Metallic Materials SessionalMilitary Institute of Science & Technology (MIST) Department of Mechanical Engineering ME 292 Metallic Materials Sessional Level-2, Term-II Contact Hr: 3/2 Credit: 0.75 Name of the Experiments: 1. Introduction to Metallographic and Metallographic Sample Specimen Preparation. 2. Study of Phase Diagrams. 3. Microstudy of steels 4. Heat treatment of steels-1 5. Heat treatment of steels-2 6. Microstudy of cast irons-1 7. Microstudy of cast irons-2 Experiment # 01 Introduction to Metallographic and Metallographic Sample Specimen Preparation Objectives: 1. To provide practice in the techniques of micro specimen selection, polishing, and etching. 2. To provide initial training in the use of metallurgical microscope. Procedure: 1. Take one sample from your instructor and identify your sample by putting on an identification number. 2. Polish the specimen manually by grinding on a series of emery papers of progressively finer grade. To polish at each paper, hold the paper on top of a glass sheet with one hand while rubbing the specimen with the other hand using moderate pressure, back and forth across the abrasive surface in one direction only. This creates a series of parallel scratches or grind marks on the specimen. 3. It is naturally very important to avoid the transfer of loose abrasive particles from one paper to another. There before proceeding to the next finer paper clean thoroughly the loose abrasive particles from the specimen and from the hands. Clean each paper carefully before use to protect the quality of the polishing job. 4. During grinding on the next finer paper, hold the specimen in such a way that the new, finer set of scratches will be approximately perpendicular to the existing set of scratches. 5. After completing the paper polishing, clean the sample thoroughly with soap water and show it to the instructor. He will check its finish and indicate whether you may proceed to the final polishing step. 6. Place some alumina powder on top of the wet polishing cloth of the grinding wheel. Hold the specimen face down on the wheel under a moderate pressure slowly move in a direction opposite to the direction of the wheel. Continue final polishing until a mirror-finish is obtained. Hold the specimen quite stationary during most of the polishing operation. Before leaving the wheel at the end of the final fine polishing, rotate the specimen counter to the direction of wheel rotation to eliminate streaks caused by draught of inclusions. 7. After a mirror-finish is attained, wash the specimen and the hands and dry the specimen surface. 8. Never touch the polished surfaces with fingers at any time because skin oil and salt will deposit a film or cause tarnish, either of which will hide the structure to be observed. 9. Etch the specimen with 2 percent natal. Avoid over etching. Under etching is preferable to over etching. Re-polish till the cloudy film has been removed and surface is again showing a mirror finish. Re-etch carefully. Ask the instructor the check your etched specimen and advise you whether to proceed to examine it on the microscope or whether you need to polish and etch again. 10. Examine the optical features of a metallurgical microscope. Draw on it a broken line to show the path of rays of light from the light source to the observer’s eye. 11. Examine the microscope. Locate each of its components. Complete the following table by listing the magnifying power of each objective lens and each eye-piece. Indicate the total magnifications available on your microscope. Objective Eye-piece Total magnification available with each lens magnification magnification 1 2 3 12. Study the structure by focusing it by ‘going away’ from the lens. Using the mechanical stage movements, explore the etched surface, adjusting the focus, if necessary, as you go. Practice using both the stage control knobs simultaneously to move the specimen in various directions. Locate a good area to sketch. If your specimen does not show a good, clear structure, ask the instructor to advise you whether you should re-polish and re-etch. 13. Complete the data sheet. DATA SHEET Material: …………………………………………………………………………… Magnification: …………………………… Etchant: …………………………… Structure: ………………………………………………………………………… Before etching After etching Experiment # 02 Study of Phase Diagrams. . • Phase transformation • Change from one phase to another • E. • Occurs because energy change is negative/goes from high to low energy state • Phase boundary • Boundary between phases in a phase diagram Gibb’s Phase Rule . S S etc.Phase Diagrams • It can be defined as a diagram which contains a good number of information about the metal or its alloy. Some basic concepts • Phase • A phase of a substance is a form of matter that is uniform throughout in chemical composition and physical state • A homogeneous region with distinct structure and physical properties • “State matter which is uniform throughout not only in chemical composition but also in physical state” J.g. • It is also known as a equilibrium diagrams or constitutional diagram. Willard Gibbs • In principle. liquid or gas • A phase transition occurs at a characteristic temperature for a given pressure • Two phases are at equilibrium when their chemical potentials are equal. L S. can be isolated • Can be solid. It’s gives information only on the constitution of alloys and not on the structural distribution of the phases. F=C-P+1 Limitations of Phase Diagram 1. • Modified Gibbs Phase Rule (for incompressible systems). L S Solid freezing Tm Tm C S 0°C D Solid Cooling t Time Ideal Real Pure metal L T L S Micro-structural changes during solidification T L S m S S t . whereas alloys in practical use are rarely in equilibrium. F=C-P+2 Where. • When Temperature. The diagram shows only the equilibrium state. P= number of phases. Phase diagram usually constructed for a fixed pressure of 1 atmosphere. F= number of degrees of freedom C= number of chemical components. 