PWHT For Stainless Steel (304/316)

Date 02-20-2009 06:42

I cant answer your question.
But why do you want to PWHT 316?
I could imagine that it must be done at reletive low temperature.

3.2

By js55

Date 02-20-2009 17:31

PWHT of SS would normally only be used to homogenize the microstructure (solution annealing). Not generally as stress relief. There might be some argument for 316, given the way Mo is supposed segregate. But I suppose in order to justify it the design would have to be cuttin it pretty close in regards to the service it will be used for.
Its quite rare to do it. I think its more cost effective just to kick the alloy content up a bit than to mess with the difficulties of solution annealing the material.

By GRoberts (***)

Date 02-21-2009 21:25

The only reason I normally see PWHT of these alloys in fabrication is to stress relieve the part so that tight machining tolerances can be held after welding. If you aren't using a low carbon grade of stainless forget about it though. It won't be stainless (i.e. it will be sensitized) after a stress relief PWHT. Solution annealing and quenching is the only option.

By Chin Terry (*)

Date 02-23-2009 01:57

Hi GRoberts, meaning after PWHT the stainless steel chemical property will be damaged? what degree C is maximum for this type of materials and how long for the holding temperature?

By jon20013 (*****)

Date 02-23-2009 03:40

Chin, as GRoberts and js55 mention, there are rarely instances where PWHT is applied to either of the alloys you mention. "Normally" temperatures are limited to around 300 - 350F although damage / changes don't actually happen until around 800F.

By GRoberts (***)

Date 02-23-2009 23:22

I have seen PWHT for austenitic stainless for dimensional stability around 700F. I'm not a machinist, so I don't know if it works, but it must do something or the companies paying for it would quit specifying it.

By DaveBoyer (*****)

Date 02-24-2009 04:45

My take on that, as a tool & die maker, is that if they could stress relieve at a higher temperature without sensatization issues, they probably would, but they can't without doing a full blown solution anneal, so they use 700 and settle for what they get.

By GRoberts (***)

Date 02-24-2009 23:11

That sounds about right to me.

By Chin Terry (*)

Date 02-25-2009 01:28

question was raised because of client spec call for, after two week discussion they decided to call off