Under the guidance of Academician Wang Guodong, the research team of essential fine grain steel of Northeastern University's State Key Laboratory of Rolling Technology and Continuous Rolling Automation (RAL), Dr. Wang Chao, based on the basic research on the principle and mechanism of essential fine grain of hot rolled steel, On the basis of scientific issues such as the evolution of two-phase particles and the mechanism of induced phase deformation, the laboratory research and industrialized trial production are combined to break through the core technology of composition and regulation of the entire process of composition-smelting-rolling-cooling. The application of crystal steel technology in the mass production of rebar products has achieved breakthrough research progress. This study makes full use of the second phase of oxygen / sulfur / nitride particles to induce fine grains, exerts the fine grain strengthening mechanism, reduces the large addition of microalloying elements, reduces alloy costs and production difficulties, and forms a stable industrial production technology. At present, the essence of fine grain steel technology has been applied to the industrial production of 12 ~ 36mm HRB400E seismic rebar with good organization performance and significant cost reduction effect. Based on the research, relevant process technology innovations have been declared for 5 national invention patents and 4 international patents, forming a complete set of industrial process technology, which can provide enterprises with a package of subsystem solutions.
Rebar is the largest and most widely used steel category in the field of construction steel. For the steel industry, the production of rebar products is relatively simple, and simple ingredients and processes should be used as much as possible to obtain high-quality products. In 2018, China implemented the new national standard GB / T 1499.2-2018 for rebar, which strengthened the requirements for metallographic organization of products. In order to meet the requirements of national standards, each rebar manufacturer further strengthened the use of vanadium or niobium microalloying technology, which not only caused an increase in production costs, but also caused a huge consumption of precious alloy resources. In response to the requirements of the new national standard for the regulation of organizational performance, especially for large-sized products, it is urgent to carry out technological innovations to achieve the economic and green production of high-quality rebar. In terms of mechanism research, Dr. Chao Chao made clear the control mechanism for the dispersion of fine second-phase particles through thermodynamic analysis of oxygen / sulfur / nitride precipitation during smelting, solidification, and rolling, and examined Austenite under different thermal deformation conditions. The body coarsening rule and microstructure transformation behavior, the mechanism of oxygen / sulfur / nitride-induced fine-grained phase deformation and nucleation are analyzed, the interaction mechanism of the second-phase particles and tissue evolution is clarified, and it provides theoretical support for the development of process technology. In the practice of industrialization of basic research results, combining industry-university-research, based on a systematic sampling analysis of the evolution of inclusions in the rebar industrial production process, the optimal content range of oxygen, nitrogen and other elements and their control methods were explored. The absorption rate of titanium and other elements and its influencing factors determine the best way to add oxygen / sulfur / nitride-forming elements, explore the ingredients and production rhythm control methods under 150t converter conditions, and focus on solving the matching between processes under fast rhythm The forward problem of continuous casting and continuous casting, and the influence of process parameters on performance under single-line rolling and split rolling.
After multiple rounds of industrial trial production, the actual problems in different production lines have been solved, and the entire process flow of smelting, continuous casting and rolling has been opened up. During the multi-round continuous trial production of thousands of tons, the production process is stable and the product performance is excellent. , Established a mature and stable industrial production process plan. Through the implementation of essential fine-grained steel technology, HRB400E threaded steel bars reduce the consumption of microalloys under uncontrolled rolling and cooling conditions, and the grain size is refined by more than 1.5 grades compared with conventional vanadium-containing steel bars. On this basis, further combined with different standards and specifications to adjust and optimize the composition and process, developed Ti-based, Ti-RE-based, Ti-Cr-based, Nb-Ti-based, V-Ti-based, Ca-Mg-based, Ti -Ca series rebar products with different composition systems and process characteristics.
Conventional vanadium-nitrogen microalloyed reinforcement structure
Intrinsic fine-grained reinforcement structure
In fact, since the beginning of his PhD, Wang Chao has been conducting basic research on essential fine-grained steel around the second-phase particle-induced microstructure refinement mechanism and process. In essence, the research on fine-grain steel is mainly aimed at the major needs of uniformity regulation of the full-section microstructure of large-sized, large-section, or thick-gauge hot-rolled steel products. It is intended to adopt relatively reasonable composition design and process control methods to achieve the refinement of the steel section microstructure. Improve the comprehensive strength and toughness of steel materials. During the PhD study, for several years, Wang Chao squatted beside the experimental smelting equipment. He concentrated on research, combined theoretical analysis and experimental research, thoroughly investigated the precipitation rules of each deoxidizing element and the organization refinement mechanism, and further penetrated into the production site of iron and steel enterprises. Focus on combining basic research results with industrial practice. The research carried out mainly includes: for the difficult to refine uniformly the microstructure of large-energy-energy welding steels, hot-rolled pipes / profiles / bars and rods, or the heat-affected zone of welding, by introducing a high thermal stability of the dispersion in the steel Second phase particles, including oxygen / sulfur / nitride of titanium, calcium, magnesium, zirconium, boron, rare earth and other elements, pin the grain boundaries and induce grain boundary / intra-grain phase deformation nuclei during heating, deformation and cooling, Obtain a uniform fine-grained transformation structure and improve the overall strength and toughness of the material. The RAL essential fine-grained steel research team focuses on the actual production needs of rebar, highlights the theoretical support role of basic research in the industry-university-research innovation chain, flexibly and effectively uses the dispersed second-phase-induced fine grain strengthening mechanism, and promotes process technology through breakthroughs in basic research Innovation and progress provide innovative ideas and technical routes for the high-quality production of rebar. At the same time, relevant research breakthroughs are also of great reference value for the realization of the essential fine-grained production of other steel products, and are of great significance for the development and production of high-quality steel materials in China's steel industry.