Hello everyone welcomes to my Blog Readsme.com self skill education and learning forum in this article, we are going to discuss the heat treatment of Steels its types process and applications.
What is Heat Treatment
So the first question is what is heat treatment it is the heating and cooling of steels at controlled afraid to get the desired improvement in mechanical properties.
The objective of Heat Treatment.
Heat treatment is used to increase mechanical properties neck ductility strength toughness of metals it is also used to increase machinability generally in cold working internal stresses are developed to relieve these internal stresses heat treatment is done after cold working it is also used to improve properties like corrosion resistance and hardness let us see the process of heat treatment.
First, the metal is heated to a specific temperature and it is kept at that temperature for a specific period of time in this time the material rearranges its grain structure depending upon the temperature and after that material is cooled at a specific rate so as to get the desired improvement in its properties to let us see what are the types of heat treatments.
Types of Heat Treatment.
5. Case Hardening
Case hardening can be done in four ways case carburizing cyanide in nitriding and flame hardening let us see the temperature range for heat treatments in this slide you can see this is the range for normalizing and this is the range for annealing in annealing and normalizing that the material is heated above its critical temperature also you can see this is the range for hardening and tempering is done below the critical temperature and the temperature range The heats treatments one by one first one is anything in an align material is heated 20° Celsius above its critical temperature then it is allowed to soak at that temperature for around done to 2 hours and then it is cooled very slowly at about 100 degree Celsius per hour.
So that the material rearranges its grain structure and releases residual stresses while queuing in Steel’s at the end of cooling we will get ferrite or pearlite.
Annealing is used to relieve internal stresses and refine grain structure it is also used to increase fertility toughness and machinability in simple words annealing is used to soften the material.
Normalizing is done by hitting the material 40 to 50 degrees Celsius about its critical temperature then it is cold at that temperature for around 15 minutes and then it is cooled slowly normalizing is done on cold work parts to remove internal stresses and restructure the material drains the temperature range. it is used to eliminate internal stresses it is also used to increase strength normalizing is done at a higher temperature than anything and the ductility obtained in normalizing is somewhat lower hardening it is of hitting steel to a temperature above critical temperature then holding it to that temperature for a specific time and very importantly.
Quenching is dipping the material directly into the bath of oil-water.
Hardening is used to increase hardness depending on the temperature of heating and the rate of Quenching mechanical properties like strength toughness and elasticity are varied
Tempering is done after hardening hence we call it as hardening and tempering is done to release internal stresses produced due to rapid cooling in the hardening process in tempering the part is reheated to a temperature less than the hardening temperature and it is folded at that temperature for some time and cooled slowly you can see the temperature. The purpose of tempering is reducing internal stresses produced due to hardening it is also used to restore ductility toughness and shock resistance.
5. Case Hardening
Case hardening is a material processing method that is used to increase the hardness of the outer surface of a metal. Case hardening results in a very thin layer of metal that is notably harder than the larger volume of metal underneath the hardened layer. Case hardening almost always requires elevated temperatures to perform. Through heating, the hardening can be caused by altering the crystal structure of a metal or adding new elements to the composition of the exterior surface of a metal. Since hardening processes reduce formability and machinability, case hardening is typically done once most other fabrication processes have been completed.
There are several reasons to case harden a material rather than attempt to harden an entire metal object. One reason is efficiency. Less energy and less time are required to heat the outermost surface of a metal as opposed to its entire cross-section. These efficiencies can result in huge cost savings in large-scale manufacturing operations. Another reason why case hardening is widely used is because of performance.
It can be advantageous to have a metal with a hard outside shell and a more ductile interior. An example of this would be when metal is needed to resist abrasion but still needs to be able to absorb an impact without resulting in a complete brittle fracture.it is also called as surface heart surface hardening is used to harden the surface case carburizing the steels are heated near its critical temperature with charcoal or carbon around its surface at such high-temperature carbon form metal solution in iron and the surface becomes high carbon steel is hard and there is tough o of mild steel inside.
This process still is immersed in a bath of sodium chloride sodium carbonate and sodium cyanide at a temperature of 800 to 900 degrees Celsius and then it is dipped in a cold bath for quenching the case hardening in this process is uniform and we can get a great surface finish.
The Nitriding steel is heated above 500 degrees Celsius in the presence of ammonia this forms Nitriding on surface nitrates and is hard in nature which forms which increase the hardness of the surface.
Next is flame hardening as the name suggests the surface is heated by the flame in this process the surface which required to harden is heated by oxyacetylene flame and it is quenched this process is quick to process and part of the completed material can be hardened only it means if a specific part of the surface is required to harden then this method is the more preferable summary treatment all done to improve mechanical properties like ductility toughness etc.
case hardening is required to reduce surface fear of parts without losing core toughness and we can find applications of heat treatment like
Also from parts its shaft various gauges dyes are also heat-treated so these are the applications of heat treatment