The blast furnace shell, converter support ring, continuous casting machine frame, and rolling mill frame of metallurgical plants all belong to giant, thick plate welded structures. They bear enormous static loads, impact loads, and thermal fatigue. The core function of heat treatment here is to ensure the overall dimensional stability and joint toughness of the structure.
Industry characteristics
The prominent feature of welding in metallurgical plants is that the components are extremely thick and the amount of weld filling is large, resulting in high levels and complex distribution of residual stresses in welding. Therefore, the focus of its heat treatment is to provide strong stress relief for thick and restrained joints to prevent low stress brittle fracture under load, rather than fine tissue adjustment.
Key points to note
Preheating before welding: Preheating is mandatory for carbon manganese steel plates with a thickness exceeding 30mm. The preheating range should be wide, usually covered with electric heating plates to ensure consistent heart temperature and prevent layer tearing.
• Hydrogen elimination treatment: In multi-layer and multi pass welding of thick plates, intermediate hydrogen elimination treatment should be carried out every time a certain thickness (such as 50mm) is welded or the arc is stopped halfway. This is particularly important for high-strength steels such as Q690, as it can effectively prevent delayed crack initiation deep in the weld seam.
Post weld heat treatment:
1. Method selection: Due to the large size of the workpiece, it is often impractical to perform overall furnace heat treatment, so local heat treatment is widely used. Wrap the weld area with insulation material and install a heater inside for heating.
2. Temperature control: The difficulty of local heat treatment lies in temperature uniformity control. Sufficient thermocouples must be arranged on the weld seam, heat affected zone, and surrounding base metal to ensure that the heating bandwidth and temperature gradient meet the specification requirements and prevent the generation of new local stress concentrations.
3. Insulation time: The insulation time should be calculated based on the maximum thickness to ensure sufficient relaxation of stress.
Product Application
Metallurgical parts are heavy and have a high degree of constraint, making it impractical to process them as a whole in the furnace. Our company's flexible ceramic heating element and high-power temperature control machine are powerful tools to solve this problem. The heater can be flexibly spliced, bundled or adsorbed according to the shape of the weld seam, achieving precise heating of specific high stress areas. Our temperature control box supports the arrangement of multiple thermocouples, which can monitor temperature in real-time at multiple key points such as welds, heat affected zones, and base materials. With powerful computing capabilities, it automatically adjusts output power to ensure that even in complex local heat treatment conditions, the temperature gradient of the entire heating area can meet the strictest specification requirements, thereby effectively eliminating huge welding stresses.