gtu msmt unit 2 study material

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QUESTION AND ANSWER BANK FOR GTU EXAMINATION,

MATERIALSCIENCE AND METALLURGY(3321902)

PREPARED BY:ANKITKUMAR A BRAHMBHATT

ASST PROFF PIET DS 1(MECHANICAL).

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UNIT 2 PHASE DIAGRAM 2 MARKS

1.a).Grain b).Grain Boundary

Answer: GRAIN: The metal structure formed by the crystal is known as grain.

GRAIN BOUNDRY:Each grain starts from the nucleus so the crystallisation obtained is dependent on the number of nucleus the orientation of the atoms arise from grain to grain. The two hereby grain meet in a surface these surface is known as grain boundary.

2.What is Equilibrium Diagram?

Answer: The temperature composition diagram shows the changes of the structure taking place during the heating and cooling is called as Equilibrium diagram.

On X AXIS: Metal Composition, Y AXIS :Temperature. It is also known as Phase Diagram

When any Alloy after heating cooled down then changes taking place in it is shown by a curve known as Equilibrium Diagram or Phase Diagram or Constitutional Diagram.

3.Define Solid Solution and give examples.

Answer: In liquid stage metal form homogeneous liquid solution, The solid Solution is formed. If Solvent &Solute atoms are of similar size and electron structure, solid solution forms very readily if elements A in B forms solid solution in B by its 10%.

E.g Brass: Copper & Zinc,Steel:Iron & Carbon,Monel:Nickel&Copper,Au-Ag:Gold & Silver, Sterling Silver: Silver & Copper.

4.What Is Cooling Curve and Draw Cooling Curve Of Metal Compound

Answer: By measuring the temperature at definate interval of time when the liquid metal or alloy is cooling the time temperature curve is plotted this curve of metal and alloy is called cooling curve.

Fig:1 Cooling Curves

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5.Properties Of Solid Solution

Answer: Properties

• Thermal &Electrical properties are reduced due to formation of solid solution.

• The strength and hardness of all the alloy metals increases due to solid solution

• Solid solution reduces the ductility &malleability of the alloys.

• The density, specific heat &heat distribution get changed according to the proportions of alloying elements.

• By changing the proportion of the alloying element, there is no possibility to change the stiffness any more.

• Solid solution alloys exhibit differential freezing.

• Solid solution are conductors but not as the pure metals on which they are based.

• The Constituents of the solid solution cannot be detected by the microscope.

• It is simply a solution in the solid state consisting of atoms combimned in one type of space lattice.

6.State Lever Rule

Answer: On basis of phase Diagram No Of phase, and Composition Of phase can be calculated .

Fig 2:Phase Diagram

lever rule is very important in two phase system to calculate the percentage of phase present two lines are drawn and point is obtained which is between liquidus and solidus line G E H

Solid Phase Percentage=GE/GH*100 Liquid Phase Percentage=EH/GH*100

7.Why Heat Treatment Should be carried Out?

Answer:(ANY FOUR)

To improve combination of different properties.

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To remove internal residual stresses from the component after basic manufacturing processes such as casting,forging,Rolling.

To improve grain size of the material.

To increase the hardness of the material.

To improve the toughness of the compomnent.

To improve machinability of the material.

To make the material soft so that the process like wire drawing,Cold Rolling,Can be performed on the same.

To improve heat,wear,and corrosion resistance of the materials.

To improve magnetic and electrical properties of the material.

To impart harder surface and softer core to the component.

To make the structure of the component homogenous.

To improve ductility and toughness of the material.

To stabilize size of the component.

To facilitate diffusion process in the steel.

To obtain desired structure in the material as per specific application requirement.

8.Differentiate between Process Metallurgy and Physical Metallurgy

Answer: Process Metallurgy: It deals with the extraction of metal from its ore.

Physical Metallurgy: Study of physical &Mechanical properties of metals of alloys as well as the governing laws by which these attribute varry owing to external influences such as thermal, mechanical, chemical, electromagnetic and radioactive effect.

9.Give Name Of Alloying Element used in Alloy Steel

Answer: C,Si,Mn,Cr,Mo,Ni,W,S,P,Nb,Ti,Ta,Etc

10.Types Of Solid Solutions

Answer:

Fig 3: Types Of Solid Solution

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11.Why Alloying is done?

Answer:(Any Four)

• increase hardenability. • improve strength at ordinary temperature. • improve mechanical properties at either high or low temperature. • improve toughness at any minimum hardness or strength. • increase wear resistance. • increase corrosion resistance. • improve magnetic properties.

12.Use OF iron carbon Diagram

Answer:

• To predict no type and composition of the phases. • To predict amount of the phases . • Guide heat treater. • Predict microstructure of an alloy.

13.Limitation Of Iron Carbon Diagram.

Answer:

• It does not give information about ferrite or cementite formed ejected from austenite on cooling.

• It does not give information about size of micro constituents present. • It does not give information of Physical and Mechanical Properties of the material.

14.Classification Of Heat Treatment Process

Answer:.

Fig 4:Classification of Heat Treatment Process

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15.Why Annealing is carried out?

Answer: Purpose Of Annealing:(Any Four)

• To produce the desired microstructure having mechanical.physical,and other properties as per the requirement.

• To reduce hardness and soften the steel

• To relieve the internal stress.

• To restore the ductility and thereby facilitate further cold working

• To improve Mach inability.

• To refine and make homogeneous structure by reducing structural in homogeneities

• To create complete stable structure.

• Increase or restore toughness.

16.Types Of Annealing?

Answer:

Fig 5:Types Of Anneling Process

17.Application OF Annealing

Answer:

• To make the parts soft. • To improve the structure of the parts. • To bring the properties required for cold working. • To remove irregularities • To prevent Cracking of the parts during process. • To relieve internal stress. • To improve machinability. • To get Good structure for hardening. • To increase formability.

