Cracking 4140 shafts when induction hardening
Cracking 4140 shafts when induction hardening
(OP)
We make a clutch shaft from a 3-3/4 dia x 20" long piece of 4140 HT'd to 270-320 as the base matl. The part has a splined section requiring induction hardening to 50-55 HRC. We are experiencing a very high percentage of scrappage after induction hardening due to cracking in the splines.
We have worked with two different heat treaters now to resolve the problem but are getting nowhere. After this last scrappage the heat treater suggested that maybe the shafts should be tempered after quenching.
Does anyone have any suggestions? Using 8620 and carburizing didn't work becuase of the part geometry. The shafts kept turning into bananas. Starting with a thru hardened material was a step in the right direction but the induction hardening process is killing us.
We are wondering whether we should abandon the induction hardening approach and switch over to a nitriding treatment in lieu of that. We are confident we can get the 50-55HRC by nitriding but the case depth will only be about .020 deep. We have very little experience with nitriding and are a little hesitant to put parts out in the field that might not stand up. The application is in a hydraulic pump drive where this splined shaft coupled with a splined gear takes the input torque from a diesel engine and transmits the torque to the output gears in the gearmesh. Most of our applications are in the 400-600HP range but we do see applications up to 1000HP
We have worked with two different heat treaters now to resolve the problem but are getting nowhere. After this last scrappage the heat treater suggested that maybe the shafts should be tempered after quenching.
Does anyone have any suggestions? Using 8620 and carburizing didn't work becuase of the part geometry. The shafts kept turning into bananas. Starting with a thru hardened material was a step in the right direction but the induction hardening process is killing us.
We are wondering whether we should abandon the induction hardening approach and switch over to a nitriding treatment in lieu of that. We are confident we can get the 50-55HRC by nitriding but the case depth will only be about .020 deep. We have very little experience with nitriding and are a little hesitant to put parts out in the field that might not stand up. The application is in a hydraulic pump drive where this splined shaft coupled with a splined gear takes the input torque from a diesel engine and transmits the torque to the output gears in the gearmesh. Most of our applications are in the 400-600HP range but we do see applications up to 1000HP





RE: Cracking 4140 shafts when induction hardening
RE: Cracking 4140 shafts when induction hardening
Can you describe your induction hardening process in more detail? Also, are the cracks in the root of the spline?
What temperature are you reaching during induction heating before quenching? Are you using an oil quench or water quench after induction heating?
RE: Cracking 4140 shafts when induction hardening
If they are using water for the quench, you can probably solve the problem by switching to a polymer quenchant. I wouldn't advise oil as it would be a severe fire hazard.
If they are using a polymer quenchant, as has been mentioned, too high of an austenitizing temperature can cause cracking. So can too high inclusion content, mainly sulfide stringers.
You might consider a lower carbon steel (4135, for example). It could lower your maximum hardness, but would be less likely to crack.
Tempering after treating can help, but I'd consider this mainly if delayed cracking was a problem (they were crack-free after heat treatment, but failed in service, or even on the shelf).
rp
RE: Cracking 4140 shafts when induction hardening
stress relieve prior to induction hardening but after finish turning & milling the parts.
4140 if not tempered within one hour can crack
yes snap temper then temper it will be a big help.
also if the heat treat procedure is not done correctly
parts will crack
When the geometry requires it I specify to our vendors to uses mar temper in oil or salt, this helps
with the cracking and distortion. But adds cost.
The geometry is the factor.
It will crack between teeth or in the general area.
extra precautions are required.
Nitriding is more desirable with nitraloy 135 material
core harden, machine then nitride.
Nitrided surfaces are brittle. it with chip easily.
However, it is very hard and has good wear resistance
RE: Cracking 4140 shafts when induction hardening
At our facility we routinely IH this stock size material to a .300" case depth without any issues, beginning with a pretreat (austenitize, oil quench and temper), followed by IH and temper within two hours of polymer quenching. The polymer concentration should be on the high side of the recommended range for alloy steel.
RE: Cracking 4140 shafts when induction hardening
RE: Cracking 4140 shafts when induction hardening
RE: Cracking 4140 shafts when induction hardening
I think this would help us to analyse how the cracking happend。