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(1)

C

airo

I

nspection

C

ompany

Module 8

Welding Metallurgy

for the Welding

(2)

Metallurgy

The science dealing with the

internal structure of metals

(3)

Welding Metallurgy

Concerned with the changes

occurring in metals during

welding

(4)

Structures

Changes on heating

Changes on cooling

Heat treatments

Alloying

Phases

Discussion Topics

(5)

Matter made up of atoms

Atoms are very small

Electrons orbit atomic nuclei

Have a home location in solids

Oscillate around home position

(6)

Atomic Structure -

Simple Cubic

(7)
(8)

Minimum internal energy

Atoms fixed in place

Atoms have ‘home’ position

Atoms vibrating

Orbiting electrons

Crystalline structure

(9)

Higher internal energy

Atoms free to move

Atoms vibrating more

Orbiting electrons

No fixed structure

(10)
(11)

Thermal expansion

on Heating

Thermal contraction

on Cooling

(12)

Remain after welding is completed (residual

stress)

Can cause distortion

(welding stress exceeds yield strength of

material)

Can cause cracking

(welding stress exceeds tensile strength

of material)

Residual stress can be as high as yield

strength

Relieved by three methods

(13)

Thermally

Vibratory

Peening

(14)

BCC - Body Centered Cubic

FCC - Face Centered Cubic

HCP - Hexagonal Close Packed

BCT - Body Centered

Tetragonal

(15)

Common

Crystal

Structures

(16)

Metal

(17)

Fine grained materials

Have good tensile strength

Have good ductility

Have good low temperature

properties

Coarse grained materials

Have slightly lower strength

Are slightly less ductile

Have good high temperature

properties

(18)

Adding elements to change

mechanical or physical

properties

(19)

Interstitial

Alloying

(20)

Interstitial Alloying -

(21)

Substitutio

nal Alloying

(22)

Substitutional Alloying -

Results in Lattice Distortion

(23)

Metals composed of grains

(crystals)

Very small

Separated by grain boundaries

Different phases within grains

(24)

Microstructure

of Iron

(25)

Iron-Carbon

Phase Diagram

(26)

Ferrite

Cementite

Austenite

Bainite

Pearlite

Martensite

Phases in Steel

(27)

Slow

- Pearlite

- softest

Moderate - Bainite

Fast

- Martensite - hardest

(28)

Lamellar Appearance of

Pearlite

(29)
(30)

Restores ductility and

toughness and reduces strength

and hardness

(31)

Alloy is AISI 4142

Tempering

temperature is in

degrees F

Effects of Tempering

Temperatures

(32)

Alloy contains 12% Cr

Note reduction in

impact strength at

885 F (475 C)

Effects of Tempering

Temperatures

(33)

Continuous Cooling

Diagram & Jominy

Hardenability

Diagram for 8630

steel. Phase formed

on cooling varies

with cooling rate.

(34)
(35)

Joules/inch = current x voltage x 60

travel speed (in./min)

(36)

Slows cooling rate

Produces less martensite

Reduces risk of cracking

Reduces distortion

Reduces hydrogen

(37)

CE

=

% C + % Mn + % Ni + % Cr + % Cu + % Mo

6 15 5

13

4

Carbon Equivalent

(38)

C.E.

Preheat Temperature

< 0.45

Optional

0.45 - 0.60

2000 - 4000 F

>0.60

4000 - 7000 F

Examples of

Preheating vs C.E

.

(39)

Super-critical - above

transformation temp.

Annealing

Normalizing

Quenching (to harden)

Sub-critical - below transformation

temp.

Tempering

Heat Treatments for

Steels

(40)

Movement of atoms within a

solution, be it a solid, liquid or gas

(41)

Diffusion of Lead and

Gold Atoms

(42)

Solid into liquid

Diffusion mechanism

Solubility limit

Temperature effects

Solubility

Dissolving Salt into

Water

(43)

Unique to metals

Solid into solid

Solubility limit

Temperature effects

(44)

Gold and lead bars

Carburizing

Nitriding

Examples of Solid

Solubility

(45)

Ferritic

Martensitic

Austenitic

Precipitation Hardening (PH)

Duplex

Stainless Steels

(46)

Formation of chromium carbides

between 800 - 1600 degrees F

(

Sensitization reduces the

corrosion resistance in many

environments

)

Sensitization of

Austenitic Alloys

(47)

Corrosion Attack of Austenitic

Stainless Steel

(48)

Heat treatment ( SAWQ )

Stabilized grades

Low carbon grades

(49)

Aluminum

Pure aluminum

Aluminum-copper

Aluminum-magnesium

Copper

Pure copper

Brasses

Bronzes

(50)

(51)

References

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