What is Heat Treatment?
Heat treating or also known as heat treatment is a group of metalworking and industrial processes that are used to modify the physical and at times, the chemical properties of a particular material. Metallurgical is the most common application. Heat treatments are used in the manufacturing of different materials similar to glass.
Heat treating is involving the use chilling or heating to the most extreme temperature in an effort to achieve the desired result similar to softening or hardening of a material. Techniques that are used in heat treatment are quite a lot and this includes case hardening, annealing, precipitation strengthening, quenching, normalizing and tempering. It’s noteworthy that while this term is applicable to only processes where cooling and heating are done for specific purpose of intentionally modifying properties, cooling and heating typically take place incidentally throughout other manufacturing procedures like welding or hot forming.
Metallic materials do consist of microstructure of small crystals otherwise referred to as crystallites or grains. The nature of grains like composition or grain size is among the most efficient factors that determine the overall mechanical behavior of metal. With heat treatment, it offers an effective way to alter metal properties by means of controlling both the diffusion and cooling rate within microstructure. More often than not, heat treatment helps in altering mechanical properties of metallic alloy, like its toughness, strength, hardness, elasticity and ductility.
The formation of martensite and the diffusion mechanism which makes the crystals to intrinsically deform and change the alloy’s homogeneity respectively are the two mechanisms that can change the alloy’s properties when performing heat treatment.
The structure of crystal includes atoms that are grouped in a particular arrangement that is referred as lattice. In many different elements, this order rearranges itself depending on conditions such as pressure and temperature. This said rearrangement is known as polymorphism or allotropy and it can occur several times, at different temperatures for certain kind of metal. Now in alloys, this rearrangement can result to an element that will not normally dissolve into base metal to be soluble while reversal of allotropy can make the element completely or partially insoluble.
When it is in soluble state, diffusion process will make the dissolved atoms to spread while forming homogenous distribution within the base metal’s crystals. If the alloy is cooled to an insoluble state, atoms of the dissolved constituents will move out of the solution. Here, the diffusion is known as precipitation which can lead to nucleation where all of the migrating atoms will regroup together at grain boundaries. When it happens, it forms microstructure that consists of 2 or several distinctive phases.