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San Mai forge welding problem


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I tried to create a San Mai knife so I prepared the low carbon(scrap pieces) and the high carbon(file steel). Ground them clean, tag welded them together. All simple so far.

I'm not sure if that's an issue but I only have simple borax not the anhydrous(I could bake it but I'm just not sure if it would make any difference).

Before forge welding I brought it up to red heat, brushed off the scale from the sides and covered it with borax(though it felt like none of the borax could get between the layers).

I forge welded it 3 times to make sure it's done(waited until the first sparks appeared and hammered it lightly), Though I couldn't see any borax spraying out between the layers(again it felt like the borax was not even there).

After it cooled down I started bending it a couple times in a wise and the layers got seperated.

Any advise how to improve my procedure?

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How is your forge welding on other projects?

When I do San Mai I start with thicker and smaller pieces and then draw out the billet. This way the weld is done on a smaller surface area. I'm not sure how clearly I'm explaining this. The welded billet is much shorter and narrower than the finished knife. The mass is in the thickness.

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Did you only apply the borax the one time? After each time you go to set the weld try brushing and reapply borax. 

The borax mainly acts as a barrier layer to keep the metal from oxidation, it is not glue. 

If using a solid fuel forge, good fire maintainence is also very important. 

There are several threads on here on forge welding with many good helpful tips. Try searching in your web browser with "iforgeiron" after it and you will get better results then with the sites search function. 

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A few good things to remember

1) thicker sections hold heat better than thin sections which is important  to forge welding

2) Virgin steel is exposed when drawing out the billet, insuring a clean weld if you remember to do this at welding heat with thicker sections

3) one should only pre weld/tac the starting billet at one end, not on all sides to allow for slippage when heating rather than buckling up when it has no where to go

4) allow ample time soaking the heat to get inner layers up to temperature

5) brush between welds

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And don’t beat the podunk out of it. Firm solid blows will set the weld, jumping in the air with a 6# hand sledge and trying to put all your muscle and weight into the swing won’t do anything but get you on America’s funkiest home visions.

Steve can coerce some finicky steels to weld, and is very clear and concise. Don’t try to read to much into it, he isn’t hiding any magic tricks from you. Clean (before starting to heat, appropriate flux to melt before oxides form and states around long enough to get the weld done), flat ( well matched close firing serfaces, with scarfed joints in other welds the first blow brings the serfaces together) hot ( heated all the way threw, slow soaking in a fire just above the welding temp of the particular steel. Think perfectly toasted marshmallow vs a burnt one hard in the inside) pressure ( this is a solid hit from the hammer that doesn’t bounce much or a steady presure from a press). Get all of them close to right and it sticks, get 2 perfect, one close and one not grossly off and it will probably stick. As Thomas and others have pointed out, NASA has had access panels weld shut in space (clean, flat, just enough pressure and almost no heat). 

Biggest eye opener was Steve “slow roasting” and turning steel to evenly heat it all the way threw. 

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I"m a newbie, but I did manage to get from exactly what you experienced, to several welded blades (pattern and san-mai). So here are my 2 cents:

1. Sounds like your fluxing isn't good enough. The borax gets between the plates only when it melts, and it take a good heat for that. Flux as you did, and make sure the borax melts. Heat the steel again and flux some more all around. After each hammering session, flux more.

2. If you use coal forge, note that the coal may brush the un-melted borax off your piece, as you push it into the forge. You may want to toast the piece in the flames first - marshmelow style.

3. Heat loss is your enemy - move fast from forge to anvil with hammer in hand. minimum contact with anvil. thicker material ect.

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Thomas Powers mentions often that with a solid fuel forge, you can get your fire very hot (lots of air) before you put the billet in. Then insert the billet into the fire and cut the air completely to create a very reducing atmosphere. Once its up to a red temp, remove, brush, flux, reinsert into fire, and go for welding heat (using air obviously.)

I have a different method than the above one, and its given me a lot of success. I always tack weld the corners of the billet before forge welding, so ill make all my arc welds fairly quickly to build up heat in the billet, and as soon as im done with the last weld (or after you weld a handle on, if you prefer) sprinkle borax on. Theres usually enough heat to just barely melt the borax. This way, you can put it in the fire and go.

In any case, good luck with it.

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Yesterday I tried it again, flattened 3 bearing balls, cleaned the surfaces, welded them to a handle with mild steel.
First I thought that my fire was too oxidizing so I made sure the whole welding area was well coated with borax. I sprinkled the borax while the steel was still black so not much scale formed.

Forge welded them 3 times and I used a piece of wood as an anvil so the heat wouldn't be sucked out of the pieces so fast. But all of them came apart after hammering hard on the sides.

Maybe I should have tried to forge weld mild steel to mild steel first. I'm thinking about that the chromium from the bearings maybe messed up the welding. I should have used more steel because after one hammer blow the temperature was already too low.

I hope next time all works out.

Thanks for the advises!

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52100 type bearing steel is not easy to forge weld at all. Also I definitely wouldn't use wood under the billet, it makes your hits real weak, as it has no rebound. Thinks me.

Good idea on the MS on MS learning. Also try to use some plain high carbon steel to test yourself at HC + MS welding.

Also apply borax when the billet is at orange heat. It clears the already formed scale off. Stops the scale from re-forming, but the flux burns off if you apply it too early.

That's all I can tell you now. Hope it's helpful.



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4 hours ago, laliman said:

But all of them came apart after hammering hard on the sides

how hot was the billet when side hammering? 


Also, I have forge welded 52100 (typical ball bearing steel) to W2 a few times, and every time  I did any hammering I had to kep it above the non-magnetic threshold. I found (with my limited experience) any cooler than that and the materials would stretch too differently, 52100 being VERY stiff, and would lead to weld failure/shear.


Good luck! 

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I posted last July (first San mail knife), took me number of billets to succeed, didn't have enough heat/heat soak, and you must not waste anytime getting to the anvil plus don't allow anvil to act like a sponge drawing out the heat before you hit it, but more of a strong set of taps, later heats still use flux ,but you hit harder. Billet will sound like thud if not welded, and ring like when bonded, hard for me to describe hope I helped now I still have to find time to finish those billets

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The issue with 52100 is the fact that it contains 1.3-1.6% chromium, the oxide produced even in such a small percentage like this is going to create issues similar to forge welding stainless. The less oxygen the better. Just grab yourself a $13 piece of 15N20 flat stock and be done with the scrap metal woes. While we assume your ball bearings are 52100, there's also a chance they could be 440C, ACD34, SV30, 316SS, 4320 or even microplated 1070M - A scrap shoot is a crap shoot and you can't learn metallurgy by making a bunch of guesses and assumptions. By the time you're done throwing money at consumables and fuel, you could have spent less and with a few clicks had the right materials sent to your door - not to mention the fact that with exact details others on here can give you exact answers, something not true with mystery metals. That's my $0.02, now back to the shadows before anyone realizes I'm here.


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