Using carbon diffusion?

[Iron Poet]

I recently started forge welding Chainsaw chain together and in my first experiment I used a mild steel flat bar just to have something to tie the chain to during welding. After I had forge welded all the chain down into a nice rectangular bar I folded it so the mild steel would form a sandwich around the tool steel, I figured that it would stop the actual usable metal from decarburizing. After forging it I was going to grind it off but I discovered that the mild steel wasn't so mild anymore. It instead threw off some pretty nice sparks, so I forged it flat sideways and made it so that the previously mild steel became the cutting edge while the chain formed a nice thick band in the middle of the blade. Now that the knife is hardened, tempered and razor sharp it has help up perfectly against ice, wood and cardboard without the edge rolling or crumpling like a tincan, so I'd be willing to guess that it's around .60% carbon.

This is really interesting to me as the differing metals have great contrast with the 'mild' steel while it also has great weldability. So making a decorative but still useable hammer for instance would cheaper and easier for someone with no money like myself. One of the many few problems I can foresee is getting the ratio of mild steel to high carbon/tool steel correct so that it can carburizes, While another problem would be forging it before all of the materials homogenize and you don't get a nice pattern.

I feel like there is at least a 60/40 chance that this is a really stupid idea but I just wanted to give you guys the chance to make sure.

[Steve Sells]

If you keep reading you will find out carbon migration happens much faster than most people realise. Also you are losing more carbon to the atmosphere than you are gaining from the fire.  welcome to the wonderful world of pattern welding

[JHCC]

I'm extremely reluctant to jump too far into this, as it is well outside my own experience, but as I understand it, unless you are only using simple carbon steels (10XX alloys), the patterns in pattern-welded steel come from other sources than simply carbon differences. For example, if one of your steels is a high-nickel alloy and the other is a high-carbon, you'll still get a high-contrast pattern, as the nickel doesn't migrate the same way carbon does. 

Steve Sells, would that be correct?

[Steve Sells]

The tests I read and referenced for my book stated clearly that there is nearly no difference in carbon content after the second forge weld course. so its not carbon that we are seeing.

Pure nickel is a barrier to carbon migration, but mearly being high nickel is not enough.

[JHCC]

I think what I'm saying (and again, this is well outside my own expertise) is not that the high-nickel alloy prevents carbon migration, but that the higher nickel content makes those layers shinier and thus increases the contrast in the pattern (i.e., independent of the relative carbon content of the individual layers). Does that sound right?

[Steve Sells]

nickel and/or chrome alloys will be brighter, higher levels of manganese increases darkness. so in many cases the plain 10XX series billets have layering visible due to Mn and a few other impurities. the carbon equalizes  too fast to be of any real issue

[JHCC]

Cool; thanks for the explanation, Steve.