1. Вступ
CF3 stainless steel, Член аустенітної родини з нержавіючої сталі, is the low-carbon cast equivalent of the popular wrought grade 304Л (США S30403).
It is defined under ASTM A351 and widely used in industries where corrosion resistance, зварюваність, and castability are paramount.
З “C” in CF3 stands for “Corrosion-resistant”, “F” denotes the steel grade (304L еквівалент), and the number “3” identifies its low carbon content (≤ 0.03%).
Історично, 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, виконання, and resistance to sensitization,
CF3 continues to be strategically important in cast stainless steel applications across chemical, нафтохімічний, очищення води, and food-processing sectors.
2. Хімічний склад & Металургія
Номінальний хімічний склад
The typical weight percentage (мас.%) of the alloying elements in CF3 stainless steel, as defined by ASTM A351, є:
| Елемент | Типовий діапазон (мас.%) | Функціонування |
|---|---|---|
| Хром (Cr) | 18.0 - 21.0% | Promotes corrosion resistance through passive film formation |
| Нікель (У) | 8.0 - 11.0% | Стабілізує аустеніту, покращує пластичність та міцність |
| Вуглець (C) | ≤ 0.03% | Reduces sensitization; improves weldability |
| Марганець (Мн) | ≤ 1.5% | Enhances hot workability; дезоксидатор |
| Кремнію (І) | ≤ 2.0% | Сприяє плинності в литі; дезоксидатор |
| Фосфор (С) | ≤ 0.04% | Залишковий; must be minimized to reduce brittleness |
| Сірка (S) | ≤ 0.04% | Залишковий; excessive S can reduce toughness |
| Прасувати (Феод) | Балансувати | Матричний елемент |
З Низький вміст вуглецю (≤ 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.
Мікроструктура: Аустенітна матриця & Carbide Control
CF3 stainless steel has a fully аустенітна мікроструктура with a face-centered cubic (FCC) решітка, which contributes to:
- Excellent toughness at both ambient and cryogenic temperatures.
- Non-magnetic behavior в розпеченому стані.
- 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 (типово < 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
| Стандартний | Призначення | Область | Equivalent Grade |
|---|---|---|---|
| ASTM A351 | Grade CF3 | США | Low-carbon cast 304L |
| ASME SA-351 | Grade CF3 | США (boiler code) | Pressure vessel compliant |
| У 10283 | GX2CRNI19-11 | European Union | Версія 1.4306 (304Л) |
| ISO 11972 | G-X2CrNi19-11 | Міжнародний | Global harmonized equivalent |
| Він G5121 | SCS13A | Японія | 304L cast grade |
4. Механічні властивості
| Механічна властивість | Типове значення |
|---|---|
| Сила на розрив | ≥485 МПа |
| Похідна сила (0.2% компенсація) | ≥205 МПа |
| Подовження | ≥30% |
| Твердість | 140–190 год |
| Вплив міцність (Темп) | > 100 J (Charpy v-notch) |
| Обмеження витривалості втоми | 240–270 МПа (in air, відшліфований) |
| Опір повзучості | Moderate up to 870°C |
При підвищеній температурі, 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. Термічний & Фізичні властивості
| Власність | Цінність |
|---|---|
| Щільність | ~ 7,9 г/см³ |
| Теплопровідність | ~ 16 Вт/м · k (при 100 ° C) |
| Коефіцієнт розширення | 17.3 мкм/м · ° C (20–400 ° C) |
| Електричний опір | 0.72 µω · м |
| Магнітна реакція | Немагнітний (відпалений) |
| Окислювальна стійкість | 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.
Плинність & Температура
CF3 melts between 1450 ° C і 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 мм.
Однак, excessive superheat can increase gas pickup і окислення, so operators typically limit superheat to 50 ° C рідкий.
Solidification Range & Усадка
З Діапазон заморожування приблизно 60–90 °C, CF3 solidifies over a broader temperature interval than simple austenitic alloys.
Отже, it exhibits Лінійна усадка на 1.9–2.3 %, necessitating careful shrink‑compensation in pattern design.
Для запобігання пористість центральної лінії, engineers employ спрямоване затвердіння: placing insulated risers above hot spots and using озноб 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.
На додаток, екзотермічні рукави on critical risers prolong feeding life without increasing overall mold volume.
Дегазація, Deoxidation & Щеплення
To minimize gas porosity, foundries typically argon‑purge the molten CF3 before pouring.
They also add кремнію (0.3–0.6 %) і алюміній (0.02–0.05 %) deoxidizers, which form stable oxides and reduce dissolved oxygen.
Нарешті, a small rare‑earth inoculant (Напр., 0.03–0.05 % Fe‑Ce) promotes fine, uniform δ‑ferrite and prevents microshrinkage, enhancing mechanical consistency.
Suitable Casting Methods for CF3 Stainless Steel
| Метод кастингу | Типові програми | Переваги | Міркування |
|---|---|---|---|
| Пісочний кастинг (Green or No-Bake) | Тіла клапана, насосні корпуси, фланці | – Cost-effective for large parts – Flexible for varied designs |
– Rougher surface finish (Ra 6–12 μm) – Tighter control needed for porosity |
| Кастинг цвілі з оболонки | 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 |
| Інвестиційне кастинг (Загублений віск) | Спонука, medical fittings, Високоточні компоненти | – Excellent surface finish (Рак < 3 μm) – High geometric complexity |
– Higher cost – Limited to small–medium parts |
| Відцентрове кастинг | Втулки, кільця, трубопровідні секції | – High density – Low porosity – Good mechanical properties in radial direction |
– Suitable only for rotationally symmetric parts |
| Вакуумна кастинг | Critical components in aerospace, nuclear applications | – Reduced oxidation – Cleaner microstructure |
– Expensive – Requires specialized equipment |
| Кастинг керамічної цвілі | Complex heat-resistant parts | – Excellent surface detail – Good dimensional precision |
– Longer mold preparation time – Higher cost |
Heat Treatment Practices
Після кастингу, CF3 typically undergoes розведення розчину в діапазоні 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 сенсибілізація і виснаження хрому на межах зерна, компрометування корозійної стійкості.
