Grain Refinement of Heat Affected Zone in High Heat Input Welding by Liquid Phase Pinning of Oxy-Sulfide

作者：Yamashita Takako^*; Shimamura Junji; Oi Kenji; Nagoshi Masayasu; Oikawa Katsunari; Ishida Kiyohito

来源：Journal of the Iron and Steel Institute of Japan, 2014, 100(3): 397-405.

DOI：10.2355/tetsutohagane.100.397

• liquid phase pinning
• grain size
• HAZ
• high heat welding
• thermodynamics
• sulfide
• oxysulfide

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 degrees 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.

• 出版日期2014