Otto Nobedder wrote:I'll pose the question on the Welding and Materials forum on linkedin. There are several metallurgists there.
As for the beer kegs, perhaps the welds are not done electrically, or the metal is normalized after welding?
Steve S
Kegs are done in an automated machine and I am betting in a 100% argon environment so they don't have to purge them and it makes no sense to normalize a lowly beer keg. I also dug this piece out of my scrap pile. It is 304 but welded with 347 filler and the welds are not magnetic neither is the piece. I have 8 strips of that 304 in the pic and every single one of them attracts a magnet pretty significantly. Also LtBadd posted a short video of 312 filler rod being attarcted to a magnet but I have a 4" 312 threaded cap for an environmental well screen that is non magnetic. WTF?
Here are some 304l fittings with a magnet stuck to them. I have smaller fittings in my little storage box that are 304 and not magnetic at all. I don't get it.
I got great detailed responses to my questions on the Welding and Materials page. I'll copy and paste:
Magnetic attraction in the weld metal of Type 304 and 316 austenitic stainless steel is due to deliberate formation of ferrite in the weld metal. Fully austenitic welds are more susceptible to hot cracking and thus the composition of the filler metal for Type 304 and 316 is deliberately adjusted to produce ~5-10% ferrite to prevent hot cracking. If welds must be ferrite free then you would use an overalloyed filler metal. Check out the following publications
pg 15 of http://www-eng.lbl.gov/~shuman/NEXT/MAT ... avesta.pdf
pg 27 of https://www.nickelinstitute.org/~/media ... 1007_.ashx
And:
The austenite phase in Type 304 is metastable and less so in Type 316. This means that when they are stressed during cold forming they precipitate martensite. This is called strain induced martensite. This can be removed by annealing
see 46-47 of http://www.outokumpu.com/sitecollection ... ndbook.pdf
As you can see, the second reply supports Erich's statement about cold-forming producing martensite.
The first reply suggests to me that your beer keg may have intentionally been welded with an "overalloyed" filler, perhaps because ferrite and beer might not get along as one would wish?
The fittings you find that are or are not magnetic, the difference may be heat treatment after being drawn versus no heat treatment. I've encounter much Chinese 304 that is strongly magnetic, and I suspect the price reflects not annealing the finished part.
Otto Nobedder wrote:As you can see, the second reply supports Erich's statement about cold-forming producing martensite.
The first reply suggests to me that your beer keg may have intentionally been welded with an "overalloyed" filler, perhaps because ferrite and beer might not get along as one would wish?
The fittings you find that are or are not magnetic, the difference may be heat treatment after being drawn versus no heat treatment. I've encounter much Chinese 304 that is strongly magnetic, and I suspect the price reflects not annealing the finished part.
Steve S
Well there we have it. I never really gave two chits about whether my SS was magnetic and never thought to check before but it is a really interesting metal and gosh it welds nice but I have been ingrained to think all SS is non-magnetic when in reality it's not. Thanks China! Thanks for getting the info Steve.
Wow thanks Eric and Steve. That answers may questions. The one sample that I have is 304 stainless. I used 308 filler.
It must have had some of that ferritte in it.
Ill have to read the articles later, but realy interesting.
Maybe I should finish reading "metals and how to weld them"
Started to read it a while ago, got in 4 chapters.
Again thanks.
Danylo
