ELEMENTS OF STEEL STRUCTURAL DESIGN

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Nov 2, 2013 (3 years and 9 months ago)

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ELEMENTS OF STEEL STRUCTURAL
DESIGN

5 MARK QUESTION

1.History of steelmaking

Ancient steel

Steel was known in antiquity, and may have been produced by managing

bloomeries
, or iron
-
smelting
facilities, in which the bloom contained carbon.
[15]

The earliest known production of steel is a piece of ironware excavated from an

archaeological
site

in
Anatolia

(
Kaman
-
K
alehoyuk
) and is about 4,000 years old.
[16]

Other ancient steel comes from

East
Africa
, dating back to 140
0 BC.
[17]

In the 4th century BC steel weapons like the

Falcata

were produced in
the

Iberian Peninsula
, while

Noric steel

was used by the

Roman military
.
[18]

The

Chinese
of the

Warring
States

(403

221 BC) had

quench
-
hardened steel
,
[19]

while Chinese of the

Han Dynasty

(202 BC


220
AD) created steel by melting together wrought iron with cast iron, gaining an ultimate product of a
carbon
-
intermediate steel by the 1st century AD.
[20]
[21]

The

Haya

people of

East Africa invented a type of
high
-
heat blast furnace which allowed them to forge carbon steel at

1,802 °C(3,276

°F)

nearly 2,000 years
ago.
[22]

Wootz steel and Damascus steel

Evidence
of the earliest production of high carbon steel in the

Indian Subcontinent

was found in
Samanalawewa area in

Sri Lanka
.
[23]

Wootz steel was produced in

India

by about 300 BC.
[24]

Along with
their original methods of forging steel, the Chinese had also adopted the production methods of
creating

Wootz steel
, an idea imported into
China from India by the 5th century AD.
[25]

In Sri Lanka, this
early steel
-
making method employed the unique use of a wind furnace, blown by the monsoon winds,

that
was capable of producing high
-
carbon steel.
[26]

Also known as

Damascus steel
, wootz is famous

for its
durability and ability to hold an

edge
. It was originally created from a number of different materials
including various

trace elements
. It was essentially a complicated alloy with iron as its main component.
Recent studies have suggested that

carbon nanotubes

were inc
luded in its structure, which might explain
some of its legendary qualities, though given the technology available at that time, they were produced by
chance rather than by design.
[27]

Na
tural wind was used where the soil containing iron was heated up with
the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil
[
citation
needed
]
, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists
were able to produce steel as the ancients did long ago.
[26]
[28]

Crucible steel
, formed by slowly heating and cooling pure iron and carbon (typically in the form

of
charcoal) in a crucible, was produced in

Merv

by the 9th to 10th century AD.
[24]

In the 11th century, there
is evidence

of the production of steel in

Song China

using two techniques: a "berganesque" method that
produced inferior, inhomogeneous steel and a precursor to the modern Bessemer process th
at used partial
decarbonization via repeated forging under a

cold blast
.
[29]

Modern steelmaking


Since the 17th cen
tury the first step in European steel production has been the smelting of iron ore into
pig iron in a

blast furnace
.
[30]

Originally using charcoal, modern methods use

coke
, which has proven to
be a great deal cheaper.
[
31]
[32]
[33]

Processes starting from bar iron

In these processes pig iron was "fined" in a

finery forge

to produce

bar iron

(wrought iron), which was
then used in steel
-
making.
[30]

The production of steel by the

cementation process

was described in a treatise published in Prague in
1574 and was in use in

Nuremberg

from 1601. A similar process for

case hardening

armour and files was
described in a book published in

Naples

in 1589. The process was introduced to England in about
1614.
[34]

It was produced by Sir

Basil Brooke

at

Coalbrookdale

during the 1610s. The raw material for
this were bars of wrought iron. During t
he 17th century it was realised that the best steel came
from

oregrounds iron

from a region of

Sweden
, north o
f

Stockholm
. This was still the usual raw material
in the 19th century, almost as long as the process was used.


2.Contemporary steel and uses

Modern steels are made with varying combina
tions of alloy metals to fulfill many purposes.
[3]
Carbon
steel
, composed simply of iron and ca
rbon, accounts for 90% of steel production.
[1]
High strength low
alloy steel

has small additions (usually < 2% by

weight) of other elements, typically 1.5% manganese, to
provide additional strength for a modest price increase.
[47]

Low alloy steel

is alloyed with other elements,
usually

molybdenum
, manganese, chromium, or nickel, in amounts of up to 10% by weight to improve
the hardenability of thick

sections.
[1]
Stainless steels and

surgical stainless steels

contain a minimum of
11%

chromium, often combined with nickel, to resist

corrosion

(rust). Some stainless steels, such as
the

ferri
tic
stainless steels are

magnetic
, while others, such as the

austenitic
, are

nonmagnetic
.
[48]

Some more modern steels include

tool steels
, which are alloyed wi
th large amounts of tungsten
and

cobalt

or other elements to maximize

solution hardening
. This also allo
ws the use of

precipitation
hardening

and improves the alloy's temperature resistance.
[
1]

Tool steel is generally used in axes, drills,
and other devices that need a sharp, long
-
lasting cutting edge. Other special
-
purpose alloys
include
weathering steels

such

as Cor
-
ten, which weather by acquiring a stable, rusted surface, and so can
be used un
-
painted.
[49]