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• To improve the electrical &Magnetic properties.

18.Purpose of Normalizing.

Answer: Purpose Of Normalizing(Any Four)

• To obtain desired microstructure and mechanical properties.

• To improve the Machinability of low carbon steels.

• To eliminate coarse grained structure resulted from working operation such as rolling, Forging etc.

• To modify and improve cast dendritic structure and reduce segregation by homogenizing the micro structure.

• To improve tensile strength of casting and forging component.

• To improve weld structure after welding process.

19.Application OF Normalizing.

Answer: Application of the normalizing Process(Any Four)

• To obtain uniform structure.

• To refine the grain size.

• To obtain desired strength of too soft & ductile steel.

• To reduce internal stress.

• To improve weld structure.

• To remove the carbide network from the grain boundaries hypo eutectoid steel.

• To improve engineering properties of steel.

20. Advantages Of Hardening Process.

Answer: Any Four

• It increases the hardness of steel. • Makes tools & machines parts useful for heavy duty.

• It increases the wear resistance of steel.

• Makes steel hard so as to cut the other materials.

• Increases the strength, toughness & ductility of steel.

• A good combination of strength & ductility is obtained.

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21.Dis advantages Of Hardening Process.

Answer: Any Four

• Cracks are developing in the part due to hardening.

• Required hardness can not be obtained.

• It increases the brittleness of the parts.

• Soft Parts develops in the part due to non uniform hardness.

• The dimension & size of the part change.

• Due to warpsage ,the shape of the part gets altered.

• Surface of the part becomes rough.

• Scaling of the surface results when high speed steel having thickness more than 12 mm is hardened.

22.Advantages Of Case Hardening.

Answer: Advantages Of Surface Hardening

• Only 1 to 5 second time is required for heating ,therefore huge work can be done with benefits.

• There is no scaling &cracking of the parts.

• Less possibility of change of shape like heat treatments.

• This is an automatic process imparts wear resistance property to the material.

• Increase fatigue limit.

• This process does not create any harm to surface finish.

• It increases impact strength.

• Cheaper material can be employed to manufacture the parts.

• Hard surface prevents wear & tough core resists he fracture

• The cost of equipment is less.

• The process is simple.

• The process can be done on lengthy parts. This process is proved most suitable for producing medium sized components by using mass production.

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23.What is Eutectic ,Eutectoid .

Answer:

Eutectic: in eutectic system certain metal melts at minimum constant temperature this temperature is known as eutectic temperature and the point at which the eutectic composition is formed is known as eutectic point E.g. 1130°C,the liquid metal containing 4.3%C is transformed into eutectic.

Eutectoid: As per eutectic system the transformation of liquid into solid state is known as eutectoid ,The point at which transformation occurs is known as eutectoid point, E.g 0.85%C if contained in an austenite it transforms at 723°Cin ferrite & cementite.

24.What is Critical Points, Delta Solid Solution.

Answer:

Critical Point: When liquid metal is allowed to cool at certain temperature heat evolution takes place and structural changes occurs in the metal. The temperature at which the structural changes are taking place are known as critical points E.g. 768°C,910°C,and 1400°C.

Delta Solid Solution: Iron is the major element of the steel. It is available in its three allotropic forms .Therefore the iron has three types of crystal transformation with respect to temperature. in all these three forms of carbon is soluble and forms the solid solution .The three allotropic forms are APLPHA,GAMMA,DELTA iron.

25.What Is Ferrite and Cementite.

Answer:

Ferrite: The iron not containing more than 0.025%C in solid solution is the Alpha iron having BCC structure. It is the major constituent in wrought iron &low Carbon Steel It is having hardness between 50-100BHN and UTS 3400Kg f/Cm2.Its elongation is about 40% and can be worked very easily.

Cementite: The iron Carbide Fe3C containing 6.67%C is known as Cementite. Its hardness is 650BHN and UTS 450Kgf/Cm2.It is brittle and white in colour. It is brittle and white in colour it is occurring due to slow cooling in steel below the temperature of 205°C it can be magnetised .It is present as a component of another constituent Pearlite in steel if %C is more than 0.8%,it exists as a grain boundary film.

3 MARKS

1.What is Phase Diagram? Write About Important terms Associated With it?

Answer: The Solidification of Metal Alloy is Clearly understood by means of equilibrium diagrams.

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• These are graphical representation of the changes in state due to variation in temperature and concentration.

• This indicate the nature and constitution of the alloys and the amount and the composition of the phases in a given system.it is also called constitutional diagram or Phase diagram.

• Equilibrium refers to the changes taking place in a system as a result of process Occurring in one direction are fully compensated by the changes due to reversal of the process in the system. Equilibrium diagram indicates the temperatures at which the solid alloy will start melting and finish melting & possible place changes which will occur as the result of the altering the composition or temperatures.

• Properties of the materials depends on the Type,Number,Amounts and Form Of the phases present, the properties can be changed by altering these quantities.

The Equilibrium Diagram

• The temperature composition diagram shows the changes of structure taking place during heating& cooling. This diagram is known as an Equilibrium Diagram. On

X axis: Metal Composition Y axis: Temperature Scales are plotted. The full name of this diagram is “Thermal Equilibrium Diagram" known as Phase Diagram or Constitutional Diagram.

• It represent the equilibrium condition. Which is not possible to have in reality.eventhough provide basic information for the heat treatment & to study the properties of alloy.

• If two elements it is known as Binary alloy, If three elements it is known as Ternary alloy.

Fig 6:Types Of Phase Diagram

• System: Part of the substance which is completely separated from the surrounding.

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• Component: Basic chemical substance, whose mass is constant and which can be used to form a chemical mixture.

