放射光を利用したオーステナイト系ステンレス鋼溶接凝固過程の解析

Abstract

In order to verify the validity of the developed numerical model to predict the solidification microstructure of austenitic stainless steel weld metal proposed in the previous report, spatially resolved X-ray diffraction measurements using synchrotron radiation have been carried out for Fe-20Cr-11.5Ni and Fe-20Cr-12.7Ni weld metals, quenched in liquid tin. X-ray diffraction analysis of Fe-20Cr-11.5Ni quenched weld metal, solidifying in FA mode (L→L +δ→L +δ+γ→δ+γ), showed that the leading γ phase crystallized in a eutectic growth mode down to a temperature drop of 6 K from the initiation of solidification. Also, from X-ray diffraction analysis of Fe-20Cr-12.7Ni quenched weld metal, which solidified in AF mode (L→L +γ→L +γ+δ→γ+δ), it was found that the leading δ phase crystallized in a eutectic growth mode within the temperature drop range between 18 and 24 K from the initiation of solidification. The crystallization temperatures predicted by the developed numerical model for leading γ and δ phases in Fe-20Cr-11.5Ni and Fe-20Cr-12.7Ni weld metals agreed with experimental data. These agreements support the validity of the developed numerical model. Furthermore, time-resolved in-situ observation of welding solidification process using synchrotron radiation have been carried out for Fe-20Cr-12.5Ni and Fe-20Cr-11.4Ni weld metals, it was found that γ and δ phase crystallized down to a temperature drop within about 47 K and 55 K from the initiation of solidification respectively. These results also coincided with the calculated results for Fe-20Cr-12.5Ni and Fe-20Cr-11.4Ni weld metal using the developed numerical model.