Warped thin parts after heat treat.

[bakerbj]

I have some 2.25mm thick parts, ring shaped, 1020 steel, that are warping after heat treating.

Case hardening spec.
Nitrocarborize 0.01 to 0.03mm Dep compound depth zone
surface hardness 60 Rc min. (file hard)
Diffusion layer depth 0.15mm min.
oil quenched

The parts are flat (w/in 0.015mm) after being stamped out and I've tried straightening the parts after heat treating. They would either spring back to the warped condition or break in half.

Analysis shows the parts meet the required case hardening specifications. I'm wondering if the stamping operation adds stress to the steel that shows up in heat treating. Should I stress relieve them before heat treating?

Materials isn't really an area of expertise of mine so any ideas would be appreciated.

Thanks.

 

[Helicopterjunky]

Yes you might try stress relief but that alone will probably not work. You may be successful by nitrocarburizing and still air cooling in upper cooling chamber and then bolting stacked pieces between thick steel plates, reheating and the quenching. Just throwing this idea out as it will take some development.

 

[Helicopterjunky]

Another more direct idea is to Gleason die quench the pieces. You nitrocarburize and still air cool, reheat and die quench. With proper die quench machine and die this will most likely be effective. Much more labor intense and costly however. Talk to heat treater with die quench capability if you do not have the facilities.

 

[tomwalz]

This is a big problem with saw blades. Standard procedure is to clamp maybe a dozen blades between two really big pieces of steel and bolt them together with all the force you can.

One of the best at this is Ken Lloyd of Peerless Saw Co. in Groveport,800 973-3753 Ohio. He said he’d be happy to talk to you although he wasn’t sure how much he could help you. They laser cut and heat treat saw blades, they don’t stamp but they do know heat treating of flat parts.

tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[bakerbj]

I'll have to look into the feasibility of clamping the parts we make. We're going to be producing hundreds of thousands of these so as mentioned, labor, handling, cost, etc... may be an issue.

Would clamping these parts and reheating them save ones that have already been warped? I have like $10k in parts that are out of spec I would like to save if possible.

Thanks again, this project just kind of got dumped on me after the bad parts were produced.

 

[Helicopterjunky]

You could try getting several squares of maybe 3/4" or one inch thick carbon steel plate and having it oil queched, tempered and stress releived. Machine multiple in line through bolt holes through each. Then grind one face of each plate as flat as you can get. Machine a good sized center hole through each plate to allow quench oil to flow though center of stacked parts. Get some large diameter bolts, nuts and washer and clamp up some stacked pcs. Reheat, quech and temper them in the clamped up plates and see what you get. Put some ultra high temperature anti-seize (available at auto or muffler stores) on the bolt threads so they are easier to get off later. Let me know if it works. Good Luck. Remeber time in furnace is going to drive diffusion zone deeper. There are also some temper presses out there were a hydraulic press is built in to a furnace. You load out of flat part thru furnace door and under press inside furnace for maybe ten minutes, release press and pull out a flatened part. However, I have no idea which heat treaters has one of these furnace presses today.

 

[tomwalz]

What kind of warping? 1. Ends curling up to form a bowl? 2. Potato chipping – sort of number one with a twist as well? 3. Are the parts elongating? E.g. do you now have a major and a minor axis? Something else?

Is this your company’s operation? What does the steel supplier say? How soft is the steel when stamped?

Steel has stresses in it.
1. Steel is never perfectly flat or perfectly homogenous.
2. Steel is rolled which induces stress. (We are fighting a project now where the direction of the original rolling determines the kind of warping we get after brazing.)
3. Uncoiling and straightening add stresses.
4. Stamping or laser cutting add stresses.
5. Heat treating releases stresses but may release stress unevenly.

Peerless has been a good supplier of ours for many years. I believe they have stress relief process before they laser cut the parts. They stress relief afterwards as well.


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[tripleZ]

Is the warp always the same? And does the end use permit you to have divots (very small...say 0.020" in diameter) on certain areas of the part? One of my father's friends back in Pgh. is an expert at peening in warped slitter knives. He does this on one of a kind knives, but the process could potentially be adapted to automatic means if the warpage were consistent. If it's variable, that option is obviously not feasible or cost-effective for the volume you're talking about.