Low-temperature welding technology of low alloy bridge steel

Abstract

The invention relates to a low-temperature welding technology of low alloy bridge steel. The technology comprises the steps of processing welding bead grooves, preheating before welding and insulating after welding, and is characterized in that high temperature resistant ceramic backings are adhered at the bottom of ''Y-shaped'' groove welding beads of two butted parent materials of the low alloy bridge steel; a double-side formation with one-side welding is adopted by the welding; meanwhile, an insulation rockwool is adopted; and an automatic temperature control heating tape is used for carrying out the preheating before welding, the temperature control during welding and the preheating, the temperature control and the insulation after welding, and finally carrying out retarded cooling. The technology has the advantages that: as the heat automatic temperature control heating tape and a thermocouple temperature measurement probe are adopted, the accurate control can be conducted on the temperature and the time of the preheating before welding, and the insulation and the retarded cooling after welding at different thicknesses and different environmental temperatures of the steel, thereby ensuring effective precipitation of hydrogen. Furthermore, the occurrence of low-temperature welding cold cracks and low-temperature brittle phenomena can be avoided effectively.

Description

technical field [0001] The invention belongs to the technical field of low-temperature welding, and in particular relates to a low-temperature welding process for low-alloy bridge steel that can ensure continuous construction of steel structure bridges in northern winter and ensure welding quality. Background technique [0002] Due to its excellent mechanical properties, low-alloy steel can reduce the cross-sectional size of components and reduce the amount of steel under the same load-bearing state, so it is widely used in steel structures, but its low-temperature welding technology has not been able to break through, that is, it cannot adapt to Including bridges and other important steel structure construction needs in winter in the north, with the rapid promotion of steel structure bridges in recent years, in northern my country, in order to ensure the continuous construction of steel structure bridges in winter and ensure the welding quality, solve the low temperature weld...

AI Technical Summary

Problems solved by technology

[0005] Although the above two methods have solved some problems in the welding construction of thick steel plates in low temperature environment under certain conditions, for example, the groove opening of the weld seam adopts double-sided groove, so it is easy to weld due to the time difference between the upper and lower weld bead during the welding process. Temperature stress is generated, which makes the delay effect obvious and the possibility of low-temperature brittle fracture increases. Preheating with acetylene flame before welding cannot control the preheating temperature, and the temperature may be too high or too low. Excessively high preheating temperature is detrimental to the toughness of the joint , which increases the brittle transition temperature of the joint and increases the possibility of low temperature brittle fracture

At the same time, due to the inability to continue heating and heat preservation, the cooling speed of the weld bead is fast, the grains become coarser, and the sensitivity to cold cracks increases. Especially for the on-site butt welding of bridge steel in winter, the ambient temperature is extremely low, and the original commonly used flame is used. Heating preheating and heat preservation measures, due to the uneven heating and the inability to accurately control the heating temperature and holding time, the temperature section of the welding area is at the optimum value, the effective precipitation time of hydrogen is shortened, the hydrogen content of the weld metal increases, and cracks are delayed Increased likelihood of occurrence

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