Many other high
-
strength alloys exist, such as

dual
-
phase steel
, which is heat treated to contain both a
ferritic and martensitic microstructure for extra strength.
[50]

Transformation Induc
ed Plasticity (TRIP)
steel involves special alloying and heat treatments to stabilize amounts of

austentite

at room temperature

in normally austentite
-
free low
-
alloy ferritic steels. By applying strain to the metal,
the

austentite

undergoes a

phase transition

to martensite without the addition of heat.
[51]

Maraging steel

is
alloyed with nickel and other elements, but unlike most steel contains almost no carbon at all. This creates
a very strong but still

malleable

metal.
[52]

Twinning Induced Plasticity (TWIP) steel uses a specific type of
strain to increase the effectiveness of work hardening on the alloy.
[53]

Eglin Steel
uses a combination of
over a dozen different elements in varying amounts to create a relatively low
-
cost metal for use in

bunker
buster
weapons. Hadfield steel (after Sir

Robert Hadfield
) or manganese steel contains 12

14%
ma
nganese which when abraded forms an incredibly hard skin which resists wearing. Examples
include

tank tracks
,

bulldozer blade

edges and cutting blades on the

jaws of life
.
[54]

Most of the more commonly
used steel alloys are categorized into various grades by standards
organizations. For example, the

Society of Automotive Engineers

has a serie
s of

grades

defining many
types of steel.
[55]

The

American Society for Testing and Materials

has a separate set of standards, which
define alloys such as

A36 steel
, the most commonly used struc
tural steel in the United States.
[56]

Though not an alloy,

galvanized

steel is a commonly used va
riety of steel which has been hot
-
dipped or
electroplated in

zinc

for protection against rust.
[57]



Uses

Iron and steel are used

widely in the construction of roads, railways, other infrastructure, appliances, and
buildings. Most large modern structures, such as

stadiums

and
skyscrapers
,

bridges
, and

airports
, are
supported by a steel skeleton.
Even those with a concrete structure will employ steel for reinforcing. In
addition, it sees widespread use in
major appliances

and

cars
. Despite growth in usage of

aluminium
, it is
still the main material for car bodies. Steel is used in a variety of other

construction

materials, such as
bolts,

nails
, and

screws
.
[58]

Other common applications include

shipbuilding
,

pipeline
transport
,

mining
,
offshore construction
,

aerospace
,

white goods

(e.g.

washing machines
),

heavy
equipment
such as bulldozers, office furniture,

steel wool
,

tools
, and

armour

in the form of personal vests
or

vehicle armour

(better known as

rolled homogeneous armour

in this role). Steel was the metal of
choice for sculptor

Jim Gary

and a frequen
t choice for

sculpture

by many other modern sculptors.


3.Germicidal and antimicrobial applications

The

copper

in brass ma
kes brass

germicidal
. Depending upon the type and concentration of
pathogens

and
the medium they are in, brass kill
s these

microorganisms

within a few minutes to eight hours of
contact.
[15]
[16]
[17]

The

bactericidal

properties of brass have bee
n observed for centuries and were confirmed in the
laboratory in 1983.
[18]

Subsequent experiments by research groups around the world reconfirmed the
antimicrobial efficacy of brass,
as well as copper and other copper alloys (see

Antimicrobial copper
-
alloy
touch surfaces
).
[15]
[16]
[17]

Extensive structural membrane damage to

bacteria

was noted after being exposed
to copper.

In 2007,

U.S. Department of Defense
’s Tel
emedicine and Advanced Technologies Research Center
(TATRC) began to study the antimicrobial properties of copper alloys, including four brasses (C87610,
C69300, C26000, C46400) in a multi
-
site clinical hospital trial conducted at the

Memorial Sloan
-
Kettering Cancer Center

(New York City), the

Medical University of South Carolina
, and the Ralph H.
Johnson VA Medical Center (South Carolina).
[19]
[20]

Commonly touched items, such as bed rails, over
-
the
-
bed tray tables, chair arms, nurse's call buttons, IV poles, etc. were retrofitted with antimicrobial
copper alloys in certain patient rooms (i.e., the “coppered” rooms) in
the

Intensive Care Unit

(ICU). Early
results disclosed in 2011 indicate that the coppered rooms demonstrated a 97% reduction in
surface

pathogens

versus the non
-
coppered rooms. This reduction is the same level achieved by
“terminal” cleaning regimens conducted after patients vacate their rooms. Furthermore, of critical
importance to health care profe
ssionals, the preliminary results indicated that patients in the coppered
ICU rooms had a 40.4% lower risk of contracting a

hospital acquired infection

versus patients in non
-
coppered ICU rooms.
[19]
[21]
[22]

The U.S. Department of Defense investigation contract, which is ongoing,
will also evaluate the effectiveness of copper alloy touch surfaces to prevent the transfer of

microbes

to

patients and the transfer of microbes from patients to touch surfaces, as well as the potential efficacy of
copper
-
alloy based components to improve

indoor air quality
.

In the U.S., the

Environmental Protection Agency

regulates the registration of antimicrobial products.
After extensive antimicrobial testing

according to the Agency’s stringent test protocols, 355

copper
alloys
, including many brasses, were found to kill more than 99.9% of

methicillin
-
resistant

Staphylococcus aureus

(
MRSA
),

E. coli

O157:H7,

Pseudomonas aeruginosa
,

Staphylococcus
aureus
,
Enterobacter aerogenes
, and vancomycin
-
resistant

Enterococci

(VRE) within two hours of
contact.
[15]
[23]

Normal tarnishing wa
s found to not impair antimicrobial effectiveness.

