Section 08 (NXPowerLite).ppt
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Transcript of Section 08 (NXPowerLite).ppt
Haward Technology Middle East 1Section 8
AWS Certified Welding Inspector (CWI)
Section 8
Welding Metallurgy for the Welding Inspector
Haward Technology Middle East 2Section 8
AWS Certified Welding Inspector (CWI)
Metallurgy
“The science dealing with the internal structure of metals and metal
properties ”
Haward Technology Middle East 3Section 8
AWS Certified Welding Inspector (CWI)
Welding Metallurgy
“Concerned with the changes occurring in metals during welding”
Haward Technology Middle East 4Section 8
AWS Certified Welding Inspector (CWI)
Discussion Topics
Structures
Changes on heating
Changes on cooling
Heat treatments
Alloying
Phases
Haward Technology Middle East 5Section 8
AWS Certified Welding Inspector (CWI)
Atomic Structure
Matter made up of atoms
Atoms are very small
Electrons orbit atomic nuclei
Have a home location in solids
Oscillate around home position
Haward Technology Middle East 6Section 8
AWS Certified Welding Inspector (CWI)
Atomic Structure - Simple Cubic
Haward Technology Middle East 7Section 8
AWS Certified Welding Inspector (CWI)
Home Location
Haward Technology Middle East 8Section 8
AWS Certified Welding Inspector (CWI)
Solids
Minimum internal energy
Atoms fixed in place
Atoms have ‘home’ position
Atoms vibrating
Orbiting electrons
Crystalline structure
Haward Technology Middle East 9Section 8
AWS Certified Welding Inspector (CWI)
Liquids
Higher internal energy
Atoms free to move
Atoms vibrating more
Orbiting electrons
No fixed structure
Haward Technology Middle East 10Section 8
AWS Certified Welding Inspector (CWI)
Solid vs Liquid
Haward Technology Middle East 11Section 8
AWS Certified Welding Inspector (CWI)
Thermal expansion on Heating
Thermal contraction on Cooling
Haward Technology Middle East 12Section 8
AWS Certified Welding Inspector (CWI)
Welding Stresses (Tensile)
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
Haward Technology Middle East 13Section 8
AWS Certified Welding Inspector (CWI)
Stress Relieving
Thermally
Vibratory
Peening
Haward Technology Middle East 14Section 8
AWS Certified Welding Inspector (CWI)
Crystal Structures
BCC - Body Centered Cubic
FCC - Face Centered Cubic
HCP - Hexagonal Close Packed
BCT - Body Centered Tetragonal
Haward Technology Middle East 15Section 8
AWS Certified Welding Inspector (CWI)
Common Crystal Structures
Haward Technology Middle East 16Section 8
AWS Certified Welding Inspector (CWI)
Metal Solidification
Haward Technology Middle East 17Section 8
AWS Certified Welding Inspector (CWI)
Grain Size Effects
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
Haward Technology Middle East 18Section 8
AWS Certified Welding Inspector (CWI)
Alloying
“Adding elements to change mechanical or physical properties”
Haward Technology Middle East 19Section 8
AWS Certified Welding Inspector (CWI)
Interstitial Alloying
Haward Technology Middle East 20Section 8
AWS Certified Welding Inspector (CWI)
Interstitial Alloying -Results in Lattice Distortion
Haward Technology Middle East 21Section 8
AWS Certified Welding Inspector (CWI)
Substitutional Alloying
Haward Technology Middle East 22Section 8
AWS Certified Welding Inspector (CWI)
Substitutional Alloying -Results in Lattice Distortion
Haward Technology Middle East 23Section 8
AWS Certified Welding Inspector (CWI)
Microstructures
Metals composed of grains (crystals)
Very small
Separated by grain boundaries
Different phases within grains
Haward Technology Middle East 24Section 8
AWS Certified Welding Inspector (CWI)
Microstructure of Iron
Haward Technology Middle East 25Section 8
AWS Certified Welding Inspector (CWI)
Iron-Carbon Phase Diagram
Haward Technology Middle East 26Section 8
AWS Certified Welding Inspector (CWI)
Phases in Steel
Ferrite
Cementite
Austenite
Bainite
Pearlite
Martensite
Haward Technology Middle East 27Section 8
AWS Certified Welding Inspector (CWI)
Cooling Rates
Slow - Pearlite - Softest
Moderate - Bainite
Fast - Martensite - Hardest
Haward Technology Middle East 28Section 8
AWS Certified Welding Inspector (CWI)
Lamellar Appearance of Pearlite
Haward Technology Middle East 29Section 8
AWS Certified Welding Inspector (CWI)
Martensite
Haward Technology Middle East 30Section 8
AWS Certified Welding Inspector (CWI)
Tempering
“Restores ductility and toughness and reduces strength and hardness”
Haward Technology Middle East 31Section 8
AWS Certified Welding Inspector (CWI)Effects of
Tempering Temperatures
Alloy is AISI 4142
Tempering temperature is in degrees F
Haward Technology Middle East 32Section 8
AWS Certified Welding Inspector (CWI)
Effects of Tempering Temperatures
Alloy contains 12% Cr
Note reduction in impact strength at 885 F (475 C)
Haward Technology Middle East 33Section 8
AWS Certified Welding Inspector (CWI)
Continuous Cooling Diagram & Jominy Hardenability Diagram for 8630 steel. Phase formed on cooling varies with cooling rate.
