Welding Metallurgy 1998/MJ1/MatJoin3/1 Welding Metallurgy.
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Transcript of Welding Metallurgy 1998/MJ1/MatJoin3/1 Welding Metallurgy.
Welding Metallurgy
1998/MJ1/MatJoin3/1
Welding Metallurgy
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,
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
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
Composite Zone Concerns
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
Introductory Welding Metallurgy,AWS, 1979
Welding Metallurgy
1998/MJ1/MatJoin3/9
Phase Diagram When Interstitial Carbon Alloys with Iron
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
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
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?
Unmixed Zone ConcernsUnmixed Zone Concerns
Partially Melted Zone Concerns
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?