ASTM A351 CF8M Material Properties

ASTM A351 CF8M is the cast equivalent of wrought Type 316 stainless steel and the standard cast austenitic grade for valve bodies, pump casings, and fittings in corrosive and high-temperature service. The “CF” in the designation stands for corrosion-resistant iron-chromium-nickel alloy, “8” indicates approximately 8% nickel content in the base composition range, and “M” denotes the addition of molybdenum. The ASTM A351 CF8M material properties make it the default choice for stainless steel castings across oil and gas, chemical, pharmaceutical, and offshore applications.

CF8M Chemical Composition

Element	ASTM A351 CF8M	ASTM A351 CF3M (Low-C)	Wrought 316 (A182 F316)
Carbon (max %)	0.08	0.03	0.08
Chromium (%)	18.0-21.0	17.0-21.0	16.0-18.0
Nickel (%)	9.0-12.0	9.0-13.0	10.0-14.0
Molybdenum (%)	2.0-3.0	2.0-3.0	2.0-3.0
Silicon (max %)	1.50	1.50	1.00
Manganese (max %)	1.50	1.50	2.00
Phosphorus (max %)	0.04	0.04	0.045
Sulfur (max %)	0.04	0.04	0.030

Note the wider chromium range (18-21%) in CF8M compared to wrought 316 (16-18%). This compensates for the segregation inherent in the casting process and ensures adequate chromium in all regions of the casting.

Mechanical Properties

Property	CF8M (ASTM A351)	CF3M (ASTM A351)
Tensile strength (min)	485 MPa (70 ksi)	485 MPa (70 ksi)
Yield strength (min)	205 MPa (30 ksi)	205 MPa (30 ksi)
Elongation (min)	30%	30%
Hardness (typical)	130-180 HBW	130-180 HBW
Service temp range	-254 to 538 degC	-254 to 425 degC
Heat treatment	Solution anneal 1040 degC min, water quench	Solution anneal 1040 degC min, water quench

Corrosion Resistance Properties

The 2-3% molybdenum content gives CF8M superior resistance to pitting and crevice corrosion compared to CF8 (cast 304), particularly in chloride-containing environments.

Corrosion Type	CF8M Performance
General corrosion	Excellent in process water, steam, organic acids
Pitting (chlorides)	Good (PREN ~24-28)
Crevice corrosion	Good in moderate chloride concentrations
Intergranular corrosion	Resistant when solution annealed; use CF3M for severe cases
Stress corrosion cracking	Better than CF8 in chloride service
Cryogenic toughness	Excellent down to -254 degC

Ferrite Content

CF8M castings contain 5-20% delta ferrite in the austenite matrix. Ferrite content is critical:

Ferrite Level	Effect
Below 5%	Risk of hot cracking during casting and welding
5-15%	Optimal balance of strength, corrosion resistance, and weldability
Above 20%	Reduced corrosion resistance and low-temperature toughness; sigma phase risk at high temperatures

Ferrite is measured using a calibrated ferritescope or calculated from the composition using the WRC-1992 or Schaeffler diagram. The ferrite number (FN) must be recorded on the mill test certificate.

Applications

CF8M pairs with ASTM A182 F316 forged flanges and ASTM A312 TP316 pipes. Common applications include:

• Chemical and petrochemical valve bodies
• Offshore platform valves exposed to seawater
• Pharmaceutical and food-grade process equipment
• LNG and cryogenic valve bodies
• Desalination plant pump casings and valve trim

Common Mistake

Assuming CF8M and wrought 316 are identical. While they share the same base composition, the wider Cr range, higher Si, and duplex (austenite + ferrite) microstructure of CF8M mean that corrosion test data from wrought 316 does not directly apply to castings. For critical corrosive service, request corrosion testing on the actual casting material or specify supplementary corrosion testing on the purchase order.

Read the full guide to forged steel