材料期刊网

Effects of Mg on the chemical component and size distribution of Tibearing inclusions favored grain refinement of the welding induced coarsegrained heat affected zone (CGHAZ), with enhanced impact toughness in Tikilled steels, which were examined based on experimental observations and thermodynamic calculations. The results indicated that the chemical constituents of the inclusions gradually varied from the TiO+TiMgO compound oxide to the TiMgO+MgO compound oxide and the singlephase MgO, as the Mg content increased from 0002 3% to 0006%. A trace addition of Mg (approximately 0002%) led to the refinement of Tibearing inclusions by creating the TiMgO compound oxide and provided favorable size distribution of the inclusions for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ with enhanced impact toughness. Otherwise, a high content of Mg (approximately 0006%) produced a singlephase MgO, which was impotent to nucleate an acicular ferrite, and a microstructure comprised of a ferrite side plate and a grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.