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Heat affected zone

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HEAT AFFECTED ZONE

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Heat affected zone

  1. 1. JAY PRAKASH MTECH 3RD SEM 16 MEIM 061 GD-1368 MECHANICAL DEPARTMENT ZHCET AMU ALIGARH
  2. 2. The Heat-Affected Zone (HAZ)  The weld interface, which is also referred to as mushy zone, is a narrow zone consisting of partially melted base material which has not got an opportunity for mixing. This zone separates the fusion zone and heat affected zone.  Refers to a non-melted area of metal that has experienced changes in its material properties as a result of exposure to high temperatures.  The alterations in material properties are usually a result of welding or high-heat cutting procedures.
  3. 3.  It can often be recognized by a series of brightly colored bands, also visible near welds. Colors are caused by surface oxidation, and are an approximate indicator of the temperature reached by the metal:
  4. 4. These colors, also called "Heat tint", depend on four factors:  Steel chromium content: this metal increases the material resistance to oxidation, therefore colors will be less intense .  Oxygen level: during welding, usage of protective gas and electrode coating can reduce the coloration because they partly shield metal from oxidation;  The rougher: the surface, the faster it oxidizes, causing darker colors .
  5. 5. Causes of the Heat-Affected Zone  Heat affected zones can be of varying size and strength. The extent and magnitude of the HAZ is inversely proportional to the thermal diffusivity and cooling rates of the material:  Where thermal diffusivity is high, the material cooling rate is high and the HAZ is small.  Where thermal diffusivity is low, the cooling rate is slower and the HAZ is larger
  6. 6. Cont.. The extent and magnitude of property change depends primarily on:  Base material  Weld filler metal  Amount and concentration of heat input by the welding process
  7. 7. Cont.. The width of the HAZ is influenced by:  Cut speed - In general, faster speeds result in a smaller HAZ.  Amperage (when using plasma) - For a given thickness of metal, a higher amperage (and consequently a faster cut speed) results in a smaller HAZ.  Type of metal being cut - Increased temperatures and longer cutting times will result in a wider HAZ.
  8. 8. Cont.. All thermal cutting processes create a heat-affected zone in the cut metal. The amount of heat inputted by the welding process plays an important role:  Oxyfuel welding uses high heat input and increases the size of the HAZ.  Laser and electron-beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ.  Arc welding falls between these two extremes.
  9. 9. Change in microstructure HAZ  Near the fusion boundary a course grain structure is formed. It is increase the ductility.  After the course grain structure the fine grain structure is formed it increase the strength of the material.
  10. 10. Effects of Heat-Affected Zones  Because the HAZ experiences sufficient heat for a long enough period of time, the layer undergoes microstructure and property changes that differ from the parent metal.  These property changes are usually undesirable and ultimately serve as the weakest part of the component.  the micro structural changes can lead to residual stresses, reduced material strength, increased brittleness, and decreased resistance to corrosion and/or cracking. As a result, many failures occur in the HAZ
  11. 11. Conclusion  HAZ can not be removed in fusion welding process.  The residual stress is formed in the weld metal  It effect the mechanical property.  The micro structural changes can lead to residual stresses, reduced material strength, increased brittleness, and decreased resistance to corrosion and/or cracking.  As a result, many failures occur in the HAZ
  12. 12. Reference  http://nptel.ac.in/  https://en.wikipedia.org  https://www.aws.org/  Text book production engineering Dr. Swadesh kumar singh

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