The Science and Engineeringof Materials, 4th edDonald R. Askeland – Pradeep P. Phulé    Chapter 12 – Ferrous Alloys       ...
Objectives of Chapter 12   Discuss how to use the eutectoid reaction    to control the structure and properties of    ste...
Chapter Outline   12.1 Designations and Classification         of Steels   12.2 Simple Heat Treatments   12.3 Isotherma...
Chapter Outline (Continued) 12.7 Specialty Steels 12.8 Surface Treatments 12.9 Weldability of Steel 12.10 Stainless St...
Figure 12.1 (a) In a blast furnace,iron ore is reduced using coke(carbon) and air to produce liquidpig iron. The high-carb...
Section 12.1    Designations and Classification                 of Steels    Designations - The AISI (American Iron and S...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
Figure 12.3 Electron micrographs of (a) pearlite, (b)bainite, and (c) tempered martensite, illustrating thedifferences in ...
9
Example 12.1 Design of a Method to Determine              AISI NumberAn unalloyed steel tool used for machining aluminumau...
Example 12.1 SOLUTIONThe first way is to heat the steel to a temperature just belowthe A1 temperature and hold for a long ...
Section 12.2       Simple Heat Treatments Process Annealing — Eliminating Cold Work: A low-  temperature heat treatment u...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.14     ...
Figure 12.6 The microstructureof spheroidite, with Fe3Cparticles dispersed in a ferritematrix (× 850). (From ASMHandbook, ...
Example 12.2   Determination of Heat Treating           TemperaturesRecommend temperatures for the process annealing,annea...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
Example 12.2 SOLUTIONFrom Figure 12.2, we find the critical A1, A3, or Acm,temperatures for each steel. We can then specif...
Section 12.3    Isothermal Heat Treatments Austempering - The isothermal heat treatment by which  austenite transforms to...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.21     ...
Example 12.3                                                                                 Design of a Heat Treatment fo...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
Example 12.3 SOLUTION• Austenitize the steel at 770 + (30 to 55) = 805oC to  825oC, holding for 1 h and obtaining 100% γ.•...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.25     ...
Figure 12.10 Dark feathers ofbainite surrounded by lightmartensite, obtained byinterrupting the isothermaltransformation p...
Section 12.4Quench and Temper Heat Treatments Retained austenite - Austenite that is unable to  transform into martensite...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.28     ...
Example 12.4  Design of a Quench and            Temper TreatmentA rotating shaft that delivers power from an electric moto...
Figure 12.12 Retained austenite(white) trapped betweenmartensite needles (black)(× 1000). (From ASM Handbook,Vol. 8, (1973...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.31     ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.33     ...
34
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
Section 12.5      Effect of Alloying Elements  Hardenability - Alloy steels have high hardenability.  Effect on the Phas...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.38     ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
Section 12.6   Application of Hardenability Jominy test - The test used to evaluate hardenability. An  austenitized steel...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under                ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.44     ...
45
Example 12.5                                                                      Design of a Wear-Resistant GearA gear ma...
47
Example 12.5 SOLUTIONFrom Figure 12.23, a hardness of HRC 40 in a 9310 steelcorresponds to a Jominy distance of 10/16 in. ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
Example 12.6      Design of a Quenching ProcessDesign a quenching process to produce a minimum hardness ofHRC 40 at the ce...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.52     ...
Example 12.6 SOLUTIONSeveral quenching media are listed in Table 12-2. We can findan approximate H coefficient for each of...
Section 12.7          Specialty Steels Tool steels - A group of high-carbon steels that provide  combinations of high har...
Figure 12.25 Microstructure of adual-phase steel, showing islands oflight martensite in a ferrite matrix(× 2500). (From G....
Section 12.8        Surface Treatments Selectively Heating the Surface - Rapidly heat the  surface of a medium-carbon ste...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under                ...
Example 12.7  Design of Surface-Hardening Treatments             for a Drive TrainDesign the materials and heat treatments...
Example 12.7 SOLUTIONThe axle might be made from a forged 1050 steel containinga matrix of ferrite and pearlite. The axle ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
Example 12.8   Structures of Heat-Affected ZonesCompare the structures in the heat-affected zones ofwelds in 1080 and 4340...
