Importance of StructureImportance of StructureMechanical Properties

(Strength formability High temperature properties)(Strength, formability, High temperature properties)

Physical Properties (Electrical, Optical and Magnetic)

Levels of Structure

Atomic Str ct reAtomic Structure

Crystal Structure

Microstructure

Crystal Structure

Unit cell

Crystal system Edge lengths Interaxial anglesCubic a = b = c = = = 90°Tetragonal a = b c = = = 90°Orthorhombic a b c = = = 90°Orthorhombic a b c = = = 90°Rhombohedral a = b = c = = 90°Hexagonal a = b c = = 90°; = 120°Monoclinic a b c = = 90°Triclinic a b c 90°

1 Triclinic

The 14 Unit Cells1. Triclinic

2. Simple Monoclinic

3. Base Centered Monoclinic

4. Simple Orthorhombic

5. Based Centered Orthorhombic

6. Body Centered Orthorhombic

7. Face Centered Orthorhombic

8 Simple Tetragonal8. Simple Tetragonal

9. Body Centered Tetragonal

10. Hexagonal

11.Rhombohedral

12.Simple Cubic

13 B d C t d C bi13.Body Centered Cubic

14.Face Centered Cubic

(a) (b)

(c)(c)

The three common crystal structures adopted by metals(a) bcc (b) fcc (c) hcp

Popular Crystal Structures

Metals

Ferrous metals Non-ferrous metals

Steels Cast Irons

Plain carbon steels Grey Iron

White Iron

Malleable & Ductile Irons

Low carbon steels

Medium carbon steels

Low alloy steels

High carbon steels

Low alloy steels

High alloy steelsStainless & Tool steels

Phase DiagramsPhase: Chemically, structurally homogeneous and physically distinctPhase: Chemically, structurally homogeneous and physically distinct

Phase Rule: P + F = C + 2 Isomorphous Phase Diagram

Phase Diagram of waterPhase Rule: P + F = C + 1

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning� is a trademark used herein under license.©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning� is a trademark used herein under license.

Fe-Fe3C Phase Diagram

Peritectic Reaction Eutectoid Reaction

L F CL + = = + Fe3C

Microstructure evolution in Eutectoid steel

Microstructure evolution in Hypoeutectoid steel

Microstructure evolution in Hypereutectoid steel

Effect of C on microstructure of steels

0% C

0.2% C

0.4% C

0.8% C

0.6% C

1.2% C

Pearlite

Coarse Pearlite Fine Pearlite

Effect of C on Mech. Properties

Effect of C on Mech. Properties

Effect of Microstructure on M h i l P tiMechanical Properties

Martensite

Lath Martensite Plate Martensite

Tempered Martensite

Tempered MartensiteAt High temperature

Spheroidite

Bainite

Upper Bainite Lower Bainite