ME3251 Revision

ME3251 Chapter One: -

Example Applications of Engineering Materials o Structural vs Functional o Product requirements vs Cost 

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Design Considerations and Materials Properties o Design for Dimensional stability/accuracy Design against fracture/failure (often localized phenomena) o

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Stresses and Strains Normal stress o Nominal (Engineering) stress o True stress o o o o

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Shear stress Nominal shear stress True shear stress Normal strain Nominal strain True strain Engineering shear strain Strain energy

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Deformation of materials under Tension Elastic Deformation o o Plastic Deformation Necking and Fracture o Elastic Behaviors o

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Young’s Modulus and Yield Strength Physical Basis of Young’s Modulus o Stretching and bending of bonds Bond types vs approximate E Covalent cross-link density vs E   

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Ceramics, Metals, Polymers, Composites vs E Ceramics, Metals, Polymers, Composites vs Yield Strength

Structure of Materials o Polycrystalline Metals and Ceramics Crystal Structures and Crystallography o

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Amorphous Solids 

Glass (3D network with no crystal structure)

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Amorphous polymers (tangled mass of chain-like molecules)

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Modulus of Polymers Modulus of tensile strength vs Temperature (Glass transition temperature) o Modulus of elasticity vs Temperature o

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Composites E vs volume fractions of stiffener o

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Design against Yielding (or Plastic Deformation) o Physical Basis of Yield Stress Stress to move dislocations Strengthening mechanisms: ways to increase the yield strength of materials Dislocations in crystals Movement of dislocation and slip of crystal    

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Deformation of single crystals

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Yield or ultimate tensile strength vs different kinds of steels

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Principal strengthening mechanisms in some common structural materials

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Measurement of Young’s modulus

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The hardness test 

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Density vs Ceramics, Metals, Polymers and Composites

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Material Cost 

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Elastic Moduli Case Studies 

Chapter Two: -

Static Fracture Ductile-to-Brittle Transition Fatigue Failure Stress Corrosion Cracking Effect of Elevated Temperature on Polymers Creep and Creep Rupture Joints Surface Engineering and Coating

Chapter Three: Engineering Alloys Ferrous Alloys:

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Carbon Steels and Low-Alloy Steels Tool Steels Stainless Steels Cast Iron

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Steels o

Common Terminology of Steels Rimmed Steels Killed Steels Clean Steels Free-machining Steels    

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General Properties of Steels Carbon Steels and Low-Alloy Steels Mill Products of Carbon Steels 

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Cold-finished (Cold-worked) – largely for low-carbon steel

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Hot-finished

Equilibrium Microstructure of Plain Carbon Steels  

Ferrite (Soft and Ductile; can be cold-worked readily)

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Cementite or Iron Carbide (Hard and Brittle with Ductility ~ Nil)

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Pearlite (Ferrite and Cementite in lamellar structure; spacing depends on cooling rate; strength decreases with increased spacing)

Resultant microstructures from Austenitising 

Eutectoid steel (Pearlite)

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Hypo-eutectoid steel (Primary or proeutectoid Ferrite + Pearlite)

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 Austenite (Soft and Ductile; can be hot-worked readily)

Hyper-eutectoid steel (Primary or proeutectoid Cementite + Pearlite)

Non-equilibrium phases from heat treatment  

Bainite

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Martensite

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Tempered Martensite

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TTT Diagram (Time-Temperature-Transformation) 

Eutectoid Steels (0.8%C)

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Hypo-eutectoid Steels

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Hyper-eutectoid Steels

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Effects of C Content on TTT diagrams

CCT Diagram (Continuous Cooling Transformation) 

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Heat Treatments of Steels 

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Annealing Processes for Ferrous Alloys Full Annealing (usually for hypo-eutectoid steel) o o Normalising o Recrystallisation Anneal Stress Relieving Anneal o Spheroidising o

Hardening by Quenching and Tempering of Eutectoid Steel 

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Constructed under constant cooling rates

Hardenability (how easy can you form martensite) Hardenability Curves Carbon Steels o Different Steels o o For Practical Purposes Effect of carbon content on quenching and tempering of plain carbon steels Martensite start and martensite Finish o o Hardness of martensite Time for pearlite transformation o Hardness of tempered martensite o Major Problems with quench hardening of plain-carbon steels Solutions Martempering o o Austempering

