Hardness test on SS321?
Hardness test on SS321?
(OP)
Hello my friends,
In front of me a specification which specifies hardness test on SS321 after welding (in the heat affected zone after heat treatment). In general the specification specifies extra requirements on SS321 to prevent (intergranulair and stress) corrosion in a Polythionacid or other corrosive products.
The limited hardness would be 225 HB.
I know this test is normal for Chromium steels (P9, P11…) but I didn’t see it for SS321 yet.
Questions:
Is this hardness test a relevant requirement on SS321 (and why)?
Thanks for your help,
MatieMan
Belgium
In front of me a specification which specifies hardness test on SS321 after welding (in the heat affected zone after heat treatment). In general the specification specifies extra requirements on SS321 to prevent (intergranulair and stress) corrosion in a Polythionacid or other corrosive products.
The limited hardness would be 225 HB.
I know this test is normal for Chromium steels (P9, P11…) but I didn’t see it for SS321 yet.
Questions:
Is this hardness test a relevant requirement on SS321 (and why)?
Thanks for your help,
MatieMan
Belgium





RE: Hardness test on SS321?
I would agree, it seems odd that a specification would require hardness testing on materials that cannot be hardened by thermal treatment (from welding). It might have been a mistake or carry-over of requirements for carbon/low alloy steels.
RE: Hardness test on SS321?
RE: Hardness test on SS321?
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Hardness test on SS321?
Other than hardening from cold work, which would be associated with forming operations of the base metal, can you explain to me HOW an austenitic stainless steel that cannot be hardened by thermal treatment from welding would have hardness limits in a base metal HAZ????? I can understand hardness limits for post forming operations of austenitic stainless steel base metal to assure no evidence of prior cold work, but not for welding.
RE: Hardness test on SS321?
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Hardness test on SS321?
There was a shop welding large 310 SS piping some years ago with GMAW (MIG) process, and it seemed they put too much heat into the large fillet welds at the slip on flanges. It resulted in cracks that were discovered when every flange weld leaked upon field hydrotest. The problem was remedied by specifying only GTAW / SMAW controlled heat input plus limit on interpass temperature for welding. At that time it seemed the austenite/ ferrite imbalance could have caused the cracking of welds, as GRoberts might agree.
Would SJones and metengr consider this scenario? There is weld shrinkage that occurs with welding. (PWHT would reduce the residual stresses, but PWHT is not common for stainless steels, except possibly for NACE applications.) Now I wonder if the weld shrinkage does result in some "cold working", such that some hardness differences might be detectable. You probably have seen weld joints where the shrinkage may have been 3 to 5% of diameter? Good welder technique, such as 'back stepping', helps deal with the distortion from shrinkage to keep dimensions within control plus reduce the amount of "cold working" from shrinkage. Good technique and procedure also seems to prevent the cracking that resulted in the leaks.
RE: Hardness test on SS321?
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RE: Hardness test on SS321?
I was thinking along those lines. It is analagous to strain ageing in carbon steel weld zones. Whether it is detectable by hardness testing (especially Rockwell C), I have no clue.
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/