The role of microstructural instability on creep behavior of a martensitic 9Cr-2W steel |
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Authors: | F Abe S Nakazawa H Araki T Noda |
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Affiliation: | (1) Second Research Group (Nuclear Materials), National Research Institute for Metals, Tsukuba Laboratories, 305 Tsukuba, Japan;(2) Materials Design Division, National Research Institute for Metals, Tsukuba Laboratories, 305 Tsukuba, Japan;(3) Second Research Group, National Research Institute for Metals, Tsukuba Laboratories, 305 Tsukuba, Japan;(4) Second Research Group, National Research Institute for Metals, Tsukuba Laboratories, 305 Tsukuba, Japan |
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Abstract: | The microstructural instability during creep and its effect on creep behavior were investigated for a martensitic 9Cr-2W steel.
The steel was developed as a low radioactive steel suitable for fusion reactor structure. Creep testing was carried out at
873 K for up to 15,100 ks (4200 hours). The creep curve consisted of transition creep, where creep rate decreased with time,
and acceleration creep, where creep rate increased with time. During creep, microstructural instability, such as the recovery
of dislocations, the agglomeration of carbides, and the growth of martensite lath subgrains, was observed to occur, which
resulted in softening but no hardening. The transition creep was a consequence of the movement and annihilation of excess
dislocations, resulting in the decrease in dislocation density and the increase in martensite lath size with time. The acceleration
creep was a consequence of a gradual loss of creep strength due to the microstructural instability which occurred from the
initial stage of creep. |
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