Welding Metallurgy 1998/MJ1/MatJoin3/1 Welding Metallurgy.
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Transcript of Welding Metallurgy 1998/MJ1/MatJoin3/1 Welding Metallurgy.
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Welding Metallurgy
1998/MJ1/MatJoin3/1
Welding Metallurgy
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Welding Metallurgy
1998/MJ1/MatJoin3/2
Lesson ObjectivesWhen you finish this lesson you will understand:• The various region of the weld where liquid forms• Mechanisms of cracking associated with these regions
Learning Activities1. Read Handbook pp
103-1232. View Slides; 3. Read Notes, 4. Listen to lecture5. Do on-line
workbook6. Do homework
KeywordsComposite Zone, Hot Cracking, Constitutional Supercooling, Unmixed Zone, Partially Melted Zone, Constitutional Liquation,
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Welding Metallurgy
1998/MJ1/MatJoin3/3
Materials Behavior
Weldability is the capacity of a material to be welded under the fabrication conditions imposed, into a specific, suitably designed structure, and to perform satisfactorily in the intended service. Materials compatibility Process Response to stress and strain during welding
Introduction
0.1.1.5.0.T1.95.12
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Welding Metallurgy
1998/MJ1/MatJoin3/4
Basic Regions of a Weld
Fusion Zone - area that is completely melted
Heat-Affected Zone - portion of the base metal not melted but whose mechanical properties and microstructure were affected by the heat of the joining process
Base Metal
Fusion zone
Heat-affected zone Base metal
Introduction
0.1.1.5.0.T2.95.12
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Composite Zone Concerns
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Welding Metallurgy
1998/MJ1/MatJoin3/6
Solidification (Hot) Cracking
Solidification (hot) cracking requires Low ductility material High tensile contraction stress
Solidification occurs over a range of temperature Low melting point intergranular films
Sulfur, phosphorus, boron Prevention by
Low C, S, P levels Increased Mn
Cracking in Welds
0.1.1.5.2.T13.95.12
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Introductory Welding Metallurgy,AWS, 1979
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Welding Metallurgy
1998/MJ1/MatJoin3/9
Phase Diagram When Interstitial Carbon Alloys with Iron
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Welding Metallurgy
1998/MJ1/MatJoin3/16
Perils of Welding Free-Machining Steels
Solidification cracking due to impurity elements
Sulfur, phosphorus, boron Lead doesn’t seem to
cause a problem, e.g. 12L14
Impurity segregation at weld centerline creates low ductility area
Combines with shrinkage stress to cause cracking
0.1.1.5.2.T13.95.12
Steel
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Welding Metallurgy
1998/MJ1/MatJoin3/17
Manganese Can Prevent Solidification Cracking
Manganese combines with sulfur to form MnS particles Use a filler metal with higher manganese to absorb sulfur
ER70S-3 Composition ER70-60.06 - 0.15 carbon 0.07-0.15
0.9 - 1.4 manganese 1.4 - 1.850.45 - 0.7 silicon 0.8 - 1.15
0.02 phosphorus 0.020.035 sulfur 0.0350.05 copper 0.5
Steel
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Turn to the person sitting next to you and discuss (1 min.):• Constitutional supercooling works for alloys with K values less than 1.0 but what happens for alloys with K greater than 1.0 (I.e. rising liguidus with increasing temperature)? Can you draw the three corves?
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Unmixed Zone ConcernsUnmixed Zone Concerns
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Partially Melted Zone Concerns
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Turn to the person sitting next to you and discuss (1 min.):• What sequence of event needs to take place for constitutional liquation to result in liquid films? Can we use a phase diagram to predict if this will happen or not?