Antimicrobial tests have also revealed significant reductions of MRSA as well as two strains of epidemic
MRSA (EMRSA
-
1 and EMRSA
-
16) on brass (C24000 with 80% Cu) at room temperature (22 °C) within
three h
ours. Complete kills of the pathogens were observed within

4

1

2

hours. These tests were performed
under wet exposure conditions. The kill timeframes, while impressive, are nevertheless longer than for
pure copper, where kill timeframes ranged between 45 t
o 90 minutes.
[17]

A novel

assay

that mimics dry bacterial exposure to touch surfaces was developed because this test
metho
d is thought to more closely replicate real world touch surface exposure conditions. In these
conditions, copper alloy surfaces were found to kill several million Colony Forming Units of

Escherichia
coli

within minutes.
[24]

This observation, and the fact that kill timeframes shorten as the percentage of
copper in an alloy increases, is proof that copper
is the ingredient in brass and other copper alloys that
kills the microbes.
[25]

The mechanisms of antimicrobial action by copper and its alloys, including brass, is a subject of inten
se
and ongoing investigation.
[16]
[24]
[26]

It is believed that the mechanisms are multifaceted and include the
following: 1)

Potassium

or

glutamate

leakage t
hrough the outer membrane of bacteria;
2)

Osmotic

balance disturbances; 3) Binding to

proteins

that do not require or util
ize copper; 4)
Oxidative
stress

by

hydrogen peroxide

generation.

Research is being cond
ucted at this time to determine whether brass, copper, and other copper alloys can
help to reduce cross contamination in public facilities and reduce the incidence of

nosocomial
infections

(hospital acquired infections) in healthcare facilities.


20 MARK QUESTION

1.Beneficial properties of copper for electrical wire and cable

Nearly all electrical devices rely on copper wiring because of its multitude of inherent b
eneficial
properties. The most useful beneficial properties for electrical applications are summarized here.



Electrical conductivity

is a measure of how wel
l a material transports an

electric charge
.
[9]
This is an
essential property in electrical
wiring systems. Copper has the highest electrical conductivity rating of all
non
-
precious metals

(electrical conductivity of copper = 101% IACS (International Annealed Copper

Standard); electrical resi
stivity of copper = 16.78 nΩ•m at 20 °C).

Oxygen
-
Free Electronic (OFE)
copper

achieves a minimum of 101% IACS.

The solid state theory of metals

[10]

helps to explain the unusually high electrical conductivity of copper.
In a copper

atom
, the outermost 4s energy zone, or

conduction band
, is only half filled, so
many

electrons

are able to carry

electric current
. When an

electric field

is applied to a copper wire, the
conduction of electrons accelerates towards the

electropositive

end, thereby creating a current. These
electrons encounter resistance to their passage by colliding with impurity atoms, vacancies, lattice ions,
and imperfections. The
average distance travelled between collisions, defined as the “
mean free path
,” is
inversely proportional to the resistivity of the metal. What is unique about copper is its lo
ng mean free
path (approximately 100 atomic spacings at room temperature). This mean free path increases rapidly as
copper is chilled.
[11]

Because of its superior conducti
vity,

annealed

copper became the international standard to which all other
electrical conductors are compared. In 1913, the

International Electrotechnical Commission

set the
conductivity of copper in its International Annealed Copper Standard (IACS) to 100%. Today, copper
conductor
s

The main grade of copper used for electrical applications, such as building wire,

motor
windings, cables
and

busbars
, is

electrolytic
-
tough pitch (ETP) copper

(CW004A or

ASTM
designation C100140). This
copper is at leas
t 99.90% pure and has an electrical conductivity of at least 101% IACS. ETP copper
contains a small percentage of

oxygen

(0.02 to 0.04%). If high conductivity copper needs to
be

welded

or

brazed

or used in a reducing atmosphere, then

oxygen
-
free high conductivity
copper

(CW008A or ASTM designation C10100) may be used.
[12]

Several electrically conductive metals are lighter than copper, but since they
require larger cross sections
to carry the same current, they are unacceptable when limited space is a major requirement.
[13]
[14]

Aluminium has 61% of the conductivity of copper.
[15]

The cross sectional area of an aluminium conductor
must be 56% larger than

copper for the same current carrying capability.
[16]

The need to increase the
thickness of

aluminium wire

restricts its use in several applications,
[17]

such as in small motors and
automobiles. In some applications such as aerial

electric power transmission

cables, thickness is an
advantage and copper is rarely used. Though more expensive, some power companies use aluminum in
high amperage / voltage scenario
s because it is less susceptible to "brown" like copper will if over
-
used
hot (be ruined, non
-
conductive, need replacing). Aluminum routing also needs careful heat dissipation
because it melts at far lower temperatures.

Silver, a

precious metal
, is the only metal with a higher electrical conductivity than copper. The electrical
conductivity of silver is 106% of that of annealed copper on the IACS scale, and the electrical resist
ivity
of silver = 15.9 nΩ•m at 20°C.
[18]
[19]

The high cost of silver combined with its

low

tensile strength

limits
its use to special applications, such as joint plating and sliding contact surfaces.

