Practical Welding Metallurgy Object Lessons of Carbon Steel at Room Temperature •Ferrite – pure...
Transcript of Practical Welding Metallurgy Object Lessons of Carbon Steel at Room Temperature •Ferrite – pure...
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Practical Welding Metallurgy Object Lessons
Larry Zirker, MS, WE
Idaho National Laboratory
November 14, 2011
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Metal Shrinks – Wyoming Pipeline
• 6000 feet of pipe
• Cut off to weld
• 40 degree drop in temperature
• Condition in the morning?
6000 ft. X 12 in.
X 0.0000065 X 40° =
18 inches Short
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Weld Metal Shrinks – Adjustable Conveyors
• 5/8-inch holes with 1/2-inch stainless steel nuts welded in
• Bolts stuck
Demonstration
• Two small spot welds—nut moves
• Two large spot welds—nut is stuck
Causes
• Drop in temperature
• Phase change
• Solidification
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Application of Shrinkage
• Weld on a broken stud in an engine block
• Weld inside of a pipe broken off in a fitting
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Annealing Application – Soot and Copper
• Coat a piece of copper with soot
• Burn off with torch
• Annealing temperature is ~500°F
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Video – Soot Coating
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Video – Annealing and Bending
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Iron Carbon Phase Diagram
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Phases of Carbon Steel at Room Temperature
• Ferrite – pure iron with very limited carbon
• Perlite – a mixture of ferrite and carbon (cementite)
• What happens as it gets heated above 1333°F?
– Carbon is dissolved into austenite
– What else happens?
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Video – Phase Change
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Object Lesson: Carrot and Apple Juice
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Video – Phase Change and Quenching
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Why is the HAZ Harder than Base Metal?
• Fastest cooling rate
• Carbon trapped in grains Base Metal Quenched Metal
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Why Do Welds Often Crack at HAZ?
• Metallurgical notch
– Hard microstructure
• Mechanical notch
– Stress riser at the toe
Diameter and depth
of center punch
indicates hardness
of material
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Video – Stress Point Demo
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Contaminant Cracking
• TMI-2 accident
• Move reactor debris into dry storage canisters
• Prove both welding and inspection
• Paradox – Perfect welds – No defects to pick up
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Video – Danger of Shielding Gas