Small angle neutron scattering and 3D-atom probe tomography studies on the formation of carbon clusters in a high-Ni-C steel

Morooka, Satoshi  ; Miyamoto, Goro*; Oba, Yojiro  ; Oishi, Kazuki*; Takata, Shinichi  

The formation of carbon clusters (C clusters) has an evidently influence on the mechanical properties of martensitic steels containing carbon atoms. In the present work, the formation of C clusters during low-temperature tempering of Fe-25Ni-0.5C alloy was investigated by means of a combined technique including small angle neutron scattering (SANS) and three-dimensional atom probe tomography (3D-AP). Here, the SANS instrument TAIKAN at J-PARC MLF has installed a large number of detectors with a wide angular range to simultaneously collect SANS patterns with Bragg diffractions. The SANS measurement indicates the evolution of C clusters in a low-temperature-annealed high-Ni-C steel during tempering. The results show that a mean size and the number density of C clusters both increase with an increase in annealing time. In addition, the axis ratio (c/a) of the martensitic phase decreases with an increase of the annealing time. On the other hand, the large scattering of magnetic domain reported by V.M. Nadutov et al. can be observed from initial SANS profile of the austenite single phase. The 3D-AP well describes the formation of C clusters and concentration of carbon elements in the Fe-25Ni-0.5C alloy. In this study, a type of the carbide is identified from the correlation among an average size of C clusters, number density, and carbon atom concentration.