Tensile strength

Tensile strength

measures the force required to pull an object such as rope, wire, or a structural beam to
the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress it c
an
take before breaking.
[20]

Copper’s higher tensile strength (200
-
250 N/mm
2

annealed) compared to aluminium is another reason
why copper is used extensively in the buildi
ng industry. Copper’s high strength resists stretching, neck
-
down, creep, nicks and breaks, and thereby also prevents failures and service interruptions.
[21]

In equipment
installations and machinery using non
-
copper wiring, nicks and scratches due to vibration
and flexing can deteriorate into large breaks in the wiring and lead to failure and long
-
term service
interruptions.
[22]

For example, when long runs of aluminium are pulled through conduit and cable trays,
they can stretch and neck
-
down. These effects reduce current carrying capacity, wastes energy, and can
cause overheating. Because o
f copper’s higher tensile strength, these problems are minimized in copper
wire.
[23]

Ductility

Ductili
ty

is a material's ability to

deform

under

tensile stress
. This is often char
acterized by the material's
ability to be stretched into a
wire
. Ductility is especially important in

metalworking

becaus
e materials that
crack or break under stress cannot be hammered, rolled, or drawn (drawing is a process that uses tensile
forces to stretch metal).

Copper has a higher ductility than alternate metal conductors with the exception of gold and silver, both
e
xpensive precious metals reserved for highly specialized wiring applications.
[26]

Because of copper’s
high ductility, it is easy to draw down to diameters with very close
tolerances.
[27]

Strength and ductility combination

Usually, the stronger a metal is, the less pliable it is. This is not the case with copper. A unique
combination of high

strength and high ductility makes copper ideal for wiring systems. At junction boxes
and at terminations, for example, copper can be bent, twisted, and pulled without stretching or breaking

Creep resistance

Creep

is the gradual deformation of a material from constant expansions and contractions under “load, no
-
load” conditions. This process has adverse effects on electrical systems: terminations can become loose,
caus
ing connections to heat up or create dangerous arcing.

Copper does not creep or loosen at its connections. For other metal conductors that creep, extra
maintenance is required to check terminals periodically and ensure that screws remain tightened to
preve
nt arcing and overheating. These extra measures can be avoided with the use of copper wire.
[29]

Corrosion resistance

Corrosion

is the unwanted breakdown and weakening of a material due to chemical reactions.
[30]

Copper
resists corrosion from moisture, humidity, industrial

pollution, and other atmospheric influences.
However, any corrosion oxides, chlorides, and sulfides that do form on copper are conductive. Therefore,
copper connections and terminations will not overheat from corrosion. Aluminium corrosion products, on
th
e other hand, are resistive and therefore can cause unwanted heat. To prevent corrosion and protect
joints, special surface preparations or oxide
-
inhibiting pastes are applied to aluminium. Copper
connections do not require these preparations and their ass
ociated additional costs.
[31]

Electrolytic
-
tough pitch (ETP) copp
er
, which is used in building wire, is a noble metal
[
dubious



discuss
]
. It is
not subject to galvanic corrosion when connected to other, less noble metals and alloys
[
dubious



discuss
]
.
[32]

Coefficient of thermal expansion

Metals and other solid materials expand upon heating and contract upon cooling.
[33]

This is

an undesirable
occurrence in electrical systems. Copper has a low coefficient of

thermal expansion

for an electrical
conducting material. Aluminium, an alternate common
conductor, expands nearly one third more than
copper under increasing temperatures. This higher degree of expansion, along with aluminium’s lower
ductility can cause electrical problems when bolted connections are improperly installed. By using proper
hard
ware, such as spring pressure connections and cupped or split washers at the joint, it may be possible
to create aluminium joints that compare in quality to copper joints.
[
34]

Thermal conductivity

Thermal conductivity

is the ability of a material to conduct heat.
[35]

In electrical systems, high thermal
conductivity is important for dissipating waste heat, particularly at terminations and connections. It is also
important for reducing energy consumption due to the generation of waste heat.

Copper has a

60% better thermal conductivity rating than aluminium,
[36]

so it is better able to reduce
thermal hot spots in electrical wiring systems.
[37]
[38]

Solderability

Soldering

is a process whe
reby two or more metals are joined together by a heating process.
[39]
[40]

This is
a de
sirable property in electrical systems. Some electrical codes require soldered joints.
[41]

Copper is
readily soldered to make durable connections when necessary.

Ease of i
nstallation

The inherent strength, hardness, and flexibility of copper building wire make it very easy to work with.
Copper wiring can be installed simply and easily with no special tools, washers, pigtails, or joint
compounds. Its flexibility makes it eas
y to join, while its hardness helps keep connections securely in
place. It has good strength for pulling wire through tight places (“pull
-
through”), including conduits. It
can be bent or twisted easily without breaking. It can be stripped and terminated du
ring installation or
service with far less danger of nicks or breaks. And it can be connected without the use of special lugs
and fittings. The combination of all of these factors makes it easy for electricians to install copper wire.


2.Types of copper wi
re and cable

Solid vs. stranded

Single
-
strand copper wire, also called solid wire or solid
-
core wire, consists of one piece of copper metal
wire surrounded by an insulator.
[44]

Single
-
strand copper conductors are typically used as magnet wire in
motors and transformers. They are relatively rigid, do not bend easily, and are typically installed in
permanent, infrequently handled, and low flex applications. Single strand copp
er wires also provide
mechanical ruggedness and good protection against the environment.

