Annealing, Normalizing, and
Quenching of Metals
Manufacturing Lab
Experiment # 1
Introduction
• Heat Treatment:
It is a method used to alter the physical and
chemical properties of a material.
Heat treatments are also used in the manufacture
of many other materials, such as glass.
It involves the use of heating, normally to extreme
temperatures, to achieve a desired result such as
hardening or softening of a material.
Introduction
(Cont.)
• Heat treatment techniques include
 Annealing
 Case Hardening
 Precipitation Strengthening.
 Tempering
 Quenching.
Case Hardening & Tempering
• Case Hardening: is the process of hardening the
surface of a metal, often a low carbon steel, by infusing
elements into the material's surface, forming a thin layer
of a harder alloy.
• Tempering is done to "toughen" the metal by
transforming brittle martensite into bainite or a
combination of ferrite and cementite.
Precipitation hardening
• It is also called age hardening or dispersion
hardening, is a technique used to increase the
yield strength of materials, including most
structural alloys of aluminum, magnesium,
nickel and titanium, and some stainless steels.
• It relies on changes in solid solubility with
temperature to produce fine particles of an
impurity phase, which impede the movement of
dislocations, or defects in a crystal’s lattice.
Annealing
• It is a heat treatment process in which a material
is exposed to an elevated temperature for an
extended time period and then slowly coold.
• In annealing the grain size obtained is coarser
than that of normalizing & thereby annealing
adds to the ductility of the steel.
Why Annealing?
• Annealing is carried out to:
 Relieve Stress
 Increase softness, ductility and toughness
 Produce a specific microstructure
Annealing Stages
• Annealing consists of three stages:
 Heating to the desired temperature
 Holding at that temperature
 Cooling to room temperature
Normalizing
• Normalizing is an annealing heat treatment
process used to refine the grains (decrease the
avg. grain size).
• Produce a more uniform and desirable size
distribution, fine grained particles
Phase Diagram
•
•
•
•
Ferrite
Austenite
Pearlite (Perlite)
Cementite
Ferrite
• Ferrite
 Known as α-iron
 Pure iron at room temperature
 Body-centered cubic structure BCC.
Austenite
• Austenite
 Known as γ-iron
 910°C
 Face-centered cubic FCC.
 Much softer than ferrite
 More easily worked
Pearlite
• Pearlite (Perlite)
 Pearly luster in the microscope
 Interference of light in its regular layers
 Most common constituent of steel
 Gives steel most of its strength
 “layered mixture of ferrite and cementite of
average composition 0.83% carbon”
Cementite
• Cementite
 Hard, brittle, white
 melts at 1837°C
 density of 7.4 g/cc
 On the phase diagram, cementite corresponds
to a vertical line at 6.7% C
 Engineers only care about compounds with
less carbon
Materials
• A stock bar of low alloy steel AISI 4340.
• It has the carbon content of about 0.4%, but the
second contains other alloying elements such as
molybdenum, nickel, and chromium.
Review Questions
• What is the effect of increasing the cooling rate
(from furnace cooling to air cooling) on the
fineness of pearlite formed and on the amounts
of the different phases of the AISI 1040
specimens and AISI 4340 specimens?
• What is the effect of increasing the cooling rate
(from furnace cooling to air cooling) on the
hardness of the AISI 1040 specimens and AISI
4340 specimens?
Review Questions
(Cont.)
• Explain why it is very difficult to determine the
carbon content of a normalized steel specimen
from its microstructure only?
• Estimate the amount of pearlite in each
specimen and compare these amounts with the
equilibrium values obtained from the iron
carbon phase diagram.
Review Questions
(Cont.)
• Mention some factors that may affect the actual
cooling rate of an air cooled specimen.
• What effects do the alloying additives have on
the microstructure and mechanical properties of
air cooled (normalized) steel specimens?
• What effects do the alloying additives have on
the microstructure and mechanical properties of
furnace cooled (annealed) steel specimens?