What Is ASTM A351 CF8M?

Quick Answer

ASTM A351 CF8M is the cast equivalent of Type 316 stainless steel. The “CF” designates a corrosion-resistant iron-chromium-nickel alloy, “8” indicates approximately 8% nickel, and “M” denotes molybdenum addition. CF8M is the standard cast stainless grade for valve bodies, pump casings, and fittings in corrosive and high-temperature service up to 538°C (1000°F).

Chemical Composition and Properties

CF8M’s 2-3% molybdenum content provides significantly better resistance to pitting and crevice corrosion than CF8 (cast 304), particularly in chloride-containing environments.

Property	CF8M
Specification	ASTM A351 / ASME SA-351
Wrought equivalent	Type 316 / UNS S31600
Carbon	0.08% max
Chromium	18.0-21.0%
Nickel	9.0-12.0%
Molybdenum	2.0-3.0%
Silicon	1.50% max
Manganese	1.50% max
Tensile strength (min)	485 MPa (70 ksi)
Yield strength (min)	205 MPa (30 ksi)
Elongation (min)	30%
Service temp range	-254°C to 538°C (-425°F to 1000°F)
Heat treatment	Solution annealed at 1040°C min, water quenched

Corrosion Resistance

The chromium-nickel-molybdenum composition gives CF8M excellent resistance to:

• General corrosion in process water, steam, and most organic acids
• Pitting and crevice corrosion in chloride environments (seawater, brackish water, brine)
• Intergranular corrosion when properly solution annealed (carbon held below 0.08%)
• Stress corrosion cracking: better resistance than 304/CF8 in chloride service

For severe chloride environments or higher temperatures, CF3M (cast 316L, 0.03% C max) or higher alloys (CK3MCuN / cast 254 SMO) may be required.

Applications

CF8M is specified wherever carbon steel lacks the corrosion resistance for the service fluid:

• Chemical and petrochemical valve bodies for acids, caustics, and solvents
• Offshore platforms and subsea systems exposed to seawater
• Pharmaceutical and food processing (sanitary and high-purity applications)
• Desalination plants and cooling water systems
• LNG and cryogenic service down to -254°C (paired with A182 F316 forgings)

CF8M pairs with ASTM A182 F316 forged flanges and fittings, and ASTM A312 TP316 seamless and welded pipes.

Quality Requirements

ASTM A351 requires solution annealing (minimum 1040°C followed by water quench or rapid cooling) to dissolve carbides and restore full corrosion resistance. All castings undergo chemical analysis, tensile testing, and visual examination.

Supplementary requirements include radiographic and liquid penetrant examination for critical valve castings per ASME B16.34. Hydrostatic testing is performed per the applicable valve standard. Mill test certificates must document chemistry (including ferrite content), mechanical properties, and heat treatment records.

Ferrite content in CF8M castings typically ranges from 5-20%. Adequate ferrite improves resistance to hot cracking during casting and welding, but excessive ferrite can reduce corrosion resistance and low-temperature toughness.

Read the full guide to valve materials