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Using stress relief for reducing internal stress after casting 1

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stanislasdz

Materials
Jan 20, 2007
250
We have cast a Austenitic Stainless Steel, but a few litle hot tearaing remains.

If we try to open the crack we can show a propagation of this crack. The parts seems have a higer internal stress. This can provide from a higher level of internal stress.

1- Can i use a stress relief heat treatment to reduce this internal stress like after welding ? but i have not welded or repaired this partr yet !

2- What about the stress relief heat treatment of Austenitic Stainless Steel? what is the best temperature ?

 
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stanislasdz;
Are you sure about this or are you simply observing internal casting defects that opened up as you excavate?

You will most likely have to perform a solution heat treatment of the casting to dissolve all existing precipitates and to remove segregation, if this is as-cast.

I would continue to remove any surface and any internal casting defects that you find, weld repair the excavations and perform a final solution heat treatment of the casting.
 
Hi METENGR

No, it's a realy a hot tearing and it's not a casting defects !

see the micrography below.

02xc9.jpg


My question is how to reduce internal stress to stop the intragranular propagation of these hots tears ? i have suggested relief stress heat treatment, is it correct ?

The sulphur and the phosphorus are as down as possible

The basic heat treatment at 1050 °C have been achieved without problems !

best regards
 
Can you tell us something more about the casting Like the part,,alloy,mold and core material to understand the process.
How are you opening the crack for weld repair?

I do not understand your statement that Internal stresses continue to exist in the casting after solution heat treatment.
 

it's an asutenitic stainless steel.
Steel casting
Chemical sand
heat tretament à 1050°C

we won't to weld this part, only use stress relief to reduce internal stress.

ca we use this heat tretament to reduce internal stress withtout any bad consequences !
 
stanislasdz;
Hot tears are casting defects. Also, looking at your photo micrograph you still have a partially dendritic structure, along with interdendritic shrinkage defects. How long did you hold for the 1050 deg C solution treatment?

Do you know the actual quality of the casting? Did you radiograph the casting to evaluate casting defects?

If the casting contains significant interdendritic shrinkage and hot tears, you might need to scrap it and pour again. A stress relief is not going to help you in this situation.
 
stanislasdz;
If the casting can be repaired, you might need to perform an homogenization heat treatment to remove the dendritic structure. This is a separate heat treatment step that requires heating the casting above 1095 deg C and holding for a period of time (hours), and slow cool.

Once this is completed, perform a separate solution anneal heat treatment at 1065 deg C minimum with rapid cooling or quenching.
 
A better anneal at 1090-1100C and a slow cool, that is providing the C is low enough to allow it without carbide formation. This will be the lowest stress condition that you can get.
How are you going to repair the hot tears? They should be ground and welded.
What was the FN of the material? How hot was it when it was shaken out? More ferrite and longer cool before shake out may be needed.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
 
stanisladz,
Your problem appears to be a foundry related one. I am not aware of the size or weight of your castings. However, in the case of stainless steel castings if such problem was to occur you would be best advised to analyse the reasons and repour.
This can be a design related or risering issue or mold and core materials issue. Please look into it carefully.

Salvaging the castings, using expensive consumables,heat treatment and post salvage inspection are costly and time consuming. At the end of the day ,there is a nagging doubt and also reputation as a good foundryman to be saved.
 
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