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I.

INTRODUCTION

SA508 Gr.3 steels are key materials used for the fabrication of nuclear reactor facilities, such as reactor pressure vessels (RPV), steam generators, and compressors.[1–3] In the past 40 years, many researchers[4–7] focused on the characteristic properties of this steel, and the results demonstrated that this steel shows an excellent combination of irradiation resistance and other properties required for applications in third-generation nuclear power reactors. In order to prolong the third generation’s life-span to more than 60 years, the pressure vessels are bigger and heavier than before, and an integrated design is used to reduce the welding. Consequently, more serious macrosegregation arises in the bigger components that are fabricated from heavier ingots. Further research is needed to elucidate the effect of chemical segregation on the mechanical properties of this steel.[8] An appropriate processing should be adopted to enhance the performance of the heavy forgings and guarantee the reliability of nuclear power components.

GUANGHUA YAN, LIZHAN HAN, CHUANWEI LI, XIAOMENG LUO, and JIANFENG GU are with the Institute of Materials Modification and Modeling, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] Manuscript submitted October 19, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

The macrosegregation originates from the solidification process, during which the alloying elements are partitioned between the solid and liquid, forming either enriched or depleted interdendritic regions. There are three typical defects that can arise due to macrosegregation, including A-segregates, V-segregates, and negative base segregation.[8,9] The V-segregates and negative base segregation are commonly physically removed by cutting. And the A-segregates can be alleviated by fragmentation of dendrites during the forging process. But chemical segregation remains and manifests in the final components. Any chemical inhomogeneities caused from macrosegregation can be expected to deliver different microstructures, and hence inconsistent mechanical properties. As might be expected, the positive segregation zone has been shown to transform into harder microstructures with reduced toughness.[10,11] Maidorn and Blind[12] found that in material which has undergone tempering following forging and quenching, the Charpy impact energy of segregated regions can be as little as half that of the homogeneous material. These results are therefore of significant influence for the safety and longevity of the nuclear power plants. Pickering and Bhadeshia[13] assessed the consequences of macrosegregation on microstructural evolution during solid-state transformations in SA508 Gr.3 steel and proposed a method for minimizing segregation from the viewpoint of chemical composition regulation. In the present work, high-temperature homogenization treatment was performed to minimize the segregation from

the viewpoint of heat treatment. The material with mac