Description Metallurgy for Non Metallurgist.pptx
- 1. Steel Metallurgy for Non Metallurgist (Part I : Basic Elements & Phase Diagram ) A Summary & Exegesis of a Short Course given by. David J. Coates, PhD.
- 2. * Opaque element, lustrous when polished , that is good electricity & heat conductor * Such properties are due to its crystalline structure in the solid state * Metal is obtained by refining the ores, and upon further treatment its properties can be enhanced. * Metal use history : Copper Age Bronze Age Iron Age Industrial Age Modern Age I. WHAT IS METAL
- 3. •Crystal is a very well-ordered lattices arrangement. • A lattice is composed of several atoms, to form a single building block •A lattice ( single block ) is repeated in very regular manner, so several lattices to create a grain. • Adjacent grains are separated by grain boundaries. . II. METAL CRYSTALLINE MICRO STRUCTURE
- 4. Microscopic View of Metal Structure 1, 2, 3, 4, 5 are called “grains”. A hair diameter is about 50 microns
- 5. Microscopic Structure of Pure Iron
- 6. Some Single Lattice Arrangements Called ”body centered cubic ( BCC )” Found in Iron under “Ferritic” phase
- 7. Some Single Lattice Arrangements Called ”face centered cubic ( FCC )” Found in Iron under “Austenite ” phase
- 8. Some Single Lattice Arrangements Called ”Body Centered Tetragonal ( BCT )” Found in Iron under “Martensite ” phase
- 9. Some Single Lattice Arrangements Called ”Hexagonal Close-Packed ( HCP )” Found in Zinc, Cadmium.
- 10. • Solution : Solute dissolved in the solvent, where solute can’t be distinguished from solvent due to fully incorporated in the solvent. • Phase : A physically homogeneous and distinct portion of a system. •Liquid Solution of CaCl2 in water, is one phase at ambient condition ( liquid phase ) , but 2 phases on elevated temperature ( liquid and gas phase ), and 2 phases on very low temperature ( liquid and solid phase ). • Solid solution : Atoms of C in Fe bar, may exists in several phase such as feritic phase ( BCC ), austenitic phase ( FCC), e.t.c. . III. SOLUTION AND PHASE DIAGRAM
- 11. Phase Diagram of CaCl2 in Water
- 12. • The amount of solute affects the phase transition ( transformation ) temperature of a solution. • There is an area where equilibrium condition takes place for 2 phases, represent the mixture of 2 phases ( called as slush zone in above diagram ). The phase composition within equilibrium zone is estimated from the diagram. E.g. at 5% salt content at -40 degF , the equilibrium contains (5/28) portion liquid phase and (23/28) portion of solid phase. The liquid phase contains 28% salt, and solid phase contain 0.1% salt. •There is a point where drastical phase change happens directly to 2 or 3 other phases. This point is called eutectic point. At Eutectic point, phase transformation happens without passing equilibrium zone. This phenomena is about same as critical temperature in VLE. What a Phase Diagram Tells Us
- 13. Steel : Solid Solution of Iron (Fe ) and Carbon ( C ) • Fe as solvent and other alloying components as solute, where solute atoms fit in the interstice in between the solvent atoms. • Plain Carbon Steel : Alloy of Fe and Carbon as main alloying atom. Carbon content typically maximum 0.2%. •Alloy Steel : Alloy of Fe and Carbon with additional alloying atom to enhance the properties, such as AISI 5160 which contain 0.6% C and 08% Chromium solute in Fe. • Stainless Steel : Alloy of Fe and Carbon with additional Chromium at least 11% solute in Fe, developed to enhance corrosion resistance. •For basic understanding purpose, the phase diagram will be given for plain Carbon Steel only.
