Metallurgy Background 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 Learning Activities 1.Read Handbook pp Look up Keywords 3.View Slides; 4.Read Notes, 5.Listen to lecture 6.View Demos 7.Do on-line workbook 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 Phases of Mater Crystal Structure Phases Changes Iron - Carbon Alloy System Structure of Materials Solid LiquidGasSolid Melting EvaporationSublimation Condensation Solidification AWS Welding Handbook, 8th Ed Vol 1 Take a moment tonight to observe the Time-Temperature Curve During Casting Demonstration found on the Demonstration Page of the WE300 Website. AWS Welding Handbook, 8th Ed Vol 1 AWS Welding Handbook, 8th Ed Vol 1 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 with one cell and 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? Imperfections in Crystals Point - Vacancies & Alloys Line - Dislocations Surface - Grain Boundaries Force Also take some time tonight to link to the Dislocation-Atom interaction during deformation Demonstration found on the Demonstration Page of the WE300 Website Grain Boundaries Metals & How to Weld Them, Lincoln Foundation, 1954 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? Equilibrium Arrangement of Iron Atoms in Pure Iron Ferrite Austenite Delta ferrite RT 910 C 1670 F 1534 C 2795 F 1390 C 2550 F (Body Centered Cubic) (Face Centered Cubic) (Body Centered Cubic) Cooling Curve for Pure Iron Magnetic Transformation Metals & How to Weld Them, Lincoln Foundation, 1954 Substitutional AlloyInterstitial Alloy Alloying Elements Added to Pure Materials Phase Diagram When Interstitial Carbon Alloys with Iron Metallurgical Systems COMPONENT Unit of the Composition Variable of the System CONSTITUENT Association of Phases in a Recognizably Distinct Fashion PHASE Homogeneous, Physically Distinct, Portion of a System 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? EUTECTOID STEEL Slow Cooling (Equilibrium) From Austenite to Just Below the Eutectoid Temperature Pearlite Growth 0.8%C 6.67%C 0.02%C X X X Garbarz et al, The effect of microalloying on microstructure and properties of medium and high carbon ferrite-pearlite steels, Microalloying 95 Conf. Proc., 1995 Please click on the Pearlite Growth Demonstration on the Demonstration Page of the WE300 Website 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? Cooling Eutectoid Steel Rapidly & To Lower Temperatures Shorter Time Lower Temp Fine Pearlite Bainite Martensite 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.