Unit 3:The Iron-Iron Carbide Equilibrium Diagram

1. Unit 3:The Iron-Iron Carbide Equilibrium Diagram SUBJECT:ENGINEERING METALLURGY (S.E) MR. ANIKET BHANUDAS KOLEKAR ASST. PROF. DEPARTMENT OF MECHANICAL ENGINEERING DYPIEMR,AKURDI,PUNE

3. PHASES OF IRON FCC (Austenite) BCC (Ferrite) BCC (Martensite)

4. Micro-structure

5. MICROSTRUCTUREOF PEARLITE Photomicrographs of (a) coarse pearlite and (b) fine pearlite. 3000X

6. MICROSTRUCTURE OF MARTENSITE

7. Solid solution of carbon in α-iron. • α-ferrite BCC crystal structure • Solubility of carbon in a-iron at R.T is 0.008% increased with increasing temp. 0.025% at 727 ˚C • Soft and ductile phase • solid solution of carbon in α-iron. • α-ferrite BCC crystal structure • low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT a(FERRRITE)

8. γ • Interstitial solid solution of carbon in γ iron. Austenite has FCC crystal structure, • high solubility of carbon up to 2.14% at (1147ºC). • Soft, ductile, malleable and non-magnetic • solid solution of carbon in α-iron. • α-ferrite BCC crystal structure • low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT γ(Austenite)

9. δ • Solid solution of carbon in δ-iron. • The crystal structure of δ-ferrite is BCC (cubic body centered). • solid solution of carbon in α-iron. • α-ferrite BCC crystal structure • low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT δ-(FERRRITE)

10. Fe3C • Intermetallic compound, having fixed composition Fe3C. • Orthorhombic crystal structure,12-iron .4- carbon • Hard and brittle • Ferromagnetic upto 210 C • solid solution of carbon in α-iron. • α-ferrite BCC crystal structure • low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT Fe3C-(Cementite)

11. Peritectic Reaction: 0.55-0.18 X 100 δ = 0.55-0.1 = 82.2 % 0.55 0.18-0.1 L = X 100 0.55-0.1 = 17.8% 1492 ºC S1 + L S2 L + δ → γ (0.55%C) (0.10%C) (0.18%C)

12. Eutectoid Reaction: 727 ºC S1 S2 + S3 6.67-0.8 α = x 100 6.67-0.008 Fe3C = 88.1% 0.8- 0.025 x 100 Fe3C = 6.67-0.008 γ → α + Fe3C Fe3C = 11.09 % (0.025%C) (6.67%C) (0.80%C) Pearlite

14. Eutectic Reaction (at) 1147 ºC L1 S1 + S2 Liquid → γ + Fe3C (4.30%C) (2.00%C) (6.67%C) Ledeburite

15. CRITICAL TEMPERATURE OF IRON- CARBON ALLOYS

16. CRITICAL TEMPERATURE OF IRON- CARBON ALLOYS

17. Paramagnetic material Ferromagnetic material Above the Curie temperature Below the Curie temperature Applied magnetic field absent

18. ALLOTROPY OF PURE IRON: Change in crystal structure is called as allotropy

19. Cooling Curves for Pure Iron Liquid 1539 δ- iron, BCC 1400 γ-iron FCC Temp 910 α- iron non-magnatic BCC 768 α- iron magnatic BCC Time

20. Microstructures a g

21. Microstructural changes in steel on cooling for different compositions

22. Microstructural changes in steel

23. Eutectoid steel

25. Hypoeutectoid steel Figure.Schematic representations of the microstructures for an iron–carbon alloy of hypoeutectoid composition.

26. Photomicrograph of a 0.38 wt% C steel having a microstructure consisting of pearlite and proeutectoid ferrite.

27. Hypereutectoid steel Figure .Schematic representations of the microstructures for an iron–carbon alloy of hypereutectoid composition

28. Figure.Photomicrograph of a 1.4 wt% C steel having a microstructure consisting of a white proeutectoid cementite network surrounding the pearlite colonies.