2. Pressure and Composition of are independent variables in the equation of state. Solidification (cooling) curves T T A Gas Cooling For Pure metal Gas C ondensing B 100°C L Liquid Cooling Temp. Solidification (cooling) curves Alloy L Soldification begins T L L+S T S Solidification S complete Micro-structural changes during solidification Alloy L T L T L L+S T S S S t Tie Line . Phase Diagrams: Two metals completely soluble in the liquid & solid states T L L L L+S L S S 0 10 20 30 40 50 60 70 80 90 100 A %B B Composition Phase Diagrams: Two metals completely soluble in the liquid state & completely insoluble in the solid state . • It is used to determine the composition of alloy for a particular temperature. • Tie line can be defined as the horizontal temperature line parallel to the x-axis connecting two difference phase region. TA Tie line L+S TB Liquid (L) m n o L+S TE T Solid (S) Eutectic T point A B (100%) (100%) Composition (weight percentage) Phase Diagrams: Two metals completely soluble in the liquid state but only partly soluble in the solid state . T L L +L +L TE L CE Wt% particles T L L +L +L TE Proeutectic + CE A+B A B Wt%B A+B . T L L +L +L TE E A+B + CE S A Wt B %B A+B . Phase Diagrams: Alloy at various composition Liquid (L) L+A Eutectic point L+AmBn L+B T A+AmBn T A m B ) n +( +B A Bn m B (A m n +B + ) B A B Composition (weight percentage) (100%) (100%) The Iron-Carbon Diagram . (present only at extreme temperatures) .General Properties: • ferrite . stoichiometric intermetalic compound. hapends to all alloys of more than 2. over 2%C can be dissolved in it. Fairly Soft.02 wt% C in solid solution and leads to two phase mixture in most of steels. . brittle. Hard ceramic material. with 4. with low wt% C alloys (almost no engineering importance). high formability.• Austenite. • Eutectic. • Cementite (iron-carbide). most of heat treatments begin with this single phase). FCC Iron with much Carbon. only up to 0.C.C. at 1148 deg.11wt% C and they are called cast irons. alloys bellow 2.C with eutectoid composition of 0. stable form of iron below 912 deg. C). hard.77wt% C. • Eutectoid. (FCC. BCC. at 727 deg.Currie point (770 deg.3wt% C. They are steels. It is Iron with a little Carbon. at 1495 deg.C.11%C miss the eutectic reaction to create two-phase mixture.Ductile•Ferrite. atomic level nonmagnetic-to-magnetic transition • Peritectic. exact melting point unknown. high solubility of C. . Microstructures in Eutectic Systems . . . . Hypoeutectic & Hypereutectic Proeutectoid – Forms before eutectoid . Iron-carbon (Fe-c) Phase Diagram Hypoeutectoid Steel . Hypoeutectoid Steel . 77%C by cooling from austenite (FCC) changes to BCC-ferrite (max 0. Hypoeutectoid Steel • With less than 0. • Mixture of proeutectoid ferrite (white) and regions of pearlite forms. At 727deg.02%C) and excess C forms intermetalic cementite. 1000X.Eutectoid Steel Pearlite Ferrite (white) Cementite (dark) • At 0. Perlite (right). Hypereutectoid Steel .C austenite transforms in to pearlite. • Chemical crystalline solid separation gives fine mixture of ferrite and cementite.77%C from austenite by cooling transformation leads to growth of low-C ferrite growth. • Magnification 500X. At 727 deg. • Structure of primary cementite and pearlite forms.C austenite changes to pearlite. Cast Irons . • Magnification 500X. from austenite transformation leads to proeutectoid primary cementite and secondary ferrite.77%C. Proeutectoid Cementite (white) Pearlite (striped) • With more than 0. good corrosion resistance and it has good fluidity needed for casting operations.0.0% Si. less than 1. good resistance to adhesive wear (self lubrication due to graphite flakes). They have pointed edges to act as voids and crack initiation sites.000 psi is a high C-equivalent metal in ferrite matrix ).11%C or more are cast irons.• Iron-Carbon alloys of 2. • Properties: excellent compressive strength. • Si-substitutes partially for C and promotes formation of graphite as the carbon rich component instead Fe3C.2% S.0%C.0%C. White Cast Iron . • It is widely used.5-3. Class 40 would have pearlite matrix.4-1. • Microstructure: 3-D graphite flakes formed during eutectic reaction. especially for large equipment parts subjected to compressive loads and vibrations.0-4. • Sold by class (class 20 has min. outstanding damping capacity ( graphite flakes absorb transmitted energy).0%Si and 0.0- 3. tensile strength of 20.0% Mn and less than 0. 1. Gray Cast Iron • Composes of: 2. • Typical composition: 2.5-4. excellent machinability.0% Mn. 9%Si and 0.35 ksi yield strength. Excellent impact strength. 