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Conner Michaux

What exactly is flux?

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Now that i've got my forge sorted out I want to see if I can forge weld something. Two pieces of mild steel. Just an experiment and i'm interested to see if it will work. Basically ill just flatten out two pieces of 1/4 round mild steel get it really freaking hot, put the two pieces on top of each other and tap them together. My question is should I use flux? What exactly is it?  If i'm not mistaken its just borax right?  Kind of a stupid experiment, but its kinda cool.

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Keep in mind that welding mild to mild requires more heat then welding blade steels together. The more carbon a steel has, the lower the welding temp becomes. 

 

You should use flux. You dont need flux to weld, but when you're new at this, use every advantage available to you. Stack the deck in your favor.

 

You can use borax as flux, yes. You can also use sand. Or about a thousand other things.

 

Borax is sodium tetraborate, a salt of boric acid. It can be found in Walmart in the laundry detergent section. It can be used as laundry soap as well as flux and many other things. 

 

A lot of people will take and "bake" borax, heat it up in the oven for example, to drive off the water present within. This is then called anhydrous borax.

 

Now generally speaking, flux is any substance used in metalworking to shield metals from oxidation, and promote melting and flowing (in soldering.) We use borax while forge welding to shield the very hot steel from oxygen, as the borax melts and creates a glossy barrier between metal and air. Borax also has the benefit of being caustic while molten, so it also slightly etches the steel and cleans it. 

 

Flux is used with many welding processes such as stick welding and soldering. 

 

It's a broad question, I hope I answered it well for you. 

Edited by Will Wilcox
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Thanks for the info, Answered exactly what i was looking for.

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That was a pretty thorough answer from Will.

 

I might just add, clean your steel up too!

Look for "20 mule team borax". 

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I tried three times, failed all attempts. Got the steel to a bright yellow sprinkled some flux, tapped it together. Nothing. 

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4 hours ago, Conner Michaux said:

I tried three times, failed all attempts. Got the steel to a bright yellow sprinkled some flux, tapped it together. Nothing. 

You need to add the flux well before that, or your surfaces will already have formed scale. You can add borax before you heat up your steel, though it doesn't stick then yet, or heat it to a dull red, so it melts directly onto the steel. When welding two or more pieces together, it's commonly already attached together. Most use a few tack welds, but if you don't have a welder, you can use some steel wire to hold the pieces together. Then apply flux at the gaps, and let it melt in between. Heat up to the point the borax starts to smoke, and gently tap the pieces together (soft hits, fast across the surface). When the pieces have joined, you can start to hit with more force again. It will take a few welding runs to make the join solid all the way. 

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What Jeroen said. 

 

Tack weld your pieces if possible. Making your pieces flat, clean, and clamped tight before tack welding all help a lot.

 

Heat the billet to where it's still a black heat (hasn't started to glow yet) as any red or orange color is associated with scale formation, the enemy of good welds. Then sprinkle flux on any exposed gap between the two pieces, and put it back in the fire. Let the flux melt and find it's way in between the pieces as you're taking it to a welding heat. 

 

I weld based on color, it takes some trial and error to figure that out, as everyone sees colors a little differently, but what Jeroen said about the smoke is another really good indicator. The billet should look like it has smoke or steam coming off of it when you take it out of the fire.

 

 

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10 hours ago, Conner Michaux said:

I tried three times, failed all attempts. Got the steel to a bright yellow sprinkled some flux, tapped it together. Nothing. 

 

Conner,

 

Forge welding is primarily temperature control.  It sounds like you weren't hot enough.

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This has already been stated, but just to make it clear, flux has two purposes:

 

1. Primarily, iIt covers the metal with goo to keep the surface from reacting with the air around it and forming scale (oxides)

2. Secondarily, it has some ability to dissolve oxides that are already there. (It can't clean off heavy scale though)

 

Now that you know what flux is for, you can reason out how to use it.  As soon as the metal is hot enough to get the flux to stick to it, put the flux on.  Hopefully you get this done before the metal is hot enough to create a heavy layer of scale.  The molten flux will keep the metal clean underneath until you have time to close the weld.

 

Temperature and cleanliness are the key things.  For mild steel you will need to be at nearly a "White hot" temperature.  I use 1095 a lot and would describe the temperature for welding it as a "butter yellow".  If you use borax, it has a nice tendency to start to boil frantically at about the right temperature.

 

I got away from using flux for quite a while, and would encourage you to do so as well once you get the hang of it.  It's messy, and eats up the forge.  It can also become an inclusion in your weld.  A while back I started doing some welds that seemed more complex and I krept back to using flux as a security blanket.  I could almost "Feel" the scale forming on the unwelded bits of my work, so I started slathering things with borax again to keep them safe :)

 

Edited by Brian Dougherty
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8 hours ago, Jeroen Zuiderwijk said:

 Heat up to the point the borax starts to smoke, and gently tap the pieces together (soft hits, fast across the surface). When the pieces have joined, you can start to hit with more force again. It will take a few welding runs to make the join solid all the way. 


