After nearly a decade of rapid development, China's steel structure industry has experienced a significant qualitative improvement. As the sector continues to grow, the demand for high-strength steel, thick plates, and various structural profiles has surged, driven by large-scale construction projects. Alongside this growth, advanced welding technologies—such as high-strength steel welding, thick plate welding, and high-heat input techniques—have become widely adopted. These advancements have positioned China’s steel structures among the world’s most competitive in terms of quality and innovation.
Over the past ten years, high-strength steels such as Q390, Q420, and Q460 have been increasingly used in major projects across the country. In addition to the traditional low-alloy high-strength steel Q345, these higher-grade materials have found applications in iconic structures like the Beijing National Stadium (the "Bird’s Nest"), the Water Cube, the Shanghai World Financial Center, the new CCTV headquarters, the Shanghai Tower, the Shenzhen Ping An Tower, and the Shenzhen Jingji 100 Center. These projects showcase the growing use of high-strength steel in modern architectural and engineering designs.
The performance of welded joints in high-strength steel is influenced not only by the material properties but also by the welding method, filler materials, and overall process parameters. Common welding techniques used in practice include gas metal arc welding (GMAW), submerged arc welding (SAW), electroslag welding (ESW), and shielded metal arc welding (SMAW). Flux-cored arc welding (FCAW) is generally avoided for high-strength steel due to its limited penetration depth. Compared to ordinary Q345 steel, high-strength steel typically has a higher carbon equivalent, which can lead to poor weldability, increased hardening in the heat-affected zone, and greater susceptibility to cracking during thermal processing.
In real-world applications, challenges such as joint cracking, hot cracking under high-heat input, and degradation of the heat-affected zone are common issues in high-strength steel welding. To address these, careful consideration must be given to several factors when selecting the appropriate welding process:
1. The material’s weldability, including carbon content, trace elements, carbon equivalent, crack sensitivity index, and the thickness of the material being welded.
2. The suitability of the welding method, especially whether post-weld heat treatment is required and how well the HAZ toughness performs under high heat input.
3. The hydrogen content in the deposited metal and the presence of trace elements in the filler material.
4. The heat input during welding, ambient temperature, groove geometry, stress concentration factors, bead configuration (single or multi-pass), preheating methods, and joint restraint conditions.
In summary, ensuring the quality and performance of welded joints is essential in high-strength steel applications. The goal is not only to achieve joint strength that matches the base metal’s grade but also to minimize brittle fracture risks by controlling maximum strength. Additionally, preventing both hot and cold cracks—especially cold cracks—is crucial. Due to the higher levels of trace elements added during smelting, it's vital to carefully select welding parameters and auxiliary measures, particularly when carbon content is high.
For more detailed information on welding techniques and best practices, please refer to the attached document or read the 18th issue of *Metalworking (Hot Processing)*.
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