17-7PH Stainless Steel Springs 3

[SMF1964]

Any thoughts on the manufacturing process for doing this? The wire is drawn to diameter, coiled and then the spring is heat treated. I have a compression spring with a hardness of RC 55 (converted from Vickers) that would suggest a H900 heat treatment if this were a forging/shaft type of application, with solution heat treatment at 1900°F followed by ageing at 900°F.

With drawn wire, is the heat treatment the same?

 

[NickE]

I'm not sure about 17-7 wire per-say, however to get 55HRc out of 17-7 requires starting in a heavily cold worked condition and then after coiling using the H900 precipitation heat treatment.

If you solution treat the steel you loose the effect of the cold work (strain induced X-Formation to Martensite) and the H900 heat treat no longer applies. The heat treats that apply to solution treated material are RH950 and TH1150, wich will not deliver as high of a strength level, and possibly wont work at all.

(that said hardness is not a good indicator for PH steels.)

 

[SMF1964]

If I understand correctly, then, there would be no solution heat treatment involved after drawing to wire, but rather a precipitation hardening to produce further hardening in excess of what the cold working would impart.

What had me bewildered in this was the fact that my spring does not react to a magnet. The martensitic transformation would produce a slightly magnetic material, would it not?

 

[metengr]

SMF1964;
I attached a technical bulletin for 17/7 from AL. It mentions that after a solution treatment, the soft austenitic structure can be formed and hardened to various strength levels by heat treatment. This would explain your non-magnetic behavior.

http://www.alleghenyludlum.com/ludlum/pages/products/xq/asp/P.113/qx/product.html#

 

[SMF1964]

That was my original thinking, metengr, that the material was drawn, solution annealed and aged. NickE indicates a second path to get the hardness which, if I understand it, starts with a solution annealed bar, cold works the snot out of it to get it to a spring temper, then adds additional hardening by adding an ageing heat treatment that is not high enough to remove the cold work. Is that right, NickE?

 

[swall]

The only difference between drawn wire and other 17-7 product forms is that it carries the designation "Condition C". The springs are coiled from this condition and then given the 900F precipitation hardening treatment, at which point the designation becomes "CH900." 17-7 CH900 springs are slightly more magnetic than spring temper 302ss, but generally not magnetic enough to perform mag particle inspection on them.

 

[NickE]

SMF1964- yep.

17-7 is funny stuff.. We use it in sheet/strip to make certain types of springs, I'm sure our parent makes coil springs out of it.

We had a part that needed forming, high strengh levels, good flatness, and be stainless... We tried having Condition C material solution treated and then doing the forming, and applying RH950 for the highest strength...

Well it seems that 17-7's reaction to the hardening processes other than Condition C to CH900 is uncertain and specially controlled chemistry must be used to produce steel that will reliably hit the right mechanicals from annealed condition.

Thats why I'm pretty sure that if you can use condition C you would, especially for coil springs.

 

[EdStainless]

The three heat treatments are exclusive of each other.
CH900, Anneal first, then heavy cold work followed by 900F aging. I have screwed this up by using too little cold work.

RH950, The parts must be re-annealed as port of the aging cycle. If you rely on the original mill anneal you will get variable results. So here you anneal, chill, age. This condition give great hardness with good toughness.

TH1050, Like above, re-anneal. This is the general purpose heat treatment.

As I recall the A condition is the least magnetic, then CH, TH, and RH is the most magnetic, but don't mistake the mangetic strength as an indication of heat treatment. I have seen sample with very similar mechanicals with very different magnetic conditions.

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