Stainless Steel CF3M—also known by its EN designation EN-JS 316LM (1.4408) and ASTM equivalent A351 CF3M—stands as a cornerstone material in corrosion-resistant castings.
Engineered for demanding environments, CF3M combines austenitic stainless steel’s toughness with cast iron’s versatility.
In this article, we explore its chemistry, microstructure, corrosion behavior, mechanical performance, foundry practices, welding protocols, applications, and how it compares to alternative materials.
1. Introduction
SA-351 CF3M Stainless Steel belongs to the family of austenitic cast stainless steels, developed in the mid-20th century to extend 300-series stainless corrosion resistance into cast components.
Whereas wrought 316L stainless dominates pipe and sheet applications, CF3M adapts the same low-carbon, molybdenum-bearing chemistry to castings—ideal for complex shapes like pump housings and valve bodies.
Unlike gray iron or 304L cast grades (CF8), CF3M resists pitting and crevice corrosion in chloride-rich media, bridging the performance gap between cast iron and high-alloy steel.
2. Chemical Composition & Microstructure
| Element | Range (% wt) | Purpose |
|---|---|---|
| Carbon (C) | ≤ 0.03 | Prevents chromium carbide precipitation |
| Chromium (Cr) | 16.0 – 18.0 | Forms a passive oxide layer; primary corrosion barrier |
| Nickel (Ni) | 10.0 – 14.0 | Stabilizes austenitic matrix; enhances toughness |
| Molybdenum (Mo) | 2.0 – 3.0 | Boosts pitting resistance and raises PREN to ≈ 25 |
| Manganese (Mn) | ≤ 2.0 | Improves hot strength; counteracts sulfur |
| Silicon (Si) | ≤ 1.0 | Acts as a deoxidizer; improves fluidity |
| Phosphorus (P) | ≤ 0.045 | Minimizes embrittlement |
| Sulfur (S) | ≤ 0.03 | Kept low to avoid inclusion-driven cracking |
CF3M solidifies into a fully austenitic matrix at room temperature, avoiding ferrite, sigma phase, or chromium carbides when properly heat-treated.
The low carbon content (≤ 0.03%) and molybdenum additions work in concert to inhibit chromium carbide formation along grain boundaries,
preserving intergranular corrosion resistance even after welding.
3. Corrosion Resistance
CF3M exhibits outstanding performance in aggressive media:
- General Corrosion: Rates as low as 0.05 mm/yr in potable water and 0.1 mm/yr in sea water at 25 °C
- Pitting/Crevice Corrosion: PREN ≈ 25 (PREN = %Cr + 3.3×%Mo + 16×%N) affords operation in up to 1 % chloride solutions at ambient temperatures
- Acid Resistance: Superior to CF8 (304L cast) in sulfuric and phosphoric acids due to Mo content
- Marine & Offshore: Withstands continuous salt spray exposure with minimal weight loss (< 0.02 g/m²·day in ASTM B117 tests)
4. Mechanical and Physical Properties of CF3M Stainless Steel
Mechanical Properties
At room temperature, CF3M delivers:
| Property | Value |
|---|---|
| Tensile Strength (UTS) | 515 – 620 MPa |
| Yield Strength (0.2% offset) | 205 – 275 MPa |
| Elongation at Fracture | ≥ 35 % |
| Brinell Hardness (HBW) | 180 – 230 |
| Charpy Impact (RT) | ≥ 80 J |
| Fatigue Limit (10⁷ cycles) | ~ 240 MPa |
Physical Properties
| Property | Value |
|---|---|
| Density | ~7.98 g/cm³ |
| Thermal Conductivity (20°C) | ~14.6 W/m·K |
| Thermal Expansion (20–100°C) | 16.0–17.5 µm/m·K |
| Specific Heat Capacity (20°C) | ~500 J/kg·K |
| Electrical Resistivity (20°C) | ~0.74 µΩ·m |
| Young’s Modulus (Elastic Modulus) | ~193 GPa |
| Relative Magnetic Permeability | ~1.0–1.05 |
| Melting Range | 1370–1400°C |
| Casting Shrinkage Rate | ~1.5–2.0% |
5. Casting Suitability for Stainless Steel CF3M
CF3M stainless steel, a low-carbon variant of 316 stainless cast alloys, exhibits favorable casting characteristics that support its widespread use in corrosion-resistant, high-integrity components.
Key Suitability Attributes:
- Good Fluidity: With a pouring temperature typically between 1550–1600 °C, CF3M demonstrates sufficient fluidity to fill intricate mold geometries and thin-wall sections (>3–5 mm).
