1. Indledning
CF3 stainless steel, a member of the austenitic cast stainless steel family, is the low-carbon cast equivalent of the popular wrought grade 304L (US S30403).
It is defined under ASTM A351 and widely used in industries where corrosion resistance, svejsbarhed, and castability are paramount.
De “C” in CF3 stands for “Corrosion-resistant”, “F” denotes the steel grade (304L equivalent), and the number “3” identifies its low carbon content (≤ 0.03%).
Historisk, CF3 emerged as part of the response to corrosion issues in chloride-rich and welding-intensive applications.
The introduction of low-carbon grades in the mid-20th century was a milestone that enabled the development of high-integrity welded structures without the need for post-weld heat treatment.
Due to its balanced combination of cost-effectiveness, præstation, and resistance to sensitization,
CF3 continues to be strategically important in cast stainless steel applications across chemical, petrokemisk, Vandbehandling, and food-processing sectors.
2. Kemisk sammensætning & Metallurgi
Nominel kemisk sammensætning
The typical weight percentage (Wt.%) of the alloying elements in CF3 stainless steel, as defined by ASTM A351, er:
| Element | Typisk rækkevidde (Wt.%) | Fungere |
|---|---|---|
| Krom (Cr) | 18.0 – 21.0% | Promotes corrosion resistance through passive film formation |
| Nikkel (I) | 8.0 – 11.0% | Stabiliserer austenit, improves ductility and toughness |
| Kulstof (C) | ≤ 0.03% | Reduces sensitization; improves weldability |
| Mangan (Mn) | ≤ 1.5% | Enhances hot workability; deoxidizer |
| Silicium (Og) | ≤ 2.0% | Fremmer fluiditet i casting; deoxidizer |
| Fosfor (S) | ≤ 0.04% | Residual; must be minimized to reduce brittleness |
| Svovl (S) | ≤ 0.04% | Residual; excessive S can reduce toughness |
| Jern (Fe) | Balance | Matrix element |
De Indhold med lavt kulstofindhold (≤ 0.03%) significantly mitigates the risk of chromium carbide precipitation at grain boundaries during welding,
making CF3 especially resistant to intergranular corrosion without requiring post-weld heat treatment.
Mikrostruktur: Austenitisk matrix & Carbide Control
CF3 stainless steel has a fully austenitic microstructure with a face-centered cubic (FCC) lattice, which contributes to:
- Excellent toughness at both ambient and cryogenic temperatures.
- Non-magnetic behavior in the annealed state.
- Resistance to stress corrosion cracking (SCC) in many chloride-containing environments.
Due to its low carbon content, CF3 contains minimal chromium carbides, particularly at grain boundaries.
This improves resistance to sensitization, a condition in which chromium-depleted zones form and become vulnerable to corrosive attack.
Some residual delta ferrite (typisk < 10%) may be present after solidification, particularly in sand-cast components.
which helps prevent hot cracking during solidification, but has minimal impact on corrosion resistance or toughness when kept at controlled levels.
3. ASTM A351 CF3 and Global Equivalents
| Standard | Betegnelse | Område | Equivalent Grade |
|---|---|---|---|
| ASTM A351 | Grade CF3 | USA | Low-carbon cast 304L |
| ASME SA-351 | Grade CF3 | USA (boiler code) | Pressure vessel compliant |
| I 10283 | GX2CRNI19-11 | European Union | Rollebesætning af 1.4306 (304L) |
| ISO 11972 | G-X2CrNi19-11 | International | Global harmonized equivalent |
| Han G5121 | SCS13A | Japan | 304L cast grade |
4. Mekaniske egenskaber
| Mekanisk egenskab | Typisk værdi |
|---|---|
| Trækstyrke | ≥485 MPa |
| Udbyttestyrke (0.2% Offset) | ≥205 MPa |
| Forlængelse | ≥30% |
| Hårdhed | 140–190 HB |
| Påvirkning af sejhed (Room temp) | > 100 J (Charpy V-Notch) |
| Fatigue Endurance Limit | 240–270 MPa (in air, poleret) |
| Krybe modstand | Moderate up to 870°C |
Ved forhøjede temperaturer, tensile and yield strengths decrease gradually, but the alloy retains sufficient structural integrity up to 400–500 °C, making it viable for moderate thermal service.
