4340 Behavior when heat treated

[Spencer77]

We are making bearing races for a customer and the outers get split and assembled over the inners. Target heat treat is 52 - 55 Hrc. My original plan was to split them after heat treat, but I had heard that one of the 4xxx materials gets pretty springy after heat treat I don't know or remember which one it was. I guess my question is would it be better to split them before or after heat treat? Which one will result in less movement?

 

[shankarviyer]

Spencer, heat treat first, followed by grinding - which we presume is necessary after the HT - and then split it

This is how we do on one of our other products for a similar application, which is not made of 4xxx.

Better results expected when the raceway is not split

Regards

VS

 

[WKTaylor]

Hmmm 4340 for bearings at that very high hardness [~=275-to-300-KSI]... seems a bit sketchy for several reasons.

What exact material/spec (conventional 4340, or VAR 4340 [4340M])... made per what specification: ASTM, AMS, MIL, ISO, etc?

Do we assume that this is a plain' sleeve bearing? with or without a flange? with or without lubricant grooves and holes?

Are You planning to rough-machine, then heat treat, then finish-machine/drill/grind as per shankarviyer's advice?

What spec are you heat-treating/tempering 'per'? Are You adding in a stress relief HT after finish-machining, before splitting?

Surface finishes: 125-microinch RA on mounting side? 8-microinch RA or finer on the sliding side... and/or a honed cross-pattern [for lube retention]? flash-chrome or other finishes applied to either side?

Are you splitting the halves with laser, water-jet, etc? Any-notch-outs? IF mechanical slitting... be careful regarding temper embrittlement due to friction

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Tmoose]

Apparently Spencer 77 is MIA.

"After joining Eng-Tips Forums on March 1, 2019, I've logged in 4 times. My last login was on Friday, March 1, 2019."

 

[Spencer77]

Well first off I'm not an engineer I'm just making them, so a lot of what you are asking is beyond what I know. From what I know this a prototype, and beyond that I'm not sure what its function is I'm just making it to the print they sent me. The material call out is pretty vague it just calls out 4340 annealed through harden to 52-55 Hrc. We are pre machining it sending it to heat treat and then to EDM to be split. No heat treat or temper spec. The roughed out rings have been drilled and taped before hardening and will be drilled reamed pined and reassembled for final machining. I ran out of time and had to come up with a plan so if this doesn't work any advice for the next run would be greatly appreciated.

 

[WKTaylor]

Wise old engineers have said he following...

You deserve to get what you ask for: but if You don’t ask for very much, don’t-expect to get very much.” [a Sr engineer in my company ]

You don't get what you want... You get what you ask for. Ask carefully!” –TheTick, Eng-Tips

You may not get what you asked for... but [for sure!] you never get more than you ask for!” –EdStainless, Eng-Tips




Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]