Thread: FAQ: Why do certain razors require more honing than others?

The ability to take an edge and keep it is the result of the type of alloy used, and the hardening and tempering. Simple steels with few alloying elements rely solely on the formation of iron carbides for their hardness. Steels with more alloying elements such as vanadium, cobalt, manganese, chromium, tungsten, etc. require a more complicated hardening process at different heats for different amounts of time because the carbon forming the vanadium carbides, cobalt carbides, tungsten carbides, etc. form at different temperatures.

Hardening temperatures are usually in excess of 1000 deg. F and are often in the 1200 - 1400 degree range. The temperature has to be closely and accurately monitored so that the steel can be quenched to low temperatures ranging from room temperature to maybe 150 deg. F very quickly. This is what gets the bladesmith the optimal performance from any alloy. The phase change in the steel (at quenching) has to happen very quickly and often within seconds or it won't work right. This is one explanation for a blade failing to perform.

Quenching liquids include water, various oils, air, or salt brine. A2 tool steel, for instance, is air-hardening and tends to warp less on cooling. 01 is an oil hardening tool steel. 1095 tool steel is best quenched in a salt brine.

Tempering temperatures range from 430 - 600 deg F and tempering is actually a softening process which also makes the metal tougher. Hardened steel that is not tempered is very brittle and not tough at all. Tempering should follow hardening fairly soon or the steel could ultimately end up not performing as expected. Tempering can be done in a toaster oven, a low temperature kiln, or in a forge - be it gas or coal.

Tempering can be done in a lead bath, as someone noted, as the temperature of molten lead is 600 deg. F. Hardening has to be done at much higher temperatures in an electric kiln, gas or coal forge, or even using a cherry tip on an oxy-acetylene torch rig (I've done this).

The end result of all this is an edge that can take an edge and keep sharp due to a variety of factors that interplay and include number of carbides present, size of carbides, grain size, zone of hardened steel along the edge, etc. It's all quite complicated and people devote lifetimes to mastering the art of heat treating. At least one prominent heat treater in the knife industry says that you can do everything right and still not get the results you expect! It's an art as well as a science.

So why do some blades fail to perform?

Alloy, heat treating, grinding (get a thin blade too hot while grinding and it will lose the heat treat), and type of grind. There are steels that don't do as well in a hollow grind as they do in a more angular, beveled grind.

That's it in a nutshell! There's a whole lot more to it if you're inclined to engage the topic.