Annealing and incomplete annealing of square tube

Steel pipe annealing: annealing is the steel pipe is heated to the critical point of AC1 above or below the temperature, holding time after a certain period of time with the furnace slowly cooled to obtain nearly equilibrium state of the organization of the heat treatment process.

Types of annealing: according to the heating temperature can be divided into the critical temperature AC1 above or below the annealing, the former includes complete annealing, incomplete annealing, spheroidal annealing, homogenization annealing, the latter includes recrystallization annealing, de-stressing annealing, according to the cooling can be divided into isothermal annealing and continuous cooling annealing.

Complete annealing: complete annealing is to heat the steel pipe to AC3 above 20-30 ℃, holding time is long enough to make the organization completely austenitized after the furnace slowly cooled to obtain nearly equilibrium state of the organization of the heat treatment process. Its main application in the sub-eutectic steel, its purpose is to refine the grain, eliminate internal stress and work hardening, improve the plastic toughness, uniform chemical composition and organization of steel, improve the cutting performance of steel, to eliminate the carbon structural steel in the Weiss organization, banding organization and other defects.

Incomplete annealing: Incomplete annealing is the steel pipe heated to AC1- AC3 (sub-eutectic steel) or AC1-ACcm (over-eutectic steel) between the insulation for a certain period of time after the furnace slowly cooled to obtain nearly equilibrium state of the organization of the heat treatment process.

For sub-eutectic steel, if the original organization of the steel distribution is appropriate, the use of incomplete annealing instead of complete annealing to achieve the elimination of internal stresses, reduce the hardness of the purpose. For over-eutectic steel, incomplete annealing is mainly to obtain spherical pearlite organization to eliminate internal stresses, reduce hardness, and improve cutting performance.