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ME 215

ME 215. ENGINEERING MATERIALS I. Content of the course. 1) Classification of engineering materials 2) Design engineering and selection of materials 3) Material properties in tension and compression 4) Material properties in bending and shear 5) Hardness of materials and hardness testing

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ME 215

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  2. Content of the course • 1) Classification of engineering materials • 2) Design engineering and selection of materials • 3) Material properties in tension and compression • 4) Material properties in bending and shear • 5) Hardness of materials and hardness testing • 6) Fatique properties of materials • 7) Fracture and impact properties of materials • 8) Creep properties of materials There will also be subjects to be investigated and reported by groups like • 9) Materials used in medical treatments and applications • 10) Nanomaterials used in engineering • 11) Smart materials and their applications • 12) Plastic and composite materials and their principles • 13) etc

  3. Grading Policy: • 2 midterm exams (each 20%) • 5-6 lab tests + quızzes + a project report (weighing as one midterm 20%) • 1 final exam (40%) • Reference book: • Properties of materials for desing, by Prof.Dr Alp ESIN Other sources • malzeme bilgisi (MEB Yayınları) • Metal meslek bilgisi (MEB Yayınları) • Malzeme bilgisi, by MEHMET YÜKSEL (MMO Yayınları) • Mekanik tasarımda çelik ve özellikleri, by Cahit TÖRE ((MMO Yayınları)

  4. CH-1 CLASSIFICATION OF ENGINEERING MATERIALS • Materials used in engineering applications cover a range • from simple daily uses like pencils and spoons • to most complex and extreme cases like automotive vehicles, space vehicles and bio-medical uses. • Engineering materials used in applications from simple daily life to extreme ones are divided into following sub-classes:

  5. Engineering materials B) Non-metals A) Metals (and Alloys) B.1)Naturals A.2) Non-ferrous metals (iron free) B.2) Artificials A.1) Ferrous metals (iron based)

  6. A) Metals and Alloys A.2) Non-ferrous metals (iron free) A.1) Ferrous metals (iron based) • Heavy metals • Copper • Chromium • Lead etc • Cast iron: (%4>C>2) • Gray CI • White CI • Ductile CI • Malleable CI • High alloy CI • Light metals • Titanium • Beryllium etc • Steel: (%C<2) • Plain Carbon steel • Alloy steel • Refractory (high temp) metals • Tungusten • Molybdenum etc • Precious metals • Gold • Silver etc

  7. B) Non-metals • B.1)Naturals • wood • granite etc B.2) Artificials • Polymers • Rubber • Thermoplastics • Thermosets etc • Ceramics • Glass • Cermets • Composites • Metal matrix composites • Ceramic matrix composites • Polymer matrix composites

  8. Metals (ferrous and non-ferrous) are used to be the main engineering materials preferred by mechanical engineers for centruies. • The main reasons for using metals were • their abundancy (being planty) in nature, • easy processing and also • their relatively more load carrying capacity. • Artificial materials, however, took place in many applications because of their advantages like better insulation, heat resistance and weight saving. • Therefore, many different new materials were “found or derived” from other materials for certain advantages in different applications.

  9. Ferrousmetals (cast iron and steel) are still the most widely used materials in many engineering applications. • Steel, in particular, has many versions (alloys) with different advantages for different applications.

  10. Steel can serve in applications varying • from simple machine construction to extreme load bearing (carrying) applications and • from simple springy (elastic) deflection applications to high temperature resistant or corrosion resistant applications. • Steels as one of the most important engineering materials are divided into following sub-classes:

  11. Steels (%C < 2) Alloy Steels (in addition to carbon) with modest amount of other alloying elements Plain Carbon steels (Only carbon) (%C < 1.5) with limited other alloying elements

  12. Plain Carbon steels with limited alloying elements (%C < 1.5) Low carbon Steel (%C < 0.3) Medium carbon Steel (0.3<%C < 0.6) High carbon Steel (0.6<%C < 1.5) Free machining carbon Steel (with special alloys)

  13. Alloy Steels with modest amount of alloying elements Tool Steel (used for tools and dies) Stainless (rust-free) Steel (%Cr > 10.5) High strength Steel (weight saving) High strength low alloy (HSLA) Steel Iron based super alloys

  14. A-METALS AND ALLOYS Were classified as; • 1) ferrous (iron based) metals & alloys, i.e. Steels and cast irons • 2) non-ferrous metals & alloys; metals other than iron (Fe), i,e, Cu,Al,Zn,Pb etc and their alloys.