The presence of nickel and molybdenum further supports melt stability and mold-filling performance. - Moderate Shrinkage (~1.5–2.0%): CF3M exhibits predictable solidification shrinkage, allowing for effective compensation through pattern allowances, riser design, and the use of exothermic sleeves.
Its shrinkage behavior can be modeled and managed using modern thermal simulation tools. - Low Hot Cracking Tendency: The fully austenitic structure of CF3M, combined with its low carbon content (≤ 0.03%),
results in minimal solidification cracking, even in geometrically constrained or sectionally thick castings. - Excellent Weldability: Cast CF3M can be weld-repaired using standard austenitic filler metals such as ER316L.
Its low carbon content limits carbide precipitation during welding, minimizing risk of intergranular corrosion.
Post-weld solution annealing is often applied to restore full corrosion resistance. - Adaptability to Heat Treatment: CF3M responds well to solution annealing (1040–1100 °C) and quenching,
which homogenize the microstructure, dissolve residual carbides, and maximize corrosion resistance.
Stress-relief treatments can also be employed to reduce residual stresses in large castings.
Suitable Casting Methods:
CF3M adapts well to multiple casting methods, each offering distinct advantages:
| Method | Strengths | Typical Tolerances & Finish |
|---|---|---|
| Sand Casting | Cost-effective for large, simple shapes | ±0.5 % linear, Ra 6–12 µm |
| Shell Molding | Tight tolerances, fine details | ±0.3 % linear, Ra 3–6 µm |
| Investment Casting | Complex geometries, thin walls (<2 mm) | ±0.2 % linear, Ra <3 µm |
| Centrifugal Casting | High density, minimal porosity in tubular parts | ±0.4 % linear, Ra 6–10 µm |
6. Welding & Heat Treatment of Stainless Steel CF3M
Stainless Steel CF3M is widely recognized for its excellent weldability and response to heat treatment.
These properties ensure structural integrity, corrosion resistance, and mechanical performance in post-casting fabrication and service.
Weldability of CF3M
One of CF3M’s strengths lies in its excellent weldability, especially when compared with high-carbon or ferritic stainless steels.
The low carbon content (≤ 0.03%) significantly reduces the risk of chromium carbide precipitation, a phenomenon that causes intergranular corrosion in the heat-affected zone (HAZ).
Key welding characteristics:
- Preheating: Not typically required due to the austenitic structure, although preheating (~100–150 °C) may be used for thick sections to reduce thermal gradients.
- Filler Metal: Use of matching or slightly over-alloyed fillers such as ER316L or ER317L is recommended to maintain corrosion resistance and ductility.
- Heat Input Control: Controlled heat input is essential to avoid hot cracking and ensure minimal delta-ferrite formation (typically 3–10% desirable).
- Post-weld cleaning: Pickling or passivation is advised to restore corrosion resistance on the weld surface.
Post-Weld Heat Treatment (PWHT)
While CF3M’s low carbon reduces sensitization risk, certain applications—particularly those in aggressive chemical environments or requiring maximum corrosion resistance—may benefit from post-weld heat treatment.
Solution Annealing:
- Temperature Range: 1040–1100 °C (1900–2010 °F)
- Purpose: Dissolves any chromium-rich carbides formed during welding and restores full austenitic microstructure
- Quenching: Rapid water or air quenching is essential to prevent sensitization and sigma phase formation
Stress Relieving (when solution annealing is not feasible):
- Temperature Range: 300–400 °C
- Effect: Reduces residual stresses without significantly altering the corrosion resistance
- Limitation: Does not dissolve carbides or reverse sensitization
7. Key Applications of CF3M Stainless Steel
Chemical Process Equipment
- Pumps: CF3M stainless steel is ideal for pumps used in the transport of corrosive fluids, particularly in applications that involve acidic or alkaline solutions.
- Valves: Used in chemical processing and pharmaceutical industries, CF3M provides durability and resistance to corrosion under high-pressure and high-temperature conditions.
- Heat exchangers: Its excellent corrosion resistance and high-temperature stability make CF3M an ideal material for heat exchangers handling aggressive media.
- Reactor vessels: For reactors processing corrosive chemicals, CF3M provides long-term durability and minimizes maintenance costs.
Marine and Offshore Applications
- Offshore platforms: Used in structural components and piping systems exposed to seawater and marine atmospheres.
- Marine hardware: Valves, pumps, and other components that require high corrosion resistance to withstand continuous exposure to saline conditions.
- Shipbuilding: Critical parts such as rudders, propeller shafts, and hull components benefit from CF3M’s ability to resist seawater corrosion and maintain integrity under mechanical stresses.