Section 12.10           Stainless Steels Stainless steels - A group of ferrous alloys that contain  at least 11% Cr, prov...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
65
Figure 12.31 (a) Martensitic stainless steel containinglarge primary carbides and small carbides formedduring tempering (×...
Example 12.9Design of a Test to Separate             Stainless SteelsIn order to efficiently recycle stainless steel scrap...
Section 12.11            Cast Irons Cast iron - Ferrous alloys containing sufficient carbon so  that the eutectic reactio...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.73     ...
Figure 12.37 The heat treatments for ferritic andpearlitic malleable irons.                          74
Figure 12.38 (a) White cast iron prior to heat treatment (× 100). (b) Ferritic malleableiron with graphite nodules and sma...
76
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.78     ...
©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.       ...
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Askeland phule 12

  1. 1. The Science and Engineeringof Materials, 4th edDonald R. Askeland – Pradeep P. Phulé Chapter 12 – Ferrous Alloys 1
  2. 2. Objectives of Chapter 12 Discuss how to use the eutectoid reaction to control the structure and properties of steels through heat treatment and alloying. Examine two special classes of ferrous alloys: stainless steels and cast irons. 2
  3. 3. Chapter Outline 12.1 Designations and Classification of Steels 12.2 Simple Heat Treatments 12.3 Isothermal Heat Treatments 12.4 Quench and Temper Heat Treatments 12.5 Effect of Alloying Elements 12.6 Application of Hardenability 3
  4. 4. Chapter Outline (Continued) 12.7 Specialty Steels 12.8 Surface Treatments 12.9 Weldability of Steel 12.10 Stainless Steels 12.11 Cast Irons 4
  5. 5. Figure 12.1 (a) In a blast furnace,iron ore is reduced using coke(carbon) and air to produce liquidpig iron. The high-carbon contentin the pig iron is reduce byintroducing oxygen into the basicoxygen furnace to produce liquidsteel. An electric arc furnace canbe used to produce liquid steel bymelting scrap. (b) Schematic of ablast furnace operation. (Source:www.steel.org. Used withpermission of the American Ironand Steel Institute.) 5
  6. 6. Section 12.1 Designations and Classification of Steels Designations - The AISI (American Iron and Steel Institute) and SAE (Society of Automotive Engineers) provide designation systems for steels that use a four- or five-digit number. Classifications - Steels can be classified based on their composition or the way they have been processed. 6
  7. 7. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.2 (a) The eutectoid portion of the Fe-Fe3C phase diagram. (b) An expanded version of the Fe-C diagram, adapted from several sources. 7
  8. 8. Figure 12.3 Electron micrographs of (a) pearlite, (b)bainite, and (c) tempered martensite, illustrating thedifferences in cementite size and shape among thesethree microconstituents (× 7500). (From The Making,Shaping, and Treating of Steel, 10th Ed. Courtesy ofthe Association of Iron and Steel Engineers.) 8
  9. 9. 9
  10. 10. Example 12.1 Design of a Method to Determine AISI NumberAn unalloyed steel tool used for machining aluminumautomobile wheels has been found to work well, but thepurchase records have been lost and you do not know thesteel’s composition. The microstructure of the steel istempered martensite, and assume that you cannot estimatethe composition of the steel from the structure. Design atreatment that may help determine the steel’s carboncontent. 10
  11. 11. Example 12.1 SOLUTIONThe first way is to heat the steel to a temperature just belowthe A1 temperature and hold for a long time. The steelovertempers and large Fe3C spheres form in a ferrite matrix.We then estimate the amount of ferrite and cementite andcalculate the carbon content using the lever law. If we measure16% Fe3C using this method, the carbon content is:  ( x − 0.0218)  % Fe3C =   ×100 = 16 or x = 1.086%  (6.67 − 0.0218)  A better approach, however, is to heat the steel abovethe Acm to produce all austenite. If the steel then cools slowly,it transforms to pearlite and a primary microconstituent. If,when we do this, we estimate that the structure contains 95%pearlite and 5% primary Fe3C, then:  6.67 - x % Pearlite =   × 100 = 95 or x = 1.065%  6.67 − 0.77  11
  12. 12. Section 12.2 Simple Heat Treatments Process Annealing — Eliminating Cold Work: A low- temperature heat treatment used to eliminate all or part of the effect of cold working in steels. Annealing and Normalizing — Dispersion Strengthening: Annealing - A heat treatment used to produce a soft, coarse pearlite in steel by austenitizing, then furnace cooling. Normalizing - A simple heat treatment obtained by austenitizing and air cooling to produce a fine pearlitic structure. Spheroidizing — Improving Machinability: Spheroidite - A microconstituent containing coarse spheroidal cementite particles in a matrix of ferrite, permitting excellent machining characteristics in high-carbon steels. 12
  13. 13. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.4 Schematic summary of the simple heat treatmentsfor (a) hypoeutectoid steels and (b) hypereutectoid steels. 13