A stranded copper wire refers to a group of copper wires that are braided or twisted together. A stranded
copper wire is more flexible and easier to install than a sin
gle
-
strand copper wire of the same cross
section. Stranding also improves wire longevity for applications with moderate to high vibration. A
particular cross
-
section of a stranded conductor gives it essentially the same resistance characteristics as a
sing
le
-
strand conductor, but with added flexibility.
[45]

Cable

A copper cable consists of two or more copper wires running side by side and bonded, twisted or braided
together

to form a single assembly.
[46]

Electrical cables may be made more flexible by stranding the wires.

Copper wires in a cable may be bare or they may be plated to reduce

oxidation

with a thin layer of
another metal, most often

tin

but sometimes

gold

or

silver
. Plating may lengthen wire life and
makes

soldering

easier.

Cables can be made with one or two differen
t types of wire. For example, all
-
copper cables are used in a
wide range of applications, including

telecommunications

and

power distribution
. Combination conductor
cables, such as copper and

steel
, are used when increased strength with high conductivity is required over
lo
ng distances
[47]

(e.g., several hundred
-
meter spans), such as for telephone cables or for thin hookups,
such as

CATV

cable.
[48]

Some cables are designed to be multi
-
functional, such as those installed in residences to carry power,
telephone, video, and control/communications signal
s.
[49]

They are usually made from copper.

Current
-
carrying cables radiate an

e
lectromagnetic field
. Cables also pick up energy from any existing
electromagnetic fields that are around it. These effects are often undesirable, in the first case amounting to
unwanted transmission of energy which may adversely affect nearby equipment o
r other parts of the same
piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal
being carried by the cable, or, if the cable is carrying power supply or control voltages, cause equipment
malfunctions.
[50]

Three principal cable designs (shielding, twisted
-
pair geometry, and coaxial geometry) help to minimize
electromagnetic pickup and transmission.

Shielding cables

Shielding c
ables are encased in foil or wire mesh. The wires inside the shielding are mostly decoupled
from external

electric fields
. Simple shielding is not too effective against low
-
fre
quency

magnetic fields
,
resulting, for example, in a magnetic "hum" from a nearby power transformer.

Twisted pair cables

Twisted pair

cabling is a type of wiring in which two conductors (the forward and return conductors of a
single circuit) are twisted together to cancel out electromagnetic interference (EMI) from external sources
and reduce signal loss
.
[51]
[52]

This is why twisted pairs have been used in telephone communications for
man
y decades. For further information regarding the application of twisted pair cables in communication
wire, see:

Copper_wire_and_cable#Twist
ed_pair_cable
.

Coaxial cables

Coaxial cables

reduce low
-
frequency magnetic transmission and pickup.
[53]

They consist of two or more
wires that are wrapped

concentrically

and separated by a

dielectric

insu
lation material. The term, coaxial,
was coined because the center conductor and the outer conductor, or shield, form concentric

cylinders
.
This causes

voltages

induced by a magnetic field between the shield and the core conductor to consist of
two nearly equal magnitudes which cancel out each other.
[54]

The center conductor of a coaxial cable may
be a single strand or it may be stranded.

Common conductor materials used in coaxial cables include copper, tinned or silver plated
copper,

copper
-
clad steel
, and

copper
-
clad aluminium
. Less freque
ntly, aluminium is used as an alternate
inner conductor.
[55]

The outer conductor is typically made from a woven copper wire mesh braid shield
layer, or less frequently, al
uminium foil. This layer also gives the wire protection from
interference.
[56]

The cables are insulated with a flexible, tubular insulating layer made
from

polyethylene

(PE),
polypropylene

(PP),

fluorinated ethylene propylene

(FEP)
or

polytetrafluoroethylene

(PTFE).

[57]

The advantage of coaxial design is that the electric and magnetic fields are confined to the

dielectric

with
little leakage outside the shield. Con
versely, electric and magnetic fields outside the cable are largely kept
from causing interference to signals inside the cable. This property makes coaxial cable a good choice for
carrying weak signals that cannot tolerate interference from the environment

or for higher power signals
that must not be allowed to radiate or couple into adjacent structures or circuits.
[58]

Electrolytic
-
tough pitch (ETP) copper
, a high
-
purity copper that contains

oxygen

as an

alloying

agent,
represents the bulk of

electrical conductor

applications because of its high

electrical conductivity

and
improved

annealability
.
[59]

ETP copper is used for

power transmission
,

power distribution
,

and

telecommunications
.
[60]

Common applications include building wire, motor windi
ngs,

cables
,
and
busbars
.

Oxygen
-
free co
ppers

are used to resist

hydrogen embrittlement

when extensive amounts
of

cold work

is ne
eded, and for applications requiring higher

ductility

(e.g.,

telecommunications
cable
)
.
[61]

When hydrogen embrittlement is a concern and low electrical resistivity is not
required,

phosp
horus

may be added to copper.
[62]

For certain applications, copper alloy conductors are preferred instead of pure copper, especially when
higher strengths or improved
abrasion

and

corrosion

resistance properties are required. An example of a
copper alloy conducto
r is

cadmium

copper

trolley

wire, which is used for

railroad

electrification

in North
America.
[63]

However, relative to pure copper, the hi
gher strength and corrosion resistance benefits that
are offered by copper alloys are offset by their lower electrical conductivities. Design engineers weigh the
advantages and disadvantages of the various types of copper and copper alloy conductors when
d
etermining which type to specify for a specific electrical application.

