superduplex craking during water cooling

[DXM]

I have diametral internal craking problems (big internal cracks) in superduplex round bars during water cooling. Of course, above all in big sizes.
Which is the best option to avoid this defect?

I would like to eliminate a post solution annealing after cooling on air.

 

[metengr]

DMX;
You need to provide background information on the above problem to receive useful tips. What was the processing history of the bars? Can you provide a picture of the internal cracking?

 

[DXM]

Here is aa picture of the defect.

This is tipical after rolling and quench in water. The temperature of the bars before quenching is over 900º C.

The bars are formed in two rolling steps, coming from ingot. The heting temperature before rolling is over 1250º C. The rolling temperature is over 1000º C.

 

[remetaper]

Metengr is right when requires more info.
However, if you are sure internal cracking is not caused by a wrong preheating process (i.e cracking before quenching ), the reason why large round bars fails is due to a premature coming out of the water quenching tank. These grades must be cooled until room temperature before come out of the tank.
Waiting for more info....

 

[remetaper]

Only now I saw the picture.
Annealing temperature is too low for these grades: intermetallic phase could exist also on surface, not only in the core.
This cracks is typical of not complete cooling as I mentioned in my previous post. You must wait for before come out from water.

 

[EdStainless]

There are size limits for these alloys.
Because of their thermal conductivity there will be thick sizes that are impossible to quench enough to suppress intermetallic formation.
You have to quench these until all of the material is below 300C

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Plymouth Tube

 

[metengr]

Agree with the above, the 900 deg C temperature before quenching is too low for this alloy, you need to be at a minimum of 1050 deg C to 1100 deg C. I would suggest you reheat to at least 1050 deg C before you quench.

 

[EdStainless]

Fully agree that you need to re-heat and soak at 1050C prior to quench.
And one more thing, make sure that the cracks are from quench and not actually hot cracks from your forging. I am a little skeptical.

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Plymouth Tube