Effect of Heat Treatment and Processing Methods on Material Properties

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How heat treatment process and other treatment methods affect the structure, properties,
and behavior of the parent material.
Heat treatment is a group of metal working or industrial processes that are used in altering the
chemical and physical properties of a material. Manufacturing of products such as glass also uses
heat treatments since this process involves too much chilling or heating normally to extreme
temperatures in order to achieve an anticipated result such as softening or hardening of materials.
The techniques used in heat treatment are case hardening, quenching, tempering, annealing,
precipitation strengthening, annealing and normalizing. This process only applies only to process
where heating and cooling takes place in order to alter properties (Brooks, 2016, p. 44).
Types of Heat Treatment
a. Annealing
This is the process for softening materials or bringing about the changes in properties needed
for example electrical, machinability or mechanical properties or dimensional stability. This
process comprises steel heating to or near the critical temperature to enable it suitable for
fabrication. Annealing of a material can be done heating the material at a well-known
temperature and then let the material to cool slowly to a room temperature in an oven.
b. Normalizing
This method is appropriate only for ferrous metals. Here, the heating of metal is done to a higher
temperature afterward it is cooled in the air after removing it from the furnace and this is what
differentiates it from annealing approach. Normalizing is used in some plate mills in the
production of large forgings for example axles and railroads wheels (Grupta, 2008, p. 76).

c. Hardening or Quenching
Hardening is done to increase the strength and wear properties. Alloy content and carbon are one
of the pre-requisites needed for hardening. A metal for example cast iron or steel needs to be
heated into the austenitic crystal phase then cooled quickly in case hardening is done by
quenching. The cooling may be done using the gas such as nitrogen, forced air, oil, the polymer
dissolved in brine or water depending on alloy and other considerations such as distortion and
cracking (Goebbels, 2009, p. 12).
Other treatment processes
a) Case hardening
This is the method of roughening the surface of the metal using low carbon steel and infusing
elements into the surface of the material leading to the formation a tinny coating of a harder
alloy. The machine parts resistance to wear without interfering with tough interior parts is
improved by case hardening (Dardyshire, 2010, p. 56).
b) Austempering

This type of heat treatment method is applied in ferrous metals mostly ductile iron and steel. A
bainite microstructure is produced in steel while acicular ferrite, high carbon, and ferrite
structures are produced in cast irons. This method is commonly is used in eliminating or
reducing distortion or improving mechanical properties (Schmitz, 2015, p. 32).
c) Tempering
Tempering is done by preheating previously normalized or quenched steel to a temperature
beneath the dangerous rang, holding and then cooling to achieve the desired mechanical features.
The brittleness of quenched steel is reduced by this method. The hardness of the material is
directly affected temperature since lower the hardness of the material is affected the higher
temperature.
Fig: Showing tempering method