Post on 07-Apr-2018
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Submitted By:Krishna Vijaywargiy
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A metal is a chemical element that is a good conductor of both electricity
and heat and forms cations and ionic bonds with non-metals.
Metals are known for their property to form ALLOYS with other metals and achieve
improved physical and chemical properties.
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An alloy is a homogeneous mixture or metallic solid solution composed of two or
more elements. Complete solid solution alloys give single solid phase microstructure,
while partial solutions give two or more phases that may or may not
be homogeneous in distribution, depending on thermal (heat treatment) history. Alloys
usually have different properties from those of the component elements.
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Steel is an alloy that consists mostly of iron and has a carbon content between 0.2%
and 2.1% by weight, depending on the grade. Carbon is the most common alloying
material for iron, but various other alloying elements are used, such
as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a
hardening agent, preventing dislocations in the iron atom crystal lattice from sliding
past one another. Varying the amount of alloying elements and the form of their
presence in the steel (solute elements, precipitated phase) controls qualities such as
the hardness, ductility, and tensile strength of the resulting steel. Steel with
increased carbon content can be made harder and stronger than iron, but such steel is
also less ductile than iron.
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The recipe for steel
Here's the recipe for a typical "batch" of molten pig iron. For each ton of molten pig iron, you
need:
2600 lbs iron ore or iron ore pellets
1000 lbs coke
and a few hundred lbs of flux (slag, calcite, dolomite, limestone, etc).
In some instances, burnt lime(manufactured by heating calcite or dolomite) is substituted. The
lime in the stone or burnt lime (when melted in blast furnaces, basic oxygen furnaces, or
electric furnaces) combines with the impurities in the ore or hot metal to form slag, which,
because it is lighter, floats on top of the molten metal. Take a few minutes and "walk through"
the process of steel-making as nicely illustrated in the 12-step diagrams below.
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Properties Alloy Steels Carbon Steels Stainless Steels Tool Steels
Density (1000 kg/m3) 7.85 7.85 7.75-8.1 7.72-8.0
Elastic Modulus (GPa) 190-210 190-210 190-210 190-210
Poisson's Ratio 0.27-0.3 0.27-0.3 0.27-0.3 0.27-0.3
Thermal Expansion (10-
6/K)9.0-15 11-16.6 9.0-20.7 9.4-15.1
Melting Point (C) 1371-1454
Thermal Conductivity(W/m-K)
26-48.6 24.3-65.2 11.2-36.7 19.9-48.3
Specific Heat (J/kg-K) 452-1499 450-2081 420-500
Electrical Resistivity (10-9;-m)
210-1251 130-1250 75.7-1020
Tensile Strength (MPa) 758-1882 276-1882 515-827 640-2000
Yield Strength (MPa) 366-1793 186-758 207-552 380-440
Percent Elongation (%) 4-31 10-32 12-40 5-25
Hardness (Brinell3000kg)
149-627 86-388 137-595 210-620
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Alloy steel is steel alloyed with a variety of elements in total amounts of between 1.0%
and 50% by weight to improve its mechanical properties. Alloy steels are broken down
into two groups: low-alloy steels and high-alloy steels. The difference between the
two is somewhat arbitrary from 4% to 8%.
The following is a range of improved properties in alloy steels (as compared to carbon
steels): strength, hardness, toughness, wear resistance, hardenability, and hot hardness.
To achieve some of these improved properties the metal may require heat treating.
Commonly alloyants include:
Manganese
Nickel
Chromium
Molybdenum
Vanadium
Silicon
Boron
Aluminum
Cobalt
Copper
Niobium
Titanium
Tungsten
Tin
Zirconium
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Element Percentage Primary functionAluminium 0.951.30 Alloying element in nitriding steels
Bismuth - Improves machinability
Boron 0.0010.003 A powerful hardenability agent
Chromium0.52 Increases hardenability
418 Increases corrosion resistance
Copper 0.10.4 Corrosion resistanceLead - Improved machinability
Manganese
0.250.40
Combines with sulfur and with phosphorus to reduce the
brittleness. Also helps to remove excess oxygen from molten
steel.
>1Increases hardenability by lowering transformation points and
causing transformations to be sluggish
Molybdenum 0.25
Stable carbides; inhibits grain growth. Increases the toughness ofsteel, thus making molybdenum a very valuable alloy metal for
making the cutting parts of machine tools and also
the turbine blades of turbojet engines. Also used in rocket
motors.
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Nickel25 Tougheness
1220 Increases corrosion resistance
Silicon
0.20.7 Increases strength
2.0 Spring steels
Higher
percentages
Improves magnetic properties
Sulfur 0.080.15 Free-machining properties
Titanium -Fixes carbon in inert particles; reduces martensitic hardness in
chromium steels
Tungsten - Also increases the melting point.
Vanadium 0.15
Stable carbides; increases strength while retaining ductility;
promotes fine grain structure. Increases the toughness at high
temperatures
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Following are the general steel types which are most extensively produced:
Boron Steels
Boron is a potent and economical alloying element that markedly increases
hardenability when added to a fully deoxidized steel, especially low carbon grades.
Additions are small, usually between .005 and .003 percent. It does not affect the
strength of ferrite, and therefore does not sacrifice ductility, formability or
machinability in the annealed state.
Steel Grade Designation: XXBXX.
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Carbon Steels
Carbon has a dual effect in hardenable alloy steels. It both controls maximum
obtainable hardness and contributes substantially to hardenability. It is the least
expensive approach to improving hardenability.
Plain carbon steels do not have any other commonly used intentional alloy additions.
