Welding Metallurgy

Dr. Eng. Hamed A. Nagy

HAZ and Heat Input


Basic Metal Structures

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


Basic Metal Structures

I. Simple Cubic II. Body Centered Cubic

(BCC)

III. Face Centered Cubic

(FCC)

Al, Cu, NiFe, Cr


Iron-Carbon Diagram

%C

Tem

per

atu

re


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


Martensite

Very Rapid Cooling Martensite

Carbon has no chance to diffuse

Metastable Phase

Acicular (Needle) Structure

Lowest Ductility

Highest Strength

Body Centered Tetragonal BCT


Tempered Martensite

Heating from Martensite

Carbon gets able to diffuse

Some relaxation.

Restore ductility

Keep strength at moderate levels


HT

Time

Tem

per

atu

re

Annealing

Normalizing

Oil Quenching

Water Quenching


HT

Tem

per

atu

re

Tempering

Time


Solidification

Coarse Grain Size

Fine Grain Size

Liquid


Solidification

Dendrites


Welding Zones

%C

Tem

per

atu

re


Welding ZonesT

empe

ratu

re


Welding ZonesT

empe

ratu

re

Preheat

HAZ Temp.


Welding Zones

Two factors can control the rate of cooling:

1- Heat Input

a) Power

b) Traveling Speed

2- Preheat


Welding Zones

Three factors can not be controlled:

1- Carbon Equivalent

2- Thickness

3- Thermal Conductivity.


HAZ


HAZ and Heat Input


HAZ and Heat Input


HAZ and Heat Input


LBZ


HAZ (Grain Growth Diagram)


Distortion and Residual Stresses

Without Clamping



Strain

Stress



Strain

Stress



Strain

Stress

Documents

Welding Metallurgy