08 - Metallurgy

Presentation : IMS – Tech Managers Conference Author : IMS Staff Creation date : 08 March 2012 Classification : D3 Conservation : Page : 1 08 – Metallurgy Author : IMS Staff Creation date : 14 Dec.2012 Classification : D3

08 - Metallurgy


The intent of this presentation is to present enough information to provide the reader with a fundamental knowledge of different metal classification systems used within Michelin and to

better understand basic metallurgy processes.


08 - MetallurgyThe Study of Metals - Metallurgy

The term metallurgy involves the deriving of metals from their ores as they are found in nature. This process involves their purification, sometimes mixing in other metals, and finally, their manufacture into shapes and forms that are useful in industry. This process can also involve the recycling of scrap metals and their reformation into useful forms. Over the years, as needs have changed, metals have become more complex. Without some means of reference or identification, specifying or using these metals would be very confusing. Systems have been developed to help choose a metal that fits the end product requirements, and also help the fabricator with processing characteristics.

Metals are divided into two main categories: ferrous and non-ferrous. Those that contain iron are ferrous. Those that do not are non-ferrous.

The following metals will be discussed: Cast iron (ferrous) Steel and its alloys (ferrous) Aluminum and its alloys (non-ferrous) Copper and its alloys (non-ferrous)


Cast Iron and Steel

Classification by Carbon Content

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Cast iron Cast irons come in several forms gray, white, malleable, and nodular. Their carbon content ranges from 3 to 4.5%, which is much higher than that of steel. Pig iron, which is the product of the blast furnace, is cast directly into molds or sent to the cupola furnace where it is mixed with scrap steel and cast iron, and combined with other elements to form cast iron. This metal is drawn off and cast into useful shapes. If cast into sand molds, gray cast iron is formed. If cast into steel molds, white cast iron is formed, because of the quicker cooling rate. The original pig iron could also be sent directly to the steel making furnaces. Gray cast iron

Gray cast iron is a mixture of carbon in an iron matrix. It has good wear qualities, but because of its hardness, it is brittle and also abrasive to cutting tools used to finish-off the castings. This form of cast iron is not malleable; it cannot be hammered or formed while cold because cracking would occur. A fracture is dark grey in color. White cast iron-

White cast irons are hard and brittle and produce a fracture that is very white in color. They have good compressive strength and have excellent resistance to wear and abrasion. If heated slowly to approximately 1700 degrees F. and held at that temperature for several days, then cooled slowly, it becomes malleable cast iron.

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Malleable cast iron–Malleable cast iron has much more strength than the above cast irons, and can be hammered, rolled, and bent without breaking. A fracture is darker gray than gray cast iron. Nodular cast iron Nodular cast iron, often called ductile or spheroidal graphitic, is a very versatile product. It keeps the advantages of regular cast iron, being easy to cast, and is easily machinable and has good wear characteristics. It also exhibits characteristics normally associated with steel (high strength, ductility, toughness, and hardenability). These additional characteristics are due to the addition of magnesium to the cast iron, which causes the carbon to form a nodule shape instead of the weaker graphite flake form. Some of these nodular cast irons are alloyed with nickel and molybdenum, which increases their hardenability (up to Rc60 with flame or induction hardening).

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Classification of Cast Irons

Cast irons are specified under two different systems; SAE (Society of Automotive Engineering) and ASTM (American Society for Testing Materials). The SAE system is more concerned with the micro-structure of the material where the ASTM system is based on actual tests on a cast specimen. The ASTM specifications are more generally used in industry, while the SAE designations are usually used for large quantities of smaller cast components.

The following chart shows some typical callouts.

