Transcript Introduction to Technical Mathematics
08 - Metallurgy
08 – Metallurgy Presentation : IMS – Tech Managers Conference Author : IMS Staff Author : IMS Staff Creation date : 14 Dec.2012
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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.
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The 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)
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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.
ASTM
Gray
SAE Class 20 Class 25 Class 30 Class 40
White
ASTM SAE 20-50
Malleable
ASTM SAE A197 32510 A220 35018 40010 45006
Nodular (Ductile)
ASTM SAE A395 A356 72 80-55 06 60-40 18 100-70 03 120-90 02 Class 50 Class 60 50005 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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Type
Mild steel or Low Carbon Steel Machinery Steel or Medium Carbon Steel
Carbon content
0.05 % to 0.20 % 0.20 % to 0.50 % Tool Steel or High Carbon Steel Classification in function of carbon content 0.50 % to 2.00 % 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
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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 Standard carbon steel Machining steel (screw steel) Machining steel, with manganese HIGH MANGANESE CONTENT STEEL NICKEL STEELS 0.50 % nickel 1.50 % nickel 3.50 % nickel 5.00 % nickel NICKEL-CHROMIUM STEELS 1.25 % nickel, 0.60% chromium 1.75 % nickel, 1.00% chromium 3.50 % nickel, 1.50% chromium 3.00 % nickel, 0.80% chromium Corrosion and heat resistant steels 1xxx 10xx 11xx X13xx T13xx 2xxx 20xx 21xx 23xx 25xx 3xxx 31xx 32xx 33xx 34xx 30xxx
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SAE STEEL CLASSIFICATION STANDARDS
MOLYBDENUM STEELS Chromium Chromium-nickel Nickel 4xxx 41xx 43xx 46xx et 48xx CHROMIUM STEELS Low chromium content Medium chromium content CHROMIUM-VANADIUM STEELS TUNGSTEN STEELS TRIPLE-ALLOY STEELS SILICON-MANGANESE STEELS 5xxx 51xx 52xxx 6xxx 7xxx et 7xxxx 8xxx 9xxx
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Classification of steels Example of this standard: Steel 51100 5 = chromium steel 1 = 1% chromium 100 = 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) process D = 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 steel 100 = 1% carbon 4340 (Good steel for shafting) 43 = Nickel-Chromium-Molybdenum steel 40 = 0.4% 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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A.I.S.I. Grade
Grade 302
Characteristics
Excellent resistance to corrosion
Uses
An all-purpose grade for food, dairy and chemical products, and for architectural fittings.
Grade 304 Grade 321 Grade 347 Grade 316 Grade 303 Carbon content 0.8% max.
For applications similar to those of grade 302, but with improved corrosion resistance on welded surfaces.
Resistance to corrosion is similar overall to that of grades 302 and 304 stabilizing additives protect it against corrosion on heated surfaces.
For high-temperature use, 800 to 1600 o F, and under harsh corrosion conditions where welded assemblies cannot be post annealed.
Exceptional resistance to corrosion. Improved resistance to creep.
Harsh corrosive conditions, particularly those including etching compounds.
Less scratching and jamming. Greatly improved machining.
Gears, valves, bolts, screws and other machined products.
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A.I.S.I. Grade
Grade 309
Characteristics Uses
Exceptional resistance to stress at high temperatures.
For operating temperatures up to 1900 o F.
Grade 310 Grade 430 Grade 446 Grade 410 Superior resistance to oxidation.
Good resistance to corrosion.
Poor stretching or stamping; not recommended for deep embossing. Excellent resistance to flaking.
Martensitic steel strengthened by quenching and tempering, and by conventional quench hardening.
For very high operating temperatures.
Automotive parts and interior architectural fittings; some specific chemical applications.
Used mainly for temperatures up to 2000 o F, fixed parts which are not subjected to high stress.
Mechanical gear parts, such as pump rods and valves.
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A.I.S.I. Grade
Grade 403 Grade 405
Characteristics
Same basic composition as grade 410 Same basic composition as grade 410
Uses
Modified composition suitable for turbine blades and other similar applications.
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.
Grade 502 Same basic composition as regular grade 501.
Used by the petroleum industry because of its strength and its resistance to corrosion and oxidation at moderately-high temperatures.
Modified composition, reduces tendency to hardening during welding.
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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.
Standard Angles
Standard angles consist of two legs at right angles (90 ° ) to each other. The symbol used to represent an angle on drawings is( ). 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.
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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 to represent the wide flange beam is . Standard callout for 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”.