7. Корозійна стійкість
Загальна корозія
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:
- Еквівалентне число опору піттінгу (Деревина): ~ 18
- Critical Pitting Temperature (Кут): ~ 20–25 ° C (varies with chloride level)
Стрес-корозія тріщини (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. Виготовлення & Обробка
Обробка ЧПУ
CF3 machines comparably to wrought 304, with a machinability index of ~45 % (де 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 мкм.
Зварювання
Fabricators weld CF3 using 309 або 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.
Формування & Приєднання
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
Клапани, Насос, and Fittings in Water Treatment
In municipal and industrial water treatment facilities, CF3 stainless steel is a material of choice for:
- Тіла клапана та капелюшки
- Насос кожухів та крильчатки
- 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. Загальні програми включають:
- Корпуси компресора
- Manifolds and flowline components
- Metering valves and flanges
In up- and midstream systems, CF3 helps prevent stress-corrosion cracking (SCC) і піттінг, 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, гладка обробка поверхні, and compatibility with cleaning agents (CIP/SIP). CF3 fits these requirements, що робить його придатним для:
- Sanitary valves and pipe fittings
- Mixing and metering equipment
- Dosing pumps and housings
Його аустенітна мікроструктура, which remains stable even after repeated sterilization cycles, helps meet FDA і 3-Санітарні стандарти 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, біофурування, і 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. Порівняння з альтернативними матеріалами
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 нержавіючий.
| Власність | CF3 (304L) | Cf3m (316L) | CF8 (304 Кадати) | Cf8m (316 Кадати) | 304L Wrought |
|---|---|---|---|---|---|
| Молібден (Mo) Зміст | Ні | Так | Ні | Так | Ні |
| Вміст вуглецю | ≤ 0.03% (Низький вуглець) | ≤ 0.03% (Низький вуглець) | ≤ 0.08% | ≤ 0.08% | ≤ 0.03% (Низький вуглець) |
| Хлоридна стійкість | Помірний | Відмінний | Помірний | Відмінний | Помірний |
| Опір (Деревина) | ~ 18 | ~ 25–27 | ~ 20 | ~ 25–27 | ~ 18 |
| Корозійна стійкість | Добрий | Відмінний | Помірний | Відмінний | Добрий |
| Зварюваність | Відмінний | Відмінний | Помірний | Помірний | Відмінний |
| Вартість | $$ | $$$ | $$ | $$$ | $$ |
| Міцність (Розтяг) | ~ 485 МПа | ~500 MPa | ~510 MPa | ~ 520 МПа | ~ 520 МПа |
| Подовження | ~ 40% | ~ 45% | ~ 45% | ~ 45% | ~ 45% |
| Формування | Excellent for cast parts | Excellent for cast parts | Good for cast parts | Good for cast parts | Відмінний (for rolled or formed parts) |
| Заявки | Water systems, food-grade parts | Хімічний, морський, офшорний | General industrial parts | Морський, хімічний, офшорний | High-ductility, тонкостінні частини |
11. Висновок
Підсумовуючи, 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.
Більше, with annual global production exceeding 50,000 tonnes and scrap rates under 6 %, CF3 delivers both economic and performance advantages.
З нетерпінням чекає, 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.
Ланге є ідеальним вибором для ваших виробничих потреб, якщо вам потрібна якісна Відливання з нержавіючої сталі.
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 Окислювальна стійкість at elevated temperatures is critical,
other grades like Cf8m або 316 нержавіюча сталь may be more appropriate due to their enhanced high-temperature properties.
Can CF3 be welded?
Так, CF3 stainless steel is highly зварювальний. Its low carbon content minimizes the risk of carbide formation during welding, reducing the chances of intergranular corrosion.
Однак, it is always recommended to use appropriate welding techniques і post-weld heat treatments when working with this material in critical applications.
Is CF3 Suitable for Cryogenic Applications?
Так, CF3 exhibits good toughness at low temperatures, making it suitable for use in cryogenic applications such as liquefied natural gas (СПГ) storage and transportation.
Can CF3 Be Heat Treated?
CF3 is generally not heat treatable for strengthening purposes. Однак, 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 молібден.
У Морські середовища with high salinity, CF3 may experience some корозія з часом, so CF3M or CF8M might be more suitable.
How should CF3 Stainless Steel be maintained?
Regular maintenance of CF3 stainless steel includes:
- Прибирання: Removing contaminants such as chlorine, соляна, and chemicals that could cause localized corrosion.
- Огляд: Checking for any signs of піттінг або Корозія щілини, особливо в морський або chemical environments.
- Зварювання: Ensuring proper післяпідання термічна обробка to avoid cracking or sensitization.
Can CF3 Stainless Steel be used in food contact applications?
Так, CF3 is often used in обладнання для переробки харчових продуктів завдяки його Корозійна стійкість і ease of cleaning.
It complies with FDA і 3-Санітарні стандарти, що робить його відповідним вибором для санітарний клапани, насос, та трубопровідні системи.