Gray White Malleable Nodular (Ductile)ASTM SAE ASTM SAE ASTM SAE ASTM SAE

Class 20 20-50 A197 32510 A395A356-72

80-55-06

Class 25 35018 60-40-18

Class 30 A220

40010 100-70-03

Class 40 45006 120-90-02

Class 50 50005 Class 60 70003

90001

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The above grades relate to the strength and percent stretch of the material. Example, a gray cast iron, Class 20, has a minimum tensile strength of 20,000 psi. Nodular or ductile cast irons have a three-part numbering system. A 60-40-18 has a minimum tensile strength of 60,000 psi, yield strength of 40,000 psi, and 18% elongation. Steels A particular steel is usually chosen because of one of the following qualities:

Hardenability Formability Weldability Machinability Availability Processing costs

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Classification in function of carbon content Steels are widely‑used ferrous alloys which have a carbon content between that of commercial iron and of cast iron. There is a great variety of steel materials on the market each with its specific uses depending on its characteristics

Type

Carbon content

Mild steel

orLow Carbon Steel

0.05 %

to0.20 %

Machinery Steel

orMedium Carbon

Steel

0.20 %

to0.50 %

Tool Steel

orHigh Carbon Steel

0.50 %

to2.00 %

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Mild and machinery steels Mild and machinery steels have a low content of carbon and are used in machine construction. They are relatively soft, which makes them good candidates for forging in moulds. This latter quality allows for their machinability to a smooth and shiny surface. High‑carbon steels High‑carbon steels, also called tool steels, can be hardened to give them better resistance to wear and abrasion. This type of steel is very hard, which allows for the maintenance of cutting edges when it is made into cutting tools. This kind of steel is used for cutting tools, friction‑bearing parts, punch dies, hammers and other tools.

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CLASSIFICATION OF STEELS SAE (Society of Automotive Engineers) Classification of steels This system was originally designed for the automotive industry, but its use has spread to other industries.

The SAE classification (Society of Automobile Engineering) is a simple method to tell various steels apart. It uses four or five digits.

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The kind of alloy is determined as follows:

1XXX = carbon steel

2XXX = nickel steel

3XXX = nickel‑chromium steel

4XXX = molybdenum steel

5XXX = chromium steel

6XXX = chromium‑vanadium steel

7XXX = tungsten steel

8XXX = triple alloy

9XXX = silicon‑manganese steel.

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SAE STEEL CLASSIFICATION STANDARDS

CARBON STEELS 1xxx Standard carbon steel 10xx Machining steel (screw steel) 11xx Machining steel, with manganese X13xx HIGH MANGANESE CONTENT STEEL T13xx NICKEL STEELS 2xxx 0.50 % nickel 20xx 1.50 % nickel 21xx 3.50 % nickel 23xx 5.00 % nickel 25xx NICKEL-CHROMIUM STEELS 3xxx 1.25 % nickel, 0.60% chromium 31xx 1.75 % nickel, 1.00% chromium 32xx 3.50 % nickel, 1.50% chromium 33xx 3.00 % nickel, 0.80% chromium 34xx Corrosion and heat resistant steels 30xxx

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SAE STEEL CLASSIFICATION STANDARDS

MOLYBDENUM STEELS 4xxx Chromium 41xx Chromium-nickel 43xx Nickel 46xx et 48xx CHROMIUM STEELS 5xxx Low chromium content 51xx Medium chromium content 52xxx CHROMIUM-VANADIUM STEELS 6xxx TUNGSTEN STEELS 7xxx et 7xxxx TRIPLE-ALLOY STEELS 8xxx SILICON-MANGANESE STEELS 9xxx

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Classification of steels

Example of this standard: Steel 511005 = chromium steel1 = 1% chromium100 = 1% carbon

Sometimes, there is a prefix before the 13XX series. The "X" means that the sulphur and manganese content deviates from that of standard steel. The "T" indicates a high manganese content. AISI Classification of steels (American Iron and Steel Institute) The AISI classification (American Iron and Steel Institute) is similar to the SAE classification described above. The main difference resides in a prefix which identifies the manufacturing process. These prefixes are:B = Bessemer process (acid carbon steel)C = open‑hearth process (standard steel)CB = Bessemer (acid) or open‑hearth (standard) processD = open‑hearth process (acid carbon steel)E = arc furnace process (alloyed steel).

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Examples of this classification of steels

52100 (Bearing steel)52 = chromium steel100 = 1% carbon

Stainless steel The main characteristic of stainless steel is its resistance to corrosion. The element that provides this property is chromium. Stainless steel contains between 11.5 and 27% of chromium and is an alloy that can undergo hot treatments which will modify its physical properties. Stainless steel is used a great deal by the pulp and paper industry, for instance, in piping. This is because stainless steel pipes offer resistance to corrosion, which helps reduce maintenance costs and conserve a good inside finish (therefore, no impurities, such as rust, are released into and absorbed by the pulp). The following chart lists various kinds of stainless steels and their characteristics.

