This forging thing is not quite as easy as it looks , so far one blade cracked in heat treat and one cracked tang in the forging process , but I will stick with it . No piece of hot metal will get the better of me.
I don't know how many blades that I've broken unintentionally but it's up there. They all seemed to have good grain structure so that was a small comfort. Make sure that you're not hitting the steel when it's too cool and watch out for stress risers before quenching.
There is certainly a learn curve to it..... but after about 100 blades, the hammer STARTS learning what its suppose to do! The majority of forging is all about developing "muscle memory".......but with each new idea comes new things to learn, and figuring out ways to do what you want. I think that's the reason I've been at it so long, and keep doing it.....because every day I work in the shop.....I learn something new and exciting (at least new and exciting to me).
Stress risers are things that increase stresses in steel, especially when quenching which pretty much maximizes stress in the steel all by itself. That's why you really don't want to delay putting a fully quenched blade into a tempering oven. One of the biggies is sharp inside angles. Always round them off just a little. Course grinds can also raise the stress. I like to grind out to about 200 grit before quenching and I might well consider going out to 400 grit if I were going to try a brine quench. Some things just can't be helped, like different thicknesses in the steel, like the difference between the thickness of a blade at the spine and the edge. Differential hardening increases stress too but if you want to make a hamon you are just going to have to risk breaking a few blade. If you have ever seen the video of a Japanese swordsmith quenching a blade in water you would be amazed that any of the blades survive the treatment.
Thanks Doug , I have seen some videos of the Japanese quench and it is amazing . The blade I cracked was ground to 220 g and stress relived , I think my problem was using the Forge as a heat source as opposed to my Evenheat oven were I could be more accurate with my quench temp as well as doing a water to quench oil . I should have just gone directly to the fast oil. The Grandkids are gone so first thing in the morning its out to the shop.
I suspect each has their own "order", but personally, when I forge a hidden tang, the blade is forged first, then the tang. I go just the opposite way when forging a full tang......tang first, then the blade. I tend to produce mostly hidden tang knives....mainly because I have both a press and air hammer, and I can produce hidden tang blades quicker, with less material then what a full tang requires. I also find it quicker and easier to rough/finish grind a hidden tang versus a full tang.
Thanks Ed, on a hidden tang I did the small tang first and as I worked the blade the smaller tang tended to get worked up and down and worried a crack in the tang so I believed that taught me a lesson.
In Japanese quenching , I have never had a blade crack on obvious stress risers . The Hamachi and Munemachi. They always seem to crack on the thin edge of blade. hamachi (刃区[SUP]?[/SUP]) - notch in the cutting edge (ha), dividing the blade proper from the tang....
munemachi (棟区[SUP]?[/SUP]) - notch in the back edge (mune), dividing the blade proper from the tang. I think mainly because that part is not fully hardened because of clay.