Susceptability of 17-4 to stress (work) hardening?

[Medmach]

I am currently manufacturing two components from 17-4 condition H900 bar stock. The processes are relativly complex, with 7 and ten machining stages each, plus multiple secondary and finishing operations. Both jobs are manufactured from the same size (1.625" diameter) stock and usually run from the same heat lot from our mateial supplier. The bars are sawed into 6' blanks and sent to heat treat prior to any machining. My machine operators struggle with dimensions and tool life. Tool life usually being the bigger of the two issues. I have compared heat lot certs from several production runs that performed well agaianst those that required excesive tooling...I have not found any consistent or significant differencces. I am suspecting possible work hardening of the blanks in our first lathe operations, but have not been able to verify this theory. Both parts have a significant amount of material removed onthe first operation...one on the ID the other on the OD. Short of rewriteing the process or modifying CNC program speeds and feeds are there any suggestions or similar experience that any one can provide?

Chet Pierce

 

[unclesyd]

One question off the top.
Why do you have to use H900 for your part?
H900 is one of the worst cases for machining 17/4.
We have found this over many years of machining and using intricate 17/4 parts.

 

[EdStainless]

In the hardened condition 17-4 will not work harden significantly.
I presume that you heat treat first since you need tighter dimensional tolerance than you can get with post-machining heat treatment.
You might consider heat treating to a higher age temp, machine, and then re-heat treating.

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Plymouth Tube

 

[Medmach]

Condition H900 is our customer spec, will the higher heat treatment improve machinability?

Thanks for your earlier replies-new options to investigate.

Chet Pierce

 

[unclesyd]

Yes.

I don't have access to the data, but if I recall correctly you can get measurable improvement at H925. All our parts are machined in the H1125 condition

 

[EdStainless]

First your customer spec should list mechanical properties. From what I recall machinabiilty improves as you increase aging temp until you get to the overaged condition where it decreases again.

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Plymouth Tube