Will straightening cast steel cause internal stress?

[homebrewdude]

Will straightening cast steel cause internal stress?

Our supplier is proposing the following process.
Cast steel part, heat treat to hardness spec, and then straighten the part in a form.

Is this going to introduce internal stress that will relax over time?

Is this a standard process for cast parts?

 

[arunmrao]

What form is the casting? A plate? Is it not possible to straighten the parts during heat treatment by placing weights on the castings. If done in the cold state there will be a build up of internal stresses. Sometimes I have straightened the parts in a press after heat treatment(normalizing) ,cold operation. Be careful of the spring back if not adequately clamped.

 

[homebrewdude]

It is a part, looks like a cam.

We are trying to hold some overall dimensions.

 

[arunmrao]

Ok, how thick is the plate? Is there a solid boss at one end of the cam casting? Are you holding the dimensions in as cast state or in the machined condition ?

Is it possible to add additional stock for this deflection?

 

[redpicker]

Is the straightening to be done cold (below 200degF)? If so, then, yes, there will be internal residual stresses and it is possible for those to relax.

What is the heat treatment? Maybe you can perform a thermal stress relief after straightening.

rp

 

[homebrewdude]

There will be no secondary machining on this part.

I am not sure if the secondary process to straighten will be done cold or hot. I am not sure what the best method is.

 

[arunmrao]

Machining is ruled out,straightening by cold process will build up internal stress.

If you have some more parts to be cast you can consider providing a negative camber on the pattern so that you get a flat face.There will be no need for straightening.

 

[arunmrao]

Can you please find out from the foundry as to at what stage of processing the warpage occurred.This will clearly give an idea of the remedial process.

 

[homebrewdude]

They are saying it is happening in the heat treat process.

 

[arunmrao]

Try hanging the casting instead of placing horizontally. This will reduce distortion.

 

[BillPSU]

If the annual volume is sufficient a quench die could be used.

 

[JStephen]

"Will straightening cast steel cause internal stress?" Yes. But then again, it already has internal stress, and just knowing that it causes internal stress doesn't mean the internal stress is a problem.

"Is this going to introduce internal stress that will relax over time?" Generally, I would not expect the stresses to relax over time unless it is operated at high temperatures.

Is this a standard process for cast parts? Don't know that one.

 

[dbooker630]

I work with ASTM A27 70-40 brackets by squeezing flaps around a tubular section prior to welding in place. As long as the hardness is below 180 HB and the silicon is no more than .80 it works fine. I've seen brittle fracture during the squeeze with higher Si and 207+ brinell.