Midterm 265 Flashcards
Engineering Stress (σ)
Force per unit area - σ = F/A - from axial loading (tension/compression) - Pa = N/m²
Engineering Strain (ε)
Change in length per unit of original length - ε = Δl/l - unitless
Shear Stress (τ)
Shear force per unit area - τ = F/A - Pa = N/m²
Shear Strain (γ)
Change in length per unit of original length caused by shear force - γ = tan(θ) = w/l - θ is angle of shear deformation
Elastic Deformation
Stress-strain relationship is proportional upon loading/unloading, not permanent, caused by small changes in atomic spacing and stretching of atomic bonds
Linear Elastic Deformation
Straight-line relationship between stress and strain
Non-Linear Elastic Deformation
Nonlinear (curved) relationship between stress and strain
Modulus of Elasticity (E)
Slope of the linear elastic region of the stress-strain curve - E is the modulus of elasticity (Young’s Modulus)
Poisson’s Ratio (ν)
Ratio of axial to lateral strain - ν = -εx/εz = -εy/εz - z (axial direction), x+y (lateral directions)
Shear Modulus (G)
Slope of the shear stress versus shear strain curve in the elastic region - G = τ/γ
Isotropic
Having material properties that are independent of direction and the same in each direction
Relationship between E and G (Isotropic Materials)
E = 2G(1 + ν)
Anisotropic
Elastic material properties depend on crystallographic direction; more parameters are required to describe behavior
Polycrystalline Materials Assumption
Crystal orientation is often random; isotropic material behavior can be assumed
Plastic/Elasto-plastic Deformation
Stress-strain relationship upon loading/unloading is non-proportional; bonds are broken and new bonds are made
Proportional Limit (P)
Defines transition from linear to non-linear elastic behavior; somewhere below yield stress - MPa
Yield Stress (σy or fy)
Defines the transition between elastic and plastic behavior; important design parameter
Determining Yield Stress
0.2% rule - parallel line drawn through point corresponding with 0.002 strain at zero load, intersection with stress-strain curve is taken as yield stress
Strain Hardening
Further increase in stress in plastic region
Ultimate Tensile Strength (UTS) (σu or fu)
Maximum tensile stress
Necking
Localized narrowing of specimen after ultimate tensile strength (UTS)
Fracture
Total failure of the specimen; fracture strength = stress at fracture
Strain Gauges
Devices that convert tension and compression forces that can be converted into resistance
Load Cell
Arrangement of four strain gauges arranged in a Wheatstone bridge
True Stress (σT)
σT = σE(1+εE)
True Strain (εT)
εT = ln(1+εE)
True vs Engineering σ + ε
Approximation is good enough under normal conditions; questionable after ultimate tensile stress due to necking
Ductility
How much plastic deformation a material can undergo before fracture - measured as %EL
Percent Elongation (%EL)
%EL = ([lf - lo]/lo) - percentage of plastic strain at fracture, lo (initial strain gauge length), lf (gauge length after fracture)
Percent Reduction (%RA)
%RA = ([Ao - Af]/Ao) - percent reduction in x-section area, doesn’t depend on a gauge length
Brittle
Materials that fracture with little deformation
Resilience
Capacity of a material to absorb energy during elastic deformation
Modulus of Resilience (Ur)
Strain energy per unit volume required to load a material up to the point of yielding
Ur Assuming Linear Elastic Behaviour
Ur = 0.5σyεy
Toughness
Capacity of a material to absorb energy up to fracture; area under the stress-strain curve up to fracture
Hardness
A measure of material resistance to local penetration or scratching
Ways to Measure Hardness
Moh’s scale, Brinell hardness number (HB), Rockwell hardness tests
Moh’s Scale
Based on the ability of one material to scratch softer material; scale of 1-10
Brinell Hardness Number (HB)
Measure of the size of indentation made from a 10mm diameter steel/tungsten carbide sphere under load
Rockwell Hardness Test
Determined by measuring depth of penetration of indenter subjected to a prescribed load
Time-Dependent Deformations
Anelastic deformation, creep
Anelastic Behaviour
Time dependent elastic behaviour; time needed for full rebound upon unloading
Creep
Permanent time-dependent deformation; visco-elastic behaviour
Fracture (Ductile/Brittle)
Separation of a body into two or more pieces
Ductile Fracture
Evidence of plastic deformation; necking, cup + cone surface, irregular fibrous appearance