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:
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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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EFFECT Improves tensile strength Improves hardness Increases resistance to wear Improves water quenching Increases ductility Improves resistance to formation of rust Improves resistance to abrasion X X X X ELEMENT C A R B O N C H R O M I U M M A N G A N E S E M O L Y B D E N U M N I C K E L X X X S I L I C O N X X X X X X X X X X X T U N G S T E N X X X X
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EFFECT Improves tenaciousness Improves resistance to shocks Reduces ductility Improves resistance to deformation Improves oil quenching Improves air quenching Gives tenaciousness to castings Facilitates lamination and forging ELEMENT C A R B O N C H R O M I U M M A N G A N E S E M O L Y B D E N U M N I C K E L S I L I C O N T U N G S T E N X X X X X X X X X X X X X X X X X X
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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 / mm² 10 - % of elongation at rupture
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MP 60 - 3 MP - Malleable Pearlitic 60 - Tensile strength in daN / mm² 3 - % of elongation at rupture FGS 70 - 2 FGS - Fonte Graphitic Spheroidal 70 - Tensile strength in daN / mm² 2 - % 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 - 2 A - A Steel (Machining steel) 33 - Tensile strength in daN / mm² 2 - Quality index E 26 - 3 E - E Steel (Structural steel) 26 - Elastic Limit in daN / mm² 3 - 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 TS CC - CC Steel 20 - Carbon content of 0.2% (Divide by 100) TS - Slightly Tempered (Special Treatment) XC 38 XC - XC Steel 38 - 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
Common Example:
35 NCD 16 35 - Carbon content of 0.35% (Divide by 100) N - Nickel C - Chromium D - Molybdenum 16 - 4% of Nickel (Divide by 4) High Quality
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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 N - Nickel K - Cobalt 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%.
M - Manganese
Alloying Elements
Fe - Iron E - Tin D - Molybdenum S - Silicon K - Cobalt A - Aluminum C - Chromium T - Titanium W - Tungsten Pb - Lead N - Nickel Z - Zinc M - Manganese U - Copper P - hosphorous
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Heavily Alloyed Steels
Heavily Alloyed Heat Treatable
Common Example:
Z6 CN 18 09 Z - Z Steel 6 - Carbon content of 0.06% (Divide by 100) C - Chromium N - Nickel 18 - 18% Chromium 09 - 9% Nickel High Quality
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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./dm 3 compared 7.8 for steel (or 166 lbs./ft 3 vs. 490 lbs./ ft 3 ). 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% Pure A8 ------ 99.8% “ A5 ------ 99.5% “ A4 ------ 99.0% “ A2 ------- Crude Aluminum
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Aluminum Alloys
Example:
A G5 S03 M03 U A - Basic element (Aluminum) G - Magnesium 5 - 5% Magnesium S - Silicon 03 - 0.3% Silicon M - Manganese 03 - 0.3% Manganese U - Copper
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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
AFNOR
XC 18 XC 38 35 NCD 16 35 NCD 6 Ft 20 A 33 E 24 100 C 6 XC 100 Y 390
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1020
AMERICAN
1018 1040 1144 1045 4340 Gray Cast 1020 1020 52100 10100 Mild Steel
TYPE
Medium carbon Steel Slightly Alloyed Cast Iron Mild Steel Mild Steel Slightly Alloyed Ball Bearing Drill Rod
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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
UE4 Z4 PB7 UE7 Z4 PB4 SAE 660 Bushings
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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
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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 It decreases: hardness 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
Pale yellow Light straw yellow Dark straw yellow Brown Purple brown Purple Blue Dark blue
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C) TEMPERATURE
221 232 243 254 266 277
END USE
Lathe and shaping tools Cutters, drill bits, boring tools Taps and dies Chisels and chopper blades Axe blades and wood chisels Mortising chisels and centering punches 293 Ratchet screwdrivers 316 Wood saws Color of tempering
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Tempering changes certain mechanical characteristics: It decreases: It increases: the elastic limit slightly resistance to rupture slightly hardness slightly the stretching percent slightly resilience 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: It decreases: the stretching percent significantly the resilience significantly 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 mm 2 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/mm 2 .
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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)
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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.
3.
4.
5.
adjustable balance weight adjustable load ball or diamond cone 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
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Summary of the Various Tests
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Summary of the Various Tests
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08 – Metallurgy Presentation : IMS – Tech Managers Conference Author : IMS Staff Author : IMS Staff Creation date : 14 Dec.2012
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End of Chapter Eight
Exit
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08 – Metallurgy Presentation : IMS – Tech Managers Conference Author : IMS Staff Author : IMS Staff Creation date : 14 Dec.2012
Creation date : 08 March 2012 Classification : D3 Classification : D3 Conservation : Page : ‹#›