8 combines the corrosion resistance of 304 with the design freedom of casting.
As a result, engineers deploy CF8 in pump bodies, valve housings, and sanitary fittings where intricate geometries and aggressive environments converge.
Historically, the shift from wrought 304 sheet goods to cast CF8 components began in the mid‑20th century.
Foundries recognized that molten CF8 could fill complex molds—features impossible to machine economically—while still delivering reliable durability.
Consequently, CF8 underpins a wide range of industrial hardware, from chemical‑processing equipment to marine fittings.
2. Chemical Composition & Metallurgy
CF8 stainless steel—classified as a cast equivalent of wrought 304 stainless steel—features a precisely balanced chemical composition designed to provide excellent corrosion resistance, strength, and castability.
As a standard grade under ASTM A351 and ASTM A743, CF8 follows specific compositional limits to ensure consistent quality and performance in industrial applications.
Nominal Chemical Composition (Weight Percent, %)
| Element | Content (%) | Function |
|---|---|---|
| Carbon (C) | ≤ 0.08 | Limits carbide formation; improves corrosion resistance and weldability |
| Chromium (Cr) | 18.0–20.0 | Provides oxidation and corrosion resistance |
| Nickel (Ni) | 8.0–10.5 | Enhances ductility and toughness; stabilizes austenitic structure |
| Manganese (Mn) | ≤ 1.5–2.0 | Deoxidizer; improves hot working properties |
| Silicon (Si) | ≤ 1.5 | Promotes fluidity in casting; acts as deoxidizer |
| Phosphorus (P) | ≤ 0.04 | Controlled to avoid embrittlement |
| Sulfur (S) | ≤ 0.04 | Minimized to reduce hot cracking susceptibility |
| Iron (Fe) | Balance | Primary matrix element |
These proportions mirror wrought 304 stainless steel, but stainless steel CF8 retains a controlled fraction of δ‑ferrite—typically 3–7%-to prevent hot cracking during solidification.
Foundry practice often targets 4–6% ferrite by adjusting cooling rates and through minor silicon or nitrogen tweaks.
Transitioning from liquid to solid, CF8 undergoes a primary austenite solidification followed by a ferrite‑austenite transformation in the interdendritic regions.
This duplex microstructure – austenite islands in a ferritic matrix – enhances toughness and crack‑arresting ability.
Moreover, the presence of δ‑ferrite curbs the growth of carbide networks at grain boundaries, thus reducing the risk of sensitization during post‑weld cooling.
3. Standards, Equivalents & Specifications
Industry specifications anchor CF8’s quality:
- ASTM A351/A743 designates CF8 under cast stainless steels and links it to UNS J92900.
- In Europe, CF8 corresponds to EN‑JS 304 (1.4372) and ISO 17916.
- Japanese standards list it as JIS FC304.
Typical procurement documents call for radiographic inspection, chemical analysis within ± 0.03 % of nominal, and maximum hardness of 200 HB.
Such criteria guarantee consistent performance in corrosive and mechanical service.
4. Physical & Mechanical Properties of CF8 Stainless Steel
CF8 stainless steel, the cast counterpart of AISI 304, is prized for its balanced mechanical strength, ductility, and excellent corrosion resistance.
These characteristics make it a versatile choice across many industries—from chemical processing to marine and food-grade applications.
Below is a detailed breakdown of its physical and mechanical properties, supported by relevant data.
Mechanical Properties (Room Temperature)
| Property | Typical Value | Notes |
|---|---|---|
| Tensile Strength | ≥ 485 MPa (70 ksi) | Ensures structural integrity under stress |
| Yield Strength (0.2% offset) | ≥ 205 MPa (30 ksi) | Adequate for moderate-load applications |
| Elongation | ≥ 30% | Reflects excellent ductility and formability |
| Hardness (Brinell HBW) | ~150–190 | Depends on cooling rate and microstructure |
| Impact Toughness (Charpy) | > 80 J at 20 °C | Varies with δ-ferrite content and temperature |
These values conform to ASTM A351/A743 requirements and can vary slightly depending on the casting method, heat treatment, and geometry of the component.
Physical Properties
| Property | Typical Value | Notes |
|---|---|---|
| Density | ~7.9 g/cm³ | Comparable to wrought 304 |
| Melting Range | 1400–1450 °C | Important for foundry pouring temperatures |
| Thermal Conductivity | 16.2 W/m·K @ 100 °C | Lower than carbon steel; affects heat dissipation |
| Specific Heat Capacity | ~500 J/kg·K | Moderate thermal inertia |
| Coefficient of Thermal Expansion | 17.2 µm/m·°C (20–100 °C) | Must be considered in thermal cycling applications |
| Electrical Resistivity | 0.72 µΩ·m | Typical for austenitic grades |
Elevated Temperature Behavior
CF8 retains reasonable strength up to ~400 °C (752 °F), beyond which grain coarsening and sensitization may reduce mechanical and corrosion performance.
