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Metallurgy Background

Metallurgy Background

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Metallurgy Background

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  1. Metallurgy Background

  2. Metallurgy Background • Learning Activities • Read Handbook pp 90-102 • Look up Keywords • View Slides; • Read Notes, • Listen to lecture • View Demos • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • Phases of mater • Crystal Structure & Crystal Defects • Phase changes and resulting properties • Iron – Carbon Alloy System Keywords: Phase, Component, Constituent, Solidification, Cooling Curve, Crystal Structure, Vacancies,Substitutional Alloy, Interstitial Alloy, Dislocations, Grain Boundaries, Allotropic Transformation, phase diagram, ferrite, pearlite, austenite, cementite

  3. Structure of Materials • Phases of Mater • Crystal Structure • Phases Changes • Iron - Carbon Alloy System

  4. Liquid Gas Solid Solid Evaporation Sublimation Melting Condensation Solidification

  5. AWS Welding Handbook, 8th Ed Vol 1

  6. Demonstration Take a moment tonight to observe the “Time-Temperature Curve During Casting” Demonstration found on the Demonstration Page of the WE300 Website.

  7. AWS Welding Handbook, 8th Ed Vol 1

  8. AWS Welding Handbook, 8th Ed Vol 1

  9. Questions? • Turn to the person sitting next to you and discuss (1 min.): • Often metallurgist want to know how many atoms are shared in any unit cell (e.g. face centered cubic unit cell). • The atoms located on the face share ½ with one cell and ½ with the other • How much of a corner atom is shared in each cell? • Adding up all the “partial atoms” how many atoms are there per unit cell in a face centered cubic structure? • In a BCC structure?

  10. Imperfections in Crystals • Point - Vacancies & Alloys • Line - Dislocations • Surface - Grain Boundaries

  11. Edge Dislocation Force

  12. Screw Dislocation

  13. Demonstration Also take some time tonight to link to the “Dislocation-Atom interaction during deformation” Demonstration found on the Demonstration Page of the WE300 Website

  14. Grain Boundaries Metals & How to Weld Them, Lincoln Foundation, 1954

  15. Questions? • Turn to the person sitting next to you and discuss (1 min.): • A grain boundary is the place where a crystal with atoms all aligned in one direction meets another crystal with atoms aligned in some other direction with a real mismatch at the boundary. This boundary can be thought of as a tangled mess of dislocations. What happens when a dislocation within one of the grains has a force applied and it moves into the boundary tangle?

  16. Equilibrium Arrangement of Iron Atoms in Pure Iron 1534 C 2795 F (Body Centered Cubic) Delta ferrite 1390 C 2550 F (Face Centered Cubic) Austenite 910 C 1670 F Ferrite (Body Centered Cubic) RT

  17. Cooling Curve for Pure Iron Magnetic Transformation Metals & How to Weld Them, Lincoln Foundation, 1954

  18. Alloying Elements Added to Pure Materials Substitutional Alloy Interstitial Alloy

  19. Phase Diagram When Interstitial Carbon Alloys with Iron

  20. COMPONENT Unit of the Composition Variable of the System CONSTITUENT Association of Phases in a Recognizably Distinct Fashion Metallurgical Systems PHASE Homogeneous, Physically Distinct, Portion of a System

  21. Questions? • Turn to the person sitting next to you and discuss (1 min.): • If we take a glass of warm water and start to dissolve sugar in it, and keep adding sugar until no more dissolves, what happens? If we heat it a little more what happens? • If we take warm steel in the austenite phase (say at 1700F) and dissolve carbon in it, and keep adding carbon until no more dissolves, what happens? If we heat it to 2200F what happens?

  22. EUTECTOID STEEL Slow Cooling (Equilibrium) From Austenite to Just Below the Eutectoid Temperature

  23. Pearlite Growth

  24. 0.02%C 0.8%C 6.67%C X X X

  25. Garbarz et al, “The effect of microalloying on microstructure and properties of medium and high carbon ferrite-pearlite steels”, Microalloying ’95 Conf. Proc., 1995

  26. Demonstration Please click on the “Pearlite Growth” Demonstration on the Demonstration Page of the WE300 Website

  27. Questions? • Turn to the person sitting next to you and discuss (1 min.): • As the pearlite forms from the very slow cooling from the austenite, carbon atoms must diffuse to make the lathes. What happens if we cool a little faster thus not giving enough time for the carbon to diffuse the complete width of the lathes?

  28. Cooling Eutectoid Steel Rapidly & To Lower Temperatures

  29. Fine Pearlite Shorter Time Lower Temp Bainite Martensite

  30. Questions? • Turn to the person sitting next to you and discuss (1 min.): • In the hot water in which we added the maximum amoount of sugar in the earlier question, we now let it cool, what happens? • In austenite steel where we cooled it fast and the carbon did not have a chance to get out but rather formed a supersaturated solution, what happens if we just let it set at room temperature? What happens if we heat it up just a little.