1. 導入
CF3 stainless steel, オーステナイトキャストステンレス鋼ファミリーのメンバー, 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, 溶接性, and castability are paramount.
The “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%).
歴史的に, 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, パフォーマンス, and resistance to sensitization,
CF3 continues to be strategically important in cast stainless steel applications across chemical, 石油化学, 水処理, and food-processing sectors.
2. 化学組成 & 冶金
公称化学組成
The typical weight percentage (wt。％) of the alloying elements in CF3 stainless steel, as defined by ASTM A351, は:
| 要素 | 典型的な範囲 (wt。％) | 関数 |
|---|---|---|
| クロム (cr) | 18.0 - 21.0% | Promotes corrosion resistance through passive film formation |
| ニッケル (で) | 8.0 - 11.0% | オーステナイトを安定させます, improves ductility and toughness |
| 炭素 (c) | ≤ 0.03% | Reduces sensitization; improves weldability |
| マンガン (Mn) | ≤ 1.5% | Enhances hot workability; deoxidizer |
| シリコン (そして) | ≤ 2.0% | 鋳造の流動性を促進します; deoxidizer |
| リン (p) | ≤ 0.04% | Residual; must be minimized to reduce brittleness |
| 硫黄 (s) | ≤ 0.04% | Residual; excessive S can reduce toughness |
| 鉄 (fe) | バランス | Matrix element |
The 低炭素含有量 (≤ 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.
微細構造: オーステナイトマトリックス & 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 (通常 < 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
| 標準 | 指定 | 地域 | Equivalent Grade |
|---|---|---|---|
| ASTM A351 | Grade CF3 | アメリカ合衆国 | Low-carbon cast 304L |
| ASME SA-351 | Grade CF3 | アメリカ合衆国 (boiler code) | Pressure vessel compliant |
| で 10283 | GX2CRNI19-11 | European Union | のキャストバージョン 1.4306 (304l) |
| ISO 11972 | G-X2CrNi19-11 | 国際的 | Global harmonized equivalent |
| 彼はG5121 | SCS13A | 日本 | 304L cast grade |
4. 機械的特性
| Mechanical Property | 典型的な値 |
|---|---|
| 抗張力 | ≥485MPa |
| 降伏強度 (0.2% オフセット) | 205 MPa以上 |
| 伸長 | ≥30％ |
| 硬度 | 140–190 HB |
| 衝撃の靭性 (部屋の温度) | > 100 J (Charpy V-Notch) |
| Fatigue Endurance Limit | 240–270 MPa (in air, 磨きました) |
| クリープ抵抗 | Moderate up to 870°C |
高温で, 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. サーマル & 物理的特性
| 財産 | 価値 |
|---|---|
| 密度 | 〜7.9 g/cm³ |
| 熱伝導率 | 〜16 w/m・k (at 100°C) |
| Coefficient of Expansion | 17.3 µm/m・°C (20–400°C) |
| 電気抵抗率 | 0.72 µΩ・m |
| 磁気応答 | 非磁性 (アニール) |
| 酸化抵抗 | 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.
流動性 & 注ぐ温度
CF3 melts between 1450 °Cおよび 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.
しかし, excessive superheat can increase gas pickup および酸化, so operators typically limit superheat to 50 °C above liquidus.
Solidification Range & 収縮
で 凍結範囲 ほぼの 60–90 °C, CF3 solidifies over a broader temperature interval than simple austenitic alloys.
その結果, it exhibits 線形収縮 の 1.9–2.3 %, necessitating careful shrink‑compensation in pattern design.
防ぐため センターラインの多孔性, engineers employ 方向凝固: placing insulated risers above hot spots and using 寒気 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.
加えて, 発熱袖 on critical risers prolong feeding life without increasing overall mold volume.
脱気, Deoxidation & Inoculation
To minimize gas porosity, foundries typically argon‑purge the molten CF3 before pouring.
They also add シリコン (0.3–0.6 %) そして アルミニウム (0.02–0.05 %) deoxidizers, which form stable oxides and reduce dissolved oxygen.
ついに, a small rare‑earth inoculant (例えば。, 0.03–0.05 % Fe‑Ce) promotes fine, uniform δ‑ferrite and prevents microshrinkage, enhancing mechanical consistency.
Suitable Casting Methods for CF3 Stainless Steel
| キャスト方法 | 典型的なアプリケーション | 利点 | 考慮事項 |
|---|---|---|---|
| 砂鋳造 (Green or No-Bake) | バルブボディ, ポンプハウジング, フランジ | – Cost-effective for large parts – Flexible for varied designs |
– Rougher surface finish (Ra 6–12 μm) – Tighter control needed for porosity |
| シェル型鋳造 | 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 |
| インベストメント鋳造 (失われたワックス) | インペラ, medical fittings, 高精度コンポーネント | – Excellent surface finish (ra < 3 μm) – High geometric complexity |
– Higher cost – Limited to small–medium parts |
| 遠心鋳造 | ブッシング, リング, pipe sections | – High density – Low porosity – Good mechanical properties in radial direction |
– Suitable only for rotationally symmetric parts |
| 真空鋳造 | Critical components in aerospace, nuclear applications | – Reduced oxidation – Cleaner microstructure |
– Expensive – Requires specialized equipment |
| セラミック型鋳造 | Complex heat-resistant parts | – Excellent surface detail – Good dimensional precision |
– Longer mold preparation time – Higher cost |
Heat Treatment Practices
キャスト後, CF3 typically undergoes ソリューションアニーリング の範囲で 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 感作 そして chromium depletion 粒の境界で, compromising corrosion resistance.
