What is Heat Treatment?
Heat treating or otherwise called as heat treatment is a group of metalworking as well as industrial processes being used for the modification of physical and chemical properties of a certain material. A very common application of this is metallurgical. There are different ways heat treatments are put into used like glass manufacturing.
Heat treating involves the usage of chilling or heating, typically to the extreme temperature to be able to attain the desired result like softening or hardening of a material. Techniques used in heat treatment are plentiful including 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 consist of microstructure of small crystals also known 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. Heat treatment does provide effective way to manipulate metal properties by controlling the diffusion rate and the cooling rate as well within microstructure. Most of the time, heat treatment is used to modify mechanical properties of metallic alloy, manipulating properties including toughness, strength, hardness, elasticity and ductility.
There are two mechanisms that could possibly change the properties of alloy during the heat treatment and it’s the diffusion mechanism which makes the changes in alloy’s homogeneity and formation of martensite that causes the crystals to deform intrinsically.
The structure of crystal composes of atoms that are grouped in specific arrangement that’s called lattice. In other elements, this order rearranges itself depending on the conditions it is on like 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. In alloys, this rearrangement might lead to an element that won’t dissolve normally into base metal to become soluble while reversal of allotropy makes the element either completely or partially insoluble.
And while it is in a soluble state, the process of diffusion would make the dissolved atoms to spread out as it forms 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. This diffusion is known as precipitation, leading to nucleation where all migrating atoms regroup together at grain boundaries. This will create 2 or several distinctive phases when it forms into microstructure.