  14. 14. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.14 steels. carbon and heat treatment on the Figure 12.5 The effect of properties of plain-carbon
  15. 15. Figure 12.6 The microstructureof spheroidite, with Fe3Cparticles dispersed in a ferritematrix (× 850). (From ASMHandbook, Vol. 7, (1972), ASMInternational, Materials Park, OH44073.) 15
  16. 16. Example 12.2 Determination of Heat Treating TemperaturesRecommend temperatures for the process annealing,annealing, normalizing, and spheroidizing of 1020,1077, and 10120 steels. 16
  17. 17. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.2 (a) The eutectoid portion of the Fe-Fe3C phase diagram. (b) An expanded version of the Fe-C diagram, adapted from several sources. 17
  18. 18. Example 12.2 SOLUTIONFrom Figure 12.2, we find the critical A1, A3, or Acm,temperatures for each steel. We can then specify theheat treatment based on these temperatures. 18
  19. 19. Section 12.3 Isothermal Heat Treatments Austempering - The isothermal heat treatment by which austenite transforms to bainite. Isothermal annealing - Heat treatment of a steel by austenitizing, cooling rapidly to a temperature between the A1 and the nose of the TTT curve, and holding until the austenite transforms to pearlite. 19
  20. 20. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.7 The austempering and isothermal annealheat treatments in a 1080 steel. 20
  21. 21. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.21 (b) a 10110 steel. Figure 12.8 The TTT diagrams for (a) a 1050 and
  22. 22. Example 12.3 Design of a Heat Treatment for an Axle A heat treatment is needed to produce a uniform microstructure and hardness of HRC 23 in a 1050 steel axle.©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.8 The TTT diagrams for (a) a 1050 and (b) a 10110 steel. 22
  23. 23. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.2 (a) The eutectoid portion of the Fe-Fe3C phase diagram. (b) An expanded version of the Fe-C diagram, adapted from several sources. 23
  24. 24. Example 12.3 SOLUTION• Austenitize the steel at 770 + (30 to 55) = 805oC to 825oC, holding for 1 h and obtaining 100% γ.• Quench the steel to 600oC and hold for a minimum of 10 s. Primary ferrite begins to precipitate from the unstable austenite after about 1.0 s. After 1.5 s, pearlite begins to grow, and the austenite is completely transformed to ferrite and pearlite after about 10 s. After this treatment, the microconstituents present are:  (0.77 − 0.5)  Primary α =   × 100 = 36%  (0.77 − 0.0218)   (0.5 − 0.0218)  Pearlite =   × 100 = 64%  (0.77 − 0.0218) 3. Cool in air-to-room temperature, preserving the equilibrium amounts of primary ferrite and pearlite. The microstructure and hardness are uniform because of the isothermal anneal. 24
  25. 25. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.25 steel. isothermal heat by interrupting the treatment of a 1050 Figure 12.9 Producing complicated structures
  26. 26. Figure 12.10 Dark feathers ofbainite surrounded by lightmartensite, obtained byinterrupting the isothermaltransformation process (× 1500).(ASM Handbook, Vol. 9Metallography and Microstructure(1985), ASM International,Materials Park, OH 44073.) 26
  27. 27. Section 12.4Quench and Temper Heat Treatments Retained austenite - Austenite that is unable to transform into martensite during quenching because of the volume expansion associated with the reaction. Tempered martensite - The microconstituent of ferrite and cementite formed when martensite is tempered. Quench cracks - Cracks that form at the surface of a steel during quenching due to tensile residual stresses that are produced because of the volume change that accompanies the austenite-to-martensite transformation. Marquenching - Quenching austenite to a temperature just above the MS and holding until the temperature is equalized throughout the steel before further cooling to produce martensite. 27
  28. 28. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.28 steel. mechanical Figure 12.11 The effect of tempering temperature on the properties of a 1050
  29. 29. Example 12.4 Design of a Quench and Temper TreatmentA rotating shaft that delivers power from an electric motor ismade from a 1050 steel. Its yield strength should be at least145,000 psi, yet it should also have at least 15% elongation inorder to provide toughness. Design a heat treatment toproduce this part.Example 12.4 SOLUTION• Austenitize above the A3 temperature of 770oC for 1 h. An appropriate temperature may be 770 + 55 = 825oC.• Quench rapidly to room temperature. Since the Mf is about 250oC, martensite will form.• Temper by heating the steel to 440oC. Normally, 1 h will be sufficient if the steel is not too thick.• Cool to room temperature. 29
  30. 30. Figure 12.12 Retained austenite(white) trapped betweenmartensite needles (black)(× 1000). (From ASM Handbook,Vol. 8, (1973), ASM International,Materials Park, OH 44073.) 30
  31. 31. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.31 Figure 12.13 Increasing carbon Mf temperatures in reduces the Ms and plain-carbon steels.
