CF3/CF8/CF3M/CF8M and F304/F316/F304L/F316L Series Guide

1. Introduction

Stainless steels in the 300-series austenitic family dominate industries requiring corrosion resistance, formability, and hygienic performance.

Among these, Type 304 and 316 appear in both cast and wrought forms, each governed by separate standards and designation systems.

Cast components follow ASTM A351 designations—CF3, CF8, CF3M, CF8M—while wrought and forged products adhere to ASTM A182 (also reflected in EN/DIN “F-grades”): F304, F316, F304L, F316L.

In the following sections, we decode these codes, compare their chemistries and microstructures, and offer guidelines to select cast versus wrought grades for valves, pump housings, piping, and other pressure-containing equipment.

2. ASTM Standards & Prefixes

• ASTM A351 covers stainless steel castings for pressure-bearing parts. In this standard, “C” stands for Casting, and the “F” in the grade codes (e.g. CF8) denotes “Cast.”
• ASTM A182 governs stainless steel forgings and wrought fittings. The “F” in F304/F316 indicates Forging (or wrought product).

Prefix	Meaning	Standard	Typical Product Types
C	Casting	A351	Valve bodies, pump housings
F	Forging/Wrought	A182	Flanges, shafts, fasteners

3. Casting Designations: CF-Series per ASTM A351

When engineers specify valve bodies, pump housings, or complex manifolds, they often turn to ASTM A351 castings for one-piece integrity and intricate geometries.

Within A351’s austenitic grades, four designations—CF3, CF8, CF3M, and CF8M—mirror the familiar wrought grades 304, 304L, 316, and 316L, respectively.

Below, we decode each CF-series grade, highlight its chemistry and microstructural traits, and explain how alloying adjustments tailor performance.

CF3

Composition:

• Chromium: 18.0–20.0 wt%
• Nickel: 8.0–10.5 wt%
• Carbon: ≤ 0.03 wt% (low-C)
• Manganese, silicon, phosphorus, sulfur: per ASTM limits

Equivalent: Cast analogue of 304L (UNS S30403, EN 1.4307).

Key Attributes:

• Low-carbon chemistry prevents carbide precipitation during slow post-pour cooling, eliminating weld-zone sensitization common in higher-C steels.
• Solution annealing at 1 040 °C for 30 minutes followed by water quench dissolves any interdendritic carbides, yielding a corrosion rate under 0.1 mm/year in neutral chloride environments.
• Tensile strength typically measures ~445 MPa, roughly 5 % lower than CF8, but with superior intergranular corrosion resistance.

CF8

Composition:

• Chromium: 18.0–20.0 wt%
• Nickel: 8.0–10.5 wt%
• Carbon: ≤ 0.08 wt%
• Trace elements within standard limits

Equivalent: Cast counterpart to 304 (UNS S30400, EN 1.4301).

Key Attributes:

• Standard-carbon 304 chemistry delivers balanced corrosion resistance and ductility.
• Dendritic grains measure 1–3 mm, so CF8’s average Charpy impact energy at –20 °C (≈ 30 J) falls about 15 % below wrought 304’s.
• Cost-effective for moderately corrosive services, CF8 valves resist pitting to ~0.2 % NaCl at 20 °C.

CF3M

Composition:

• Chromium: 16.0–18.0 wt%
• Nickel: 10.0–14.0 wt%
• Molybdenum: 2.0–3.0 wt%
• Carbon: ≤ 0.03 wt%
• Minor alloying per ASTM specification

Equivalent: Cast analogue of 316L (UNS S31603, EN 1.4404).

Key Attributes:

• Low-C plus 2–3 % Mo raises the PREN (Pitting Resistance Equivalent Number) from ~18 (in CF3) to ~25, roughly doubling resistance to chloride-induced pitting.
• Solution treatment at 1 040 °C dissolves Mo-rich carbides, granting creep resistance up to 250 °C with < 5 % strength loss over 1 000 h.
• Hydrocarbon and sour-gas service benefit from CF3M’s minimal carbide network and Mo-enhanced passive film stability.

CF8M

Composition:

• Chromium: 16.0–18.0 wt%
• Nickel: 10.0–14.0 wt%
• Molybdenum: 2.0–3.0 wt%
• Carbon: ≤ 0.08 wt%
• Other elements per ASTM limits

Equivalent: Cast version of 316 (UNS S31600, EN 1.4401).

