Welding Metallurgy 1998/MJ1/MatJoin3/1 Welding Metallurgy

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 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 T

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 T

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 T

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 T 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?

Unmixed 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?