Cold Finish vs Hot Finish SS Machinability

I have an opportunity to buy a bunch of 3" x 3/8" wall round seamless tube in 304SS for an ongoing production part. The specs are perfect but I need to understand the implications of cold vs hot finished. When it comes to machining with carbide cutters, will cold finished 304SS be more difficult to machine on a lathe? Better? Same? O.D. and I.D. cleaning passes, inside grooving, cross port live tool milling and some axial live tool M6 tapping all required. I don't care about marginal differences. I'm just looking for big red flag issues.

Cold work will harden 304, but the amount of WH in a tube product alone probably won’t kill carbide, I think it’s really the consistency and control of the chemistry that is more important, as far as machinability is concerned.
The use of mixed and poorly sorted scrap in a melt is common in some operations, particularly at the lower end of the quality “spectrum” ( India and China).
This can result in all kinds of junk being in the melt and in the metal, in particular carbon and carbides ( niobium and titanium from 347 and 321 getting in there, along with carbon steel for instance). These can destroy carbide tooling in short order.
The other consideration even if it’s got good chemistry Is dimensional stability. If your tolerances are tight, the cold worked could cause problems as you relive some internal stresses by cutting, I’d think particularly in a tube?
I’d say be careful and insist on certs and a known Sorce from a quality mill. Get a sample and test it!

if cold finished is work hardened it effects reliable cutting parameters and tool life and part warpage from internal metal stress when material is removed and part unchucked
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and even if carbide used are you going to use carbide taps ? that is you have to think about all tooling costs. hard spot if it breaks a carbide drill can be expensive. that is if $20. part is breaking a $200. carbide drill bit it obviously adds to total costs. that is if tooling cost is $20. per part or $200. per part made, obviously that factors into decision if $10. annealing part with lower tooling costs lowers total cost to manufacture part. if you track actual costs over the year sometimes results data says what at first seems odd is actually a better way to manufacture
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unless there is a reason to leave it cold finished and hard many places have all metal stress relieved or annealed to make it easier to machine and less part warpage when unchucked. part warpage especially round parts that are not round and straight can often be a problem
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also data might say buying cheap SS thats $1. cheaper per part that uses $10. more in tooling cost and $10. more in machining time well that not saving anything but actually costing more. that one a guy in a office might not realize that cheaper metal is actually costing more to manufacture a part often times. if no data is recorded its harder to prove it. its like office guy buys cheap drill bits that break 10x easier and you end up spending more per year on drill bits cause you are using 10x more drill bits

"Seamless" shouldn't have any cold working into it - should it?
That is an extruded product - correct?

Not the same as rolled and welded sheet products.
(which is prolly annealed post opp?)

???


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Think Snow Eh!
Ox

Ox said:

"Seamless" shouldn't have any cold working into it - should it?
That is an extruded product - correct?

Not the same as rolled and welded sheet products.
(which is prolly annealed post opp?)



???


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Think Snow Eh!
Ox

Click to expand...

wow, where to start... most seamless is not extruded, its pierced during a rolling operation, (the Mannesmann process) at a red heat for steel. subsequent processing can be done hot or cold, so the state of work hardness is independent of how the bloom is formed.
extruded product such as aluminum is not in an annealed condition as formed. while the extrusion is done hot, it is not hot enough as it emerges to be in an annealed state. the process imposes significant deformation as well.
most welded pipe and tube is not annealed "post opp"

I've seen bars called " cold finished " where they really just mean it was ground to size instead of having that extra few thou from just a rough pealing cut on the outside. Same stuff inside otherwise as far as I know? I'm not entirely what it means when its about pipe or tubing, unless its "special" stuff?
I'd be more curious about where its from, most stainless pipe I normally see is from China. Anything that isn't, is probably better.

It was moot. I got the spec today. A511 cold finished, annealed. Looks like it will work well.