Through Thickness Microstructure and Mechanical Properties in a Forged Thick Section Mod. 9Cr-1Mo Steel

고온 원자로용 Mod. 9Cr-1Mo강 후판재의 깊이에 따른 미세조직 및 기계적 특성 변화

The purpose of this study is to investigate the effects of through thickness on the mechanical properties and microstructural features in Mod. 9Cr-1Mo steels for RPVs. The microstructures at all locations were typically tempered martensite, but small amount of delta ferrite was observed at the center region. The prior austenite grain size increased with the depth from the surface. The yield strengths of center and 1/4T location were higher than that of surface by 30MPa. The impact toughness of center was low compared to those of other specimens. Also, upper shelf energy was low at the center. The toughness deterioration in center might be caused by larger size of the prior austenite grains and existence of the delta ferrite.