Heat Treatment
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Heat treatment involves controlled heating and cooling of metals to alter their properties and is used to improve machining, reduce forming forces, and restore ductility. Key heat treatments include annealing to reduce hardness and residual stresses, normalizing to obtain a uniform structure, and precipitation hardening using a solution treatment, quench, and aging steps. Heat treatment processes are aided by phase diagrams which show temperature effects. Proper design and material selection are important to avoid issues from nonuniform sections or residual stresses during heat treatment.
Heat Treatment
- 2. Heat Treatment The controlled heating & cooling of metals for the purpose of altering their properties
- 3. Heat Treatment It is used in manufacturing, providing simple and low-cost means of obtaining desired properties
- 4. Processing Heat Treatments thermal processes designed to increase strength-preparing materials for fabrication
- 5. which includes: improving machining characteristics reducing forming forces and energy consumption restoring ductility for further deformation
- 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
- 8. Processing Heat Treatments for Steel
- 9. Annealing a number of process heating operations
- 10. Annealing reducing hardness removing residual stresses improving toughness restoring ductility altering mechanical , physical magnetic properties
- 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. 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. 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. Process Anneal metal is heated below A1, held long enough to achieve softening, then cooled in air
- 15. Advantages of Process Anneal cheaper more rapid tends to produce less scaling
- 16. Stress-Relief Anneal employed to remove residual stresses in large steel castings and welded structures
- 17. Stress-Relief Anneal parts are heated below A1 (550-660°C;1000-1200°F), held for period of time, then slowly cooled
- 18. Spheroidization employed when high-carbon steels must be prepared for machining and forming required for above 0.6% carbon
- 20. Heat Treatments for Nonferrous Metals
- 21. Purpose for Nonferrous Metals to be heat-treated: obtaining uniform structure providing stress relief bringing about recrystallization
- 22. 6 Major Mechanisms: Solid Solution Hardening Strain Hardening Grain Size Refinement Precipitation Hardening Dispersion Hardening Phase Transformation Next
- 23. Solid Solution Hardening a base metal dissolves other atoms in solid solution either as substantial solutions or as interstitial solutions Back
- 24. Strain Hardening increases strength by plastic deformation under cold-working conditions Back
- 25. Grain Size Refinement used to increase strength, except at elevated temperatures where failure is by grain-boundary diffusion-controlled creep mechanism Back
- 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. Dispersion Hardening strength is obtained from distinct second-phase particles in a base matrix Back
- 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. 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. 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. Silver- Copper Equilibrium Diagram
- 33. Aids to understanding the nonequilibrium processes Isothermal transformation (IT) or time-temperature-transformation (T-T-T) diagram
- 34. Bainite Electron microscopy maybe required for to resolve the carbides in the resulting structure Martensite Exceptionally strong, hard & brittle
- 35. Martensite
- 36. Tempering Subsequent cooling required to restore some desired degree of toughness at the expense of a decrease in strength & hardness
- 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. Jominy Test for Hardenability Used to assist understanding of nonequilibrium heat treatment
- 39. Hardness - a mechanical property related to strength and is strong function of the carbon content of a metal
- 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. 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. Quench Media Stages of quenching First Stage (Vapor Jacket Stage) Second Stage of Quenching Third Stage
- 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. Brine (Salt) more severe quenching medium than water because salt creates bubbles , forcing a more rapid transition through the vapor jacket stage
- 45. The Role of Design in the Heat Treatment of Steel
- 46. Design Details & Material Selection Proper consideration of it leads: more simple, more economical more reliable products
- 47. Undesirable Design Features Nonuniform sections or thickness Sharp Interior Corners Sharp Exterior Corners
- 50. Residual Stresses are often-complex results of the various dimensional changes that occur during heat treatment
- 51. Austempering The process called if the piece is held at this temperature long enough, the austenite will transform to bainite.
- 52. Martempering/Marquenching The process called if the piece is stabilized and then slowly cooled through the martensite transformation
- 53. Ausforming a treatment used to strengthen metals and improve its wear properties
- 54. Surface Steel Hardening Selective Heating of the Surface Altered Surface Chemistry Deposition of Additional Layer
- 55. Selective Heating Techniques Selective Heating Flame Hardening Induction Heating Laser beam hardening Electron beam hardening
- 56. Altered Surface Chemistry Pack Carburizing Gas Carburizing Liquid Carburizing/Cyaniding Nitriding Ionitriding
- 57. Heat Treatment Equipment Batch Furnaces Continuous Furnaces
- 58. Box-Type Furnace
- 64. Thank You! Sario , Pamela May Reporter