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?