Heat Treatment Processes : Types , Purpose , Classification

This article is about Jasa Heat Treatment medan the heat treatment process which used in manufacturing industries for changing some properties of the material. Heat treatment processes involve high heating of metal at some Jasa Heat Treatment temperature and sudden cooling it using a quenching medium. In this article you will learn heat treatment processes and their clJasa Heat Treatment assification. we will also see the Purpose of heat treatment processes, why they are carried out.

Steel and other alloys have a large number of applications in engineering practice under varying conditions, requiring different properties in them. At one place they may be subjected to bending while at the other to twisting. They may be required to withstand various types of stresses and as a tool, materials to have hardness, especially red hardness, combined with toughness along with anon-brittle cutting edge. They may be required to bear static or dynamic loads, revolve at extremely high speeds, operate in highly corrosive media, carry an extremely hard skin with a tough core, subjected to fatigue and creep, etc. Such varying conditions of their applications require these materials to possess specific properties of the required order to successfully serve under these conditions. But, a material may lack in some or all of these properties either fully or partially. These deficiencies are fulfilled through the process of heat treatment. Generally all steels can be heat treated as per need. Aluminum is the only non-ferrous metal which can be effectively heat treated.

The process of heat treatment involves heating of solid metals to specified (recrystallization)temperatures holding them at that temperature and then cooling them at suitable rates to enable the metals to acquire the desired properties to the required extents. All this takes place because of the changes in size, form, nature, and the distribution of different constituents in the microstructure of these metals. All heat treatment processes, therefore, comprise the following three stages of components:Stages of heat treatment Process :

1. Heating the metal to a predefined temperature.

2. Holding it at that temperature for sufficient time so that the structure of the metal becomes uniform throughout.

3. Cooling the metal at a predetermined rate in a suitable media to force the metal to acquire a desired internal structure and thus, obtain the desired properties to the required extent. All this takes place because of the changes in size, form, nature, and the distribution of different constituents in the microstructure of these metals.

Read More about heat treatment process : tiga Basic Of Heat Treatment Purpose of Heat Treatment

Metals and alloys are heat treated to achieve one or more of the following objectives:1. To relieve internal stresses set up during other operations like casting, welding, hot and cold working, etc.

2. To improve mechanical properties like hardness, toughness, strength, ductility, etc.

4. To change the internal structure to improve their resistance to heat, wear, and corrosion.

lima. To effect a change in their grain size.

6. To soften them to make suitable for operations like cold rolling and wire drawing.

7. To improve their electrical and magnetic properties.

8. To make their structure homogenous to remove coring and segregation.

9. To drive out trapped gases.Classification of Heat Treatment Processes

Various heat treatment processes can be classified as follows:

Annealing is indeed one of the most important heat treatment processes. The internal structure of the metal gets stabilized through this process. This heat treatment is given to the metal to achieve one on more of the following objectives:

1. To refine the grains and provide a homogenous structure.

2. To relieve internal stresses set up during earlier operations.

3. To soften the metal and, thus, improve its machinability.

4. To effect changes in some mechanical, electrical, and magnetic properties.

5. To prepare steel for further treatment or processing.

6. To drive out gases trapped during casting.

7. To produce the desired macrostructure.

Different type of annealing processes can be classified as follows:

1. Full annealing – The main objectives of this type of annealing are to soften the metal, relieve its stresses, and refine its grain structure. It is also known as high-temperature annealing. In this process complete phase recrystallization takes place and, therefore, all imperfections of the previous structure are wiped out. This involves heating of steel to a temperature about 30 degrees to 50 degrees above the higher critical point for hypereutectoid steels, and by the same amount above the lower critical point for hypereutectoid steels, holding it at that temperature for sufficient time to allow the internal changes to take place and then cooling slowly.

dua. Process annealing –The purpose of process annealing is to remove the ill effects of cold working and often the metal so that its ductility is restored and it can be again plastically deformed or put to service without any danger of its failure due to fracture. It is also known as a slow temperature annealing or sub-critical annealing or commercial annealing. The process is extremely useful for mild steels and low carbon steels and is cheaper and quicker than full annealing. Also, less scale is produced during this process. The main output of this process is increased ductility and plasticity, improved shock resistance, reduced hardness, improved machinability, and removal of internal stresses. During cold working operations like cold-rolling, wire drawing, a metal gets severely strain-hardened.

3. Spheroidise annealing – The main purpose of spheroidise annealing is to produce a structure of steel that consists of globules or well-dispersed spheroids of cementite in the ferrite matrix. Following are the main methods through which the above objective can be obtained:

1. High carbon steels: Heating the steel to a temperature slightly above the lower critical point (say between 730 deg C to 770 deg C, depending upon the carbon percentage), holding it at that temperature for sufficient time and than cooling it in the furnace to a temperature 600 deg C to 550 deg C, followed by slowly cooling it down to room temperature instill air.

2. Tool steels and high-alloy steels: Heating to a temperature of 750 deg C to 800 deg C, or even higher, holding at that temperature for several hours and then cooling slowly.

4. Diffusion annealing –  The purpose of diffusion annealing is to remove the heterogeneity in the chemical composition of steel ingots and heavy castings This process is mainly used before applying full annealing to steel castings. In this process, the metal is heated to a temperature between 1100 degrees C to 1200 degree C, where diffusion occurs and grains are homogenized. The metal piece being treated is held at the diffusion temperature for a short time to allow complete diffusion and then cooled down to between 800 degrees C to 850 degrees C by keeping it inside the shut-off furnace for a period of about 6 to 8 hours. Then it is removed from the furnace and cooled in the air down to the room temperature. Then full annealing is performed.

lima. Isothermal annealing – The isothermal annealing consists of heating steel to austenite state and then cooling it down to a temperature of about 630 deg C to 680 deg C at a relatively faster rate. It is followed by holding it at this constant temperature (i.e isothermal) for some time and then cooling it down to the room temperature at a rapid rate. During the isothermal holding full decomposition to pearlite structure takes place and that is why the process is known as isothermal annealing. Because of the two rapid coolings the total annealing time is considerably reduced.Normalizing

Leave a Reply

Your email address will not be published.