Welding 304H PWHT and Hardness issue

[Nashanas]

Hello everyone,

I have a question regarding the welding of 304H plates. My client is asking a hardness of 200BHN max in the HAZ. Normally we have 225BHN in that zone. The welding process is SAW. The raw material has a BHN of 180. Is there a way to play with SAW variables or with PWHT variables to reach 200BHN?

 

[EdStainless]

So the raw material is right at the max allowed hardness.
That is cause for concern. If it was 20pts lower then you would be in business.
The 200max does sound very tight.

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[mk3223]

I thought to use a high pre-heat temperature which may be reducing the hardness of the welded metal as an alternative per API Code. But, it may apply to CS material, but not 304H. Alloy 304H is sensitized after ending, which becomes an issue in the H2S service without PWHT.

 

Nashanas,

1) Your client is clueless about stainless steel, as is anyone worried about hardening in the 'heat-affected zone' in 300 SS.
2) I hope you are not trying to measure BHN of the 'HAZ' using BHN. (or really, anywhere - BHN should be banned from everywhere other than foundries).

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Nashanas]

Hello,

Well, actually we have been asked to find BHN in the HAZ. My client is a huge company with probably more than 100 engineers in its technical office. I am new to this field so I cant confront anyone, just trying to get more information. I read somewhere that PWHT of 304H is actually bad for material. But I dont have a literal reference to support my argument.

 

[EdStainless]

1. Austenitic SS cannot be PWHT unless you use a full solution anneal. Any lower temp will promote the formation of Cr carbides and sensitize the material. This lowers its corrosion resistance significantly.
2. A std BHN indenter is way too large to be using on a HAZ of a weld. Select a more appropriate method.
3. The max hardness on Aus SS is rarely limited, unless you are preventing the use of cold worked material. In the specs for annealed material this 304N is limited to 98HRB (201BHN). Expecting a little senitization in the HAZ from welding you would have to allow some margin for this to increase. It sounds like they just copied the value for annealed material and didn't give this any thought.
The question that you can ask is why the weld hardness limit is set the same as the raw material limit.


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P.E. Metallurgy, consulting work welcomed