I’m not a professional knife maker, let alone a blacksmith, but I have read lot on the subject and I have made some knives in the past (up to now, none of them even broke or hurt anybody…) and I have gathered some experience. So here’s what I do, what worked for me and what I have an eye on.

My way of hardening:

“Simple Steels” (I use 1.2842) can be hardened around a temperature of about 830 – 850 °C (that’s 1520 – 1560 °F).

• Try to heat up your blade as fast as possible.
• I don’t care about about holding the temperature for certain amounts of time. IMHO, as soon as the blade is glowing evenly in a dark orange, it was heated for long enough.
• Take the temperature. If you don’t have a thermometer, do the magnetic test: Hold a magnet to your glowing blade; if it has become non-magnetic, you have reached the right temperature.
• Now into the oil (I use the cheapest sunflower oil). You can warm it up a little before quenching, but I don’t think it makes very much of a difference, so I don’t care.
• Dip into the oil cautiously, edge side first and downwards. 20 – 30 seconds is enough. Move the blade in the oil for even cooling.
• When cooled to the touch, make the file test: If a metal file run over the surface with very little pressure doesn’t leave any marks, the blade should be hardenend enough.
• So, put your blade in your normal kitchen oven at around 200 °C (390 °F) for two hours to anneal it. You can do this twice.

That should do for achieving a reasonable hardness in a non-professional environment. Nonetheless, I will of course gratefully take any form of correction and constructive criticism from a professional!