• Phase: The part of material system uniformly mixed physically.

• Constituent:The part of multiphase mixture which can be identified seperately.

• Liquidus:The locus of temperature at which solidification is complete. below solidus only solids are stable.

• Solidus:The locus of temperature of a transformation at which solidification starts.

• Solvent: The major element of a sold solution.

• Solute: The minor element of a solid solution.

2.What is Solid Solution? Types Of Solid Solution?

• Answer: Solid Solution

• In liquid stage metal form homogeneous liquid solution,The solid Solution is formed.If Solvent &Solute atoms are of similar size and electron structure,solid solution forms very readily if elements A in B forms solid solution in B by its 10%.

• Hume Rodhery Rule :if metal A is in lesser proportion than B,therefore A is known as solute and metal B is known as solvent.There is homogenouus distribution of two or more constituents in the solid state so as to form a single phase known as solid solution.A is solid solution is the result of metals dissolving in each other’s crystal Lattice.In solid solution in both the liquid and the solid state.While in solid solution of Cu and Zinc both having sub valence electrons,forms substitutional solid solution.

• Solid Solution

• Substitutional Solid Solution

• The substitutional solid solution is formed when the atoms of solute metal occupy the position of the atoms of solute metal.due to the size differencde in atoms of the two metals,there is the possibilities lattice distortion.e.g Cu-Ni and Bi-sb alloys.

• As per the arrangement of the solvent &solute atoms in the substitutional solid solution there are two types as stated below:

• Random or Disordred substitutional solid solution,Ordered substituitonal solid solution.

• Disordered Substitutional Solid Solution

• While forminmg the solid solution soluter atoms instead of occupying specific position get distributed random in the lattice structure of the solvent.This alloy is in

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the disordered condition.in this type of condition the concentration of solute atoms can vary considerably in the lattice structure.

• Ordered Solid Solution

• If an alloy of disordered condition,cooled slowly because of diffusion .its atoms get rearranged .The diffusion products uniform distribution of solvent & solute atoms and solute atoms move into definite orderly positions in the lattice .The structure is then known as super lattice or ordred substitutionasl solid solution.The prolonged anneling of the alloy can produce still more uniform &ordred solid solution.

• Interstitial Solid Solution

• When the solute atoms are smaller in size than solvent atoms this type of solid solution is formed. The solute atoms in this case occupies the vacant spaces between the solvent atoms. Due to mixing of small atomic radii elements like Carbon,Nitrogen,&hydrogen in the metal interstitial solid solution is formed. In this type of solid solution the constituent elements are in flexible proportions. They have very strong bonding forces between them. The alloy Fe3C and Fe4N are solid solution of this type. This solid solution is shown in figure.

• Properties










3.Factor Of Hume Rodhery Rule

Answer:

• Hume Rodhery Rules

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• Size Factor: The difference of atomic diameter of solvent & solute metals is not more than 15%the possibilities of forming solution is 100 %.if this difference is more than 15% the possibilities of forming solid solution is limited .The monel metal is an alloy of Cu and Ni formed by substitution solid solution has

Atomic Diameter Of Cu=da 2.551A

Atomic diameter of Ni=da 2.487A

The difference is 2.508%

• Chemical affinity factor: The greater chemical affinity of two metals tends to form an intermediate phase instead of solid solution. Due to their greater affinity the metals are further apart elements in the periodic table.

• Crystal Structure Factor: The crystal lattice structure of the metals should be same means both must posses BCC or FCC or HCP structure .The similar structure gives complete solubilities .Dissimilar structure of metals does not allow then to merge into each other .For complete solubility the size should also be complied

• The binary alloy of similar space lattice & two types of atoms in solid state is known as Isomorphism alloy. The alloy metal solidifies at a fixed temperature while the isomorphism alloy has arrange of temperature for solidification.

• E.g Brass: Copper & Zinc,Steel:Iron & Carbon,Monel:Nickel&Copper,Au-Ag:Gold & Silver, Sterling Silver: Silver & Copper.

• Relative Valency Factors:The metal of high valancy electron can dissolve in small amount in alowerr vacnacy metal.While the lower valency metals have good solubility in the higher valency metal.Al-Ni alloy,Ni has lower valency then Al hence Ni can dissolve only n0.04%of Al and Al can dissolve 5 of Ni in therir solid states

4.What is Alloy? Types Of Alloys

Answer:

An Alloy is an intimate mixture with metallic properties and is composed of two or more elements of which at least one is metal.

While the other is constituents or elements are known as alloying element, The cast iron,brass,Wrought iron,Steel,Bronze,White metal,Gun Metal, Duralumin and Mangalium are all alloys.

Binary and Ternary Alloy:Pur metal are considered as single phase,like wise the solid solution is also a single phase.

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If pure metal and chemical compounds are in existance together in an alloy then in existance together in an alloy than in that alloy there exists two phases which are different from each other .in this way solid solution & pure metal together will give two phase .

This phase formed by physical &Chemical mixture occupies different positions with respect to one another.

P=C+E-F

P=No of Phase, C-No Of Composition, E=No of Environment Factor, F=Degree OF Freedom

Single phase Alloy, Two Phase Alloy based on the Metallurgical Structure.

Aluminium Alloy ,Copper alloys etc based on principal metals

Cast Alloys wrought alloys, based on method of fabrication.

Solder Alloys, bearings alloys, based on application.

Binary Ternary etc based on no of element.

5.Write Effect Of Any Three alloying Element

Answer: Effect of Alloying Element on Mechanical Property of The Material

Carbon

• The basic metal, iron, is alloyed with carbon to make steel and has the effect of increasing the hardness and strength by heat treatment but the addition of carbon enables a wide range of hardness and strength.

