Most stainless steel ball valves are cast, so their bodies are not “304” or “316” but CF8 or CF8M. The names are often used interchangeably with the wrought grades — which is nearly right, and the small difference matters when you choose between them. Carbon steel WCB is the third option for many applications.
What the grade names mean
| Cast grade | Casting standard | Closest wrought grade | Key difference |
|---|---|---|---|
| CF8 | ASTM A351 | 304 | Chromium–nickel austenitic stainless steel |
| CF8M | ASTM A351 | 316 | Adds about 2–3% molybdenum |
| WCB | ASTM A216 | — (carbon steel) | Not stainless; usually painted or coated |
“CF” stands for corrosion-resistant casting, “8” relates to the maximum carbon content, and “M” means molybdenum is added. Balls and stems are usually machined from wrought bar, so a CF8M valve normally has a 316 ball and stem, and a CF8 valve a 304 ball and stem.
CF8 or CF8M?
The molybdenum in CF8M improves resistance to pitting and crevice corrosion, especially from chlorides. In practice:
- CF8 is a good, economical choice for clean water, air, neutral liquids and most indoor utility service.
- CF8M is the safer choice for anything with chlorides — sea air, brackish or chlorinated water, de-icing salts — and for many food, beverage and mild chemical applications.
- For aggressive chemicals, neither grade is chosen from a rule of thumb. Check a corrosion table for the specific medium, concentration and temperature, or send us the details.
The price difference between CF8 and CF8M is usually modest compared with the cost of a failed valve, which is why many distributors stock CF8M as their standard stainless line.
When carbon steel WCB makes sense
WCB is strong, economical and widely used for oil, gas, steam condensate and other non-corrosive services, especially in larger flanged sizes. It is not suitable where the medium or environment would corrode carbon steel, and it needs a protective coating outside.
How to check what you received
Cast valve bodies carry the material grade in the casting, for example “CF8M” next to the size. That marking is a useful first check. It is not proof of chemistry: if your customer needs proof, agree on material certificates for the order before production, and say which standard they should follow. A portable alloy analyser at incoming inspection is another common, quick check for molybdenum.
What we supply
All our current series are available with CF8 or CF8M stainless bodies, or WCB carbon steel, with SUS304 or SUS316 balls and stems:
- Threaded: 1-piece, 2-piece, 3-piece and high-pressure 3-piece
- Flanged: ANSI Class 150 two-piece
Tell us the medium and where the valve will be installed, and we will recommend a body and trim material — and confirm which documents we can provide with the order.