Basic Structures Of Ferrous Metals

Ferrous metals is mainly based on iron-carbon alloy with the combination of other alloys such as plain carbon steels, alloy, tools steels, stainless steels and cast iron. Alloys having iron with a valance of +2 are known as ferrous; those alloys which have iron with a valence of +3 are called as ferric. Ferrous metals or alloys are metals that contain the element iron in it. Depending on the end of use, metals can be simply cast into the finished part or cast into an intermediate form, such as an ingot, then worked, wrought by rolling, or processed by forging, extruding or another deformation process. All ferrous metals are magnetic. They contain a small quantity of other metals in order to give the correct properties. Manipulation of atom-to-atom relationships between iron, carbon and various alloying elements establishes the specific properties of ferrous metals. As atoms transform from one specific arrangement, or crystalline lattice, to another its gives good mechanical properties.

Pure iron: It is also called as Pure Ferrite. The carbon content is calculated. From 0 to 0.5%.It has the BCC structure when it is in room temperature. Also known as Alpha iron.

Plain Carbon Steel: Consists of iron containing small amounts of carbon. The carbon content can vary from 0.008% to approximately 2.0%.

Low- Alloy steel: Steel containing alloy additions which usually do not exceed a total about 10% are referred to allow-alloy steels

Ultra-High-Strength steel: Steel capable of developing yield strength greater than about 1104 Mpa are considered ultra-high-strength alloys.

Medium-carbon low-alloy steel: These alloys consists of grades such as 4130,4330 and 4340, which can be quenched and tempered to yield strengths on the order of 1725 Mpa

Maraging steel: This class of steel consists basically of extra-low-carbon (less than 0.3%) iron-based alloys to which a high percentage of nickel has been added.

Corrosion-Resistant (stainless) steel: Stainless steel may be divided into four categories: ferritic, martencitic, austenitic, and age-hardenable.

Ferritic stainless Steels: This group of stainless steel contains between 11.5 and 27% chromium as the only major alloying element in addition to a maximum of 0.25% carbon

Martensitic stainless steels: This type of stainless steel is also primarily chromium steel, but in contrast to the ferritic group, consists enough carbon to produce martensite by quenching 0.15 and 0.75% carbons.

Austenitic stainless steels: This Stainless Steel is alloyed to the extent that they remain austenitic at low temperatures. The principal alloying elements added to the chromium and nickel, generally totaling than 23%

Precipitation-hardening stainless steels: The last class of stainless steel we will discuss depends on precipitation hardening for the optimum development of properties. Very high strength together with corrosion resistance

Cast iron: Cast irons are iron-carbon-silicon alloys. More than 2% of carbon

Grey cast-iron: Also known as graphite cast iron. They depend on the distribution size and amount of the graphite flakes and matrix structure.

Spheroid graphite cast-iron: Also known as Ductile or nodular iron. It has high modulus of elasticity.

Austempered Ductile iron: Recent addition to cast iron family, outstanding combination of high strength, toughness, wears resistance.

Compacted cast iron: Referred as vermicular iron. Consists of 80% graphite and 20% spherodial graphite

Malleable Cast iron: Carbons present as an irregular shaped nodules of graphite. Also classified as white heart malleable cast iron. Blackheart malleable cast iron.Pearlitie malleable cast iron

Austentic carbon: They are high alloy cast iron. Mainly nickel in which carbon is present

List of advantages

• These are materials with high specific strengths when compared with weight that is high strength to weight ratio.
• High quality materials exist in abundant quantities within earth’s crust and are readily available worldwide in various certificate grades.
• It increases the speed of construction in the field of civil engineering.
• Versatility;steel suits range of construction methods & sequences.
• Modification & repair can be easily done with left effort.
• Recycling can be done easily.
• Durability of these materials are very high
• Aesthetics;steel has a broad architectural possibilities

Limitation of the material in engineering applications:

• The principal limitation of many ferrous alloys is their susceptibility to corrosion
• Costly waste as scrap
• High cost of final finishing & polishing
• Environmental issuebecause of improper disposal
• Ferrous metals get rusted easily (oxidize) unless protected eg. with oil

b) Non-ferrous metal

Non-ferrous metals are metals other than iron and they do not contain an appreciable amount of iron in them. Non-ferrous metals are aluminum, magnesium, titanium alloys, copper, zinc and miscellaneous alloys like nickel, in, lead, zinc as base metals. The precious metals silver, gold and platinum are also coming under non-ferrous group. Non ferrous metals are alloys which are non magnetic.

