Heat affected zone

HEAT AFFECTED ZONE

1. HEAT AFFECTED ZONE JAY PRAKASH MTECH 3 RD SEM 16 MEIM 061 GD-1368 MECHANICAL DEPARTMENT ZHCET AMU ALIGARH

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. 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. 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. 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. 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. 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. 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. 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.  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. 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. Reference http://nptel.ac.in/ https://en.wikipedia.org https://www.aws.org/ Text book production engineering Dr. Swadesh kumar singh