Effect of Calcium and Magnesium Addition on the Inclusions Distribution in the Cast Microstructure of HSLA Steel

A new technology to obtain a fine-structured and high-toughness HAZ of HSLA steel for high heat input welding is developed using metallurgical thermodynamics, physical chemistry of metallurgy and material processing methods synthetically in this study. A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding calcium and magnesium into the steel in the form of Si-Ca alloy and Mg-Zr alloy, respectively. The effect of calcium and magnesium addition on the morphology and distribution of the inclusions in the cast microstructure of HSLA steel was analysed. The results show that the distribution of the inclusions is more dense and uniform with respect to the raw steel, and the size of the inclusions is smaller than the ones in the raw steel after adding Ca and Mg elements. Ca and Mg elements can accelerate the nucleation of the inclusions. The nucleation rate of the Mg element is relatively higher. The number of the inclusions in the adding Mg steel decrease more slowly relative to the adding Ca steel with the extension of the steelmaking time.