It is not recommended for high-stress service above this range unless stabilized or modified.
Fatigue and Creep Resistance
- Fatigue strength (10⁷ cycles): ~240 MPa (35 ksi) in air at RT
- Creep resistance: Acceptable for light to moderate thermal stress but not suitable for long-term high-temperature exposure like CF8C or heat-resistant alloys.
Machinability
Although not as free-machining as some ferritic or martensitic steels, stainless steel CF8 offers good machinability for an austenitic alloy.
Tools with optimized cutting angles, proper feeds/speeds, and coolant systems are recommended.
Its non-magnetic nature in fully austenitic states can also be advantageous in select technical environments.
5. Corrosion Resistance
CF8 excels in general corrosion scenarios—resisting dilute acids and chlorides up to 200 ppm at ambient temperature.
Its Pitting Resistance Equivalent Number (PREN) of roughly 17 reflects a modest improvement over 304, translating to pitting initiation times 20–30 % longer in 3.5 % NaCl solutions.
Nonetheless, CF8 remains susceptible to stress corrosion cracking (SCC) in high‑chloride, high‑temperature environments.
To mitigate SCC, designers often limit service temperatures to < 60 °C or specify CF8M/CF3M (with added molybdenum) for harsher conditions.
6. Castability & Foundry Practices of CF8 Stainless Steel
CF8 stainless steel—cast equivalent to wrought 304—offers excellent casting characteristics that enable the production of complex geometries, pressure-bearing components, and corrosion-resistant structures.
Its castability is one of the key reasons for its widespread use in demanding industrial sectors. Below is a professional analysis of its casting behavior and best foundry practices.
Key Castability Features
Good Fluidity
CF8 stainless steel exhibits moderate to good fluidity, which allows it to fill intricate mold cavities effectively.
This is especially important for producing components with thin walls or fine details.
The typical pouring temperature ranges from 1450°C to 1550°C, depending on part geometry and section thickness.
Wider Freezing Range
Stainless steel CF8 solidifies over a temperature range of approximately 50–80°C, making it more prone to micro-porosity and shrinkage defects compared to materials with narrow solidification ranges.
As such, proper feeding systems and riser designs are essential.
Moderate Linear Shrinkage (~1.8–2.2%)
The alloy’s contraction during solidification is relatively predictable, allowing foundries to design molds with appropriate shrinkage allowances and compensation strategies to achieve dimensional accuracy.
Resistance to Hot Cracking
The presence of a small amount of δ-ferrite (3–7%) in the microstructure enhances resistance to hot tearing and cracking during cooling, especially in thicker cross-sections.
Suitable Casting Methods for CF8 Stainless Steel
| Casting Method | Key Features | Advantages | Typical Applications |
|---|---|---|---|
| Sand Casting | Uses bonded sand molds; suitable for medium to large components | Cost-effective for low-to-medium volumes; supports complex geometries | Pump bodies, valve housings, pipe fittings, covers |
| Investment Casting (Lost Wax) | Produces high-precision castings with fine details and smooth surfaces | Excellent surface finish (Ra < 3 µm), tight tolerances (±0.1–0.2 mm), minimal machining | Sanitary fittings, aerospace parts, food-grade components |
| Shell Mold Casting | Thin-walled sand mold with resin coating | Superior dimensional accuracy over green sand; good surface finish | Instrument housings, small precision parts |
| Centrifugal Casting | Metal poured into a rotating mold; produces cylindrical parts | High-density structure, minimal porosity, excellent mechanical strength in radial direction | Pipes, bushings, sleeves, hydraulic cylinders |
| Permanent Mold Casting (Gravity Die) | Uses reusable metal molds (rare for CF8 due to thermal stresses) | Good surface finish; fast cycle time for simpler geometries | Small fittings, couplings (limited use for CF8 due to chill tendency) |
| Vacuum Casting (Optional) | Performed under reduced pressure to limit gas porosity | Enhances cleanliness, reduces inclusions, improves fatigue and corrosion performance | High-purity castings in nuclear, medical, and chemical sectors |
7. Welding & Heat Treatment
CF8 welds readily with ER304 or ER304L fillers. To limit sensitization, fabricators maintain heat input between 1.0–2.0 kJ/mm and control interpass temperatures below 250 °C.
Post‑weld solution annealing at 1 040–1 100 °C—followed by quenching—restores full corrosion resistance.
Alternatively, stress relief at 650–750 °C reduces residual stress without significant sensitization risk.
