【正文】 ning of carbides and thus increasing secondary hardening [8], increase the embrittlement. With precipitation and coalescence of carbide phase, occurring simultaneously with polygonization of dislocations, the boundaries bee more perfect and the matrix is weakened. Both these effects lead to a drop of the ductilebrittle transition temperature, which is in fact observed. CONCLUSIONS 1. Steels of the 15Kh3MFA type are susceptible to embrittlement, which reaches a peak at a given tempering temperature. The upper limit of the peak (Tso) coincides with the temperature at which the material begins to weaken. 2. The height of the peak and the tempering temperature corresponding to it increase almost linearly when the vanadium concentration is raised from 0 to %, but they are independent of the phosphorus concentration within limits of %. 3. Temper brittleness of the steel investigated depends on the change in the carbide phase (from cementite to special carbides) that occurs with retention of the dislocation arrays preferentially in the boundaries of fragments. LITERATURE CITED . M. Utevskii, Temper Brittleness of Steels [in Russian], Metallurgizdat, Moscow (1961),p. 138. 2. P. B. MikhailovMikheev, Thermal Embrittlement of Steels [in Russian], Mashgiz, MoscowLeningrad (1956), p. 56. 3. J. Hollomon, Trans. ASM, 36, 473 (1946). 4. E. Houdremont, Special Steels [Russian translation], Vol. I, Metallurgiya, Moscow (1966),p. 455. 5. V. A. Korablev, Yu. I. Ustinovshchikov, and I. G. Khatskelevich, Embrittlement of chromium steels with formation of special carbides, Metalloved. Term. Obrab. Met., No. I,16 (1975). 6. A. P. Gulyaev, I. K. Kupalova, and V. A. Landa, Method and results of phase analysis of hlghspeed steels, Zavod. Lab., No. 3, 298 (1965). 7. J. Heslop and N. Perch, Phil. Mag., ~, No. 34, 1128 (1958). 8. V. V. Rybin et al., The mechanism of hardening of sorbitehardening steel and the possibility of determining it theoretically and experimentally, in: Metal Science [inRussian], No. 17, Sudostroenie, Leningrad (1973), p. 105. 9． L. K. Gordienko, Substrucutral Hardening of Metals and Alloys [in Russian], Nauka, Moscow(1973), p. 64. 10． E. E. Glikman et al., Nature of reversible temper brittleness, Fiz. Met. Metalloved.,36, 365 (1973). 11. Oliver WC, Pharr GM (2020) J Mater Res 19:3 12. Kim JY, Lee BW, Read DT, Kwon D (2020) Scr Mater 52:353 13. Kim JY, Lee JS, Lee KW, Kim KH, Kwon D (2020) Key Eng Mater 326–328:487 14. Kim JY, Lee JJ, Lee YH, Jang JI, Kwon D (2020) J Mater Res 21:2975 15. Kim JY, Kang SK, Lee JJ, Jang JI, Lee YH, Kwon D (2020) Acta Mater 55:3555 16. Dowling NE (1993) Mechanical behavior of materials. Prentice Hall, Englewood Cliffs 17. Kim JY, Lee KW, Lee JS, Kwon D (2020) Surf Coat Technol 201:4278 18. DIN 1717579 (1979) Seamless steel tubes for elevated temperatures 19. Ahn JH, Kwon D (2020) J Mater Res 16:3170 20. Dieter GE (1988) Mechanical metallurgy. McGrawHill, Singapore 。. The morphology of the carbide phases also changes. Finely dispersed rounded precipitates with a size of ~250 A are located in the junctions of the dislocation work. Along with them there are larger rounded precipitates~2). The height of the peak and its position depends on the vanadium content of the steel. When the vanadium concentration is changed from 0 to % the peak rises %60 176。. For heat 1, beginning with tempering at temperatures around 300 176。 文獻(xiàn)引用 . M. Utevskii, Temper Brittleness of Steels [in Russian], Metallurgizdat, Moscow (1961),p. 138. 2. P. B. MikhailovMikheev, Thermal Embrittlement of Steels [in Russian], Mashgiz, MoscowLeningrad (1956), p. 56. 3. J. Hollomon, Tra