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-100 deg F cold stabilize causing intergranual cracks
6

-100 deg F cold stabilize causing intergranual cracks

-100 deg F cold stabilize causing intergranual cracks

(OP)
Carburize & Harden in accordance with AMS2759/7, selective carburizing, parts are having issues with intergranual cracks, it appears to be happening during the cold stabilize treatment after quench, AISI 9310 steel, AMS6265.

is a rare but it has happened twice.

Parts are quenched, then cold stabilize, then tempered.

some parts are having issues, any recommendations
snap temper after quench?

Mfgengear.

RE: -100 deg F cold stabilize causing intergranual cracks

"Parts are quenched, then cold stabilize, then tempered."

We've never done it that way around.
It's always been quench, temper and then cold temper.
I don't think it's such a good idea "snap freezing" untempered martensite so am not surprised to hear of the cracking.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: -100 deg F cold stabilize causing intergranual cracks

(OP)
Gearcutter

Per AMS2759/7 para 3.6.5
sub zero treatment part the verbiage states
The sub-zero treatment shall be initiated with in 2-4 hrs after the start of the quench or completion of of a snap temper.

according to one of our vendors the sub zero treatment transforms all of the left over austinite to martensite.
if the sub zero is process after the temper, it will not transform any of the existing austinite." any way".
I was informed of such.

it would be great if some one could quantify that for me.
sounds like I answered my own question ~snap temper.

Thanks

mfgenggear.  

RE: -100 deg F cold stabilize causing intergranual cracks

"The sub-zero treatment shall be initiated within 2-4 hrs after the start of the quench or completion of a snap temper."

Umm, I think that pretty much says what I just did........"after the start of the quench" not before.

"if the sub zero is process after the temper, it will not transform any of the existing austenite." any way"."

While I'm not a Metallurgist; I don't believe this to be true.
I've always understood a cold tempering operation as simply being a continuation of the usual tempering process that will initiate further transformation.
 

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: -100 deg F cold stabilize causing intergranual cracks

(OP)
Gearcutter

Yes yes the original question stated cold stabilize after quench but before temper.

Mfgenggear

RE: -100 deg F cold stabilize causing intergranual cracks

Yes, sorry you are correct.
I refer back then to my original post where I think that it should be done after the initial temper and not before.
It will be really interesting to hear what others have to say as we have never done it the way the standard is suggesting.
It's interesting to note how the standard does say that it can be done after a snap temper.
 

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
 

RE: -100 deg F cold stabilize causing intergranual cracks

(OP)
Gearcutter

No Problem, I'm with you that cold stabilize should be after Temper. Thats why I asked this question to this forum.
but the vendor states that it will lock in the Austinite.

but the vendors have to follow the specification.

Mfgenggear

RE: -100 deg F cold stabilize causing intergranual cracks

There is a phenomenon known as "austenitie stabilization" that occurs with retained austenite that makes it more difficult for it to transform to martensite.  It is more of an aging process of the austenite and, while it makes it more difficult for the retained austenite to transform, it does not prevent it from transforming.  What I mean is if 95% of the retained austenite will transform when cooled to -100F, if the austenite has stabilized, you may only get 90% to transform at -100F.  That is the concern and why the requirement is in the specification.  

It does seem to be a poorly worded requirement, if that is a direct quote from the specificaton, as "within 2-4 hours" seems to be a bit odd.  Do they mean "longer than 2 but less than 4"?  If so, that is what they should say.  Generally "within" in this sense means "not more than" and a requirement of "not more than 2-4 hours" doesn't make much sense.  If it must be within 4 hours, then why say 2-4?  If they really mean "not less than 2, but more than 4", they should not be saying "within".

Since they do say "after the start of the quench or completion of a snap temper", I would go ahead and give it a temper (original time and temperature), then cyro to -100F within 2-4 hours of coming out of the temper, then the final temper.  That should alleviate your problem and still stay within the wording of the specification.  It may be worthwhile to ask SAE/AMS for a clarification of this clause.

rp

RE: -100 deg F cold stabilize causing intergranual cracks

That makes it a bit clearer, the 2 hour limit is for parts less than 2.5 inches thick and the 4 hour limit is for parts more than 2.5 inches in thickness.  

The snap temper should help, considerably.

rp

RE: -100 deg F cold stabilize causing intergranual cracks

The answer is in the next paragraph of AMS 2759/7, which has not yet been referenced:

"3.6.5.1   When authorized by the cognizant engineering organization, a snap temper not exceeding 300 deg.F (149 deg.C) may be used after quenching and prior to the sub-zero treatment when part design and thermal stresses may result in part cracking."

Aaron Tanzer
www.lehightesting.com

RE: -100 deg F cold stabilize causing intergranual cracks

(OP)
Thank You all for the geat responces & help.
I now have a task to follow with my suppliers.

Thanks You

Mfgenggear

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