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Crack On the Surface of Thick Plate

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AAtaie

AAtaie

Industrial
Joined
May 22, 2007
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We have one 80 mm thickness plate which has welded to a part. After MT and PT we saw some indications like crack near the welded zone. First we thought that they are HAZ cracks but finally we understood that these indications can be seen even in non-welded plates and also these indications are not related to surface scales because they can be seen on grinded parts.
After grinding to 0.5 mm they disappeared and their Accumulation increase near welded area and machined edges. They lay in the rolling direction.
Finally we think that they are the rolling defects
What are they? What is the reason of these indications? Can they influence on the mechanical properties?
 
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What is the plate material, and heat treatment condition?
 
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It is a nuisance but now you are aware of their existence you cannot ignore them. At only 0.5mm depth it is likely thast these cracks can be safely removed without reducing the plate below the minimum design thickness. This shoud be carbon steel, otherwise the MT will not work, so stick to just MT in two mutually perpendicular directions, the PT is superfluous.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan
 
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I'm assuming that these indications are are in a perfect straight line and when looked closely appear to be slightly jagged... these will almost certainly be rolling defects as you suggested... 80 mm plate is quite subsantial and i'm sure grinding out 0.5 mm wont affect the integrity of the metal... however, are you sure they are 0.5 mm in depth or are you only guessing? 0.5 mm is deeper than usually expected?! If you can confirm that these are only rolling defcts i probably wouldnt even bother with the grinding, waste of time and money for no benifit... I would however contact your supplier!

Hope this helps...

Regards

SWM
 
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From your explanation I think that is Lamination. The defect came from steel making process where some inclusion metalic or non metallic even porosity when through to rolling they will be reduce of dimension and come falttening and make the layyer whcih no fusion to others. When we apply welding, or grinding they will be vissible like crack or shape grinding.

Please do lamination check with UT to detect that defect.
 
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As usual, the questions asked by "metengr", is the best response I've seen to this thread.

Without knowing what the material is and what condition it is in, i.e, as rolled, annealled, normalized, quenched and temperered, at best the other responses are conjecture.

As to their influence on the service of the component, what is the direction of stress relative to the "cracks" you observed? Is it going to be used at elevated temperature or room temperature, is the service conditions static or cyclic in nature?

The responses are only as good as the information provided.

Any response for "metengr" is always on the money.

Best regards - Al
 
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