1. Uvod
CF3 stainless steel, a member of the austenitic cast stainless steel family, is the low-carbon cast equivalent of the popular wrought grade 304L (SAD S30403).
It is defined under ASTM A351 and widely used in industries where corrosion resistance, zavarivost, and castability are paramount.
A “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%).
Povijesno, 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, performanse, and resistance to sensitization,
CF3 continues to be strategically important in cast stainless steel applications across chemical, petrokemijski, obrada vode, and food-processing sectors.
2. Kemijski sastav & Metalurgija
Nominalni kemijski sastav
The typical weight percentage (tež.%) of the alloying elements in CF3 stainless steel, as defined by ASTM A351, je:
| Element | Tipičan raspon (tež.%) | Funkcija |
|---|---|---|
| Krom (CR) | 18.0 - 21.0% | Promotes corrosion resistance through passive film formation |
| Nikla (U) | 8.0 - 11.0% | Stabilizira austenit, improves ductility and toughness |
| Ugljik (C) | ≤ 0.03% | Reduces sensitization; improves weldability |
| Mangan (MN) | ≤ 1.5% | Enhances hot workability; deoxidizer |
| Silicij (I) | ≤ 2.0% | Promiče fluidnost u lijevanju; deoxidizer |
| Fosfor (P) | ≤ 0.04% | Residual; must be minimized to reduce brittleness |
| Sumpor (S) | ≤ 0.04% | Residual; excessive S can reduce toughness |
| Željezo (FE) | Uravnotežiti | Matrix element |
A Sadržaj niskog ugljika (≤ 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.
Mikrostruktura: Austenitna matrica & 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 (tipično < 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 | Oznaka | Regija | Equivalent Grade |
|---|---|---|---|
| ASTM A351 | Grade CF3 | SAD | Low-carbon cast 304L |
| ASME SA-351 | Grade CF3 | SAD (boiler code) | Pressure vessel compliant |
| U 10283 | Gx2crni19-11 | European Union | Lijeva verzija 1.4306 (304L) |
| ISO 11972 | G-X2CrNi19-11 | Međunarodni | Global harmonized equivalent |
| On g5121 | SCS13A | Japan | 304L cast grade |
4. Mehanička svojstva
| Mehaničko svojstvo | Tipična vrijednost |
|---|---|
| Zatečna čvrstoća | ≥485 MPa |
| Snaga popuštanja (0.2% nagib) | ≥205 MPa |
| Produženje | ≥30% |
| Tvrdoća | 140–190 HB |
| Žilavost utjecaja (Temp.) | > 100 J (Charpy V-Notch) |
| Fatigue Endurance Limit | 240–270 MPa (in air, poliran) |
| Otpornost na puzanje | Moderate up to 870°C |
Pri povišenim temperaturama, 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. Toplinski & Fizička svojstva
| Vlasništvo | Vrijednost |
|---|---|
| Gustoća | ~ 7,9 g/cm³ |
| Toplinska vodljivost | ~ 16 w/m · k (at 100°C) |
| Coefficient of Expansion | 17.3 µm/m · ° C (20–400°C) |
| Električni otpor | 0.72 µω · m |
| Magnetski odgovor | Ne-magnetski (žarkin) |
| Otpornost na oksidaciju | 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.
Fluidnost & Temperatura ulijevanja
CF3 melts between 1450 ° C i 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.
Međutim, excessive superheat can increase gas pickup i oksidacija, so operators typically limit superheat to 50 ° C above liquidus.
Solidification Range & Skupljanje
S a domet zamrzavanja otprilike 60–90 °C, CF3 solidifies over a broader temperature interval than simple austenitic alloys.
Stoga, it exhibits linearno skupljanje od 1.9–2.3 %, necessitating careful shrink‑compensation in pattern design.
Da se spriječi Poroznost središnje linije, engineers employ usmjeravanje: placing insulated risers above hot spots and using zimica 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.
Uz to, egzotermični rukavi on critical risers prolong feeding life without increasing overall mold volume.
Nagaranje, Deoxidation & Inoculation
To minimize gas porosity, foundries typically argon‑purge the molten CF3 before pouring.
They also add silicij (0.3–0.6 %) i aluminij (0.02–0.05 %) deoxidizers, which form stable oxides and reduce dissolved oxygen.
Konačno, a small rare‑earth inoculant (Npr., 0.03–0.05 % Fe‑Ce) promotes fine, uniform δ‑ferrite and prevents microshrinkage, enhancing mechanical consistency.
Suitable Casting Methods for CF3 Stainless Steel
| Metoda lijevanja | Tipične primjene | Prednosti | Razmatranja |
|---|---|---|---|
| Lijevanje pijeska (Green or No-Bake) | Tijela ventila, Kućiva pumpe, prirubnice | – Cost-effective for large parts – Flexible for varied designs |
– Rougher surface finish (Ra 6–12 μm) – Tighter control needed for porosity |
| Lijevanje kalupa | 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 |
| Investicijski lijev (Izgubljeni vosak) | Ronilaca, medical fittings, Komponente visoke precize | – Excellent surface finish (Ram < 3 μm) – High geometric complexity |
– Higher cost – Limited to small–medium parts |
| Centrifugalno lijevanje | Čahure, prstenovi, pipe sections | – High density – Low porosity – Good mechanical properties in radial direction |
– Suitable only for rotationally symmetric parts |
| Vakuumsko lijevanje | Critical components in aerospace, nuclear applications | – Reduced oxidation – Cleaner microstructure |
– Expensive – Requires specialized equipment |
| Lijevanje keramičkog plijesni | Complex heat-resistant parts | – Excellent surface detail – Good dimensional precision |
– Longer mold preparation time – Higher cost |
Heat Treatment Practices
Nakon lijevanja, CF3 typically undergoes otopina u rasponu od 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 osjetljivost i chromium depletion na granicama zrna, compromising corrosion resistance.
