1. مقدمة
CF3 stainless steel, عضو في عائلة الفولاذ المقاوم للصدأ الأوستنيتي, is the low-carbon cast equivalent of the popular wrought grade 304ل (الولايات المتحدة S30403).
It is defined under ASTM A351 and widely used in industries where corrosion resistance, قابلية اللحام, and castability are paramount.
ال “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%).
تاريخيا, 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, أداء, and resistance to sensitization,
CF3 continues to be strategically important in cast stainless steel applications across chemical, البتروكيماويات, معالجة المياه, and food-processing sectors.
2. التكوين الكيميائي & المعادن
التكوين الكيميائي الاسمي
The typical weight percentage (بالوزن ٪) of the alloying elements in CF3 stainless steel, as defined by ASTM A351, يكون:
| عنصر | النطاق النموذجي (بالوزن ٪) | وظيفة |
|---|---|---|
| الكروم (كر) | 18.0 - 21.0% | Promotes corrosion resistance through passive film formation |
| النيكل (في) | 8.0 - 11.0% | يستقر الأوستينيت, improves ductility and toughness |
| الكربون (ج) | ≤ 0.03% | Reduces sensitization; improves weldability |
| المنغنيز (MN) | ≤ 1.5% | Enhances hot workability; deoxidizer |
| السيليكون (و) | ≤ 2.0% | يعزز السيولة في الصب; deoxidizer |
| الفسفور (ص) | ≤ 0.04% | Residual; must be minimized to reduce brittleness |
| الكبريت (ق) | ≤ 0.04% | Residual; excessive S can reduce toughness |
| حديد (Fe) | توازن | Matrix element |
ال محتوى الكربون المنخفض (≤ 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.
البنية المجهرية: مصفوفة أوستنيكية & 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 (عادة < 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
| معيار | تعيين | منطقة | Equivalent Grade |
|---|---|---|---|
| ASTM A351 | Grade CF3 | الولايات المتحدة الأمريكية | Low-carbon cast 304L |
| ASME SA-351 | Grade CF3 | الولايات المتحدة الأمريكية (boiler code) | Pressure vessel compliant |
| في 10283 | GX2CRNI19-11 | European Union | نسخة يلقي 1.4306 (304ل) |
| ISO 11972 | G-X2CrNi19-11 | دولي | Global harmonized equivalent |
| انه G5121 | SCS13A | اليابان | 304L cast grade |
4. الخصائص الميكانيكية
| خاصية ميكانيكية | القيمة النموذجية |
|---|---|
| قوة الشد | ≥485 ميجا باسكال |
| قوة العائد (0.2% الإزاحة) | ≥205 ميجا باسكال |
| استطالة | ≥30 ٪ |
| صلابة | 140-190 HB |
| تأثير المتانة (درجة حرارة الغرفة) | > 100 J (Charpy V-Notch) |
| Fatigue Endurance Limit | 240-270 ميجا باسكال (in air, مصقول) |
| مقاومة زحف | Moderate up to 870°C |
في درجات حرارة مرتفعة, 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. حراري & الخصائص الفيزيائية
| ملكية | قيمة |
|---|---|
| كثافة | ~ 7.9 جم/سم |
| الموصلية الحرارية | ~ 16 ث/م · ك (at 100°C) |
| Coefficient of Expansion | 17.3 µm/m · ° c (20–400°C) |
| المقاومة الكهربائية | 0.72 µΩ · م |
| الاستجابة المغناطيسية | غير مغناطيسية (صلب) |
| مقاومة الأكسدة | 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.
سيولة & درجة الحرارة
CF3 melts between 1450 ° C و 1550 درجة مئوية, 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 مم.
لكن, excessive superheat can increase gas pickup والأكسدة, so operators typically limit superheat to 50 درجة مئوية above liquidus.
Solidification Range & انكماش
مع نطاق التجمد تقريبا 60–90 °C, CF3 solidifies over a broader temperature interval than simple austenitic alloys.
بالتالي, it exhibits الانكماش الخطي ل 1.9–2.3 %, necessitating careful shrink‑compensation in pattern design.
لمنع مسامية خط الوسط, engineers employ التصلب الاتجاهي: placing insulated risers above hot spots and using قشعريرة 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.
فضلاً عن ذلك, الأكمام الحرارية on critical risers prolong feeding life without increasing overall mold volume.
degassing, Deoxidation & Inoculation
To minimize gas porosity, foundries typically argon‑purge the molten CF3 before pouring.
They also add السيليكون (0.3-0.6 %) و الألومنيوم (0.02–0.05 %) deoxidizers, which form stable oxides and reduce dissolved oxygen.
أخيراً, a small rare‑earth inoculant (على سبيل المثال, 0.03–0.05 % Fe‑Ce) promotes fine, uniform δ‑ferrite and prevents microshrinkage, enhancing mechanical consistency.
Suitable Casting Methods for CF3 Stainless Steel
| طريقة الصب | التطبيقات النموذجية | المزايا | اعتبارات |
|---|---|---|---|
| صب الرمال (Green or No-Bake) | جثث الصمام, مضخة العلب, الشفاه | – Cost-effective for large parts – Flexible for varied designs |
– Rougher surface finish (Ra 6–12 μm) – Tighter control needed for porosity |
| قذيفة القالب صب | 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 |
| صب الاستثمار (فقدت الشمع) | مدافع, medical fittings, مكونات عالية الدقة | – Excellent surface finish (ر < 3 μm) – High geometric complexity |
– Higher cost – Limited to small–medium parts |
| الطرد المركزي الصب | البطانات, الخواتم, pipe sections | – High density – Low porosity – Good mechanical properties in radial direction |
– Suitable only for rotationally symmetric parts |
| صب فراغ | Critical components in aerospace, nuclear applications | – Reduced oxidation – Cleaner microstructure |
– Expensive – Requires specialized equipment |
| صب القالب السيراميك | Complex heat-resistant parts | – Excellent surface detail – Good dimensional precision |
– Longer mold preparation time – Higher cost |
Heat Treatment Practices
بعد الصب, CF3 typically undergoes الحل الصلب في نطاق 1040-1120 درجة مئوية (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 التوعية و chromium depletion في حدود الحبوب, compromising corrosion resistance.
