I decided to set myself a challenge and have a go at forging a blade I had not yet attempted the two layer deba knife. Half mild steel the other half in 80CrV2 sometimes known as 1080+ or 5160 on steroids. This is the construction of many single beveled knifes that you see when traditional Japanese bladesmiths forge tools. Importantly this construction only works for asymmetrical grinding because the hardenable steel should be on one side only. The major challenge this poses for the bladesmith is that when the steel hardens the martensite expands a little. So the high carbon portion of the blade warps with nothing to expand on the other half and push back against it. To guard against how dramatic the curve is proper normalization after forging should be adhered to. Another thing I believe the Japanese blade smiths might do is quench the blade on a bias… I noticed in some videos that instead of quenching vertically (i.e. blade edge directly down spine towards roof) they slide the steel into the quench soft cladding side down. I didn’t try this myself but if I have another go today I might. At any rate these measures will only minimise the warping at best. I waited until after hardening to grind the blade.
Heat treatment for 80CrV2 that I followed.
Forge to shape
Normalise at descending temperatures allowing to room temp in between 900, 850, 700. I soak at these temps for about 5 minutes when the steel is equalised. In the video you see my middle normalisation cycle.
Austenitise (harden) I chose to harden it from the lower end of the advised hardening range for 80CrV2, 840-880 degrees. I used a digital thermocouple reader for this as the lighting conditions vary in my shop. Colour is not a great gauge for temperature. I quenched into Houghtons G quench a medium speed steel. The added chromium and vanadium aid deep hardening in this steel so I feel no need to go for a fast quench and risk blowing the weld just yet.
I tempered this following the grinding at 190 degrees twice for 2 hours each allowing it to cool to room temperature between cycles. I will use hardness test files for a quick check of hardness. If I achieved maximum hardness in the quench the blade edge should be just above 60 HRC.
After grinding and etching I found that there was a small bit of delam near the heel of the blade which I will take out now the bade is tempered. In the next video I will show the final grinding etc. I want to hollow grind the back and see if by removing an amount of the 80CrV2 from the body the warp relieves a little before I go hitting the blade about too much.
