Ading of Inco 718 1

[Ledeburite]

I would like to know the concern of double aging Inco 718. Basically, our aging cycle is 1325 8hrs, cool in furnace at 100 degrees per hour until 1150, then hold 8 hours with an air cool. Basically, our furnace chart got stuck and I have no objective evidence that the cycle was fulfilled. According to NADCAP concerns, I need objective evidence. Will it hurt to go thru the aging cycle again. Is there a risk of over aging?

Thank you!

 

[EdStainless]

Objective evidence? What about destructive testing of an item from the load?

At what point did you loose the chart?
I can't find a reference, but I recall that re-agin 718 is not a good idea.

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[Ledeburite]

Actually, before the furnace reached temperature for the higher temp. Testing is fine but NADCAP auditors believe in the charts and spend considerable time looking them over. Most findings stem from the charts.

 

[metengr]

The technical bulletin below contains good information about Inconel 718, including heat treatments. If you have a concern or doubt related to an improper heat treatment cycle, you should re-heat treat (solution anneal followed by aging) the coupon to achieve the necessary properties.

http://www.specialmetals.com/products/inconelalloy718.htm

 

[Ledeburite]

Thanks, I have this bulletin as well. The only problem is that my procurement spec does not allow me to solution anneal again because I will lose my necessary cold working in critical areas of the part.

 

[metengr]

You stated in your response above that testing is fine, I would presume that you sampled one or two specimens to confirm mechanical properties? If this is the case, this should be enough objective evidence, especially if your chart recorder suffered from a mechanical problem unrelated to operation of the furnace controls.

 

[EdStainless]

You may need to send some of those samples to an outside lab that speciallizes in Ni alloy work. Microhardness, grain size, and a few SEM pics adn you will have a great story that it was heat treated correctly.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[unclesyd]

There is an time/temperature aging curves for 718 in the following pdf that might give you some insight on you problem.

http://www.imphyalloys.com/information_technique/propriete_produit/upload_pdf/Superimphy718UK1.pdf

 

[rd400guy]

Yes you can over-age this material.

Is this machining bar, forging stock, sheet, etc.? What specifications are you working to, and what are the grain size requirements? Did you solution this material, or did you order it in the solution annealed condition, and what was the solution temperature?

The ideal fix would be to re-solution below delta solvus but above the gamma-double-prime/gamma-prime solvus, then age using the conventional heat treatment you used before. There is still a chance you will have some grain growth.

If you can get back to me with some answers to the questions above, particularly regarding what specifications you're working to, I might be able to shed some more light on this.

 

[Ledeburite]

The material is to AMS5662 and it is in coil form. It is bought in the solution annealed condition with subsequent cold reduction of 15/17 percent. This is done to boost the shear strength and is required by our customer this way. Unfortunately, this particular part prohibits us from re-solution annealing because we would lose the effects of the cold reduction that improves shear strength.

 

[rd400guy]

Short answer: you're in a tough spot.

First off, I have to ask why no one realized the furnace chart wasn't moving. This is ~20 hour aging cycle, and from what you stated, the problem occurred early on, which begs the question that nobody looked at the equipment for 20 hours??

Second, you should have documented procedures that take certain situations into account. In this event, there should at the very least be some sort of documentation stating that there was an equipment (recorder) failure. A "deviation" or "variance" form would be filled out in this case.

Depending on your end user(s) you may be able to notify them that there was a deviation from your standard practice (with the applicable documentation), and if the parts meet all the testing requirements, you might be able to ask for some sort of relief from the record retention requirements in this particular case.

Since you are working with superalloy, and certifying to AMS specs, I imagine you're making parts for the aviation industry, in which case, is there any way to divert or specify to non-critical application? Ask yourself, would you want to fly on a plane that these parts are going into? If it were some other company's parts in a similar situation, would you trust their word and fly on a plane their parts went into?

If you do extensive enough testing, and prove that your parts meet or exceed properties of correctly heat treated parts, and have all the necessary documentation to back it up, you might be alright. Talk to the QA person that deals with the NADCAP auditors (unless you're it), and find out what their thoughts are.

Worst case scenario, re-solution, re-work to smaller size (if possible), and re-age, and make sure your recorder is working. Or don't take the chance and scrap it.

 

[Ledeburite]

Thank you everyone for your time and expertise. We have also come to the conclusion that the parts are tp be scrapped. Our only option is to go to the customer for a waiver and the thought is why should they accept the responsibilty? It's a tough call to make but ultimately it is the right answer.

 

[Metalguy]

If it's not too late and the cost of re-doing the job is very high, you might consider having a good met. lab. use a transmission electron microscope (TEM) to check the gamma prime phases(s). That *might* be enough to prove the aging temp.

 

[yates]

Oops, sounds very much like fasteners to me. You have made a sound decision to scrap. In the absence of conforming heat treat charts, a complete investigation of mechanical properties (grain size, tensile, stress rupture....)would probably cost more than the batch is worth. And the customer and Nadcap would not settle for less than a complete investigation.