7. Otpor korozije
Opća korozija
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:
- Zamjenjivi broj otpora (Drvo): ~ 18
- Critical Pitting Temperature (CPT): ~ 20–25 ° C (varies with chloride level)
Pucanje korozije stresa (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. Izrada & Obradivost
CNC obrada
CF3 machines comparably to wrought 304, with a machinability index of ~45 % (gdje 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.
Zavarivanje
Fabricators weld CF3 using 309 ili 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.
Formiranje & Spajanje
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
Ventili, Pumpe, 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. Uobičajene prijave uključuju:
- Kućišta kompresora
- Manifolds and flowline components
- Metering valves and flanges
In up- and midstream systems, CF3 helps prevent stress-corrosion cracking (SCC) i zadirkivanje, 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, glatka površinska završna obrada, and compatibility with cleaning agents (CIP/SIP). CF3 fits these requirements, što ga čini prikladnim za:
- Sanitary valves and pipe fittings
- Mixing and metering equipment
- Dosing pumps and housings
Njegov austenitic microstructure, which remains stable even after repeated sterilization cycles, helps meet FDA i 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, biohouling, i 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. Usporedba s alternativnim materijalima
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 nehrđajući.
| Vlasništvo | Cf3 (304L) | Cf3m (316L) | Cf8 (304 Bacanje) | Cf8m (316 Bacanje) | 304L Wrought |
|---|---|---|---|---|---|
| Molibden (Mokar) Sadržaj | Ne | Da | Ne | Da | Ne |
| Udio ugljika | ≤ 0.03% (Niski ugljik) | ≤ 0.03% (Niski ugljik) | ≤ 0.08% | ≤ 0.08% | ≤ 0.03% (Niski ugljik) |
| Otpornost na klorid | Umjeren | Izvrstan | Umjeren | Izvrstan | Umjeren |
| Otpor (Drvo) | ~ 18 | ~ 25–27 | ~20 | ~ 25–27 | ~ 18 |
| Otpor korozije | Dobro | Izvrstan | Umjeren | Izvrstan | Dobro |
| Zavarivost | Izvrstan | Izvrstan | Umjeren | Umjeren | Izvrstan |
| Koštati | $$ | $$$ | $$ | $$$ | $$ |
| Jačina (Zatezanje) | ~ 485 MPa | ~500 MPa | ~510 MPa | ~520 MPa | ~520 MPa |
| Produženje | ~ 40% | ~45% | ~45% | ~45% | ~45% |
| Oblikovanje | Excellent for cast parts | Excellent for cast parts | Good for cast parts | Good for cast parts | Izvrstan (for rolled or formed parts) |
| Prijave | Water systems, food-grade parts | Kemijski, morski, na obali | General industrial parts | Morski, kemijski, na obali | High-ductility, Dijelovi s tankim zidovima |
11. Zaključak
Ukratko, 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.
Štoviše, with annual global production exceeding 50,000 tonnes and scrap rates under 6 %, CF3 delivers both economic and performance advantages.
Veseliti se, 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.
Laga je savršen izbor za vaše potrebe za proizvodnjom ako vam treba visokokvalitetna odljevi od nehrđajućeg čelika.
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 otpornost na oksidaciju at elevated temperatures is critical,
other grades like Cf8m ili 316 nehrđajući čelik may be more appropriate due to their enhanced high-temperature properties.
Can CF3 be welded?
Da, CF3 stainless steel is highly zavariv. Its low carbon content minimizes the risk of carbide formation during welding, reducing the chances of intergranular corrosion.
Međutim, it is always recommended to use appropriate welding techniques i post-weld heat treatments when working with this material in critical applications.
Is CF3 Suitable for Cryogenic Applications?
Da, 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. Međutim, 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 molibden.
U morsko okruženje with high salinity, CF3 may experience some korozija s vremenom, so CF3M or CF8M might be more suitable.
How should CF3 Stainless Steel be maintained?
Regular maintenance of CF3 stainless steel includes:
- Čišćenje: Removing contaminants such as chlorine, sol, and chemicals that could cause localized corrosion.
- Inspekcija: Checking for any signs of zadirkivanje ili korozija pukotine, Pogotovo u morski ili chemical environments.
- Zavarivanje: Ensuring proper poslije najave toplotna obrada to avoid cracking or sensitization.
Can CF3 Stainless Steel be used in food contact applications?
Da, CF3 is often used in Oprema za preradu hrane zbog svog otpor korozije i ease of cleaning.
It complies with FDA i 3-A Sanitary Standards, čineći ga prikladnim izborom za sanitarni ventili, pumpe, i sustavi cjevovoda.
