Best stainless for vacuum work.

[Bob Reite]

I'm picking your brain Doug. What do you think is the best stainless alloy to use for inside a vacuum chamber. 304, 316, 303, 416, 420 or ???

[johnf]

300 grades are best IMHO
304 has the best bang for buck

[Doug Coulter]

I agree with John with what little I know. The 300 series is most of what I have going on here, and I'm pretty sure that most of it is represented somewhere. It tends to be non magnetic unless come sorts of welding or other extreme treatment is put on it, an advantage for most of what we do. A downside with 316 is almost immediate work-hardening if any tool rubs it without cutting, or as Joe Pieczynski says "no dwell, no yell". 316L is a lot better in that regard if you're stuck with 316 family stuff, often the case. The L stands for "less carbon". I believe a lot of my big tank is 304, or similar stuff at Lesker says it is, but I've not put tools to most of that, it's fine as is for what I'm doing.

Straight 316 is an absolute pain to machine due to that work hardening, it's easy to break off tools in. No light cuts, you gotta go for it with machines you can trust the dials on and setups that have no spring whatever, with sharp tools and plenty of power. But you get there after breaking a few bits and making some chips, after you learn what you have to do from ruining a couple pieces of stock. It tends to kill you if you'e timid -

My only work with the 400's is with rifle barrels, where it's popular. It's not super bad to machine, but not super easy either. Easier than the 300's it seems, but still tends to gall a bit. Slightly magnetic out of the box, or the stuff I've encountered is.