Some of the major application markets for copper wire and cable are summarized below.


3.Types of stainless steel

Stainless steel does not

corrode
,

rust

or stain with water as ordinary steel does, but despite the name it is
not fully stain
-
proof, most notably under low oxygen, high salinity, or poor circulati
on environments.
[3]

It
is also called

corrosion
-
resistant steel

or

CRES

when the alloy type and grade are not detailed,
particularly in the aviation industry. There are different

grades and surface finishes of stainless steel to
suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and
resistance to corrosion are required.

Stainless steel differs from carbon steel by the amount of c
hromium present. Unprotected carbon
steel

rusts

readily when exposed to air and moisture. This

iron oxide

film (the rust) is

active and
accelerates corrosion by forming more iron oxide, and due to the dissimilar size of the iron and iron oxide
molecules (iron oxide is larger) these tend to flake and fall away. Stainless steels contain sufficient
chromium to form a passive film
of chromium oxide, which prevents further surface corrosion and blocks
corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and
oxide molecules they bond very strongly and remain attached to the surface


Th
ere are different types of stainless steels: when

nickel

is added, for instance, the austenite structure of
iron is stabilized. This crystal structure makes such steels virtually non
-
magnetic
and less

brittle

at low
temperatures. For greater

hardness

and strength, more

carbon

is added. With proper

heat treatment
,
thes
e

razor blade steels

are used for such things as razor blades, cutlery, and tools.

Significant quantities of

manganese

have been used in many stainless steel compositions. Manganese
preserves an austenitic structure in the steel, similar to nickel, but at a lower
cost
.

Stainless steels are also c
lassified by their

crystalline structure
:



Austenitic
, or 300 series, stainless steels have a
n austenitic crystalline structure, which is a

face
-
centered cubic

crystal structure. Austenite steels make up over 70% of total stainless steel production.
They cont
ain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel
and/or manganese to retain an austenitic structure at all temperatures from the

cryogenic

region to the
mel
ting point of the alloy. The most widely used austenite steel is the

304

grade or A2 stainless
steel(
not to be confused with A2 grade steel, also named

Tool steel
, a steel). The second most
common austenite steel is the

316

grade, also called marine grade stainless, used primarily for its
increased resistance to corrosion. A typical composition of 18% chromium and 10% nickel,
commonly known as

18/10 stainless
, is often used in

cutlery

and high
quality

cookware
.

18/0

and

18/8

are also available.

Superaustenitic

stainless steels, such as alloy

AL
-
6XN

and 254SMO, exhibit great resistance to
chloride pitting and crevice corrosion because of high

molybdenum

content (>6%) and nitrogen

additions, and the higher nickel content ensures better resistance to stress
-
corrosion cracking
versus the 300 series. The higher alloy content of superaustenitic steels makes them more
expensive. Other steels can offer similar performance at lower cost a
nd are preferred in certain
applications, for example ASTM A387 is used in pressure vessels but is a low alloy carbon steel
with a chromium content of 0.5% to 9%.
[18]

Low
-
carbon

versions, for example

316
L or 304L, are
used to avoid corrosion problems caused by welding. Grade 316LVM is preferred
where
biocompatibility

is required (such as body implants and piercings).
[19]

The "L" means that
the carbon content of the alloy is bel
ow 0.03%, which reduces the

sensitization
effect

(precipitation of chromium carbides at grain boundaries) caused by the high temperatures
involved in welding.



Ferritic

stainless steels generally have better engineering properties than austenitic grades, but
have reduced corrosion resistance, because of the lower chromium and nickel conten
t. They are
also usually less expensive. They contain between 10.5% and 27% chromium and very little
nickel, if any, but some types can contain lead. Most compositions include molybdenum; some,
aluminium or titanium. Common ferritic grades include 18Cr
-
2Mo
, 26Cr
-
1Mo, 29Cr
-
4Mo, and
29Cr
-
4Mo
-
2Ni. These alloys can be degraded by the presence of


chromium, an intermetallic
phase which can precipitate upon welding.



Martensitic

stainless steels are not as corrosion
-
resistant as the other two classes but are
extremely strong and tough, as well as highly

machinable
, and can be hardene
d by heat
treatment. Martensitic stainless steel contains chromium (12

14%), molybdenum (0.2

1%),
nickel (less than 2%), and carbon (about 0.1

1%) (giving it more hardness but making the
material a bit more brittle). It is quenched and magnetic.



Precipitat
ion
-
hardening martensitic

stainless steels have corrosion resistance comparable to
austenitic varieties, but can be
precipitation hardened

to even higher stren
gths than the other
martensitic grades. The most common,

17
-
4PH
, uses about 17% chromium and 4% nickel. The
Lockheed
-
Martin

Joint Strike Fighter

is the first aircraft to use a precipitation
-
hardenable
stainless steel

Carpenter Custom 465

in its airframe.