  32. 32. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.14 Formation of quench cracks caused by residualstresses produced during quenching. The figure illustratesthe development of stresses as the austenite transforms tomartensite during cooling. 32
  33. 33. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.33 cracking. Figure 12.15 The to reduce residual marquenching heat treatment designed stresses ands quench
  34. 34. 34
  35. 35. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.16 The CCT diagram (solid lines) for a 1080 steelcompared with the TTT diagram (dashed lines). 35
  36. 36. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.17 The CCT diagram for a low-alloy, 0.2% C Steel. 36
  37. 37. Section 12.5 Effect of Alloying Elements  Hardenability - Alloy steels have high hardenability.  Effect on the Phase Stability - When alloying elements are added to steel, the binary Fe-Fe3C stability is affected and the phase diagram is altered.  Shape of the TTT Diagram - Ausforming is a thermomechanical heat treatment in which austenite is plastically deformed below the A1 temperature, then permitted to transform to bainite or martensite.  Tempering - Alloying elements reduce the rate of tempering compared with that of a plain-carbon steel. 37
  38. 38. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.38 CCT curves for a 4340 steel. Figure 12.18 (a) TTT and (b)
  39. 39. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.19 The effect of 6% manganese on the stability ranges of the phases in the eutectoid portion of the Fe-Fe3C phase diagram. 39
  40. 40. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.20 When alloying elements introduce a bayregion into the TTT diagram, the steel can be ausformed. 40
  41. 41. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.21 The effect of alloying elements on the phasesformed during the tempering of steels. The air-hardenablesteel shows a secondary hardening peak. 41
  42. 42. Section 12.6 Application of Hardenability Jominy test - The test used to evaluate hardenability. An austenitized steel bar is quenched at one end only, thus producing a range of cooling rates along the bar. Hardenability curves - Graphs showing the effect of the cooling rate on the hardness of as-quenched steel. Jominy distance - The distance from the quenched end of a Jominy bar. The Jominy distance is related to the cooling rate. 42
  43. 43. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.22 The set-up for the Jominy test used fordetermining the hardenability of a steel. 43
  44. 44. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.44 Figure 12.23 The for several steels. hardenability curves
  45. 45. 45
  46. 46. Example 12.5 Design of a Wear-Resistant GearA gear made from 9310 steel, which has an as-quenchedhardness at a critical location of HRC 40, wears at an excessiverate. Tests have shown that an as-quenched hardness of atleast HRC 50 is required at that critical location. Design a steelthat would be appropriate.©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.23 The hardenability curves for several steels. 46
  47. 47. 47
  48. 48. Example 12.5 SOLUTIONFrom Figure 12.23, a hardness of HRC 40 in a 9310 steelcorresponds to a Jominy distance of 10/16 in. (10oC/s). If weassume the same Jominy distance, the other steels shown inFigure 12.23 have the following hardnesses at the criticallocation:1050 HRC 28 1080 HRC 36 4320 HRC 318640 HRC 52 4340 HRC 60In Table 12-1, we find that the 86xx steels contain lessalloying elements than the 43xx steels; thus the 8640 steel isprobably less expensive than the 4340 steel and might be ourbest choice. We must also consider other factors such asdurability. 48
  49. 49. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.24 The Grossman chart used to determine thehardenability at the center of a steel bar for differentquenchants. 49
  50. 50. Example 12.6 Design of a Quenching ProcessDesign a quenching process to produce a minimum hardness ofHRC 40 at the center of a 1.5-in. diameter 4320 steel bar. 50
  51. 51. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.24 The Grossman chart used to determine thehardenability at the center of a steel bar for differentquenchants. 51
  52. 52. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.52 Figure 12.23 The for several steels. hardenability curves
