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Heat Treatment

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heat treatment is the controlled heating and cooling of metals for the purpose of altering their properties.
it is used in manufacturing providing simple and low cost means of obtaining desired properties

Published in: Engineering
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Heat Treatment

  1. 1. Heat Treatment
  2. 2. Heat Treatment The controlled heating & cooling of metals for the purpose of altering their properties
  3. 3. Heat Treatment It is used in manufacturing, providing simple and low-cost means of obtaining desired properties
  4. 4. Processing Heat Treatments thermal processes designed to increase strength-preparing materials for fabrication
  5. 5. which includes: improving machining characteristics  reducing forming forces and energy consumption  restoring ductility for further deformation
  6. 6. Equilibrium Diagram as Aid to Heat Treatment  It indicates the temperatures that must be attained to achieve a desired product and change that will occur upon subsequent cooling
  7. 7. Simplified Iron-carbon diagram
  8. 8. Processing Heat Treatments for Steel
  9. 9. Annealing  a number of process heating operations
  10. 10. Annealing reducing hardness  removing residual stresses  improving toughness  restoring ductility  altering mechanical , physical magnetic properties
  11. 11. Full Annealing Hypoeutectoid steels are heated to 30-60 °C above the A3 to convert to homogeneous single-phase austenite of uniform composition and temperature then slowly cooled to below A1 temperature
  12. 12. Full Annealing it is time consuming require considerable energy to maintain the elevated temperature Gen. Rule: 1hr at temperature/inch of thickness of largest section
  13. 13. Normalizing metal is heated to 60°C (100°F) above the A3 or Acm, soaked to obtain uniform austenite, then removed and cooled in still air
  14. 14. Process Anneal metal is heated below A1, held long enough to achieve softening, then cooled in air
  15. 15. Advantages of Process Anneal cheaper more rapid tends to produce less scaling
  16. 16. Stress-Relief Anneal employed to remove residual stresses in large steel castings and welded structures
  17. 17. Stress-Relief Anneal  parts are heated below A1 (550-660°C;1000-1200°F), held for period of time, then slowly cooled
  18. 18. Spheroidization employed when high-carbon steels must be prepared for machining and forming required for above 0.6% carbon
  19. 19. Graphical Summary
  20. 20. Heat Treatments for Nonferrous Metals
  21. 21. Purpose for Nonferrous Metals to be heat-treated: obtaining uniform structure providing stress relief bringing about recrystallization
  22. 22. 6 Major Mechanisms: Solid Solution Hardening Strain Hardening Grain Size Refinement Precipitation Hardening Dispersion Hardening Phase Transformation Next
  23. 23. Solid Solution Hardening a base metal dissolves other atoms in solid solution either as substantial solutions or as interstitial solutions Back
  24. 24. Strain Hardening increases strength by plastic deformation under cold-working conditions Back
  25. 25. Grain Size Refinement  used to increase strength, except at elevated temperatures where failure is by grain-boundary diffusion-controlled creep mechanism Back
  26. 26. Precipitation/Age Hardening is a method whereby strength is obtained from a nonequilibrium structure produced by a three step ( solution treat-quench and age) heat treatment Back
  27. 27. Dispersion Hardening strength is obtained from distinct second-phase particles in a base matrix Back
  28. 28. Phase Transformations strengthening involves alloys w/c can be heated to form a single high-temperature phase, transformed to one or more low-temperature phase upon cooling Back
  29. 29. Strengthening Heat Treatments for Nonferrous Metals Aging - a continuous process which begins by the clustering of solute atoms on distinct planes of the parent lattice
  30. 30. Precipitation-hardening materials can be classified: Naturally Aging - the req. diffusion at unstable to the stable 2-phase structure at room temperature Artificially Aging - require elevated temperature
  31. 31. Silver- Copper Equilibrium Diagram
  32. 32. Enlargement of Copper
  33. 33. Aids to understanding the nonequilibrium processes Isothermal transformation (IT) or time-temperature-transformation (T-T-T) diagram
  34. 34. Bainite Electron microscopy maybe required for to resolve the carbides in the resulting structure Martensite Exceptionally strong, hard & brittle
  35. 35. Martensite
  36. 36. Tempering Subsequent cooling required to restore some desired degree of toughness at the expense of a decrease in strength & hardness
  37. 37. Continuous Cooling Transformation (C-C-T) Diagram These diagrams are used to represent which types of phase changes will occur in a material as it is cooled at different rates.
  38. 38. Jominy Test for Hardenability Used to assist understanding of nonequilibrium heat treatment
  39. 39. Hardness - a mechanical property related to strength and is strong function of the carbon content of a metal
  40. 40. Hardenability - a measure of the depth to which full hardness can be attained under a normal hardening cycle and is related primarily to amounts and types of alloying elements.
  41. 41. Adding alloy to steel The primary reason for adding alloy elements to commercial steel is to increase the hardenability , not to improve the strength properties
  42. 42. Quench Media Stages of quenching First Stage (Vapor Jacket Stage) Second Stage of Quenching Third Stage
  43. 43. Water is fairly good quenching medium because of its high heat of vaporization.  is cheap, but the bubbles may cause soft spots in metal
  44. 44. Brine (Salt)  more severe quenching medium than water because salt creates bubbles , forcing a more rapid transition through the vapor jacket stage
  45. 45. The Role of Design in the Heat Treatment of Steel
  46. 46. Design Details & Material Selection Proper consideration of it leads:  more simple,  more economical  more reliable products
  47. 47. Undesirable Design Features Nonuniform sections or thickness Sharp Interior Corners Sharp Exterior Corners
  48. 48. Residual Stresses are often-complex results of the various dimensional changes that occur during heat treatment
  49. 49. Austempering The process called if the piece is held at this temperature long enough, the austenite will transform to bainite.
  50. 50. Martempering/Marquenching The process called if the piece is stabilized and then slowly cooled through the martensite transformation
  51. 51. Ausforming  a treatment used to strengthen metals and improve its wear properties
  52. 52. Surface Steel Hardening Selective Heating of the Surface Altered Surface Chemistry Deposition of Additional Layer
  53. 53. Selective Heating Techniques Selective Heating Flame Hardening Induction Heating Laser beam hardening Electron beam hardening
  54. 54. Altered Surface Chemistry Pack Carburizing Gas Carburizing Liquid Carburizing/Cyaniding Nitriding Ionitriding
  55. 55. Heat Treatment Equipment Batch Furnaces Continuous Furnaces
  56. 56. Box-Type Furnace
  57. 57. Car-Bottom Box-Type Furnace
  58. 58. Vertical Pit Furnace
  59. 59. Bell-Type Pit Furnace
  60. 60. Elevator-Type Furnace
  61. 61. Continuous Furnace
  62. 62. Thank You! Sario , Pamela May Reporter

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