Annealing là gì

Annealing is a heat treatment process that changes the physical and sometimes also the chemical properties of a material khổng lồ increase ductility & reduce the hardness to make it more workable.

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The annealing process requires the material above its recrystallization temperature for a set amount of time before cooling. The cooling rate depends upon the types of metals being annealed. For example, ferrous metals such as steel are usually left to lớn cool down khổng lồ room temperature in still air while copper, silver & brass can either be slowly cooled in air or quickly quenched in water.

The heating process cause atoms lớn migrate in the crystal lattice và the number of dislocations reduces, which leads khổng lồ the change in ductility và hardness. The heat treated material recrystallizes as it cools. The crystal grain form size & phase composition depend on the heating and cooling rates & these, in turn, determine the material properties.

Hot or cold working of the pieces of metal following annealing alters the material structure once more, so further heat treatments may be required to attain the desired properties.

However, with knowledge of material composition & phase diagram, heat treating can soften metals and prepare them for further working such as forming, shaping và stamping, as well as preventing brittle failure.

How does an Annealing Furnace Work?

An annealing furnace works by heating a material above sầu the recrystallization temperature and then cooling the material once it has been held at the desired temperature for a suitable length of time. The material recrystallizes as it cools once the heating process has caused atom movement khổng lồ redistribute và eradicate dislocations in the workpiece.

Annealing works in three stages – the recovery stage, recrystallization stage and the grain growth stage. These work as follows:

1. Recovery Stage

This stage is where the furnace or other heating device is used to raise the temperature of the material lớn such a point that the internal stresses are relieved.

2. Recrystallization Stage

Heating the material above sầu its recrystallization temperature but below its melting point causes new grains lớn khung without any residual stresses.

3. Grain Growth Stage

Cooling the material at a specific rate causes new grains lớn develop. After which the material will be more workable. Subsequent operations khổng lồ alter mechanical properties can be carried out following annealing.

When is Annealing Required và Why is it Important?

Annealing is used khổng lồ reverse the effects of work hardening, which can occur during processes such as bending, cold forming or drawing. If the material becomes too hard it can make working impossible or result in cracking.

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By heating the material above sầu the recrystallization temperature, it is made more ductile & therefore ready to be worked once more. Annealing also removes stresses that can occur when welds solidify. Hot rolled steel is also shaped và formed by heating it above the recrystallization temperature. While steel và alloy steel annealing is comtháng, other metals can also benefit from the process, such as aluminium, brass, và copper.

Metal fabricators use annealing khổng lồ help create complex parts, keeping the material workable by returning them cthua thảm to lớn their pre-worked state. The process is important in maintaining ductility & reducing hardness after cold working. In addition, some metals are annealed khổng lồ increase their electrical conductivity.

Can Annealing be Used with Alloys?

Annealing can be carried out with alloys, with a partial or full anneal being the only methods used for non-heat treatable alloys. The exception lớn this is with the 5000 series alloys, which can be given low temperature stabillisation treatments.

Alloys are annealed at temperatures of between 300-410°C, depending on the alloy, with heating times ranging from 0.5 to 3 hours, depending on the form size of the workpiece và the type of alloy. Alloys need lớn be cooled at a maximum rate of 20°C per hour until the temperature is reduced to 290°C, after which the cooling rate is not important.

Advantages

The main advantages of annealing are in how the process improves the workability of a material, increasing toughness, reducing hardness & increasing the ductility and machinability of a metal.

The heating và cooling process also reduces the brittleness of metals while enhancing their magnetic properties & electrical conductivity.

Disadvantages

The main drawbachồng with annealing is that it can be a time consuming procedure, depending on which materials are being annealed. Materials with high temperature requirements can take a long time to lớn cool sufficiently, especially if they are being left lớn cool naturally inside an annealing furnace.

Applications

Annealing is used across a variety of industries where metals need lớn be worked inkhổng lồ complex structures or worked on several times.

Who Discovered Annealing?

Annealing dates bachồng hundreds of years, as evidenced by the word itself, which comes from the Middle English ‘anelen,’ meaning lớn phối on fire or kindle, as well as bake & temper.

Middle English was spoken và written in Englvà from 1150 until 1500 và is a descendant of Old English.The term had spelling variations, such as the Middle English ‘onǣlan,’ & was used as in this instruction from 1400, ‘Take þe plates of bras pannes or of cawdrouns và anele hem in þe fire rede hoot’ (“Take the plates of brass pans or of cauldrons & anneal them in the fire red hot”).

While we bởi not know exactly who discovered annealing, the etymology shows that it was in practice at least 900 years ago.