Non ferrous metals:

Aluminum: Abundant element of 8% on earth crust and normally found in Oxide forms (Al2O3), i.e., bauxite, kaolinite, nepheline and alunite

Aluminum – base alloys: Aluminum is used in its commercially pure state as well as in its many alloy forms. The heat –treatable types have the advantage of being relatively easy to fabricate in their soft condition, after which they are heat treated to develop their higher strengths.

Copper- base alloys: Copper is seldom industrially employed in its pure state. Copper has its most value when alloyed with other elements. It dissolves with elements such as tin, zinc, and silver in rather wide proportions.

Magnesium – base alloys: Magnesium are noted for their lightness. The specific gravity of magnesium is 0.064 lb per cu.; in comparison, aluminum, steel, and titanium are 0.09, 0.28, and 0.16 lb per cu., respectively. Magnesium alloys lend themselves to welding and filler are protected by an inert gas. They are relatively easy to cast by most foundry methods, particularly die casting.

Nickel –base alloys: Nickel is one of the oldest metals known to man. Currently this metal is almost indispensable in the alloying of steels to confer toughness, uniformity of hardness, and good workability; and as a basic alloy to resist high corrosion and high temperatures

Lead-Tin alloys: The principal lead –tin alloys consist of solders and bearing materials.

The 70% tin -30% lead solder is used mainly in the joining and coating of metals. The 63% tin-37% lead is a eutectic type solder developed primarily for making electrical joints.

Zinc-base alloys: Zinc base alloys predominate as die casting materials. These alloys have high cast ability and favorable mechanical and chemical properties. Zinc base alloys can be cast in the range 750-800 º F, and, therefore, have a low –temperature advantage over other alloys

Less common metals and alloys:

Titanium and its alloys: Because of their high strength- weight ratio, titanium and its alloys have received a great amount of attention from the aircraft and missiles industries.

Molybdenum: This element has long been known for its ability to confer the property of high temperature stability to steels.

Zirconium: Zirconium metal has a density of 0.24 lb per cu in. And a melting point of 3355ºF. The metal has fair tensile strength, depending somewhat upon its method of manufacture. It fabricates similar to titanium, and it’s eminently suited to the resistance to corrosion.

List of advantages

• Non ferrous metal do not corrode (aluminum for example)
• High thermal conductivity
• High electrical conductivity
• Non ferrous metals have relatively high density
• Nonmagnetic properties
• Higher melting points
• Resistance to chemical
• They are also specified for electrical applications
• They are comparatively low in electrical conductivity
• Non ferrous have inherent susceptibility to corrosion in some common environment
• Non ferrous metals are usually light weight but ferrous metals are heavier

Limitation of the material in engineering applications

• They are not as strong as carbon steel (ferrous metal).
• Non ferrous metals are typically not used in structural applications.
• Non ferrous metals are usually more expensive by the pound than are ferrous metals.
• Low tensile strength but excellent specific strength.
• They don’t show ductile to brittle transition in low temperature.

c) Polymers:

Compounds that are formed by the joining of smaller layers, usually repeating, units linked by covalent bonds are called polymer. A polymer is a large molecule consists of repeating structural units connected by covalent bonds. Polymer in popular used as plastic; the term polymer refers to a large category of natural and synthetic materials with a wide spectrum of properties. Natural polymers are those which come from plants and animals have been used for many centuries; these materials include wood, rubber, cotton, wool, leather, and silk. Other polymers such as proteins, enzymes, starches, and cellulose are important in biological and physiological processes in plants and animals. The backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. Polymer in popular used as plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties

Polymers: Polymers are classified into several ways, by how the molecules are synthesized, by their molecular structure, or by their chemical family.

