17-4 PH

[rms1956]

We are machining a part out 17-4PH. The bar stock is annealed 5.25"dia x 12" long. We will be machining a section to approx 4.5" outside diameter X 5" long with an internal 3.75-12 thread (4.5" deep). The application requires we restrict rotation so the 4" diameter internally threaded section will be split with (4) (0.125"x4" deep slots 0, 90, 180, 270 degree locations) allowing us to clamp the part in place. After machining we will precipitation harden it to approx 35RC. My question is should I expect any movement when I machine the slots? Is there a stress relieving operation that we should perform after rough maching? What temp and time? Where can I find this information?

Thanks,

 

[unclesyd]

Here is information on 17/4 PH SS from the people who developed it. I think this paper will give you all the information needed. After reading it and you have a specific question comeback with it.

http://www.aksteel.com/pdf/markets_products/stainless/precipitation/17-4_PH_Data_Bulletin.pdf

We have literally thousands of precision parts machined from 17/4 and we normally machine the parts after precipitation hardening. We use mostly in the H1000 or H1150 condition. 17/4 contacts during the precipitation hardening process. We have never used any form of stress relief and we work in tenths. I think you metal is in Condition A.

 

[israelkk]

Even if there will be no movement due to the slots the thread diameter will decrease by up to 0.001 in/in. Meaning that the diameter can decrease by 0.004". This may affect the accuracy of the thread. As far as I know it is easier to machine the 17-4PH in the H1075 or H1025 condition than in the annealed condition. Therefore, to my best knowledge it is preferred to first heat treat the bar and then machine part in the heat treated condition.

It has one more advantage that the part will be clean and ready for passivation while in the way you suggested it will have a heat tint after the heat treatment which will require the removal of the heat ting before passivation. This heat tint removal process can change the dimensions further by 0.004".

 

[mfgenggear]

Yes agree with all

machines nicely at/upto 45 HRc
it is preferable to machine in the harden condition.
35 HRc is perfect for machining.:/

then stress relieve at a lower temperature if
its needed after machining. but I know some of you will say it alters physical properties.