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Welding component heat treatment process control process

In order to ensure the performance and quality of the welded components, improve the plasticity of the weld metal, eliminate or reduce the welding residual stress, prevent cracks, and heat-treat the welded components if necessary. According to the order of the heat treatment process and the welding process, the heat treatment of the welded component is often divided into three types: pre-heat treatment, post-heat treatment and post-weld heat treatment.
 
1. Pre-heat treatment is required before the heat treatment, that is, the structural member is heated integrally or locally before welding. The purpose is to slow down the temperature gradient and cooling speed of the welded joint heating, and appropriately extend the cooling time of the welded joint from 800 ° C to 500 ° C to facilitate the escape of hydrogen in the weld, reduce the occurrence of hardened structure and prevent the occurrence of cold cracks. .



Second, the post-heat treatment is to heat the weldment or the weld zone with the preheating device immediately after the welding is stopped, and keep it for a certain period of time. The purpose is to allow the hydrogen in the weld metal to escape sufficiently to prevent the generation of cracks. In practical applications, the effect of post-heat treatment to prevent cracks is more pronounced for low-alloy steels with higher strength grades and welded members with larger thicknesses. Choosing a reasonable post-heat treatment temperature can reduce the preheating temperature to some extent or even cancel the preheating.

3. After the welding component is welded, it is heat treated in whole or in part. Its purpose is to improve the microstructure and properties of the metal, reduce the welding residual stress, soften the hardened structure of the weld heat affected zone, improve the toughness of the welded joint and the geometric stability of the structure. According to the purpose of post-weld heat treatment, it can be divided into stress-relieving heat treatment, post-weld annealing, normalizing, quenching, and low temperature stress removal.
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