65-105 ksi tensile strength. • Spheroidal shape of the graphite nodule is achieved in each case. • It is used where a high wear resistance is dominant requirement (coupled hard martensite matrix and iron-carbide).8%Mn. Fe3C will dissociate and form irregular shaped graphite nodules.8-3. • Composition: 1-4% EL. • Ferritic MCI: 10% EL. 50 ksi tensile strength.25-0. • Ductile iron with ferrite matrix (top) and pearlite matrix (bottom) at 500X. • All of its carbon is in the form of iron-carbide (Fe3C). 45-85 ksi yield strength.5-1. Less voids and notches. • It is very hard and brittle (a lot of Fe3C). Pearlitic Malleable Cast Iron • Pearlitic MCI: by rapid cooling through eutectic transformation of austenite to pearlite or martensite matrix. Rapid cooling restricts production amount to up to 5 kg. good corrosion resistance and good machinability. 0. Thin coatings over steel (mill rolls). Not as machinable as ferritic malleable cast iron. Malleable Cast Iron • Formed by extensive heat treatment around 900 degC. It is called white because of distinctive white fracture surface. • Composes of: 1. Ductile Cast Iron .6%C. 40-90 ksi yield strength. • Attractive engineering material due to: good ductility. • Without a heat treatment by addition of ferrosilicon (MgFeSi) formation of smooth spheres (nodules) of graphite is promoted. machinability and low melting point castability. • Properties: 2-18% EL. Globular cast iron List of Metallographic Samples: 1. 60-120 ksi tensile strength. high strength. wear resistance. toughness. steel samples . Cast iron samples a. Ductile cast irons (Ferritic) f. File steels (Annealed) d. Malleable cast irons (Pearlitic) e. File steels 2. and etched carefully to reveal microstructures with optimum clarity. medium carbon steels d. Grey cast irons b. White cast irons c. a. The samples are packed and marked in neat. Mild steels (Normalized) c. File steels (Quenched) f. mild steels (Annealed) b. Malleable cast irons (Ferritic) d. File steels (Tempered) Total number of samples = 16 Please note All samples are mounted. \ Experiment # 03 . mild steels c. Heat treatment samples a. Ductile cast irons (Pearlitic) 3. File steels (Normalized) e. dead soft steels b. grinned and polished. Obtain a specimen of steel from the instructor. 2.Microstudy of Steels Objective: To study the micro constituents present in the microstructure of low carbon steels. labeling all microconstituents carefully and neatly. Procedure: 1. What will be the approximate tensile strength of the steel sample? 4. In the case of dead soft steel. Examine the specimen on the microscope. 3. Estimate the approximate relative amounts of the microconstituents present in your sample. Complete the report by answering the following questions: a) Which is the predominant constituent in the dead soft steel? What is the estimated percentage of carbon in dead soft steel you have observed? b) The matrix of the materials microstructure often plays a major role in determining the properties that the material has. Polish and etch the specimen according to the procedures as used in the previous experiment. using a magnification of X400. Reproduce the microstructure. Identify the steel by calculating the carbon content. what particular property does the matrix contribute? Explain. c) What is the predominant constituent of mild steel? How does it affect the properties of the steel? d) How does an increase in carbon affect the structure of plain carbon steels? e) Why are high carbon steels less ductile than steels of lower carbon content? For what purposes are high-carbon steels best suited? DATA SHEET . Magnification ………………… Microstructure of ………………………………… showing grains of………………..Magnification ………………… . Etched in ……………………. and …………………..Microstructure of ………………………………… showing grains of……………….. and …………………. Etched in …………………….... Etched in ……………………. Microstructure of ………………………………… showing grains of………………. and …………………. and …………………...Magnification ………………… Microstructure of ………………………………… showing grains of………………..Magnification ………………… Experiment # 04 .. Etched in ……………………... DATA SHEET . Discuss the difference in structures of annealed and normalized mild steel. Obtain a specimen of steel from the instructor for heat treatment. Observe the heat treating furnace. 3. the method of heating and measuring temperature used. e. holding and cooling cycles of heat treatment. Observe the method of packing the sample in heat treatment box and then charging into the furnace. Take the heat treated sample and grind and polish it as before to study its microstructure. 4. Indicate the purposes of annealing and normalizing. Why an accurate temperature measurement in heat treatment process is important? b. Which equipment is used in your experiment to measure temperature? Name three other temperature measure devices. Indicate the proper annealing and normalizing temperatures of mild steel and a file steel samples. 8. List the names of some common defects that you may found in heat treated steel sample. 2.Heat treatment of steels-1 Objective To understand the reasons for heat treating steels. complete the report by answering the following questions: a. Procedure: 1. Observe the programming or setting up the temperature and time for heating. 