Annealing process

Annealing is to metals and alloys of heating to proper temperature, keep a certain time, and then slowly cooling heat treatment process. Organization hypoeutectoid steel after annealing is add lamellar pearlite ferrite; Eutectoid steel or hypereutectoid steel is a granular pearlite. In short annealing is close to equilibrium state. • 1 the purpose of annealing. Reduce the hardness of steel, improve the plastic for machining and cold deformation processing. 2. Fine grains, eliminate tissue defect caused by casting, forging, welding, steel organization and composition, to improve the performance of the steel or for after heat treatment as a group. 3. Eliminate the internal stress in steel, to prevent deformation and cracking. • Annealing process of type 1. Homogenizing annealing ( Diffusion annealing) Homogenizing annealing is to reduce the chemical composition of metal casting, casting or forging billet segregation and tissue inhomogeneity, it is heated to high temperatures, long time, and then slowly cooling, with uniform chemical composition and organization into the purpose of annealing process. The heating temperature homogenizing annealing, as a general rule, be Ac3 + ( 150～200℃） , which is 1050 ~ 1150 ℃, holding time, generally is 10 ~ 15 h, thorough, to ensure that the diffusion of eliminate or reduce uneven ingredients or organization. Due to the diffusion annealing temperature is high, long, coarse grains, for this reason, the diffusion annealing after full annealing or normalizing, to enable an organization to refine. 2. Annealing annealing, also known as recrystallization annealing, completely is austenitizing the iron carbon alloy completely, then slowly cooling, to get close to equilibrium state annealing process of the organization. Full annealing is mainly used in hypoeutectoid steel, usually in medium carbon steel and the low, medium carbon alloy steel forging, casting and hot rolling profiles, sometimes for their welded components. Completely does not apply to hypereutectoid steel annealing for hypereutectoid steel annealing is heated to Acm more completely, in the slow cooling, carburizing experience along the austenite grain boundary precipitation, net-like distribution, lead to material brittleness increases, to the final heat treatment. Completely annealing temperature of carbon steel is commonly Ac3 + ( 30～50℃） ; Alloy steel for Ac3 + ( 500～70℃） ; Holding time is depending on the types of steel, the size of the workpiece, furnace charging quantity, chooses equipment types, and other factors to determine. In order to guarantee the supercooled austenite to pearlite transformation, completely full annealing cooling must be slow, with the furnace cooled to about 500 ℃ from air cooling. 3. Not completely annealing is not completely annealing heat the iron carbon alloy temperature between Ac1 ~ Ac3, incomplete austenitizing, then slowly cooling annealing process. Incomplete annealing is mainly suitable for medium and high carbon steel and low alloy steel forged parts and so on, its purpose is to refine the organization and to reduce the hardness, heating temperature of Ac1 + ( 40 ~ 60) ℃, slow cooling after heat preservation. 4. Isothermal annealing follow suit