Abstract
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 into the steel in the form of Si-Ca alloy. The effect of calcium addition on the morphology and compositions of the inclusions in the cast microstructure of HSLA steel was analyzed by using SEM and EDS. The results show that lots of calcium oxides and inclusions formed after pouring into ingots owing to the adding calcium element. The distribution of the inclusions is homogeneous, the size of the inclusions is even small, and most calcium inclusions are spherical and ellipsoidal. Adding calcium element in different amounts can lead to the large difference in the composition of the inclusions. The main components of the inclusions formed are calcium oxides and the composite inclusions, as well as the oxides, sulfides and composite inclusions of the other metallic elements.
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