At present, China's construction steel structure industry has gradually moved from the development stage to the mature stage, and both steel production and steel consumption rank first in the world. In many steel structure projects, thick steel high-strength steel is used more and more widely in construction engineering in order to meet the requirements of architectural modeling and structural load.
Key points and difficulties in the welding process of high strength steel:
1 According to international practice, the test of weldability of new steel grades should be undertaken by the manufacturer and the research institute. However, there is no clear regulation on such weldability tests in China, which is generally undertaken by the construction unit. Therefore, the weldability test of new steel grades is studied. It will become the focus and difficulty in building steel structure engineering.
2 In the alloy structure, with the increase of alloying elements, it will affect the hardening, softening and cracking tendency of welded joints. Therefore, how to prevent welding cracks and embrittlement in heat-affected areas will become the key and difficult points in the welding process of high-strength steel. .
3 Prevention of thick-walled high-strength steel The layered tear in the welding process is also the key and difficult point to control the welding of high-strength steel.
4 Because the size of the slab high-strength steel groove directly affects the construction period and the internal quality of the weld, the design of the slab weld joint groove has always been the focus of the process.
In view of the key points and difficulties in the above welding process, the main technical measures taken are as follows:
(1) Select the welding material that matches the base metal. Select the low-hydrogen and ultra-low-hydrogen welding materials in the selection of the welding consumables to reduce the welding defects such as cracks and pores during the welding process. For the specific welding material selection standards, please refer to GB8110—2008 “Carbon steel for low-alloy welding of gas-shielded arc weldingâ€, GB/T5293 “Carbon steel welding wire and flux for submerged arc weldingâ€.
(2) Groove design Because of the large amount of welding and the difficulty of thick plate welding, if the welding is carried out with narrow and deep small groove, not only the weld forming coefficient is small, but also affects the primary crystallization, is prone to regional segregation, and is restrained. Under the premise of high stress, the welding hot crack is generated. If the welding is carried out with large groove, not only the welding amount is increased, but also the welding residual stress of the weld is increased, which is extremely unfavorable for controlling the initial stress of the steel structure system. It also affects the construction period. Therefore, 30°～35° groove is used in the construction (the groove angle is proportional to the thickness of the base metal plate), the groove gap is 6～10mm, and when the plate thickness exceeds 40mm, it is required to open the layer. Tearing the groove.
The bevel processing requires a flame cutting machine to avoid manual opening and thus affect the quality of the later welding.
(3) Measures to control welding cracks
1 Pre-heating the weld and its surrounding 100mm range before welding. For preheating temperature, refer to GB50661 "Code for Welding of Steel Structures".
2 Strictly control the interlayer temperature during the welding process, the requirement is not lower than the preheating temperature. When welding, try to use small current to control the welding heat input, which can effectively reduce the welding deformation and welding stress; it is strictly prohibited to use the multi-layer multi-pass welding for welding. arc.
3 After welding, it is necessary to carry out post-heating and hydrogen-removing treatment on the weld in time, so that the hydrogen ions remaining in the weld can escape in time and reduce the tendency of cold cracking.
For more details, please refer to the attached content or read the 18th issue of Metalworking (Hot Processing).
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