  53. 53. Example 12.6 SOLUTIONSeveral quenching media are listed in Table 12-2. We can findan approximate H coefficient for each of the quenching media,then use Figure 12.24 to estimate the Jominy distance in a 1.5-in. diameter bar for each media. Finally, we can use thehardenability curve (Figure 12.23) to find the hardness in the4320 steel. The results are listed below.The last three methods, based on brine or agitated water, aresatisfactory. Using an unagitated brine quenchant might be leastexpensive, since no extra equipment is needed to agitate thequenching bath. However, H2O is less corrosive than the brinequenchant. 53
  54. 54. Section 12.7 Specialty Steels Tool steels - A group of high-carbon steels that provide combinations of high hardness, toughness, or resistance to elevated temperatures. Secondary hardening peak - Unusually high hardness in a steel tempered at a high temperature caused by the precipitation of alloy carbides. Dual-phase steels - Special steels treated to produce martensite dispersed in a ferrite matrix. Maraging steels - A special class of alloy steels that obtain high strengths by a combination of the martensitic and age-hardening reactions. 54
  55. 55. Figure 12.25 Microstructure of adual-phase steel, showing islands oflight martensite in a ferrite matrix(× 2500). (From G. Speich,‘‘Physical Metallurgy of Dual-PhaseSteels,’’ Fundamentals of Dual-Phase Steels, The MetallurgicalSociety of AIME, 1981.) 55
  56. 56. Section 12.8 Surface Treatments Selectively Heating the Surface - Rapidly heat the surface of a medium-carbon steel above the A3 temperature and then quench the steel. Case depth - The depth below the surface of a steel at which hardening occurs by surface hardening and carburizing processes. Carburizing - A group of surface-hardening techniques by which carbon diffuses into steel. Cyaniding - Hardening the surface of steel with carbon and nitrogen obtained from a bath of liquid cyanide solution. Carbonitriding - Hardening the surface of steel with carbon and nitrogen obtained from a special gas atmosphere. 56
  57. 57. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.26 (a) Surface hardening by localized heating. (b)Only the surface heats above the A1 temperature and isquenched to martensite. 57
  58. 58. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.27 Carburizing of a low-carbon steel to produce ahigh-carbon, wear-resistant surface. 58
  59. 59. Example 12.7 Design of Surface-Hardening Treatments for a Drive TrainDesign the materials and heat treatments for an automobileaxle and drive gear (Figure 12.28). Figure 12.28 Sketch of axle and gear assembly (for example 12.7). ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. 59
  60. 60. Example 12.7 SOLUTIONThe axle might be made from a forged 1050 steel containinga matrix of ferrite and pearlite. The axle could be surface-hardened, perhaps by moving the axle through an inductioncoil to selectively heat the surface of the steel above the A3temperature (about 770oC). After the coil passes anyparticular location of the axle, the cold interior quenches thesurface to martensite. Tempering then softens the martensiteto improve ductility. Carburize a 1010 steel for the gear. By performing agas carburizing process above the A3 temperature (about860oC), we introduce about 1.0% C in a very thin case at thesurface of the gear teeth. This high-carbon case, whichtransforms to martensite during quenching, is tempered tocontrol the hardness. This high-carbon case, whichtransforms to martensite during quenching, is tempered tocontrol the hardness. 60
  61. 61. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Section 12.9 Weldability of Steel Figure 12.29 The development of the heat-affected zone in a weld: (a) the structure at the maximum temperature, (b) the structure after cooling in a steel of low hardenability, and (c) the structure after cooling in a steel of high hardenability. 61
  62. 62. Example 12.8 Structures of Heat-Affected ZonesCompare the structures in the heat-affected zones ofwelds in 1080 and 4340 steels if the cooling rate in theheat-affected zone is 5oC/s.Example 12.8 SOLUTIONThe cooling rate in the weld produces the followingstructures:1080: 100% pearlite4340: Bainite and martensite The high hardenability of the alloy steel reducesthe weldability, permitting martensite to form andembrittle the weld. 62
