Homemade san mai question

[GaryPogueCustomKnife]

I have started my journey into forging San mai steel. I looked around at the steel scrap I had lying around my shop. I settled on using a old airgun barrel for the outside of the steel, since it has low carbon content. I threaded the ends so i could put bolt on either end to enclose it. I swept up all of my high carbon steel dust, which ranges from 1095 to old high carbon file dust. I heated up a old garage door spring and straightened it out into a straight bar of spring steel. I put the spring inside the barrel and filled the excess space with the steel dust. I enclosed it with the bolts and started forging and fluxing. I ran out of charcoal half way through.

My question is do you guys think it will turn out ok enough to be used as blade steel? I ground the half I did flat and the welds appear to be good. It also sparks really well to. I will finish the forging on the next nice free day I have. I will post the results when I am finished. Another thing is what should I use as etchent?

 

[A C Richards]

The way you described it no I do not think it will make a good blade. Barrel steel is normally 4140 but an airgun is probably not even that. Your steel dust is not a good way of getting high carbon steel powder. The sparks are quite hot and will possibly burn off any carbon they may have. I have not done any testing so i am making an educated guess there. You are also picking up crap that should not be in the mix. I have been tempted to do the same from time to time but I don't want the aluminum oxide and concrete dust mixed in with my steel.

Another problem is the spring down the middle of the barrel. There is not enough steel there to prevent excessive carbon migration thus rendering the steel all the same carbon content. Proper San Mai uses a full width high carbon steel core. Not a thin tube. There are other forms of steeling the edge but you asked about San Mai.

 

[GaryPogueCustomKnife]

A C, I should have mentioned that i separated the AO from the steel dust with a very powerful magnet. I did this multiple times to achieve nearly 100% pure steel. The width of the steel is roughly 3/4 inches wide. Wehen I ground it on my grinder, it gave off great sparks. People make san mai with wrought iron, so the gun barrel on the outer art of the steel shouldn't be a big issue. The only reason I don't weld a billet together is simply because I do not have welding equipment or a press.

 

[A C Richards]

Yes we do use wrought to make San Mai. The proportions are important though. An airgun barrel is either .177 or .22 inches. So you probably have 5 to 10 percent high carbon to 90 95 percent medium carbon at best. Then carbon migration occurs at .01 inch per hour at 1700f. The thinner and hotter it gets the faster it occurs. If you are using .177 bore you have about an hour at welding heat before all the carbon is disbursed. So at best you are going to have 1041 or 1042 material. Will it make a knife that cuts? Sure just how often are you willing to sharpen it.

You should use more equal proportions of material. Yes it might spark nicely but what do you have, no way of telling. How are you bringing the center out to the edge? That is going to be interesting to. I forged many bullets by hand including my first San mai. It is doable and is not that difficult. Use some wrought and a piece of leaf spring, this would give you a much greater chance of a survivable knife than what you described.

It is good you are thinking outside the box, I just think this one was a little too far outside. Now if you had split the barrel and used it for sides with a larger core that would be more realistic imho.