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MATERIAL SCIENCE

Nov 25, 2014

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

MATERIAL SCIENCECAST IRON Is obtained by re-melting pig iron with coke and limestone in a furnace known as cupola. It is primarily an alloy of iron and carbon. The carbon content in the cast iron varies form 2.1% to 4.5%. It may be present either as free carbon [ or graphite ] or combined carbon or cementite. Cast iron is brittle material, therefore it cannot be used in those parts which are subjected to shocks. It has very good casting characteristics, high compressive strength, wear resistance and excellent machinability. The compressive strength of cast iron is much greater than tensile strength. The cast iron also contains small amount of impurities such as silicon, sulphur, manganese and phosphor. Effect of the Impurities on CI :Silicon Maybe present upto 4% in CI . It provides the formation of free graphite which makes the iron soft and machinable. Sulphur makes CI hard and brittle. It must be kept well below 1% for most foundry purposes Manganese It makes CI white and hard. It is often kept below 0.75% Phosphor It aids flexibility and fluidity in CI, but induces brittleness. It is rarely allowed to exceed 1%. The Important Types of CI 1. 2. 3. 4. 5. 6. 7. Grey CI White CI Chilled CI Molten CI Malleable CI Nodular or Spheroidal Graphite CI Alloy CI

GRAY CAST IRON This is ordinary commercial iron having 3 to 3.5% carbon

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

The grey color is due to presence of carbon in the form of free graphite IT has low tensile strength High compressive st. No ductility It can be easily machined WHITE CAST IRON This has 1.75 to 2.3% of carbon The white color is due to the presence of carbon in the form of carbide [ known as cementite] which is the hardest constituent of iron Has high tensile st. Low compressive st. CHILLED CAST IRON: Produced by quick cooling of molten iron The quick cooling is generally called chilling MOLTEN CAST IRON Is product in between grey and white CI in composition color and general properties MALLEABLE CAST IRON Obtained from white cast iron by suitable heat treatment process. [ annealing ]

Nodular or Spheroidal graphite cast iron Called ductile cast iron or high st. cast iron Obtained by adding small amount of magnesium [ 0.1 to 0.8% ] to molten grey iron just after tapping. ALLOY CAST IRON Produced by adding alloying element like nickel, chromium, molybdenum, copper and vanadium in sufficient quantities. Properties Increased strength High wear resistance Corrosion resistance Heat resistance.

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

STEELSIs an alloy of iron and carbon, with carbon content up to a maximum of 1.5% most of the steel produced now-a-days are plain carbon steel. Divided into following types based on carbon content DEAD MILD STEEL UPTO 0.15% CARBON LOW CARBON MILD STEEL 0.15 0.45% MEDIUM CARBON STEEL 0.45% TO 0.8% CARBON HIGH CARBON STEEL 0.8% TO 1.5% CARBON PLAIN CARBON STEEL [ UPTO 0.5% SILICON MANGANESE ARE CALLED PLAIN CARBON STEEL ] AND 1.5%

These steels are strong, tough, ductile and used in expensive materials. They can be cast worked, machined and heat treated to a wide range of properties. Unfortunately, plain carbon steel has poor atmospheric corrosion resistance. But it can be protected easily by painting, enameling or galvanizing. The properties of plain carbon steel depend upon the presence of carbon content. Properties Hardness and strength increases with increase in carbon content. Effect of Impurities on Steel Impurities Silicon, Sulphur, Manganese and Phosphor Silicon [ 0.05% to 0.30% ] Prevents steel from becoming porous Removes the gases and oxides Prevents Blow holes and thereby makes steel tougher and harder. Sulphur [ as iron sulphide or manganese sulphide ] Iron sulphide has low melting point Manganese sulphide does not effect much Manganese Serves as valuable deoxidizing and purifying agent in steel. When used in ordinary low carbon steel, manganese makes the metal ductile with good bending qualities.

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

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Phosphor Makes steelBrittle Cold shortness in steel In low carbon steel , raises the yield point and improves resistance to atmospheric corrosion. Alloy Steel Maybe defined as a steel to which elements other than carbon are added in sufficient amount to produce an improvement in the properties. The chief alloying elements used in steel are NICKLE [ 2 to 5%] Improves tensile strength Raises elastic limit Imparts hardness, toughness Reduces rust formation CHROMIUM Increases strength Hardness Corrosion resistance VANADIUM [ LOW AND MEDIUM CARBON STEEL ] increases yield and tensile st. TUNGSTEN Raises critical temp of steel Imparts cutting hardness Abrasion resistance properties High speed steel [ 18:4:1] 18% tungsten, 4% chromium 1% vanadium and 0.7% carbon Manganese Reduces the formation of iron sulphide by combing with sulphur. Makes steel, hard, tough and wear resistance. SILICON Increases strength and hardness of steel without lowering its ductility

