Heat Treating
Performance
The bottom line is that a knife is a tool and it needs to be able to function. Forty years ago when I began making knives I wanted to make beautiful knives that met the highest levels of function possible. The motto on my first brochure in the early 1980s was “beauty within the confines of function.” I still strive for that. My knives have been used in cutting competitions and on at least one occasion used to win the competition. I have competed with my own knives in competition at hammer-ins. Performance matters.
Most knifemakers use one or more steels and they use the same heat treat for a given steel whether it will be used as a camp knife or a small utility knife. The balance between hardness, geometry, edge-holding and toughness needs to match the function of the knife. Each of those characteristics is taken into account when I make a knife.
Because performance matters I have invested in the time and equipment to make my knives the best. More precisely, I use well controlled salt tanks and precisely heat treat specific steel to an intended outcome. There typically is no one best heat treat for a knife unless you know what impact changing certain variables in the heat treat process will do. There is no one best steel that does it all, nor is there one heat treat that does it all. If the blade is large and will be used for chopping then I adjust to maximize those properties. If the blade is going to be used as a utility little cutter, then the heat treat would be different even if it is the same steel used in the large chopper. Of course different steels have different attributes that can be emphasized by the heat treatment.
Having said all that, typically each knife blade is normalized to reduce grain size. With certain hypereutectic steels, such as 52100, I am very careful about where all that that extra carbon ends up. If the intended use is as a small cutting instrument where edge retention is most important, then the heat treat temperature and tempering temperature will vary. For the same steel, if the intended use is as a large cutting/chopping instrument, then the heat treatment will again vary both prior to quenching and during tempering.
The use of high temperature and low temperature salt tanks and reliable, calibrated instruments to measure the temperature of the liquid salts allows me to control the outcome in variety of positive ways. By the way, this is all science and technology and while it takes some study, there is no magic to it.
I do on occasion use 52100 and L6 and austemper the blades to achieve a very tough blade. This produces a bainite blade with good hardness that is very tough and still holds a good edge.
Take a look at the following video. A customer of mine took a knife I had made for him to “Wicked Edge” to have it sharpened. This is a 52100 blade heat treated using a rapid cycle quench technique using a reducing austenitic temperature sequence of 1575, 1550 and a final quench at 1525 F with a hold of 10 minutes on the first cycle and then two minutes on each sequential hold. The blade was quenched in a low temperature salt on the first two quenches in the cycle and then immediately after reaching room temperature following removal from the low temp tank (375 F) transferred back to the high temperature tank where the salt temperature which had dropped by 25 degrees. The research had shown that rapid cycling could produce significant reductions in grain size of the martensite structure. Anyway, Wicked Edge liked the result and decided to make a video out of it. You can view the video and the cutting results on Youtube. Follow the link below:
Steels
I prefer steels that I can forge. With that having been said my preference is to use W2, L6, 5160 or 52100 depending on the kind of knife I am making and what kind of performance I want from the blade. I like to laminate steels. I think a great blade can be made with W2 as a core and L6 laminated on either side. I also think this is true using Damascus to laminate both side of a W2 core.
I make my own Damascus using W2 and L6 or a bit of 203E. I like to end up with a uniform carbon content of about .8 percent. My W2 was tested at 1.05% carbon. Because there is carbon migration during the forge welding process I like adding a bit of 203E (low carbon nickel bearing steel) to the billet. This gives nice contrast in the final blade pattern and helps bring my carbon content down to about .8 or so.
Dan Petersen