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4340 (Good steel for shafting)43 = Nickel-Chromium-Molybdenum steel40 = 0.4% carbon


A.I.S.I. Grade

Characteristics

Uses

Grade 302

Excellent resistance to corrosion

An all‑purpose grade for food, dairy and chemical products, and for architectural fittings.

Grade 304

Carbon content 0.8% max.

For applications similar to those of grade 302, but with improved corrosion resistance on welded surfaces.

Grade 321 Grade 347

Resistance to corrosion is similar overall to that of grades 302 and 304stabilizing additives protect it against corrosion on heated surfaces.

For high‑temperature use, 800 to 1600o F, and under harsh corrosion conditions where welded assemblies cannot be post annealed.

Grade 316

Exceptional resistance to corrosion. Improved resistance to creep.

Harsh corrosive conditions, particularly those including etching compounds.

Grade 303

Less scratching and jamming. Greatly improved machining.

Gears, valves, bolts, screws and other machined products.


A.I.S.I. Grade

Characteristics

Uses

Grade 309 Exceptional resistance to stress at high temperatures.

For operating temperatures up to 1900o F.

Grade 310

Superior resistance to oxidation.

For very high operating temperatures.

Grade 430

Good resistance to corrosion.

Automotive parts and interior architectural fittings; some specific chemical applications.

Grade 446

Poor stretching or stamping; not recommended for deep embossing. Excellent resistance to flaking.

Used mainly for temperatures up to 2000o F, fixed parts which are not subjected to high stress.

Grade 410

Martensitic steel strengthened by quenching and tempering, and by conventional quench hardening.

Mechanical gear parts, such as pump rods and valves.


A.I.S.I. Grade

Characteristics

Uses

Grade 403

Same basic composition as grade 410

Modified composition suitable for turbine blades and other similar applications.

Grade 405

Same basic composition as grade 410

Modified composition for applications calling for on‑the‑spot welding and when air‑hardening cannot be rectified by quenching and tempering.

Nuance 409

Limited resistance to corrosion due to low chromium content.

Used for car mufflers and other applications requiring resistance to heat and corrosion.

Grade 501

Hardened by welding. Must be annealed to recover its malleability.

Used by the petroleum industry because of its strength and its resistance to corrosion and oxidation at moderately‑high temperatures.

Grade 502

Same basic composition as regular grade 501.

Modified composition, reduces tendency to hardening during welding.


Structural Steels ASTM Structural Steel (American Society for Testing Materials) American structural steels are usually made of ASTM A36 steel and come in a variety of sizes and shapes. The most commonly used shapes are standard angles, standard beams, wide-flange beams or columns, and standard channels.

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Standard Angles

Standard angles consist of two legs at right angles (90°) to each other. The symbol used to represent an angle on drawingsis( ). The standard callout for a drawing is to state the symbol, the long leg, the short leg, the thickness, and the length. An example would be: 3 x 2 x 3/16x 6’-0”. Even when both legs are equal, 2 x 2 x 3/16, the length of each leg is stated.


Standard Beams Standard beams (S beams) are commonly referred to as “I” beams because they resemble the capital letter “I”. A capitol “I” is used to represent a standard beam on drawings. The standard callout for a drawing is to state the depth, the symbol, the weight per foot and the length. An example would be: 8 I 18.4 x 12’.

Wide Flange Beams Wide flange beams are basically the same as Standard “I” Beams, but with wider flanges. The symbol used torepresent the wide flange beam is . Standard calloutfor a drawing is to state the depth, the symbol, the weight per foot, and the length. An example would be: 10 45.0 x 10’.

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Standard Channels Standard channels are commonly referred to as “C” channel or even “channel iron”. The standard callout for a drawing or bill of material is to state the symbol, the depth, the weight per foot, and the length. An example would be: C 6 x 13.0 x 24”.

