Exam 1 Review

Rockwell Hardness Testing

Diamond Indenter Process: minor load applied, major load applied, major load removed Minor Loads - Superficial: 3 kg , Regular: 10 kg Major Loads - Superficial: 15, 30, 45 kg , Regular: 60, 100, 150 Superficial is used for thin materials

Comparison of Hardness Tests

Knoop/Vickers: Diamond indenter, 1-2000g load, microhardness of soft steels to ceramics Brinell: Ball indenter, 500 and 3000 kg, soft steels Rockwell (Bc)(Tc)(Rc): ball indenter, 100 kg - superficial major loads - for soft Rockwell (Nc)(Ad)(Cc): Diamond indenter  - for hard  HARD to SOFT: Knoop/Rockwell C, Brinell, Rockwell B, Shore

Mechanical Properties

Strength Tensile Yield Compression Flexural Shear Creep Stress rupture Stiffness modulus of elasticity flexural and shear modulus

Formability elongation area reduction bend radius Toughness Impact strength notch sensitivity Durability Hardness wear resistnce fatigue strength

Stress and Strain

STRESS = force/area (psi) STRAIN = change in length/length (in/in) found by tensile test

Stress-Strain Curve

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Caption: : more ductile = longer x axis, a stretched graph

.2% offset yield

When yield point cannot be found: set at .2% elastic strain using young's modulus of elasticity (slope) find point of the curve if the slope is used where x=.2%

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Modulus of Elasticity

stress/strain = E (psi) - SLOPE of graph, at the beginning important in choosing materials Steel = 30x10^6 psi Aluminum = 10x10^6

Standard gage length

gage length for tensile testing = very great in comparison to diameter

Impact Testing

used to determine material behavior at higher deformation speeds  the higher the impact strength, the greater the fracture resistance will be pivoting arm drops, breaks specimen notch samples can be used to test notch sensitivity Nil-Ductility Transition: the temperature above which a material is ductile and below which it is brittle 

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Fatigue Strength

tested by repeating fluctuating loads the number of cycles required to cause failure in a specimen against the amplitude of the cyclical stress developed

Creep Strength

prolonged tensile or compressive load at a constant temperature. The rate of deformation of a sample material to stress at a constant temperature is known as the creep rate. It is the slope created by the creep vs. time.

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Material Selection Factors

Chemical composition phases grain size inclusions Physical Specific Heat thermal conductivity heat distortion temperature magnetic electrical optical acoustic density color

Mechanical Tensile/compressive properties toughness ductility fatigue strength hardness creep resistance shear strength Manufacturing Considerations size shape surface texture tolerances

Blast Furnace

outputs pig iron, high in carbon (3.5%) slag used in concrete

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Limestone and Coke

the production of iron historically required three important raw materials: iron ore, coke and limestone reduces impurities produces slag coke = converted coal

Reduction

Happens in a blast furnaceRemoves carbon with help of oxygeniron (III) oxide+carbon monoxide =iron+carbon dioxideFe2O3(s)+3 CO(g)         =2 Fe(l)+3 CO2(g)

Steel Refining

Wrought iron and refined iron are products of pig iron refining Refining: purifying an impure metal Primary steelmaking: uses mostly  new iron from a blast furnace Secondary steelmaking: uses scrap steel as raw material in electric arc furnace.

Furnaces

Blast Furnace - iron ore, limestone and coke, hot air goes in.  product: PIG IRON.  Basic Oxygen Furnace (BOF) - uses scrap metal to make new steel by pushing in oxygen, nitrogen and argon (oxygen lance) oxygen forms CO and CO2, removes carbon, sulfur and phosphorus - 40% used in america. Capacity: 150-300 tonnes per "heat" every 30 minutes. pours out. 

Electric Arc Furnace (EAF) - uses old steel, sends electricity through to raise temperature.  35 minutes per heat. 1-400 tonnes. SECONDARY steelmaking. graphite electrodes, oxygen, lime create electric arcs. Can be shut down between uses.

Continuous Casting

from furnace, liquid steel is in ladle, goes through tundish feeding to caster mold, straightens out and is cut. water cooled. produces 3000 heats between shutdowns. Inclusions, porosity, segregation and grain size

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Secondary Refining

Vacuum degassingvacuum arc remeltingelectroslag meltingvacuum induction meltingelectron beam refiningladle stirring injection and ladle furnace heatingKNOW ACRONYMSWhat are the metals used for after?

Steel Grades

list, how are they achieved?killedrimmedcappedsemi-killed

Ingots

how are they made

Non-metallic inclusions

?

Semi-finished steel forms

figure 12-12

integrated mill vs minimill

finished forms of steel

what is the difference between plate and sheet?strip and bar?

BCC FCC

what it means, looks likecharacteristicshow is impact strength affected?

Allotropic

definediscuss importanceknow about Fe (delta iron, gamma iron, alpha iron)

Progression of solidification

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grain and grain boundaries

phase diagram

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steel terminology

rimmed -slightly deoxidized with outer shell of low impurities, surface cleanliness killed - strongly deoxidized, chemical additions galvanized - zinc-coated steel galvannealed - zinc-coated and heat treated steel. better paint adhesion  sheet - 0.01-0.025 x >24 in, big and thin bar - rounds/squares/hexes 0.25 - 3 in coil - rolled steel, very thin flat wire - rolled rectangles made by cold-reducing rounds wire - coiled rounds diameter <.25 in  shapes - hot rolled shapes, >3 in tin plate - steel with .005-0.014 in (may be tin coated) strip - rolled steel 0.01-0.025 x <24 in, less big and thin

plate - thick, heavy steel shapes free machining - steels with sulfur lead or others- machine easier drawing quality - for satisfying elongation requirements merchant quality - M suffix, nonstructural applications, low quality commercial quality - from rimmed, capped, concast, or semikilled steel h steels - H suffix, guaranteed hardness in heat treatment b steels - small boron additions as hardening agent pickling - acids used to remove oxides and scale temper rolling - eliminates stretcher strains, improve surface finish temper - amount of cold reduction in rolled sheet/strip e steels - E prefix, melted by electric furnace

cold rolling vs hot rolling

propertieshowdynamic re-crystallizationwhich to choose for what

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Fe-Fe3C diagram

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Caption: : Pearlite, Austenite, Cementite, Ferrite

% ferrite, % pearlite

given carbon content or approximate tensile strength

annealing

definewhat is the condition of the material after treatment?how is it donetemperatures and timesexplain how mechanical properties are affected