They are generally used for less-critical applications in non-corrosive environments,
and are not usually heat treated. Except for spring and bearing steels, more than .60
percent C is seldom used in steels for machined parts.
Steel Grade Designation: 10XX, 11XX,15XX
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Chromium - Stainless Steel
Chromium stainless steels are iron-based alloys that contain at least
10.5 percent Cr. They achieve their stainless characteristics through the formation of
the invisible and adherent chromium-rich oxide surface film. Other elements can be
added to improve product characteristics. Stainless steels may be selected based on
corrosion resistance, fabrication characteristics, availability and mechanical properties
in specific temperature ranges.
Steel Grade Designation: 4XX
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Chromium Steels
Chromium is used in low alloy steels to increase hardenability. In addition, it brings
resistance to corrosion and oxidation, high temperature strength and abrasion
resistance.
Straight chromium steels are susceptible to temper embrittlement and can be brittle.
Steel Grade Designation: 50XX, 51XX, 50XXX, 51XXX. 52XXX
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Chromium-MolybdenumSteels
Chromium and molybdenum both individually increase the hardenability of low alloy
steel. Important synergistic effects, not yet fully defined, can also occur when Cr and
Mo are used in place of single elements.
Chromium brings resistance to corrosion and oxidation, high temperature strength and
abrasion resistance. Molybdenum helps maintain a specified hardenability and
increases high temperature tensile and creep strengths. These grades are generally heat-
treated to specified properties.
Steel Grade Designation: 41XX, PSXX (formerly EX grades)
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Chromium-Molybdenum-Vanadium
CrMoV steel is a heat resistant steel typically used in applications such as shafts and
fasteners used in high temperature service.
The chromium is used in this steel to increase resistance to corrosion and oxidation, to
impart high temperature strength and to increase the hardenability. The molybdenum
addition also imparts higher hardenability and increases high temperature tensile and
creep strengths. The vanadium addition inhibits grain growth during heat treating while
improving strength and toughness. This steel is referenced in the industry specification
AMS 6304.
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Chromium-Vanadium Steels
Both chromium and vanadium increase the hardenability of steel. Important synergistic
effects, not yet fully defined, can also occur when combinations are used in place of
single elements.
Chromium brings resistance to corrosion and oxidation, high temperature strength and
abrasion resistance. Vanadium inhibits grain growth during heat treating while
improving toughness of hardened and tempered steels.
Steel Grade Designation: 61XX
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Manganese Steels
Manganese is one of the least expensive means of increasing hardenability at a given
carbon content. It can also enhance machinability in the presence of sulfur.Steel Grade Designation: 13XX
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Molybdenum Steels
Molybdenum increases hardenability and helps maintain a specified hardenability. It
also increases high temperature tensile and creep strengths. These grades are generally
heat-treated to specified properties.
Steel Grade Designation: 40XX, 44XX
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Nickel-Chromium Steels
Both Ni and Cr increase the hardenability of steel. Chromium brings resistance to
corrosion and oxidation, high temperature strength and abrasion resistance. Steels with
added nickel offer much greater toughness at a specified carbon level.Steel Grade Designation: 31XX, 32XX, 33XX, 34XX
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Nickel-Chromium-MolybdenumSteels
Ni, Cr and Mo all increase the hardenability of steel. In general, Ni is the most
expensive per unit of increased hardenability, but is warranted when toughness is a
primary consideration. Chromium brings resistance to corrosion and oxidation, hightemperature strength and abrasion resistance. Molybdenum increases hardenability and
helps maintain a specified hardenability. It also increases high temperature tensile and
creep strengths. These grades are generally heat treated to specified properties.
Steel Grade Designation: 43XX, 43BVXX, 47XX, 81XX, 86XX, 87XX, 88XX,
93XX, 94XX, 97XX, 98XX, PSXX (Formerly EX grades)
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Nickel-MolybdenumSteels
Both Ni and Mo increase the hardenability of steel. Steels with added nickel offer
much greater toughness at a specified carbon level. Mo also increases high
temperature tensile and creep strengths. These grades are generally heat treated to
specified properties.
Steel Grade Designation: 46XX, 48XX
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Nitriding Steels
These are steels that are specially formulated to undergo a nitriding operation on a
machined part. Nitriding consists of heating the part in an atmosphere containingammonia.
A thin, very hard case results from the formation of nitrides. Nitriding grades contain
the strong nitride-forming elements aluminum, chromium and molybdenum.
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Silicon-Manganese Steels
Silicon increases the strength without a serious loss of ductility. It also adds scale
resistance. These steels are generally heat treated to specific properties.
Manganese is one of the least expensive means of increasing hardenability at a given
carbon content. It can also enhance machinability in the presence of sulfur.
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Maraging steels
This type of steel is known for possessing superior strength and toughness withoutlosing malleability, although they cannot hold a good cutting edge. Agingrefers to the
extended heat-treatment process. These steels are a special class of low-carbon ultra-
high-strength steels which derive their strength not from carbon, but from
precipitation of inter-metallic compounds. The principal alloying element is 15 to
25% nickel. Secondary alloying elements are added to produce intermetallic
precipitates, which include cobalt, molybdenum, and titanium.
Maraging steel's strength and malleability in the pre-aged stage allows it to be formed
into thinner rocket and missile skins than other steels, reducing weight for a given
strength. Maraging steels have very stable properties, and, even after over aging due
to excessive temperature, only soften slightly. These alloys retain their properties at
mildly elevated operating temperatures and have maximum service temperatures of
over 400 C (752 F).
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THANK YOU!!