Key Attributes:

• Standard-C 316 chemistry provides broad corrosion resistance—including seawater and 5 % HCl—while Mo combats localized attack.
• Higher tensile strength (~480 MPa) versus CF3M makes CF8M suitable for thicker sections and elevated-temperature parts.
• Elevated-Temperature Capability: CF8M maintains 80 % of room-temperature yield strength at 300 °C, outperforming CF8 by 20 %.

Summary: CF Designations and Equivalents

4. Wrought/Welded “F-” Grades in EN/DIN/FSSA

Shifting from castings to wrought and forged components, the “F-” prefix in European (EN/DIN) and Japanese (JIS/FSSA) standards denotes materials supplied as bars, fittings, flanges, or valve trim.

These products follow ASTM A182 in the U.S. and correspond to EN numbers below.

F304 (EN 1.4301 / AISI 304)

• Nominal Composition: 18.0–20.0 % Cr, 8.0–10.5 % Ni, C ≤0.08 %, Mn ≤2 %, Si ≤1 %
• Mechanical Properties:

• • Yield Strength (Rp0.2): ~215 MPa
  • Tensile Strength (Rm): 505–735 MPa
  • Elongation: ≥ 40 %

• Corrosion Traits:

• • General corrosion rate < 0.1 mm/year in neutral media
  • Pitting threshold ~ 0.2 % Cl⁻ at 20 °C

• Applications: Food-service fittings, moderate-duty valve trim, architectural trim

F316 (EN 1.4401 / AISI 316)

• Nominal Composition: 16.0–18.0 % Cr, 10.0–14.0 % Ni, 2.0–3.0 % Mo, C ≤0.08 %
• Mechanical Properties:

• • Yield Strength (Rp0.2): ~205 MPa
  • Tensile Strength (Rm): 515–715 MPa
  • Elongation: ≥ 40 %

• Corrosion Traits:

• • Pitting threshold up to 0.5 % Cl⁻—150 % higher than F304
  • Superior resistance to sulfuric and hydrochloric acids

• Applications: Marine fittings, chemical-process valve internals, heat-exchanger tubes

F304L (EN 1.4307 / AISI 304L)

• Low-Carbon Variant: C ≤0.03 % prevents chromium-carbide precipitation in weld heat-affected zones (HAZ).
• Mechanical Properties:

• • Rp0.2: ~205 MPa (slightly below F304)
  • Elongation: ≥ 45 % (enhanced formability)

• Corrosion Traits:

• • Eliminates intergranular attack in HAZ without post-weld solution annealing
  • Pitting threshold: ~ 0.2 % Cl⁻

• Applications: Welded pressure vessels, pharmaceutical tanks, piping in food/beverage industries

F316L (EN 1.4404 / AISI 316L)

• Low-Carbon, Mo-Bearing: 16–18 % Cr, 10–14 % Ni, 2–3 % Mo, C ≤0.03 %.
• Mechanical Properties:

• • Rp0.2: ~200 MPa
  • Rm: 485–680 MPa
  • Elongation: ≥ 40 %

• Corrosion Traits:

• • High PREN (~ 25)—excellent for chloride and sour-gas service
  • Weld-zone stability without annealing

• Applications: Sour-service valves (H₂S environments), marine piping, heat exchangers

Cross-Reference Table

5. Comparative Analysis: Cast vs. Wrought

Microstructure & Mechanical Properties

Whereas cast CF-grades display coarse dendritic grains and ASTM tensile strengths around 450 MPa,

wrought F-grades possess fine, worked grains with tensile ~515 MPa and 15–20 % higher impact toughness at –20 °C.

Corrosion Performance

Although nominal chemistries match, cast parts can harbor micro-porosity and segregation, leading to localized attack if not properly heat-treated.

In contrast, wrought steels exhibit uniform composition, conferring slightly better pitting thresholds and SCC resistance.

Fabrication Considerations

Casting excels for complex geometries—valve bodies and pump housings—eliminating dozens of machining operations.

Conversely, forgings cost more per kilogram but offer superior fatigue strength, uniform grain flow, and minimal defects.

Cost & Lead-Time Trade-Offs

Foundries typically quote 6–8 weeks for custom CF castings, whereas standard F-grade bars and flanges ship in 2–4 weeks.

Per kilogram, cast CF8M runs about 10 % cheaper than forged F316, although total component cost may favor casting for intricate shapes.

