Today, after finishing with my bonsai trees for now, I got an hour or so to use and get a shot at hardening the blade.
I was so stressed from working almost non-stop the whole weekend and trying to manage to replant all my outdoor bonsai trees that I forgot to take pictures of the process and only could take pictures afterwards. So here is a picture of my setup. I was hardening two blades.
Slight contrast with Marcus’s fully equipped workshop I guess :-). On the right is gas mini-forge where a future kitchen knife was heated up most of the time, on the left is a charcoal fire between fireclay bricks for the dagger and in the middle is quenching oil. This is the main reason why I cannot harden blades in bad weather – I have to go outside to do it.
And here are the blades after hardening and before tempering, covered in burned oil and, in the case of the dagger, slag and scale.
I am not all together sure It was a complete success. I am sure it was a 50% success. I definitively successfully hardened the kitchen knife. Which is slightly strange, because the kitchen knife is made from N690 steel that is allegedly difficult to harden in impromptu settings, whereas the dagger is simple carbon steel that should have been easy-peasy. The kitchen knife is completely without deformation, the dagger got a very slight bend that I was able to correct after tempering the blades in kitchen oven at 150°C for an hour. In fact, it was maybe too easy to correct. File skids on the kitchen blade like on glass, but it is possible to make a shallow bite with it into the dagger.
The problem might be that I tried to coat the dagger with an experimental anti-scaling solution that unfortunately did not work as intended. Back to the drawing board there I guess. So it might be that the blade is hardened, but a few tenths of a mm on the surface have slightly lowered carbon content due to decarburization. The N690 steel blade was not covered in the solution, but was covered with stainless steel foil that burned through towards the end.
I have no way to measure the hardness of the steel, and I am probably not going and try to re-harden the blade. I will proceed and we will see what comes out of it.