Manganese

• Manganese is added to steel to improve hot working properties and increase strength, toughness and hardenability. Manganese, like nickel, is an austenite forming element and has been used as a substitute for nickel in the A.I.S.I 200 Series of Austenitic stainless steels (e.g. A.I.S.I 202 as a substitute for A.I.S.I 304)

Chromium

• Chromium is added to the steel to increase resistance to oxidation. This resistance increases as more chromium is added. 'Stainless Steel' has approximately 11% chromium and a very marked degree of general corrosion resistance when compared with steels with a lower percentage of chromium. When added to low alloy steels, chromium can increase the response to heat treatment, thus improving hardenability and strength.

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6.What Is Cooling Curve? Draw Cooling Curve for Alloy

Answer: By measuring the temperature at various locus of temperature when the metal or alloy is cooled the Time Temperature Curve is plotted that curve is called as Cooling Curve

Fig 7:Cooling Curves

One Method of plotting this curve is at which temperature the phase change occurs in a system consists of following the temperature as a function of time as different alloys in the system are very slowly cooled.

7.Draw TTT Diagram

Answer:

Fig 8:TTT Diagram

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8.Explain Allotropic forms Of Iron, What Is Curie Temperature?

Answer:

• Iron, as shown in figure, exists in three crystal (atomic) allotropes, namely: alpha (a) iron, delta (d) iron, and gamma (g) iron.

• The a-iron form exists below 1625oF (885oC) while d-iron is stable above 2540oF ( 1395oC). Gamma iron exists at the temperatures between these two ranges. It is the allotropy of iron that allows for these crystal structures to change with temperature. At room temperature, the a-iron crystal structure has its atoms arranged in a geometric pattern known as body-centered cubic or bcc .

Fig 9:Allotropic Forms Of Iron

• This atomic arrangement of iron atoms is magnetic up to 1420oF (770oC), called the curie temperature. This temperature was of practical importance to the early blacksmiths who used an iron horseshoe magnet with a steel bar across the two ends for temperature measurement.

• When the steel bar fell from the magnet, the blacksmith knew the approximate temperature of the hearth and was able to adjust the heat treat schedule accordingly. Above the curie temperature is still bcc but is no longer magnetic.

• Slow heating of a-iron to 1625oF (885oC) produces an allotropic change to gamma (g) iron, a face-centered cubic (fcc) crystal structure which is non-magnetic. A change from one crystal structure to another is called a transformation and the temperature at which it occurs is called the transformation temperature.

• When fcc g- iron is slowly heated above 2540oF (1395oC) it transform back to bcc iron. To distinguish the elevated temperature bcc iron from its lower temperature counterpart, it is given its own name, delta (d) iron. This d-iron is non-magnetic and exists until the temperature is raised to 2800oF (1540oC) which causes melting of the solid d-iron to liquid iron. Since atoms in the liquid iron have no distinct

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arrangement (each atom moving freely within the liquid) there no longer exists a crystal structure above the melting temperature.

• For the allotropic transformations described, there is another driving force equally important to the transformation temperature, namely, time. For allotropic transformations to occur at the temperatures suggested in figure 1, sufficient time is required for the atoms to reorganize themselves in the new crystal structure. At the lower end of the temperature ranges for each allotrope of iron, lower energy levels exist, so more time is required for crystal structure transformation to occur. The interaction of time and temperature to achieve the allotropic transformations shown in figure is called equilibrium.

9.Define Heat Treatment Process? Objectives Of Heat Treatment?

Answer:

• It is sequential process of heating and cooling the steel component to get desired combination of properties in the component.

• Heating Component at higher temperature called austenitizing temperature, during which the previous structure of steel is converted in to Austenite phase.

• Holding the steel at austenitizing temperature for some time period so that formation of homogenous austenite can occur throughout the entire cross section of the part.

• Cooling back the part which is having homogenous austenitic structure to the room temperature at a particular cooling rate depending upon the properties required.

• Reheating of component to a higher temperature but lower than lower critical temperature and cooling again this is an optional process and performed if required.

Objective Of Heat Treatment





To improve the toughness of the component.

To improve machinability of the material.Etc

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10.What is Carburising? Types Of Carburising Process ?Explain any one.

Answer:

• Carburizing: It is the process of increasing the carbon content in the surface or case of the part. Due to this parts becomes hard. Hardness of the parts is obtained only on its surface. While its interior known as core is remains soft and tough.

1.Pack Carburizing

2.Liquid Carburizing

3.Gas Carburizing

• The Addition of carbon in low carbon steel parts surfaces to make them hard is known as carburising.This process is known as carburizing it is also called as cementation.

• In pack Or Solid Carburizing The parts along with the carburizing mixture are packed in steel box after machining.

• The carburizing mixture contains 50-70% charcoal .5-10%barium Carbonate,2-15%calcium and 3-13%sodium carbonate.

• First of all 25 mm thick layer of this mixture is provided at the bottom of the steel box.

• The parts are kept in the box such that they should not touch one another and to the box.

• Then cover is place on the box and packed with the fire clay to prevent gases to flow in or Out.

• The surface of the parts which is not to be hardened are passed through a process like electroplating to make it non absorbent of carbon.

• The box is placed in the furnace and heated to 900-980°c for a period of the time 6 to 8 hours.

•

Fig 10:Carburizing Process

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• After heating box along with parts is allowed to cool in the furnace it self. Austenite absorb the carbon at high temperature. So %C of surface gets increased. During the process of carburizing ,due to heating the grain near to core becomes becomes coarser. To refine these coarse grains parts are heated to 880°C temperature and then cooled by quenching in oil or allowed to cool in air.

• Grain refinement part are heated to 760-780°c and quenched in water to make its surface hard.

• By obtaining required hardness parts also becomes brittle, so part are tempered around 180-280°c.The hardness depth of 1-1.5 mm is obtained in low carbon steel containing 1.1-1.2%C.

