The development and application of controlled rolling and cooling technology
The development and application of the new generation of controlled rolling and controlled cooling process technology with ultrafast cooling as the core has been more than ten years. After continuous improvement and process expansion, the application of post rolling cooling in the hot continuous rolling production line has been expanded from the application of post rolling cooling to a large-scale ultrafast cooling system integrating temperature control cooling of intermediate billets in the rolling process and ultra fast cooling after rolling. The flexible temperature control of the multi process rolling process provides a process means to realize the temperature control and organization regulation of rolling cooling integration. At present, its typical process configuration is shown in Figure 1.
The rolling temperature control cooling system has three process layout forms according to the process requirements. First, it is arranged on the roughing mill, which aims to realize the instant cooling between roughing passes. Through the effective combination of cooling and rolling passes, it can realize the instant temperature control in the roughing process, and provide support for the integrated control process of rolling and cooling; Second, it is arranged behind the roughing mill. Its purpose is to cool the intermediate billet after roughing, reduce the steel swing waiting time of typical steel grades, and effectively redden the time before entering the finishing mill to ensure the uniformity of the surface temperature of the intermediate billet; Third, it is arranged in front of the finishing mill. After the cooling system and before the intermediate billet enters the finishing mill, the temperature return time is relatively short, the surface temperature return is insufficient, and there is a certain gradient in the slab thickness direction, so as to realize the differential temperature rolling process of finishing rolling, promote the deformation of the center of the intermediate billet, and then improve the center structure of hot continuous rolling strip.
Based on the understanding of the organization regulation mechanism under ultra fast cooling after rolling and the development practice of ultra fast cooling equipment, post rolling cooling processes such as ufc-f, ufc-b, ufc-m and post ufc-dp have been developed successively, giving full play to the comprehensive role of various strengthening mechanisms, so that the consumption of main alloy elements in steel can be saved by 20%-30%, or the performance of steel materials can be greatly improved, and the characteristic and high-quality hot strip rolling process technology and product development can be realized, It is conducive to cost reduction and efficiency increase, quality improvement and efficiency increase in steel production.
For Hot-Rolled Structural Steel characterized by ferrite pearlite structure, based on ufc-f process, fine-grained structural steel, such as ordinary carbon structural steel, wheel steel and hot-rolled coil products with narrow performance fluctuations, have been developed. After rolling, it is quickly cooled to the temperature below the dynamic transformation point through the ultrafast cooling system, and cooled at a high rate, so that the hardened austenite rich in defects is saved to the ferrite transformation range, so as to realize the refinement of ferrite and pearlite structures, and improve the strength and toughness of products at the same time.
For high-grade pipeline steel products, especially thick specification pipeline steel, using ufc-b process technology, the high cooling capacity can ensure that the center of the steel plate still has a high cooling rate, which is conducive to obtaining a large number of refined acicular ferrite in the center, so that pipeline steel products with stable performance such as low-temperature impact toughness and DWTT can be obtained under the condition of low-carbon equivalent composition design, and the thickness range of pipeline steel products can be further expanded, The development and industrial application of X70 pipeline steel with limit thickness of 25.4mm have been realized. It provides process methods and technical support for effectively solving the contradiction between the low carbon equivalent composition design of thick high-grade pipeline steel and good low-temperature impact toughness, DWTT and other properties. At the same time, taking advantage of the characteristics of ultra fast cooling and high-strength homogenization cooling, a new generation of control cooling process control strategy is adopted for high-grade pipeline steel. Under the single use of ultra fast cooling process, the problem of high residual stress of pipeline steel under conventional process is effectively solved by using the temperature gradient in the direction of plate thickness, and the development and mass industrial production of low residual stress high-grade pipeline steel are realized.
For hot-rolled dual phase steel and other products, using ufc-m process technology, martensitic transformation can be realized under the C-Mn composition, and the reduction of composition can be realized while ensuring the good and stable service performance of the steel plate. At the same time, a multi-stage duplex steel product with high strength, toughness and elongation flange properties was developed by using the flexible regulation of two-stage cooling path. The development and production of hot-rolled dual phase steel with thickness of 3.0-11.0mm and strength of 540-800mpa have been completed by using post placed ultrafast cooling. The development and practice of process technology of series products have made contributions to promoting the production process and technology progress of high-quality hot-rolled dual phase steel in China.
It can be expected that in the field of hot strip rolling, based on the new generation of controlled rolling and controlled cooling process, the laminar cooling system will be cancelled in the post rolling cooling area, and 7-8 groups of new generation of controlled cooling systems characterized by ultra fast cooling will be configured, which is of great practical significance for realizing the high-precision control of post rolling temperature and the precise regulation of microstructure and performance of plate and strip steel, and realizing the low-cost and efficient development and production of high-quality plate and strip steel.
