When you work with knife steel there comes the moment you want to harden the steel. There are companies offering it as a service – and as I am living very close to Solingen, which is world famous for its long history of blade industries – there is most certainly a company who could do that for me. But is there anything more beautiful than a piece of red hot glowing steel?
I had looked up some dealers on the internet who offer gas forges or electric ovens specialized in this task. Especially the electric ovens are way too expensive for what is needed to build one. The approach with a gas torch looked like the best solution for me to start with.
I read about aerated concrete as a cheap material which could withstand a pretty high amount of heat – and so this was the way to go for my first knives. As i only do stockremoval I would not need extremely high temperatures and especially not over a longer time.
I bought 8 Blocks and stacked them to a simple forge inside my garage. Also I bought a short gas torch with three different burners online. To harden my first knife I just put the steel in the forge and held the torch in my hand and blasted inside the front opening of the forge. That worked out better than expected and I put the cherry red steel into the oil.
One big thing is that the burned gas and heaut that comes back out of the forge could suffocate the torch itself so i moved the top concrete blocks a bit and put the torch between them. That worked better but the problem stayed. I put some holes in the burner caps to have air being pulled in by the stream of gas and this is where I have to work on further. The results get better but I will have to build something like a Venturi Burner which builds up a steady air and gas flow from outside the forge.
Disclaimer: I do not recommend to build a forge this way. This is dangerous and could result in fire or injury. Opposite to the picture taken for this post I only operate the forge when the garage door is open.