HT warping 3

[glj1017]

Have a very thin inner race stamped from 1075 and 90 degree lip cold worked. Material is sperodize prior to being stamped and then sent for q&t by an outside heat treater on a continuous belt. Been having warping issues. Question: would getting the stamped and formed part REsphereodized or normalized to wipe out the coil memory and residual stresses make a difference with the warping? Would there be a considerable difference between the two treatments if the part is getting quenched anyways?

Geometry on this bearing race is not favorable, trying to avoid clamp hardening.

Thanks

 

[racookpe1978]

Is it "loose" on the belt, or can you restrain it in fixtures while heating/cooling on the belt?

 

[Lyrl]

To the extent that movement is due to forming stresses being relieved at high temperatures, re-normalizing would just relieve the stresses and cause the same movement. I don't think you'd see any overall benefit from adding a stress relieve process before hardening.

Are the parts dumped onto the continuous belt, or hand-loaded one piece at a time onto the belt? If dumped, is there any action to get the parts all lined up the same way on the belt (i.e. not laying on their sides)? What is the pounds per hour processed, and has the heat treater tried lowering that rate?

What percent of the parts are affected by the warping? Has this part always been affected by this problem, or has it gotten worse recently?

Does the part geometry allow consideration of induction hardening as an alternative heat treat?

 

[CoryPad]

Parts like these usually are austempered for reduced distortion compared to what you are experiencing with traditional quench hardening.

 

[racookpe1978]

Lyrl

I think I was somewhat inelegently trying to get to the same point: Form the parts, then fix them in place rigidly and stress relieve (so they can't move/don't move/relax,then-move-but-get-forced-into-the-right-shape) then go back for hardening.

More difficult. more expensive. But ....

 

[glj1017]

Thanks so much for your responses.

Looked into it and restraining them is more expensive than scrapping them.

The parts are hand placed on belt in single layer, quench at 250f. These parts have always warped, current scrap rate is signficant. They are processed at 24" per minute (11 minutes in belt). Approx 58 hrc after hardening. Would slowing down belt speed help with the movement? Can this grade be hardened to 58 hrc via austemper? Wouldn't it have to be a mixture of martensite with the bainite to achieve that hardness?

 

[tbuelna]

Have you considered some type of spin forming operation to produce the race from a flat blank? Spin forming would produce more of a circumferential grain flow in a part made from rolled sheet stock, and would seem more likely to give a uniform shape after quenching. The problem described might be due to the longitudinal grain flow in rolled sheet if it is used as the raw material. Spin forming would allow the race to be formed in a single operation. Spin forming would also allow adding compensation for some of the quench distortions.

 

[Lyrl]

Slowing down the belt would not help. I was thinking more of increasing the spacing to reduce any incidence of parts hitting each other when falling into the oil.

I'm not sure 58 HRC would be acheived by austemper, a Google search turned up a table that shows 53-56 HRC (

https://books.google.com/books?id=b...LtwAd#v=onepage&q=austempering 1075&f=false).

You might also see if any heat treaters in your area can do high-pressure gas quench. 1075 in very thin sections might fully harden with less distortion with high pressure nitrogen cooling vs. oil.

 

[tbuelna]

The idea of HPGQ is attractive since it would reduce quench distortions, plus it also leaves the surface of the part very clean. But HPGQ is performed in a chamber and requires the parts to be racked to get the best result. More of a batch process than the continuous belt process described in the OP.

As for your existing process, look at how the parts enter the quench oil. Ideally an axisymmetric bearing race shape would be plunged axially with the thicker part section leading, rather than plunging radially or edgewise. Maybe you can make some simple modifications to the belt system so the parts are plunged into the oil at a more favorable and consistent orientation.

 

[Maui]

You could have them press quenched in order to minimize the distortion issues that you have been experiencing. The links below provide a description of this process. Page 24 in Thermal Processing:

http://www.thermalprocessing.com/me...azines/ThermalProcessing_Spring_Summer_15.pdf

Or the ASM Handbook Volume 4A:

http://www.asminternational.org/web...journal_content/56/10192/16265619/PUBLICATION

Maui