ME215 Exam 2 Study Guide

Annealing

- Cooling in furnace
- Cost effective and time consuming
- The furnace imposes cooling conditions at all locations
- Result in identical structures and properties

Normalizing

- Cooling in air
- Cooling will be different in different locations
- Properties will vary between the surface and interior

Process Anneal

- Cooling in air

Recrystallization Anneal

- Recrystallization is induced after a material has been cold worked to reduce strain hardening effects
- Induces a change in size, shape and distribution

Stress-Relief Anneal

- Reduces residual stresses
- Materials are heated and then slow cooled
- Microstructures and mechanical properties remain unchanged

Spheroidizing Anneal

- Slow cooling
- For high carbon materials

Heat Treatment

- A process of controlled heating and cooling of materials for the purpose of altering their structures and properties, which changes in physical and mechanical properties can be introduced with no change in product shape

Processing heat treatments are used to...

- increase strength
- prepare the material for fabrication
- improve machining characteristics
- reduce forming forces
- restore ductility for further processing

Heat Treatments for Nonferrous Metals

Three purposes
- Produce a uniform, homogenous structure
- Provide a stress relief
Induce recrystallization

Solid-Solution Strengthening

Substitutional solutions or interstitial solutions

Strain Hardening

Increases strength by plastic deformation

Grain Size Refinement

Metals with smaller grains tend to be stronger

Precipitation hardening or Age hardening

Strength is obtained from a nonequilibrium structure

Dispersion Hardening

Dispersing second-phase particles through a base material

Phase transformations

Heated to form a single phase at an elevated temperature and subsequently transform to one or more low temperature phases upon cooling (austenite -> martensite)

Precipitation Hardening

- Most effective mechanism to strengthen nonferrous metals
- Non-equilibrium heat treatment procedure

Process of Precipitation Hardening

Three-step Sequence: solution treatment -> quench -> aged

Coherency - A Coherent Precipitate

The crystallographic planes of the parent structure are continuous through the precipitate cluster, and the solute aggregate tends to distort the lattice to a substantial surrounding regiong

Non-Coherency (Overage)

Second phase particles have their own crystal structure and distinct interphase boundaries

Overaging

The decrease in hardness and strength of precipitation or age hardened materials

Aging Step

Divide precipitation-hardening materials into two types: natural aging materials (ages at room temperature) and artificial aging material (requires elevated temperature to produce aging)

Tempering

To sacrifice strength and hardness for ductility and toughness

Age Hardening

To sacrifice toughness and ductility for strength

Continuous Cooling Transformations (CCT)

The modification of ttt diagram, shows the phase and composition of steels upon cooling as functions of temperature and time

Jominy Test

The hardenability test - a material is heated and quenched from one end, then hardness along the material length is determined

Carbon Content

The larger carbon content the higher strength, the higher hardness

Alloy Additions

Related to the amounts and types of alloying elements; Primary reason to add an alloying element is to increase hardenability

Quench Media

Quenchants are the medium in which a material is quenched

Stages of Quenching

Formation of the vapor jacket -> Nucleate boiling phase -> Conduction and convection

Quenchant Consideration

- Water is an effective quenching medium because of its high heat of vaporization and relatively high boiling point
- Brine is similar to water as a quenchant medium
- Oil is utilized if slower quenching rates are desired
- Water based polymer quenchants have properties between oil and water and brine
- Other slow cooling quenchants: Molten salt baths, cooling in air, bury the hot material in sand, etc.

Residue Stress

- Exist in a part independent of an applied stress
- Undesirable residual stresses result in cracking, warping, dimensional changes

Causes of dimensional changes during heat treatment

- Thermal expansion during heating and thermal contraction during cooling
- Volume expansion and contraction

Ways to prevent quench cracking and residual stresses

- More uniform cross-sectional area
- Generous fillets at interior area
- Radiused exterior corners
- Smooth transitions
- Adding additional holes

Austempering

Austenite -> Bainite, rapidly quench into liquid medium 15 degrees celcius above Martensite start temperature and held for sufficient time

Ausforming

Thermomechanical processes in which deformation and heat treatment are intimately combined. Material is heated to form austenite and then quenched to a temperature between pearlite and bainite; then slowly cooled to produce bainite or rapidly quench to martensite

