Stability of 316SS, without heattreatment

[123Cat]

Im machining a V block from 316 SS ,,,,,450 long by 70 mm square
And it has to stay dimensionally stable within 1 thou over about 20 years
Im doing it out of bar stock
If I just rough and machine it without any heattreatment would it be OK
And also can you recommend a heattreatment to demagnetise it

Best Regards

123Cat

 

[lgearhart]

123Cat, I can't think of any reason it would move, even after 20 years. If the residual stresses you put into it while machining are balanced, I can't believe they would go away or change suddenly. Regarding demagnetization, you should not have to worry about that either. A 70 mm thick piece of 316 stainless steel has insufficient cold working to be ferromagnetic.

Good luck!

 

[metman]

Igearhart could be correct if the V block will not see any thermal cylcling during service. It would seem that this machined shape would have inherently unbalanced residual stresses. Therefore if it is going to be subjected to thermal cycling, I suggest: rough machine, stress relief anneal or at least heat above any temperature it will see in service, then finish machine or grind to final size.

Jesus is THE life,
Leonard

 

[arunmrao]

Control of residual stresses, is the controlling factor.. Hence do not give more feed,and run slowly the machine. This will minimise the heat generation and corresponding distortion. I had experienced this while making a gage of 535 mm diameter and 600 mm length. The initial wall thickness of the was 20 mm and was finished to 6mm.The material was CF8.I had rejection of 6 gages till I could get the last one accepted with some concession. It is being used for the past 6 years without any problem. The only care taken is that it is kept in a air condition room while not in use.

Your 70 mm thick V block should not pose any problem ,I feel. Please let us know your experience once you have finished.

 

[123Cat]

Thanks Guys
Yes it holds parts in a high vacuum and the max temp is 95C when it is dishwashed, for cleaning , after finishing
Hope this doesnt move it
And arunmrao yes you mean use sharp tools and, not to rough it too fast, or hard I guess
Its 304 or 316 grade
What is CF8.1 if I may ask

Thanks for the input

123Cat

 

[arunmrao]

Cf8 is cast equivalent for 304
Let the feed rate be low, is what I meant.

 

[BTIGUY]

123Cat

I suggest that you could stress relieve your 316SS block with sub-harmonic processing and put your mind at ease. This is the "accelerated seasoning" process that the high performance race engine builders have been using for years to accomplish what you are hoping to achieve.

Sub-harmonic processing does not cuase treatment distortion, relieves only thermally induced stress, and enables the workpiece to remain stable (and resist distortion when working in a high tmeperature environment).

Many of the world's most sophisticated components are made using this sub-harmonic stress relief process like space probe telescope components.

Best of Luck.
BTI Guy

 

[EdStainless]

If the bar was well annealed to start with you shouldn't have any issues. The bar should be fully non-magnetic to start with. If you can measure any feromanetism - reanneal it.
This could distort if you heat and cool it unevenly. After all a 70C temp change will cause about 0.5mm length change

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