The only thing I'll add is that many of us will immediately return the piece to the forge after the initial 'soft hits' that close the weld (and depending on the size of the billet, may do multiple, what I call "setting" heats), before starting to actually forge the piece.

 

Just keep adjusting, trying, learning....repeat as necessary, or until is no longer enjoyable. ;)

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2 hours ago, Brian Dougherty said:

I got away from using flux for quite a while, and would encourage you to do so as well once you get the hang of it.  It's messy, and eats up the forge.  It can also become an inclusion in your weld.  A while back I started doing some welds that seemed more complex and I krept back to using flux as a security blanket.  I could almost "Feel" the scale forming on the unwelded bits of my work, so I started slathering things with borax again to keep them safe :)

 

I had stopped using flux too, but seeing as how I haven't been able to do any forging for the past 10 months, I'm probably going to use it for the first few billets when I get my forge set up again. 

Which looks like it may be in a week!!!! (insert happy-dance/jig emogee here)

 

One thing that can help with the mess and preserve the forge floor is to put a layer of old fashioned clay cat litter in the bottom of the forge before firing it up to soak up any flux.

 

And (not trying to be nit-picky here, Brian.  Or critique your technique, because slather is quite a vague amount:unsure::P), but one last thing Darryl Nelson (not a bladesmith, but arguably in the top 5-10 blacksmiths in the world) says every time he demonstrates forge welding, "Remember, flux ISN'T glue!" 

 

Have fun!  Can't wait to see the damascus you start doing in a couple of months!

Edited by billyO

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What mild steel are you using 1018-1020   or I think the junk stuff is a36....or something like that.

I tried a san mai a year or so ago with the a36 or what ever it is.....it sorta stuck but not well enough to try and grind a blade. 

If I try again I am gonna use some 1018 or 20 and use kerosene initially/before going in the forge...and then borax after.

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Thanks, I don’t actually know what steel it is, all I know is that it’s mild steel from Tractor supply.

Edited by Conner Michaux

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16 hours ago, Will Wilcox said:

A lot of people will take and "bake" borax, heat it up in the oven for example, to drive off the water present within. This is then called anhydrous borax.

Sorry, but this is not correct.  While baking borax will help dry it of the excess moisture that any milled item will absorb (Sugar, salt, flour, etc), the max temperature of an household oven is less then half the temperature needed to remove the water molecules in borax Na2B4O7·10H2O.  Last I checked, it needs more then 1300 degrees, which is near melting temperature of borax.

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Right you are Gerald! 

 

I meant to drive off moisture, not to remove chemically bound water. 

 

Thanks for the clarification. 

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1 hour ago, Conner Michaux said:

Thanks, I don’t actually know what steel it is, all I know is that it’s mild steel from Tractor supply.

The stuff at hardware stores is generally more along the lines of A36 and not likely to be 1018.  The metallurgy of A36 isn't very tightly specified, and it doesn't matter what all is in the steel as long as it meets a minimum strength requirement.  That means it can contain a number of other elements that make the welding less than predictable.  No harm in playing around with it, but if all of the other parameters seem like they should be right, you might end up frustrated for no good reason.

 

2 hours ago, billyO said:

And (not trying to be nit-picky here, Brian.  Or critique your technique, because slather is quite a vague amount:unsure::P), but one last thing Darryl Nelson (not a bladesmith, but arguably in the top 5-10 blacksmiths in the world) says every time he demonstrates forge welding, "Remember, flux ISN'T glue!" 

I absolutely agree, and almost wrote that.  "Slather" was used to make the process sound less than attractive :)

 

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The best advice I can give if you are trying to weld a36 mild, which is probably the majority of what I've welded with, is that it almost needs to be white hot. If you have big enough pieces, you can even watch for the steel to begin to burn and that's about your best time to hit it.  However for little stuff under 1/2 an inch, its probably not going to blend out and you can be left with a nasty looking carbonized section. 

 

I watch for the steel to become one color, if there happens to be a shadow in the two pieces where they are meeting, its not ready yet.  Continually rotate the stock to make sure the heat is even throughout the two meeting pieces.  Depending on the size of stock, your welding passes have to be fast.  Striking it below the welding temp can cause the weld to fail.  I work with some fellows that do as many as 5 welding passes to ensure their welds stick, the more passes you do, the better chance the steels will fuse.

 

Don't forget about scarfing the pieces either, depending on what your doing.  You can work a cold shut right into the pieces which causes failures. 

 

I did some fire welding with some low carbon steels this summer, and I was surprised at how easy it was in comparison to mild steel.

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