5. Termisk & Fysiske egenskaber
| Ejendom | Værdi |
|---|---|
| Densitet | ~ 7,9 g/cm³ |
| Termisk ledningsevne | ~ 16 W/M · K. (at 100°C) |
| Coefficient of Expansion | 17.3 µm/m · ° C. (20–400°C) |
| Elektrisk resistivitet | 0.72 µω · m |
| Magnetisk respons | Ikke-magnetisk (Annealed) |
| Oxidationsmodstand | Good up to ~800°C |
6. Casting Characteristics of CF3 Stainless Steel
CF3 stainless steel—cast equivalent of 316—brings molybdenum‑enhanced corrosion resistance into complex geometries.
To harness its full potential, foundries must account for its unique casting behavior, from melt handling to solidification control.
Fluiditet & Hældningstemperatur
CF3 melts between 1450 ° C og 1550 ° C., slightly higher than CF8 due to its Mo content.
At a pouring superheat of 1500–1560 °C, CF3 achieves a fluidity of 220–280 mm (ISO 243), enabling fill of thin‑walled sections down to 4 mm.
Imidlertid, excessive superheat can increase gas pickup og oxidation, so operators typically limit superheat to 50 ° C. above liquidus.
Solidification Range & Krympning
Med en fryseområde af omtrent 60–90 °C, CF3 solidifies over a broader temperature interval than simple austenitic alloys.
Følgelig, it exhibits Lineær krympning af 1.9–2.3 %, necessitating careful shrink‑compensation in pattern design.
For at forhindre Centerline porøsitet, engineers employ Retningsstørrelse: placing insulated risers above hot spots and using kulderystelser to accelerate freezing in thick sections.
Feeding & Riser Design
Given its moderate shrinkage, CF3 castings benefit from risers sized to feed 30–40 % of the casting mass they support.
Finite‑element thermal simulation often guides riser placement, ensuring uninterrupted metal flow into contracting zones.
Derudover, Eksotermiske ærmer on critical risers prolong feeding life without increasing overall mold volume.
Afgasning, Deoxidation & Inoculation
To minimize gas porosity, foundries typically argon‑purge the molten CF3 before pouring.
They also add silicium (0.3–0,6 %) og aluminium (0.02–0.05 %) deoxidizers, which form stable oxides and reduce dissolved oxygen.
Endelig, a small rare‑earth inoculant (F.eks., 0.03–0.05 % Fe‑Ce) promotes fine, uniform δ‑ferrite and prevents microshrinkage, enhancing mechanical consistency.
Suitable Casting Methods for CF3 Stainless Steel
| Casting -metode | Typiske applikationer | Fordele | Overvejelser |
|---|---|---|---|
| Sandstøbning (Green or No-Bake) | Ventillegemer, Pumpehuse, flanger | – Cost-effective for large parts – Flexible for varied designs |
– Rougher surface finish (Ra 6–12 μm) – Tighter control needed for porosity |
| Shell Mold Casting | Instrumentation covers, small valves | – Good dimensional accuracy (±0.3%) – Fine surface finish (Ra 3–6 μm) |
– More expensive molds – Best for small to medium-sized parts |
| Investeringsstøbning (Mistet voks) | Skader, medical fittings, Komponenter med høj præcision | – Excellent surface finish (Ra < 3 μm) – High geometric complexity |
– Higher cost – Limited to small–medium parts |
| Centrifugalstøbning | Bøsninger, ringe, pipe sections | – High density – Low porosity – Good mechanical properties in radial direction |
– Suitable only for rotationally symmetric parts |
| Vakuumstøbning | Critical components in aerospace, nuclear applications | – Reduced oxidation – Cleaner microstructure |
– Expensive – Requires specialized equipment |
| Keramisk formstøbning | Complex heat-resistant parts | – Excellent surface detail – Good dimensional precision |
– Longer mold preparation time – Higher cost |
Heat Treatment Practices
Efter casting, CF3 typically undergoes Løsning af annealing i intervallet af 1040–1120 ° C. (1900–2050°F) followed by rapid water quenching. This process serves several purposes:
- Dissolves residual carbides, restoring corrosion resistance
- Homogenizes the microstructure, eliminating segregation from solidification
- Improves ductility and toughness by removing delta ferrite or brittle phases
Strict temperature control during annealing is critical. Insufficient quenching rates can result in Sensibilisering og chromium depletion ved korngrænser, compromising corrosion resistance.