11.Explain Induction Hardening

Answer:

Induction Hardening

• Parts are heated by induction heating.

• High frequency induction current is used.

• Required current is produced by using motor generator set with spark gas oscillator or tube oscillator.

• Frequency of 1000-1000C/s.

Fig 11:Induction Hardening Process

• The gap oscillator can generate the current having frequency of 100000 to 400000 C/s.

• When Current of required frequency is passed through induction coil, magnetic lines will pass through the part surface, due to that AC current will induce in the surface which cause hysteresis loss in it and as a result of that parts get heated.

• The induced current travels along the surface of the part. For Quenching ,water is sprinkled on the parts through the voids of inductor block & coil.

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• This contain 0.35-0.55%c can be done. The induction hardening process is used for the parts like camshafts,Gears,Cranckshaft,axles,and other automobile parts and tractor parts.

12Explain Flame Hardening and Cyaniding.

Answer: Flame Hardening:

• This process is used for hardening stell,dye,gears,tappet screw,rocker arms and valves. This is the process of obtaining wear resistant layer on the tough core by heating the parts using gas torch.

• This process is utilized for the parts containing 0.4 % to 0.6% C.The surface is heated by the oxy acetylene flame. By heating for sufficient time the temperature of the part is raised above AC3 temperature and thereafter fast quenching is done. The surfaces of large size parts can be hardened is an advantage of this process.

Fig 12:Flame Hardening

• Heating cycle is less,which cause scaling. A fixed temperature can not be maintained is the disadvantage of this process.

• The parts are also damaged due to overheating or cracks are formed in it.

Cyniding:

In liquid Carburizing Salt is used which is solid in normal temperature but it becomes liquid at carburizing temperature.

Basically Cynogen radical are there in the Salt.They are basically Sodium and potasium cynide salt it is called as cyniding process.

Heated parts what are to be made are immersed in the salt bath,Salt bath is having 30%Sodium Cynide part to be immeressed at 870° for 1 hour .Cynide gives Co and N which react with iron .

N increses the hardness of the case .The case thickness is 0.25 mm thin but time required is very slow.

Sonow liquid cyniding in which floating Calcium Cynide is used From that case depth is incresed in which amt of N is less and carbon is more,Cynidi is very poisunous.

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4 MARKS

1.Explain Quenching Mediums.

Answer: From Red hot Condition of work piece to relieve the heat in which medium it is immersed in called as Quenching Medium.Quechnching medium should be able of so that no Pearlite is transformed from Austenite.

1.5-10% Caustic Soda,2.5-10%Nacl,3.Cold Water,4.Hot Water,5.Mineral Oil,6.Anemal Oil

7.Vegetable Oil ,8.Air Quenching

Factor Affecting for liquid coolant:

Temperature of Quenching Medium, Amount Of Heat To form Vapour, Specific heat of liquid, Thermal Conductivity Of liquid, Viscosity Of Liquid, Motion Of Liquid.

Factor Affecting for Solid Work piece:

Dimension Of WorkPiece,Temperature Of WorkPiece,Specific Heat Of Work Piece, Surface Condition OF Work Piece.

Different Quenching Mediums: According to severity of Quench

Brine(5-20% Nacl in Water),Cold Water, Warm Water,Oil,Salt Bath, Air

2.Draw Equilibrium Diagram ,Write the Terms Related To it.

Answer: Concept Of Equilibrium Diagram

• The Solidification of Metal Alloy is Clearly understood by means of equilibrium diagrams.

• These are graphical representation of the changes in state due to variation in temperature and concentration.

• This indicate the nature and constitution of the alloys and the amount and the composition of the phases in a given system.it is also called constitutional diagram or Phase diagram.

• Equilibrium refers to the changes taking place in a system as a result of process Occurring in one direction are fully compensated by the changes due to reversal of the process in the system. Equilibrium diagram indicates the temperatures at which the solid alloy will start melting and finish melting & possible place changes which will occur as the result of the altering the composition or temperatures.

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Properties of the materials depends on the Type,Number,Amounts and Form Of the phases present, the properties can be changed by altering these quantities.

• The information regarding phase changes in many alloy systems are recovered as data in the form of Phase, Equilibrium Consolidated Diagrams.

• In order tom specify completely the state of a system in equilibrium,temperatures,purposes and the composition are the three variables which are extremely controlled be specified.

• If the pressure is assumed to be constant of atm,The equilibrium diagram indicates the structural changes due to temperatures and composition by equilibrium it is meant that under equilibrium condition, there will be no change with time .These condition are approached by extremely slow heating and cooling.

Equilibrium Diagram

• The temperature composition diagram shows the changes of structure taking place during heating& cooling. This diagram is known as an Equilibrium Diagram. On

X axis: Metal Composition Y axis: Temperature Scales are plotted. The full name of this diagram is “Thermal Equilibrium Diagram" known as Phase Diagram or Constitutional Diagram.

Fig 13:Phase Diagram

• It represent the equilibrium condition. Which is not possible to have in reality.eventhough provide basic information for the heat treatment & to study the properties of alloy.

• If two elements it is known as Binary alloy, If three elements it is known as Ternary alloy.

• System: Part of the substance which is completely separated from the surrounding.

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• Component: Basic chemical substance, whose mass is constant and which can be used to form a chemical mixture.

• Phase: The part of material system uniformly mixed physically.

• Constituent:The part of multiphase mixture which can be identified seperately.

• Liquidus:The locus of temperature at which solidification is complete. below solidus only solids are stable.

• Solidus:The locus of temperature of a transformation at which solidification starts.

• Solvent: The major element of a sold solution.

• Solute: The minor element of a solid solution.

• When an alloy after heating ,cooled down then the changes taking place in it is shown by a curve known as “Equilibrium Diagram” known as Phase Diagram.It is graphical description of the alloy system.

