T22 Initial Heat Treatment Cooling Rate per Industry Standard

[purduemateng]

Hi,

I'm working on an atlas of microstructures for T22... I know pretty basic stuff, but I'm having an issue mimicking an industrial heat treatment in our little box furnace here at the lab. Ultimately, I'm performing an isothermal anneal and a normalize/temper heat treatment. The goal is to then take these freshly heat treated samples and temper them at a time/temperature schedule that would be representative of some operational conditions observed in the field (i.e. 200,000 hours at 1050F).

With all of that being said I'm normalizing 1 inch T22 cubes (do not have full chemistries) at 1000C for ~1 hour and 20 minutes and then cooling. I've attached the cooling rates that I've measured and am wondering if these rates mimic industrial cooling rates (green line - "air-cooled", red line - "furnace-cooled"). I'm assuming that they do not agree with industrial cooling rates, but I'd like to get some feedback. My initial thought is that my "furnace-cooled" rate is probably the "air-cooled" rate for industrial practices and that I'll have to program our furnace to step down the temperature much more slowly to get a more true "furnace-cooled" scenario in our box furnace.

Any thoughts? Thanks!

 

[metengr]

The goal is to then take these freshly heat treated samples and temper them at a time/temperature schedule that would be representative of some operational conditions observed in the field (i.e. 200,000 hours at 1050F).

Not to be a smart-ass here but is this some kind of student research project? Why do you need this atlas? You will not be able to replicate the extent of spheroidization damage observed for serviced exposed boiler tubes or components using an extended tempering cycle. You would need to hold the material below the lower critical transformation temperature and try to induce accelerated spheroidization damage to simulate 200,000+ hours of service. Even with this, it will not be useful information because you have a stress component in service, which contributes to degradation damage in Cr-Mo steels. How are you going to account for this?

Regarding cooling rates. Most Cr-Mo components today are not supplied isothermally annealed, unless specifically required, because of furnace time cost. Typically, Cr-Mo material is supplied as either normalized (N) (air cooled - item removed from the car bottom or batch furnace and cooled in still air or with fans), N&T and Q&T.

If you really need to understand the behavior of Cr-Mo alloys join EPRI because all of this has been done. Don’t try to re-invent the wheel.

 

[mrfailure]

In fact, just such an atlas for T22 (and other boiler tube materials) already exists in the EPRI Boiler Tube Metallurgical Guide TR-102433 Volume 2 1993.I do not know if this was also published elsewhere. Access to this and other guides is restricted, though. The current Steam/HRSG boiler tube failure field guide retails for $15,000 (yes, not a misprint) for nonmembers by their web site, though I think it is free to members; however, membership is restricted.

Aaron Tanzer

http://www.lehightesting.com

 

[EdStainless]

Since it is an older EPRI publication is may now be available no charge. Check and see.

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