Carpenter Biodur CCM Alloy 1 and Stress Relieving Process

[barkranch]

We make a medical device from Carpenter Biodur CCM Alloy 1 .2165" barstock and it is stress relieving after machining, causing out of tolerance conditions. We are researching stress relieving this material prior to machining but we are not sure how much we can heat it up without changing the material properties. Any information provided is greatly appreciated.

 

[MagBen]

you will not see any structure and mechnical change anneal up to 1050F. Anneal at 1350F can cause some fcc to hcp transformation, leading to an increase in hardness. what temeprature did you use after machining?

 

[barkranch]

Thanks MagBen! Do you know if a specification exists that I can reference? We do not heat treat them after machining.

 

[EdStainless]

Bark,
In your first post you say that you do stress relieve after machining. This is a heat treatment.
You really need to go near the anneal temp to get good stress relief and avoid phase changes.
The problem is that the uniformity of heating and cooling is critical to minimizing residual stresses.
You might experiment with multiple anneal cycles prior to machining.
Remember, uniform cooling.

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Plymouth Tube

 

[barkranch]

Thanks EdStainless. What I should have said is that "the parts we are machining are stress relieving after machining, causing the thin arms of the part to splay outwards". We are not heat treating after machining. We want to stress relieve the material before we machine it, but I can't find a specification that documents what temperature to heat this particular type of material to in order to take some stresses out prior to machining. MagBen said we could anneal the material up to 1050F. He must know this temperature from personal experience or is this parameter mentioned in a specification somewhere? I would like to provide my customer with a specification that specifies the process we are following to stress relieve. We don't have time to experiment.

 

[EdStainless]

Ask Carpenter, they have data showing the impact of aging at various temperatures.
If the arms are moving because of machining stresses then stress relief won't help.
If they are moving because of prior residual stresses then you have a chance.
Find the highest temp that does not lead to any increase in hardness.
And then be ready for long stress relief times, maybe 15 hours or more.

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Plymouth Tube