Deformation After Machining Cast Stainless Steel

Hi

Thank you very much for your Guidance. Sorry for the delay in answering.

Best regards,

We used to have a similar problem with a Super Duplex Stainless wrought barstock. Stuff would NEVER stop moving.... heat treating it was out of the question because it would screw up the Ferrite/Austenite balance and cause grain growth and loss of nitrogen from the alloy. Machinist found that doing a little work and leaving some stock on, and then sitting the partially machined blanks out in the hot summer texas sun for a couple weeks would allow MOST of the stress to relieve and allow him to hold closer tolerances. But even then, the stuff would check good at incoming inspection, but would distort after being in inventory for a month...That stuff was a true PITA...

Depending on how much time you have you may consider soaking part in liquid nitrogen then packing it in dry ice in a good insulated container and let it come back to ambient temperature over a few weeks or months. This cryogenic procedure works well in many applications in relieving stress while maintaining grain structure. I am not a metallurgist but have had parts stress relieved in this manner in the auto performance industry with excellent results.

Roy in our case we found that the thermal cycling was the key. hot in the day, cool at night, lather rinse repeat for a couple weeks.

Sometimes you just have to try some different approaches. The book is not cast in stone but real life experiences as we are passing on here at CR4 has a lot of value and possible solutions.

You might also want to look at your chucking force and procedures as they might be inducing apringback. I believe that your castings are too close to the finish machined size, so your removal of the slight amount of "O.D." Is leaving the part unstable. Also 316 is an austenitic grade. I can only see your comments describing the parts as castings. Were these 'annealed' prior to machining? Milo

It may also be that you have stable, fully annealed, stress relieved stainless steel and that the machining process is causing the stress and distortion. In this case, I suggest that you remove minimal material,use very sharp cutting tools, and try to remove the material symmetrically. It kind of depends on the hardness requirement of your finished product.