Fundamental research of the microalloying theory based on oxide metallurgy technology

In China’s marine strategy, using oxide metallurgy technology to develop high heat input welding steel is an important guarantee for developing marine engineering equipment and high-tech ships. The theory of microalloying based on oxide metallurgy studies the mechanism of multiple factors that induce preferential competitive precipitation of ferrite in grain. This theory integrates the oxide metallurgy technology into the entire process of design, production, and welding of high heat input welding steels and considers the requirements of strength, toughness, and weldability of thick plate steel. Herein, the development of oxide metallurgy technology at home and abroad was introduced, and then the progress of microalloying theory based on oxide metallurgy was expounded. Meanwhile, the coordination and interaction of various microalloying elements, as well as the influence of the precipitation and evolution of inclusions and second-phase particles on the microstructure transformation and steel properties, were investigated. The thermodynamics and kinetics of the precipitation of beneficial inclusions during smelting and solidification were analyzed. The effects of the inclusions’ properties, size, and distribution on the nucleation of Ferrin were analyzed. The mechanisms of microstructure evolution, grain refinement, preferential precipitation of ferrite, and improvement of strength and toughness of base steel and weld heat-affected zone during hot working and welding were reviewed. The research progress and existing problems of oxide metallurgy were completely summarized. Combined with the results of the research group, the theory of microalloying based on oxide metallurgy was put forward, and microalloying based on oxide metallurgy has been proposed. Including the design theory of the microalloy system, the synergistic and interactive mechanism of microalloying elements under the condition of multi-element coexistence, and the effects of microalloying elements oxidation, carbonitriding, and sulfurization on the formation, evolution, and distribution of inclusions and second-phase particles in the whole process. The mechanism of inclusions and the properties and distribution of the second-phase particles improving the strength and toughness of coarse-grain heat-affected zone (CGHAZ) and inducing the preferential precipitation of ferrite in grain were also discussed. Microalloying based on oxide metallurgy is a further development of the oxide metallurgy technology. This research will greatly promote the development of oxide metallurgy technology. This will provide a theoretical and technical basis for developing steel materials with high strength, high toughness, and excellent weldability. It will provide an effective method for producing high-strength and high-toughness thick plate steel, section steel, and nonquenched and tempered steel by oxide metallurgy technology.