I work for a spring company that specializes in large compression springs. We are working on a project that requires 17-7 stainless wire for the customer's product. Normally, for the larger ones, we use 17-4PH, since we heat up the bars 1800-2000F before we wrap them in coils. From there we air quench, then bake for 90 mins @ 900 degrees to obtain the H900 condition.
With 17-7 though, it needs to be cold worked/drawn before you can bake to get H900. The problem we are running into is that the wire size the customer requires is 1.875" diameter, and we need to wrap it around a 4.625" ID. We cannot feasible do that with annealed bar @ room temperature, so we need to heat it up.
I am not as familiar with 17-7 and the subsequent heat treating, but I'm guess we cannot get the high strength H900 condition and will need to settle for RH950 or TH1150.
What I am proposing is this, heat the wire, coil it, then air quench. Afterwards we'll solution treat and anneal, then heat treat to either RH950 or TH1150. We won't get quite the tensile as H900, but it will be enough for the application. Does anyone see any problems with this process, or have any suggestions? Any help is greatly appreciated!
You're going to need to run this all past your customer and let them decide how they'd like to proceed. Apparently they were expecting 17-7 and its properties at CH 900 condition and supposedly a better resistance to fatigue. Yield drops from 260ksi at CH900 down to 220ksi at RH950. That's still tougher than the 17-4 at 200ksi when H900 and maybe there's room in their design to accommodate? Maybe a couple more wraps needed? Maybe change to disc springs that would better lend themselves to the 17-7 processing?
I don't know what they are asking for or their exact requirements so I really can't guess as to whether or not they'd be O.K. with the processing changes you've suggested. Give them a call. Better to start out on the right track by discussing your capabilities and possibly lose the job... than to try to ship something less than they expected to them and end up eating the job and probably any future quotes?