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LECTURE 11
NOOR MAZNI ISMAIL
FACULTY OF MANUFACTURING ENGINEERING
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METAL1. INTRODUCTION TO METALS & ALLOYS : GENERAL PROPERTIES & APPLICATIONS2. PHASE DIAGRAM3. FABRICATION & THERMAL PROCESSES OF METALS
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PHASE DIAGRAM
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Introduction Phase diagram provides valuable information about melting,
crystallization, etc. It shows the relationships among temperature, composition,
and phases present in a particular alloy system at equilibrium. Binary alloy- consist 2 components (e.g. Cu-Ni, Cu-Ag, Pb-Sn) Ternary alloy- consist of 3 components (e.g. Fe-Ni-Cr)
Why study phase diagram?
Important to engineers, related to design and control of heat-treating procedures since there is a strong correlation between
microstructure and mechanical properties
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The lowest temperature at which the alloy is still completely liquid isknown as the Eutectic point
The lowest temperature at which a single solid phase (austenite)transforms into two other solid phase (ex. ferrite and cementite) isknow as the Eutectoid point
Ferrite Austenite Cementite Pearlite Spherodite Bainite Martensite Retained Austenite Tempered Martensite
TERMS THAT YOU NEED TO KNOW
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Ferrite
Alpha ferrite denoted -ferrite or ferrite
Delta ferrite (-ferrite) is stable only at very hightemperatures
Ferrite is soft and ductile
It is magnetic from room temperature to 768C,Curie temperature
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Austenite Within a certain temperature range, iron undergoes
a polymorphic transformation from a bcc to a fccstructure,
Becomesgamma iron (-iron) or austenite
Austenite is denser than ferrite and important inheat treatment
Possesses good formability
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Cementite Also called carbide
Cementite is very hard and brittle intermetallic
compound Has a significant influence on the properties of
steels
Pearlite
Fine pearlite is where ferrite and cementite
lamellae in the pearlite structure of the eutectoidsteel are thin and closely packed
Coarse pearlite is thick and widely spaced
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Spheroidite
Subcritical annealing is when pearlite is heated tojust below the eutectoid temperature for a period oftime
Spheroidites are less conducive to stress concentrationbecause of their rounded shapes
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Bainite
Bainite is a very fine microstructure consisting offerrite and cementite having a differentmorphology
Produced in steels with alloying elements and atcooling rates that are higher than those required fortransformation to pearlite
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Martensite
As austenite is cooled at a high rate, fcc structure istransformed into a body-centered structure
Does not have as many slip systems, thus lackstoughness and limited use
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Retained Austenite
When alloy temperature is not quenched
sufficiently low, only a portion of the structure istransformed to martensite.
The rest is retained austenitewhich can cause
dimensional instability and cracking. Lower the hardness and strength of the alloy.
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Tempered Martensite Tempered to improve its mechanical properties
Tempering is a heating process to reduce hardness
and improve toughness With increasing tempering time and temperature,
the hardness of tempered martensite decreases
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1
Phases: The physically and chemically distinct material
regions, e.g., and in Aluminum-Copper alloy
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2
Components: The elements or compounds which are
present in the mixture (e.g. Al and Cu)
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3
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END OF LECTURE 11
Thank you