I use to do heat treating of aluminum and different types of steel. Are you tempering the stainless or what? I doubt you'd be aging any stainless. Aging is what we'd do with aluminum. It was at low temps 250-350f for several hours sometimes 36 hours. It would harden the aluminum. Aging steel would soften it I believe but it would be in the 1200f range. Unless youre heating the steel up and quenching it in oil you are softening the stainless.
Btw 1700f isn't that hot just enough to give it a solid red glow. Not hot enough to work with the metal just yet. 2400f furnaces are hot.
Read up a little and it seems you can age stainless. But the precipitation hardening of the steel occurs when the stainless is made, correct? Precipitation hardened stainless contains different ingredients that as far as I know can't be added during the heat treating process. So you mean you're just heat treating precipitation hardened stainless?
I was always I fascinated by metalugy but was just the grunt worker. I did get to talk to our metalurgist quite often and saw how the science side of it worked and why we heat treated the metals.
i'm solution treating the stainless steel. One thing to note is that the steel I'm working with is actually relatively carbon-free < 0.04% C). Your typical steel will have carbon up to ~0.1-0.2% usually, IIRC. i do have another sample that i'll be solution treating and ageing though.
what's happening in the steel (not to treat you like an idiot, just explaining it) is that all of your alloying elements will go into solid solution when you hit the annealing temperature (~1700F or so). Since this steel is carbon free, it actually isn't very hard at this point. The nickel content provides phase stability and basically keeps all of the alloying elements in despite falling temperatures as you air cool (normally you have to quench in water/oil to get fast enough cooling rates to lock all of the alloying elements in). One benefit of this is that you avoid warping/distortion from an oil/water quench.
So now that all of the alloying elements are "locked in" so to speak, you can precipitate them out by heat treating again at lower temperature (say 900F). This will cause some of the alloying elements to precipitate out into intermetallic compounds that provide a huge degree of strengthening.
The cool part is that because precipitation hardening is the strengthening mechanism, you can heat treat PH steels over and over and the (mechanical) properties won't change that much (in theory. i'm sure in practice things like residual stresses will play a huge role).
Standard carbon steels work the other way around. When the carbon enters into solution at the annealing temperature, you get solution hardening. You then quench to keep the carbon in and end up with an extremely hard, extremely strong but very brittle steel, and when you heat treat, you actually get precipitation softening and increased ductility.
Hope that was helpful in explaining how PH and plain carbon steels work in general
🙂 There are some other cool ones - duplex/dual phase, ausformed, etc but I don't know much about those really.