Martempering

Austenite -> Martensite, rapidly quench into liquid medium 15 degrees celcius above Martensite start temperature and slow cool in air through martensite transformation

Cold Treatment and Cryogenic Processing

- Cooling into sub-zero temperature with dry ice or liquid nitrogen
- It can complete austenite to martensite transformation and increase strength and hardness
- Improve wear resistant
- Longer lifetime

Selective heating of the surface

- Flame Hardening
- Induction Hardening
- Laser Beam Hardening
- Electron Beam Hardening

Altered Surface Chemistry

- Carburizing
- Nitriding
- Ionitriding
- Ion Carburing
- Carbonitriding
- Nitrocarburizing

Deposition of an Additional Surface Layer

- Ion Plating
- Ion Implantation

Oxidation Process

Decreases the amount of carbon, silicon, manganese, phosphorous, and sulfur in pig iron or steel scrap

Steel Processing

Continuous casting produces feedstock material (slab, bloom, billet, strand) that is used in forging or rolling, steel have large amount of oxygen dissolved in molten metal

Deoxidation

Oxygen reacts with deoxidizers and produce solid metal oxide that are removed from the molten metal or become dispersed throughout the structure

Vacuum Degassing

A stream of molten metal passes through a vacuum chamber into a mold

Vacuum Arc Remeltinig (VAR), Vacuum Induction Melting (VIM)

Solidify metal electrode, then metal electrode is remelted, molten droplets pass through a vacuum

Electroslag Remelting (ESR)

Solidify metal electrode, then remelting is conducted under a blanket of molten flux, non metallic, impurities float and are collected in the flux

Low-Carbon Steel

Excellent ductility and fracture resistance but lower strength

Medium-Carbon Steel

Balanced properties

High-Carbon Steel

High strength and hardness but at the the expense of ductility and fracture resistance

AISI SAE Classification System

Four-digit number
- First number indicates the major alloying elements
- Second number designates a sub-grouping within the major alloy system
Last two digits indicate the carbon Percentage expressed as "points"

Constructional Alloys

Purchased by AISI-SAE, which effectively specifies chemistry

High-Strength Low-Alloy Structural Steels (HSLA)

Focus on product (size and shape) and desired properties

HSLA

- Provide increased strength to weight ratio
- Modest increase in cost
- High yield strength, good weldability, and good corrosion resistance

Microalloyed Steels

- Low and medium carbon steels with small amounts of alloying elements
- Offer maximum strength with minimum carbon
- Preserves weldability, machinability, and formability

Bake-Hardenable Steel

- Low carbon steel that is resistant to aging during normal storage, but begins to age during sheet metal forming
- A significant role in automotive applications

Advanced High-Strength Steels (AHSS)

- AHSS is primarily ferrite-phase, soft steels with varying amount of martensite, bainite or retained austenite - which offers high strength with enhanced ductility
- Improved formability
- Possibility of weight reduction

Types of AHSS

- Dual Phase Steels
- Transformation-Induced Plasticity Steels
- Complex-Phase Steels
-Martensitic Steels

Dual Phase Steels

Microstructure of ferrite and martensite

Transformation-Induced Plasticity Steels

Microstructure of ferrite, hard martensite or bainite and at least 5% volume of retained austenite

Complex-phase Steels

Microstructure of ferrite and bainite with small amount of martensite, retained austenite and pearlite

Martensitic Steels

Almost entirely martensite

Free Machine Steels

Steels machine readily and form small chips when cut

Pre-coated Steel Sheet

- The coating is applied when steel is still in the form of a long, continuous strip
- To reduce the cost and time consuming in finishing process

Steels for Electrical and Magnetic Applications

Amorphous Metals
- No crystal structure , grains, or grain boundaries
- Magnetic domains can move freely
- Properties are the same in all directions
- Corrosion resistance is improved

Special Steels

Maraging Steel - Extremely high strength
Steels for High-Temperature Service - for using at high tempearture

Tool Steels

High carbon, high strength, ferrous alloys that have a balance of strength, toughness, and wear resistance