Duplex

stainless steels have a mixed microstructure of austenite and ferrite, the aim usually being
to produce a 50/50 mix, although in commercial allo
ys the ratio may be 40/60. Duplex stainless
steels have roughly twice the strength compared to austenitic stainless steels and also improved
resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion
cracking. They are
characterized by high chromium (19

32%) and molybdenum (up to 5%) and
lower nickel contents than austenitic stainless steels.

The properties of duplex stainless steels are achieved with an overall lower alloy content than
similar
-
performing super
-
austeniti
c grades, making their use cost
-
effective for many applications.
Duplex grades are characterized into groups based on their alloy content and corrosion resistance.



Lean duplex

refers to grades such as

UNS

S32101 (LDX 2101), S32304, and S32003.



Standard duplex

is 22% chromium with UNS S31803/S32205 known as 2205 being the most
widely used.



Super duplex

is by definition a duplex stainless steel with a pitting c
orrosion equivalent
(PRE) > 40, where PRE =

%Cr + 3.3x(%Mo + 0.5x%W) + 16x%N. Usually super duplex
grades have 25% chromium or more and some common examples are S32760 (
Zeron 100
),
S3275
0 (2507) and S32550 (Ferralium), although not all Ferralium grades are super duplex
grades.



Hyper duplex

refers to duplex grades with a PRE > 48 and at the moment only UNS S32707
and S33207 are available on the market.

Stainless steel grades

There are a nu
mber of different systems for

grading stainless and other steels
. The article on US

SAE
steel gra
des

details a large number of grades with their properties.

Stainless steel in 3D printing

Some

3D printing

providers have developed proprietary stainless steel

sintering
[20]

blends for use in rapid
prototyping. Currently available grades do not vary significantly in their properties.


4
.Carbon steel

Carbon steel
, also called

plain
-
carbon steel
, is

steel

where the main interstitial

alloying
constituent
is

carbon
. The

American Iron and Steel Institute

(AISI) defines carbon steel as the follo
wing: "Steel is
considered to be carbon steel when no minimum content is specified or required
for

chromium
,

cobalt
,

molybdenum
,

nickel
,

niobium
,

titanium
,
tungsten
,

vanadium

or

zirconium
, or any
other element to be added to obtain a desired alloying effect; when the specified minimum for copper
does not exceed 1.04 percent; or when the maximum content specified for any of the following elements
does not exceed th
e percentages noted:

manganese

1.65,

silicon

0.60,

copper

0.60."
[1]

The term "carbon steel" may also be used in reference to steel which is not

stainles
s steel
; in this use
carbon steel may include alloy steels.

As the carbon content rises, steel has the ability to become

harder

and

stronger

through
heat treating
, but
this also makes it less

ductile
. Regar
dless of the heat treatment, a higher carbon content
reduces

weldability
. In carbon steels, the higher carbon content lowers the melting point

4.Types of carbon steel

Carbon steel is

broken down in to four classes based on carbon content:

Mild and low carbon steel

Mild steel is the most common form of steel because its price is relatively low while it provides material
properties that are acceptable for many applications. Low carbon s
teel contains approximately 0.05

0.15% carbon
[1]

and mild steel contains 0.16

0.29%
[1]

carbon; mak
ing it malleable and ductile, but it
cannot be hardened by heat treatment. Mild steel has a relatively low tensile strength, but it is cheap and
malleable; surface hardness can be increased through

carburizing
.
[3]

It is often used when large quantities of steel are needed, for example as

structural steel
. The density of
mild steel is approximately 7.85

g/cm
3

(7850

kg/m
3

or 0.284

lb/in
3
)
[4]

and the

Young's modulus

is
210

GPa (30,000,000 psi).
[5]

Low carbon steels suffer from

yield
-
point runout

where the material has two

yield points
. The first yield
point (or upper yield point) is higher than the second and the yield drops dramatically after the upper yield
point. If a low carbon steel is only stressed to some point between th
e upper and lower yield point then
the surface may develop

Lüder bands
.
[6]

Low carbon steels contain l
ess carbon that other steels and are
easier to cold
-
form, making them easier to handle.
[7]

Higher carbon steels

Carbon steels which can successfully undergo heat
-
treatment have a ca
rbon content in the range of 0.30

1.70% by weight. Trace impurities of various other

elements

can have a significant effect on the quality
of the resulting steel. Trace amo
unts of

sulfur

in particular make the steel

red
-
short
. Low alloy carbon
steel, such as

A36

grade, contains about 0.05% sulfur and melts around 1426

1538 °C (2599

2800

°F).
[8]

Manganese

is often added to improve the

hardenability

of low carbon steels. These additions
turn the material into a

low alloy steel

by some definitions, but

AISI
's definition of carbon steel allows up
to 1.65% manganese b
y weight.

Medium carbon steel

Approximately 0.30

0.59% carbon content.
[1]

Balances ductility and strength and has good wear
resistance; used for large parts, forging and automot
ive components.
[9]

High carbon steel

Approximately 0.6

0.99% carbon content.
[1]

Very strong, used for
springs and high
-
strength wires.
[10]

Ultra
-
high carbon steel

Approximately 1.0

2.0% carbon content.
[1]

Steels that can be tempered to great hardness. Used for special
purposes like (non
-
industrial
-
purpose) knives, axles or

punches
. Most steels with more than 1.2% ca
rbon
content are made using

powder metallurgy
. Note that steel with a carbon content above 2.0% is
considered

cast iron
.

