Welding Metallurgy

Dr. Eng. Hamed A. Nagy

HAZ and Heat Input

Dr. Eng. Hamed A. Nagy

Basic Metal Structures

I. Pure Metal II. Substitutional Atom III. Interstitial Atom

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Basic Metal Structures

I. Simple Cubic II. Body Centered Cubic

(BCC)

III. Face Centered Cubic

(FCC)

Al, Cu, NiFe, Cr

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Iron-Carbon Diagram

%C

Tem

per

atu

re

Dr. Eng. Hamed A. Nagy

Mechanical Mixtures

Coarse Pearlite

Slow Cooling

High Ductility

Low Strength

Fine Pearlite

Moderate Cooling

Moderate Ductility

Moderate Strength

Bainite

Rapid Cooling

Low Ductility

High Strength

Lamellar

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Martensite

Very Rapid Cooling Martensite

Carbon has no chance to diffuse

Metastable Phase

Acicular (Needle) Structure

Lowest Ductility

Highest Strength

Body Centered Tetragonal BCT

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Tempered Martensite

Heating from Martensite

Carbon gets able to diffuse

Some relaxation.

Restore ductility

Keep strength at moderate levels

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HT

Time

Tem

per

atu

re

Annealing

Normalizing

Oil Quenching

Water Quenching

Dr. Eng. Hamed A. Nagy

HT

Tem

per

atu

re

Tempering

Time

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Solidification

Coarse Grain Size

Fine Grain Size

Liquid

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Solidification

Dendrites

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Welding Zones

%C

Tem

per

atu

re

Dr. Eng. Hamed A. Nagy

Welding ZonesT

empe

ratu

re

Dr. Eng. Hamed A. Nagy

Welding ZonesT

empe

ratu

re

Preheat

HAZ Temp.

Dr. Eng. Hamed A. Nagy

Welding Zones

Two factors can control the rate of cooling:

1- Heat Input

a) Power

b) Traveling Speed

2- Preheat

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Welding Zones

Three factors can not be controlled:

1- Carbon Equivalent

2- Thickness

3- Thermal Conductivity.

Dr. Eng. Hamed A. Nagy

HAZ

Dr. Eng. Hamed A. Nagy

HAZ and Heat Input

Dr. Eng. Hamed A. Nagy

HAZ and Heat Input

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HAZ and Heat Input

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LBZ

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HAZ (Grain Growth Diagram)

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Distortion and Residual Stresses

Without Clamping

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Distortion and Residual Stresses

Strain

Stress

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Distortion and Residual Stresses

Strain

Stress

Dr. Eng. Hamed A. Nagy

Distortion and Residual Stresses

Strain

Stress