Stages of Ductile Fracture
- Formation of microvoids, 2. Coalescence of microvoids, 3. Crack propagation, 4. Fracture
Brittle Fracture
No sign of plastic deformation; little to no prior deformation, rapid crack propagation occurs, grainy texture (change in cleavage planes), breaking of atomic bonds
Charpy V-Notch Test
Means of determining impact energy or ‘notch toughness’; impacting specimen with a weighted pendulum, causing fracture at notch, measure of how far pendulum continues to swing beyond point of impact
Purpose of Impact Fracture Testing
Model conditions under which ‘brittle fracture’ is most likely; low temp, high strain rate + triaxial stress state
Ductile to Brittle Transition Temp
Determined from impact fracture test; transition is pronounced for low strength steels that have a BCC crystal structure
Design Against Ductile Fracture
Limit the load level so that: σ < Fy –> P < A*Fy
Factor of Safety (Ductile Fracture)
P < [A*Fy]/f.s., where f.s. > 1; the less that is known about parameters, the bigger f.s. should be
Limit States Design Approach
±dPd + ±lPl < ¦AFy, where ± = load factor (> 1), ¦ = resistance factor (< 1), d = dead loads, l = live loads
Stress Concentration Factor (σm)
For an elliptical hole - σm = (1 + 2sqrt(a/Δ))σo, a = 1/2 of hole width, Δ = notch radius
Stress Intensity Factor (K)
Measure of the ‘crack driving force’ - K = Yσsqrt(π*a), Y = correction factor
Material Fracture Toughness (Kc)
Material property affected by: 1. temperature, 2. strain rate, 3. grain size
Fracture Mechanics-Based Design
K1c > Yσsqrt(π*a), K1c refers to mode 1 crack
Mode 1 Fracture
Crack that results in an opening
Mode 2 Fracture
Fracture caused by sliding (shearing)
Mode 3 Fracture
Fracture caused by tearing (shearing)
Correction Factor (Y)
Takes into account: true crack shape, effect of finite plate dimensions, effect of a non-uniform stress distribution
Rheological Models
Used to model mechanically the time dependent behaviour of materials
3 Basic Elements of Rheological Models
- Hookean, 2. Newtonian, 3. St. Venant - combined in series or parallel to define material behaviours
Hookean Element
Represents a perfectly linear elastic material - deformation is completely recovered following unloading, modeled as a linear spring, deformation if proportional to force F by a constant M
Newtonian Element
Represents a perfectly viscous material - deformation remains following unloading, modeled as a dashpot/shock absorber, deformation is proportional to amount of time force is applied
St. Venant Element
Represents the force required to overcome the static friction - modeled as a sliding block on friction, unrealistic element and is always combined with other basic elements
Maxwell Model
Total deformation = sum of deformation of individual elements - made of a spring and dashpot element - in series
Kelvin Model
Total deformation = sum of deformation of individual elements - made of a spring and dashpot element - in parallel, force starts in dashpot and ends up in the spring –> stop deforming
Burger’s Model
Shows 3 phases of behaviour: 1. Instantaneous deformation, 2. Combined deformation, 3. Continued constant deformation - combines Maxwell and Kelvin models in series
Prandtl Model
Represents elastic-perfectly plastic materials - when small load is applied, material responds elastically until it reaches yield point, after that material exhibits plastic deformation - combines St. Venant and Hookean elements in series
Strain Hardening Power Law
σT = K*εT^n - K and N are constants
Fatigue
Failure at relatively low stress levels of structures that are subjected to cyclic stresses - formation of cracks as a result of repeated application of loads - fails at stress levels less than tensile strength - with no prior warning
3 Stages of Fatigue Failure
- Crack initiation, 2. Crack propagation, 3. Final failure
Crack Initiation
Cracks normally initiate at stress concentrations - cyclic loading produces microscopic surface discontinuities due to dislocation slip
Crack Propagation
Crack surface characterized by striations - corresponds with crack growth per cycle, can be counted to estimate the number of cycles to grow cracks from one depth to another
Final Failure
Occurs rapidly once crack reaches critical size - can be ductile or a brittle fracture
Stress Cycles (N)
Unit of measure for determining when fatigue failure will occur
S-N Curve Approach
