Over 40 Years of Quality Service
What makes a metal hard? Iron, steel, carbon, heat, tempering?
What makes materials hard is a complicated subject that relates to the internal crystal structures. These in turn are affected by heat treating or mechanical working. Most non-ferrous metals can only be hardened by “work hardening,” hammering, rolling and bending. On the other hand, “annealing” can soften them, which is a process of heating to red heat and then cooling quickly (opposite to steel).
The hardness of steel is mainly determined by carbon content. Increasing the content from 0.01% to .10% increases the harden ability and the strength. This is then modified by the addition of alloying metals, which also have their own properties.
To harden most steel it is heated to medium red or slightly above the point where it becomes non-magnetic. It is then quenched in water, oil or air depending on the type of steel. The steel is now at its maximum hardness but is very brittle. To reduce the brittleness, the metal is tempered by heating it to somewhere between 350 degrees Fahrenheit and 1350 degrees Fahrenheit. This heating reduces the hardness just a little and the brittleness very significantly. Even though all steel is slightly different, most steels need to be tempered to about 450 degrees Fahrenheit for maximum usable hardness.
To soften steel so that it can be cold worked and machined is called annealing. To anneal steel it is heated to slightly above the hardening temperature and then cooled as slowly as possible. Cooling is done in an insulating medium such as dry powdered lime or vermiculite. High carbon and many alloy steels can only be cooled slow enough in a temperature controlled furnace since the cooling rate must be only 20 degrees Fahrenheit per hour for several hours.
The set of processes of annealing, hardening and tempering are collectively known as “heat treating.” Advanced Flame Hardening Inc. has played a huge role in the “heat treating” industry for over 40 years of quality service. Advanced Flame Hardening Inc. specializes in selective flame hardening, straightening, and also in-house tempering.
Advanced Flame Hardening Inc.
1209 Marquette Street
Cleveland, OH 44114
216.431.0370
