Ferrous and non ferrous alloys by Hari Prasad

All important Ferrous alloys and Non-ferrous alloys are thoroughly discussed with their microstructures

1. Ferrous and Non-ferrous alloys Unit – 7

2. Ferrous metals and alloys What is a ‘ferrous metal’ or ‘ferrous alloy’? It is simply a metal or alloy that contains Iron (the element ferrous) as the base (starting) metal. 26 th element  Iron or Ferrous  55.85 Atomic Mass

3. General Categories of Ferrous Metals and Alloys Carbon and alloy steels Stainless steel Tool and Die steel Cast Irons Cast Steels **Ferrous tools first appear about 4000 to 3000 BC, made from meteoritic iron. Real ironworking started in about 1100 BC in Asia Minor, and started the Iron Age.

4. Production of Iron and Steel

5. Raw Materials for Production Iron Ore Limestone ----------  Coke

6. Iron Ore Abundant, makes up 5% of earth’s crust Is not found in ‘free state’, must be found in rocks and oxides, hence Iron ore. After mining, the ore is crushed and the iron is separated, then made into pellets, balls or briquettes using binders, such as water. The pellets are typically 65% iron, and about 1” in diameter.

7. Coke Coke is formed by heating coal to 2100*F (1150 C), then cooling it in quenching towers. You need more than Iron? Why coke is used… 1. Generates high heat, needed in order for chemical reactions in iron making to take place. 2. Produces CO (carbon monoxide) which reduces iron-oxide to Iron.

8. Lastly, Limestone Limestone (calcium carbonate) is used to remove impurities. When the metal is melted, limestone combines with impurities and floats to the top of the metal, forming slag . The slag can then be removed, purifying the iron.

9. Ferrous alloys can be broadly classified into 2 groups: Steels (C% is <2.1) Cast iron (C% is >2.1-6.67) Steels have carbon in the combined form (austenite, cementite etc.) Cast irons have carbon in the free form as graphite These ferrous alloys are not only iron and carbon alloys, few other alloying elements are also added for special properties

10. Steels Steels can be classified in many ways, the basic classification of steel according to: Types of steel based upon deoxidization process Carbon content Grade Method of manufacture Applications Standard institutions

11. Killed – Semi-Killed – Rimmed Steel Killed Steel – This is a fully deoxidized steel, and thus, has no porosity. This is accomplished by using elements like aluminum to de-oxidize the metal. The impurities rise and mix with the slag. It is called killed because when the metal is poured it has no bubbles, it is quiet. Because it is so solid, not porous, the ingot shrinks considerably when it cools, and a “pipe” or “shrinkage cavity” forms. This must be cut off and scrapped.

12. Killed – Semi-Killed – Rimmed Steel Semi-Killed Steel : This is practically the same as killed steel, with some minor differences. It is only partially de-oxidized, and therefore, is a little more porous than killed steel. Semi-Killed does not shrink as much as it cools, so the pipe is much smaller and scrap is reduced. It is much more economical and efficient to produce.

13. Killed – Semi-Killed – Rimmed Steel Rimmed Steel : This is produced by adding elements like aluminum to the molten metal to remove unwanted gases. The gasses then form blowholes around the rim. Results in little or no piping. HOWEVER, impurities also tend to collect in the center of the ingot, so products or rimmed steel need to be inspected and tested.

14. Carbon Steels Medium carbon

15. Low carbon steel These steels contain less than about 0.25 wt % C These unresponsive to heat treatment because of very less amount of martensite Can be strengthened by cold work Microstructures consist of ferrite and pearlite constituents these alloys are relatively soft and weak but have outstanding ductility and toughness; in addition, they are machinable, weldable, and, of all steels, are the least expensive to produce Applications B ridges , towers, support columns in high-rise buildings, and pressure vessels

16. Medium Carbon Steel These steels have 0-25 – 0.6 wt % C It is stronger than low carbon steel but less tougher than it These alloys may be heat-treated by austenizing, quenching, and then tempering to improve their mechanical properties These steels are often called machinery steels Applications These are used for making camshafts, connecting rods, gears, piston rods, etc.

