Dating and random bits

Question 1

When was cast iron invented

Answer 1

5th century in china

Question 2

What is a Catalan forge

Answer 2

Cold air blast.

Falling water is used to act as a compressor.

Higher temperatures achieved, but still uses charcoal, and produces pig iron.

This is undesirable because higher temperature (upto 1200oC) mean that liquid iron is created and causes Carbon pick-up.

Question 3

What is Pig iron

Answer 3

where lines run off the base of the forge in lines (like pigs drinking milk from stomach)

Question 4

When was the iron bridge built? How was it constructed?

Answer 4

(1781), constructed with wood joints, built as if it was being built with wood. Not welded together. All pieces cast individually. Bridged into gorge.

Question 5

What is the metastable phase on the Fe Fe carbide phase diagram

Answer 5

Fe3C marsenite

Question 6

What is bloomers iron?

Answer 6

ferrite+ pearlite. Forms flake and SG (spheroidal graphite iron)

Question 7

Give some properties of graphite

Answer 7

Graphite is very brittle, shouldn’t be used to build anything. It is very low strength and brittle.

Question 8

What is Flake grey cast iron?

Answer 8

graphite flakes with pearlite. Formed due to alpha + graphite, eutectic transformation. If a tensile load is applied, matrix supports all of the applied load.

Question 9

What is Spheroidal grey

Answer 9

some C content, microstructure altered to get graphite, spheres improve mechanical properties, greater distance between graphite sphere is best shape for avoiding STRESS RAISERS. Graphite wraps itself around itself and structure is built up from cone like structure/ segments.

Question 10

Why is the Fe-Fe carbide diagram not an equilibrium diagram?

Answer 10

because Fe3C is not an equilibrium compound –> breaks down even with no driving force.

Can get a equilibrium diagram – has a eutectic point where austenite (alpha) + graphite formation occurs.

Question 11

What happened in 2500BC

Answer 11

Chinese made SG

Question 12

What happened in 1600 BC

Answer 12

western were making flake grey iron

Question 13

What is compacted graphite iron

Answer 13

intermediate form between flake and spheroidal, properties are halfway between.

Question 14

1943

Answer 14

added mg to cast iron – solidified, formed spheres ductile iron

Question 15

1948

Answer 15

successful production of spheroidal graphite in hypereutectic grey iron by addition of small amounts cerium

Question 16

1808

Answer 16

– discovery that al could be produced by electrolytic reduction from alumina

Question 17

1825

Answer 17

Hans Oersted (Denmark) was successful

Question 18

1920’s

Answer 18

addition of salt to Al-Si alloy  modification, sodium had effect on silicon structure, forms Al dendrites with eutectic structure alpha + Si. When NaCl added into melt long shape changed to a finer structure, gives double the mechanical properties associated with silica.

Question 19

What is faceting?

Answer 19

• • graphite facite – ledge builds up into angular structure –> silicon needles & blocks.

Question 20

Why did the Chinese have SG before the west?

Answer 20

1) Normally Al-Si alloys produce facetted eutectic Si
2) Al-Si with Na modifies & (Si) prevents growth along edges – addition of Na + Si increases properties
3) Chinese iron ores were high purity – when Fe produced contained eutectic (facetted) graphite spheres
4) In the west – iron ores contaminated with S&P – pig iron acted as modifiers leading to reduced properties

Question 21

What is the composition of steel?

Answer 21

upto 12%C – grains of ferrite & pearlite.

Question 22

What is peralite

Answer 22

lamellae of ferrite & cementite.

Question 23

Describe carburisation/ nitidisation

Answer 23

diffusion of carbon from exterior to interior of microstructure. Heating in C rich atmosphere: C diffusion into surface, because surface cooled more quickly than interior. Quenching  surface martensitic layer (brittle) & tougher inner pearlite core.

Question 24

Boiling curve?
Nucleate boiling?
Transition boiling?

Answer 24

rapid cooling at the surface creates a temperature gradient.

Nucleate boiling: formation of nuclear bubbles, bubbles penetrate surface flaws, pocket of water vapour, bubbles then released.

Transition boiling: vapour film forms and collapses continuously.

Question 25

What is pattern welding

Answer 25

patterns are a by product of process. Sword made from thin sheets of carburised iron – thin sheet allows a homogeneous C-content to be achieved. “Piling” / welding sheets  sword with varying properties E.g. Nydan sword 3rd century AD. Surface carburised strips could be forged together  make a layered structure with a more homogeneous C content (up to ~ 0.5%)

Question 26

Describe the 4 properties of pattern welding

Answer 26

1) Medium -C core (0.5% C)
2) Backed either side with soft iron strip 0.1% C
3) Either side are 6 piled & twisted strips (0.1-0.5% C)
4) Cutting edge made from plain C-steel

Question 27

Damescening?