7. Korrosionsmodstand
Generel korrosion
In neutral and mildly acidic environments, CF3 maintains excellent resistance due to its chromium-rich passive film. Corrosion rates are typically < 0.05 mm/year in potable water and wastewater systems.
Localized Corrosion Resistance
The alloy shows good performance in environments containing chlorides up to ~200 ppm:
- Pitting modstandsækvivalent nummer (Træ): ~ 18
- Critical Pitting Temperature (CPT): ~ 20–25 ° C. (varies with chloride level)
Stresskorrosionskrakning (SCC)
CF3’s low carbon content improves SCC resistance in chloride-bearing environments, particularly in the 50–100°C range, a known danger zone for austenitic grades.
8. Fremstilling & Bearbejdningsevne
CNC -bearbejdning
CF3 machines comparably to wrought 304, with a machinability index of ~45 % (hvor 304 equals 50 %).
Shops typically use carbide tools, cutting speeds of 100–150 m/min, and feeds of 0.12–0.18 mm/rev, delivering surface finishes around Ra 1.6 µm.
Svejsning
Fabricators weld CF3 using 309 eller 312 filler alloys without preheat.
Post‑weld annealing at 1,050 °C for one hour restores corrosion resistance, reducing delta‑ferrite and dissolving weld‑zone carbides.
Dannelse & Deltag i
Although CF3’s work‑hardening rate lags that of carbon steel, it tolerates cold forming reductions up to 40 %.
To prevent springback, designers recommend bend radii of at least 3× material thickness.
9. Applications of CF3 Stainless Steel
Ventiler, Pumper, and Fittings in Water Treatment
In municipal and industrial water treatment facilities, CF3 stainless steel is a material of choice for:
- Valve bodies and bonnets
- Pump casings and impellers
- Pipe fittings and couplings
Its resistance to chloride-induced corrosion, even in brackish or mildly saline environments, ensures long service life with minimal maintenance.
The low carbon content reduces the risk of sensitization during welding, which is critical for pressure-retaining systems.
Petrochemical and Oil & Gas Components
The oil and gas industry frequently uses CF3 for castings that encounter corrosive fluids, including hydrocarbons, hydrogen sulfide, and CO₂-rich environments. Almindelige applikationer inkluderer:
- Kompressorhus
- Manifolds and flowline components
- Metering valves and flanges
In up- and midstream systems, CF3 helps prevent stress-corrosion cracking (SCC) og pitting, which are accelerated by high chloride content or wet sour gas.
Food Processing and Pharmaceutical Equipment
Hygienic process systems require materials with excellent corrosion resistance, Glat overfladefinish, and compatibility with cleaning agents (CIP/SIP). CF3 fits these requirements, Gør det velegnet til:
- Sanitary valves and pipe fittings
- Mixing and metering equipment
- Dosing pumps and housings
Dens austenitic microstructure, which remains stable even after repeated sterilization cycles, helps meet FDA og 3-A Sanitary Standards in critical production environments.
Power Generation and Marine Hardware
- Steam and condensate system components
- Seawater pumps and valve parts
- Heat exchanger end covers
Its resistance to aqueous corrosion, biofouling, og oxidation at elevated temperatures enhances component longevity in these aggressive settings.
In marine environments, CF3 performs reliably in both surface and submerged service.
Other Emerging Applications
- Hydrogen handling systems: Due to its non-magnetic and crack-resistant nature
- Semiconductor wet-processing tools: Where ultra-clean, non-reactive materials are needed
- Additive-manufactured cast components: For reduced weight and complex design integration
10. Sammenligning med alternative materialer
Selecting the appropriate stainless steel grade for a given application requires a deep understanding of the performance trade-offs between available options.
