What is this method?
Heat-treating is a term used to describe all the controlled heating and cooling operations performed on a material in the solid state for altering its microstructure and/or properties.
Different metals respond to treatment at different temperatures. Each metal has a specific chemical composition, so changes in physical and structural properties take place at different, critical temperatures. Even small percentages of elements in the metal composition, such as carbon, will greatly determine the temperature, time, method, and rate of cooling that needs to be used in the heat-treating process. Depending on the thermal treatment used, the atomic structure and/or microstructure of a material may change due to movement of dislocations, an increase or decrease in solubility of atoms, an increase in grain size, the formation of new grains of the same or different phase, a change in the crystal structure, and other mechanisms.
Why is this method done?
In the welding and fabrication industry heat treatment is used to remove internal stresses in the weld and the heat affected zone (HAZ). It is also used to make a metal either softer or harder (tempering colours) depending on what is required. There are very large furnaces that take fabricated components and heat treat them over a period to remove the stresses that are built up in fabrications E.g.: Chassis, excavator booms etc. This increases component life.
When is this method used?
The large bearing sets being removed from Metlab180″ diameter by 156″ high carburizing furnace from the hardening temperature (1550°F) for subsequent quenching into agitated, hot oil. Parts were carburized to a case depth more than 0.200″ ECD. Fixture and component weight is about 40,000 pounds.