tig welding 400 series stainless to 300 series

[markct]

i have a bunch of 400 series stainless around from some commercial freezers that i stripped the outsides off of, i want to make a maple syrup pan and a few other things from them. i did not know they were 400 series at first, and when making a roofjack for the stovepipe to pass thru i welded some 300 series to some 400 series with 309 filler rod, it seemed to work great, and they arnt rusting, been on the roof a while now. is this ok, is there a better rod for welding 400 to 400? or is 309 ok, anything to do or not to do? or to watch out for? thanks guys

[journyman]

309 is for welding SS to carbon steel. It will work for most other SS's. Since you are not working to code it's not really relevant. As a rule you want to use the wire that corosponds to the higher grade of steel.

[markct]

by higher you mean numericaly higher, like i should use a 400 series filler? what would be the appropriote filler for 300 series like 304, i just used 309 since i had used that before at a previous employer and it worked well, no real reasoning other than that! what will happen if i mix the wrong filler and base, or two wrong base metals? nothing? cracking?

[weldor2005]

Well i would think that for most stainless i would try a 316 filler rod. As for welding different metals, it is right to tend to go to the higher grade of steel to match filler rod to. Keep in mind that that doesn't refer to things like tool and die, as you would probably need to do a composite weld if welding two different metals together so that you don't get a bad admixture of the two dissimilar metals. Other than that i would say that typically welding most S.S. to a low to medium carbon steel, that it would be best to use the higher stainless filler rod.

[markct]

so by higher i should get a 400 series filler, or just higher 300 series number, or is what im using ok for simple sheetmetal work like im doing?

[journyman]

What you doing is fine and will work. If you were working on something engineered it would requier the use of a 400 grade wire or some other semi-exotic like Inco 92 or 625 or 2205. The onle problem you might encounter could be corosion, ( yes stainles steel corodes) due to some chemistry in the alloys or the conditions under which the item is employed. For example de-ionized water will leach the chrome out of SS and it will fail in a year or 2, particulary if it hot.

[Some Creep]

Originally Posted by journyman

.... For example de-ionized water will leach the chrome out of SS and it will fail in a year or 2, particulary if it hot.

Uh, not to hijack the thread... but huh? I thought SS was rated an 'A' for compatability with DI water. Where do you get this information from?

[USMCPOP]

Page 21 of this technical handbook http://www.atlasmetals.com.au/files/...l_handbook.pdf
says: "Welding together of different metals, such as of Grade
304 to Grade 430 or a stainless steel to a mild steel, can
be carried out, although some extra precautions need to
be taken. It is usually recommended that over-alloyed
austenitic welding rods, such as Grade 309, be used to
minimise dilution effects on the stainless steel
component."

The SERVICES pulldown menu (technical services) has links to a few technical documents and tech notes that look useful: http://www.atlasmetals.com.au/index.asp

ALso see the info in the table at the bottom here, including the footnote about the other fillers that are OK with the 400 series stainless:

http://www.azom.com/details.asp?ArticleID=1178

[journyman]

Some creep, I get the info from years of replacing SS DI water lines at a major brewery, that is untill they switched to AL6xN, (which will still corode unless the WPS is followed meticulasly).

[Some Creep]

Originally Posted by journyman

Some creep, I get the info from years of replacing SS DI water lines at a major brewery, that is untill they switched to AL6xN, (which will still corode unless the WPS is followed meticulasly).

I've run pumps and UV systems in stainless on ultrapure DI systems for years and have never replaced a hard part yet due to any type of corrosion. What meg DI water quality is that?

Every chem resistance chart I have lists SS as an 'A' (excellent) for use with DI water, no notations for temp or alloy or any other limiting factor.