Linear polymer – Any polymer in which molecules are in the form of spaghetti-like chains.

Thermoplastics – Linear or branched polymers in which chains of molecules are not interconnected to one another.

Thermosetting polymers – Polymers that are heavily cross-linked to produce a strong three dimensional network structure.

Elastomers – These are polymers (thermoplastics or lightly cross-linked thermo sets) that have an elastic deformation > 200%.

Polymers are classified into three main categories;

Thermoplastics:

Branched polymer – Any polymer consisting of chains that consist of a main chain and secondary chains that branch off from the main chain. Crystalline is important in polymers since it affects mechanical and optical properties. Tacticity – Describes the location in the polymer chain of atoms or atom groups in nonsymmetrical monomers.

Liquid-crystalline polymers – Exceptionally stiff polymer chains that act as rigid rods, even above their melting point.

Elastomers (Rubbers):

Geometric isomer: A molecule that has the same composition as, but a structure different from, a second molecule.

Diene: A group of monomers that contain two double-covalent bonds. These monomers are often used in producing elastomers.

Cross-linking: Attaching chains of polymers together to produce a three-dimensional network polymer.

Vulcanization: Cross-linking elastomer chains by introducing sulfur or other chemicals.

List of advantages

• Polymers are ultra durable
• Flexible
• doesn’t rust
• slow to degrade
• They can be molded into virtually any shape conceivable
• can be custom colored in the production stage
• Polymers are recyclable
• quite a good electrical insulator and has a low dielectric constant
• The biggest advantage for PP is its low cost
• It also has a flexibility in cold whether with ultraviolet stability
• can be easily repaired from mechanical damage with simple field tools

Limitation of the material in engineering applications

• In the production stage, polymers are susceptible to contamination
• The least bit of dirt or cross-contamination w/other polymers, and at best the end product is corrupt, at worst the polymers are rendered useless
• Any variances in heat and timing in the molding process and, again, the final product will be corrupt or useless.
• lower melting point
• flammability
• Elevated temperatures will make any crystalline more isotropic
• non bio-degradable
• easily breakable
• when polymers incorporated with additives are burnt they emit a lot of poisonous gases into the atmosphere
• improper disposal leads to environmental pollution
• undergo oxidation and ozonation easily

d) ceramics:

These are materials that are produced when two materials are joined together to give a combination of properties that cannot be achieved in the original state. Ceramics can be divided into two classes: advanced and traditional. Advanced ceramics consist of carbides, pure oxides, nitrides, non-silicate glasses and many others; while Traditional ceramics include clay products, silicate glass and cement. A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous.

Agglomerated materials:

Concrete: This is one of the oldest agglomerated composite materials to be used for engineering construction, and consists of a mixture aggregate and sand bonded together by the hydrated silicate the gel formed when the Portland cement “sets” with water.

Ratio of aggregate, sand and cement: A very common mix consists of 4parts aggregate, 2parts sand and 1 part cement powder.

The water-cement ratio: The water added to the concrete is used in the hydration of the cement itself, and any water in excess of the amount required for setting reactions has a weakening effect upon the concrete.

The nature of the aggregate and sand: The bond between the hydrated cement and the aggregate and sand is improved if the both the aggregate and sand are sharp-cornered rather than rounded. Strong fine-grained igneous rocks like basalt, dolerite, and quantize are commonly used for concrete aggregate, the size of which varies with the size of the job.

Mixing and laying: Under-or over-mixing gives a poor concrete, and the method of lying is of the utmost importance. Concrete vibrated into place is always stronger than concrete poured and hand-screwed

Curing time: The hardening of cement occurs over a considerable length of time and it is important to prevent the evaporation of moisture .during the initial stages. Concrete is often covered with wet sand or bags for seven days to prevent the evaporation of moisture, and concrete cured under water after taking its initial set achieves its maximum strength.

