Welding Tips and Tricks

Hi, newbie here,
Wanting to know how best to weld 4340 low alloy steel blocks 2"x2"x3" to 1/2" x 3"x 4"mild steel plates to mount ]. They are the dies [1 upper die and 1 lower die], for an air hammer I am building to forge knives - save my arm after 22 yrs by hand. [TIG preferred, or Stick + what rod?]

On your video to weld 4130 low alloy steel you recommend E70S2 mild steel rod, to preheat part, and go slow. Is this the same method/rod with 4340 low alloy steel? It has a bit more carbon and the addition of nickel to the chrome/molly mix.

Even though forging or forge welding the steel is hot [1500F. - 2500F. - forging to forge welding range], and therefore plastic, mild steel as dies just don't hold up and the 4340 like the 4130 steels work harden besides, make great dies.

Couldn't find it in the forum search, but maybe I am not using it correctly, so decided to post my question here.

DB

There are far better qualified here that I expect will chime in - but the laymans answer is if you Tig dissimilar alloys then 309 ( L / LSI ) is considered the norm - but on bigger pieces such as yours I would stick weld them - again with a dissimilar rod such as Esab almat - these are usually in the austenitic stainless group with a general designation between 309 / 312 according to make.

Sounds an interesting project & welcome to the forum.

I think, in this case, 4340 to mild (a36?), the ER70s-2 Jody recommended for 4130 should be a good choice, especially if you intend a pre- and post-heat/slow cool. I'd normally be in agreement with 309, but for an air-hammer, I'd like to see a more consistent carbon-content change across the weld profile. I'd suggest a 3/8" weld in three passes.

The other option would be a higher nickel content filler, like used piston rings (Don't laugh, it works).

Edit:
Another though would be to silver-braze the parts together (If you're competent at the process), because you'll not affect the hardness, and won't crack a weld.

Steve S

used rings really woulda never thought of that learn something everyday

JDIGGS82 wrote:used rings really woulda never thought of that learn something everyday

Thank WerkSpace for that one... He pointed it out on a cast iron-cast/steel thread a long time ago. Basic cast steel piston rings have a relatively high nickel content.

Steve S

Thank you one and all for the feedback.

Also, thanks Otto for the new nickel source. Any idea of the carbon content? Might make interesting pattern welded billets w/ maybe mild steel, enough folding and layer count, get lots of carbon migration, water down the 2-5% C to 1% to be useful.

Can't wait till I get the chunks of 4340 in the mail to start the dies. See how the hammer goes from there. Next hurdle is the anvil of massive weight - 10:1 or more to the tull. Difficult to find cubic steel on the island to achieve this.

David

I'm asking, not telling. Would the Hastelloy W rod Jody talks about work in this application? Or 312 stainless?

Bill Beauregard wrote:I'm asking, not telling. Would the Hastelloy W rod Jody talks about work in this application? Or 312 stainless?

That's a good question. Maybe I'll "poke the bear" and see if I can get Jody to comment on this thread. I know he's extra busy just now, but I'd bet he can answer the original question off the top of his head, and this one as well.

Steve S

Attenurb wrote:Hi, newbie here,
Wanting to know how best to weld 4340 low alloy steel blocks 2"x2"x3" to 1/2" x 3"x 4"mild steel plates to mount ]. They are the dies [1 upper die and 1 lower die], for an air hammer I am building to forge knives - save my arm after 22 yrs by hand. [TIG preferred, or Stick + what rod?]

On your video to weld 4130 low alloy steel you recommend E70S2 mild steel rod, to preheat part, and go slow. Is this the same method/rod with 4340 low alloy steel? It has a bit more carbon and the addition of nickel to the chrome/molly mix.

Even though forging or forge welding the steel is hot [1500F. - 2500F. - forging to forge welding range], and therefore plastic, mild steel as dies just don't hold up and the 4340 like the 4130 steels work harden besides, make great dies.

Couldn't find it in the forum search, but maybe I am not using it correctly, so decided to post my question here.

DB

Hey there, This is Jody

there are a bunch of ways you could weld 4340 to mild steel. So you might choose one your good at.

for Tig welding, I would use er70s-2 or er309 stainless. The last job I did welding thick 4140 steel , both rods worked well provided I used a 500f preheat. preheat is the key to success on anything with that much carbon.

I would lean toward er70s-2 because its cheaper and seems to work every bit as well.

If you are better at stick, that is a good choice also. Again preheat is the key. along with slow cool.
It sounds like you are just welding those 4340 blocks onto a base plate made of mild steel using a fillet weld all the way around so a 7018 rod will fit the bill just fine but just make sure the 7018 rods are either new out of the box or hav been kept in a rod oven. 309 or 312 stick welding rod will also work with a preheat and slow cool but cost about 3-4 times as much as 7018. I would preheat even before making the first tack weld. Tack welds should be a bit bigger than normal due to the tendency for really small tack welds to crack on low alloy steels....also, inspect the tack welds for cracks.

in case you have not seen it, here is a link to a video where I was tig welding 4140 high strength steel. its very similar to 4340 as far as weldability.
http://welding-tv.com/2013/12/03/tig-we ... gth-steel/

Preheat and slow cool no matter what process you choose.
What you want here is a ductile weld that will survive lots of cycles of compressive stress and also lots of thermal cycles from the hot knife blade...so the under matched 7018 rod should work well.

Hope this helps,

Jody

Otto Nobedder wrote:

Bill Beauregard wrote:I'm asking, not telling. Would the Hastelloy W rod Jody talks about work in this application? Or 312 stainless?

That's a good question. Maybe I'll "poke the bear" and see if I can get Jody to comment on this thread. I know he's extra busy just now, but I'd bet he can answer the original question off the top of his head, and this one as well.

Steve S

Steve,

I just replied to the original post so I might as well weigh in here too.

Hastelloy W would definitely work but has become super expensive at over 100 bucks a pound.

312 ss would work too.

but I really think a good ole 7018 stick along with 500f preheat and slow cool will do the trick for this.


Best,

jody