Conducting fatigue tests in a lab - plot the results as log(σ) vs. log(N) - S-N curve is the line of best fit of the data, the higher the stress range -> lower fatigue life
Fatigue Life
Number of cycles (N) until failure
Fatigue Strength
Stress range Δσ to cause failure
Low Cycle Fatigue
N = 10^4 to 10^5 - high stress range - some plastic deformation
High Cycle Fatigue
N > 10^5 - low stress range - elastic loading only
Fatigue Limit
Stress range where fatigue life is practically infinite - ferrous alloys have a fatigue limit, non-ferrous alloys do not
Factors Affecting Fatigue Life
- Stress range, 2. Mean stress level, 3. Surface conditions, 4. Stress concentration, 5. Surface treatment - polishing (smoother), grinding (removes defects), shot peening (increases fatigue life, decreases mean stress)
Fatigue Life (Notch Effects)
Fatigue life decreases with notch sharpness - notch sharpness increases Kt - fillet
Miner’s Sum
Used to predict fatigue life under variable amplitude loading conditions - D = Σni / Ni - ni = actual number of cycles at given stress range, Ni = number of cycles that would cause failure at stress range, failure: D > 1
Cycle Counting Methods
- Rainflow, 2. Reservoir, 3. Range-mean
S-N Curves - Pros
Simple, widely used - curves can be refined over time with new test results - considers crack initiation + propagation
S-N Curves - Cons
Gives no information about crack size/crack growth rate vs. time - can’t be used to evaluate remaining fatigue life when a crack is detected or to determine optimal inspection frequency
Where Are Fatigue Cracks Most Likely to Form?
At the welds, which contain defects + are located at sudden changes in geometry
3 Types of Primary Chemical Bonds
- Ionic, 2. Covalent, 3. Metallic - determined by valence electrons
Net Force (F) Between 2 Atoms
Fn = Fa + Fr - Fa = attractive forces, Fr = repulsive forces at equilibrium - Fa + Fr = 0 –> Force (F) vs. Atomic Spacing (r)
Potential Energy (E) Between 2 Atoms
E = +F dr - net energy –> En = +Fn dr = +Fa dr + +Fr dr –> En = (-A/r) + (B/r^n) –> Potential Energy (E) vs. Atomic Spacing (r)
Ionic Bond
Between metallic and non-metallic elements - predominant bonding type in ceramic materials - non-directional - brittle, insulative, strong
Bonding Energy (Ionic Bonds)
Attractive energy: Ea = -A/r - A = constant, repulsive energy: Er = B/(r^n) - B = constant - n = 8
Covalent Bond
Electrons are shared between neighboring electrons - between non-metallic atoms - polymeric materials - directional - large range in bond strength –> # of bonds possible = 8 - N’ –> N’ = # of valence electrons
Metallic Bond
Electrons are not associated with a particular atom, free to drift through entire metal - non-valence electrons and nuclei form ionic cores w/ net positive charge - free electrons act as a glue to hold ion cores together - non-directional - high electrical + thermal conductivity
Secondary Bonds
Van Der Waals - generally very weak bonding energy - no electrons are exchanged/shared
Fluctuating Dipole Bonds
Electrons moving within an atom - when 2 stable atoms are close - they may interact cooperatively
Polar Molecule-Induced Dipole Bonds
When a polar molecule is bonded with another polar molecules, opposite end - responsible for high boiling points
Potential Energy (E)
Measure of the separation resistance of adjacent atoms - measure of material stiffness - in the same range for ceramics + metals (non directional bonding) - weaker for polymers (directional)
Material Structures
- Crystalline structures, 2. Non-crystalline structures, 3. Amorphous
Crystalline Structures
Atoms in repeating pattern over large atomic distances - atoms position themselves upon solidification
Unit Cells
Small repeating entities based on lines of symmetry
Coordination #
of atoms touching a given atom
Atomic Packing Factor
Volume of atoms in unit cell/ total unit cell volume
Parameter ‘a’
Length of cube side
Parameter ‘R’
Atomic radius
Most Common Crystal Structures
- Face centre cubic (FCC), 2. Body centre cubic (BCC), 3. Hexagonal close-packed (HCP)
Face Centre Cubic (FCC)
Cubes with atoms at each corner and at centres of each face - ie: aluminum, copper, nickel, silver - a = 2.828*R - n = 4 whole atoms/unit cell - coordination # = 12 - APF = 0.74
Body Centre Cubic (BCC)
Cube with atoms at each corner and one atom at centre - ie: iron, chromium, tungsten - a = 2.309*R - n = 2 atoms/unit cell - coordination # = 8 - APF = 0.68