Types of tool steels

- Water-hardening tool steels
- Cold-work steels
- Shock resisting tool steels
- High speed tool steels
- Hot-work steels
- Plastic mold steels
- Special purpose tool steels

Grey Cast Iron

Graphite flakes

White Cast Iron

Excess carbon in form of iron-carbide - hard and brittle

Malleable Cast Iron

Irregularly shaped cluster of graphite - improved ductility compared to grey cast iron

Ductile or nodular cast iron

Smooth spheroidal graphite - provide ductility

Austempered ductile iron

Ductile cast iron which go to austempering heat treatment - provide double strength with same ductility compared to ductile cast iron, excellent strength-to-weight ratio

Compacted graphite cast iron

Compacted graphite is intermediate to flake graphite of gray cast iron and nodular graphite of ductile iron

High-alloy cast iron

Enhance corrosion resistance and/or good elevated temperature service

Copper and Copper Alloys

- High electrical and thermal conductivity
- Useful strength with high ductility
- Corrosion Resistance

Aluminum and Aluminum Alloys

- Workability
- Light weight
- Corrosion Resistance
- Thermal and electrical conductivity
- Optical reflectivity
- Easily finished

Magnesium and magnesium alloys

- Lightest of commercially important materials
- Poor wear, creep and fatigue properties
- Highest thermal expansion of all engineering metals
- Modulus of elasticity is less than that of alminum
- High energy absorption and good damping

Titanium and Titanium Alloys

- Strong lightweight, corrosion resistant metal
- Less dense than steel, high strength-to-weight ratio
- Can be used in high temperature applications
- High cost, fabrication difficulties, high energy costs for fabrications

Nickel-Based Alloy

- Outstanding strength and corrosion resistance at high temperatures
- Good formability, creep resistance, strength and ductility at low temperatures
- Wrought alloys are known as Monel, Hastelloy, Inconnel, Incoloy, and others

Superalloys and other metals designed for high-temperature service

- Alloys based on nickel, iron, cobalt
- Refractory metal: niobium, molybdenum, tantalum, rhenium, and tungsten
- Intermetallic compounds

Lead and Tin, and their alloys

- Lead and lead alloys - provide high density with strength and stiffness that are the lowest of engineering metals
- Tin - use as a corrosion resistant coating on steel
- Lead and tin are used together as bearing materials and solder

Graphite

Good thermal and electrical conductivity, can withstand high temperatures and lubricity

Plastic

- Large molecules that are built up by the joining of smaller molecules
- Low density, low tooling costs, good corrosion resistance, low cost

Addition

- A number of basic units (monomer) link together to form a large molecule (polymer) in which there is a repeated unit (mer)

Degree of Polymerization

Average number of mers in polymer

Copolymer

Two different types of mer

Terpolymer

Combining three different monomers

Condenstion

Occurs when a polymer is formed plus by-products

Thermoplastics

- Linear Polymer
- Heat-softening material
- Reversible reaction at elevated temperature

Thermosets

- Highly cross-linked or three-dimensional framework structure
- Produced by condensation polymerization
- Irreversible Reaction at elevated temperature - material is unable to recycle

Elastomer or Elastic Polymer

- Linear polymer with large amount of elastic deformation when a force is applied

Ceramic

- High temperature usage
- Hard and brittle
- High melting point
- Low thermal expansion
- Good creep resistance
- High compressive strength

Composite Materials

Non-uniform solid consisting of two or more different materials that are mechanically or metallugically bonded together

Anisotropic

Properties of laminar composites, distinct layers of materials bonded together

Isotropic

Properties of particulate composite, particles of one material in a matrix of another material

Fiber-reinforced Composites

- They are composite that continuous or discontinuous thin fibers of one material are embedded in a matrix
- Common objective is high strength and lightweight

General Sequence of Product Design

1. Design
2. Material Selection
3. Process Selection
4. Production
5. Evaluation
6. Redesign / Modification

Materials Processing

The science and technology that converts a material into a product of a desired shape in the desired quantity

Casting Processes

Exploit the properties of a liquid as its flow into and flows into and assumes the shape of a prepared container, and the solidifies upon cooling

Material Removal Processes

Remove selected segment from an initially oversized piece