chapter 6 welding matl properties & classification vr 0905

8/11/2019 Chapter 6 Welding Matl Properties & Classification Vr 0905

1/31

1

WELD INSPECTION LEVEL 2 COURSE

CHAPTER 6

WELDING MATERIAL, PROPERTIES& CLASSIFICATION


2/31

2

CHAPTER 6 WELDING MATERIALS, PROPERTIES & CLASSIFICATION

PROPERTIES OF METALS

What is a metal?

Technically, it is an element which has the following properties:

It is solid at room temperature (mercury is an exception)

It is opaque (that is, you cantsee through it)

It conducts heat and electricity

It reflects light when polished

It expands when heated, contracts when cooled

It usually has a crystalline structure


3/31

3


An alloyis a metal to which:-

another metal (or metals), or a non-metallic element such as carbon

or silicon, has been added to modify the physical or mechanical

properties of the pure metal.

iron, aluminum, titanium, and magnesium are used predominantly in

alloy form.

pure iron, in fact, is something of a laboratory curiosity.


4/31

4


PROPERTIES OF METALS CAN BE CLASSIFIED

Physical Properties

Mechanical Properties

Chemical Properties


5/31


6/31

6


Density

Mass (weight) of a specific volume of metal.

Light metals aluminum and magnesium low density

Ferrous metal carbon steel and stainless steel high density

Density is variously expressedas

Grams per cubic centimeter (g/cm3),

Kilograms per cubic meter (kg/m3),

Pounds per cubic inch (lb./in.3),

Poundsper cubic foot (lb./ft.3

).

for comparative purposes, density is often expressed asspecific

gravity.

Steel

Aluminum


7/31

7


METAL DENSITY (lb/cu. In)

ALUMINUM

COPPER

GOLD

IRON / STEEL

MAGNESIUM

MANGANESE

MOLYBDENUM

NICKEL

TIN

TITANIUM

TUNGSTEN

ZINC

2.71

8.96

19.32

7.87

1.74

7.43

10.20.

8.90

7.30

4.54

19.30

7.13

Densities of CommonMaterials


8/31

8


Melting Point

Extremely important in welding affect the fusibility of material

Temperature solid to liquid state.

Metals with low temperature welded at lower weld temperature.

At this state , metals does not have any crystalline structures.

Solid State Liquid State


9/31

9


Specific Heat Specific heat required to bring the metal to melting point.

Low melting material - required high specific temperature to melt.

High melting material - required low specific temperature to melt.

Factors influenced :

1. Area

2. Thermal, Electrical Conductivity

3. Joint Design

4. Chemical Composition

ALUMINIUM REQUIRED HIGHER SPECIFIC

TEMPERATURE DUE TO HIGH IN THERMAL

CONDUCTIVITY


10/31

10


Thermal Conductivity

Is a measure of metalsability to conduct heat.

Metal good electric conductivity good in heat conductivity.

Good thermal conductivity material disperse heat easily and localizeheat is unlikely.

Poor thermal conductivity material is said easy to be welded &

distortion is likely.

Excellent conductor of heat :Silver & copper

Poor conductor of heat :

Titanium & Manganese


11/31

11


Thermal Expansion Solids expand in all dimensions when heated and contract when

cooled.

The increase in unit length when solid is heated 1 degree is called

coefficient of linear expansion.

Aluminum has 2X thermal expansion compared to steel at same

temperature.

Thermal of expansion may vary depends on material types and area.

Large area / thick

high thermal expansion high distortion & stress


12/31

12


Electrical Conductivity

Is the measure of abilitysmaterial to conduct electricity.

Metal with low electrical conductivity - high in resistance transfer

welding current slower (heat build up).

Low conductivity may lead to distortion and stresses.

Silver

Copper

AluminumLead

Tungsten

Zinc


13/31

13


Corrosion Resistance

The ability of a given metal to resist corrosion.

Corrosion may reduce the tensile strength of the material.

Corrosion may caused by liquid chemicals and noxious gasses.

Chromium & nickel based alloys is less susceptible to corrosion atelevated temperature.

Lead & aluminum are weather resistance due to protective layer

formed by oxide.

Oxide

Layer

Aluminum


14/31

14


MECHANICAL PROPERTIESMechanical properties shows the reaction of metal on certain forces such

as :

Tension Compression

Torsion

Shear

Impact

Cold shaping


15/31

15

Plasticity - Ease of material to be bent or molded into givenshape.

Brittleness - Tendency of a metal to break suddenly without

plastic deformation.

Malleability - Property possessed by a metal of becoming

permanently flattened or stretched by hammering or

rolling.

