3. Classification Of Alloys 6g354q

Classification of Alloys Alloys are classified further as follows: 1) Based on metallurgical structure 1. Single phase alloys 2. Two phase alloys 2) Based on the presence or absence of iron 1. Ferrous Alloys 2. Non Ferrous Alloys 3) Based on principle metals in alloy 1. Alloys of Mg 2. Alloys of Lead 3. Alloys of Nickel etc. 4) Based on method of fabrication 1. Wrought alloys 2. Casting alloys  Ferrous Alloys 1) Alloys which contain iron as the major component and it is mixed with some other metals or non metal then it is called as ferrous alloys. 2) Iron along with carbon form alloys with other metals like nickel, chromium or both 3) Based on the composition ferrous alloys are either. 1. Three components (Fe, C, Ni) 2. Four components (Fe, C, Cr, Ni) 4) Ferrous alloys containing iron and carbon are known as carbon steels. The carbon steels are named based on the percentage of carbon present in them.    Plain Carbon Steels 1) Earlier we studied all about ferrous alloys. But iron mostly forms alloys by mixing with carbon and these are known as plain carbon steels 2) In these alloys the percentage of carbon ranges from 0.008 to 2 % Classification of Plain Carbon Steel. The plain carbon steels are further classified on the basis of percentage of carbon present in them.

Steel Hypereutectoid steel/ Very Hard Steel (0.5 to 2% Hypo eutectoid Steel (0.008 toPlain 0.8%Carbon carbon)

Low Carbon Mild Carbon High Carbon/Hard Steel) Steel (0.008 – 0.2% Carbon) Steel (0.2 – 0.5% Carbon) 0.5 – 0.8% Carbon)

Drawbacks of Plain Carbon Steels 1) If the percentage of carbon is increased in plain carbon steels, it increased the brittleness of the alloy 2) Heat treatment on plain carbon steels only shows hardening on the surface but the inner layers of the alloy remain soft 3) Higher temperatures affect the mechanical properties of plain carbon steels. Thus there is a restriction on the range of temperature within which this alloy can be used 4) Plain carbon steels possess very low corrosion resistance which further reduce their further scope of use in only industry 5) Thus the above mentioned drawbacks make the plain carbon steel unfit for engineering purpose and thus there is no use of bringing further modification in properties of plain carbon steels to bring them in to use    Stainless Steel (Corrosion Resistant Steels) 1) These steels do not get corroded when exposed to atmosphere or to chemicals 2) Their composition is chromium, nickel and molybdenum 3) Chromium to import corrosion resistance to steel forms its oxide film on the surface. The property of this formed oxide film is that it gets healed by itself even if it is broken. 4) There are two types of corrosion resistant steels based on the percentage of carbon and chromium present in them. a) Heat treatable stainless steel Contain Chromium = Less than 18% [12-16%] Carbon = 1.2%

Properties 1) They are magnetic and tough 2) They can be molded easily Uses In surgical instruments, cutlery, blades etc.    Heat Resistant Alloy Steels 1) These are the steels which are used to sustain high temperatures during any industrial operation 2) The heat resistance of these alloys are improved by adding specific metals in appropriate proportion 3) Following metals are added in stainless steel to make them heat resisting 1. Molybdenum: - 3.5% addition of this metal improves heat resistance of steel 2. Chromium: - More than 12% addition of this metal imports high grade heat resistance to steel. Such steel is called as ‘Nichromes’. Uses of Heat Resistant Steels For manufacture of equipments that face high temperatures i.e. Gas turbines, parts of boilers, annealing boxes etc. b) Non heat treatable stainless steel 1) These steels generally lose their strength as temperature increases, but their corrosion resistance increases with temperature 2) Depending upon percentage of carbon and chromium, these steels are categorized as, 1. Magnetic Chromium = 12 – 22% Carbon = Less than 0.35% Properties 1) They can be machined, cold drawn or forged 2) They have good corrosion resistance Uses They are used in making parts for automobiles, chemical equipments etc. 2. Non magnetic Chromium = 18 – 26% Carbon = Upto 1.5% Nickel = 8 to 21%

Properties 1) Total percentage of chromium and nickel is approximately 23% 2) High corrosion resistance 3) Steels with 18% chromium + 8% nickel are very common, known as “18/8 stainless steels 4) Addition of little molybdenum increases their corrosion resistance further Uses To make dental, surgical instruments, decorative articles etc.    Special Effects of Alloying Elements on Alloy Steels 1) Various elements have been added up to the plain carbon steels. It is then observed that every element affected the properties of plain carbon steel differently 2) Most commonly added elements are p and d-block elements like aluminium boron, chromium, cobalt, copper, lead, manganese, nickel etc. 3) The special effects of addition of these elements to the alloy steels is as follows Sr. No. 1.

Element

Special Effects

Nickel

2.

Chromium

3.

Cobalt

Enhances ductility, toughness, resistance to heat and corrosion, elasticity, tensile strength etc Added up to 18% Enhances harden ability, corrosion and oxidation resistance increases high – temperature strength. In high carbon steels, it increases abrasion resistance and toughness Contributes to hardness of steel

4.

Manganese

5.

Molybdenum

6.

