General welding questions that dont fit in TIG, MIG, Stick, or Certification etc.
exnailpounder
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My report. The strips of SS I have (pictured) are absolutely magnetic so didn't even bother to polish one to see if it added magnetic attraction. I have a brand new sheet of 1/8"304 SS plate that I just picked up for a job that is not magnetic whatsoever and the magnets do not stick to my 304 SS beer keg casting furnace that has been heated to over 1500 degrees inside and the outside gets way too hot to touch on the outside. I tried the shroud on my burner that is 304 and gets cherry red when I use it and it's not magnetic at all so apparently heating SS doesn't induce magnetic attraction...so why does welding?. I thought because these little magnets are so strong that they were able to stick to the very slight magnetism that SS has but they do not. I sent in this pic because if you read the print on the strips( ya gotta stand on your head...sorry) it clearly states it is 304l and is magnetic. What alloy of SS is this? I don't have any other SS to polish at the moment but when I cut up the SS plate for my job coming up, I'll polish a piece and see what happens.
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Poland308
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I think the bar is magnetic because of it being roll formed. Welding ss causing it to become magnetic I believe happens because of the electricity from the process realigning the molecules in a parallel direction. The heating it up beyond a certain temp ( not sure exactly what temp) with flame allows them to randomly realign, relieving stress and magnetism. You could confirm this by welding ss with oxy/ acetylene.
I have more questions than answers

Josh
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Poland308 wrote:I think the bar is magnetic because of it being roll formed. Welding ss causing it to become magnetic I believe happens because of the electricity from the process realigning the molecules in a parallel direction. The heating it up beyond a certain temp ( not sure exactly what temp) with flame allows them to randomly realign, relieving stress and magnetism. You could confirm this by welding ss with oxy/ acetylene.
You could be right about the cold forming but is strip cold formed? I thought SS came in a natural non-magnetic state because the manufacturer doesn't know what application the metal will be used in and magnetic metal can spell trouble in some applications. Interestingly enough...the welds on my beer kegs are NOT magnetic and beer kegs are pressed into shape and welded around the circumference...so they should be magnetic right? I'm scratching my head right now.
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Poland308
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We need a metallurgist fromiliar with the manufacturing proscess in the forum.
I have more questions than answers

Josh
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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
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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?
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exnailpounder
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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.
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Erich
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The microstructure of annealed 300 series stainless is Austenitic. This is non magnetic.

Cold rolling Stainless forms some amount of Martensite. This microstructure is magnetic.

Heating and quenching is another way of forming Martensite. There can be a bit of that going on in a weld puddle.
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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

For any questions about stainless steels and nickel alloys check out the Nickel Institute website
https://www.nickelinstitute.org/
You can even ask questions
https://www.nickelinstitute.org/Knowled ... lHelp.aspx

Credit goes to a gentleman named Geir Moe.

Steve S
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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
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This also suggests that polishing is not likely to make anything magnetic...

Steve S
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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.
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Poland308
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Yes thanks!
I have more questions than answers

Josh
Danylo66
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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 :D
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