Summary on Plain Carbon Steels Effect of Alloying Elements Modify tempering characteristics Grades 

Carburising Grades (Low-alloy steel)

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H Steels

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B Steels

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High-Strength Sheet Steels

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High-Strength Low-Alloy Steels

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Mill-Heat Treated Steels

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Ultrahigh-Strength Steels

Austenitic Manganese Steels (Hadfield Steels) Summary on Carbon and Low-alloy Steels Tips on Application of Carbon and Low-alloy Steels Review of Heat Treating Thermal Cycles for Carbon and Low-alloy Steels Some Practical Aspects of Quenching Prediction of Hardness Profile Case Hardening 

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High Alloy Steels Tool Steels 

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Effects of alloying elements Main characteristics of Tool Steels High austenitising temperature o o Secondary Hardening o Temper Embrittlement  Different Categories of Tool Steels o Cold-worked Tool Steels W-grade (Water hardening) O-grade (Oil hardening) A-grade (medium-alloy, Air hardening) D-grade (high C and high Cr, air-to-oil hardening) S-grade (Shock resisting tool steel) Hadfield’s Manganese Steels (12% Mn, 1% C) Special Purpose Tool Steels Hot-work Tool Steels o H-grades (Hot-work die and mould steels)       

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Cr-type

Mo- and W- types High Speed Steel (T- or M-grade) Mold Steel (P grade) 

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Considerations in Selection of Tool Steels o Hardening Characteristics Safety in hardening Depth of hardening required Distortion in hardening Resistance to decarburization Use Characteristics o    

Resistance to heat softening Wear resistance Depth of hardening required Distortion in hardening Other considerations Toughness Machinability Weldability Cost factor    

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Comparisons of tool steel properties

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Useful tips

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Selection and designing with tool steels Working hardness o o Avoidance of crack-sensitive shapes Stock size (scale removal and finish grinding allowance) o Heat treating (stress relieving) o o Avoidance of man-made defects/mistakes Grinding burns Electrical discharge machining damage Hydrogen embrittlement    

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Standard specifications for a tool steel part in an engineering drawing Rough machine o Stress relieve o Finish machine leaving grinding allowance o o Harden and temper to XXXHRC Finish grind to tolerances o

Stainless Steels 

Passivation and Corrosion Resistance of Stainless Steels

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Effects of Alloying Elements

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Types of Stainless Steels and their properties o Ferritic S.S (16-20%Cr, = 8 Ni + Mn) o P.H alloys o Martensitic P.H Semi-austenitic P.H Austenitic P.H Duplex alloy o o Proprietary alloys   

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Designation of Stainless Steels

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Why at times stainless steels corrode?

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Sensitisation/weld decay of Stainless Steels Pitting of Stainless Steels Stress corrosion cracking in stainless steel

Different grades of Stainless Steels Grades of Austenitic S.S o Grades of Martensitic S.S o o Properties and cost comparison Applications of Stainless Steels

Cast Iron (iron with >2.1%C + other alloying elements) 

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Types of cast iron Gray Iron o White Iron (Chilled Iron) o o Malleable Iron Ductile (noduluar) Iron o Alloy iron (mainly gray or white irons altered by alloy o additions to make them harder or more corrosion resistant) White Cast Iron (2-4%C, 0.5-2%Si, 0.5%Mn) o 3 reactions upon cooling from the liquid phase Grey Cast Iron (2-4%C,1.0-3.0%Si) 3 reactions upon cooling from the liquid phase o Subsequent heat treatment of gray cast iron o Normalizing Annealing Stress-relieving Quench-hardening o Alloy Classification General Properties of Gray Iron o Applications of Gray Cast Iron o    

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Malleable Iron (2-3%C, 1-1.8%Si) Properties of Malleable Iron o o Alloy Designation (5 digits) Ductile (nodular) Iron (2.2Si + small amounts of MG/Ce) 3 reactions o Subsequent heat treatment similar to grey cast iron o Alloy Designation o o Properties of ductile iron Cast Iron with other matrix structures o Bainitic Gray Iron (Bainitic) Austempered Ductile Iron (ADI) o Austenitic Gray Iron (Fe-3C-2Si-20Ni-2Cr) o o Austenitic Ductile Iron (Fe-3C-2Si-20Ni+Mg/Ce)