Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Regular Article
Grain Refinement of Heat Affected Zone in High Heat Input Welding by Liquid Phase Pinning of Oxy-Sulfide
Takako YamashitaJunji ShimamuraKenji OiMasayasu NagoshiKatsunari OikawaKiyohito Ishida
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2014 Volume 100 Issue 3 Pages 397-405

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Abstract

Effect of REM (Ce, La, Nd) addition on the austenite grain refinement of heat affected zone in Fe-0.07/C-0.05/Si-1.5/Mn-0.003/S (mass%) steel has been investigated by microstructural observation of SEM/EDS and thermodynamic analysis. It is observed that the 30 ppm of REM addition is most effective for reducing the austenite grain size annealed at 1450 °C for 10 sec, but the grain size increases with increasing REM contents more than 30 ppm. Since the total numbers of precipitates of oxide, sulfide and oxysulfide increase with increasing REM contents, the austenite grain growth can not be explained by Zener’s pinning model. Thermodynamic calculation shows that REM-oxide and MnS in oxysulfides are formed by the miscibility gap in the 30 ppm REM steel, which results in the formation of the liquid MnS-rich precipitates due to eutectic reaction. On the other hand, the melting temperature of MnS-rich precipitates increases with increasing REM amount in oxysulfide, which is not effective for inhibiting grain growth. It is suggested that the austenite grain growth is suppressed by liquid phase pinning effect of MnS-rich precipitates.

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© 2014 The Iron and Steel Institute of Japan
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