【Abstract】Based on the analysis of the structure and welding process of the H-beam of the Tibet Cangkeba Bridge, a combined process using CO 2 welding bottoming and submerged arc welding filling cover was developed to select the correct welding parameters and slope. Process measures such as the form of the mouth and the arcing point of the control arc can fully meet the design requirements of the structure.

With the wide application of steel bridges, the use of formed or welded steel is also growing rapidly. Welded H-beams are commonly used in steel bridges because they can be made into various specifications required by design and can be used as important force-bearing parts. Generally, the welds are required to be fully penetrated and ultrasonic inspection is required. In order to ensure the quality of the products, we ensure the quality of the H-beams by adjusting and formulating reasonable welding process measures to ensure the quality of the products. , to meet the technical requirements of process technology.

First, process analysis

1. Weldability analysis

The welded H-beam of Jiaojiaoba Bridge is welded by three Q345C steel plates with a length of 5000-6000mm and a thickness of 16mm. The chemical composition and mechanical properties are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, Q345C is a low alloy high strength steel. According to the carbon equivalent formula recommended by the International Welding Society (Ceq = C +1/6Mn+1/5Cr+1/5v+1/5Mo+1/15Ni+1/15Cu), the Ceq = 0.39% to 0.4 of Q345C can be calculated. %, good weldability. However, when welding under low ambient temperature and large plate thickness, the cooling rate is too fast, which will result in hardened martensite structure, which leads to an increase in the hardening tendency of the weld heat affected zone, which is easy to produce cold cracks. At the same time, under the welding heat cycle When the welding heat affected zone is heated to 1100 °C, the welding heat input is too large, so that the grain in the heat affected zone is sharply grown to produce a Wei's body structure, which causes the coarse grain zone to be embrittled. Therefore, when welding Q345C, in order to reduce the tendency of hardening and prevent cold cracking, measures such as small heat input welding can be taken to prevent the occurrence of cold cracks and reduce the welding stress.

2. Structural analysis

H-shaped steel is welded by three Q345C steel plates with a length of 5000-6000mm and a thickness of 16mm. If the welding sequence and welding process are improperly selected, it is easy to produce bending and distortion.

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