7. 耐食性
一般的な腐食
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:
- ピッティング抵抗相当数 (木材): 〜18
- Critical Pitting Temperature (CPT): 〜20–25°C (varies with chloride level)
ストレス腐食亀裂 (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. 製造 & 加工性
CNC加工
CF3 machines comparably to wrought 304, with a machinability index of ~45 % (どこ 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.
溶接
Fabricators weld CF3 using 309 または 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.
形にする & 接合
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
バルブ, パンプス, 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. 一般的なアプリケーションには含まれます:
- コンプレッサーハウジング
- Manifolds and flowline components
- Metering valves and flanges
In up- and midstream systems, CF3 helps prevent stress-corrosion cracking (SCC) そして ピッティング, 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, 滑らかな表面仕上げ, and compatibility with cleaning agents (CIP/SIP). CF3 fits these requirements, それを適切にします:
- Sanitary valves and pipe fittings
- Mixing and metering equipment
- Dosing pumps and housings
その austenitic microstructure, which remains stable even after repeated sterilization cycles, helps meet FDA そして 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, バイオフーリング, そして 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. 代替資料との比較
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 ステンレス.
| 財産 | CF3 (304lキャスト) | CF3M (316lキャスト) | CF8 (304 キャスト) | CF8M (316 キャスト) | 304L Wrought |
|---|---|---|---|---|---|
| モリブデン (MO) コンテンツ | いいえ | はい | いいえ | はい | いいえ |
| 炭素含有量 | ≤ 0.03% (低炭素) | ≤ 0.03% (低炭素) | ≤ 0.08% | ≤ 0.08% | ≤ 0.03% (低炭素) |
| 塩化物耐性 | 適度 | 素晴らしい | 適度 | 素晴らしい | 適度 |
| ピッティング抵抗 (木材) | 〜18 | 〜25–27 | ~20 | 〜25–27 | 〜18 |
| 耐食性 | 良い | 素晴らしい | 適度 | 素晴らしい | 良い |
| 溶接性 | 素晴らしい | 素晴らしい | 適度 | 適度 | 素晴らしい |
| 料金 | $$ | $$$ | $$ | $$$ | $$ |
| 強さ (引張) | 〜485 MPa | ~500 MPa | ~510 MPa | ~520 MPa | ~520 MPa |
| 伸長 | 〜40％ | ~45% | ~45% | ~45% | ~45% |
| 形成性 | Excellent for cast parts | Excellent for cast parts | Good for cast parts | Good for cast parts | 素晴らしい (for rolled or formed parts) |
| アプリケーション | Water systems, food-grade parts | 化学薬品, 海兵隊, 沖合 | General industrial parts | 海兵隊, 化学薬品, 沖合 | High-ductility, 薄壁の部品 |
11. 結論
要約すれば, 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.
さらに, with annual global production exceeding 50,000 tonnes and scrap rates under 6 %, CF3 delivers both economic and performance advantages.
楽しみにしている, 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.
ランゲ 高品質が必要な場合は、製造ニーズに最適です ステンレス鋼の鋳物.
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 酸化抵抗 at elevated temperatures is critical,
other grades like CF8M または 316 ステンレス鋼 may be more appropriate due to their enhanced high-temperature properties.
Can CF3 be welded?
はい, CF3 stainless steel is highly 溶接可能. Its low carbon content minimizes the risk of carbide formation during welding, reducing the chances of intergranular corrosion.
しかし, it is always recommended to use appropriate welding techniques そして post-weld heat treatments when working with this material in critical applications.
Is CF3 Suitable for Cryogenic Applications?
はい, 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. しかし, 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 モリブデン.
で 海洋環境 with high salinity, CF3 may experience some pitting corrosion 時間とともに, so CF3M or CF8M might be more suitable.
How should CF3 Stainless Steel be maintained?
Regular maintenance of CF3 stainless steel includes:
- クリーニング: Removing contaminants such as chlorine, 塩, and chemicals that could cause localized corrosion.
- 検査: Checking for any signs of ピッティング または 隙間腐食, 特に 海兵隊 または chemical environments.
- 溶接: Ensuring proper ポストウェルド 熱処理 to avoid cracking or sensitization.
Can CF3 Stainless Steel be used in food contact applications?
はい, CF3 is often used in 食品加工装置 そのため 耐食性 そして ease of cleaning.
It complies with FDA そして 3-A Sanitary Standards, それを適切な選択にします サニタリー バルブ, パンプス, および配管システム.