Asphalt paving: This is composite in which rock aggregate is bounded by viscous asphalt: it is used extensively for road surfacing. The material is not as rigid as concrete, this being an advantage for road construction.

Cermets: These are agglomerates that consist of combinations of metal and ceramics, the metal acting as the binder. Cermets are made using the techniques of powder metallurgy, the sintering temperature usually being above the melting point of the metal powder.

Laminates: Many different types of laminated materials are made of different applications, the mild-steel-stainless combination being a good example of a modern metal-to-metal laminate.

Plywood: This is made by bonding together an odd number of sheets of wood veneer so that the grain directions of alternate sheets are perpendicular to each other.

Laminated plastic sheet: This is usually made from sheet of paper or cloth and a suitable thermosetting resin. The paper or cloth passes or cloth passes through a tank containing the resin solution, between rollers that squeeze out the excess resin, and then through a drying oven in which excess solvents are removed and the resin is partially cured.

Reinforced Materials: It forms the biggest and most important group of composite materials, the purpose of reinforcement always being the improvement of strength properties. Reinforcement may involve the use of a dispersed phase, or strong fiber, thread, or rod

Reinforced concrete: This is the most widely used of all construction materials, since it is not only comparatively easy to place into position and finish, but is also maintenance free during its service life.

Glass-fiber reinforced plastics: These combine the strength of glass fiber with the shock resistance and formability of a plastic. The usual types of reinforcement are the chopped strand mat and the woven fabric, the latter giving increased strength to the composite.

List of advantages

• They are harder and stiffer than steel
• more heat and corrosion resistant than metals or polymers
• less dense than most metals and their alloys
• plentiful and inexpensive
• doesn’t conduct electricity
• Ceramics are used in the manufacture of knives. The blade of the ceramic knife will stay sharp for much longer than that of a steel knife, although it is more brittle and can be snapped by dropping it on a hard surface
• Ceramic engines are made of lighter materials and do not require a cooling system and hence allow a major weight reduction
• Ceramics are also more chemically resistant and can be used in wet environments where steel bearings would rust
• High-tech ceramic is used in watch making for producing watch cases
• scratch-resistance
• In very high speed applications, heat from friction during rolling can cause problems for metal bearings; problems which are reduced by the use of ceramics
• Durability and smooth touch.
• ceramic materials may be used as bone replacements

Limitation of the material in engineering applications

• The main disadvantage of medical ceramic materials is their fragility
• The ceramic materials cannot deform under the stress, as can do plastics and metals
• Ceramics do not perform well with tension or tensional loads.
• A hard, brittle material that can withstand high temperatures and resist corrosion
• Ceramics cannot be joined (and repaired) by welding.
• The other disadvantage is that ceramics are strong in compression, but weak in tension
• Ceramics don’t bend much, and when they break, instead of slowly pulling apart the way metals will, they generally snap
• they have a tendency to shatter when something hits them hard

Q-2 An overview of the engineering properties and behavior of ferrous metals, Non-ferrous metals, polymers & composites, and ceramics

a) Ferrous metals.

Pure iron: Easily weld able, good corrosion resistance, effective electrical conductivity. Used in iron rods

Plain Carbon Steel: Expensive, soft and weak, easily weld able, good ductility, Good toughness. Used in hammers, chisels, a drill, knives, wire and dies for all purposes.

Low- Alloy steel: Machinable, ductility of more, than 25%. Used in transportation, agriculture, construction, and military applications.

Ultra-High-Strength steel: Ductile, Formable, and Machinable. Has higher strength that other steel. Mainly used in Bridges, towers, and pressure vessels.

Medium-carbon low-alloy steel: Has low Harden ability. Used in rocket motor cases, aircraft components, including bolts, pins, main landing gears, and brake housings, and a wide variety of structural and machinery parts.

