17-7 PH SS 3

[soundbite64]

I have made some retaining clips from 17-7 PH SS and have had them heat treated for one hour at 900F for what should be CH900 but the material has become very soft (rockwell C8). These parts were made from 0.071 sheet stock that has the 17-7 stamped on it from the mill. Why is the material so soft?

 

[israelkk]

Is the material magnetic? It may be that the stamps from the mill are mistaken and it is actually an annealed 18-8 austenitic stainless steel. In this case it will be non-magnetic.

Do you have the COT (certificate of tests) for this plate? A serious supplier should have one and there you can see the tensile properties before and after heat treatment recieved in the mill for this specific batch of sheet.

 

[NickE]

How hard was the material before you formed the clips? Condition C has a HRc min of 41 in the AK data book.

 

[soundbite64]

Thank you for the help. Yes the material is magnetic, and I have ask for the COT from my supplier. Prior to heat treating the material had a hardness of B82.

 

[EdStainless]

My guess is that it was in the annealed condition, not the cold worked condition. If you try to age annealed material without the austenite conditioning step you get mush.

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Corrosion, every where, all the time.
Manage it or it will manage you.

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[NickE]

YEp edstainless is right. You did not start with condition C material. The hardest you will be able to get with this material is RH950, even then without prior knowledge you may not get a very hard part.

Nick
I love materials science!

 

[soundbite64]

Is there a procedure to repair the parts that I have or are they scrap? Do I need to have the sheet supplied in condition C?

 

[NickE]

Yep, the only way to get to condidtion C is with large amounts of mechanical deformation. Hopefully you can make the clips from condiditon C, 17-7C has around 6% elongation at that point.

Good luck

 

[EdStainless]

Well, you could re-heattreat the existing material (anneal, condition, refrigerate, age) and end up with RH950.
This should give you about 200ksi min tensile. This isn't the 240ksi that CH900 should give you, but it might be workable.

When you order cold finished material you have to make sure that it was worked enough. I think that the AMS spec calls for 175ksi yield and 200ksi tensile in the cold worked condition prior to aging for CH material.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm