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www.padeepz.net ME6403

ENGINEERING MATERIALS AND METALL URGY

LT P C 3 0 0 3

OBJECTIVES: · To impart knowledge on the structure, properties, treatment, testing and applications of metals and non-metallic materials so as to identify and select suitable mat erials for various engineering applications. UNIT I ALLOYS AND PHASE DIAGRAMS 9 Constitution of alloys – Solid solutions, substit utional and interstitial – phase diagrams, Isomorphous, eutectic, eut ect oid, peritectic, and perit ectoid reactions, Iron – carb on equilibrium diagram.Classification of steel and cast Iron microstructure, properties and application. 10 UNIT II HEAT TR EATMENT Definition – Full annealing, stress relief, recrystallisation and spheroidising – normalising, hardening and Tempering of steel. Isothermal transformation diagrams – cooling curves superimposed on I.T. diagram CCR – Hardenability, Jominy end quench test -Austempering, martempering – casehardening, carburizing, Nitriding, cyanidin g, carbonitriding – Flame and Induction hardening – Vacuum and Plasma hardening . . UNIT III FERROUS AND NON-FERROUS METALS 9 Eff ect of alloying additions on st eel- α and β stabilisers– stainles s and tool steels – HSLA, Maraging st eels – Cast Iron - Grey, whit e, malleable, spheroidal – alloy cast irons, Copper and copper alloys – Brass, Bronze and Cupronickel – Aluminium and Al-Cu – precipitation strengthening treatment – Bearing alloys, Mg-alloys, Ni-based super alloys and Tit anium alloys. UNIT IV NON-METALLIC M ATERIALS 9 Polymers – types of polymer, commodity and engineering polymers – Properties an d applications of various t hermosetting and thermoplastic polymers (P P, PS, PVC, PMMA, PET,PC, PA, ABS, PI, PAI, PPO, PPS, PEE K, PTFE, Polymers – Urea and Phenol formaldehydes)- Engineering Cer amics – Properties and applications of Al2O3, SiC, Si3N4, PSZ and SIALON –CompositesClassifications- Metal Matrix and FRP - Applications of C omposites. UNIT V MECHANICAL PROPERTIE S AND DEFORMATION MECHANISMS 8 Mechanisms of plastic deformation, slip and twinning – Types of fracture – Testing of materials under tension, compression and shear loads – Hardness tests (Brinell, Vickers and Rock well), had r ness t ests, Impact test lzod and charpy, fatigue and creepfailure mechanisms. TOTAL : 45 PERIODS OUTCOMES: · Upon completion of this course, the students can able t o apply the differ ent materials, their processing, heat treatments in suitable application in mechanical engineering fields. TEXT BOOKS: 1. Avner,, S.H., “Introduction to Physical Met allurgy”, McGraw Hill Book C ompany,1994. 2. W illiams D Calli ster, “Mat erial Science and Engineering” W iley India Pvt Ltd, R evised Indian Edition 2007 REFERENCES: 1. Raghavan.V, “Mat erials Science and Engineering”, Prentice Hall of I ndia Pvt. Ltd., 1999. 2. Kenneth G. Budinski and Michael K. Budinski, “Engineering Mat erials”, Prentice Hall of India Private Limit ed, 4t h Indian Reprint 2002. 3. Upadhyay. G.S. and Anish Upadhyay, “Mat erials Science and Engineering”, Viva Books Pvt . Ltd., New Delhi, 2006. 4. U.C.Jindal : Mat erial Science and Metallurgy, " Engineering Materials and Met talurgy", First Editio n, Dorling Kindersley, 2012

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www.padeepz.net ME6403

ENGINEER ING MA TERIALS AND METALLURGY

Course Material Index S.No

1

2

3

4

5

6

CONTENTS

Un it I ALLOYS AND PHASE D IAGRAMS Un it II HEAT TREATMENT

Un it III FERROUS AND NONF ER ROUS ME TALS

Un it IV NON METALLIC MATERIA LS

Page No

4

23

64

66

Un it V MECHANICAL PROPERTIES AND TES TING M E CH AN ISM S

115

TWO MARKS QUESTIONS WITH ANS WER

1 35

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www.padeepz.net UNIT – I ALLOYS AND PHAS E DIAGRAMS 1. INTRO DUCTION Phase diagrams provide a graphical means of presenting the results of experimental studies of complex n atural processes, such that at a given temperature and pressu re for a specific s ystem at equilibrium the phase or phases present can be d etermined. SYSTEM - An y portion of the universe which is of in terest and can be s tudied experimentally . PHASE - any particular portion of a sys tem, which is phys ically hom ogeneous, has a specifi c compositi on, and can be mechanically rem oved or separated from any other phase in the system. e.g. A sys tem con taini ng a mixture of ol and pl in equilibrium cont ains two ph ases - ol and pl . In pe trology we gen erally deal with primary phases - any crys tallin e phase which can coexist with li quid, i.e . it formed/crystallized directly from the liquid . EQUILIBRIUM - The conditi on of minimum energy for the sys tem such that th e stat e of a reaction will not change with time provided that pressure and temperature are kept constant. COMPONE NT - the smallest number of independent v ariable chemical constituents necessary to defin e any phase in the system . •

