steel alloys main

8/4/2019 Steel Alloys Main

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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!!

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