• The system shows the Melting points and Freezing points of all its alloy.

• Temperature, Pressure of Element& Proportion of the constituent are the major factors in this equilibrium diagram with the help of variation the equilibrium diagram is constructed.

3. What Is Solid Solution? Types Of Solid Solution

Answer: Solid Solution

• In liquid stage metal form homogeneous liquid solution, The solid Solution is formed.If Solvent &Solute atoms are of similar size and electron structure,solid solution forms very readily if elements A in B forms solid solution in B by its 10%.

Solid Solution

• Substitutional Solid Solution



• Random or Disordred substitutional solid solution,Ordered substituitonal solid solution.

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Fig 14:Types Of Solid Solution

• Disordered Substitutional Solid Solution

While forminmg the solid solution soluter atoms instead of occupying specific position get distributed random in the lattice structure of the solvent.This alloy is in the disordered condition.in this type of condition the concentration of solute atoms can vary considerably in the lattice structure.

• Ordered Solid Solution

If an alloy of disordered condition,cooled slowly because of diffusion .its atoms get rearranged .The diffusion products uniform distribution of solvent & solute atoms and solute atoms move into definite orderly positions in the lattice .The structure is then known as super lattice or ordred substitutionasl solid solution.The prolonged anneling of the alloy can produce still more uniform &ordred solid solution.

• Interstitial Solid Solution

When the solute atoms are smaller in size than solvent atoms this type of solid solution is formed. The solute atoms in this case occupies the vacant spaces between the solvent atoms. Due to mixing of small atomic radii elements like Carbon,Nitrogen,&hydrogen in the metal interstitial solid solution is formed. In this type of solid solution the constituent elements are in flexible proportions. They have very strong bonding forces between them. The alloy Fe3C and Fe4N are solid solution of this type. This solid solution is shown in figure.

Properties






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4.Draw Diagram Of Heat Treating Temperature For Carbon Steel.

Answer:

Fig 15:Heat Treating Temperature Diagram

5.Draw TTT Diagram

Answer:

Draw As Shown on Page No

6.What Is Tempering ?Explain it

Answer: Tempering

• It is Process of heating previously hardened steel to temperature below the lower critical temperature (A1) and cooling back to room temperature.

PROCESS

• Tempering Temperature for a hardened steel can very from 100 to 680 °C depending upon the requirements. Low alloy constituents steels are tempered above 400°C to get good combination of strength and ductility. Spring steels are tempered between 300 to 400°C.Folowing guideline are generally adopted for deciding tempering temperature.

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1.Low temperature is used for carbon and alloy cutting tools and measuring tools, They are also carburized and surfaced hardened.

2.Medium Temperature is used to increase elongation and ductility by reducing hardness and strength.

3.High temperature is used to maintain the ration of strength and ductility of structural steel

Table 1:Tempering Temperature

Effects Of Tempering

• Relief Of Internal Stress.

• Formation Of Stable Phases.

• Increase In Toughness.

• Decrease in Hardness

• Provide Right structural Condition Combined with toughness and Shock Resistance.

• Surface Hardening Process

• All load bearing Component requires this treatment for better properties at the outer region than the inner region.

7 MARKS

1.What Is Solid Solution? Types Of Solid Solution, Properties Of Solid Solution?

Answer: Solid Solution:

Type of tempering Temperature of tempering

Properties obtained Application

1st stage / low temp. Tempering

LESS THAN 250C. Improve strength Useful for high carbon and low alloy steels used for cutting and measuring tools.

2nd stage / Medium temp. Tempering

350-500c Steel develops maximum elastic properties.

Useful for coil and laminated spring.

3rd stage/ high temp. Tempering.

500-680c Improves yield, tensile, and impact strength makes steel free from internal stresses.

Useful for connecting rods shaft and gear.

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• In liquid stage metal form homogeneous liquid solution, The solid Solution is formed. If Solvent &Solute atoms are of similar size and electron structure, solid solution forms very readily if elements A in B forms solid solution in B by its 10%.

• Hume Rodhery Rule :if metal A is in lesser proportion than B,therefore A is known as solute and metal B is known as solvent. There is homogenous distribution of two or more constituents in the solid state so as to form a single phase known as solid solution. A is solid solution is the result of metals dissolving in each other’s crystal Lattice. In solid solution in both the liquid and the solid state. While in solid solution of Cu and Zinc both having sub valence electrons, forms substitutional solid solution.

Hume Rodhery Rules

• Size Factor: The difference of atomic diameter of solvent & solute metals is not more than 15%the possibilities of forming solution is 100 %.if this difference is more than 15% the possibilities of forming solid solution is limited .The Monel metal is an alloy of Cu and Ni formed by substitution solid solution has

Atomic Diameter Of Cu=da 2.551AAtomic diameter of Ni=da 2.487A

The difference is 2.508%

• Chemical Affinity Factor: The greater chemical affinity of two metals tends to form an intermediate phase instead of solid solution. Due to their greater affinity the metals are further apart elements in the periodic table.

• Crystal Structure Factor: The crystal lattice structure of the metals should be same means both must posses BCC or FCC or HCP structure .The similar structure gives complete solubilities .Dissimilar structure of metals does not allow then to merge into each other .For complete solubility the size should also be complied

• The binary alloy of similar space lattice & two types of atoms in solid state is known as Isomorphism alloy. The alloy metal solidifies at a fixed temperature while the isomorphism alloy has arrange of temperature for solidification.

• E.g Brass: Copper & Zinc,Steel:Iron & Carbon,Monel:Nickel&Copper,Au-Ag:Gold & Silver, Sterling Silver: Silver & Copper.

