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Stainless CNC

Which Stainless Grade Belongs on Your Drawing?

Five questions. The answer shows what the grade costs you in the machine as well as what it survives, because those two always pull against each other.

1. What does the part meet in service?

Chloride is the single thing that decides most stainless parts. Cleaning chemicals, brine, food acids and de-icing salt all count.

2. Does it touch food, drink or the body?

This rules out the free-machining grades whatever the environment, because their sulphide inclusions trap residue and start pits.

3. Is it welded, now or later?

Including a fitting somebody welds on at assembly, and including weld repair.

4. Does it need hardness above 30 HRC?

A wear surface, a bearing race, a knife edge or a shaft that must not gall or brinell.

5. Does it slide or thread against another stainless part?

Repeated assembly, a valve stem, a shaft in a bore. Answer yes only if lubricant is not an option.

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What this tool will not tell you

It does not know your temperature or your chloride concentration, and both move the real threshold a long way. It does not know whether your part is stressed, which is what decides chloride stress corrosion cracking rather than pitting. It does not know your regulatory position.

Use it to narrow the field, then write the environment in words on the drawing. A sentence such as immersed in 3 percent brine at 60 C, cleaned weekly with caustic tells a shop more than any grade name, and lets them tell you when a cheaper alloy still survives.

The full picture is in the grade reference and the buyer guide.