With our blade ready to heat treat, it now goes to the oven, an operation I usually do with a batch of four or five blades at a time. Certainlym, this is the most crucial process of the whole knifemaking process as a blade that is not heat treated is soft , unable to hold an edge and thus completelly useless.
The heat treatment consists, generally speaking, of heating the blade to a given temperature – that varies from steel to steel -and then quickly cooling it (hardening). Then he blade is again heated to a much lower temperature (tempering). In the first step of the process, we make the blade very hard and in the next, lower this hardness to the desired degree, wich is measured in points in the Rockwell scale (HRC).
As we are using 52100 steel, we will heat the blade to 825C (Celsius scale) and then quench it in vegetable oil. Then, once my oven cools enough, they go back inside it and undergo two two-hour cycles at 195C. Just to be sure, I polish the edges of the blades so I can follow the tempering process by color. At the end, this polished area should have a straw -light gold color.
There are other recipes for this steel but this one works very well for me so I stick to it. Maybe in teh future I try using a cryo quench as this is also indicated for this steel.
Sorry for the horrible pictures but taking pics with a cell phone while holding a red hot piece of steel on the other isn´t exactly easy. Henrique Peron, where are you now???
The oven used is a standard Fornilcio made by Emilcio Cardoso in Campinas.
52100 steel can also be heat treated by eye using a forge, torch or other source of heat to reach hardening temperature and a kitchen oven for the tempering, beside a good eye to judge the temperatures, of course.
The heat treatment is strictly a technical process and no albine black sheep pee, dance around the anvil or sacrifice of virgins will affect its results although many people seem to believe in this bullshit. I confess I used to believe for some time but now I see that all those virgins were sacrified in vain…