Weldability and metallurgy

Weldability and metallurgy

Weldability and Metallurgy of Welding Heat Sources: Arc, Flames, Resistance, Friction, explosion, impact, chemical, radiation, energy beams (Most common is Arc) Effects of Heat: Residual Stresses and Distortion Reduction of ductility or a degree of hardening in HAZ leading to cracking Deterioration of toughness properties (primarly in HAZ) Loss of strength in HAZ of certain workhardened, quenched, and tampered material Calculation of Heat Input: Weldability and Metallurgy of Welding Weld Thermal Cycles - Time Temperatue History Weldability and Metallurgy of Welding Weld Thermal Cycles – Temperature Distribution Around moving Arc Weldability and Metallurgy of Welding Welding Metallurgy Welding metallurgy deals with • Interaction of different metals • Interaction of metals with Gases and chemical • Changes in Physical Properties • Solubility of gases in metals • Effect of impurities For welding processes, reaction times are in order of minutes, seconds and fraction of seconds Weldability and Metallurgy of Welding Structure of Metals Liquid State – Free movement of atoms Solid State - Space Lattices (imaginary lines connecting atoms of symmetrical arrangements) Pure Metals 1. Common Space Lattices 2. (over a dozen types are possible) 3. Allotropic Forms and Allotropic Change Alloys 4. Solid Solution 5. (Interstitial & Substitutional) 6. Intermetallics (Chemical Compounds with complicated crystal structures) 4. Phases in an alloy Weldability and Metallurgy of Welding Solidification Does not occur simultaneously throughout the melt Formation of multiple nuclei at different points Growth – Adding on of additional crystals as temperature decreases Growth Directions - Six directions normal to the main axis of crystal – Cube Dendritic Growth – Growth in a tree like pattern with branches and sub Branches Grains – Nuclei occur randomly and dendrites from different nuclei are at odd angles with one another.  They cannot merge as they meet.  They grow untill they meet dendrites from adjacent crystals.  This gives rise to irregularly shaped areas called grains Weldability and Metallurgy of Welding Phase Transformations 1. With Temperature-Allotropic Transformation (Iron, Titanium, Zirconium, Cobalt etc) 2. Recrystalization (melts or Resolidifies) Weldability and Metallurgy of Welding Equilibrium Diagram, Constitution Diagram or Phase Diagram Weldability and Metallurgy of Welding Equilibrium Diagram and Welding Processes  Phase diagrams are based on equilibrium conditions  For Welding – temperature changes are rapid and equilibrium conditions rarely occur  Still, Equilibrium diagrams are the best available tools to determine phases Hardenability Heat Treatment process to increase hardness is similar to the process occurring in welding Hardenability depends on several factors, such as  Grain Size and Microstructure  Deformation in crystals  Temperature to which steel has been heated  Rate of Cooling (CCT and TTT diagrams)  Alloying elements Weldability and Metallurgy of Welding Welds Factors during welding  Changes in temperature  Changes in dimensions  Growth of crystals and Grains  Phase Transformations  For Arc Welding – Thermal Cycles are most important (depend on process, procedure, metal and mass)  Rate of change decrease as the distance from weld increases  Many different cooling rates will result – thus many different microstructures will result  The system is more complex when filler metal is added across the arc [...].. .Weldability and Metallurgy of Welding Welds – Thermal Cycles Weldability and Metallurgy of Welding Equilibrium Diagram and Welding Processes Weldability and Metallurgy of Welding Welds – Different Microstructures Weldability and Metallurgy of Welding Welds – Changes in Composition  When the composition of filler... rates will produce a range of microstructures across the weld  Each microstructure will have its own properties Weldability and Metallurgy of Welding Welds – Changes in Composition Weldability and Metallurgy of Welding Stresses and Distortion Weldability and Metallurgy of Welding Stresses and Distortion . properties Weldability and Metallurgy of Welding Welds – Changes in Composition Weldability and Metallurgy of Welding Stresses and Distortion Weldability and Metallurgy. the arc Weldability and Metallurgy of Welding Welds – Thermal Cycles Weldability and Metallurgy of Welding Equilibrium Diagram and Welding Processes Weldability