Haward Technology Middle East 34Section 8
AWS Certified Welding Inspector (CWI)
Weld Area & Fe - Fe3C Diagram
Haward Technology Middle East 35Section 8
AWS Certified Welding Inspector (CWI)
Heat Input
Joules/inch = Current x voltage x 60
Travel speed (in./min)
Haward Technology Middle East 36Section 8
AWS Certified Welding Inspector (CWI)
Preheat
Slows cooling rate
Produces less martensite
Reduces risk of cracking
Reduces distortion
Reduces hydrogen
Haward Technology Middle East 37Section 8
AWS Certified Welding Inspector (CWI)
Carbon Equivalent( CE )
CE = % C + % Mn + % Ni + % Cr + % Cu + % Mo
6 15 5 13 4
Haward Technology Middle East 38Section 8
AWS Certified Welding Inspector (CWI)
Examples of Preheating vs C.E.
C.E. Preheat Temperature
< 0.45 Optional
0.45 - 0.60 200 - 400 °F
>0.60 400 - 700 °F
Haward Technology Middle East 39Section 8
AWS Certified Welding Inspector (CWI)
Heat Treatments for Steels
Super-critical - above transformation temperature
• Annealing
• Normalizing
• Quenching (to harden)
Sub-critical - below transformation temperature
• Tempering
• Stress Relieving
Haward Technology Middle East 40Section 8
AWS Certified Welding Inspector (CWI)
Diffusion
“Movement of atoms within a solution, be it a solid, liquid or gas”
Haward Technology Middle East 41Section 8
AWS Certified Welding Inspector (CWI)
Diffusion of Lead and Gold Atoms
Haward Technology Middle East 42Section 8
AWS Certified Welding Inspector (CWI)
SolubilityDissolving Salt into Water Solid into liquid
Diffusion mechanism
Solubility limit
Temperature effects
Haward Technology Middle East 43Section 8
AWS Certified Welding Inspector (CWI)
Solid Solubility
Unique to metals
Solid into solid
Solubility limit
Temperature effects
Haward Technology Middle East 44Section 8
AWS Certified Welding Inspector (CWI)
Examples of Solid Solubility
Gold and lead bars
Carburizing
Nitriding
Haward Technology Middle East 45Section 8
AWS Certified Welding Inspector (CWI)
Stainless Steels
Ferritic
Martensitic
Austenitic
Precipitation Hardening (PH)
Duplex
Haward Technology Middle East 46Section 8
AWS Certified Welding Inspector (CWI)
Sensitization of Austenitic Alloys
“Formation of chromium carbides between 800 - 1600 °F”
(Sensitization reduces the corrosion resistance in many environments)
Haward Technology Middle East 47Section 8
AWS Certified Welding Inspector (CWI)Corrosion Attack of Austenitic Stainless
Steel
Haward Technology Middle East 48Section 8
AWS Certified Welding Inspector (CWI)
Avoiding Sensitization
Heat treatment ( SAWQ )
Stabilized grades
Low carbon grades
Haward Technology Middle East 49Section 8
AWS Certified Welding Inspector (CWI)
Other Common Alloys
Aluminum
• Pure aluminum
• Aluminum-copper
• Aluminum-magnesium
Copper
• Pure copper
• Brasses
• Bronzes
Haward Technology Middle East 50Section 8
AWS Certified Welding Inspector (CWI)
End of this Section