Answer 27

pattern welding with finer steel strips & more of them. Suggested that it takes 25 hours to make, 128 reheats to weld pieces together

Question 28

Wootz steel?

Answer 28

damascening using layers of higher C steel (contains cementite), or fragments of cast iron mixed with low-C bloom steels

Question 29

Describe steel making cementation

Answer 29

Bars of wrought iron are packed together in furnace (c.1100) for ~ 1 week. Carbon diffused into steel  0.1% C (blister steel). Bars, cut, forged and reheated to create a more homogeneous composition (shear steel).

Question 30

What is Hunstman’s crucible steel made from?

Answer 30

1) Carburised wrought iron, solid: low C, carburisation

2) Decarburised cast iron, decarburisation of High C cast iron

Question 31

Describe the Hunstman process

Answer 31

Hunstman (1740) developed process where coke used as fuel (de-volatilised coal), to obtain high furnace temp. Blister steel (~0.1%C) was melted in pots with a flux, and cast to shape. As a liquid is involved, carbon pick-up from coke occurred, increasing C content of the steel

Question 32

Bessemer converter?

Answer 32

method for reducing C-content of liquid cast iron by blowing in air. Oxygen reacts with C in iron  CO2, lowers C-content, subsequent deoxidisation process is required to remove residual oxygen dissolved in the melt (otherwise embittle the steel)

Question 33

describe the modern steelmaking ironmaking process

Answer 33

Iron as Fe2O3 & Fe3O4 reduced by reaction with C, from coke;

Fe203+3CO –> 2Fe +3CO2

In blast furnace at high temperature, high carbon content liquid iron.

Steel has low C content (0-1.4wt %) reduce C content a lace is used to blow oxygen trough liquid steel: O2 +2C = 2CO.

Liquid steel contains too much O, reduced by added element with strong preference for reaction with O:
Si + O2 = SiO2
2Al + 3O2 = 2Al2O3

Deoxidisation products should float out from steel – removed with the slag, mat become trapped as inclusions.

Final stages

i) Degassing to remove N under vacuum
ii) Removal of impurities S,P by reaction with slag
iii) Alteration of composition by addition of ferroalloys Mn, Cr, Ni…
iv) Stirring with Ar gas to make T & composition uniform

Question 34

Name and describe the 3 types of malleable iron

Answer 34

White cast iron with pearlite matrix. Subsequent annealing causes (metastable) cementite to decompose to graphite.
3 forms :
• Whiteheart malleable – heating casting to 900°C in an oxidising atmosphere results in surface decarburisation.
• Blackheart malleable – heating casting to 900°C in a neutral atmosphere results in decomposition of iron carbide into a graphite rosette shape, (which does not have the disadvantages of graphite flakes in cast iron).
• Pearlitic malleable – heating to 900°C and then rapid quenching produces a pearlitic or martensitic matrix.

Question 35

What is the diffusion model

Answer 35

implicit model of the human past based upon diffusion

items dated by association

Question 36

Give an example of a useful date list

Answer 36

king-list of Persia to astronomical events, (e.g., the helical rising of Sirius), however, this only extends back to about 800 BC

Question 37

how were the neolithic tombs dated

Answer 37

initially thought to be built by Mycenaeans - corralled roofs

dated the Egyptian chronology 1500BC

so must be later (giving time to sail) so around 1200BC

Question 38

What is seriation

Answer 38

relative dating method , if object found at same archeological level as another assumed to be form the same period, older objects found below

Question 39

describe c-14 dating

Answer 39

absolute dating method developed in late 1940’s by willard libby

living organisms take up C, C-14 has half life of 5730 yrs

c14 in atmosphere produced by cosmic ray neutrons interacting with n14. at point of plant death organism has same amount of c14 as in atmosphere

dating by measuring amount of c14 present now and relating to amount of stable 12C

by emissions of beta, or mass spectroscopy

Question 40

why does C14 dating need calibration

Answer 40

because 14C content in the atmosphere is not constant

past c14 data achieved from long lived trees that could be dated by counting growth rings

Question 41

What does accurate radiocarbon dating require

Answer 41

(i) . The calibration curve is not smooth, but has plateaus in it. This means applying the calibration curve results in a range of equally possible dates.
(iii) . Different types of samples give different results.
(iv) . Fractionation. Where different C isotopes, having different atomic masses, are processed in different ways.
(v) . Reservoir effects. For example, molluscs extract carbonate dissolved in sea water, which is depleted of 14C; molluscs were a valuable contribution to the diet and are thus often radiocarbon dated, but this would make them appear older than they actually are

Question 42

Sr- isotope analysis?