Food and Pharmaceutical Industry Components
- Food processing equipment: CF3M is used in equipment that handles aggressive cleaning agents and extreme temperatures, such as mixing tanks, pipelines, and valves.
- Pharmaceutical production: CF3M is widely used in the manufacturing of components like reactors and mixers, where contamination-free environments are necessary.
- Bottling and packaging: Parts in beverage production lines, such as nozzles and fittings, benefit from CF3M’s resistance to acidic and alkali solutions.
Power Generation & Heavy Industries
- Piping systems in high-temperature power plants handling steam and chemical fluids.
- Pressure vessels and turbine parts that require resistance to high temperatures, thermal cycling, and corrosive media.
- Heat exchangers in power plants dealing with hot gases or cooling water that may contain aggressive contaminants.
Oil and Gas Industry
- Downhole equipment: CF3M is used in components like wellheads, valves, and tubing that require exceptional resistance to corrosion and wear during oil extraction.
- Pipeline systems: Its excellent performance in both sweet and sour environments makes it suitable for high-pressure oil and gas pipelines.
- Refining equipment: CF3M is commonly used in heat exchangers, reactors, and cracking units in refineries that process sour gas and other corrosive materials.
Other Critical Applications
- Pressure vessels and reactors: CF3M’s resistance to stress corrosion cracking and excellent tensile strength make it ideal for high-pressure applications such as in chemical reactors or high-temperature vessels.
- Turbine and compressor components: Their resistance to oxidation at elevated temperatures ensures reliability in turbines and compressors in the aerospace and power generation industries.
8. Standards, Equivalents & Specifications
| Standard Body | Designation | Equivalent |
|---|---|---|
| EN | EN-JS 316LM / 1.4408 | — |
| ASTM | A351 CF3M | — |
| ISO | ISO 1083 EN-GJN-316LM | — |
| JIS | SUH316LM | SUS316L (wrought) |
| NORSOK | DIN 17460 GG-316LM | — |
Typical purchase specs call for ASTM A351 CF3M castings with radiographic inspection, hardness limits of 200 HB max, and PMI verification of Mo content.
9. Comparison of CF3M Stainless Steel with Alternative Materials
| Property / Material | CF3M (316L Cast) | CF8M (316 Cast) | CF3 (304L Cast) | CF8C (317 Cast) | 316L (Wrought) |
|---|---|---|---|---|---|
| Carbon Content (max, %) | 0.03 | 0.08 | 0.03 | 0.08 | 0.03 |
| Molybdenum Content (%) | 2–3 | 2–3 | None | 3–4 | 2–3 |
| Pitting Resistance (PREN) | ~25 | ~25 | ~18 | ~30 | ~25–27 |
| Chloride Resistance | High | Moderate–High | Low–Moderate | Very High | High |
| Intergranular Corrosion Risk | Very Low | Moderate | Low | Moderate | Very Low |
| Tensile Strength (MPa) | ~485–620 | ~485–620 | ~450–600 | >600 | 515–690 |
| Yield Strength (MPa) | ~170–300 | ~170–300 | ~170–275 | >300 | 205–310 |
| Elongation (%) | ≥25 | ≥25 | ≥30 | 20–25 | ≥40 |
| Weldability | Excellent | Good | Excellent | Moderate | Excellent |
| High-Temp Resistance | Moderate | Moderate | Low | High | Good |
| Castability | Excellent | Excellent | Excellent | Moderate | Not Applicable |
| Machinability | Moderate | Moderate | Good | Moderate | Good |
| Surface Finish (as supplied) | Coarse (as-cast) | Coarse | Coarse | Coarse | Smooth (rolled) |
| Cost Level | Moderate | Moderate | Low | High | Moderate–High |
| Typical Use Cases | Chemical pumps, valves, pharma, marine | General industrial and marine | Food, light chemicals | Aggressive chemicals, high-temp service | Precision tanks, piping, architecture |
10. Conclusion
Stainless Steel CF3M stands at the forefront of cast stainless alloys,
marrying 316L-equivalent corrosion resistance, robust mechanical properties, and cast component versatility.
As industrial demands rise, CF3M enables engineers to design complex,
cost-effective components that endure the harshest chemical, marine, and processing environments.
By adhering to best practices in chemistry control, foundry processing, and post-weld heat treatment,
manufacturers unlock CF3M’s full potential, ensuring longevity, reliability, and lifecycle value.
LangHe is the perfect choice for your manufacturing needs if you need high-quality stainless steel castings.
