Lately it seems like a lot of knife makers are trying to become armchair metallurgists. They are throwing around a lot of big words.  What do words like cementite, austenite and pearlite mean?

It is good that more knife makers are getting interested in metallurgy. It can only help the quality of their knives and increase the level of the entire craft. Although there are many more than this, these are the terms you will see used most often in knife making:

Soft or annieled states:
1. Ferrite - Iron

2. Cementite - Iron Carbide or Fe3C.

3. Pearlite - A equilibrium mixture of ferrite and cementite that occurs at .83% Carbon.

 Heated States:
1. Austenite - A heated state of steel where the carbon is in solution with the iron and free to move around. This state is non-magnetic.

Hardened states:
1. Martensite - The standard hardened state of steel.

2. Banite - Another hardened state of steel formed by inturrupted quenching called austempering. Banite is not as hard as martensite, but it is very tough.

Heat Treating :
1. Austenizing - Heating the steel to the point where it contains austenite. Also called the critical temperature.

2. Quenching - Cooling the steel, from the critical temperature, at a prescribed rate so that the structure will be martensite or banite. Quenching can be done in water, oil, molten salt or air depending on the type of steel used.

3. Hardening - Both steps 1 and 2 above.

4. Tempering - A secondary heating of the hardened piece. This removes excess hardness and/or stress formed during hardening. Some people incorrectly call steps 1, 2,  and 4  "tempering".

5. Martempering - A type of quenching where the cooling is interrupted slightly above the temperature that martensite starts to form. This is usually around 400F. The steel is held there for a minute or so and then allowed to cool in air to room temperature. The resulting structure is martensite with much lower internal stress than a standard quenched piece.

6. Austempering - Similar to martempering in that the quench is interrupted slightly above the temperature that martensite starts to form. The difference is in the time that the steel is held there, instead of a few minutes it can be several hours. The resulting structure is banite.

7. Annieling - Softening steel by heating it to , or near , the austenizing temperature and cooling very slowly.

8.Spherodize Annieling - A special type of annieling that leaves the cementite in the shape of spheres. Steel in this state machines easier and builds up less internal stress than those that are full annieled. Most new steels come from the mill spherodize annieled.