  15. FERROUS METALS AND ALLOYS • Iron is always the basic part of the ferrous metals • Iron is found in nature as “iron ore” which consist of iron oxides,carbonates and sulphides and gaunge. • Iron is obtained (produced) by reduction of iron oxides with carbon (i.e. coke) in the blast furnace. • Limestone is usually added into the blast furnace charge to remove gang i.e. SiO2 as calcium silicate slags.

  16. Pig iron Blast furnace for ıron production

  17. The product of blast furnace is called “pig iron” which is impure iron containing too much C,Mn,P,S and Si. • Pig iron is either transformed into • “cast iron” containing > 2% C or • converted into “steels” in a secondary process, where C is reduced to <2%.

  18. Pig iron Secondary process for steel production

  19. STEELS • Steels are made • by the removal of excess C and other impurities of pig iron by “oxidation” followed • by a “deoxidation” process and • addition of C and alloying elements to the “required level”. • Oxidation is carried out by blowing air or oxygen through molten pig iron in either • 1) Basic Oxygen Furnace • 2) Siemens-Martin (open heart furnace) • 3) Bessemer-Thomas furnace • 4) Electric Furnace

  20. STEELS • Scrap iron is usually converted into steel in electric arc furnaces • Steels usually contain up to 2%C,1%Mn, 0.5%Si, 0.05%S and 0.05%P

  21. Plain carbon steels and • Alloy steels are the two main groups of steels • 1-Plain carbon steels are the ones in which C is the significant alloying addition and therefore they are are termed as “plain carbon steels”. They contain upto 1.5%C and also 1.65%Mn max, 0.6%Si max, 0.6%Cu max.

  22. Plain Carbon steels with limited alloying elements (%C < 1.5) Low carbon Steel (%C < 0.3) Medium carbon Steel (0.3<%C < 0.6) High carbon Steel (0.6<%C < 1.5) Free machining carbon Steel (with special alloys) Classification of plain carbon steels

  23. A) Low carbon steels 1)Dead soft mild steels: contain <0.15%C and are very soft ,easily fabricated by cold forming and welding. used in construction where strength is not very important. 2) Mild steels: contain 0.15%-0.30%C also called structural steels. used for structure and machine applications, structural shapes i.e. Channels, angles, I-beams, etc.

  24. B) Medium carbon steels contain 0.3-0.6%C, combined properties are strength, toughness and wear resistance, used for crankshaft, axles, railway wheels and gears. • C) High carbon steels contain 0.6- 1.5%C, they have low ductility and are used for high strength steels, wire production etc. • D) Free machining carbon steels these are specially developed for fast and economic machining of parts. Machinability of the plain carbon steels is improved by addition of elements such as Pb,S,P and Te,Se,Bi.

  25. 2-ALLOY STEELS (second group of the steels) Other than carbon, they contain modest amount of other alloying elements. They are heat treated to improve some desired mechanical properties. They usually contain more than 1.65%Mn, 0.60%Si and 0.60%Cu. They have • Through hardenable grades • Carburizing grades and • Nitriding grades

  26. Some of the steel properties and alloying element effects

  27. EFFECTS OF ALLOYING ELEMENTS Some of the alloying elements and their effect on the alloy steels are: • C :increase hardness and tensile strength but decrease ductility and forging and welding properties • Mn(1.65-2.1%) increases strength, hardenability and corrosion resistance • Ni :increase strength, shock resistance, corrosion resistance and heat resistance, and lower the critical temperature for heat treatment.

  28. Cr :increase hardness, hardenability, wear resistance, corrosion resistance and heat treatment, reduce resilience and promotes formation of carbides • Mo :used in common with Mn and Cr to increase hardenability, tensile and creep strength. • Vanadium :increase hardenability • Ti :increase yield point & weldability. • Tungsten (Wolfram ) :increase hardness and tensile strength

  29. Al(max 1%) promotes nitriding properties • Si(0.6-2.2%) raises the critical temperature for heat treatment and increases resilience • Elemental Cu & Pb increase machinability. • Sulphides and nitrides increase hardness • P(max 0.03-0.05%) harmful • S(max 0.025-0.05%) harmful P and S make steel brittle and prevent hot or cold forming.