Tungsten

Improve certain properties with respective range of properties: e.g. 1 – 1.5% = Steel gains toughness plus brittleness, also improves strength. If high percentage i.e. 11 to 14% = Steel gains high degree of hardness Enhances 1) Resistance to softening in tempering 2) Tensile and creep strengths at high temperatures 3) Harden ability 4) Corrosion resistance of stainless steel especially in chloride environment 5) In austenite the grain coarsening temperature 6) Resistance to embrittlement during tempering It helps to form hard and abrasion resisting carbide film in tool steels. Increases shock resistance Imparts high temperature hardness in tempered steels

It enhances creep strengths in some high temperature steels

7.

Vanadium

Increases harden ability, tensile strength, shock resistance, ductility

   Non Ferrous Alloys

Non Ferrous Alloys

Alloys of Aluminium

Alloys of Copper

Alloys of Lead Solders

Wrought Alloys

Casting Alloys

Brass

Bronze

Tinmann’s Solder

1) Ferrous alloy are widely used in various industrial works because of their various properties. However they posses some limitations which are: 1. They are relatively heavier in weight 2. They possess low electrical conductivity 3. They show low corrosion resistance in some environments 2) Thus for some purpose it is necessary to make use of alloys which do not contain iron and these are known as “non ferrous alloys”. 3) Since these alloys do not involve iron as a major component so generally metals like copper, lead, aluminium etc are added in them. Alloys of Aluminium

Soft Solde Wood’s me

Alloys of aluminium 1) These alloys contain higher percentage with other metals like copper, manganese, magnesium etc 2) Two of its alloys which are widely used are 1. Duralumin 2. Magnalumin 3) The composition, properties and uses of these two alloys of aluminium are as follows: Elements a) Duralumin Aluminium = 95% Copper = 4% Manganese = 0.5% Magnesium = 0.5%

Properties It is light weight, tough, highly ductile, easily constable, good conductor of heat and electricity and corrosion resistance It can easily be worked as it possesses high machinability. Its tensile strength can be raised by heat treatment up to 2000 kg- cm2 without affecting its ductility. It approaches steel in strength and yet its density is one third that of steel.

Uses Due to high resistance with low density, it finds extensive use in aircraft industry in the form of a ‘clad’ It is also used in making surgical instruments, cables, fluorescent tube caps etc. It is also used in making automobile and locomotive parts because of its high ductility and good electrical conductivity.

b) Magnalumin Aluminium=70-90%

It is strong and tough and lighter than aluminium It possesses mechanical properties similar to brass

It is used for making scientific instruments, balances airplane parts etc.

Magnesium=30-10% Alloys of Copper: - Brasses and Bronzes

Alloys of Copper 1) These are the alloys in which percentage of copper is found to be higher. 2) There are two types

1. Brasses and 2. Bronzes

3) Brasses are the alloys of copper and zinc while bronzes are the alloys of copper and tin Comparison of Brasses and Bronzes Brasses

Bronzes

1) These are the alloys of copper along with zinc, known as “common brasses”

1) These are the alloys of copper with tin

2) They may contain some amount of tin apart from copper and zinc known as “Special Brasses”

2) They may contain little amount of phosphorus/aluminium/iron known as Special Bronzes

3) Main brasses are 1. Commercial Brass 2. Dutch Metal 3. Catridge Brass

3) Main Bronzes are 1. Coinage / common bronze 2. Gun Metal 3. High Phosphorus Bronze

4) Special Brasses are 1. German Silver 2. irality Brass

4) Special Bronzes are 1. Nickel Bronze 2. Aluminium Bronze

5) Amount of copper ranges between 25 to 90% in different brasses

5) Amount of copper ranges from 80 to 95% in different bronzes

Alloys of Copper – Bronzes Name of Alloy Composition a) Commercial Brass Copper – 90% Zinc – 10%

Properties Golden in colour, harder and stronger than copper

b) German Silver

Possess good strength, high corrosion resistance to electrolyte

Copper – 25 – 50% Zinc = 10 – 35% Tin = 5 – 35%

Uses Architecture metal works, imitation jewellary, hardwares, screws, rivets etc Decorative articles, utensils, table wares, ornaments, cutlery etc

Alloys of Copper – Bronzes Name of Alloy a) Gun Metal

Composition Copper = 85% Zinc = 4% Tin = 8% Lead = 3%

Properties Highly strong, can resist explosion, hard, tough

Uses For hydraulic fittings, high pressure steam plants marine pumps, water filings etc

b) High Phosphorus Bronze

Tin = 10 – 13% Lead = 0.4 – 1% Copper = Rest %

Good strength and resistance to corrosion under sea water, castable, can be rolled or drawn into wires. Abrasion resistant, hard, brittle, law coefficient of friction

For springs, turbine blades, pumps, boiler, fittings, bearing plates, spindle for valves

Alloys of Lead

Alloys of Lead These alloys are commonly known as solder and they are as follows Name of Alloy 1) Woods metal

Composition Bismuth = 50% Lead = 25% Tin = 12.5% Cium = 12.5%

2) Tinmann’s Solder

Lead = 34% Tin = 66%

Properties Melting point 65.50c Density 9.7 gms/cu.cm stable. Incompatible with acids, oxidizing agents, interhalogen compounds Low melting alloys

Uses Wood’s metal is useful as a law – melting solder, law temperature casting metal, as filler when bending thin walled tubes. Use for ing articles and tinning