What Is CF8M Stainless Steel? CF8M vs 316 Explained

If you have ever turned over a stainless steel ball valve and found CF8M cast into the body, you have run into one of the most common — and most misunderstood — markings in the valve industry. CF8M is the ASTM cast-grade designation for 316 stainless steel. In other words, a valve sold as "316 stainless" will almost always have CF8M stamped on its body, because the body is a casting, and castings use a different naming system than wrought (bar, plate, forged) material. The two grades are chemically equivalent for nearly all practical purposes.

This guide decodes the CF8M designation, compares CF8M to wrought 316 stainless, explains what the molybdenum addition does for corrosion resistance, and shows when you should specify CF8M valves for your application.

In This Guide

• Decoding the CF8M Designation
• CF8M vs 316: What's the Difference?
• Corrosion Resistance: What the Molybdenum Buys You
• Common Cast Grade Reference Table
• When to Specify CF8M Valves
• Standards & References
• Frequently Asked Questions

Decoding the CF8M Designation

CF8M comes from the Alloy Casting Institute (ACI) naming system, which is used in casting specifications such as ASTM A351 and ASTM A743. Each part of the designation has a meaning:

• C — a corrosion-resistant casting alloy (as opposed to "H" grades, which are heat-resistant).
• F8 — places the alloy in the austenitic stainless family with roughly 19% chromium and 9–10% nickel. The second letter and number locate the alloy on the ACI chromium-nickel composition chart.
• M — a molybdenum addition, typically 2–3%, which significantly improves resistance to chlorides and pitting.

Using the same logic: CF8 (no "M") is the cast equivalent of 304 stainless, CF8M is the cast equivalent of 316, and CF3M — with lower carbon — is the cast equivalent of 316L. The "3" in CF3 and CF3M indicates a maximum carbon content of 0.03%, which improves weldability and resistance to intergranular corrosion after welding.

CF8M vs 316: What's the Difference?

The short answer: CF8M is 316 stainless steel in cast form. The differences come from how each is produced and specified, not from any meaningful gap in corrosion performance.

This is why a single stainless ball valve will often list both materials on its datasheet: the body is cast CF8M per ASTM A351, while the ball and stem are machined from wrought 316 bar per ASTM A276. Both are "316 stainless" in everyday language.

The slightly wider chromium range in CF8M and its small ferrite content (typically 5–20%) are intentional — the ferrite improves castability, weld repairability, and resistance to stress corrosion cracking in the cast structure.

Corrosion Resistance: What the Molybdenum Buys You

The 2–3% molybdenum is the entire reason CF8M/316 exists as a step up from CF8/304. Molybdenum dramatically improves resistance to pitting and crevice corrosion in chloride environments — the failure mode that destroys 304 stainless in salt water, brines, and many chemical services.

Compared to CF8 (cast 304), CF8M handles:

• Chlorides and brines — salt water spray, coastal atmospheres, brine cooling loops, water treatment chemicals.
• Dilute acids — sulfuric, phosphoric, acetic, and many organic acids at moderate concentrations and temperatures where 304 pits or etches.
• Seawater exposure — suitable for splash zones and intermittent contact (continuous seawater immersion generally calls for super-duplex or higher alloys).

Against brass or bronze valves, CF8M offers far broader chemical compatibility, no dezincification risk, and much higher temperature capability. Against carbon steel (WCB), it eliminates rust and product contamination concerns entirely.

Specify CF8M whenever the media contains chlorides, the environment is marine or coastal, the process involves acids or aggressive cleaning chemicals, or product purity matters (food, beverage, pharma support utilities).

Common Cast Grade Reference Table

Keep this table handy when reading valve markings — these are the cast designations you will see most often on valve bodies:

When to Specify CF8M Valves

• Chemical processing — dosing, transfer, and isolation of acids, caustics, and solvents where brass and carbon steel fail quickly.
• Water treatment chemical feed — ferric chloride, alum, polymer feed lines. One caveat: concentrated sodium hypochlorite (bleach) attacks even 316/CF8M over time; for dedicated hypo service, consider PVC/CPVC or higher alloys, and use CF8M only for dilute or intermittent exposure.
• Marine and coastal installations — dockside piping, ballast systems, salt-air environments where 304 develops tea staining and pitting.
• Food and beverage — CIP chemical lines, process water, and product-adjacent utilities where corrosion-free, contaminant-free wetted parts are required.
• Steam-adjacent and high-temperature service — CF8M retains strength and oxidation resistance at temperatures well beyond brass or iron-bodied valves; ASME B16.34 ratings for A351 CF8M extend into the 800°F+ range with appropriate pressure derating.

Standards & References

• ASTM A351 — Castings, Austenitic, for Pressure-Containing Parts. The spec most valve bodies are cast to; covers Grade CF8M.
• ASTM A743 / A744 — Iron-Chromium-Nickel corrosion-resistant castings for general and severe service; also define CF8M chemistry.
• ACI designation system — the Alloy Casting Institute naming convention (C/H prefix, composition letter, modifier suffixes) used throughout ASTM casting specs.
• ASME B16.34 — Valves, Flanged, Threaded, and Welding End; establishes pressure-temperature ratings for valves made from A351 CF8M and other material groups.

Frequently Asked Questions

Is CF8M the same as 316 stainless steel?

Functionally, yes. CF8M is the cast-grade designation for 316 stainless under ASTM A351/A743, with essentially the same chemistry. A valve body marked CF8M is correctly described as a 316 stainless steel valve.

What does CF8M stand for?

In the ACI naming system: C = corrosion-resistant casting, F8 = the ~19% chromium / 9–10% nickel austenitic family, and M = a 2–3% molybdenum addition. Together: a corrosion-resistant cast austenitic stainless with molybdenum — the cast form of 316.

Is CF8M magnetic?

Slightly. Unlike fully austenitic wrought 316, CF8M castings intentionally contain a small amount of ferrite (typically 5–20%), which makes them weakly magnetic. A magnet sticking lightly to a CF8M valve body is normal and is not a sign of counterfeit or inferior material.

CF8M vs SS316 — which is better?

Neither is "better" — they are the same alloy in different product forms. CF8M is used where the part must be cast (valve bodies, complex shapes); wrought 316 is used where parts are machined from bar or plate (balls, stems, fittings). Corrosion resistance is equivalent in nearly all services.

Is CF8M food grade?

Yes. As the cast equivalent of 316, CF8M is widely accepted for food and beverage contact and meets the material expectations of 3-A and FDA-recognized stainless requirements, provided surface finish and design requirements for the specific application are met.

Related Resources

• Ball Valve Materials Guide
• Valve Body Materials: Ductile Iron vs Carbon Steel vs Stainless
• Chemical Compatibility Chart for Fluid Handling
• Industrial Valves Hub
• Technical Resource Center

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