• Relative Valency Factors:The metal of high valancy electron can dissolve in small amount in alowerr vacnacy metal.While the lower valency metals have good solubility in the higher valency metal.Al-Ni alloy,Ni has lower valency then Al hence Ni can dissolve only n0.04%of Al and Al can dissolve 5 of Ni in therir solid states

Fig 16 :Types Of Solid Solution

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Substitutional Solid Solution


Fig 17:Substitutional Solid Solution


• Random or Disordred substitutional solid solution, Ordered substitutional solid solution.

Disordered Substitutional Solid Solution

• While forming the solid solution solute atoms instead of occupying specific position get distributed random in the lattice structure of the solvent.

• This alloy is in the disordered condition. in this type of condition the concentration of solute atoms can vary considerably in the lattice structure.

Fig 18:Ordered and Disordered Solid Solution

Ordered Solid Solution

• If an alloy of disordered condition, cooled slowly because of diffusion .its atoms get rearranged .The diffusion products uniform distribution of solvent & solute atoms and solute atoms move into definite orderly positions in the lattice .The structure is then known as super lattice or ordred substitutional solid solution. The prolonged annealing of the alloy can produce still more uniform &ordred solid solution.

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Interstitial Solid Solution

• When the solute atoms are smaller in size than solvent atoms this type of solid solution is formed. The solute atoms in this case occupies the vacant spaces between the solvent atoms. Due to mixing of small atomic radii elements like Carbon,Nitrogen,&hydrogen in the metal interstitial solid solution is formed.

Fig 19:Intertstitial Solid Solution

• In this type of solid solution the constituent elements are in flexible proportions. They have very strong bonding forces between them. The alloy Fe3C and Fe4N are solid solution of this type. This solid solution is shown in figure.

Properties









• It is simply a solution in the solid state consisting of atoms combined in one type of space lattice.

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2.Draw TTT Diagram ,and Explain Need & Application Of TTT Diagram.

Answer:

Fig 20:TTT Diagram

• The IC Diagram shows the Change of Phase of Iron as per the change of carbon content in percentage .This is happening due to slow Heating & Cooling known as Equilibrium Diagram.

• The Iron Carbon Equilibrium Diagram does not show the change due to Different Cooling Rates as the time is not takes as a variable on any axis in this Diagram.

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• The steel is passed through the process with different rate of cooling in the industries for which any kind of information is not available from the IC Eqm Diagram.

• From TTT the Information related to formation of pearlite ,bainite,martensite by the different cooling rates of the austenite are obtained. Hence TTT diagram shows the austenite transformation by relating it with the Time & Temperature and Gives information related to the structure formed.

• The principal source of information on the actual process of austenite decompose under non equilibrium condition the TTT Diagram which relates the transformation of austenite to the time & Temperature.

• X Scale: Time on logarithmic Scale,Y Scale:Tempearature.

3.Draw Neat and Clean Labelled Iron Carbon Diagram, Also Define Ferrite,Cementite,Austenite,Pearlite

Answer:

Ferrite: The Iron not Containing more than 0.025% C in solid solution is the Alpha iron having BCC structure .It is the major Constituent in Wrought Iron &low Carbon Steel Its Hardness is in between 50-100BHN and ultimate Strength is about 3400Kgf/cm2.Its Elongation is about 40% and can be worked very easily.

Fig 21:Iron Carbon Diagram

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Fig: Iron Carbon Diagram in °F and°C.

Cementite: The iron Carbide Fe3C containing 6.67%C is known as Cementite. Its Hardness is 650BHN and Ultimate Tensile Strength 450Kgf/cm2,It is brittle and White in Colour It is occurring due to slow cooling in steel below temperature of 205°C.It can be magnetised it is present as a component of another constituent "pearlite "in steel containing less than 0.8%C in steels if % elongation is more than 0.8% it exists as again boundary film.

Austenite: Austenite is a solid solution of carbon in gamma iron. It has face centered cubic structure(FCC).It contains 0.2%C at 1130°C.It is non magnetic and tough above critic temperature it exists in plain carbon steel elements like Mn ,Cr in steel present all or some of Austenite down to 0°C.The austenite consists of polyhedral grains showing twins.

Pearlite: In the microstructure of pearlite there is alternate layers of ferrite and cementite it is contained about 0.8%C in iron it is the strongest constituent of steel having hardness of about 180BHN ,UTS 9400Kgf/Cm2,%Elongation of about 5% after polishing of Viewer with oblique lighting under microscope it appears like Mother of Pearl hence it is known as Pearlite.

4.What Is Heat Treatment? Objective Of Heat Treatment, Classification Of Heat Treatment 0f Process.

Answer:The Entire heat treatment process depends upon following three important principle

a. Phase transformation during heating

b. Structural changes during cooling due to different cooling rates.

c. Effect of carbon content and other alloying elements.

Definition of Heat treatment Process

• It is sequential process of heating and cooling the steel component to get desired combination of properties in the component.

Fig 22:Basic Of Heat Treatment

• Heating Component at higher temperature called austenitizing temperature, during which the previous structure of steel is converted in to Austenite phase.

• Holding the steel at austenitizing temperature for some time period so that formation of homogenous austenite can occur throughout the entire cross section of the part.

TEMP

TIME

ROOM TEMP

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• Cooling back the part which is having homogenous austenitic structure to the room temperature at a particular cooling rate depending upon the properties required.

• Reheating of component to a higher temperature but lower than lower critical temperature and cooling again this is an optional process and performed if required.

Objective Of Heat Treatment





To improve the toughness of the compomnent.

To improve machinability of the material.

To make the material soft so that the process like wire drawing,Cold Rolling, Can be performed on the same.

To improve heat,wear,and corrosion resistance of the materials.

To improve magnetic and electrical properties of the material.

To impart harder surface and softer core to the component.

To make the structure of the component homogenous.

