CF8M vs CF3M vs CF8: Stainless Steel Casting Grades Explained

What Are CF8, CF8M and CF3M?

CF8, CF8M, CF3 and CF3M are casting grades of austenitic stainless steel defined in ASTM A351, the standard for castings for pressure-containing parts (valve bodies, pump casings, fittings and flanges). They are the cast equivalents of the wrought grades you already know:

Casting Grade (ASTM A351)	Wrought Equivalent	Common Name
CF8	AISI 304	304 stainless (cast)
CF8M	AISI 316	316 stainless (cast)
CF3	AISI 304L	304L stainless (cast)
CF3M	AISI 316L	316L stainless (cast)

In the "CF" code, the letters indicate corrosion-resistant, iron base, and the number/letter suffix tracks the carbon and alloy content. Knowing this mapping saves a lot of confusion when comparing quotes, drawings and mill certificates.

Chemical Composition at a Glance

The practical differences between the four grades come down to carbon content and molybdenum:

Grade	C (max)	Cr	Ni	Mo	Key Feature
CF8	0.08	18.0–21.0	8.0–11.0	—	Standard 18-8 austenitic
CF8M	0.08	18.0–21.0	9.0–12.0	2.0–3.0	Mo added for pitting resistance
CF3	0.03	17.0–21.0	8.0–12.0	—	Low carbon, weld-friendly
CF3M	0.03	17.0–21.0	9.0–13.0	2.0–3.0	Low carbon + Mo

All four grades meet the same minimum mechanical properties in ASTM A351: tensile strength 485 MPa, yield strength 205 MPa, and elongation 30%. Lowering the carbon does not reduce strength — it improves weldability and corrosion resistance in service.

CF8 vs CF8M: The Difference Is Molybdenum

CF8M adds 2.0–3.0% molybdenum compared with CF8. Molybdenum is the element that gives 316 its superior resistance to pitting and crevice corrosion, especially in chloride environments:

• CF8 (304 equivalent) — ideal for general service: water, steam, mild chemicals, food processing. Cost-effective for most valve and fitting applications.
• CF8M (316 equivalent) — required where chlorides, seawater, acids or aggressive media are present. The standard choice for pump casings, impellers and chemical-process components.

CF8M vs CF3M: The Difference Is Carbon

CF3M is CF8M with a maximum carbon of 0.03% instead of 0.08%. Why does 0.05% of carbon matter? During welding or service above ~425°C, carbon can combine with chromium at grain boundaries and form chromium carbides — a process called sensitization — which depletes the surrounding metal of corrosion protection and leads to intergranular corrosion.

• CF8M (316 equivalent) — fine for most castings that will not be heavily welded or exposed to high temperatures.
• CF3M (316L equivalent) — the preferred grade for thick-section castings, weld-repaired parts, and service above 425°C, where sensitization risk is real.

Many end customers now specify CF3M by default for pressure-retaining castings because the low-carbon version costs almost the same but removes a whole class of field failures.

How to Choose the Right Grade for Your Casting

Application / Service	Recommended Grade	Why
Water, steam, general valve bodies	CF8	Corrosion resistance at the lowest cost
Seawater, marine, pumps, chemical media	CF8M	Molybdenum resists pitting and crevice attack
Thick sections, welded assemblies, service > 425°C	CF3M	Low carbon prevents sensitization
Food, beverage, sanitary equipment	CF3M / CF8	Cleanability and corrosion resistance
Aggressive acids, chloride stress cracking	CF3M, Duplex 2205, Hastelloy	Upgrade beyond standard austenitic grades

Common Confusions — Settled

• "Is CF3M weaker than CF8M?" No. Per ASTM A351 both have identical minimum tensile (485 MPa) and yield (205 MPa). Low carbon improves weldability; it does not lower strength.
• "Can I substitute CF8 for CF8M?" Only if the environment allows. Without molybdenum, chloride resistance drops sharply. Check the service media before substituting.
• "Does casting 316L automatically mean CF3M?" Only if the foundry melts to ASTM A351 CF3M chemistry and provides the certificate. Insist on the casting grade designation, not just "316L" written on a drawing.

How We Guarantee the Grade You Ordered

At Huayong, every CF8 / CF8M / CF3M heat is verified before and after pouring:

• Spectrometer analysis of each heat against the ordered grade chemistry
• Material test certificate (MTC/COA) with heat number traceability for every batch
• PMI testing on request, before shipment
• NDT and dimensional reports as specified

We cast valve bodies, pump casings, impellers, fittings and custom parts in CF8, CF8M, CF3M — plus WCB carbon steel, 4140/45 alloy steel, duplex 2205, Hastelloy C276 (CW2M) and copper alloys, from 10 g to 100 kg.