17-7 Condition TH950? 1

[swall]

I ran across a situation with one of our products made from 17-7 strip, condition A, and no heat treat condition was called out, only a hardness range (Rc 43-47). I called the heat treat vendor to find out what they are doing,and they are performing the TH 1050 treatment, EXCEPT they are using 950F for the final age cycle, not 1050F. I am somewhat reluctant to continue with a non standard treatment for no known reason and wonder if this process might even be detrimental. Comments?

 

[EdStainless]

First I suggest that you specify a strength level not a hardness.
17-7 has some transformation 'issues'. The TH950 is not recommended. You may be ending up with very low ductility.

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[mighoser]

swall,

This proceedure may be not recommended but it isn't "non-standard". The aging temperature designates the number after the "TH". Edstainless is right, and my customer (USAF) prohibits aging temperatures below 1000F for all PH alloys except for 17-7PH in the CH900 condition for springs or where applications exposed to temperatures above 600F. If would think that a switch to PH 13-8MO aged to H1000 or H1025 condition would be a better approach.

 

[swall]

We switched the callout to TH1050.

 

[mighoser]

swall,

17-7PH TH950 has a min. tensile of 210 ksi. Whereas, TH1050 has min. tensile of 180 ksi. Before switching you should make sure this is acceptable. Personally, I've had bad luck with 17-7PH TH1050 in sheet or strip. How about RH1050 or PH 13-8MO H1000 or H1025 as mentioned above?

 

[EdStainless]

The RH is more reliable, in trems of getting consistant ductility out of 17-7.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

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

 

[israelkk]

mighoser

I would like to note that PH 13-8MO has only moderate resistance to stress corrosion cracking and is forbidden for cases where stress corrosion is an issue while 17-7PH in the CH900 condition is has high resistance to stress corrosion cracking and is recommended according to NASA MSFC-STD-3029, GUIDELINES FOR THE SELECTION OF METALLIC
MATERIALS FOR STRESS CORROSION CRACKING RESISTANCE
IN SODIUM CHLORIDE ENVIRONMENTS.

 

[mighoser]

israelkk,

PH13-8MO is more resistant to stress corrosion cracking than non-cold worked grades of 17-7. I suggested PH13-8MO because the original posting spoke to 17-7 in condition A. I'm assuming this application requires forming which prevents the use of condition C material. If not, and stress corrosion is an issue, 17-7 CH900 would be a good solution to the problem.

 

[swall]

The thickness of the strip required was in excess of what is available in Condition C.