To improve ductility and toughness of the material.

To stabilize size of the component.

To facilitate diffusion process in the steel.

To obtain desired structure in the material as per specific application requirement.

Fig 23 :Classification Of heat Treatment

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5.What is Annealing Process? Types Of Annealing and Purpose of Annealing Process, Explain Any One In Detail.

Answer:Annealing

• Heating the steel to austenite phase and then cooling slowly through the transformation range. Slow cooling is generally achieved in a closed furnace by switching off the supply to the furnace.

Fig 24:Types Of Anneling

Purpose Of Annealing:

• To produce the desired microstructure having mechanical.physical,and other properties as per the requirement.

• To reduce hardness and soften the steel

• To relieve the internal stress.

• To restore the ductility and thereby facilitate further cold working

• To improve Machinability.

• To refine and make homogeneous structure by reducing structural in homogeneities

• To create complete stable structure.

• Increase or restore toughness.

6.Difference Of Annealing & Normalising Process.

Answer Table 2:Comparsiom Annelinf And Normalizing

Sr No

Annealing Process Normalizing Process

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7.What is Hardening? Types Of Hardening Process, Explain Any One Case Hardening Process.

Answer: Hardening

• It is defined as heating the steel to form uniform austenite phase and cooling the same rapidly by quenching it in a suitable medium such as water,oil,brine etc.as per the requirements.

Surface Hardening Process

surface hardening Case hardening

1.Induction Hardening 1.Carburizing

2.Flame Hardening 2.Nitriding

3.Cyniding Case Hardening

Flame Hardening:

1 Components are heated to form uniform austenite and then cooled slowly by keeping the same in the switched off furnace.

Components are heated to form uniform austenite and then cooled faster than annealing process in the steady air.

2 Amount of pearlite is less in annealed structure.

Amount of pearlite is more in normalized structure.

3 Hardness Of annealed Steel Varies from 110BHN to 230BHN

Hardness Of normalized steel varies from 120 BHN to 300 BHN

4 Annealed steels can have less strength and more elongation.

Normalized steels can have more strength and less elongation.

5 Impact strength of annealed parts less.

Impact strength of normalized parts is more.

6 Annealing process is slow and more costly.

Normalizing process is faster then annealing process.

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• This process is used for hardening stell,dye,gears,tappet screw,rocker arms and valves. This is the process of obtaining wear resistant layer on the tough core by heating the parts using gas torch.

• This process is utilized for the parts containing 0.4 % to 0.6% C.The surface is heated by the oxy acetylene flame. By heating for sufficient time the temperature of the part is raised above AC3 temperature and thereafter fast quenching is done. The surfaces of large size parts can be hardened is an advantage of this process.

• Heating cycle is less,which cause scaling. A fixed temperature can not be maintained is the disadvantage of this process.

• The parts are also damaged due to overheating or cracks are formed in it.

• Case Hardening Process: Hardness of the steel increase in carbon content. Nitrogen Content can also increase the hardness by forming hard nitrides.

• Low carbon steel are heat treated to increase carbon and nitrogen contents at the surface of the component to increse the hardness at the surface.

• Carburizing: It is the process of increasing the carbon content in the surface or case of the part. Due to this parts becomes hard. Hardness of the parts is obtained only on its surface. While its interior known as core is remains soft and tough.

1.Pack Carburizing

2.Liquid Carburizing

3.Gas Carburizing

• The Addition of carbon in low carbon steel parts surfaces to make them hard is known as carburising.This process is known as carburizing it is also called as cementation.

• In pack Or Solid Carburizing The parts along with the carburizing mixture are packed in steel box after machining.

• The carburizing mixture contains 50-70% charcoal .5-10%barium Carbonate,2-15%calcium and 3-13%sodium carbonate.

• First of all 25 mm thick layer of this mixture is provided at the bottom of the steel box.

• The parts are kept in the box such that they should not touch one another and to the box.

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Fig 34 :Flame Hardening

Then cover is place on the box and packed with the fire clay to prevent gases to flow in or Out.

• The surface of the parts which is not to be hardened are passed through a process like electroplating to make it non absorbent of carbon.

• The box is placed in the furnace and heated to 900-980°c for a period of the time 6 to 8 hours.

• After heating box along with parts is allowed to cool in the furnace it self. Austenite absorb the carbon at high temperature. So %C of surface gets increased. During the process of carburizing ,due to heating the grain near to core becomes becomes coarser. To refine these coarse grains parts are heated to 880°C temperature and then cooled by quenching in oil or allowed to cool in air.

• Grain refinement part are heated to 760-780°c and quenched in water to make its surface hard.

• By obtaining required hardness parts also becomes brittle, so part are tempered around 180-280°c.The hardness depth of 1-1.5 mm is obtained in low carbon steel containing 1.1-1.2%C.

8.Types Of Furnaces ,Classify it ,Draw Any One Heat Treatment Furnace?

Answer:

A.According to Use

1.Anneling Furnace

2.Tempering Furnace

3.Carburizing Furnace

B.According to Source Of Heat

1.Oil Fired Furnace

2.Gas Fired Furnace

3.Electric Furnace

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C.According to type of Work

1.Batch Furnace

2.Contiunous Furnace

3.Semi Countinuous Furnace

D.According to Working Environment

1.Air Furnace

2.Protective Atmosphere Furnace

3.Special Environment Furnace

4.liquid bath furnace a.Slat bath,b.Lead bath,c.Oil bath

5.Universal furnace:

6.Batch Furnaces

a.Vertical Pit Furnace

b.Horizontal Box

c.Stationary Hearth 1.Direct Fuel Fired 2.Indirect Fuel Fired.

d.Movable Hearth 1.Carbottom Furnace 2.Rotary Type Furnace

Fig 35:Heat treatment Furnace (Countonous)

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