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Crack in A485-1 ring during plug quenching

Crack in A485-1 ring during plug quenching

(OP)
I am facing quench cracking during plug hardening of ring with oil quench (`40C).
Hardening temp at 830C. Ring is transfered to plugging press and quenched with oil.
Material is A485-1, ring dia is 250mm and thickness is 23mm.
Crack always in the same location of undercut. Any reasons / solution ?

RE: Crack in A485-1 ring during plug quenching

Pictures please!

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

RE: Crack in A485-1 ring during plug quenching

You need a metallurgical evaluation of the component from a reputable lab. I do not share speculation in such a case without getting the data in an examination, which includes testing.

RE: Crack in A485-1 ring during plug quenching

(OP)
We have done all the metallurgical tests
No decarb / recarb
Fine martensite
Grain size 8 or finer
No any segregation
No GBO / NMTP
Hardness - 64 HRc as quenched both core and surface.

RE: Crack in A485-1 ring during plug quenching

Sounds like this ring is intended for a rolling element bearing race. A sketch of the ring cross section and undercut would be helpful. Also a sketch showing how the quench die interfaces with the ring, including any oil flow paths provided, would be good.

Is the quench die possibly restricting oil flow to the undercut surface?

RE: Crack in A485-1 ring during plug quenching

(OP)
Hi tbuelna yes you are right.
Quench die is not restricting the oil flow to the undercut. Undercut is open to oil.
I have shown a small sketch for understanding. And crack always on the top undercut area.
Die is a taper die which sits on both top and bottom bore. Oil flow is from both top and bottom.

RE: Crack in A485-1 ring during plug quenching

Of course the crack is always at the top undercut area. All things equal, failures always occur at the weakest point, which in this design would be at the top undercut. That does not necessarily mean it is a design issue though. Again, you need more than just the testing you did - you need actual failure analysis from someone experienced in the process.

RE: Crack in A485-1 ring during plug quenching

Without a sketch of how the quench die(s) constrain the bearing race, how the oil flows over the race surfaces, it's hard to offer potential solutions to resolve your fracture problem.

In general quench cracks often occur where there is a significant local difference in heat transfer and cooling rate. The re-entrant profile of the grinding relief might be creating a separated recirculating local flow condition preventing the cool bulk oil flow from reaching the obscured undercut surfaces, thus inhibiting local heat transfer significantly. Also, the radial section is thick below the undercut, the flange above the undercut is even radially stiffer, and the narrow undercut groove between with its relatively small root radius provides a very effective local stress concentration.

Might be worth spending some time on modeling to optimize the cooling oil flows and heat transfer of your quench tooling.

RE: Crack in A485-1 ring during plug quenching

(OP)
Thank You tbuelna, will try to make a sketch of die and send as soon.
Thanks

RE: Crack in A485-1 ring during plug quenching

(OP)
Hi tbuelna can you please share your email id.

RE: Crack in A485-1 ring during plug quenching

(OP)
Hi one more information parts with out undercut also is cracking the same way.
What's your opinion on this?

RE: Crack in A485-1 ring during plug quenching

If you don't want to pay for the paper I referenced in my previous post, you can type "Understanding Process Sensitivities in Press Quenching: an integrated Approach" into Google and then click on the first link that comes up with a pdf file of that title. The paper will download for free.

Maui

RE: Crack in A485-1 ring during plug quenching

(OP)
Thank You Maui. I have downloaded the paper will spend some time to read now.
Thanks again.

RE: Crack in A485-1 ring during plug quenching

(OP)
Oh Thank You Maui nice paper & good informative.
What will happen if we take out the parts from quenching at slightly higer temperature (may be at 100C surface temperature instead of 50C).
So martensite formation in the core can be made uniform with the surface at the end.
Will this help.

RE: Crack in A485-1 ring during plug quenching

Haran, based on what you have told us, it appears that the crack is forming at a stress concentration located in the undercut. You should make the radius in this location as large as the design will allow. The oil flow in this same area will very likely be reduced due to the formation of a vapor barrier that is trapped in the undercut because of the geometry and the manner in which you have chosen to orient this part during quenching. I would suggest that you flip it upside down from the orientation you have provided. When a vapor barrier forms during the initial stage of quenching it will not be locked into position in the undercut if you do this. Your oil flow rate around the part should also be carefully selected so that the entire cross section transforms to martensite, but the oil flow rate should not be so fast that cracking occurs. What is the oil flow rate that you are currently using? The pulsing capability on the quenching machine should be activated. Have you been using pulsing?

