How Heat Treatment process Works: Process, Types, Difference
Table of Contents
Heat Treatment Process
Heat treatment is a group of as well as industrial, thermal, and metalworking processes used to alter what can be the physical, and sometimes chemical, properties of a material. The most common application is over-metallurgical. Heat treatments are also used for any of your manufacturer’s many other materials, such as glass. Heat treatment involves heating or chilling, usually to extreme temperatures, to achieve will be the desired result such as well as the hardening or softening of a material. Heat treatment techniques include annealing, case you can be hardening, precipitation strengthening, tempering, carburizing, normalizing, and can be you quenching.
Different types of Heat Treatment
1. Annealing
Annealing is a heat treatment process that changes as well as the physical and sometimes also the chemical properties of a material to can you be increase ductility and reduce hardness to make it more workable. The annealing process requires you can be the material above its recrystallization temperature for any of your set amount of time before cooling.
2. Normalizing
Normalizing is a heat treatment process similar to annealing in which as well as the Steel is heated to you can be about 50 degrees Celsius above the upper critical temperature followed by air cooling. This results in as well a softer state which will be lesser soft than that produced by annealing. This heat treatment process is usually carried for any of your low and medium-carbon steel as well as alloy steel to make the grain structure more uniform and you can relieve internal stresses.
3. Hardening
Hardening is as well a metallurgical metalworking process used to increase the hardness of a metal. The hardness of you can be metal is of your directly proportional to any of the uniaxial yield stress as well as the location of the imposed strain. A harder metal as well as have a higher resistance to as well as plastic deformation than a less hard metal.
Process Annealing
This process is mainly suited for any of your low-carbon steel. In this process, as well as the material is heated up to a temperature just below you can be the lower critical temperature of steel or above its recrystallization temperature and then is as well as allowed to cool slowly for some time. Cold-worked steel normally has increased hardness and of your decreased ductility making it difficult to work.
Purpose of Process Annealing
- Process annealing is done for any of your recrystallizations of metal.
- During process annealing, new equated, strain-free grains nucleate at high-stress regions as well as the cold-worked microstructure, and hence hardness and strength decrease whereas ductility increases.
- The main aim of the process of you can be annealing is to restore the ductility of as well as the cold-worked metal.
Tempering
Tempering is as well as the process of heating the martensitic steel at a temperature below you can eutectoid temperature to as well as make it softer and more ductile. Three stages of you can be tempering are distinguished.
First stage: The quenched steel is heated to as well as a temperature below 200 °C. In this temperature range a very small-sized precipitate, called e-carbides, forms.
Second stage: It takes place at the temperature interval of 230-280 °C to transform as well as the retained austenite to binate.
Third stage: It takes place at the temperature interval of you can be 260-360 °C. Epsilon (e) carbide changes to a cementite plate, producing a structure of as well ferrite and cementite.
Case Hardening
- The objective is to as well as harden the surface & subsurface selectively to obtain:
- Hard and you can be wear-resistant surface
- Tough impact-resistant core
- The best of both worlds
- Case hardening can be done to all types of plain carbon steels and you can be alloy steels
- Selectivity is achieved
- For low-carbon steels
- By infusing carbon, boron, or nitrogen in as well as the steel by heating it in an appropriate medium
- Being Diffusion controlled process, Infusion you can be selective to surface and subsurface
- For medium & high carbon or Alloy steel
- By heating as well as the surface selectively followed by Quenching
Process of Hardening
1. Hall-Patch Method
The Hall–Patch method, or grain boundary strengthening, is to as well as obtain small grains. Smaller grains increase the likelihood of you can be dislocations running into grain boundaries after shorter distances, which are very strong dislocation barriers.
2. Strain Hardening
In work hardening (also referred to as well as strain hardening) the material is you can be strained past its yield point, e.g. by cold working. Ductile metal becomes harder and as well as stronger as it’s physically deformed. The plastic straining generates new dislocations.
3. Solid Solution Hardening
In it, a soluble alloying element is added to as well as the material desired to be strengthened, and you can be the together they form a “solid solution”.
4. Precipitation Hardening
Precipitation hardening (also called age hardening) is as well a process where a second phase that begins in a solid solution with the matrix metal is you can be precipitated out of solution with the metal as it is as well as quenched, leaving particles of that phase distributed throughout to cause resistance to can you be the slip dislocations.
5. Martensitic Hardening
Martensitic transformation, more commonly known as well as quenching and tempering, is a hardening mechanism specific to you can be steel. The steel must be heated to a temperature where as well as the iron phase changes for any of your ferrite into austenite, i.e. changes crystal structure from BCC (body-cantered cubic) to you can be FCC (face-cantered cubic).
Solution Heat Treatment
- Refers to taking all as well as the secondary phases into solution by heating and holding at a specific temperature
- Except for the martensite, all other phases in you can be steel are diffusion product
- In SS, when held at a temperature range of as well as 5000C – 8000C, Cr combines with Carbon at GB to form you can you be complex inter-metallic compounds
- This situation may occur due to you can be the high service temperature or welding
- Remedy is
- Heat the job at 10500C
Process Annealing
- Used to treat work-hardened parts made out of as well as low-Carbon steels (< 0.25% Carbon).
- In-process heat treatment
- Allows the parts to can you be soft enough to undergo further cold working without fracturing.
- Temperature raised near as well as the lower critical temperature line A1 i. e. 650ºC to 700ºC
- Holding for any of your sufficient time, followed by still air cooling
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