types of post weld heat treatment, also known as stress relieving, is a process used to reduce or eliminate residual stresses in welded materials. Residual stresses are caused by the rapid heating and cooling that occurs during the welding process and can cause problems like hydrogen induced cracking. Post weld heat treatment is used to reduce or eliminate these stresses and improve the strength and durability of welded structures.
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There are a few different types of post weld heat treatment, including artificial aging, normalizing and quenching. Artificial aging is used in precipitation hardened alloys that have been welded because these metals rely on the formation of precipitates to block dislocations within the crystalline structure of the material, increasing its strength and hardness. When these metals are welded, the precipitates may be changed or destroyed by the welding heat and require a post weld heat treatment to ensure they are formed to the correct size.
Another type of post weld heat treatment is normalizing, which is used in TMCP steels to increase their corrosion resistance and strength. This is achieved by raising the temperature of the weldment to a point that it approaches its critical yield strength, and then allowing it to cool gradually. This increases the strength of the weldment, and reduces distortion.
The final type of post weld heat treatment is quenching, which is used in many welded steel structures to ensure they do not crack during cold weather operations. This is done by rapidly heating the weldment to its critical temperature, and then allowing it to cool gradually. The quick heating and cooling reduces the levels of tensile residual stresses in the weldment, and this helps to prevent the formation of hydrogen induced cracking.