Everything About 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. Case hardening, annealing, precipitation strengthening, quenching, normalizing and tempering are only few of the many different techniques that are being used for heat treatment. 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. Heat treatment is providing an effective way of manipulating metal properties by controlling the diffusion rate as well as cooling rate within microstructure. Heat treatment is mostly used for altering the mechanical properties of metallic alloy, manipulating properties similar to 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 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. 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.
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. Now, when the alloy is cooled to insoluble state, the constituents of the dissolved atoms 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. This will create 2 or several distinctive phases when it forms into microstructure.