Re-Austentizing to correct Aluminum Nitrided Embrittlement

[DAVIDSTECKER]

thread330-184119
We have a very large casting in house (ASTM A757 Gr C1Q) that has Lab confirmed Aluminum Nitride Embrittlement.
The last post in the linked thread stated that Re-Austentizing could often remedy this condition.
My question is how reliable is this process.
The casting is mostly a cylinder; 31" ID X 6" Wall X 60" LTB.
The more we try to arc out crakes for repair the more the casting cracks.
We have been pre-heating the casting to at least 300F while air arcing.

Please let me know your thoughts and/or experience's regarding this condition.

Best regards, David

 

[arunmrao]

I am skeptical about reversal process.To my mind, it is safer to reject the casting.

I could mail you a technical paper from Flowserve, if you could provide your mail id.

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

Mahatma Gandhi.

 

I concur.
It sounds very much like this localized, high concentration of aluminum nitrides is abnormal and likely not reversible.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[bobjustbob]

I have never seen an austenatize cycle correct aluminum nitride embitterment. I don't understand what mechanism would be involved. Neither the Al nor N are being removed from the part and the same quench and temper would be required. How much Nitrogen and aluminum is being reported in the casting?

Bob

 

[DAVIDSTECKER]

First, thank you to all for your input.
This is a large investment and would be the second one scraped and it is part of a very large project which is being held up waiting for this.
The original foundry report had AL at around 0.7.
Two samples from the casting were sent in to another lab.
Sample from the interior wall were the cracking is had AL at 0.91, no Nitrogen was reported. Carbon in that area shot up to 0.64.
The sample from the exterior had AL at 0.41 and again no Nitrogen reported. No carbon was reported in this sample.
These reports are from a SEM equipped with EDS.
From what I understand this is a grain boundary issue related to slow cooling rates associated with heavy wall castings and can occur with as little as 0.3 AL
Assuming this is a thermal related issue tied to grain structure, and as someone who knows just enough to be dangerous, I could see how re-austentizing or something like that could correct this.
But that is why I am reaching out to those more knowledgeable than myself.
Best regards, David

 

[arunmrao]

I normally limit my residual Al content to 0.05% approximately, though literature supports 0.08%.

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

Mahatma Gandhi.

 

[bobjustbob]

Do you mean an Al of .07%. .70% would be way too high.

For a 6" section .07% is high. I would keep it below .04% for thick sections. How are they melting, induction or EAF? How large is their heat size.

 

[DAVIDSTECKER]

The report units are listed as Weight %,so I would agree that there is a decimal point shift.
Iron on the report is 91.20.
The foundries web site states that they have 5 and 23 ton arc furnace's.
The casting is around 13,000 lb.

 

[DAVIDSTECKER]

Link
I have found this to be a very interesting article.

 

EDS is very much like PMI / XRF and so it is very much approximate.
That said, the numbers look high. The iron number will be meaningless.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[DAVIDSTECKER]

In regards to the original foundry report AL was 0.07 range.
Still a high number.
We looked back at other products made from C1Q that we've welded successfully and found that the AL was also very high but they have thinner cross sections for the most part.

 

[bobjustbob]

You can get away with higher Al content on thinner cross sections.

I have never poured anything that large. We topped out at an 8000lb pour weight due to ladle size. However, when pouring heavy sections it was standard to keep the Al below .04%. The Al fades through the heat so it will start off a bit high in the sample just after the tap (.05%) and reduce through the heat. We would not pour the large castings if the Al did not fade into spec on the slug from the first ladle out. The reported chemistry would be taken in the middle of the pour. A 13,000lb cast weight would be almost half of their heat when including the gates and risers. It's odd that a foundry pouring such large parts would normally run with that high of aluminum. Unless they are keeping their nitrogen levels very low.

Bob

 

[DAVIDSTECKER]

Making the -50F Charpy values is the reason for the high AL is what we're being told.
Based on the Charpy numbers they're getting it's working.
Maybe a little too well.
I have a C1Q casting in the shop for another project with AL at .078 which seems to have welded up well.
The Charpy required is 15 Ft-Lb but the test reported 38 Ft-Lb.

 

[DAVIDSTECKER]

The cross section of this item is almost an equilateral triangle with about 9-1/2" legs.
Again the AL for this casting is recorded at 0.078.
No issues at all.
With the induction heater we do have very tight control over the heating and cooling all the way through PWHT.

 

[bobjustbob]

I find that explanation dubious. I admit that I have never cast that material. I do that quite a bit of experience with similar materials and testing them out of large test coupons. With the Ni, Mo and Mn in that material, a quench and temper heat treat, and only a 75ksi UTS I don't expect any issue meeting 15ft-lbs and -50°F.

Bob

 

[DAVIDSTECKER]

I used to work with an old Metallurgist named Charlie Yoh.
Most of what little I know about metallurgy came from talking with him on the loading dock smoking and having our morning coffee.
He's now since past but that guy could come up with steel alloys and heat treatments like Betty Crocker makes up cake recipe's.

 

[kingnero]

While that welding sure looks nice, I wonder why no run on/off plates were used?

 

[MagBen]

What was your re-Austentizing temp? AlN is not easy to be dissolved, temp needs to be >1250C! then cool down as quick as possible through 1150-1250C that was the easiest AlN formation temp range. Checking the phase diagram, if that high austentizing temp approaches the solidus temp, you could be better off just scrapping.

 

[DAVIDSTECKER]

MagBen, we haven't re-austentized, I was asking if it would fix the problem.
I believe they have decided to scrap the part.
We made some major changes this next go around including a new foundry.

Thanks to everyone for their input.

 

[arunmrao]

David,,
Sorry to note that you have finally decided to scrap the casting. Can you please share the lessons learnt .
Please come back and share your experience after you receive the new casting.


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

Mahatma Gandhi.