8 February 2016

What is hardening?

Hardening is a metallurgical metalworking process used to increase the hardness and strength of a metal. The hardness is directly proportional to the uniaxial.

Hardening is a way to make the steel knife harder by first heating the steel knife to between 1050 and 1090 ° C (1922 and 1994 ° F) and then immediately cooling it will be called quenching it, making the steel knife much harder but also more brittle.

The hardening process has three steps :
  • The specimen to heat depends upon the carbon content.
  • Sock at that temperature for sufficient time.
  • Quenching is called fast cooling. 
The hardness of metal at the location of the imposed strain is directly proportional to the uniaxial yield stress.

For hardening of steel required a change in structure from the body-centered cubic structure to the face-centered cubic structure while BCC structure found at room temperature and FCC structure found in the austenitic region.
  • If suddenly quenched, the Martensite is formed. This is a very strong and brittle structure. 
  • If slowly quenched, it would form Austenite and Pearlite which is a partly hard and partly soft structures. 
  • It would mostly be extremely soft Pearlite if the cooling rate is extremely slow.

Purpose of hardening?

  • The main purpose is to develop high hardness. 
  • To improve wear resistance for steel tool. 
  • To improve tensile strength for structural steel. 
  • To improve yield strength for spring steel. 

Factors affecting the hardening process 

  • Chemical composition 
  • Hardening cycle
  • Size and shape of steel part
  • Homogeneity and grain size of austenite
  • Quenching media 
  • The surface condition of the metal

Applications of hardening 

  • High-strength construction material 
  • Machine cutting tools like drill bits, taps, lathe tools 
  • Knife blades 
  • Bearings
  • Armor plating 
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