More Knives

[Captain_Bandaid]

There are lots of 'mystical' methods in blademaking. I read where one blade smith aligns his blades with true north before quenching them. Piffle. The practice of peening actually has some benefit, though. When you quench a high carbon steel, first you heat it up to form a phase called austenite, a crystal structure different than room temperature steel. Austenite, when rapidly cooled, will transform to martensite, another crystal shape. Martensite is quite hard but brittle and needs to be tempered to be useful. However, some of the austenite may not transform to martensite. This leaves the hardness lower than it should be. Austenite can be induced to form martensite by deformation, e.g., peening. When you peen it to form the rest of the martensite, it should be tempered again as it will form hard, brittle martensite. An easier way to do this is to quench the blade, give it a light temper (200F), pack it in dry ice and leave it in the freezer overnight. When it is warmed back to room temperature, temper it again at 450F. On an industrial scale, this process is routinely applied to cutting and forming tools. As for my process, it is almost exactly the same as Ricks, except I normalized (air cool) the blade instead of annealing (slow cooling). Annealing will allow the carbon to form larger carbides as is slowly cools. The carbon tied up as carbides will not help to harden the blade. However, if you have a steel with a lot of carbides, it might be more abrasion resistant even though the hardness might be less. I might just have to try an experiment and do some lab tests to see which method of cooling works best. I do not use edge-only quenching as it can cause cracking and warping. I quench the blade straight down, tip first. Swirl it in a figure 8 until cool. Temper it at about 425F. If you want to soften the spine and leave the edge hard, you can apply a propane torch to just the spine but you must be very careful or you will soften the edge too. On small blades, I temper them uniformly at one temperature.

[Captain_Bandaid]

I forgot to mention that work hardening (e.g., peening) a blade will significantly reduce the toughness and ductility. Tempering will help restore the toughness but not completely. Freezing and tempering will achieve a better balance of hardness and toughness than work hardening. :

Folks,

I really appreciate y'all taking the time to share your skill
and wisdom.

thanks again,

[AlArchie]

One of the more 'mystical' methods of tempering comes from those venerated Damascus Blade makers of the Byzantine era, who would temper their finest blades by running them through the liver of a live slave. Kinda rough on the 'quencher', I would imagine!


Don't think I'll try tempering any knives I make, by running the blade in my finger while it's hot. Might cauterize the cut and stop the bleeding quickly, but there gotta be a better way!

Al

[Captain_Bandaid]

: I too have heard about quenching into a slave but I have been told that it is pure fiction. Besides, the hot blade would staunch the flow of blood and make for a poor quench. Before ferrous metallurgy was understood, it was assumed that the composition of the quench is what made the steel hard. They did not realize it was the cooling rate that did it. In very old manuscripts, formulas for quenchants included things like 'spring water, urine, blood, acids, salts, and distilled spirits'. What is not understood can be a great source of profit, if you can throw in a bit of showmanship.

[AlArchie]

Dang, Capt. ya mean my 5th grade social studies book was promoting a myth???? I honestly can't say I remember exactly how the practice was couched in the book, but it definitely got my attention, to still be stuck in my head some 50 years later!


Al