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Common Alloys And Their Affect On Steel

Alloying elements are added to steels for many different reasons. Some of the more important are to: increase hardenability improve strength at ordinary temperatures improve mechanical properties and reduce distortion and cracking during quenching improve toughness at minimum hardness or strength increase corrosion resistance improve magnetic properties

The following is a list of the more common alloying elements and their effect on steel:


NICKEL - Nickel is one of the oldest, most fundamental of the steel alloying elements. It contributes to strength, ductility, toughness, and corrosion resistance, especially at low temperatures. Nickel-alloyed steels have a wider range of thermal treatment temperatures and are not prone to distortion and cracking during quenching. It is generally easier to heat treat nickel-alloy steels.

CHROMIUM - Chromium is a less expensive alloying element than nickel. This element forms a very stable, hard, wear resistant carbide in the steel that is useful for elevated temperature applications. It increases hardenability. Steels containing between 11.5% and 27% chromium are noted for their corrosion resistance and are called stainless steels.

NICKEL-CHROMIUM - In the approx. ratio of 2.5 parts nickel to 1 part chromium, this combination imparts the increased toughness and ductility of the nickel to the hardenability and wear resistance of the chromium. The combined effect on hardenability of the two together is greater than either of the elements used separately. Good for case-hardening.

MANGANESE - Manganese is one of the least expensive alloying elements and the steel is not classed as an alloy until in excess of 0.8%. Manganese contributes significantly to strength and hardness, but to a lesser degree than carbon. It enables the steel to be hot-worked with a reduced tendency to crack..

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MOLYBDENUM - An expensive alloying element that has a strong effect on hardenability and, like chromium, increases the high-temperature hardness and strength of steels. It is second only to manganese in its ability to improve hardness. It is often used in combinations with nickel or chromium or both.

TUNGSTEN - Tungsten has a strong effect on hardenability (like molybdenum), but requires larger quantities. Tungsten at 2 to 3% is equivalent to 1% molybdenum. It retards softening during tempering. It is not normally used in engineering steels because of its costs.

VANADIUM - Vanadium is the most expensive of the common alloying elements. It has a marked effect on hardenability, yielding high mechanical properties, and also inhibits grain growth during heat treatment.

BORON – Boron is a non-metallic element that is used to increase the depth to which steel will harden when quenched. Typical uses are for dredges, crankshafts, and machinery parts

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SILICON - Silicon is good for increasing strength, toughness, and shock resistance. Combined with manganese, it produces a steel with unusually high strength with good ductility and toughness. It is sometimes used in structural applications requiring a high yield point. It is widely used for coil and leaf springs, and also for chisels and punches.

It is important to be familiar with the effect of various alloying elements on the physical properties of steel. The above list shows the effects that the addition of various elements will have on standard steel. For instance, it shows that molybdenum improves:

tensile strength; toughness; quenching (water, oil and air).

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ELEMENT

EFFECT

CARBON

CHROMIUM

MANGANESE

MOLYBDENUM

NICKEL

SILICON

TUNGSTEN

Improves tensile strength

X

X

X

X

X

Improves hardness

X

X

Increases resistance to wear

X

X

X

X

X

Improves water quenching

X

X

X

X

X

Increases ductility

X

Improves resistance to formation of rust

X

X

Improves resistance to abrasion

X

X


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ELEMENT

EFFECT

CARBON

CHROMIUM

MANGANESE

MOLYBDENUM

NICKEL

SILICON

TUNGSTEN

Improves tenaciousness

X

X

X

Improves resistance to shocks

X

X

Reduces ductility

X

X

Improves resistance to deformation

X

X

Improves oil quenching

X

X

X

X

Improves air quenching

X

X

Gives tenaciousness to castings

X

Facilitates lamination and forging

X

X


AFNOR Metal Classification Carbon Content

Cast Iron: 3.0% to 6.5% Steels: Low Carbon - 0.05% to 0.2%

Medium Carbon - 0.2% to 0.5%High Carbon - 0.5% to 1.7%

Definitions Tensile Strength - The maximum amount of load a material can withstand before rupture.

( Measured in daN / mm² ) % of Elongation - The amount of permanent stretch at rupture. Elastic Limit - The amount of force a material can withstand before permanent deformation.

