Conclusions
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1.
Small cobalt additions (0.2–0.5%) have almost no effect on the kinetics of phase transformations, structure, or mechanical properties of steel 18Kh2N4MA, but lower its hardenability.
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2.
The addition of as much as 3% Co raises the change points and reduces the amount of retained austenite in the structure; cobalt strengthens the steel and lowers the notch toughness by 1–3 kgf-m/cm2 at all testing temperatures; the value of T50 rises 20o after quenching and high-temperature tempering, but after low-temperature tempering the percentage of brittle components in the fracture increases. The hardenability decreases as much as 40% at this cobalt concentration.
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3.
The cobalt concentration of structural steel 18Kh2N4MA, melted with use of ferronickel containing cobalt, should not exceed 0.5%.
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Literature cited
A. P. Gulyaev, Metal Science [in Russian], Metallurgiya, Moscow (1966), p. 215.
R. K. Guseinov and V. N. Zikeev, "Medium-carbon structural steels with high strength and toughness alloyed with 9% Ni and 4% Co," Metalloved. Term. Obrab. Met., No. 1, 48 (1974).
E. Houdremont, Special Steels [Russian translation], Vol. 2, Metallurgiya, Moscow (1967), p. 175.
A. P. Gulyaev, "Determining the work of crack propagation," Zavod. Lab., No. 12, 1494 (1970).
B. A. Drozdovskii and Ya. B. Fridman, Effect of Cracks on Mechanical Properties of Structural Steels [in Russian], Metallurgizdat, Moscow (1960), p. 260.
Additional information
I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 14–17, April, 1977.
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Sharov, B.P., Zikeev, V.N. Effect of cobalt on the structure and properties of steel 18Kh2N4MA. Met Sci Heat Treat 19, 265–268 (1977). https://doi.org/10.1007/BF00700806
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DOI: https://doi.org/10.1007/BF00700806