Under normal circumstances, according to the sequence of the heat treatment process and the welding process, the Welding Parts Suppliers divides the heat treatment of the welded parts into three steps of pre-heat treatment, post-heat treatment and post-weld heat treatment.
1. Pre-heat treatment: The pre-heat treatment is to heat the structural parts in whole or in part 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 cold cracks. The production. In addition, the overall preheating of the components can also appropriately improve the uniformity of the temperature distribution of the weldment and reduce the internal stress.
The preheating temperature can be determined by an empirical formula or with reference to relevant experimental data. It should be noted that these calculation formulas or experimental data are established under certain test conditions according to the minimum preheating temperature without cracking. Therefore, special attention should be paid to the applicable range to avoid unnecessary losses. The preheating temperature is too high, which not only increases the cost, but also deteriorates the labor conditions of the welder. Therefore, a lower preheating temperature should be used wherever possible to meet the process requirements. In the case of interlayer heating of the multilayer welded member, in order to prevent the occurrence of delayed cracks, the interlayer temperature should not be lower than the preheating temperature, otherwise the generation of delayed cracks cannot be effectively prevented.
2. Post-heat treatment: Post-heat treatment is to heat the weldment or weld zone with a 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 a certain extent (generally 50 ° ° C), or even cancel the preheating. Reducing the preheating temperature is beneficial to improving the working conditions of workers, increasing production efficiency, reducing energy consumption, and reducing the chance of defects such as hot cracks due to excessive preheating temperatures.
3. Post-weld heat treatment: Post-weld heat treatment is the overall or partial heat treatment of the welded components after the welding is completed. 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.
Post-weld heat treatment has the effect of improving the toughness of steels such as low-carbon steel, but it may reduce the toughness of some high-strength steels. For quenched and tempered high-strength steel, if the heat treatment temperature exceeds the tempering temperature, the material will lose its original quenching and tempering effect, resulting in a decrease in strength and toughness of the steel.
After reading the above introduction, you must have a better understanding of the welding parts. If you are interested in our company's products, please come and give us a message.<!--?xml:namespace
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