( Measured in daN / mm² )

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1st Melt Cast Iron Mottled Pig - used for ballast, man hole covers, anchors, etc. 2nd Melt Cast Iron Common Examples:

FT 20 FT - Gray Cast Iron (Fonte)20 - Tensile Strength in daN / mm²

MB 40 - 10

MB - Malleable White Heart (Malleable Blanc)40 - Tensile strength in daN / mm²

MN 35 - 10

MN - Malleable Black Heart (Malleable Noir)35 - Tensile strength in daN / mm²10 - % of elongation at rupture

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MP 60 - 3MP - Malleable Pearlitic60 - Tensile strength in daN / mm²3 - % of elongation at rupture

FGS 70 - 2FGS - Fonte Graphitic Spheroidal70 - Tensile strength in daN / mm²2 - % of elongation at rupture

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A - Steel and E - Steel

Plain Carbon Non Alloyed Non Heat Treatable Low Quality Common Examples:

A 33 - 2A - A Steel (Machining steel)33 - Tensile strength in daN / mm²2 - Quality index

E 26 - 3

E - E Steel (Structural steel)26 - Elastic Limit in daN / mm²3 - Quality index

Additional Notes -- The first set of numbers for A and E steels have different designations.-- A Steel - usually comes in flat bar and round bar.-- E Steel - usually comes in structural steel; channel, angle iron, etc.

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CC Steel and XC Steel

Plain Carbon Non Alloyed Heat Treatable High Quality Common Examples:

CC 20 TSCC - CC Steel20 - Carbon content of 0.2% (Divide by 100)TS - Slightly Tempered (Special Treatment)

XC 38XC - XC Steel38 - Carbon content of 0.38% (Divide by 100)

Additional Notes -- CC Steel is a slightly lower quality steel than an XC Steel-- Special Treatment Designations for A,E,CC,and XC steels:

S - Weldable (Soudure) M - Castable (Mouldable) TS - Slightly Tempered

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Slightly Alloyed Steel

Slightly Alloyed Heat Treatable High Quality Common Example:

35 NCD 1635 - Carbon content of 0.35% (Divide by 100)N - NickelC - ChromiumD - Molybdenum16 - 4% of Nickel (Divide by 4)

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Additional Notes -- Slightly Alloyed steels will not have any major alloying elements that exceed 5%.-- To find the % of the alloying element, if the element is one of the following, then divide it by 4:

C - Chromium K - Cobalt M - ManganeseN - Nickel S - Silicon

-- All other elements will be divided by 10.-- If the percentage of the element is not listed, then the element is less than 1%.

Alloying Elements

Fe - Iron A - Aluminum N - NickelE - Tin C - Chromium Z - ZincD - Molybdenum T - Titanium M - ManganeseS - Silicon W - Tungsten U - CopperK - Cobalt Pb - Lead P - hosphorous

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Heavily Alloyed Steels

Heavily Alloyed Heat Treatable High Quality Common Example:

Z6 CN 18 09

Z - Z Steel6 - Carbon content of 0.06% (Divide by 100)C - ChromiumN - Nickel18 - 18% Chromium09 - 9% Nickel

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Additional Notes -- Heavily Alloyed steels have at least one major alloying element that exceeds 5%.

-- The % of an alloying element for a “Z - Steel” should be read directly, do not divide by anything.

-- If a “0” is present before a number for % of an alloying element, the “0” should be dropped and the number read directly. (Use example above)

-- If the % of an alloying element is not shown, then the element will be less than or equal to 1%.

-- If the steel has 11% or more Chromium then it is considered to be Stainless Steel.

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Aluminum The metal aluminum is refined from is a clay-like mineral called bauxite. Through electrolysis, the ore is reduced to the base metal. This process depends on large quantities of electricity and also, a large supply of bauxite. The ore is abundant in many parts of the world. Aluminum’s importance lies in its weight/strength ratio. Weight for weight, aluminum is exceeded in tensile strength only by high quality cast steel. Its density is only 2.7 kgs./dm3 compared 7.8 for steel (or 166 lbs./ft3 vs. 490 lbs./ ft3). For this reason, it is a popular choice for aircraft and also automobiles.

Aluminum, which is a very malleable and ductile metal, is fairly weak in its pure form. When it is alloyed with other metals, it finds its widest uses. The addition of small amounts of other metals converts this soft, weak metal into a hard, strong metal with a wide range of applications.