CF3 stainless steel, as the low-carbon cast equivalent of 304L, is often compared to related alloys such as CF3M, CF8, CF8M, and wrought 304 rustfrit.
| Ejendom | CF3 (304L rollebesætning) | CF3M (316L rollebesætning) | CF8 (304 Rollebesætning) | CF8M (316 Rollebesætning) | 304L Wrought |
|---|---|---|---|---|---|
| Molybdæn (Mo) Tilfreds | Ingen | Ja | Ingen | Ja | Ingen |
| Kulstofindhold | ≤ 0.03% (Lavt kulstof) | ≤ 0.03% (Lavt kulstof) | ≤ 0.08% | ≤ 0.08% | ≤ 0.03% (Lavt kulstof) |
| Chloridresistens | Moderat | Fremragende | Moderat | Fremragende | Moderat |
| Pitting modstand (Træ) | ~ 18 | ~ 25–27 | ~20 | ~ 25–27 | ~ 18 |
| Korrosionsmodstand | God | Fremragende | Moderat | Fremragende | God |
| Svejsbarhed | Fremragende | Fremragende | Moderat | Moderat | Fremragende |
| Koste | $$ | $$$ | $$ | $$$ | $$ |
| Styrke (Træk) | ~ 485 MPa | ~500 MPa | ~510 MPa | ~520 MPa | ~520 MPa |
| Forlængelse | ~ 40% | ~45% | ~45% | ~45% | ~45% |
| Formbarhed | Excellent for cast parts | Excellent for cast parts | Good for cast parts | Good for cast parts | Fremragende (for rolled or formed parts) |
| Applikationer | Water systems, food-grade parts | Kemisk, marine, Offshore | General industrial parts | Marine, kemisk, Offshore | High-ductility, Tyndvæggede dele |
11. Konklusion
Sammenfattende, CF3 stainless steel merges the proven corrosion resistance of 304 with the versatility of casting.
Its balanced chemistry, robust mechanical profile, and proven long‑term durability make CF3 an authoritative choice for medium‑duty corrosive environments.
Desuden, with annual global production exceeding 50,000 tonnes and scrap rates under 6 %, CF3 delivers both economic and performance advantages.
Ser frem, integrating CF3 into hybrid casting–additive workflows and exploring surface treatments promises to extend its service envelope—ensuring CF3 remains a cornerstone alloy in industrial applications.
Langhe er det perfekte valg til dine produktionsbehov, hvis du har brug for høj kvalitet Rustfrit stålstøbning.
FAQs on CF3 Stainless Steel
Is CF3 Stainless Steel suitable for high-temperature applications?
CF3 is generally suitable for moderate-temperature applications (up to about 800°F or 427°C).
For higher temperatures, or when Oxidationsmodstand at elevated temperatures is critical,
other grades like CF8M eller 316 Rustfrit stål may be more appropriate due to their enhanced high-temperature properties.
Can CF3 be welded?
Ja, CF3 stainless steel is highly Svejsbar. Its low carbon content minimizes the risk of carbide formation during welding, reducing the chances of intergranular corrosion.
Imidlertid, it is always recommended to use appropriate welding techniques og post-weld heat treatments when working with this material in critical applications.
Is CF3 Suitable for Cryogenic Applications?
Ja, CF3 exhibits good toughness at low temperatures, making it suitable for use in cryogenic applications such as liquefied natural gas (LNG) storage and transportation.
Can CF3 Be Heat Treated?
CF3 is generally not heat treatable for strengthening purposes. Imidlertid, it can be annealed to relieve stresses and improve machinability.
How does CF3 Stainless Steel perform in seawater?
CF3 offers moderate resistance to seawater corrosion, but it is not as resistant as CF3M or CF8M, which have enhanced chloride resistance due to the presence of Molybdæn.
I marine miljøer with high salinity, CF3 may experience some Pitting korrosion Over tid, so CF3M or CF8M might be more suitable.
How should CF3 Stainless Steel be maintained?
Regular maintenance of CF3 stainless steel includes:
- Rensning: Removing contaminants such as chlorine, salt, and chemicals that could cause localized corrosion.
- Inspektion: Checking for any signs of pitting eller spredningskorrosion, især i marine eller chemical environments.
- Svejsning: Ensuring proper efter svejsning Varmebehandling to avoid cracking or sensitization.
Can CF3 Stainless Steel be used in food contact applications?
Ja, CF3 is often used in Fødevareforarbejdningsudstyr På grund af dets Korrosionsmodstand og ease of cleaning.
It complies with FDA og 3-A Sanitary Standards, Gør det til et passende valg til Sanitær ventiler, pumper, og rørsystemer.
