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The principle and technology of annealing furnace

Annealing furnace is one of the heat treatment equipment in the mechanical industry. Its purpose is to soften the material or workpiece after casting, forging, welding or cutting, reduce the hardness, improve the plasticity and toughness, homogenize the chemical composition, remove the residual stress, or obtain the expected physical properties.

Principle of annealing furnace:

A annealing furnace is a metal heat treatment process in which metal parts are slowly heated to a certain temperature in a different heating furnace for a period of time and then cooled at a suitable rate (usually natural, sometimes controlled).

Common annealing processes are:

Fully annealed. Ball annealing. D. Isothermal annealing. E recrystallization annealing. Graphite annealing. D diffusion annealing. To remove stress annealing.


The principle and technology of annealing furnace


What is a annealing furnace

Complete annealing is the overheat structure of medium and low carbon steel after casting, forging and welding. All into the workpiece heated to ferrite austenite temperature more than 30 ~ 50 ℃, the heat preservation for a period of time, and then with the slow cooling furnace, austenite during cooling to change again, can make the organization of the steel.

Spheroidizing annealing is used to reduce the high hardness of tool steel and bearing steel after forging. The workpiece heated to begin to form austenitic steel temperature above 20 ~ 40 ℃, slow cooling after heat preservation, in the process of cooling of pearlite lamellar cementite into a ball, reducing the hardness.

Isothermal annealing is used to reduce the hardness of some alloy structural steels with high content of nickel and chromium for machining. Generally, the austenite is cooled to the most unstable temperature of the austenite at a relatively fast speed. If the temperature is kept at a proper time, the austenite is transformed into tortoids or sorbite, and the hardness can be reduced.

Recrystallization annealing is used to eliminate the hardening phenomenon (increase in hardness and decrease in plasticity) of wire and sheet during cold drawing and cold rolling. Heating temperature is commonly steel began to form the austenitic temperature below 50 ~ 150 ℃, only in this way can eliminate the strain hardening effect to soften a metal.

Graphitizing annealing is used to turn cast iron containing a large amount of carburized body into forgeable iron with good plasticity. Casting process is be heated to 950 ℃ or so, appropriate cooling after heat preservation time, make cementite decomposition form flocculent mass graphite.

Diffusion annealing is used to homogenize the chemical components of alloy castings and improve their performance. The method is to heat the casting to the highest temperature possible without melting, and keep it for a long time, until the various elements in the alloy diffuse to a uniform distribution and then cool down.

Stress relief annealing is used to eliminate the internal stress of steel castings and welding parts. For began after the formation of austenitic steel heating temperature under 100 ~ 200 ℃, holding in the air after cooling, can eliminate internal stress.

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