The effect of tungsten on creep |
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Authors: | Fujio Abe Shizuo Nakazawa |
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Affiliation: | (1) Second Research Group (Nuclear Materials), National Research Institute for Metals, Sengen 1-2-1, 305 Tsukuba, Japan;(2) Materials Design Division, National Research Institute for Metals, Sengen 1-2-1, 305 Tsukuba, Japan |
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Abstract: | The effect of tungsten on creep behavior and microstructural evolution was investigated for tempered martensitic 9Cr steels
with various W concentrations from 0 to 4 wt pct. The creep rupture testing was carried out at 823, 873, and 923 K for up
to 54 Ms (15,000 hours). The creep and creep rupture strength increased linearly with W concentration up to about 3 wt pct,
where the steels consisted of the single constituent of the tempered martensite. It increased only slightly above 3 wt pct,
where the matrix consisted of the tempered martensite and δ-ferrite. The minimum creep rate was described by a power law.
The apparent activation energy for the minimum creep rate showed a tendency similar to the W concentration dependence of the
creep-rupture strength and was larger than the activation energy for self-diffusion at high W concentrations above 1 wt pct.
The martensite lath microstructure with fine carbides along lath boundaries was responsible for a high resistance to creep
deformation. With increasing W con- centration, the martensite lath microstructure became stabilized, which decreased the
minimum creep rate and increased the apparent activation energy for the minimum creep rate. |
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