  30. HIGH ALLOY STEELS • High alloy steels are the ones specially produced with certain objectives by using again certain elements as alloying elements. • These steels are: • Tool steels • Stainless steels • High strength steels • High strength low alloy steels and • Iron based alloys

  31. Tool steels: these are clean,(i.e. no inclusion), high alloy steels produced carefully in elelctric furnaces. They usually contain Cr,V,W,Mo or Co besides C,Mn and Si. They are wear resistant, tough and have high hot hardness. This type of steels are used mainly in tools and dies. • Stainless steels: they contain minimum of 10.5%Cr. Addition of higher amount of Cr and Ni further improve corrosion resistance.They have high strength, hardness, corrosion resistance and abrassion resistance.

  32. High strength steels: these steels were developed for specific high strength applications and used for weight saving in constructions. • High strength low alloy (HSLA) steels: specially developed to improve mechanical properties and corrosion resistance while benefitting from weight saving too. • Iron based super alloys: These are used primarly for high temperature applications they are cheaper than Co and Ni based super alloys. Superalloys are used at temperatures from 540C to 1090C. Iron based superalloys are used at lower end of this range.

  33. CAST IRON • Cast iron is a four element alloy containing iron, carbon (2 to 4%),silicon and manganese. • Some cast iron types may contain additional alloying elements. • Cast iron contains large amount of carbon in the form of Fe3C (cementite) and this composition is not stable and decomposes under certain conditions: Fe3C  3Fe + C

  34. According to this breakdown of cementite, cast irons are classified as: • 1) Gray cast iron • 2) Ductile cast iron • 3) white cast iron • 4) malleable cast iron • 5) high alloy cast iron

  35. 1) Gray cast iron • Gray cast iron gives gray fracture surface hence called gray CI. • They are widely used therefore they are important in engineering. • In the manufacture of gray cast iron cementite separetes into graphite and austenite or ferrite by controlling the alloy composition and cooling rates. • Most gray cast irons contain C between 2.5-4%. • High compressive strength and excellent vibration damping of gray CI makes it well suited fpr heavy equipment and machine tool foundations.

  36. 2) Ductile (nodular) cast iron • In production of ductile (or nodular) cast iron Mg (magnesium) is used as an alloying element. • Mg causes formation of graphite in spherical or nodular forms. This operation of Mg addition to molten cast iron precipitates out carbon in the form of small spheres this, then improves some of the mechanical properties gray cast iron. • Compared to gray CI, ductile CI will have improved tensile strength, ductility and toughness

  37. 3) White cast iron • This type of cast iron is produced by a process called “chilling” (controlled cooling) which prevents graphite carbon from precipitating out. • Either gray or ductile iron can be chilled to produce a surface of white iron • In cast irons most of carbon is combined with iron as iron carbide (cementite) a very hard material, and grades of white iron depend on the amount of cementite in the surrounding structure. • white iron, so called because of its very white structure, can be formed only during solidification. • White CI’s are very hard and resistant to wear, corrosion and oxidation.

  38. 4) Malleable cast iron • This is a white cast iron that has been converted to a malleable condition by a two stage heat treatment. • They are, as the name malleable implies, more ductile and have relatively higher toughness values. • Compared to gray CI, they can be used in applications which require higher tensile strengths, ductilities and toughness. • Two basic types of malleable iron are ferritic and pearlitic. • The third type of malleable iron -martensitic-is a pearlitic or ferritic grade that has been heat treated and transformed to a martensitic structure.

  39. 5) High alloy cast iron • High alloy cast irons are ductile, gray or white irons that contain over 3% alloy content. • These irons have properties that are signifiantly different from the unalloyed irons and are usually produced by specialized foundries. • Selecting the proper metal alloy for a casting is difficult, primarily because the properties of the finished part depend strongly upon the size and the shape of the part. • This is very important to bear in mind when deciding about the casting process.

  40. DESIGNATION OF STEELS Similar to standarts of various equipments and machineries there are also various standardization bodies for steels. Examples are: • 1) American AISI & ASTM • 2) German DIN • 3) Turkish TS, MKE • 4) British BS • 5) Euronorm • etc

  41. Designations of equipments in standarts usually require some kind of criteria and steels as materials are usually specified or designated by the criteria of ; 1) process of manufacture 2) method of deoxidation 3) chemical composition and 4) mechanical properties

  42. 1)Designation by the process of manufacture The purification of pig iron into steel is accomplished by four basic processes; 1-the basic Thomas or acid Bessemer converter 2-the open heart furnace 3-the electric furnace 4-the basic oxygen furnace (which is an evolution of the steel making process) The last two (the electric furnace and the basic oxygen furnace) are the most widely used processes and are replacing the other two old type processes. The electric furnace is employed when steel free-from undesirable impurities is required

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