8. Applications of CF8 Stainless Steel
Chemical Processing Industry
Pumps, valves, pipe fittings, and agitator shafts
Water & Wastewater Treatment
Pipe systems, valve bodies, backflow preventers
Food & Beverage Industry
Sanitary valves, heat exchangers, mixers, and containers
Marine & Offshore Hardware
Deck fittings, water intakes, underwater housings
Pharmaceutical Systems
Clean-in-place (CIP) piping, sterile containers, instrument housings
Energy & Power Generation
Turbine housings, heat exchanger components, support structures
9. Comparison with Alternative Materials
| Property | CF8 Stainless Steel | CF8M Stainless Steel | CF3 / CF3M (Low-C) | Ductile Iron | Carbon Steel |
|---|---|---|---|---|---|
| Corrosion Resistance | Good | Excellent (especially chlorides) | Excellent (post-weld) | Poor (unless coated) | Very Poor (requires coating) |
| Weldability | Good, some sensitization risk | Good | Excellent | Good | Excellent |
| PREN (Pitting Index) | ~17 | ~25–27 | ~25–28 | <10 (typically unmeasured) | <10 |
| Tensile Strength | ~485 MPa | ~485 MPa | ~450–480 MPa | ~450–550 MPa | ~415–485 MPa |
Machinability |
Moderate | Moderate | Moderate | Very Good | Excellent |
| Thermal Stability | Up to ~400 °C | Up to ~400 °C | Up to ~400 °C | ~300–400 °C | ~400 °C |
| Density | ~7.9 g/cm³ | ~7.9 g/cm³ | ~7.9 g/cm³ | ~7.0 g/cm³ | ~7.85 g/cm³ |
| Cost (Relative) | Medium | High | High | Low | Very Low |
| Best Use Cases | General corrosion-resistant castings | Marine, chemical, acidic service | Welded, sanitary, or low-carbon critical systems | Structural parts, housings, baseplates | Structural, dry environments with coating |
10. Emerging Trends & Innovations in CF8 Stainless Steel
Development of Advanced Alloy Variants
To address the growing need for higher corrosion resistance in aggressive media, research is focusing on optimizing CF8 through microalloying and composition refinement.
Adjusting the ferrite-to-austenite ratio, controlling residual delta ferrite, and incorporating trace elements like niobium (Nb) and molybdenum (Mo) can improve hot cracking resistance and mechanical stability.
- Hybrid CF8 grades with tailored ferrite contents (~5–7%) are being developed to balance weldability and strength.
- Molybdenum-enriched CF8 variants act as an intermediate option between CF8 and CF8M, offering moderate chloride resistance without the full cost of 316L equivalents.
Additive Manufacturing (AM) Integration
One of the most disruptive innovations in metal casting is the integration of additive manufacturing (AM) techniques, especially binder jetting and direct energy deposition.
While CF8 is traditionally cast in sand or investment molds, hybrid AM-casting workflows now allow:
- Rapid prototyping of complex geometries
- Near-net-shape production for small-batch or customized components
- Reduced material waste and lead time
Industries such as aerospace, medical, and defense are exploring AM-fabricated CF8 or equivalent 304L alloys for lightweight, corrosion-resistant assemblies.
Surface Engineering & Coatings
To extend the operational life of CF8 components in high-wear or highly corrosive environments, surface modification techniques are being employed. These include:
- Thermal spray coatings (e.g., Cr3C2-NiCr) to enhance erosion resistance
- Electropolishing and passivation to reduce surface roughness and improve corrosion behavior
- Laser cladding for site-specific strengthening and wear protection
These methods are increasingly standard for CF8 parts in the marine, chemical, and pharmaceutical sectors.
11. Conclusion
CF8 stainless steel remains an authoritative choice for moderate‑duty, complex‑geometry cast components.
By carefully balancing its chemistry, foundry practices, and post‑weld treatments, engineers can harness CF8’s cost-efficiency, corrosion resistance, and mechanical reliability.
For harsher environments, CF8M or CF3M provides enhanced performance at a modest premium.
LangHe is the perfect choice for your manufacturing needs if you need high-quality stainless steel castings.
FAQs
Q: What is the main difference between CF8 and CF8M?
A: CF8M contains molybdenum (~2–3%), improving its resistance to pitting and crevice corrosion compared to CF8.
Q: Can CF8 be welded?
A: Yes, CF8 is weldable using ER304/304L filler wire. Post-weld solution annealing is recommended to restore corrosion resistance.
Q: Is CF8 magnetic?
A: As an austenitic steel, CF8 is generally non-magnetic in the annealed state. Cold working or improper heat treatment may induce slight magnetism.
Q: What is the maximum temperature CF8 can withstand?
A: CF8 maintains useful strength up to around 400°C. Prolonged exposure above 450°C may cause embrittlement or sensitization.
Q: What are the common applications of CF8?
A: Valves, pump casings, marine hardware, food processing equipment, and chemical plant components.
Q: How does CF8 compare to ductile iron?
A: CF8 offers far superior corrosion resistance but at a higher cost. Ductile iron is cheaper but unsuitable for aggressive environments.