17. High Carbon Steels These steels have 0.6 – 2.1 wt % C These are mainly tool steels They have very good hardness and wear resistance values The tool and die steels are high-carbon alloys, usually containing chromium, vanadium, tungsten, and molybdenum. These alloying elements combine with carbon to form very hard and wear resistant carbide compounds (e.g., Cr 23 C 6 , V 4 C 3 , and WC These steels are utilized as cutting tools and dies for forming and shaping materials, as well as in knives, razors, hacksaw blades, springs, and high-strength wire

18. High Carbon Steel Nails

19. High alloy Steels Alloying elements are added to steel for many purposes: T o i mprove strength To increase the hardenability To improve wear and abrasion resistance To improve oxidation and corrosion resistance To increase high temperature resistance To increasing the toughness with retaining strength

20. Alloying Elements used in Steel Manganese ( Mn ) combines with sulfur to prevent brittleness >1% increases hardenability 11% to 14% increases hardness good ductility high strain hardening capacity excellent wear resistance Ideal for impact resisting tools

21. Alloying Elements used in Steel Sulfur (S) Imparts brittleness Improves machinability Okay if combined with Mn Some free-machining steels contain 0.08% to 0.15% S Examples of S alloys: 11xx – sulfurized (free-cutting)

22. Alloying Elements used in Steel Nickel (Ni) Provides strength, stability and toughness, Examples of Ni alloys: 30xx – Nickel (0.70%), chromium (0.70%) 31xx – Nickel (1.25%), chromium (0.60%) 32xx – Nickel (1.75%), chromium (1.00%) 33XX – Nickel (3.50%), chromium (1.50%)

23. Alloying Elements used in Steel Chromium (Cr) Usually < 2% increase hardenability and strength Offers corrosion resistance by forming stable oxide surface typically used in combination with Ni and Mo 30XX – Nickel (0.70%), chromium (0.70%) 5xxx – chromium alloys 6xxx – chromium-vanadium alloys 41xxx – chromium-molybdenum alloys Molybdenum (Mo) Usually < 0.3% increase hardenability and strength Mo-carbides help increase creep resistance at elevated temps typical application is hot working tools

24. Alloying Elements used in Steel Vanadium (V) Usually 0.03% to 0.25% increase strength without loss of ductility Tungsten (W) helps to form stable carbides increases hot hardness used in tool steels

25. Alloying Elements used in Steel Copper (Cu) 0.10% to 0.50% increase corrosion resistance Reduced surface quality and hot-working ability used in low carbon sheet steel and structural steels Silicon (Si) About 2% increase strength without loss of ductility enhances magnetic properties

26. Alloying Elements used in Steel Boron (B) for low carbon steels, can drastically increase hardenability improves machinability and cold forming capacity Aluminum (Al) deoxidizer 0.95% to 1.30% produce Al-nitrides during Nitriding

27. Cr, W, Ti, V, Mo, Mn Si, Co, Al, Ni Mn, Ni, Co, Cu Cr, W, Mo, Si

28. Effect of alloying elements on steel Elements which tend to form carbides: Chromium, Tungsten, Titanium, Vanadium, Molybdenum, Manganese etc. Elements which tend to graphitize carbon: these elements are added to oppose the formation of carbides and they stabilize the carbon to occur in its free form as graphite. E.g.: Si, Co, Al, Ni etc. Austenite stabilizers: these elements raise the peritectic point, increase the austenite range, and stabilize the austenite. E.g. Mn, Ni, Co, Cu

29. Effects of Elements on Steels Boron : Improves hardenability without the loss of (or even with some improvement in) machinability and formability. Calcium : Deoxidizes steels, improves toughness, and may improve formability and machinability. Carbon : improves hardenability, strength, hardness, and wear resistance; it reduces ductility, weldability, and toughness. Cerium : controls the shape of inclusions and improves toughness in high-strength low alloy steels; it deoxidizes steels. Chromium : improves toughness, hardenability wear and corrosion resistance, and high-temperature strength; it increases the depth of the hardness penetration resulting from heat treatment by promoting carburization. Cobalt : improves strength and hardness at elevated temperatures.

30. Effects of Elements on Steels Copper : improves resistance to atmospheric corrosion and, to a lesser extent, increases strength with little loss in ductility; it adversely affects the hot-working characteristics and surface quality. Lead : improves machinability; it causes liquid-metal embrittlement. Magnesium : has the same effects as cerium. Manganese : improves hardenability, strength, abrasion resistance, and machinability; it deoxidizes the molten steel, reduce shot shortness, and decreases weldability. Molybdenum : improves hardenability, wear resistance, toughness, elevated-temperature strength, creep resistance, and hardness; it minimizes temper embrittlement.

31. Effects of Elements on Steels Nickel : improves strength, toughness, and corrosion resistance; it improves hardenability. Niobium (columbium): imparts fineness of grain size and improves strength and impact toughness; it lowers transition temperature and may decrease hardenability. Phosphorus : improves strength, hardenability, corrosion resistance, and machinability; it severely reduces ductility and toughness. Selenium : improves machinability. Silicon : improves strength, hardness, corrosion resistance, and electrical conductivity; it decreases magnetic-hysteresis loss, machinability, and cold formability.

