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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