- 14. IV. STEEL PHASES VIEWED FROM PLAIN STEEL PHASE DIAGRAM Called “Ferritic / Alpha Iron “ BCC Lattice Block Magnetism Very Small Carbon Solubility , practically pure Iron
- 15. Called “Austenite” / Gamma Iron FCC Lattice Block Non Magnetism Higher Carbon Solubility, higher strength then BCC
- 16. CEMENTITE GRAINS ( DARK ) Called “Cementite” Very complex lattice block Non Magnetism Iron Carbide compound, Fe3C Very hard but brittle very brittle just as graphite Lamellar Structures are called “Pearlite”, an equilibrium zone between Ferrite and Cementite
- 17. Called “Martensite” BCT Lattice Block Magnetism Non equilibrium phase, formed during quenching the austenite. Very hard but brittle due to its needle grains structure
- 18. EUTECTIC DIAGRAM : SOLID-LIQUID OR SOLID- SOLID EQUILIBRUM PHASE DIAGRAM
- 19. READING THE BASIC EUTECTIC DIAGRAM STAR POINT LIQUID PHASE ALPHA PHASE BETA PHASE PHASE % %B in L PHASE % %B in ALPHA PHASE % %B in Beta BLUE 100 20 0 0 0 0 RED 99.9 20 ~0. 1 5 0 0 GREEN 25 50 75 10 0 0 PURPLE 0 0 83.4 5 16.6 ~90 •Amount of Solute B within Solvent A affects the phase transition temperature. • Alpha phase will contain not nonly A element but also B element, as alpha B wil not only contain B element but also A element. The amount of elements within a phase varies depending on the temperature.
- 20. LEAD-TIN EUTECTIC DIAGRAM •SOLDER is ~60% of Tin within Lead , which has eutectoid temperature about 200 degC. The eutectoid condition enables solder ( Pb-Sn 60%) to melt and quickly solidify as temperature drops below 200 degC.
- 21. Iron (Fe) and Cementite (Fe3C) Eutectic Diagram
- 22. Iron (Fe) and Cementite (Fe3C) Eutectic Diagram •The Ferrite pure iron can only dissolve max. 0.02% C, hence it’s not so strong in physical properties. •Austenite iron can dissolve more carbon, hence it’s stronger, but adding too much carbon will start emerging the cementite phase which is hard but brittle. •Pure Fe transforms from ferrite ( alpha iron ) to austenite ( gamma iron ) at high temperature, about 910 degC. • Alloying the carbon will reduce the transformation temperature required from alpha to gamma phase. •Other alloying atoms such as Ni & Cr may reduce transformation temperature such that ferrite, or ferrite + asutenite ( duplex steel ) can exist under ambient temperature.
- 23. Iron (Fe) and Cementite (Fe3C) Eutectic Diagram •A steel bar containing 0.4% Carbons, upon heating to 850 degC, all phases inside it will be austenite. Then upon gradual cooling till 760 degC, the ferrite grains will grow and final composition will be N ferrite and M austenite. Upon further cooling, ferrite portion increases to N’. •A steel bar containing 0.9% Carbons, upon heating to 850 degC, all phases inside it will be austenite. Then upon gradual cooling till 760 degC, the cementite grains will grow and final composition will be O cementite and P austenite. Upon further cooling, cementite portion increases to O’. •Region below the eutectoid isotherm line , apart from Ferrite and Cementite Phase, is called Pearlite phase, which is mixture between cementite and ferrite (alpha + Cm) , having lamellar grain structure. •The carbon element content in each phase discussed above is read from phase boundary line at the mentioned temperature.
- 24. Iron (Fe) and Cementite (Fe3C) Eutectic Diagram •Hence austenite phase never exists in Plain Carbon steel cooled gradually – following the equilbrium phase diagram-- from austenite temperature range to ambient temperature, only perlite phase will formed. Pearlite due to its thin lamellar structure is not strong eventhough not brittle, hence not desired in general application. •But upon quick cooling / quenching – non equilibrium process– autenite grains will be trapped and retained austenite phase may exist in ambient temperature. The retained austenite phase will be surrounded by side effect of non equilbrium process : hard but brittle martensite structure. •Hence : steel mechanical properties is controlled by its microstructure, and its microstructure is controlled by its temperature –and alloying element present in it -- . Technique to control the microstructure of steel is called metal heat treatment.
- 25. Plain Carbon Steel Complete Phase Diagram
- 26. Steel Metallurgy for Non Metallurgist (Part II : Mechanical Properties and Heat Treatment ) Will continue to………………..