Sensitisation instainless steel 1

[enmax]

The effect of sensitisation on the corrosion resistance of austenitic stainless steel is well documentated. My question is - what is the effect on mechanical properties? If a 304 grade stainless steel (i.e. with more than 0.03% carbon) is sensitised by welding or by heating to 700C for 30 minutes do the mechanical properties of the sensitised material alter? Theoretically the precipitation of carbides at grain boundaries might lower the Charpy impact resistance or reduce the tensile properties but does it happen in practice? Does anyone know of any data on this matter?

 

[EdStainless]

I have never seen anyone claim to be able to detect a change in toughness related to sensitization. You are talking about a very small amount of carbide, and you are dealing with very tough alloys.

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Plymouth Tube

 

[unclesyd]

The only Austenitic SS that is really affected is by sensitization is 302 SS.

Here are some values for 304 SS @ 300F.
304 annealed 80 ftlb
304 sensitized 60 ftlb: 100 hrs @ 1020F

The effect of cold work has a much more pronounced effect than sensitization.
All values @ -300F
304 SS annealed + 0 CW 79 ftlb
304 SS annealed + 10% CW 62 ftlb
304 SS annealed + 20% CW 52 ftlb

304 SS annealed + sensitized +0 CW 60 ftlb
304 SS annealed + sensitized + 10% CW 35 ftlb
304 SS annealed + sensitized + 20% CW 22 ftlb

302 SS sensitized + any CW averages 10 ftlb

Data taken from USS materials Manual for Low Temperature and Cryogenic Steels (June 1966)

 

[strider6]

roberts,

i've found this article that probably can give u some good hints on what you're looking.

A Short Review on Wrought Austenitic Stainless Steels at High Temperatures:
Processing, Microstructure, Properties and Performance

http://www.scielo.br/pdf/mr/v10n4/a21v10n4.pdf

S

Corrosion Prevention & Corrosion Control

 

[enmax]

Thank you for your advice and references. I should have said that the sensitised material will be used in liquid nitrogen. The question is - has the impact resistance(or other mechanical property) in the heat affected zone of the welds been reduced because of sensitisation of the material? I feel the answer is "no" but can't find any information in the literature, so to prove it one way or the other I may do some testing and thought of taking a piece of 304 with, say, 0.05-0.06% carbon, sensitising it at 700C for 30mins and carrying out a Charpy test which could then be compared with unsensitised maeterial. there would have been no issue if the material had been 304L since there would have been little likelihood of sensitisation. Is there any recorded practical experience of 304 (not 304L) being used in the welded condition at liquid nitrogen temperatures?
Many thanks for your help.

 

[EdStainless]

Yes, heavy sensitization will lower impact toughness.
No, I don't think that you can measure the effect from welds.
The biggest reason is that there are other issues (chemistry, cold work, strength) that have greater influence on the impact values.

Of course, why in the world aren't you using low C material?

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Plymouth Tube

 

[unclesyd]

Impact data for welds in "Inert-Gas-Shielded Metal-Arc Welds om 3 1/2" 304 Stainles Steel Plate"

V-Notch values(ftlb) at a test temperature of -320F

304 SS
Weld Metal 38.5 lbft
HAZ @ 1/16" 51.5
HAZ @ 1/8" 63.0
HAZ @ 1/2" 64.5

304L SS
Weld Metal 48.5
HAZ @ 1/16" 58.5
HAZ @ 1/8" 56.0
HAZ @ 1/2" 75.5

 

[enmax]

EdStainless - why not use 304L? Exactly my question when I heard of the problem. The vessel was made in 304 before someone queried the material so I'm trying to justify the use of the vessel in grade 304.
Unclesyd - could you point me to the reference you've quoted? Could be my "get out of jail for free" card !!

Regards

 

[unclesyd]

It was taken from the same source as mu previous post used.

"Data taken from USS Materials Manual for Low Temperature and Cryogenic Steels (June 1966)"
I also have some notes taken a couple of in house seminars that show the essentially the same impact data for SS weldments.

Further references for my first post are:

V.N Krivobok "Properties of Austenitic Stainless Steels at Low Temperature" NBS Circular 520.

E. H. Schmit "Low Temperature Impact of Annealed and Sensitized 18-8" Metal Progress Aug (1950)


They are no further references for the weld impact data shown in my second post.

Here is one article taken from the 10 page Bibliography for this booklet.

"Impact Properties of Stainless Steel Weldments" H.W. Mishler & H.J. Nichols Welding Vol 40 Dec. 1961, pp 564-568

I would try the Linda Hall Library to see if these papers are still available.

http://www.lindahall.org/

 

[EdStainless]

and check the actual carbon levels for the steel used. You need to know the actual values that you are working with.

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Plymouth Tube

 

[enmax]

Edstainless and Unclesyd - thank you for your valuable replies. The Linda Hall contact was very useful - I purchased a couple of articles from there and they'll be useful in the future too! I couldn't locate "USS Materials Manual for Low Temperature and Cryogenic Steels (June 1966) Inert-Gas-Shielded Metal-Arc Welds om 3 1/2" 304 Stainles Steel Plate" (could I be cheeky and ask if you could supply an electronic copy of the relevant parts?). For your information, I found a considerable amount of technical data on stainless steel on the Nickel Institute website (publications section) - one of them (Publication No 313) quoted Krivobok and Schmidt as well.

Thanks again - Terry

 

[unclesyd]

I don't have a scanner but will try to get access to one and scan the pages to post on engineering.com. Give me few days as my wife and I have some medical testing coming up this week.