Conclusions
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1.
At temperatures below the equcohesive temperature, i.e., with transcrystalline fracture, the long-term strength of Cr−Ni and Cr−Ni−Mo steels increases continuously with increasing boron additions up to 0.005%. At temperatures above the equicohesive temperature, where fracture is intergranular, the long-term strength of the steels is highest at boron concentrations of 0.001–0.0018%.
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2.
The following mechanisms of the increase in the long-term strength with small boron additions were established: a) small boron additions increase the strength of the grain boundaries, which is manifest at temperatures above the equicohesive temperature; b) small boron additions slow down the diffusion processes of precipitation of excess phases in the boundaries and within the grains during creep; c) additional strengthening of the grain boundaries evidently occurs at concentrations of 0.004–0.005% B due to precipitation of dispersed borides.
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Additional information
Volgograd Scientific-Research Institute of Heavy Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 2–4, June, 1973.
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Morozov, Y.A., Sidel'kovskii, M.P. & Rozenberg, V.M. Heat resistance of Cr−Ni and Cr−Ni−Mo steels with boron additions. Met Sci Heat Treat 15, 447–450 (1973). https://doi.org/10.1007/BF01153257
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DOI: https://doi.org/10.1007/BF01153257