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The following list shows some of the attributes of aluminum:

it can be rolled into thin sheets – foil drawn into thin wire machined stamped because it easily melts, it can be cast a fine finish can be obtained by burnishing and polishing it is a good electrical conductor its high resistance to corrosion make it a good choice for cooking pans in powdered form, it is a base for aluminum paint it is non-magnetic and it is non-sparking when exposed to air, it forms a microscopic oxide coating on the surface and seals the metal against the

environment

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Pure Aluminum( A + 1 digit ) Examples

A9 ------- 99.9% PureA8 ------- 99.8% “A5 ------- 99.5% “A4 ------- 99.0% “A2 ------- Crude Aluminum

08 - MetallurgyAluminum Alloys Example:

A G5 S03 M03 UA - Basic element (Aluminum)

G - Magnesium5 - 5% MagnesiumS - Silicon03 - 0.3% SiliconM - Manganese03 - 0.3% ManganeseU - Copper


Copper Copper (Cu) is a reddish‑brown, soft, malleable and ductile metal which is used extensively in industry. It can be cast, forged, rolled and drawn into wire forms. It resists well to corrosion and can easily be welded or soldered with tin. However, since it is a soft metal, it is hard to machine because it tends to crush; this is why it is important to use well honed cutting tools. Its major characteristics are electrical and thermal conductivity. Copper is used in the manufacturing of electric wire and plumbing pipes. The two main alloys of copper are:

‑ brass;‑ bronze.

Brass Brass is an alloy of copper and zinc, where the copper content can vary between 55% and nearly 100%. Its main characteristics are a good resistance to stress and corrosion, and high ductility. Brass offers good malleability and is easy to machine. All these characteristics make brass suitable for electrical accessories, gas or water conduits, tanks, tubular assemblies in radiators and rivets.

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Bronze Bronze was initially an alloy of copper and tin. Eventually, this two‑element alloy fell into disuse. Today, bronze alloys contain other elements. Additional Notes for Aluminum and Copper -- The number for % of an alloying element should be read directly.-- If a “0” is present before a number for % of an alloying element, a decimal point should be added between the

zero and the number. (Use example above)-- If a number is not given for % of an alloying element, then the element will be less than 0.1%.

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Steel Cross-Reference

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AFNOR AMERICAN TYPE XC 18

1020 1018 Mild Steel

XC 38

1040 1144 1045 Medium carbon Steel

35 NCD 16 35 NCD 6

4340 Slightly Alloyed

Ft 20

Gray Cast

Cast Iron

A 33

1020 Mild Steel

E 24

1020 Mild Steel

100 C 6

52100 Slightly Alloyed Ball Bearing

XC 100 Y 390

10100 Drill Rod


Note: When cross-referencing steels from AFNOR to American, you must remember that the exact steel may not be available; therefore, you must select the American steel that is most suitable for the job.

Bronze Cross-Reference

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UE4 Z4 PB7 UE7 Z4 PB4

SAE 660

Bushings


Heat treatment

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What Is Heat Treatment and Why

The objective of heat treating is to improve the mechanical properties of an alloy by heating and then cooling it. Some of these properties that we could be interested in changing are: hardness, wear resistance, tensile strength, elasticity, and toughness.

This application is usually not carried out on pure metals, but only on alloys (i.e. steel is an alloy of iron and carbon). Heat treatments modify the structure of an alloy, without changing the chemical composition.

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Various Heat treatments for Steels At times, carbon steels require treatments when certain properties are needed; these treatments are hardening, tempering, case hardening and annealing. Hardening Hardening involves heating the part to a given temperature and quenching (cooling); it hardens the alloy so that it can be used for tools (file, saw, chisel, scriber., etc.). Only those steels containing between 0.30% and 0.80% of carbon can successfully be heat treated. ‑ The heating to a specified temperature can be done with a blow torch (for very small parts), or in an oven. ‑ The cooling can be done in water, oil or air, depending on the type of steel being quenched and the use to which the steel will be put.Hardening improves certain mechanical characteristics:

It increases: the elastic limit resistance to rupture

hardnessIt decreases: the stretching percent

Resilience

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Case hardening Case hardening involves incorporating carbon into the surface of mechanical parts made from mild steel. After this, tempering is carried out, in order to obtain a high degree of superficial hardness while keeping a resilient central area. With the use of surface heating it is possible to case harden carbon and alloy steels.