Hexagonal Close Packed (HCP)
Hexagonal unit cell - ie: zinc, titanium, cobalt - n = 6 atoms/unit cell - coordination # = 2 - APF = 0.74
Theoretical Density Calculation
Á = (nA)/(VcNa) - Á = density - n = # atoms per unit cell - A = atomic weight - Vc = unit cell volume - Na = avogadro’s number
Chemical Impurities
Solid solutions contain impurity atoms/ions which alter the structural regularity of materials - always present in real materials
Types of Chemical Impurities
- Substitutional, 2. Interstitial
Hume-Rothery Rules for Substitutional Solid Solutions
- <15% difference in atomic radius, 2. Same crystal structure, 3. Similar electronegativities, 4. Similar valence - if one rule is violated, only partial solubility is possible
Interstitial Impurities
Difference between atom sizes is large - solubility is limited in this case
Types of Defects
- Point, 2. Line, 3. Planar defects
Point Defects
Occur due to thermal vibration of atoms above absolute zero - vacancy defects, self-interstitial defects
Linear Defects
Associated primarily with mechanical deformation - referred to as ‘dislocations’
Types of Linear Defects
- Edge, 2. Screw, 3. Mixed
Burger’s Vector
Displacement vector necessary to close mxn loop around defect
Edge Dislocation
Burger’s vector –> perpendicular to dislocation line
Screw Dislocation
Burger’s vector –> parallel to dislocation line
Mixed Dislocation
Burger’s vector –> fixed in space
Types of Planar Defects
- Material surfaces, 2. Grain boundaries, 3. Tilt boundaries, 4. Twin boundaries
Material Surfaces
Atoms not bonded to maximum number of neighbours - higher energy state (surface energy) - materials tend to minimize surface energy - minimum = surface area/volume
Grain Boundaries
As crystal grows, it establishes its own orientation in space - more difficult for last atom to take up a position –> results in transition zone (grain boundary) –> atoms are more strained (higher energy)
Tilt Boundaries
Accommodated by a few isolated edge dislocations
Twin Boundaries
Low energy state since boundary atoms occupy normal atom positions on both sides of boundary - produced by applied mechanical shear force
Diffusion
Material transport by atomic motion
Mechanisms for Diffusion in Metals
- Vacancy diffusion, 2. Interstitial diffusion
Vacancy Diffusion
Interchange of atoms between normal lattice positions + adjacent vacancies
Interstitial Diffusion
Migration of atoms from one interstitial position to an adjacent one
Fick’s First Law (Steady State)
J=-D(dC/dx) - J = diffusion flux [kg/m²*s] - D = diffusion coefficient [m/s²] - C = concentration [kg/m³] - x = distance within solid [m]
Fick’s First Law (for Linear Concentration Profile)
dC/dx = Δc/Δx = (Ca - Cb)/(xa-xb) - C = concentration [kg/m³] - x = distance within solid [m]
Fick’s Second Law (Non-Steady State)
(Cx - Co)/(Cs - Co) = 1-erf[x/2sqrt(D*t)] - C = concentration [kg/m³] - x = distance within solid [m] - D = diffusion coefficient [m/s²] - t = time (s) - erf = gaussian error function
Plastic Deformation (in Perfect Crystals)
Can be explained by the ‘slip’ movement or large number of dislocations - all metals + alloys contain some dislocations introduced during solidification - yielding of a crystal is caused by shear stresses
Peierls-Nabarro Stress
Stress required for dislocation motion - σ = GEXP(-2πa/[(1-ν)b]) - a = b
Direction of Dislocation Motion
Edge dislocations: parallel to the slip direction, Screw dislocations: perpendicular to the slip direction, Mixed dislocations: inbetween
Characteristics of Dislocations
- Strain fields exist around dislocations –> affects mobility of dislocations + ability to multiply, 2. Strain fields present for: Edge dislocations: tensile, compressive + shear strains, Screw dislocations: only shear strains, 3. During plastic deformation the number of dislocations increases dramatically as a result of: - dislocations multiplying + forming grain boundaries - surface irregularities - internal defects
Plastic Deformation (Polycrystalline Materials)
In each grain of a polycrystalline material, there are preferred slip planes in the crystal structure - direction of pref. slip plane varies from one grain to another • overall distortion of the material is due to the distortion (elongation) of individual grains • during deformation, grain boundaries do not come apart - neighbouring grains constrain each other • polycrystalline materials tend to be stronger than their single-crystal equivalents • fine grain materials tend to be stronger
