Materials Science: Cast Iron and Ferrous Metals

Introduction to Engineering Materials

• Engineering materials are crucial for everyday life and survival.
• Gold was the first metal used, followed by copper.
• Areas of science studying materials include Engineering Materials, Material Science, and Materials Engineering.

Basic Concepts of Crystal Structure

• Properties of crystalline solids are determined by their crystal structure.
• Atoms, ions, or molecules are arranged in a periodic manner.
• A space lattice or lattice is a 3D network of points in a material.
• A lattice point represents an atom, located where the lines intersect.
• A lattice array shows the arrangement of lattice points.
• A lattice space shows the region covered by lattice points.
• A unit cell is a small repeating block representing the symmetry of a crystal structure.
• Unit cells can be defined as finite representations of an infinite lattice or as small repeating entities, and basic structural units and building blocks of crystal structure.

Lattice Parameters

• Lattice parameters (a, b, c, α, β, γ) describe the dimensions and angles of a unit cell.
• These parameters are typically in the range of a few ångströms (0.1 nanometers).
• Seven crystal systems are defined based on the relationships between lengths and angles (a = b = c and α = β = γ = 90° for cubic).

Basic Types of Crystal Systems

• Different crystal systems are defined by the relationships between the unit cell axes (a, b, c) and the angles between them (α, β, γ).
• Cubic, Hexagonal, and Tetragonal systems are included.

Bravais Lattices

• There are 14 types of Bravais lattices.
• These are categorized based on the types of centering (Face-Centered, Body-Centered, and Base-Centered).

Metallic Crystal Structures

• Simple Cubic (SC)
• Atoms are located at the corners of a cube.
• Low packing density.
• Body-Centered Cubic (BCC)
• Atoms are at the corners and center of the cube.
• Coordination number is 8.
• Face-Centered Cubic (FCC)
• Atoms are at the corners and face centers of the cube.
• Higher packing efficiency.
• Hexagonal Close-Packed (HCP)
• Layers of atoms arranged in hexagonal patterns.
• High packing efficiency.

Crystallographic Directions

• Crystallographic directions are lines or vectors in a crystal.
• Directions are specified using coordinate notation [uvw].
• Converting between four- and three-index notation is possible

Properties of Crystals

• Atomic Packing Factor (APF) - the ratio of atomic volume to unit cell volume.
• Planar Density - density of atoms on a given plane.
• Linear Density - number of atoms per unit length along a given direction.

Metals

• Metals are used in various engineering applications.
• Iron is a popular engineering metal.
• All metals have a crystalline structure.

Alloys

• An alloy is a mixture or compound of two or more elements, at least one being metallic.
• Alloying enhances properties like strength and hardness.
• Alloys are classified into solid solutions and intermediate phases.

Solid Solutions

• Solid solutions occur when one element dissolves into another to form a single-phase structure.
• The solvent is typically metallic, while the dissolved element can be either metallic or non-metallic.
• Solid solutions are classified as substitutional or interstitial.
• Substitutional: atoms of the solute element replace atoms of the solvent element in the lattice.
• Interstitial: atoms of the solute element fit into spaces between the solvent atoms.

Intermediate Phases

• Intermediate phases form when the concentration of one element exceeds its solid solubility limit.
• They have intermediate compositions and unique crystalline structures.

Importance of Metals

• High stiffness and strength
• Good electrical and thermal conductivity
• Toughness
• Cost effectiveness, especially for steel

Metals Used in Manufacturing Processes

• Cast Metal - prepared by casting.
• Wrought Metal - mechanically worked after casting.
• Powdered Metal - treated using powders for shaping.

Classification of Metals: Ferrous and Non-ferrous

• Ferrous metals: contain iron as the main constituent (e.g., cast iron, wrought iron, steel).
• Non-ferrous metals: do not contain iron as the main constituent (e.g., aluminum, copper, tin, zinc, lead).

