| As the developments of constructional engineering and shipbuilding industry, the need for constructional steel is increasing more and more. However, the quality requirements are also more and more strickly. In order to improve welding effeiency, the technology of high heat input welding is adopted, it is expected that steel remain keep excellent toughness when liner power more than 100kJ/cm is input. It is important to choose inclusions with high melting point and stability as pinning particle.Accoring to the Dehoff Equation, proper dissolved oxygen content for different oxides are estimated to meet the oxide metallurgy. Through the thermodynamics and kinetics study, the result of nuclei rate and grow velocity for Al2O3, MnO, SiO2, MgO, CaO, ZrO2 are got. According to the nuclei and grow mechanism of inclusion, the conditions of deoxidants are got:with low interface energy of liquid iron and strong deoxidation ability.Based on above calculation and analysis, Ti-Al, Mg, Ti-Mg, Ca, Ti-Zr were choosen as deoxide alloys respectively to study the characteristics of inclusions and its influence on toughness of steel. Quantitative metal lographical and SEM analysis show that Ti-Mg deoxide alloys addition induce a large number of inclusions with small size formation, the number of inclusions attains to 12404 per square millimeter. The inclusions in size less than 0.6μm and 1μm are 56.6 and 75.2 percent of the total inclusions respectively, and distribute uniformly in steel, the components of most of inclusions are MgO-TiOx-SiO2-MnO, and MgO, TiOx are the main body, the Charpy absorped energy attains to 65.9J/cm2, which is the maximum of all the five experiments. However, the other experiments show different results of inclusions, and the toughness is lower than Ti-Mg addition.
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