Ultrasonic induction heating equipment for heat treatment of large welded parts

Large welded parts are usually used for parts that are very difficult to cast or forge as a whole. Considering the ease of processing and welding to meet special service conditions, such parts are usually assembled parts, such as machine tool bases and bodies, and large oil tanks. , large parts of power stations, surface repair of large rolls, etc., they have certain different properties and functions. Therefore, from the aspects of reducing manufacturing costs, reducing processing procedures, reducing processing difficulty, and ensuring the required performance, large-scale weldments are carried out. The homework is very correct. In order for the welded parts to meet their working needs, they must meet the design requirements and undergo appropriate heat treatment to ensure their dimensional stability and eliminate possible defects. The most commonly used equipment for heat treatment of large welded parts is ultrasonic induction heating equipment, which has very good results.

(1) Mechanical processing process. The processing procedures for large-scale welding parts are obviously different depending on the specific part requirements. Most welding parts are assembled or welded together after parts are processed in sections according to the requirements, and finally processed and formed. The more important one is the heat treatment after welding. This process directly affects the overall quality and performance of large welded parts and should be paid enough attention to.

(2) Heat treatment process. Post-weld heat treatment in a broad sense should include the following types of heat treatments: stress relief, complete annealing, normalizing, normalizing + tempering, quenching + tempering, low temperature stress relief, precipitation or aging heat treatment, etc. In addition, point heating and line heating in welding deformation are corrected. Generally speaking, the purpose of post-weld heat treatment can be summarized as follows: ① Relax the welding residual stress ② Stabilize the size and shape (for mechanical processing, etc.) ③ Improve the base metal, welding area and Performance of structural members.

The purpose of heat treatment after welding of large welded parts is to eliminate welding stress, refine grains, improve machinability, etc. After electroslag welding of cylinders, pipe fittings, bases, etc., it can improve the microstructure of welds and heat-affected zones. , eliminate welding stress, obtain good mechanical properties, etc., and at the same time prepare for mechanical processing.

(3) Heat treatment process analysis and implementation key points

① As there are many types of heat treatments for large welded parts, they should be reasonably selected according to the material and performance requirements of the specific parts. Usually, ultrasonic induction heating equipment is used for stress relief annealing after welding, and the temperature should be 500-650°C. The holding time is determined based on the effective thickness, welding area, area and size of the heat affected zone.

② The heat treatment for refining the grains and improving the performance of the welding zone is complete annealing. The heating temperature is above the phase transition point. After the heat preservation is completed, the temperature is slowly cooled. Finally, stress relief annealing is performed to ensure the mechanical properties of the welded parts and obtain Effective guarantee, while also eliminating and reducing the effects of hardening, brittleness and other effects caused by deformation and welding.

③ Regarding preheating before welding, it is particularly important in the welding of cast iron parts. Its purpose is to prevent hardening and cracks. Slow heating should be used to heat to the specified temperature with a gentle gradient without overheating.

This article briefly introduces the heat treatment process of large welded parts. Many manufacturers perform heat treatment according to the above process, and the workpieces produced are of good quality and meet their working requirements.