Com ponents may be ox id es, elements or minerals, dependant on the sys tem being examined .

For ex am ple, experiments carried out in the H 2O system, show that the ph ase s which appear over a wide temperatur e and pressure range are ice, liquid water and water v ap our. Th e composition of each phase is H2O and on ly on e che mical parameter or component is requ ired to describe the co mposition of each ph ase.

THE PHASE RULE For a system at equilibriu m the phase ru le relat es: • • • •

P = nu mber of ph ases that can coex ist, to C = number of comp onents making up the phases, and F = d e g r e e s o f f r e e do m . Where these three var iables are related in the equation P+F=C+2

The degrees of freedom represent the environment al conditions which can b e independently var ied without changing the nu mber of phases in the sys tem . Conditions include:

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www.padeepz.net • • • • • •

Temperature, Pressure, Chemical Composition, pH, E h, Ox ygen Fugacity.

Therefore th e maximum number of phase which can stably coexist in a on e co mponen t system is three, and they do so on ly if there are no degrees of freedom . Definitions: PHASE: a homogenous, phys ically distinct portion of the sys tem , e.g., liquid, solid, gas . COMPONENT: pure che mical substance, e.g., element or compound. H 20 is one com ponen t, a com pound . DEGR EE OF FREEDOM : state var iab les wh ich can be changed continuously and independently, e.g., pressure, temperature, com pos ition. CONSTITUENT: the association of ph ases in a recognizably distinct fashion with a distinct m elting po int, e.g., eutect ic. COMPOSITION: fracti on of one com ponent to all the co mponents. May b e i n terms of wei ght or atoms. Ph ase Rule of W illard Gibbs Let P = number of phases Let F = number of degrees of freedom Let C = nu mber of componen ts These are r elated by the phase rule: P+F=C+2 1.1 Phase Diagram The phase diagram is a map s howing wh ich phases of a material are in equilibrium at any given temperature, com position, and pressure. It is drawn fro m expe rim ent al data and may b e used to determine at equilibr iu m: the number of phases present (P) th e composition of each ph ase (X) the amount of each phase present as a functi on of temperature and composition .

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www.padeepz.net Of particular int erest to integrated circuit fabricati on is the binary par tial solid solubility ph ase d iagr am. The solidus curve can be used for determining the solid solubility limit (N sl) used in diffusion problems .

Figur e -1.1 wher e: L = liqu id A+B fully intermixed α = im pure solid A ( A doped with B) β = impure solid B ( B doped with A) L+α = li quid A+B, with solid α L+β = li quid A+B, with solid β solidus = maximum compositi on where a solid soluti on (α or β ) can ex ist Note in the figure tha t for a binary phase diagram th ere can exist three degrees of freedom ( two components (C=2), at least one phase must be present (P=1), so F=3). In order to present the diagram elegantly, the sys tem is shown for pressure = 1 atmosphere (isob aric), leaving temperature for the ve rtical axis and composition for the hor izon tal axis . The composition, X, of a system can b e defined two ways .

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www.padeepz.net Traditional

where w = weigh t Modern

where n = mo les Given the initial composition (x i) and weight (wA + wB) of a binary system, the composition and weight of each phase can b e calculat ed. For the liquid ( L), α, and β cas es, the compositi on and weight are the same as the initial composition and weight (onl y one ph ase is present). The two phase regions (L+α and L+β) require th e use of the Lever Rule to calcu late the weight and co mposition of each phas e (solid and liquid). Lever Ru le

where w S = w eigh t of the solid (α or β) wL = weight of the liquid (liquid A+B) xi = original compos ition xS = co mpos ition of the solid (α or β) xL = composition of the liquid (liquid A+B) xS and x L are found from the phase d iagram - xS correspo nds to the in terse ction of th e solidus curve with the system temperature and is read from the horizontal axis - xL corresponds to the intersecti on of the liquidus curve with the sys tem te mperature and is read from the ho rizontal axis

