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Tempering is done after the blade is re hardened. This process makes the blade less brittle. Its done by baking the blade at approx 375 degrees for 2-3 hours and then let it cool in the oven
Re Harden the steel by heating in a forge until its cherry red and non magnetic. Then quench it quickly in oil.
Please check out page on Leaf Spring Knife Making for details on how to cut and shape the annealed spring steel.
After the knife is cut and shaped and the majority of the polishing is done the material can be heat treated to re harden it. The process again uses a forge or torches to heat the material to a non magnetic state. This time the material will be quickly quenched in oil. Please note that heat treating will make the material hard but it will also leave it brittle. For a knife we want the material hard enough to hold an edge but do not want the blade to break.
The last process is called Tempering. Tempering will make the blade less brittle. Use and over and heat the blade to approx 350 degrees for three hours. Then let it cool slowly in the oven. If done correctly the blade should be hard enough to hold an sharp edge and strong enough to withstand a lifetime of outdoor use.
Above: On left is a piece of mild steel threaded rod. This soft steel is easy to cut, grind or even bend but it would never be hard enough to hold an edge. In the middle is a piece of high carbon spring steel. This material is hard enough to hold an edge and strong enough to last a lifetime. only problem is it is so hard that its very difficult to work with. On the Right is a file. This tool steel is even harder than the spring steel but it also brittle. It would hold a great edge but it would break easily with any side load.
For knife making we want to anneal or soften the spring steel so its easy to work with. We can then re harden it which would bring the steel into a Tool Steel hard but brittle state. Last step is to Temper the steel so it returns to spring steel and is hard enough to hold an edge yet not brittle.
The process of knife making is fairly simple. The first step is to anneal the spring or High Carbon steel. Use a forge to bring the metal to cherry red and a non magnetic state and then let it cool down gradually. This process softens the material and makes it much easier to cut, shape and grind into the desired design.
Easy DIY annealing and hardening high carbon steel for knife making
DIY Easy Crafts
Re Hardening Steel
For Knife Making