Tempering This involves a thermal cycle after hardening, which includes:‑ reheating at a predetermined temperature, but below the hardening temperature;- a subsequent cooling in a liquid or with air. Tempering aims at diminishing the brittleness and fragility consequent to hardening, while maintaining the hardness that was obtained, and to release some of the internal stress.

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Color of tempering

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COLOR TEMPERATURE (C)

END USE

Pale yellow

221

Lathe and shaping tools

Light straw yellow

232

Cutters, drill bits, boring tools

Dark straw yellow

243

Taps and dies

Brown

254

Chisels and chopper blades

Purple brown

266

Axe blades and wood chisels

Purple

277

Mortising chisels and centering punches

Blue

293

Ratchet screwdrivers

Dark blue

316

Wood saws


Tempering changes certain mechanical characteristics:

It decreases: the elastic limit slightlyresistance to rupture slightlyhardness slightly

It increases: the stretching percent slightlyresilience slightly

Annealing

Annealing is a heat treatment which consists of heating the parts to a temperature which is higher than the upper transformation zone or to at least a temperature which is equal that of the hardening followed by a very slow cooling. Annealing is carried out for a number of reasons:

It increases: the stretching percent significantlythe resilience significantly

It decreases: the elastic limit significantly

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Hardness Testing

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Hardness and Hardness testing

The hardness of a piece of metal is defined as its resistance to penetration by a harder body.Consider two blocks of metal: one of aluminum – the other of steel. The one that is easier to file is the aluminum block. So, certain metals are more difficult to machine than others because they are harder Why would we want to know or test the hardness of a metal?

The resistance to wear by friction The quality of machinability The homogeneity of the part (is it the same throughout?) The effectiveness of the heat treatments An approx. indication of the breaking load (for steel only)

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Brinell testing (Symbol HB) Description of the machine

penetrater = 10 hardened & tempered steel ball load = 3,000 daN (6,743 lbs.)

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Operation:

The test part (a flat surface) is brought into contact with the ball penetrater The load is released The ball is driven into the test part and then stabilizes The load is removed The part now bears a spherical imprint This imprint is then measured (with a shop microscope) The imprint diameter is then converted to surface area in mm2

The surface area and load are entered into the following formula

With different materials, the diameter of the imprint varies, depending on the hardness of the part. The unit of the Brinell number is N/mm2.

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Advantages and disadvantages of the Brinell test/tester Advantages:

Simple sturdy machine tests can be carried out rapidly and accurately (on thin parts, thin metal sheets)

Disadvantages:

Cannot ball test: metal which is too soft, case hardened metals that are harder than the ball penetrater The hardness is a calculated number (rather than a direct reading)

Comments:

In certain cases, tests may be carried out using different loads and balls of diameter 5, 2.5, and 1 mm

There do exist tables which indicate the hardness, once you know the imprint diameter

.There are also mechanical characteristic tables which use the kilogram as the unit of force

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The Rockwell Method (Symbol HR)

Description of the machine

penetrater = 1.59 mm (or 1/16”) ball – b scale for softer materials = 120° diamond cone – c scale for harder materials

effective load = 150 daN (337 lbs.) for the cone= 100 daN (225 lbs.) generally used for the ball

Legend:1. scale is graduated in microns (1/1000 of a

mm)2. adjustable balance weight3. adjustable load4. ball or diamond cone5. adjustable anvil

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The Vickers Method (Symbol HV) Description of the machine

the penetrater is brought into contact with the part the load is applied progressively until a pre-selected value is reached, in order to obtain a diagonal of ≥

0.4 mm scale of values: 10 to 1200 N (this load is indicated in the symbol for the test Eg. : HV 300 The hardness may be calculated with the same formula as the Brinell test penetrater = a right pyramid with a square base and an apex angle of 136° (diamond)

Advantages:

Suitable for all metals Particularly: thin parts, case hardened parts, nitrided parts Can also be used on non-metals – plastics

08 - Metallurgy


Summary of the Various Tests

08 - Metallurgy

Summary of the Various Tests


08 - Metallurgy


08 - Metallurgy




08 - Metallurgy

End of Chapter Eight

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08 - Metallurgy

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08 - Metallurgy