1.2 The Iron- Carbon Equilibrium Dia gr am A s tudy of the constitution and structure of all steels and irons must f irst start with the iron-carbon equilib rium diagram. Many of th e basic features of this sys tem (Fig. 1) influence the behavior of even the most complex alloy steels. For example, the phases found in the s imple binary Fe-C system persist in complex steels, but it is necessary to examine the effects alloyi ng elem ents have on the

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www.padeepz.net form ation and properties of these phases. The iron-carbon diagram provid es a valuable found ation on which to build knowledge of both plain carbon and allo y s teels i n their immense var iety . It sh ould first be pointed out th at th e norm al equilibrium diagram really represents the m etastable equilibrium between iron and iron carbid e (cementite). Cementite is m etas table, and the true equilibrium should be between iron and graphite. Although graphite occurs extens ively in cas t irons (2-4 wt % C), i t is usually diff icult to obtain this equilibrium phase i n steels (0.03-1.5 wt %C). Therefo re, the m etastable equilibrium between iro n and iron carbide should b e cons idered, because it is relevant t o the behavior of most s teels in practice . The much larger phase field of γ-iron (aus tenite) compared with th at of α-iron (ferrite) reflects the much greater sol ubility of carbon in γ-iron, with a maximum v alue of just over 2 wt % at 1147°C (E, Fig .1) . This high solubility of carbon in γ- iron i s of ex treme impor tance in heat treatment, when solution treatment in the γ-regi on follow ed by rapid quenching to room temperature allows a supers atu rated solid so lution of carbon in iron to be formed. The α-iron phase fiel d is sev erely restricted, with a maximum carbon solubility of 0.02 wt% at 723°C (P), so ov er the carbon range encountered in s teels from 0. 05 t o 1.5 wt%, α-iron is normally asso ciated with iron c arbide in one form or another. Similarly, the δ-phase field is very restricted between 1390 and 1534 °C and disappears completely wh en th e c arbon con tent reaches 0.5 wt% (B) . There are s everal temperatures or c ritical points in the diagram, which are important, both from the basic and from the practical point of view. • •

•

Firstly, th ere is the A 1, temperature at whi ch the eutectoid reaction oc curs (P-S-K), which is 723°C i n the bin ary d iagr am. Secondly, there is the A 3, temperature when α-iron transforms to γ-iron. For pure iron this occurs at 910°C, bu t the transformation temperature is progressivel y low ered along the line GS by the addition of carbon. Th e third point is A 4 at which γ-iron tr ansforms to δ-iron, 1390° C in pure iron, hu t this is raised as carbon is added. The A2, point is the Curie point when iron chang es from the ferroto the p aramagnetic condition. This temperature is 769°C for pure iron, but no change in crys tal stru cture is involved. The A 1, A3 and A4 points are easily d etected b y thermal an alysis or dilatome try during cooling or heating cycles, and some hysteresis is observed. Consequently, three values for each point can be obtained. Ac for heating, Ar for cooli ng and Ae (equilibrium}, but it s hould be emphasized that th e Ac and Ar values will be sensitive to the rates of heating and cooling, as well as to the presence of allo ying elem ents.

The great difference in carbon solubility be tween γ- and α-iron leads normally to the rejecti on of carbon as iron carbide at the bounda ries of the γ phase field . Th e transformation of γ to α - iron occurs via a eute ctoid reacti on, which p la ys a dominant role in heat treatment .

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Figur e 1. 2 The eutectoid temper ature is 723°C whil e the eutectoid compositi on is 0.80% C(s). On cooling alloys containing less th an 0,80% C slow ly, hypo-eutectoid ferrite is formed from aus tenite in the range 910-723°C with enrichment of the res idual aus tenite in carbon, until at 723°C the remaining austenite, now containing 0.8% carbon transforms to pearlite, a lamellar mixture of ferrite and iro n carbide (cem entite). In austenite with 0,80 to 2,06% carbon, on cooling s lowly in the temperature interval 1147°C t o 723° C, cementit e f irst forms progressively dep leti ng the austenite in carbon, until at 723 °C , the austeni te con ta ins 0.8% c arbon and transforms to pe arli te.