Heat treatment

The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility,
hardness, yield strength, or impact resistance. Note that the electrical and thermal conductivity are slightly

altered. As with most strengthening techniques for steel,
Young's modulus

is unaffected. Steel has a higher
solid solubility for carbon in the

austenite
phase; therefore all heat treatments, except spheroidizing and
process annealing, start by heating to an austenitic phase. The rate at which the steel is cooled through
the

eutectoid
reaction affects the rate at which carbon diffuses out of austenite. Generally speaking,
cooling swiftly will give a finer

pearlite

(until the

martensite

critical temperature is reached) and cooling
slowly will give a coarser pearlite. Cooling a hypoeutectoid (less than 0.77 wt% C) steel results in a
pearlitic structure with

α
-
ferrite

at the grain boundaries. If it is hypereutectoid (more than 0.77 wt% C)
steel then the structure is full pearlite with small grains of

cementite

scattered throughout. The relative
amounts of constituents are found using the

lever rule
. Here is a list of the types of heat treatme
nts
possible:



Spheroidizing
: Spheroidite forms when carbon steel is heated to approximately 700

°C for over
30 hours. Spheroidite can form at lower temperatures but the time needed drastically increases, as this
is a diffusion
-
controlled process. The resul
t is a structure of rods or spheres of cementite within
primary structure (ferrite or pearlite, depending on which side of the eutectoid you are on). The
purpose is to soften higher carbon steels and allow more formability. This is the softest and most
duc
tile form of steel. The image to the right shows where spheroidizing usually occurs.
[11]



Full annealing
: Carbon steel is heated to approximately 40

°C above Ac
3

or Ac
1

for 1 hour; this
assures all the

ferrite

transforms into

austenite

(although

cementite

might still exist if the carbon
content is greater than the eutectoid). The steel must then be cooled slowly, in the real
m of 38°C
(68.4°F) per hour. Usually it is just furnace cooled, where the furnace is turned off with the steel still
inside. This results in a coarse pearlitic structure, which means the "bands" of

pearlite

are thick. Fully
annealed steel is soft and
ductile
, with no internal stresses, which is often necessary for cost
-
effective
forming. Only spheroidized steel is softer and m
ore ductile.
[12]



Process annealing
: A process used to relieve stress in a cold
-
worked carbon steel with less than
0.3

wt% C. The steel is usually heated up to 550

650

°C for 1 hour
, but sometimes temperatures as
high as 700

°C. The image rightward shows the area where process annealing occurs.



Isothermal annealing
: It is a process in which hypoeutectoid steel is heated above the upper
critical temperature and this temperature is mai
ntained for a time and then the temperature is brought
down below lower critical temperature and is again maintained. Then finally it is cooled at room
temperature. This method rids any temperature gradient.



Normalizing
: Carbon steel is heated to approxima
tely 55

°C above Ac
3

or Ac
m

for 1 hour; this
assures the steel completely transforms to austenite. The steel is then air
-
cooled, which is a cooling
rate of approximately 38

°C (100.4 °F) per minute. This results in a fine pearlitic structure, and a
more
-
un
iform structure. Normalized steel has a higher strength than annealed steel; it has a relatively
high strength and ductility.
[13]



Quenching
: Carbon steel with at least 0.4

wt% C is heated to normalizing temperatures and then
rapidly cooled (quenched) in water, brine, or oil to the critical temperature. The critical temperature is
dependent on the carbon content, b
ut as a general rule is lower as the carbon content increases. This
results in a martensitic structure; a form of steel that possesses a super
-
saturated carbon content in a
deformed body
-
centered cubic (BCC) crystalline structure, properly termed body
-
cent
ered tetragonal
(BCT), with much internal stress. Thus quenched steel is extremely hard but

brittle
, usually too brittle
for practical purposes. These internal stresses cause stress cracks o
n the surface. Quenched steel is
approximately three to four (with more carbon) fold harder than normalized steel.
[14]



Martempering

(Marquenching)
: Martempering is not actually a tempering procedure, hence the
term "marquenching". It is a form of isothermal heat treatment applied after an initial quench of
typically in a molten salt bath at a temperature rig
ht above the "martensite start temperature". At this
temperature, residual stresses within the material are relieved and some bainite may be formed from
the retained austenite which did not have time to transform into anything else. In industry, this is a
process used to control the ductility and hardness of a material. With longer marquenching, the
ductility increases with a minimal loss in strength; the steel is held in this solution until the inner and
outer temperatures equalize. Then the steel is coole
d at a moderate speed to keep the temperature
gradient minimal. Not only does this process reduce internal stresses and stress cracks, but it also
increases the impact resistance.
[1
5]



Quench and tempering
: This is the most common heat treatment encountered, because the final

properties can be precisely determined by the temperature and time of the tempering. Tempering
involves reheating quenched steel to a temperature below the
eutectoid

temperature then coo
ling. The
elevated temperature allows very small amounts of spheroidite to form, which restores ductility, but
reduces hardness. Actual temperatures and times are carefully chosen for each composition.
[16]



Austempering
: The austempering process is the same as martempering, except the steel is held in
the molten salt bath through the bainite transformation te
mperatures, and then moderately cooled.
The resulting bainite steel has a greater ductility, higher impact resistance, and less distortion. The
disadvantage of austempering is it can only be used on a few steels, and it requires a special salt bath