  63. 63. Section 12.10 Stainless Steels Stainless steels - A group of ferrous alloys that contain at least 11% Cr, providing extraordinary corrosion resistance. Categories of stainless steels: • Ferritic Stainless Steels • Martensitic Stainless Steels • Austenitic Stainless Steels • Precipitation-Hardening (PH) Stainless Steels • Duplex Stainless Steels 63
  64. 64. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.30 (a) The effect of 17% chromium on the iron-carbon phase diagram. At low- carbon contents, ferrite is stable at all temperatures. (b) A section of the iron- chromium-nickel-carbon phase diagram at a constant 18% Cr-8% Ni. At low-carbon contents, austenite is stable at room temperatures. 64
  65. 65. 65
  66. 66. Figure 12.31 (a) Martensitic stainless steel containinglarge primary carbides and small carbides formedduring tempering (× 350). (b) Austenitic stainlesssteel (× 500). (From ASM Handbook, Vols. 7 and 8,(1972, 1973), ASM International, Materials Park, OH44073.) 66
  67. 67. Example 12.9Design of a Test to Separate Stainless SteelsIn order to efficiently recycle stainless steel scrap, we wish toseparate the high-nickel stainless steel from the low-nickelstainless steel. Design a method for doing this.Example 12.9 SOLUTIONPerforming a chemical analysis on each piece of scrap is tediousand expensive. Sorting based on hardness might be lessexpensive; however, because of the different types oftreatments—such as annealing, cold working, or quench andtempering—the hardness may not be related to the steelcomposition. The high-nickel stainless steels are ordinarily austenitic,whereas the low-nickel alloys are ferritic or martensitic. Anordinary magnet will be attracted to the low-nickel ferritic andmartensitic steels, but will not be attracted to the high-nickelaustenitic steel. We might specify this simple and inexpensivemagnetic test for our separation process. 67
  68. 68. Section 12.11 Cast Irons Cast iron - Ferrous alloys containing sufficient carbon so that the eutectic reaction occurs during solidification. Eutectic and Eutectoid reaction in Cast Irons Types of cast irons: • Gray cast iron • White cast iron • Malleable cast iron • Ductile or nodular, cast iron • Compacted graphite cast iron 68
  69. 69. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.32 Schematic drawings of the five types of castiron: (a) gray iron, (b) white iron, (c) malleable iron, (d)ductile iron, and (e) compacted graphite iron. 69
  70. 70. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.33 The iron-carbon phase diagram showing therelationship between the stable iron-graphite equilibria (solidlines) and the metastable iron-cementite reactions (dashedlines). 70
  71. 71. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.34 The transformation diagram for austenite in acast iron. 71
  72. 72. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.35 (a) Sketch and (b) photomicrograph of theflake graphite in gray cast iron (x 100). 72
  73. 73. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.73 on the tensile gray cast irons. properties of two Figure 12.36 The rate or casting size effect of the cooling
  74. 74. Figure 12.37 The heat treatments for ferritic andpearlitic malleable irons. 74
  75. 75. Figure 12.38 (a) White cast iron prior to heat treatment (× 100). (b) Ferritic malleableiron with graphite nodules and small MnS inclusions in a ferrite matrix (× 200). (c)Pearlitic malleable iron drawn to produce a tempered martensite matrix (× 500).(Images (b) and (c) are from Metals Handbook, Vols. 7 and 8, (1972, 1973), ASMInternational, Materials Park, OH 44073.) (d) Annealed ductile iron with a ferrite matrix(× 250). (e) As-cast ductile iron with a matrix of ferrite (white) and pearlite (× 250). (f)Normalized ductile iron with a pearlite matrix (× 250). 75
  76. 76. 76
  77. 77. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.Figure 12.17 (Repeated for Problem 12.20) The CCTdiagram for a low-alloy, 0.2% C steel. 77
  78. 78. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.78 steels. Figure 12.23 (Repeated for Problem 12.54) The hardenability curves for several
  79. 79. ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license. Figure 12.30b (Repeated for Problem 12.48) (b) A section of the iron-chromium- nickel-carbon phase diagram at a constant 18% Cr-8% Ni. At low-carbon contents, austenite is stable at room temperature. 79
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