Effect of Magnesium on Inclusion Formation in Ti-Killed Steels and Microstructurai Evolution in Welding Induced Coarse-Grained Heat Affected Zone |
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Authors: | CHAI Feng YANG Cai-fu SU Hang ZHANG Yong-quan XU Zhou |
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Affiliation: | 1. Central Iron and Steel Research Institute,Beijing 100081,China 2. Shanghai Jiaotong University,Shanghai 200030,China |
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Abstract: | 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. |
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Keywords: | non-metallic inclusion magnesium acicular ferrite coarse-grained heat affected zone (CGHAZ) |
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