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

COBALT It is added to HSS [ 1 to 12% ] Give red hardness by retention of hard carbide at high temperatures. MOLYBDENUM [ 0.15 to 0.30%] of molybdenum is used with chromium and manganese [0.5-0.8%] to make molybdenum steel. Possess extra tensile strength Used in airplane fuselage and automobile parts. Stainless Steel Properly heat treated and finished steel that which resists oxidation and corrosive attack from most corrosive media. Different Types of Steel1. MARTENSITIC STAINLESS STEEL 2. FERRITIC STAINLESS STEEL 3. AUSTENITIC STAINLESS STEEL

MARTENSITIC STAINLESS STEEL Are Chromium steel, containing Chromium 12 to 14% Carbon 0.12 to 0.35% Properties Magnetic in nature Maybe hardened by suitable heat treatment Hardness depends on Carbon content Can be easily welded and machined

FERRITIC STAINLESS STEEL Chromium 16 to 18% Carbon - about 0.12 % Properties Good Corrosion Resistance than martensitic steels

AUSTENITIC STAINLESS STEEL Chromium 18% Nickel 8%

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

Known as 18/8 steel

Properties Non magnetic Greatest Corrosion Resistance and good mechanical properties at elevated temperatures.

NON FERROUS METALS AND ALLOYS ARE THOSE WHICH CONTAIN METALS OTHER THAN IRON AS THEIR CHIEF CONSTITUENT. The non ferrous metals are usually employed in the industry due to the following characteristics 1. Ease of Fabrication, [ Casting, rolling, forging welding and machining ] 2. Resistance to corrosion 3. Electrical and thermal conductivity 4. weight They are I. Aluminium : It is a white metal prepared from bauxite. Its light in weight and has specific gravity 2.7 and melting point 660deg cel. Aluminium alloys Alloyed with other metals like copper, magnesium, manganese, silicon and nickel. Addition of these metals converts Soft metal into hard and strong metal still retaining its light weight. The main aluminum alloys are 1. Duralumin Composition Copper : 3.5 to 4.5% Manganese 0.4 to 0.79% Magnesium 0.4 to 0.70% and remaining is aluminium Possesses max.strength [ abt 400mpa] after heat treatment and age hardening. After working it is allowed to age for 3 to 4 days till it is hardened through the process of age hardening

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

2. Y-alloys Called also copper-aluminum alloy Copper 3.5 to 4.5% Manganese 1.2% to 1.7% Nickel 1.8 to 2.3% Silicon, magnesium, iron 0.6% each and Remaining is aluminum This is heat treated and age-hardened to get better strength than duralumin at high temperatures. 3. magnesium It is made by melting aluminum with 2 to 10% magnesium in a vacuum and then cooling it in a vacuum or under a pressure of 100 to 200 atmospheres. It also contains about 1.75% copper.

II. copper : Most widely used non-ferrous metals in industry. It is a soft, malleable and ductile material with a reddish brown appearance. Specific Gravity 8.9 Melting Point 1083deg Celcius It is Good conductor of Electricity Used for making useful alloys with tin, zinc, nickel and aluminum.

The main copper alloys are

Copper zinc alloys [brass] in which zinc Is the principal alloying material

Copper tin alloys [bronze] in which tin Is the principal alloying material

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

Brass:Most widely used copper-zinc alloy. This is fundamentally a binary alloy with each copper and zinc in 50% consistency. There are various types of brasses depending upon the proportion of copper and zinc. Brass is resistant to atmospheric corrosion and can be easily soldered.

Types of Brass: CARTRIDGE BRASS: Copper 70% zinc-30% Is a cold working brass used for cold rolled sheets, wire drawing, deep drawing pressing and tube manufacturing Yellow brass Copper 60% zinc 40% Suitable for hot working by rolling and extrusion and stumping Leaded brass Copper 62.5% Zinc 36% Lead 1.5% Used plates, tubes, etc Naval brass Cu 59% zinc 40%, tin 1% Used morque castings Nickel brass [ german silver] Cu 60.45% zinc 35.20% nickel 5.35% Admirality brass 70% 24% tin 1%

Used for valves, plumb fittings, automobile fittings, type writer parts and musical instruments.

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MATERIAL SCIENCE IIIE PRILIMINARY RJ

Bronze:Composition 75 to 95% copper and 5to25% tin Properties corrosion resistant, Superior to brasses Types of Bronze: Phosphor bronze Copper 87-90%

tin 9 to 10%

Phosphor 0.1 to 0.3%

High strength, superb ductility and soundness of castings Possesses good wearing qualities and high elasticity.

Silicon bronze Copper 96%

silicon 3% manganese or zinc 1%

High strength and good corrosion resistant properties Used boilers,