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www.padeepz.net Steels with less than about 0.8% carbon are thus h ypo-eutectoid alloys with ferrite and pearlite as the prime constituents, the relative volume fractions b eing determined by the lever rule which s tates th at as the carbon content is increased, the volume percentage of pearlite increases, until it is 100% at the eutectoid co mposition. Abov e 0.8% C, cementite becom es the h yper-eutectoid phase, and a similar var iation in volume fraction of cementite and p ear lite occurs on this sid e of the eutectoid compos ition . The three ph ases, f errite, cementite and pearlite are thus the principle constituents of the infrastructure of plain carbon s teels, provided they have been subjected to relatively slow cooling rates t o avoid the formation of m etastable phases . The austenite- ferrite transformation Under equilibrium conditions, pro-eutectoid ferrite will form in iron-carbon alloys containing up to 0.8 % carbon. The reacti on occu rs at 910° C in pure iron, but takes place between 910°C and 723°C in iron-c arbon alloys. However, by quen chi ng from th e austenitic state to temperatures below the eutectoid temperature A e 1, ferrite can be formed down to temperatures as low as 600°C . There are pronounced morphological changes as the transformation temperature is lowered, which it should be emphasized apply in general to hypo-and hyper-eutectoid phases, alt hough in each case there will be var iations due to th e pre cise cryst allograph y of the phases involved. For example, the same principles apply to the form ati on of cementite from austenite, but it is not difficult to distinguish ferr ite from cementi te morphol ogically. The austenite-cement it e transformation The Dube classification applies equally well to the various morphologies of cementite formed at progressively low er transformation temperatures. The initial dev elopment of grain boundary allotriomorphs is v ery similar to that of ferrite, and the growth of side pla tes or Widmans taten cementite follows the same pattern. The cementi te p lates are more ri gorously crystallograph ic in form, despite the fact that the orientati on relationship with austenite is a more complex one . As in the case of ferrite, mos t of the side pl ates originate from grain boundary allotriomorphs, but in the cementite reacti on more side plates nu cleate a t twin boundaries in austenite . The austenite-pearlit e reaction Pe arlite is probably the most famil iar micr o s tructural fe ature in the who le science of m etallography . It was discovered b y Sorby over 100 years ago, who correctly assumed it to be a lamellar mix ture of iron and iron carbide. Pearlite is a very common constituent of a wide v ar iety of steels, where it provides a substantial contr ibution to strength. Lamellar eutectoid s tructures of this typ e are widespread in metallurgy, and frequently pearlite is used as a generic term to describe them .

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www.padeepz.net These structures have much in comm on with th e cellular precipitation reactions. Both t ypes of reaction occur by nucleati on and growth, and are, therefore, diffus ion controlled. Pearlite nuclei occur on aus tenite grain boundaries, but it is clear that they can also b e associ ated with bot h proeutectoid ferrit e and cem entite. In commercial s teels, pearlite nodules can nucleate on inclus ions .

1.3 Classification of Carbon and Low-Alloy Steels Abstra ct: The Amer ican Ir on and Steel Institute (AIS I) defines carbon steel as follows: Steel is cons idered to be carbon steel when no minimu m content is specified or required for chromium, cobalt, columbium [ni obium], molybdenum, nickel, titanium, tungs ten, vanadium or zirconium, or any other element to be added t o obtain a d esired alloying effect; when the s pecified minimum for copper does not ex ceed 0.40 per cent; or when the maximum content specified for any of the following elements does no t exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60. Steels can be cl assified b y a variety of different sys tems depending on: • • • • • • • • •

The composition, such as carbon, low-allo y or s tainless steel. The manufacturing m ethods, such as open heart h, basic ox ygen process, or electri c furn ace methods . Th e f inishing met hod, such as hot rolling or cold rolling The produ ct form, such as bar p late, sheet, strip, tubing or s tructural shape The deoxidation practice, such as killed, semi-killed, capped or r immed steel The micros tructure, such as f erritic, pearlitic and martensitic Th e required strength level, as specified in AS TM s tandards The heat treatment, such as annealing, quenching and tempe ring, and thermomechan ical processing Quality d escripto rs, such as forging quality and commercial quality.

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Figur e 1.3 Carbon Stee ls The American Iron and Steel Institute (AISI) defin es carbon s teel as follows: Steel is considered to be carbon s teel when no minimum content is specif ied or required for chromium, cobalt, columbium [ni obium], mol ybdenum, nickel, titanium, tungs ten, vanadium or z irconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 per cent; or when the maximum content specified for any of the following elements does not ex ceed the percentages noted: mangan ese 1. 65, silicon 0.60, copper 0.60. Carbon steel can be classif ied, according to various deoxidation practices, as rimmed, capped, semikilled, or killed s teel. Deoxidation practice and the steelmaking process will have an effect on the properties of the s teel. However, v ar iations in carbon have the gr eatest effect on mech an ical

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www.padeepz.net properties, with increasing carbon content leading to increased hardness and strengt h. As such, carbon steels are gen erally categor ized ac cording to th eir carbon con tent....