29. Widmanstatten structure Separating pro-eutectoide ferrite or cementite had definite orientation relationship with austenite phase.

30. 1.Composition of steel: Pro-eutectoid Phase Grain boundary

31. Grain Size: Larger Smaller

32. Cooling rate Fast cooling Less diffusion time Pro-eutectoid phase get precipiated inside the grain

33. Property variation with microstruture Mechanical properties are structure dependent. Average Property = (Amount of a × The property of a) + (Amount of b× The property of b) For hypereutectoid steels: Hardness(B.H.N) = 80× Amount of a + 230 × Amount of Pearlite For hypereutectoid steels: Hardness(B.H.N) = 900× Amount of Fe3C + 240 × Amount of Pearlite

35. Classification and application of steels Amount of carbon Amount of alloying element and carbon Amount of deoxidation Grain coarsening characteristics Method of manufacture Depth of hardening Form and use

36. On the basics of carbon content • Low carbon steel: (0.008-0.3%) • Soft, ductile , malleable, machinable, weldiablity • Non-hardened by heat treatment • They are used for cold working and fabrication • (0.15-0.30) structural steel • Rivets, camshaft, wires. Connecting rod

37. Medium carbon steel:(0.3-0.6%) • Intermediate properties • Depth of hardening is less • Difficult to cold work • Machinary steel, Springs, crank pins, hammer, cylinder liner • High carbon steel:(0.6-2.0%) • Hard wear resistance, brittle, difficult to weld • Hardened by heat treatment • Ball bearing, cutters, mandrel

38. On the basics of alloying elements and carbon: 1.Low alloy steels < 10% 2. High alloy steels > 10% A- low carbon low alloy- good strength B- low carbon high alloy- good corrosion resistance C- high carbon high alloy- excellent hardness, wear resistance

39. On the basis of depth of hardening: 1.Non-hardenable steels: Low carbon and no alloying element Fabrication by cold working and welding 2.Shallow hardenable steel: Medium carbon and no alloying element Gears and camshaft 3.Deep hardenable steel: High carbon and alloying element

40. On the basics of form and use: • Boiler steel • Case hardening steels • Corrosion and heat resistant steel • Deep drawing steel • Electrical steel • Machinery steel • Structural steel • Tool steel

41. On the basics of grain coarsening characteristics • Coarse grained steel • Fine grained steel • On the basics of deoxidation: • Rimmed steel • Killed steel • Semi-killed steel

42. Specification of steels: Indian standard designation system(ISI): Part-1:- covers destination of steel based on letter symbols Part-2:- covers destination of steel based on numerical Code designation is basis of mechanical properties Fe- minimum tensile strength in N/mm2 Fe E- minimum yield strength in N/mm2 Fe 410 K- killed steel with minimum T.S of 410 N/mm2 Fe E 270- steel with minimum Y.S of 270 N/mm2 St:- T.S in kg/mm2 St E :- Y.S in kg/mm2 St 42- steel with minimum T.S of 42 kg/mm2

43. C- Plain carbon steel T- Tool steel C 20-steel with avg. Carbon content 0.20 % C 40-............................. 25 C 5-.................................. 80 T 11-................................. 15 Ni 13 Cr 1 Mo 12- steel with avg. Compostion C-0.15 Ni-1.3 Cr-1 Mo= 0.12 35 S 18-............................................ 35 Mn 1 S 18-...................................

44. 20 Mn Cr 1:................................................................ 35 Ni Cr-60:................................................................

45. AISI/SAE Designation system 1- Carbon steel 2- Nickel steel 3- Ni-Cr steels 4- Molybdeum steel 5- Chromium steel 6- Cr-V steel 7- tungsten steel 8- Ni-Cr-Mo- steels 9- Si-M n steels

46. 10 × × Carbon Content/100 Steel Type % of alloying element 2 5 2 0 20/100= 0.2 % C Ni-Steel 5.00 % Ni

47. 1040:- carbon steel contain 0.4 % C 2440:- Nickel steel with approximately 4 % nickel and 0.4 % C 9260:-...............................................................................................