Heat treatment of Low Carbon Steel via heat treatment processes of annealing, quenching and normalising and observing the structural changes affecting the hardness property of material.

1. CONVENTIONAL HEAT TREATMENT OF LOW
CARBON STEEL
GROUP 6
140110064 : Ayush Chaurasia 140110069 : Devendra
Malav
140110066 : Rishabh Dosi 140110070 : Aditya Kumawat
140110067 : Burhanuddin Attar Wala 140110071 : Himmat Singh
Rajput
140110068 : Rahul Chopra 140110074: Mohd Bilal

2. AIM
To perform various heat treatment processes
(Quenching, Normalizing and Annealing) and
measure the hardness and investigate microstructure
of low carbon and medium carbon steels

3. IRON-CARBON PHASE DIAGRAM
Source : http://www.tf.uni-kiel.de/matwis/amat/iss/kap_6/illustr/s6_1_2.html

4. WHY HEAT TREATMENT ?
 To increase hardness, wear and abrasion resistance and cutting ability of steels
 To resoften the steel after it has been hardened by heat treatment or cold rolling
 To adjust its other mechanical, physical or chemical properties such as hardness, Tensile Strength,
Ductility, electrical or mechanical properties, microstructure or corrosion resistance
 To reduce or eliminate internal residual stresses
 To induce controlled residual stresses e.g. compressive stresses on the surface sharply increase the
fatique life of the components
 To stabilize the steel so that it does not show dimensions with time.
 To decrease or increase the grain size of steels.
 To produce special microstructures to increase machinability or corrosion resistance.

5. CONVENTIONAL HEAT TREATMENT PROCESSES
 Annealing
 Heating material to above its recrystallization temperature, then cooling it slowly
 Diffusion of atoms within the material thereby redistributing and eradicating
dislocations
 Relives Residual stresses
 Normalizing
 Austenitized and cooled in open atmosphere ( Moderate cooling rate)
 Quenching
 After heating, cooling the material in water. Here make sure you stir the water
continuously to dissolve the layer of vapor forming outside the sample

6. HARDNESS
Hardness is the property of a material that enables it to resist plastic deformation, usually by
indentation.
Methods to measure Hardness:
Method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of
a specific shape, with a specific force applied for a specific time.
• Rockwell Hardness Test; diamond cone shaped indenter
• Brinell Hardness Test; sphere shaped indenter
• Vickers Hardness Test; right pyramid with square base shaped indenter and angle of 136 degrees between opposite
faces

7. ROCKWELL HARDNESS TEST
 Rockwell Hardness Scales
:
Source : http://www.gordonengland.co.uk/hardness/rockwell.htm

8. EFFECT ON MECHANICAL PROPERTIES
 Quenching
1. Hardest of the
three
2. Least Ductile
3. Brittle i.e. least
toughness
 Normalising
1. Intermediate
Hardness
2. Intermediate
Ductility
3. High Toughness
 Annealing
1. Soft (release of
internal stresses)
2. Highly Ductile
3. Slightly less
Tough

9. MICROSTRUCTURAL CHANGES DURING HEAT TREATMENT
 Austenite (FCC)
 Carbon occupies the
interstitial sites in lattice
 Ferrite + Austenite
 Ferrite being BCC has
very less solubility of
carbon
 Carbon diffuses to
Austenite
 Ferrite+Pearlite
 On reaching 0.8%
carbon Austenite
transforms to Pearlite
In Annealing and Normalising
Source : https://m.youtube.com/watch?v=Bmd7T6SLKSE

10. QUENCHING
 No time for Carbon to diffuse
 Gets trapped inside space lattice as Austenite transforms
 Results in distorted body centred lattice i.e. Body Centred Tetragonal Lattice also
known as ‘Martensite’ having needle shaped microstructure

11. OBSERVATION
Quenched > Normalized >
Annealed
Heat Treatment Hardness value (HRB)
As Received 47
Annealed 45
Normalized 53
Quenched 72

12. MICROSTRUCTURES
 Microstructure of Eutectoid
steel
Single phase of
Austenite
transforms to a
layered (alternate)
structure of ferrite
and cementite
Dark regions are cementite and
bright regions are ferrite
Mechanical properties of pearlite is in between are in between
that of ferrite (soft) and cementite (brittle)
Source : Callister

13. HYPO EUTECTOID STEEL
Source : Callister

14. CCT AND TTT DIAGRAMS
Time temperature transformation diagram Continous cooling transformation
diagram
Source : Nptel Lectures of Prof. R.N. Ghosh

15. EFFECT OF COOLING RATE ON THE FORMATION OF DIFFERENT
REACTION PRODUCTS
Very slow cooling rate (furnace cooling),
typical of conventional annealing, will result
in coarse pearlite with low hardness.
Air cooling is a faster cooling rate than
annealing and is known as nonrmalizing. It
produces fine pearlite.
In water quenching, entire substance remains
austentic until the Ms line is reached, and
changes to martensite between the Ms and
Mf lines.

16. ANNEALED FROM 1223 K
Coarsened phase of pearlite
Pro Eutectoid Ferrite

17. NORMALIZED FROM 1223K
Fine phase of pearlite
Pro Eutectoid Ferrite

18. WATER QUENCHED FROM 1223K
Martensite
Needles
Ferrite