In addition to high enough strength (mainly yield strength), low alloy high strength steel also has good processability, weldability and corrosion resistance. Compared with low carbon steel, the low-alloy high-strength steel heat-affected zone is easy to harden and has strong sensitivity to hydrogen. When the welded joint is subjected to large stress, various cracks are easily generated. In addition, under the action of the welding thermal cycle, the microstructure performance of the heat-affected zone is changed, and the tendency of brittle fracture is increased, especially the thick plate structure. Therefore, the main difficulty in welding such steels is to prevent cracks (including cold cracks, hot cracks, lamellar tears, etc.) and to improve the toughness of welded joints.
(1) The wire used should be subjected to oil removal and drying treatment, and the drying temperature is 350-400 °C.
(2) Strictly control the preheating temperature and interlayer temperature before welding. Preheating should be carried out by heating with flame heater or electric heating sheet. The heating area for preheating should be on both sides of the welding groove, and the width should be the welding position of the weldment. More than 1.5 times the thickness and ≥100mm, the temperature between the solder layers (channel) is controlled to ≤250 °C, not lower than the minimum preheating temperature.
(3) Multi-layer multi-pass welding with medium welding current.
(4) Appropriately increase the dry elongation of the wire under the premise of ensuring the stability of the arc.
(5) Pay attention to the surface cleaning of the groove.
(6) After the hydrogenation treatment, the heating temperature of the hydrogen elimination treatment should be 200~250°C, the holding time should be ≥0.5h according to the thickness of the workpiece, and the total holding time should not be less than 1h, and the holding time is reached. After that, it should be slowly cooled to normal temperature.
The welding methods and equipment commonly used in high-strength steel in steel structures are as follows:
(1) SMAW (electrode arc welding) It is mainly used for the welding of auxiliary welds in the manufacture of steel structures. The supporting welding rods are CJ607RH, CJ707RH, CJ807RH and CJ107.
(2) SAW (submerged arc welding) It is mainly used for the welding of the main weld in the production of steel structure. The matching welding wire and flux are H10Mn2 and SJ101, H08MnA and HJ431. The welding equipment types commonly used by our company are MZ-1000/1250 submerged arc welding machine, LHC cantilever submerged arc welding machine and LHE box type gantry type three wire submerged arc welding machine, as shown in Figure 1~3.
(3) GMAW (CO2 solid wire welding gas shielded welding) is mainly used for the welding of primary and secondary welds in the field installation and production engineering. Commonly used welding wire is WH50-6, WH60-G, WH70-G, commonly used The equipment is the Austrian NBC-500 (see Figure 4), the Panasonic KRII500 (see Figure 5) and the XQ15 cantilever type gas shielded welder.
(4) FCAW-G (CO2 flux cored wire gas shielded welding) is mainly used for on-site installation and fabrication of welding of primary and secondary welds. The commonly used welding wire is CHT711.
(5) ESW (Electro-Slag Welding) Mainly used for the welding of BOX member ribs. Commonly used welding wire and flux are WH50-6 and JF600. The commonly used equipment type is XSD15 cantilever type wire electro-slag welding machine (see Figure 6). .
(6) SW, SW-P (stud welding) Mainly used for bolting of stiff components and penetration welding of floor panels.
For more information, please see the attachment or read the 18th issue of Metalworking (Hot Processing).
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