1998/MJ1/MatJoin3/2 Lesson Objectives When you finish this lesson you will understand: The various region of the weld where liquid forms Mechanisms of cracking associated with these regions Learning Activities 1.Read Handbook pp 103-123 2.View Slides; 3.Read Notes, 4.Listen to lecture 5.Do on-line workbook 6.Do homework Keywords Composite 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
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
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 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?
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?