Forge welding - Mild Steel - Questions

[Malice9610]

So I am new to this whole blacksmithing thing, have been actively smacking hot metal with a big hammer since about the second week in January of this year. 

Today, I attempted forge welding for the second time,  The first time being a Rail road spike, i tried to fold it on itself, it failed in a spectacular fashion as to be expected when a newb does something beyond their abilities. 

I took some 1/2 inch flatbar ( A36 I think. not exactly sure. ) and cut it to 6 inch lengths and stacked it 4 deep ( bar 3 is longer to use as a handle ) heated it, fluxed it, heated it till a coat hanger stuck to it,  and then lightly tapped it.. 

Eureka.... Success, I was able to feel the difference tapping once the 4 layers had bonded. So I wire brushed it all off, refluxed it, and stuck it back in the fire.. 

And thats where things went wrong. I was able to forge weld about the first inch or so of the 6 inches, but no matter the amount of flux, nor the heat I reached I could not get the rest of this " Test Billet " to forge weld. 

I suspect that the flux ( I did flux the entire piece, not just the first part ) burned off further down and scale developed which prevented the success after the initial heating. 

So I spread it apart and sure enough, there was scale in between the pieces, I should add that i took each piece to my new belt sander, and made sure the metal to metal contact was pure metal, no scale or oxy layers before I started. 

 

So my questions are these. 

Is it better to heat the entire billet, and attempt to forge weld the entire length in a single heat, rather then attempt to do it in sections ? 

It would seem based on my results, that doing it that way would be the most likely to work, However I have seen youtube videos where they did multiple heatings to get the entire billet welded, I would guess the placement in the fire had a lot to do with the success they had where I failed. 

Since forge welding mild steel occurs at a higher temperature then forge welding high carbon steel types, and you have to be careful not to burn the steel, Its obvious I have the needed heat level to forge weld High carbon steels ( O1 specifically as thats what I have on hand ) So my next question is 

I Plan to attempt to forge weld O1 to a Rail spike tomorrow for a " Rail Knife " that is a real knife. My thoughts are to split the spike, let it cool , Flatten a bit from the O1, cut the O1 to match the current blade length, clean the crap out of both pieces, heat the spike, clean and flux while still hot, insert O1 and place in the forge " edge up " so the spike / mild steel takes the brunt of the heating forces, and use the " coat hanger " trick on both parts of the knife to check for forge welding temp.

Is there a better way to do what I am attempting to do?

I have watched a few different videos on ' Bitting a Hatchet/Tomahawk/Random metal project " with O1 and Rail spikes specifically and item placement in the fire with relation to the different specifics of each steel is never covered nor is placement in the fire. I am on a limited budget, so wasting quality steel is not an option for me, the spikes themselves are free to me, but the O1 isnt something I want to burn up experimenting if I can help it. 

Ohhh, and here is a cross section of the forge weld I did today. There are some minor lines on one side, however I will say I did not do much hammering on the cross section of the weld, I would say I MIGHT have hammered the cross section of the weld once on each side, with the majority of the work being to push the stack together more. 

 

Any suggestions that might prevent the waste of quality O1 steel would be Greatly appreciated, Thank you everyone, I have already learned so much from lurking on this site for the past few months, Now that I am moving beyond working with mild steels and basic shaping, I certainly hope to learn a great deal more. 
 

[BlackKnight0739]

First off, great weld! Looks really nice!

Practice a LOT before attempting to weld your O-1, but other than that you're on the right track. I don't personally use the coat hanger trick as it takes precious time to conduct, what I'd suggest is to use it until you can recognize welding heat when you see it without the test. Forge welding is all about speed, accuracy, and just the right amount of force behind the blows. Tapping lightly is the key to it, which it seems you have learned

"Is it better to heat the entire billet, and attempt to forge weld the entire length in a single heat, rather then attempt to do it in sections?" A single heat is best in nearly every circumstance, as it takes less time and fuel to perform a task. If it's possible to forge weld it in one shot, do it.

Keep at it and you'll be there in no time!

[Frosty]

You don't want to heat the steel bit and insert it into a cold body, that's backwards. The bit being hot won't penetrate the slit completely and will shrink as it cools. The spike isn't going to heat right up so it'll suck the heat from the bit making a loose joint. This invites inclusions, crud will literally get sucked into the gaps by capillary action as it cools.

Instead, slit the spike and forge the bit with a slight wedge shape full length. Clean the snot out of it like you are, the shinier the better. Flux the slit in the spike and begin warming it, when the flux begins to melt drive the bit in. The cold bit will be hard enough to cut itself into the spike at the bottom of the slit and the molten flux will keep air off it. Then gently close the slit on the bit. Flux the joint and bring to welding heat, let it soak a little and set the weld. Then clean, flux and refine the weld twice. It should now be a done deal.

Frosty The Lucky.

Edited February 22, 2015 by Frosty