Quenching of CF* Casting 3

[Guest102023]

I have a 1000lb CF8 casting that is fairly complex in shape with sections ranging from 0.3" up to about 3". It has undergone weld repair so solution annealing is called for by ASTM A351.

The question is whether to 'rapid air quench' the part rather than water quench. I am wary of this suggestion, due to too slow and non-symmetrical cooling, leading to other types of distortion. Also because of the wide range in sections thickness. It is a pressure part that will see chlorides in service.

Any thoughts/experiences on this?

 

[metengr]

I would water quench to obtain the maximum corrosion resistance for this grade of casting.

 

[arunmrao]

Was there any distortion observed originally when the part was cast and not yet machined ? If no,then you can once again subject to water quenching. Is there any way you can mechanically support the tin sections during heat treatment? A simple fixture may be devised for the purpose.

 

[Guest102023]

This is a repair of a spare part and is my first involvement. Restraint is not really practicable. The machined surfaces can be restored to their specified tolerances I believe.

It just seems like an air fan, even a high powered one, won't do the job adequately for this part.

 

[arunmrao]

" The machined surfaces can be restored to their specified tolerances"

Good,then you can take the splash! No issues.

 

[Guest102023]

I just got off the horn with a proper heat treating shop who offer rapid gas quenching. They warned agains water quenching - too rapid.
I will recommend the customer $pend$ a little more

Thanks to all.

 

[metengr]

brimstoner;

They warned agains water quenching - too rapid

Why??? You have up to 3" in thickness in some locations. I would re-think this position very carefully for cast austenitic stainless steel.

 

[arunmrao]

In my experience, I have not come across any heat treater who recommends, that water quenching is a severe process for cast stainless steels.

 

[metengr]

arunmrao;
Well said, from an expert on castings.

 

[Guest102023]

metengr, the issue for me is the wide range in sections, and the distortion that could result. The thin areas are near the centre are restrained by a massive outer ring. I am uncertain what shape things might take, even though I still think all machined surfaces can be restored.

See picture attached - the outer ring is more massive than I recalled, while the middle cone gets fairly thin.

This kind of heat treatment is outside my normal range as a welding engineer, and I don't want to make this piece an expensive data point in my experience

 

[arunmrao]

The part does not appear to be too daunting to pose any problem during quenching. The only concern of any damage or distortion looking at the picture, are the weldments done (pipes with end flanges). Hope they do not get bent or damaged. If they happen,too,you could easily correct them.

Finally,as you mentioned that you do not desire to make this an expensive experience. You are right in expressing your concern. Request you to take assistance of an independent consultant,.

 

[Guest102023]

Possibly I projected my own concerns onto the heat treat shop's reply; they also did not have the benefit of a picture.

The flanged nozzles are probably the least of my concerns, as they are free to move. The flange face location is not critical, as the feed piping is somewhat flexible (I would assume).

I have already decide to defer to the specialist's expertise. As it turns out, nobody here in town does anything other than stress relief of welds and are not even equipped for simple water quenching.

 

[swall]

ASM Heat Treater's Guide lists forced air, oil or water quenching for the CF-8 series cast stainlesses. If you're squeamish about water and doubtful of the effectiveness of forced air, oil might be the way to go.

 

[mfgenggear]

hey guys what are the heat treat parameters?

I would be a hesitant to reheat treat a machined part.

 

[unclesyd]

I have water quenched CF8 pump casings weighing around 700 lbs after making weld repairs. There was very little distortion and it took probably no more than 1/16" overall to square up the back and the two nozzles. Some smaller pumps were QA several times.

One way to get better cooling rates with air is to use a low thermal mass furnace similar to these at Pinson Valley Heat Treatment. Look at he two pdfs and in the standard pdf you can see something similar to a pump casing being cooled and there is no background radiation. The stress relief pdf shows one way to do this build the furnace around the part.

http://www.pvht.com/home.asp

http://www.pvht.com/flyers/Standard.pdf

http://www.pvht.com/flyers/StressRelief.pdf

 

[EdStainless]

The key to cooling rate is the carbon content.
If you are below 0.045% then you can use rapid air cooling.
Higher than that then you need to water quench.

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Plymouth Tube

 

[GRoberts]

Brimstoner: some additional things to consider

From the tone of your posts, I would guess that you are the material manufacturer/foundry. Is that correct? I am just guessing here, but if you were, you would probably be solution annealing/water quenching daily. If you are not the foundry, you are not responsible to manufacture the part to ASTM A351. There are no rules that require solution annealing by fabricators or repairers of castings once the material has already been certified to ASTM A351 by the original foundry.

Also, from the pictures, it appears that the part has welded on flanges in addition to any repairs you may have made. In this case, if solution annealing is required, you have to make sure all welding procedures used, including repair, fabrication, or possibly repair at the original foundry are qualified for this sort of heat treatment.