What is the purpose of post-weld heat treatment?

The purpose of post-weld heat treatment is centered on relieving residual stresses and improving the metallurgical properties of the weld. When welding, the intense heat causes the metal to expand and subsequently contract as it cools, which can introduce stresses within the weld and the heat-affected zone. These residual stresses can lead to issues such as cracking, distortion, or decreased structural integrity over time.

Post-weld heat treatment involves heating the welded joint to a predetermined temperature and maintaining that temperature for a specified duration before allowing the weld to cool down slowly. This process helps in normalizing the material structure and reduces the hardness created by the welding process. Additionally, it allows for the reformation of the microstructure, leading to improved toughness and ductility.

In contrast, enhancing the color of the weld, preparing the metal for painting or coating, and allowing for faster cooling do not address the fundamental issues of stress relief and metallurgical enhancement that post-weld heat treatment is designed to solve.