Understanding Heat Treatment
When a material’s physical or chemical property is altered especially in industrial and metalworking processes, this is automatically referred to as heat treating or heat treatment. Metallurgical is the most common application. Heat treatments are being used in manufacturing of various materials like 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 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 have microstructure of small crystals that are known also as crystallites or grains. One of the most effective aspects to figure out the mechanical behavior of metal is seeing the nature of grains similar to its size or composition. With heat treatment, it offers an effective way to alter metal properties by means of controlling both the diffusion and cooling rate 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.
Structure of crystal consists of atoms that are specifically arranged in a group known 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 the subject of alloys, this rearrangement can make the element not dissolve normally into a base metal to be soluble while allotropy reversal can make the element to be either completely or partially insoluble.
When in soluble state, the diffusion process makes the atoms of dissolved element to spread while trying to form 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. Precipitation is what’s called to the diffusion that lead to nucleation in which all migrating atoms are regrouping together at grain boundaries. When it happens, it forms microstructure that consists of 2 or several distinctive phases.