Here is something that I periodically post on blacksmithing related forums. I hope you find it useful.
Heat Treating Terms
One highly misused word is “Tempering”, when the person should be using the term “Heat Treating”. These are very basic and important terms, and misusing them could cause not only a loss of respect, but a loss of interest of an experienced smith in answering your questions about heat treating and/or smithing in general.
Definition of Heat Treating Terms
Each steel has its own heat treatment specifics. That said, most tool and knifemakers seem to be using oil hardening steels, even sometimes with steels that are identified as water quenching. I suggest checking the recommended quenchant and temperature recommendations for the quenchant for both the hardening stage, and the tempering stage, for both your selected steel and the intended use of the blade. Actually not as complicated as it sounds, since most smiths will likely use a limited number of steels for a limited range of products.
Heat Treating of Steel, such as for a knife, or other edged tool, is a
multi-step process.
Hopefully we can all agree on the definitions of a few standard terms:
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Heat Treating – the process of achieving a desired hardness in steel.
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Hardening – the step in heat treating where the blade is brought up to temperature appropriate for that alloy of steel, and quenched, locking in a hardness that for knives, and other edged tools. is likely to be brittle.
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Tempering – the step after Hardening in the Heat Treating process where the
steel is softened to the desired level of hardness for the tool, or knife's application. For example, a skinning knife will likely have a higher level of hardness at its edge than a knife that is used for chopping.
And then there is:
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Normalizing – the process of softening to air temperature in order to reduce stresses within the metal, or to soften for drilling or milling. Usually much softer than would be achieved by the Tempering process. Normalizing is often done by placing the blade/tool out of the way in a safe place where it will not be stepped on, such as under a forge or work table.
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Annealing – the process of achieving **maximum** softening by heating then cooling as slowly as possible, such as in a slowly cooling forge or oven or by slowly cooling within an insulating medium such as in a bucket of vermiculite, or iron scale collected from around the smith's anvil. When I took a course with Rob Hudson on Damascus (Pattern Welding) the class used Annealing in a bucket of vermiculite overnight to reduce stress in the blades rather than Normalizing. Some very hard steels may require Annealing prior to being able to drill holes in them.