Strengthening Mechanisms
- Dislocations generated through plastic slip - dislocation strain interactions are repulsive - dislocations interact, interfere + pile up - dislocation movement is obstructed by other dislocations, impurities + grain boundaries - strain hardening results
Results of Strain Hardening
Upon unloading, dislocation movement cannot be reversed - when a load is reapplied, no plastic deformation occurs until previous max stress is reached –> yield stress increases
Degree of Cold Work
%CW = [(Ao-Ad)/Ao] - Ao = original, Ad = deformed area
Purpose of Strain Hardening
Enhance the yield strength of metals during fabrication
Methods of Work Hardening
- Tensile pre loading, 2. Cold rolling, 3. Forging, extrusion + drawing
How Do Grain Boundaries Strengthen Materials
–> provide resistance to dislocation movement - stronger than coarse grained materials b/c larger boundary area
How to Regulate Grain Size
By controlling the rate of solidification/annealing
Solid Solution Strengthening
High purity metals = weaker than metals w/ impurities –> b/c they form a substitutional/interstitial solid solution + obstruct dislocation movement
Substitutional Impurities
Smaller impurity –> tensile lattice strains, Larger impurity –> compressive lattice strains
Annealing
Process of reheating to return the material properties of cold worked metal to return to its pre-worked state
Annealing Process
- Recovery, 2. Recrystallization, 3. Grain growth
- Recovery
Thermal energy is supplied to the cold-worked metal –> causes rearrangement of dislocations into lower energy configurations through atomic diffusion - rate of diffusion is dependent on temperature - accompanies by reduction in σy + increase in ductility –> # of dislocations decreases
- Recrystallization
New strain-free equiaxed grains, w/ lower dislocation density are formed - driving force = difference in internal energies of strained + unstrained materials - new small grains begin to form + grow until it completely consumes the parent material - accompanied by further reduction in σy + increase in ductility
- Grain Growth
Strain-free grains continue to grow if left at an elevated temperature - driving force = increase in grain size resulting in a decrease in the total grain boundary area –> reduction in total energy - results in decrease in strength results
Equilibrium Phase Diagram
Material properties depend on atomic + microscopic structure - tool for explaining the development of microstructure - solutions consist of components - (solutes + solvents consist of pure metal + compounds)
Phase
A homogeneous, physically/chemically distinct region of matter
One Component Phase Diagrams
3 controllable parameters 1. Temperature - plotted, 2. Pressure - plotted, 3. Composition - fixed - data is determined experimentally
Invariant Point
Point where all 3 phases are in equilibrium
Two Component (Binary) Phase Diagrams
Isomorphous (complete solid solution) systems - 2 components (A+B), fully soluble - pressure is held constant @ 1atm
Binary Phase Diagrams: Possible Phases
- Liquid (L), - Solid (α), - Liquid + Solid (L + α)
Eutectic Systems
- No solubility 2 components (A + B), not soluble possible phases: 1. Liquid (L), 2. Liquid + Solid (L + A), 3. Liquid + Solid (L + B), 4. Solid (A + B)
Eutectic System - Some Solubility
2 components (A + B), partially soluble α - mostly A, β - mostly B possible phases: 1. Liquid (L), 2. Liquid + Solid (L + α), 3. Liquid + Solid (L + β), 4. Solid (α + β)
Solus Line
Line between 2 solid phases - ie. between α + β
Ferrite (α iron)
Exists at room temperature - stable - BCC crystal structure - magnetic, soft, ductile
Austenite (γ iron)
Pure iron transforms into austenite at 912° C - FCC crystal structure - non-magnetic - not stable below 727°C
Ferrite (δ iron)
Forms at 1394° C, melts at 1538 °C - BCC crystal structure
Cementite/Iron Carbide (Fe3C)
Forms at concentration of 6.70% carbon, very hard + brittle - metastable
Metastable
Gradually transforms into α iron + graphite
Iron-Carbon Alloy Types
- Iron –> 0-0.008% C, 2. Steel –> 0.008-2.14% C, 3. Cast iron –> 2.14-6.7% C
Development of Microstructure
- Eutectic point, 2. Eutectoid point
Eutectoid Cooling
Results in pearlite
Pearlite
Layers of ferrite and cementite
Hypo-eutectoid Cooling
Primary/pro-eutectoid α + pearlite
Hyper-eutectoid Cooling