Aspect	CF8/CF8M/CF3/CF3M (Cast)	F304/F316/F304L/F316L (Forged)
Geometry	Complex shapes in one piece	Simpler shapes; may require welding/fabrication
Mechanical Strength	Lower toughness; ASTM tensile ~450 MPa	Higher toughness; ASTM tensile ~~515 MPa
Corrosion Resistance	Matches composition (304/316 equivalents)	Equivalent composition, slightly better due to finer grains
Weldability	Requires careful heat treatment	Excellent; low-C versions avoid sensitization
Cost & Lead Time	Lower cost for complex parts; longer cast lead times	Higher raw-material cost; quicker standard stock delivery

6. Applications & Material Selection Guidelines

• CF3/CF8/CF3M/CF8M Cast Components: Valve bodies, pump casings, heat-exchanger shells—where single-piece integrity and intricate internal passages reduce assembly costs.
  CF3M and CF8M appear in chemical and offshore service, thanks to Mo-enhanced chloride resistance.
• F304/F316/F304L/F316L Wrought Products: Pipe flanges, shafts, fasteners, and high-pressure valve trim;
  weld-critical assemblies in petrochemical and power-generation plants favor low-C variants to avoid HAZ corrosion.
• Decision Matrix:

• • Choose CF-grades when geometry complicates machining, and service conditions do not demand wrought toughness.
  • Select F-grades for high-cycle fatigue parts, thin-wall sections, or where QA/QC protocols require ultrasonic inspection of wrought material.

7. Conclusions

Despite sharing base chemistries, CF3, CF8, CF3M, CF8M (ASTM A351) and F304, F316, F304L, F316L (ASTM A182/EN/DIN) serve distinct roles:

• CF-cast grades match wrought equivalents in corrosion resistance and temperature capability but exhibit coarser microstructures and modestly lower strength.
• F-forged grades deliver finer grains, higher toughness, and consistent properties—ideal for high-stress and fatigue-critical components.

By understanding these prefixes and their implications, engineers can optimize material choice—balancing cost, performance, and manufacturability—to ensure reliable, economical valve and pump components.

8. References & Standards

• ASTM A351/A351M: “Standard Specification for Castings, Austenitic, for Pressure-Containing Parts”
• ASTM A182/A182M: “Standard Specification for Forged or Rolled Alloy-and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service”
• EN 1.4301/1.4307/1.4401/1.4404 (DIN equivalents)
• UNS S30400/S30403/S31600/S31603 designations

 

FAQs

How do CF8 and CF8M differ?

CF8 matches 18–20 %Cr–8–10.5 %Ni with standard carbon (≤ 0.08 %), the cast equivalent of 304.

CF8M adds 2–3 %Mo (16–18 %Cr–10–14 %Ni–2–3 %Mo, C ≤ 0.08 %), mirroring 316 and improving pitting and high-temperature strength.

Why choose CF3 or CF3M over CF8/CF8M?

CF3 and CF3M limit carbon to ≤ 0.03 %, preventing weld-zone sensitization in slow-cooling castings. CF3 ≈ 304L; CF3M ≈ 316L.

When should I specify cast CF-grades instead of wrought F-grades?

Use CF castings for complex, one-piece geometries (valve bodies, pump housings) where machining cost would be prohibitive.

Choose F wrought grades for high-stress, fatigue-critical or thin-wall parts (shafts, flanges, fasteners) requiring superior toughness and defect-free microstructure.

What advantages do F304L and F316L offer?

Their low carbon (≤ 0.03 %) virtually eliminates intergranular corrosion in weld heat-affected zones, often removing the need for post-weld annealing.

How do corrosion resistances compare?

CF8/CF3/304/F304 resist pitting up to ~0.2 % Cl⁻.

CF8M/CF3M/316/F316 resist to ~0.5 % Cl⁻.

Low-carbon variants (CF3/CF3M/F304L/F316L) maintain these thresholds while ensuring weld-zone stability.

Do cast and wrought grades require different heat treatments?

Cast CF-grades undergo solution annealing at ~1 040 °C for 30 min and rapid quench to dissolve carbides and homogenize.

Wrought F-grades typically follow ASTM A182 guidelines: solution anneal at 1 040–1 060 °C for 15 min per 25 mm, then quench.

Which grade offers better mechanical strength?

Wrought F-grades (e.g., F304, F316) achieve higher tensile (~515 MPa) and impact toughness than cast CF-grades (~450 MPa tensile), due to finer forged microstructures.

How do cost and lead time compare?

CF castings generally cost 10–15 % less per kilogram for complex shapes but require longer lead times (6–8 weeks).

F wrought stock often ships in 2–4 weeks, at a premium of 5–10 % per kilogram.