Heat treatment of AISI 321 stainless steel 3

[bagnamento]

According to ASME Code, section II, SA 240, heat treatment of material shall be in accordance with SA 480.
In the case of austenitic stainless steels, the material shall be solution annealed.
For Type 321 Ti-stabilized stainless steel, section 15.2.3 of SA 480 states that a stabilization anneal may be used in case solution a nealing temperature is higher than 1950°F and the steel is subsequently exposed to sensitizing conditions.
If this is not the case, it appears that AISI 321 stainless steel can be purchased in the solution annealed condition (no stabilization).
According to ASM Handbooks Type 321 stainless steel is to be given stabilization HT only if in contact with highly corrosive media.
Is this correct?
How would the steel be stabilized and resist to intergranular corrosion if it solution annealing isn't followe by stabilization, i.e. no specific heat treatment for Ti-carbides precipitation is applied?

 

[Goahead]

It is correct that AISI 321 stainless steel should be purchased in the solution annealed condition.
If not welding, use as is.
The problem is which treatment to apply after welding.
The most appropriate heat treatment would be in any case resolution treatment: but is it possible without incurring in unacceptable deformations?
Any other treatment would be less favorable for corrosion resistance, but may be needed for stress relieving of residuals welding stresses.

http://www.welding-advisers.com/

 

[sayee1]

Bagnamento's question was probably misunderstood. ASM clearly defines stabilized annealing for 321 tyope materials as folliows "It is carried out where maximum corrosion resistance of stabilized stainless steels of type 321 is required. The heat treatment involves heating to the range 1550-1650 degrees F and mainitaining this temperature for about 5 hours depending on the thickness prior to or in course of fabrication followed by short time stress annealing if reqd at 1300 F without danger of harmfull carbide precip[itation."
What Bagnamemto is querying is that why only for extremely corrosive media a stabilized solution annealing treatment is required? Also he goes on to ask, in case of normal corrosive media, where ordinary solution annealing is used, how the Ti carbides precipitate in prefernce to Cr carbides and in the case that the ss is not stabilized, how IGC resistance is built into the ss.
In my experience, again, it is the designers call. Depends on what maximum corrosion rates the material is designed for. In case of ordinary solution annealing, the Ti carbides do prefernetiall deposit in preference to Cr carbides, however not 100% of the Ti is utilized for the formation of carbides. Thus the material should show IGC resistance but not to the extent that wiould be desired if the medium was highly corrosive.

In any case, would be good to see what the experts on ss say to this query.

Thanks and regards
Sayee Prasad R CEng MWeldI MIOMMM


If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[mcguire]

The advice to have special solution heat treatment for 321 largely dates from times when it was difficult to reduce carbon and nitrogen to the levels they normally are today. A level of 0.025% for both C and N is pretty routine. The titanium would be over 0.3%. That means that the possibility for Cr23C6 formationis about nil. This carbon level would qualify as an "L" grade, so sensitization is really no danger.
Previously when carbon levels were higher you could get enough carbon quenched into solution that it could precipitate as Cr23C6 if subsequently re-heated,as by welding.
Mills keep C and N low now to avoid the surface defects associated with TiN. The beneficial by-product of this is the lack of need for solution heat treatments to form TiC and TiN. If you're unsure, just look at the carbon level on the certification. If it's below 0.3%, it's an L grade anywway. It won't present chromium carbide problems.

 

[arunmrao]

Mcguire a typo I suppose. Carbon 0.03% for L grade.

 

[mcguire]

Thank you Arun, my friend. Yes, of course, I have the wrong decimal point.