5. g. 6. Describe the function of each ingredient used to prepare the heat treatment mixture. Observe the method of cooling of sample during each heat treatment process. 9. Study the ingredients and observe the method of producing the mixture that is to be used to control the furnace atmosphere. c. the ways of doing it. 7. f. d. and to study the nature and type of resultant microconstituents that influence the properties of heat-treated steels. Draw the representative microstructure of the heat treated steel and label it. . Microstructure of annealed steel sample showing ………………………………. Experiment # 05 ...Etched in………………………Magnification………………. Microstructure of annealed steel sample showing ………………………………...Etched in………………………Magnification……………….and ………………………....and ………………………. Microstructure of annealed steel sample showing ………………………………..and ……………………….Etched in………………………Magnification………………. and to study the nature and type of resultant microconstituents that influence the properties of heat-treated steels. Take the heat-treated samples and grind and polish them as before to study their microstructures. Complete the report by answering the following questions: a) What is the principle reason of hardening a steel sample? b) Indicate why low carbon steels are not hardened? c) List the salient features of martensitic transformation. 2. Observe the method of quenching of sample after hardening. 3.Heat Treatment of Steels-2 Objective: To understand the principles of hardening and tempering operations of steel. 5. Procedure: 1. Take one hardened sample and temper it at the temperature indicated. 7. the methods of doing it. Draw the representative microstructures and label them. Obtain a specimen of steel from the instructor for heat treatment. what should be the proper tempering temperature? DATA SHEET . 4. d) Why tempering is necessary after heat treatment? e) What happens to the hardened structure during tempering? f) If you want to retain a maximum hardness. 6. holding and cooling cycles of hardening treatment. Observe the programming or setting up the temperature and time for heating. and ………………………. Microstructure of annealed steel sample showing ……………………………….and ……………………….. Microstructure of annealed steel sample showing ………………………………..and ……………………….Etched in………………………Magnification………………..Etched in………………………Magnification………………. Experiment # 06 ... Microstructure of annealed steel sample showing ……………………………….....Etched in………………………Magnification………………. using a magnification of X400. Complete the report by answering the following questions: a) What is the range of carbon percentage in cast irons? Why those materials are named as cast irons? b) How cast irons are usually classified? c) Which is the predominant constituent in grey cast iron? d) Why graphite flakes are observed in unetched conditions? e) Which properties of grey cast irons are attributed respectively by the matrix and graphite flakes? f) Why white cast irons are not used as structural materials? Name some applications of white cast irons. Procedure: 1. Polish the specimen according to the procedures as used in the first experiment. 3. Obtain two specimens of cast iron from the instructor. DATA SHEET .Microstudy of Cast Irons-1 Objective: To study the microconstituents present in the microstructure of grey cast irons and white cast irons. labeling all microconstituents carefully and neatly. 2. Reproduce the microstructure. Examine the specimens under the microscope. both etched and unetched conditions. and ………………….Magnification ………………… Experiment # 07 . Etched in …………………….. and ………………….Magnification ………………… Microstructure of ………………………………… showing grains of………………. Etched in …………………….. Etched in ……………………..Magnification ………………… Microstructure of ………………………………… showing grains of………………. and …………………....... Microstructure of ………………………………… showing grains of………………. Examine the specimens under the microscope. second and third stages of malleableising heat treatment. 3. Obtain two specimens of cast iron from the instructor.Microstudy of Cast Irons-2 (Microstudy of Malleable and Ductile Cast Irons) Objective: To study the microconstituents present in the microstructures of malleable cast irons and ductile cast irons. 2. silicon and manganese contents between malleable and ductile cast irons. b) Why cast irons are used as raw material for producing malleable irons? c) Discuss what happens during first. using a magnification of X400. Complete the report by answering the following questions: a) Indicate the difference. f) Why desulphurization treatment is necessary during ductile iron production? g) Summarize a comparison between malleable and ductile irons about their quality. Procedure: 1. Reproduce the microstructure. d) Why bull’s eye structure is produced? e) Indicate the functions of magnesium in producing ductile iron. Polish the specimen according to the procedures as used in the first experiment. both etched and unetched conditions. labeling all microconstituents carefully and neatly. DATA SHEET . . Etched in …………………….Magnification ………………… .Magnification ………………… Microstructure of ………………………………… showing grains of………………... Etched in ……………………. and …………………... Etched in …………………….Magnification ………………… Microstructure of ………………………………… showing grains of………………..Microstructure of ………………………………… showing grains of………………. and ………………….. and …………………...