Primary/pro-eutectoid cementite + pearlite
Isothermal Transformation (T-T-T) Diagrams
Time-temperature-transformation diagrams - used to predict phase transformations while temperature is held constant
Iron-Carbon Eutectoid Reaction
Diffusional reaction - rate depends on atom migration which depends on temperature
Products of Eutectoid Reaction
- Coarse pearlite, 2. Fine pearlite, 3. Bainite
Coarse Pearlite
At high temperatures - diffusion rates are higher - atoms travel more + faster - layers are thicker –> resulting in coarse pearlite
Bainite
Like pearlite, very fine + needle like - not layered - occurs at temperatures below the ‘nose’ of the isothermal transformation diagram
Martensite
Forms when austenite is rapidly cooled - non-equilibrium single phase which eventually decomposes into ferrite + cementite - forms when quenching rate is fast enough to prevent carbon diffusion
Product of Non-diffusional Reaction
Martensite
Spheroidite
Forms when a steel alloy w/ pearlitic/bainitic microstructure is held for a long time at a temperature below eutectoid temp. - not shown on the T-T-T diagram
Continuous Cooling Transformation(C-C-T) Diagrams
Modified T-T-T diagrams used to predict transformations under steady cooling by shifting curves down and to the right - longer times and lower temperatures
Martensite
Quenching produces:
Faster Cooling Produces
Pearlite + martensite
Normalizing or ‘Air Cooling’ Produces
Fine pearlite
Annealing or ‘Furnace Cooling’ Produces
Coarse pearlite
Effects of Non-eutectoid Composition on C-C-T Diagrams
- If a composition other than eutectoid (0.76% C) is used, a proeutectoid phase will also be present - curves corresponding w. the proeutectoid transformation can be shown on T-T-T or C-C-T diagrams
Effects of Other Alloying Elements on C-C-T Diagrams
Change in the shape of the T-T-T or C-C-T diagrams - ie shifting the nose of the diagram to the right - ie formation of a separate bainite ‘nose’
Tempering
Heat treatment @ 250-650°C - improves ductility + relieves internal stresses or any temp. below eutectoid temperature - used for martensite (too brittle)
To Make Tempered Martensite
- Quench to make martensite, 2. Reheat and hold temp. for a period of time
Increasing Carbon Content Results In
Increase in strength + hardness - decreases ductility
How Steel is Made
- Iron ore, coke + lime are mixed in a blast furnace to produce liquid iron, 2. Liquid iron is passed through Basic Oxygen Steelmaking (BOS) furnace - to reduce carbon content, 3. Secondary processing - further cleaning the steel + refine chemical composition, 4. Steel is continuously cast into solid slabs, blooms or billets - hot rolled into more useful shapes
Final Processing of Steel Includes
- Shaping (cold rolling), - Machining (drilling), - Joining (welding, bolting), - Coating (galvanizing), - Heat treatment (tempering), - Surface treatment (shot peening)
Advantages of Ferrous Alloys
- High strength to weight ratio –> light structures, - Recyclable, - Abundance of iron, - Relative economy of refining process, - Versatility
Disadvantage of Ferrous Alloys
- Corrosion susceptible, - Cast iron (cast = brittle, easily melted)
Wrought Iron
Wrought = easily deformed - low in C content
Cast Iron
Cast = brittle, but easily melted - high in C content
Low-Carbon Steel
- Typically pearlite-ferrite microstructure - difficult to form martensite - soft, weak, highly ductile ex: car bodies, structural applications, pipelines
High Strength Low Alloy (HSLA) Steel
- More corrosion resistant - other alloys compose up to 10% - higher material strength
Medium-Carbon Steel
- Commonly: tempered martensite microstructures ex: railway wheels + tracks, gears, crank-shafts and other machine parts
High-Carbon Steel
- Hardest, strongest + least ductile steel - wear resistance, sharp cutting edges possible ex: tool + die steels
Stainless Steel
- Highly corrosion resistance - can be martensitic, ferritic or austenitic - can be magnetic - cannot be heat treated, only cold worked ex: used in high temp. environments (jet engines)
Structural Steel Naming
Ex. 350W (very common) yield strength: Fy = 350MPa letters: denote treatment
Rebar
Steel bars used to reinforce concrete - hot rolled from steel billets
Steel in Prestressed Concrete
Steel used in prestressing wires + strands have higher strength than structural steel/rebar - high carbon steel and wires are cold worked to achieve required material strength
