Recently, Baosteel Co., Ltd. successfully developed and trial-produced 690MPa grade square steel for tunnel-embedded parts, and the product has been sent to users for trial use.

It is understood that tunnel-embedded parts are to increase the stability of the tunnel structure, support the tunnel foundation, and effectively improve the safety of engineering construction, so the steel used for embedded parts must have sufficient strength, rigidity, and corrosion resistance. For a long time, most of the domestic tunnel embedded parts have been made of carbon structural steel and low-alloy strength steel. During the market visit, the technical center learned that the 690MPa grade material will be used for the first time in the design of embedded parts of a tunnel project. Immediately, the manufacturing department, special steel branch, steel mill, and other units were united to quickly link production, sales, and research, and cooperate to complete the contract review of new products as soon as possible. According to user needs and usage, the technical center organized the formulation of the chemical composition and production process route of 690MPa grade square steel and issued a quality plan to carry out industrial trial production, and test and verify the subsequent heat treatment process of 690MPa grade square steel and perform performance inspection. At present, 500 tons of 690MPa grade square steel for tunnel-embedded parts have been rolled and sent to users for trial use.

Song Zhendong, a researcher at the Long Profile Research Institute of the Technology Center, said: "The strength level of 690MPa is not only the highest strength level among low-alloy high-strength steels, but also requires 0℃ low-temperature toughness. Since users need to process it into steel for tunnel-embedded parts through complex processes in the future, it is very important to design the quenching and tempering system of 690MPa grade square steel according to the user's production process." The annual demand for 690MPa grade steel for tunnel-embedded parts can reach more than 4,000 tons, which has considerable economic benefits. The development of 690MPa grade square steel for special purposes will make a positive contribution to improving the core competitiveness of enterprises.