32. Sulphur : Improves machinability when combined with manganese; it lowers impact strength and ductility and impairs surface quality and weldability. But decreases the high temperature strength. Tantalum : has effects similar to those of niobium. Tellurium : improves machinability, formability, and toughness. Titanium : improves hardenability; it deoxidizes steels. Tungsten : has the same effects as cobalt. Vanadium : improves strength, toughness, abrasion resistance, and hardness at elevated temperatures; it inhibits grain growth during heat treatment. Zirconium : has the same effects as cerium

33. High alloyed steels Tool steels Stainless steels

34. Tool and die steels are alloyed steels design for high strength, impact toughness, and wear resistance at normal and elevated temperatures. High-speed steels Maintain their hardness and strength at elevated operating temperatures. There are two basic types the M-series and T-series

35. Tool and Die Steels M-series contain 10 % molybdenum and have higher abrasion resistance than T- series T- Series contain 12 % to 18 % tungsten. They undergo less distortion in heat treatment and are less expensive than the M-series. M- series steel drill bits coated with titanium

36. Dies are tools used for drawing wire, and for blanking, bending, cutting, machine forging, and embossing. . H-series (Hot-working steels) for use at elevated temperatures . They have high toughness and high resistance to wear and cracking. S-series (shock resisting steels) designed for impact toughness.

37. Defining property AISI-SAE grade Significant characteristics Water-hardening W Cold-working O Oil-hardening A Air-hardening; medium alloy D High carbon; high chromium Shock resisting S High speed T Tungsten base M Molybdenum base Hot-working H H1–H19: chromium base H20–H39: tungsten base H40–H59: molybdenum base Plastic mold P Special purpose L Low alloy F Carbon tungsten

38. Steel specifications The steels are sold with standard specifications and associated notations Some knowledge of the specifications is essential These specifications and notations may vary from country to country In India not only the knowledge the of the Indian standard specifications is essential, but the familiarity with American, British , etc. standards is essential

39. Indian standard specifications The steels have been classified on the basis of properties, and the chemical compositions Code designation based on Mechanical properties E.g. Fe E 210 – steel with minimum yield strength = 210N/mm 2 St E 250 – steel with minimum yield strength = 250 kg/ mm 2 Code designation based on chemical composition E.g. C15 – C=0.15% 30C5 – C=0.30; Mn =0.5% 37Mn2 – C=0.37%; Mn =2.0%

40. AISI/SAE Specifications The American Iron and Steel Institute and Society of Automotive Engineers have cooperated together and have similar specifications based on chemical compositions of the steel. The specifications normally have four numerical digits (sometimes 5 digits) A=Alloy steel, basic open - hearth B=carbon steel, acid bessemer C=carbon steel, basic open-hearth D=carbon steel, acid open-hearth E= electric furnace steel

41. AISI CXXXX: is the basic open hearth carbon steel due to the letter prefix ‘C’. The first digit of the numerical represents the following types of steels 1= Carbon steel 2= Ni steel 3= Ni-Cr Steel 4= Mo steel 5= Cr steel 6= Cr-V steel 7= W steel 8= Ni-Cr-Mo(Low)- Triple alloy steel 9= Si- Mn Steel

42. AISI A X X XX Indicates the method of steel making Type of steel % of main alloying element Indicate Carbon points

43. Stainless Steels Excellent corrosion resistance Contain 12 to 30% Chromium Cr oxidizes easily and forms a thin continuous layer of oxide that prevents further oxidation of the metal Cr is a ferrite stabilizer Austenite is restricted to a small region of the phase diagram Ferritic Stainless Steels are essentially Fe-Cr Alloys Ferrite phase (bcc structure) Inexpensive, high strength

44. Austenitic Stainless Steels Nickel is an austenite stabilizer. The addition of both Cr and Ni results in the austenite ( g , fcc ) phase being retained to room temperature The austenite phase is very formable ( fcc structure) Ni makes these alloys expensive Martensitic Stainless Steels Have both Cr and C There is more Cr than in ferritic SS since Cr tends to form Cr 23 C 6 , which removes available Cr for corrosion protection Can be heat treated to high strength

45. Stainless Steels The reason for the name stainless is due to the fact that in the presence of oxygen, the steel develops a thin, hard, adherent film of chromium. Even if the surface is scratched, the protective film is rebuilt through passivation. For passivation to occur there needs to be a minimum chromium content of 10% to 12% by weight.