Answer 42

uses the 86Sr / 87Sr ratio nature of the geology influences the diet, which is expressed by measurement of the Sr isotopes in the tooth enamel of skeletons. Knowing the Sr isotope ratio one can assign a possible origin for an individual

Question 43

Dendrochronology

Answer 43

trees grow I bark ring per year, can be thick or thin depending on the climate

sereis has been put together dating back to 26,000 yrs ago

gives precise date for wood, if the bark is still attached

Question 44

Describe the hardness test

Answer 44

Indentor is forced into the surface of a material, until it reaches an equilibrium depth. The diameter of the impression is then measured, and related to an arbitrary hardness scale

Question 45

Describe the Brinell test

Answer 45

uses a steel ball indentor, the Rockwell and Vickers test use conical and pyramid-shaped indentors, respectively. The Knoop tests uses an elongated pyramid for determination of micro-hardness

Question 46

what happens as the inventor in a harness test is forced into the material

Answer 46

material must plastically deform, and flow away from the moving indentor.

The hardness test measures:
ability of a material to elastically and plastically deform,
relationships between the measured hardness of a material, and its tensile properties.

Question 47

when do materials creep

Answer 47

Materials will creep (i.e., deform) under a low load, particularly at elevated temperatures. In creep terms, elevated temperatures means at T > 0.4 Tm

Question 48

what is the most famous example of creep

Answer 48

turbine blades in jet engines. These are operated at temperatures close to their melting point, and under great stress due to the high density of the material, (a Ni-based alloy), and the centrifugal forces that consequently occur during operation

Question 49

how is creep resistance achieved

Answer 49

improved by directional solidification; this aligns columnar crystals in the direction of loading, which means that the grain boundaries are aligned parallel to the centrifugal force the blades experience

Question 50

What happens during a creep test?

Answer 50

standard specimen is held in a furnace at the temperature of interest, (with an inert atmosphere if necessary) and its deformation recorded as in a tensile test.

This gives rise to the characteristic creep curve, which shows regions of primary creep, secondary creep, and tertiary creep, leading to failure

creep accelerated as usually takes place over a number of years

Question 51

why does fatigue occur

Answer 51

due to cyclic loading with a stress below the normal failure stress of the material

Question 52

how are fatigue tests carried out?

Answer 52

at defined stress amplitudes, where the stress varies from a maximum to a minimum, giving a characteristic stress amplitude;

S = stress.a = (stress.max - stress.min)/2

The number of cycles to failure is recorded, which can be typically in the range of 105 to 106, and plotted on an S-N curve.

Question 53

How do fatigue failure originate

Answer 53

originate from a flaw, often a surface flaw

concentration of the applied stress occurs at the tip of such a flaw;

crack can initiate from this point and slowly grow across the section with each application of the cyclic load.

Once CSA< an area below that which can support the applied load, the crack propagates rapidly across the section, leading to sudden failure

Question 54

how is the fracture surface characterised

Answer 54

by concentric rings

Question 55

Statergies to reduce or prevent fatigue failure

Answer 55

(i) . improving the surface finish to reduce surface flaws that might act as crack initiators.
(ii) . Eliminating internal defects, such as pores or inclusions, that could also act as crack initiators.
(iii) .design modifications to reduce stress raisers
(iv) . surface treatments (in metals) such as shot-peening or carburising, which will impart compressive residual stresses to the surface and reduce surface-related crack initiation.

Question 56

describe impact testing

Answer 56

A standard specimen is placed in a fixture, and a weighted arm released to swing down and impact on the specimen. The specimen is notched to ensure its fracture, and the height to which the arm reaches, after passing the specimen, is used as a measure of the energy absorbed by fracturing the specimen

Question 57

what phenomenon to steels exhibit

Answer 57

ductile-brittle transition

caries with steel composition, generally around -30oC to -50oC

Question 58

when does the brittle failure of steels usually occur and what is the implication?

Answer 58

use at low temperatures

sinking of the liberty ships in WW2 because of the welded construction, and in the sinking of the titanic