Effect of Segregation of Alloying Elements on Creep Strength in Heat Resistant Steels K. Sawada 1, T. Hatakeyama 1 and K. Kimura 1 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) Effect of segregation on creep strength was investigated in heat resistant steels. For ASME T91 and T92 steels, the Cr segregation was observed along the longitudinal direction of the boiler tube. Heat-to-heat variation of Cr segregation was confirmed for the steels. The creep strength was lower when the Cr segregation was strong. The coarsening of M23C6 carbides and recovery of martensitic lath structure during creep exposure were promoted in the strongly segregated heat of the steels. The creep life of ASME T91 steel was improved by normalization at 1200oC because the normalization decreased the Cr segregation. The alloying elements such as V, Nb and Mo were also segregated along the longitudinal direction of the boiler tube in the same way as Cr. If the segregation of Nb is remained, prior austenite grain size becomes smaller in the segregation zone since undissolved NbC can pin grain boundaries in the segregation zone. The segregation should be reduced to obtain homogenous distribution of prior austenite grain size. The segregation of Cr and Ni was also confirmed in austenitic stainless steels such as SUS304HTB, SUS316HTB, SUS321HTB and SUS347HTB. There was heat-to-heat variation of Cr and Ni segregation for the steels. However, no large effect of the segregation on creep strength and creep ductility was recognized for the steels. High-throughput Evaluation MProcess Temperature Graded Bulk Samples A. Ikeda, T. Osada, T. Abe, K. Kawagishi and T. Ohmura Research Center for Structural Materials, National Institute for Materials Science (NIMS) A high quality database of mechanical properties and phase diagrams is key to the development of novel Ni-based superalloys. The compositional combinations of multi-component alloys increase exponentially with the number of constituents. Since Ni-based superalloys can consist of more than ten constituents, the construction of a database covering the compositional space using classical methods with homogeneous specimens requires a great deal of time and effort. In this study, a method has been developed to collect mechanical property and phase diagram data sets with remarkable efficiency by introducing a series of different compositions or process temperatures into a single sample and then performing micro-area tests (nanoindentation, oxidation tests, microstructural observations). A compositionally graded sample preparation technique with a spatial scale suitable for micro area testing has been developed using the diffusion couple and unidirectional solidification methods, as well as a method for heat treatment of single sample under a temperature gradient. These techniques have provided frameworks for the construction of isothermal quasi-quaternary state diagrams and the optimization of process temperatures, etc. Poster Presentation ｜NIMS Award Symposium 2023ethods for Ni Based Superalloys Using Composition and P3 ｜ EvaluationPP33--0033 PP33--0044 59
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