Ferritic stainless Steels: Good resistant to wear and tear, highly ductile. Tensile strength – 380Mpa, Yield strength 205Mpa, Ductility 20%, High tensile strength. Good corrosion resistant. Used in furnace parts, boiler baffles, kiln linings, stack dampers, chemical processing equipment, automobile trim, catalytic converters, and decorative purposes in general.

Martensitic stainless steels: Tensile strength 485Mpa, Yield strength 275Mpa. Used in cutlery, surgical instruments, valves, turboine parts, pump parts, and oil well equipment.

Austenitic stainless steels: Outstanding resistance too many types of corrosion and erosion. Superior cast ability, Good mach inability, and Tensile strength 515Mpa, and Yield strength 170Mpa. Used in decorative purposes, interior show cases, automobile trim, aircraft is fitting, food handling.

Precipitation-hardening stainless steels: Very high strength towards corrosion and resistance. Used for aircraft parts, nuclear reactor components, landing gear parts, high-performance shafting and petrochemical applications requiring stress corrosion resistance.

Grey cast-iron: Ease of melting and casting process. Air-cooled cylinders clutch housing clutch plates.

Spheroid graphite castiron: Modulus of elasticity, Wear resistance, excellent machinability, High thermal conductivity, Outstanding cast ability.

Austempered Ductile iron: Higher tensile strength, higher ductility, Machinability and corrosion resistance are similar to g.c iron. Automotive and agricultural products like Axle housing, brake calipers, brake cylinders. Boiler segments, conveyor frames, bulldozer parts.

Compacted cast iron: Good wear resistance used in automotives and engineering applications. Used in shafts, helical gears, couplings, and conveyor rollers.

Malleable Cast iron: Higher tensile strength ductility. Fatigue life impact strength. Brake drums, discs. Cylinder heads piston rings. Used in Automotive transmission parts, clutch pedals. Steering knuckle, wheel hubs.

Austentic carbon: Good fatigue strength, good damping capacity. Used in pump components valves, compressors. Alloy steels have greater harden ability than plain carbon steels

Alloy steel have greater harden ability than plain carbon: The difference between the two is somewhat arbitrary definition. However, most agree that while the steel alloyed with more than eight percent of its weight of other elements besides iron and carbon steel is a strong ally. Low alloy steel is slightly higher. The physical properties of these steels are modified by other factors, making them more hardness, strength, corrosion resistance or hardness compared to carbon steel. For these properties, these alloys are often heat-treated.

Carbon steel is steel that does not contain significant amounts of alloying elements other than carbon. There are three major categories of carbon steel. A low-carbon steel, medium carbon and alloy.

Alloy steel is a type of steel that many advantages over steel offers. It is much harder and stronger than ordinary carbon steel by. It is used in cars, trucks, cranes, bridges and other structures can handle a large number of strains

The difference between the two is defined somewhat arbitrarily. However, most agree that while the steel is alloyed with more than eight per cent of its weight of other elements being next to iron and carbon steel is strong ally. low alloy steels are slightly more frequent. The physical properties of these steels are modified by other elements, giving them a greater hardness, strength, corrosion resistance, or hardness compared to carbon steel. To achieve these properties, these alloys often require heat treatment.

Carbon steel is a steel which does not contain significant amounts of alloying materials other than carbon. There are three major categories of carbon steel. low carbon steel, medium carbon steel and alloy.

Alloy steel is a type of steel that offers many advantages over steel. It is much harder and stronger than ordinary carbon steel by. It is used in cars, trucks, cranes, bridges and other structures to be able to handle a large number of strainsThe difference between the two is defined somewhat arbitrarily. However, most agree that while the steel is alloyed with more than eight per cent of its weight of other elements being next to iron and carbon steel is strong ally. low alloy steels are slightly more frequent. The physical properties of these steels are modified by other elements, giving them a greater hardness, strength, corrosion resistance, or hardness compared to carbon steel. To achieve these properties, these alloys often require heat treatment.

