CRYOGENICS. The American Society of Cryogenics defines it as,
"...the art and science of achieving extremely low

HARDNESS. "Resistance to permanent indentation." There are about a dozen hardness measurement systems, but the most widely known for hard metals is the Rockwell "C" scale. A diamond point cone is pressed into the sample with a light load, then a heavy load. A chart converts the difference in penetration to a number on the hardness scale. The Brinell test is for soft metals and  presses a 10 mm ball into the sample. The Brinell hardness number is the ratio of the diameter of the ball over the area of the dent in the material.

TOUGHNESS. "Resistance to gouging."

HEAT TREATING. Steel containing carbon is heated red hot, then quenched. The quench may be in water, salt brine, oil, liquid nitrogen or air. The part is then tempered in an oven. The first temper after the quench determines the hardness. Heat treating books contain tables showing the proper temperature to be used to produce a given hardness.

AUSTENITE. The coarse crystalline molecular structure formed in
steel during heat treating.

MARTENSITE. The fine crystalline molecular structure formed in
steel during the quench portion of the heat treating

TEMPERING. The final phase of traditional heat treating where the
steel is put in an oven to stabilize the fresh martensite
formed during the quench as well as set the final hardness.
It is also performed after cryogenic processing because
more fresh martensite is formed.

WEAR. The progressive loss or removal of material from a surface.