Vendor provided over-strength material, is our old testing valid?
Vendor provided over-strength material, is our old testing valid?
(OP)
We purchased a run of specialized stainless forgings and the product the vendor delivered is testing about 30% higher than the yield and ultimate properties we requested in the spec. While the additional strength itself is not problematic, it is causing concern among our team because it's above the strength level we have done material testing on previously and are confident in. We are not sure if the different properties might cause a change in the fatigue, corrosion (particularly SCC), or other reliability characteristics. The vendor does not share our concerns and claim they provided superior material at no extra cost.
The material certs indicate they provided the condition we asked for (and tested in the past), but both the mechanical properties and the hardness are well over the "min" values provided in the ASTM spec. This has caused disagreement over what the validity of our past testing should be, whether it is the material heat treat condition (regardless of properties) or the as-delivered strength/hardness.
The material certs indicate they provided the condition we asked for (and tested in the past), but both the mechanical properties and the hardness are well over the "min" values provided in the ASTM spec. This has caused disagreement over what the validity of our past testing should be, whether it is the material heat treat condition (regardless of properties) or the as-delivered strength/hardness.





RE: Vendor provided over-strength material, is our old testing valid?
RE: Vendor provided over-strength material, is our old testing valid?
You did not mention the specs for the material and HT process. But for example, say the material and HT specified is 17-4PH condition H1025 (Ftu 155ksi min) and a batch of forgings tested 30% above the min UTS (~202ksi). That would mean the forgings were probably not heat treated properly since 202ksi UTS is around the upper limit for an H900 condition. Most HT specs (MIL-H-6875, AMS 2759/3) usually control age hardening temperature for 17-4PH to something like +/-10degF. So if the HT vendor is working to a proper HT spec they would not get H900 properties using an H1025 process. This would also pose an issue with stress corrosion since 17-4PH H1025 is usually the upper strength limit allowed for applications sensitive to stress corrosion, and H900 condition would not be acceptable.
Regardless, it is good that you are looking into this issue. Initiate some MRB activity so that others can provide input on how to disposition (accept, reject, rework, etc) this batch of forgings. The corrective action might also include changes in the engineering documentation for this part no. so that this problem does not re-occur.
Lastly, I got a chuckle at the comment from your vendor, "The vendor does not share our concerns and claim they provided superior material at no extra cost.". You've got to admire their salesmanship efforts.
RE: Vendor provided over-strength material, is our old testing valid?
Thanks again!
RE: Vendor provided over-strength material, is our old testing valid?
In these alloys the toughness (notch or low temp) may be hurt by higher strength.
BUT, if the old material was just above the mins then 30% higher is very reasonable.
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P.E. Metallurgy, Plymouth Tube