About Tool Steel
The three qualities that most effect the selection of a steel for a hand-tool application are edge-holding, sharpenability, and corrosion-resistance. For metallurgical reasons, you can only have two of the three. We at HOCKTOOLS feel that in woodworking, corrosion-resistance is the least important of the three, and prefer an edge that is easily sharpened and long lasting.
A steel's carbon content determines its ability to harden with heat treatment. That hardness determines a tool's ability to hold a sharp cutting edge under abrasive pressure (wear). Generally, the harder the metal the better its edge holding, but it will be more brittle. Tempering reduces that brittleness, although it also reduces the tool's hardness and wear resistance. So a balance must be struck to decide how hard a blade should be. Our blades are hardened to Rc62 for long edge life. This is harder than most available replacement blades yet not as hard or brittle as most Japanese blades. (Some Thoughts on DIY Heat Treatment)
"Tool Steel" refers to a class of steels that are metallurgically very "clean" and fall within strict limits for alloy proportions. Vanadium, tungsten, and molybdenum are often added to tool steels to make the steel resist annealing (softening) when used in "high-speed" (high heat) applications. Chromium is added in very large quantities for corrosion resistance ("stainless"). High-speed steels are essential in metal-working tools (drills, milling cutters, etc.) and "stainless" steels can be cost effective by resisting rust during the manufacture, shipping, and storage of the tool itself. Correctly heat-treated, tools made from high-speed, stainless, and "chrome-vanadium" steels may hold an edge well in woodworking applications, but, due to the large, hard carbide particles that form during hardening, they are difficult to sharpen and cannot be honed as sharply as a blade of plain high-carbon steel. Our choice of High-Carbon Tool-Steel (.95% Carbon: either O1, our "high carbon" or A2) offers the finest, sharpest edge possible. Its chromium and vanadium additions amount to only 1/2% each allowing quick, clean honing with traditional techniques. High-carbon steel holds and takes an edge better than anything else. We guarantee it.
I've written a long chapter about tool steel metalurgy in The Perfect Edge. A reader comments: "It's been 38 years since I was in Materials Science class, a course I enjoyed and did well in, and your section on metallurgy should be adopted as a supplement for those courses. Much better written than any textbook I've ever had to wade through. It is a credit to you on how you've written this that I find it draws the reader in and I just keep reading along."