Ferrous Metals: Properties and Types

• Cast iron (C.I.) - high carbon content (2-4.23%).
• Properties: Hard, Brittle, Fusible, Non-Temperable, Resistant to Corrosion
• Grey cast iron
• White cast iron
• Chilled cast iron
• Malleable cast iron
• Toughened cast iron
• Wrought iron - almost pure iron (0.15% carbon).
• Properties: Soft, Malleable, Ductile, Tough, High Melting Point, Corrosion-Resistant
• Steel - iron alloy with a carbon content up to 2%.
• Properties: Hardened and Tempered, Malleable, Ductile, Forgeable
• Types: Low Carbon (Mild Steel), Medium Carbon, High Carbon; each with variables in properties and applications (springs, tools, structural components).
• Alloy steels - steels with additional elements to obtain specific properties.
• Alloy steels - Chromium, Cobalt, Manganese, Tungsten, Vanadium, Nickel. Each alloyed steel with different benefits

Non-ferrous Metals: Properties and Uses

• Aluminum - a lightweight, corrosion-resistant metal, good conductor of heat and electricity
• Copper - a reddish-brown metal, excellent conductor of electricity and heat
• Tin - a silvery-white, soft metal resistant to corrosion
• Zinc - a bluish white metal, used for galvanization of steel.
• Lead - a soft, heavy metal, used in various applications.

Superalloys

• Materials with superior high temperature strength, hardness, creep resistance, and corrosion resistance used in high-temperature applications (e.g., jet engine components). Superalloys are categorized as Iron-based, Nickel-based, or Cobalt-based.
• Understanding how superalloys are used helps determine their importance in demanding high-temperature systems.

Metal Processing

• Processing methods affect the mechanical properties of the material.
• Grain size affects material strength and ductility.
• Quenching - hardening by rapid cooling from a high temperature.
• Annealing - softening by heating and slow cooling.
• Tempering- a post-hardening heat treatment that enhances toughness and reduces brittleness.
• Cold working - improving a material or component by changing its shape without altering its temperature.

Metal Manufacturing: Production

• Casting - producing metal parts by pouring molten metal into molds.
• Powder processing - forming parts by pressing and sintering powdered metal.
• Metal forming - changing the shape of metal pieces by applying stress (e.g., rolling, forging).

Metal Manufacturing: Fabrication

• Processes that alter the shape or dimension of metal components.
• Deformation includes bending, rolling, forging, and drawing, used to change the shape and size.
• Bulk, like Rolling or forging, or Sheet-based, like drawing or stamping
• Machining - material removal methods to refine components. Includes grinding, drilling, milling, shaping etc
• Joining - combining multiple components (e.g., welding, brazing).
• Finishing - includes coating or plating, used to enhance desired properties.

Mechanical Properties of Materials

• Strength, Elasticity, Plasticity, Ductility, Tensile Strength are significant measures of material behavior under load.

• Stress is the ratio of force on an object to the area upon which it is applied when considering tensile, compressive, shearing, or bearing stress.

• Strain is the change in length when forces are applied (unitless quantity).

• Stress-Strain Diagram - a graphical representation of stress versus strain, that can indicate whether a material is ductile or brittle, or the threshold before yielding.

Polymers

• Polymers are high molecular weight materials formed by linking monomers.
• Extensive use in various applications.
• Types of polymerization - Addition and Condensation. Branching affects the properties of the polymer, with linear polymers being more dense and strong.
• Types of polymers include homopolymers and copolymers (which combine two or more different types of monomers).
• Polarity influences various material properties.

Nanomaterials

• Nanomaterials are materials with structures at the nanoscale (1-100nm).
• Manufacturing (either "top-down"), or "bottom-up" from atomic level components").
• Properties: influenced by their size, shape, surface area, ratio of width/height/length, and how effectively they stick together.
• Potential real-world effects in health and the environment. Manufacturing methods, such as chemical vapor deposition, and atomic layer epitaxy are now used.