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Practical Welding Metallurgy Object Lessons

Larry Zirker, MS, WE

Idaho National Laboratory

November 14, 2011

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

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

Application of Shrinkage

• Weld on a broken stud in an engine block

• Weld inside of a pipe broken off in a fitting

Annealing Application – Soot and Copper

• Coat a piece of copper with soot

• Burn off with torch

• Annealing temperature is ~500°F

Video – Soot Coating

Video – Annealing and Bending

Iron Carbon Phase Diagram

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?

Video – Phase Change

Object Lesson: Carrot and Apple Juice

Video – Phase Change and Quenching

Why is the HAZ Harder than Base Metal?

• Fastest cooling rate

• Carbon trapped in grains Base Metal Quenched Metal

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

Video – Stress Point Demo

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

Video – Danger of Shielding Gas