With the continuous development of the national economy, the demand for the diversification of hot-rolled products is growing, requiring steel companies to continuously develop new products and improve product quality to meet demand.
AG700L of high-strength automotive girder steel is an important variety of steel for commercial automotive steel in Ansteel's hot continuous rolling production line.
Its process route is molten iron pretreatment - 150t converter - LF refining - double-flow slab casting machine - 1780 hot continuous rolling. Due to the complex deformation conditions and welding process in subsequent processing, in order to prevent cracking and deformation, the performance and plate shape requirements are extremely strict.
In order to obtain a fine and uniform final organization (F + P) to meet the complex deformation and welding conditions, the process adopts a centralized and rapid cooling method for the post-rolling steel strip.
This cooling method has high requirements for the cooling uniformity and cooling speed of laminar flow, in order to improve the uniformity and cooling capacity of laminar flow cooling, ansteel's 1780 hot continuous rolling production line has transformed and upgraded laminar flow cooling.
During the commissioning process after the transformation, the AG700L steel has a batch plate shape defect problem after the user opens the flat. The resulting quality objections increase processing costs and seriously affect product quality.
Regarding the research on the plate shape of hot-rolled steel strip, many scholars have studied micro-medium wave rolling, laminar flow homogeneous cooling, edge shielding technology, thermal-force-phase change coupling finite element analysis and achieved certain results.
Among them, micro-medium wave rolling production as a method to alleviate plate shape defects has been widely used, but there is no more reference to the causes and countermeasures of plate shape defects after opening and leveling.
Aiming at the plate shape problem of hot-rolled steel strip, combined with the outstanding problems encountered after the transformation and commissioning of laminar flow equipment, the causes and process improvement measures of plate shape defects after hot-rolled broadband steel are opened and leveled are discussed.
(1) The common reason for the high-strength automotive steel AG700L after leveling the wave and the lateral bending after the longitudinal cutting is that the side temperature drops too fast when the steel belt is cooled by laminar flow, and the uneven phase change causes the edge pressure stress to be too large, and the stress is released after the opening and leveling.
(2) By optimizing the micro-medium wave and temperature distribution (edge high temperature) of the fine-rolled outlet strip, the plate shape problem can be alleviated, but the plate shape defect after opening and leveling cannot be fundamentally eliminated.
(3), laminar flow cooling is crucial to the strip plate shape, by optimizing the water ratio to stabilize it at 1:1.35, increasing the side spray pressure to 2.0MPa and optimizing the cooling mode, it can improve the uniformity of laminar flow cooling and reduce the plate shape defect after opening and leveling.
(4) Through the use of edge shielding, the temperature drop of strip edges can be effectively slowed down, and after combining with other optimization measures, the plate shape defects after opening and leveling can be basically eliminated.