Maui

RE: Crack in A485-1 ring during plug quenching

Haran, I would not recommend taking the parts out of the oil prematurely so that they are at a higher temperature than the oil. A better approach would be to slow down the quench by reducing the oil flow rate. But in order to make any recommendation regarding what oil flow rate is appropriate, I need to know what rate you are currently using.

Maui

RE: Crack in A485-1 ring during plug quenching

(OP)
Hi Maui we have already tried by flipping the part upside down but no use and parts still cracked. Bottom oil flow is 300 LPM (this is to quench bore) and top flow 350 LPM (to quench OD) In our quench press we do not have pulsing facility.
Do you suggest to reduce the oil flow and what is your recommendation.
Thanks

RE: Crack in A485-1 ring during plug quenching

Several changes are required to reduce the severity of your problem, and one of those changes should be flipping the part as recommended. The second change is to increase the radius of curvature at the stress concentration where the crack is forming. The third change is to reduce your oil flow rate by 50%. If you had pulsing available I would also recommend that you activate it. Pulsing in these situations is often critical, and without it you may not be able to completely eliminate this problem, although implementing the other changes will help improve the situation.

Are you measuring the temperature of the parts as they come out of the quench? What is their average temperature?

Maui

RE: Crack in A485-1 ring during plug quenching

(OP)
Exit temp is 50 C.
Quench time is 160 Sec.
Ok let me try with reduced flow rate.

RE: Crack in A485-1 ring during plug quenching

(OP)
What is the expected risk if we take out the parts from quench at 100C and do an air cooling?
Oil flash point is 175 C is there any risk of fire because if the part surface is at 100C then the core may be at higher temperature.
So after some time the surface temp may increase and if it reaches 175 C it may fire.
Is this can happen ? Also part dimension may distort to some level.
Any other reason for not recommending this concept.?
THanks

RE: Crack in A485-1 ring during plug quenching

If you pull these parts from the oil prematurely and you are not below the martensite finish temperature then distortion is a very real concern. I do not know what your martensite finish (Mf) temperature is for this particular alloy, but I suspect that the Mf temperature is probably in the neighborhood of 200 to 250 degrees F. So if you pull it out of the oil at 100C, it may not be done transforming. And if it is too hot coming out of the oil, then other transformation products could precipitate. And this could result in hardness variations and lower than expected hardness readings. That would be bad. Very bad. I don't recommend it.

And yes, fire could also be a concern if you decide to do this.

Maui

RE: Crack in A485-1 ring during plug quenching

Haran,

What were the results of your testing with the reduced oil flow rate? Did you implement any of the other recommendations?

Maui

RE: Crack in A485-1 ring during plug quenching

(OP)
Hi Maui,
Reducing the oil flow did not help, upon further reduction we are getting NMTP.
Undercut design change not possible. Will update you all after further trials.
Thanks for all your ideas.

RE: Crack in A485-1 ring during plug quenching

Haran, if you free quench these parts in an open oil tank and don't use your quenching machine, do they still crack?

Maui

RE: Crack in A485-1 ring during plug quenching

(OP)
No it does not crack.
In quench press with out die only with quenching also it cracks.

RE: Crack in A485-1 ring during plug quenching

Hi HaranSR

Look at the pressure of outer expander and if used, the inner expander of the press.
lower all pressure to the minimum.

what is the size of the id of the part and what is od of the plug quench. what is the diffrence in size.

also very little information on the heat treat cycle and temp's. is the oil slow or medium quench.
when ruff turning these parts is it possible to do a stress relief. or can this steel be normalize.
I could not find any data sheets on this stuff, if any one can supply that it would help.
what is the heat treat procedure, or what heat treat specification.

the press outer expander plate may be cracking the parts do to the configuration of the part.
pressing with to much pressure. with parts like this I want my supplier to use slow acting oil with the
highest oil temperture possible. as to not crack parts. if permissible.
so the term mar quench or martemper. but not as high.

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