Ductility - Ability of material to deform plastically without

fracture.

Creep - Ability of material to withstand gradual changes indimension (contraction & expansion).

Hardness - Property of material to resist plastic deformation

by scratching & indentation.

Fatigue - Tendency of a metal to fail under a rapidly alternating

loading.



16/31

16


CHEMICAL PROPERTIESMany elements may present in steel. Alloyed steel is a steel contains

various type of chemical element such as :

Carbon ( C ) Nickel (Ni)

Chromium (Cr)

Molybdenum (Mo)

Copper (Cu)

Manganese (Mn) Silicon (Si)

Tungsten (W)

Vanadium (V)

Aluminum (Al)


17/31

17


Affect on steel :

Carbon ( C )

Key element of steel.Major influence on strength, toughness, ductility

and hardness.

High carbon would reduce the strength &toughness ; Increase hardness


18/31

18

Ductility

HardnessTensile Strength

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 % Carbon

0.83 % Carbon (Eutectoid)*

Increasing the carbon content will increase the strength, but will

also increase greatly the formation of martensite in the weld.

This may now produce H2Cracks across weld*


19/31

19


Affect on steel :

Nickel ( Ni )

Widely used in stainless steel.Commonly for heat and corrosion resistance.

Increases strength & toughness.

In some cases the ductility would be increase.


20/31

20


Affect on steel :

Chromium ( Cr )

Widely used in stainless steel.Commonly for heat and provides basic corrosion

resistance.

Increases hardness, strength & toughness.In some cases the ductility decrease.


21/31

21


Affect on steel :

Molybdenum ( Mo )

Expensive element which has strong effect onhardenability and high creep strength at high

temperatures.

Steels would be less susceptible to temperbrittleness.


22/31

22


Affect on steel :

Copper ( Cu )

Main value is to assist in the resistance of steel toatmospheric corrosion.


23/31

23


Affect on steel :

Manganese ( Mn )

Extensively used as an alloying element hasconsiderable effect on its structure.

Similar affect as carbon and able to compensate

hardness & toughness.Main element for de-oxidizing oxygen*.

*During welding - Oxygen + carbon = carbon monoxide (trapped in weld metal porosity)


24/31

24


Affect on steel :

Silicon ( Si )

Small amounts of silicon present in steel.Does not effect on the metal properties.

Main function is as a deoxidizer.

*During welding - Oxygen + silicon = prevent the formation of carbon monoxide (trap in weld

metal porosity)


25/31

25


Affect on steel :

Tungsten ( W )

Element which has strong effect on hardness ,toughness and high creep strength at high

temperatures.

Steels would be less susceptible to temperbrittleness and resistance to abrasion wear


26/31

26


Vanadium ( V )

Promotes grain structure refining (welding)

Increase hardness and may also be used as adeoxidizer.

Aluminum ( Al )

Promotes grain structure refining (steel production)

Increase hardness and may also be used as a

deoxidizer.


27/31

27


Affect on steel :

Sulphur & Phosphorous

Element which has strong effect machinability onsteel.

Always keep below 0.04% due to :

Sulphur - Hot shortness (fast cooling rate)

Phosphorous - Cold shortness (slow cooling rate)


28/31

28


CLASSIFICATION OF MATERIALMaterial may be classified as :

Ferrous Metal1. Carbon Steel - Low, Medium & High Carbon

2. Alloy Steel - Quenched, Tempered, HSLA, Cr+Moly3. Stainless Steel - Ferritic, Austenitic & Martensitic

Non-ferrous Metal

1. Aluminum & its Alloy2. Copper & its alloy

3. Magnesium based alloy

4. Nickel based alloy - Monel, Inconel, Incoloy, Hastealloy

5. Reactive and refractory metals Titanium, Tungsten


29/31


30/31

30

An Alloyed carbon steelis one that contains more than Iron &Carbon as a main alloying elements.

Mainly to improve strength, hardness, and toughness.

Increase resistance to corrosion, heat and environmental damage.

Alloy steels are divided into 2 groups

1. Low Alloy Steels < 7% extra alloying elements

2. High Alloy Steels > 7% extra alloying elements

Carbon Steel Classification



31/31

31

Corrosion resisting steel are alloys of iron with chromium, nickel etc.

Stainless Steels can be categorized into:

Stainless Steel Classification


Group Elements Hardenable byheat treatment

Magnetic

Austenitic

Austenitic

Martensitic

Ferritic

Chromium nickel manganese

Chromium nickel

Chromium

Chromium

Non Hardenable

Non Hardenable

Hardenable

Non Hardenable

No

No

Yes

Yes

chapter 6 welding matl properties & classification vr 0905

Documents