46. Magnetic alloys Magnetic alloys are the combination of Iron, Nickel, and Cobalt They are classified into: Soft magnetic materials: where the hysteresis loop is very thin and these alloys posses high permeability (used in transformer cores). E.g. Permalloy (45%Ni) Hard magnetic materials: are those whose hysteresis loop gives a large area under the B-H Curve. These all are used for permanent magnetic materials and used for magnetic poles for alternators and motors E.g. Alnico= Ferrous alloy with Al, Ni, Co It has high magnetic coercivity (resistance to loss magnetism)

47. Cast Irons Fe-C alloys with 2-4%C 1-3% Si is added to improve castability Phase diagram shows graphite rather than Fe 3 C since C may be present in the form of both graphite and cementite Temperatures and compositions are different from the Fe-Fe 3 C diagram Features: Low melting temperature (1153ºC to 1400ºC) Low shrinkage Easily machinable Low impact resistance Low ductility

48. Gray Cast Iron Gray iron 2.5-4% Carbon graphite flakes weak & brittle under tension stronger under compression excellent vibrational dampening wear resistant High fluidity Used for pressure vessels, clutch plates, base structure for machines

49. Ductile Iron (SG) Ductile iron (SG) add Mg or Ce graphite in nodules not flakes matrix often pearlite - better ductility

50. White iron <1wt% Si so harder but brittle 1.8-3.2% Carbon more cementite Fe 3 C-light phase, Pearlite dark phase Fracture surface – whitish surface Malleable iron heat treat at 800-900ºC graphite in rosettes more ductile

51. Nonferrous Alloys Non Ferrous Alloys • Al Alloys -lower r : 2.7g/cm 3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip . strengthened ( struct . aircraft parts & packaging) • Mg Alloys -very low r : 1.7g/cm 3 -ignites easily - aircraft, missiles • Refractory metals -high melting T - Nb , Mo, W, Ta • Noble metals -Ag, Au, Pt - oxid ./corr. resistant • Ti Alloys -lower r : 4.5g/cm 3 vs 7.9 for steel -reactive at high T - space applic. • Cu Alloys Brass : Zn is subst. impurity (costume jewelry, coins, corrosion resistant) Bronze : Sn, Al, Si, Ni are subst. impurity (bushings, landing gear) Cu-Be : precip. hardened for strength

52. Over view of Non-Ferrous alloys

53. Non-Ferrous alloys Among the above Al, Mg, and Ti alloys are called “Light Alloys”

54. Copper and its alloys

55. Properties of copper Excellent electrical conductivity: next to silver Excellent thermal conductivity: used in heat exchangers, boiler tubes and parts Good ductility and malleability: can be drawn into wires easily Good corrosion resistance: used in fuel and oil lines in aircrafts Copper is non magnetic

56. Classification of Cu-alloys Brasses (Cu + Zn) Bronzes (Cu + Sn, Al, Si, Be) Cupronickels (Cu + Ni) Nickel silver (Cu + Ni, Zn) Recording Brass trumpet Bronze Coin Cupronickel piping system

57. Nickel Silver is also known as German Silver, Argentan, New Silver, and Nickel Brass Nickel Silver is used in saxophones and cutlery A German Silver hair comb

58. Brass Copper and zinc form solid solution up to ~ 39% zinc at 456 o C , giving a wide rage of properties . Sn , Al, Si, Mg, Ni, and Pb are added elements, called ‘ alloy brasses ’. Commercially used brasses can be divided into two important groups : 1) α brasses ( hypo-peritectic) with α structure containing up to ~35% Zn. 2) α+β brasses ( hyperperitectic ) with α+β two phase structure, based on 60:40 ratio of Cu and Zn

59. α phase – FCC structure β phase – BCC structure (disordered) β’ phase – BCC structure (ordered) γ phase – complex structure (brittle)

60. Alpha Brasses are classified as: Yellow alpha brass Red brass

61. Alpha-Brasses Alpha – brasses having up to 20% Zn are reddish in colour, and are often called red – brasses When the Zn is between 20% to 36% and are called yellow brasses Season cracking occurs in alpha – brasses when intergranular corrosion occurs specially in ammonia atmosphere As high residual stresses are responsible for season cracking, the defect can be avoided if alpha brasses are stress annealed at 750 C

62. α+β brasses 40% Zn addition provides a complex structure of α and β phases. 60%Cu-40%Zn (Muntz metal) is the most widely used . These brasses are stronger and have very good wear resistance They have low ductility at room temperature Can’t be cold worked that easily

63. Bronze It is an alloy of Copper and Tin (Cu + Sn ) The addition of tin increases the strength significantly but ductility drops

64. There are different kinds of bronzes: Tin Bronzes (Phosphor Bronzes) Silicon Bronzes Aluminum Bronzes Beryllium Bronzes

65. Tin Bronzes Wrought Cu- Sn bronzes contain about 1-10% Cu, 1.25-10 % Sn with up to 0.1% P; hence usually called phosphor bronzes. ‘P’ is added as deoxidizing agent to improve castability . The wrought tin bronzes possess higher strength than brasses , especially in the cold-worked condition and has better corrosion resistance.

66. Types of Tin Bronzes 1. Admiralty gun metal: Cu = 88%, Sn = 10%, Zn 2% (Used for steam pipe fittings and bearings) 2. Bell metal: Cu = 70%, Sn = 30% Gun metal products