Heat Treatment Method of Steel Pipe

hardening: hardening is a metallurgical metalworking process used to increase the hardness of a metal. the hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. a harder metal will have a higher resistance to plastic deformation than a less hard metal. precipitation hardening also known as age hardening, is one of the hardening processes. it creates uniformity in a metal’s grain structure, making the material stronger. the process involves heating a solution treatment to high temperatures after a fast cooling process. precipitation hardening is usually executed in an inert atmosphere at temperatures ranging from 900 degrees fahrenheit to 1,150 degrees fahrenheit. it can take anywhere from an hour to four hours to carry out the process. the length of time typically depends on the thickness of the metal and similar factors.

tempering: tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air.

annealing: annealing is a form of heat treatment that brings a metal closer to its equilibrium state. it softens metal, making it more workable and providing for greater ductility. in this process, the metal is heated above its upper critical temperature to change its microstructure. afterward, the metal is slow-cooled.

normalizing: normalizing involves heating steel, and then keeping it at that temperature for a period of time, and then cooling it in air. the resulting microstructure is a mixture of ferrite and cementite which has a higher strength and hardness, but lower ductility. normalizing is performed on structures and structural components that will be subjected to machining, because it improves the machinability of carbon steels.

carburization: carburization is a heat treatment process in which steel or iron is heated to a temperature, below the melting point, in the presence of a liquid, solid, or gaseous material which decomposes so as to release carbon when heated to the temperature used.

surface hardening: in many engineering applications, it is necessary to have the surface of the component hard enough to resist wear and erosion, while maintaining ductility and toughness, to withstand impact and shock loading. this is known as surface hardening. this can be achieved by local austentitizing and quenching, and diffusion of hardening elements like carbon or nitrogen into the surface. processes involved for this purpose are known as flame hardening, induction hardening, nitriding and carbonitriding.

quenching: less expensive than annealing, quenching is a heat treatment method that quickly returns metal to room temperature after it is heated above its upper critical temperature. the quenching process stops the cooling process from altering the metal’s microstructure. quenching, which can be done with water, oil, and other media, hardens steel at the same temperature that full annealing does.

stress relieving: stress relieving is a heat treatment process that decreases stress in metals after they have been quenched, cast, normalized, and so on. stress is relieved by heating metal to a temperature lower than that required for transformation. after this process, the metal is then slowly cooled.

cryogenically treated: when a metal part is cryogenically treated, it is slowly cooled with liquid nitrogen. the slow cooling process helps prevent thermal stress of the metal. next, the metal part is maintained at a temperature of roughly minus 190 degrees celsius for about a day. when it is later heat tempered, the metal part undergoes an increase of temperature up to approximately 149 degrees celsius. this helps to lower the amount of brittleness that may be caused when martensite forms during cryogenic treatment.