Carbon steel is a steel which does not contain significant amounts of alloying materials other than carbon. There are three major categories of carbon steel. low carbon steel, medium carbon steel and alloy.

alloy steel is a type of steel that offers many advantages over steel. It is much harder and stronger than ordinary carbon steel by. It is used in cars, trucks, cranes, bridges and other structures to be able to handle a large number of strainsThe difference between the two is defined somewhat arbitrarily. However, most agree that while the steel is alloyed with more than eight per cent of its weight of other elements being next to iron and carbon steel is strong ally. low alloy steels are slightly more frequent. The physical properties of these steels are modified by other elements, giving them a greater hardness, strength, corrosion resistance, or hardness compared to carbon steel. To achieve these properties, these alloys often require heat treatment.

Carbon steel is a steel which does not contain significant amounts of alloying materials other than carbon. There are three major categories of carbon steel. low carbon steel, medium carbon steel and alloy.

Alloy steel is a type of steel that offers many advantages over steel. It is much harder and stronger than ordinary carbon steel by. It is used in cars, trucks, cranes, bridges and other structures to be able to handle a large number of strainsThe difference between the two is defined somewhat arbitrarily. However, most agree that while the steel is alloyed with more than eight per cent of its weight of other elements being next to iron and carbon steel is strong ally. low alloy steels are slightly more frequent. The physical properties of these steels are modified by other elements, giving them a greater hardness, strength, corrosion resistance, or hardness compared to carbon steel. To achieve these properties, these alloys often require heat treatment.

Carbon steel is a steel which does not contain significant amounts of alloying materials other than carbon. There are three major categories of carbon steel. low carbon steel, medium carbon steel and alloy.

Alloy steel is a type of steel that offers many advantages over steel. It is much harder and stronger than ordinary carbon steel by. It is used in cars, trucks, cranes, bridges and other structures to be able to handle a large number of strainsBottom of Form

b) Non ferrous alloys

Aluminum: Weak and ductile, Electrical conductivity is better. High thermal conductivity, Good resistance towards corrosion. Used in Aircraft, boats, pistons and cranks.

Aluminum – base alloys: copper has high electrical and thermal conductivity. Tensile strength and hardness can be improved. Used in Power lines, controllers, signaling devices.

Miscellaneous copper base alloys: Electrical conductivity of 60%, Good corrosion resistance, has the Hcp structure. Used in applications like Aircraft and Spacecraft.

Magnesium – base alloys: Has the melting point of 1455’C. Good formability. Good Corrosion Resistance. The pure Zinc has the melting point of 419’cIt has two types of alloys; Alloy A – Good ductility Alloy B- Higher effective strength. Used in Petroleum industry, Chemical industry Food processing plants, Fuel pump, optical instruments, car doors etc.

Lead-Tin alloys: Excellent corrosion resistance, Good strength. Resistant to high temperatures. Some important types of alloys, alpha titanium alloys, near alpha titanium alloys, Alpha-beta titanium alloys, Beta titanium alloys. Used in Compressor blades, Engine forging and space craft’s.

Differences between non-ferrous alloys in the cast vs. wrought forms

Nonferrous Alloy

• Specified for use in electrical and electronic applications.
• Reduced weight
• Higher strength
• Nonmagnetic properties
• Higher melting points
• Resistance to chemical and atmospheric corrosion.

A type of cutting material is relatively expensive and must be directly casted into the form. Non-ferrous cast alloy tools have largely been replaced by carbide.

Wrought alloy: Solid metal that has been bent, hammered, or physically formed into a desired shape.

Wrought copper alloys can be utilized in the annealed, cold-worked, stress-relieved, or hardened-by-heat-treatment conditions, depending on composition and end use.

Bronzes comprise four main groups:

• copper-tin-phosphorus alloys (phosphor bronze)
• copper-tin-lead-phosphorus alloys (leaded phosphor bronze)
• copper-aluminum alloys (aluminum bronzes)
• copper-silicon alloys (silicon bronze)

Wrought copper-nickel alloys, like the cast alloys, have nickel as the principal alloying element. The wrought copper-nickel-zinc alloys are known as “nickel silvers” because of their color.

c) Polymers:

Polymers are classified in various way