7. مقاومة التآكل
التآكل العام
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:
- رقم ما يعادل مقاومة الحفر (خشب): ~ 18
- Critical Pitting Temperature (CPT): ~ 20-25 درجة مئوية (varies with chloride level)
تكسير التآكل (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. التصنيع & القابلية للآلات
تصنيع CNC
CF3 machines comparably to wrought 304, with a machinability index of ~45 % (أين 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 ميكرون.
لحام
Fabricators weld CF3 using 309 أو 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.
تشكيل & الانضمام
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
الصمامات, مضخات, 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. وتشمل التطبيقات الشائعة:
- علب الضاغط
- Manifolds and flowline components
- Metering valves and flanges
In up- and midstream systems, CF3 helps prevent stress-corrosion cracking (SCC) و الحفر, 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, الانتهاء من السطح الأملس, and compatibility with cleaning agents (CIP/SIP). CF3 fits these requirements, جعلها مناسبة ل:
- Sanitary valves and pipe fittings
- Mixing and metering equipment
- Dosing pumps and housings
إنه austenitic microstructure, which remains stable even after repeated sterilization cycles, helps meet FDA و 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, الوقود الحيوي, و 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. مقارنة مع المواد البديلة
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 غير القابل للصدأ.
| ملكية | CF3 (304ل يلقي) | CF3M (316ل يلقي) | CF8 (304 يقذف) | CF8M (316 يقذف) | 304L Wrought |
|---|---|---|---|---|---|
| الموليبدينوم (شهر) محتوى | لا | نعم | لا | نعم | لا |
| محتوى الكربون | ≤ 0.03% (كربون منخفض) | ≤ 0.03% (كربون منخفض) | ≤ 0.08% | ≤ 0.08% | ≤ 0.03% (كربون منخفض) |
| مقاومة الكلوريد | معتدل | ممتاز | معتدل | ممتاز | معتدل |
| تحرض المقاومة (خشب) | ~ 18 | ~ 25-27 | ~20 | ~ 25-27 | ~ 18 |
| مقاومة التآكل | جيد | ممتاز | معتدل | ممتاز | جيد |
| قابلية اللحام | ممتاز | ممتاز | معتدل | معتدل | ممتاز |
| يكلف | $$ | $$$ | $$ | $$$ | $$ |
| قوة (الشد) | ~ 485 ميجا باسكال | ~500 MPa | ~510 MPa | ~520 MPa | ~520 MPa |
| استطالة | ~ 40 ٪ | ~45% | ~45% | ~45% | ~45% |
| قابلية التشكيل | Excellent for cast parts | Excellent for cast parts | Good for cast parts | Good for cast parts | ممتاز (for rolled or formed parts) |
| التطبيقات | Water systems, food-grade parts | كيميائية, البحرية, في الخارج | General industrial parts | البحرية, كيميائية, في الخارج | High-ductility, أجزاء رقيقة الجدران |
11. خاتمة
في ملخص, 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.
علاوة على ذلك, with annual global production exceeding 50,000 tonnes and scrap rates under 6 %, CF3 delivers both economic and performance advantages.
نتطلع, 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.
لانجهي هو الخيار الأمثل لاحتياجات التصنيع الخاصة بك إذا كنت بحاجة إلى جودة عالية مصبوبات الفولاذ المقاوم للصدأ.
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 مقاومة الأكسدة at elevated temperatures is critical,
other grades like CF8M أو 316 الفولاذ المقاوم للصدأ may be more appropriate due to their enhanced high-temperature properties.
Can CF3 be welded?
نعم, CF3 stainless steel is highly قابل لحام. Its low carbon content minimizes the risk of carbide formation during welding, reducing the chances of intergranular corrosion.
لكن, it is always recommended to use appropriate welding techniques و post-weld heat treatments when working with this material in critical applications.
Is CF3 Suitable for Cryogenic Applications?
نعم, 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. لكن, 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 الموليبدينوم.
في البيئات البحرية with high salinity, CF3 may experience some تآكل التآكل متأخر , بعد فوات الوقت, so CF3M or CF8M might be more suitable.
How should CF3 Stainless Steel be maintained?
Regular maintenance of CF3 stainless steel includes:
- تنظيف: Removing contaminants such as chlorine, ملح, and chemicals that could cause localized corrosion.
- تقتيش: Checking for any signs of الحفر أو تآكل شق, خاصة في البحرية أو chemical environments.
- لحام: Ensuring proper بعد الليباد المعالجة الحرارية to avoid cracking or sensitization.
Can CF3 Stainless Steel be used in food contact applications?
نعم, CF3 is often used in معدات تجهيز الأغذية بسبب مقاومة التآكل و ease of cleaning.
It complies with FDA و 3-A Sanitary Standards, مما يجعلها خيارًا مناسبًا لـ صحية الصمامات, مضخات, وأنظمة الأنابيب.
