Evolution of grain–subgrain structure and carbide subsystem upon annealing of a low-carbon low-alloy steel subjected to high-pressure torsion

G. G. Maier; E. G. Astafurova; E. V. Melnikov; A. I. Smirnov; V. A. Bataev; E. V. Naydenkin; P. D. Odessky; S. V. Dobatkin

doi:10.1134/S0031918X16110090

Evolution of grain–subgrain structure and carbide subsystem upon annealing of a low-carbon low-alloy steel subjected to high-pressure torsion

Authors: Maier G.G.¹, Astafurova E.G.¹, Melnikov E.V.¹, Smirnov A.I.², Bataev V.A.², Naydenkin E.V.¹, Odessky P.D.³, Dobatkin S.V.⁴
Affiliations:
1. Institute of Strength Physics and Materials Science, Siberian Branch
2. Novosibirsk State Technical University
3. Central Research Institute of Building Structures
4. Baikov Institute of Metallurgy and Materials Science
Issue: Vol 117, No 11 (2016)
Pages: 1101-1110
Section: Structure, Phase Transformations, and Diffusion
URL: https://journals.rcsi.science/0031-918X/article/view/166405
DOI: https://doi.org/10.1134/S0031918X16110090
ID: 166405

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Abstract

The effect of annealing on the evolution of an ultrafine-grain structure and carbides in a 06MBF steel (Fe–0.1Mo–0.6Mn–0.8Cr–0.2Ni–0.3Si–0.2Cu–0.1V–0.03Ti–0.06Nb–0.09C, wt %) has been studied. The grain–subgrain structure (d = 102 ± 55 nm) formed by high-pressure torsion and stabilized by dispersed (MC, M₃C, d = 3–4 nm) and relatively coarse carbides (M₃C, d = 15–20 nm) is stable up to a temperature of 500°C (1 h) (d = 112 ± 64 nm). Annealing at a temperature of 500°C is accompanied by the formation in regions with a subgrain structure of recrystallized grains, the size of which is close to the size of subgrains formed by high-pressure torsion. The average size and distribution of dispersed particles change weakly. The precipitation hardening and the increase in the fraction of high-angle boundaries in the structure cause an increase in the values of the microhardness to 6.4 ± 0.2 GPa after annealing at 500°C as compared to the deformed state (6.0 ± 0.1 GPa). After 1-h annealing at 600 and 700°C, the microcrystal size (d = 390 ± 270 nm and 1.7 ± 0.7 μm, respectively) increases; the coarse M₃C (≈ 50 nm) and dispersed carbides grow by 5 and 8 nm, respectively. The value of the activation energy for grain growth Q = 516 ± 31 kJ/mol upon annealing of the ultrafine-grained steel 06MBF produced by high-pressure torsion exceeds the values determined in the 06MBF steel with a submicrocrystalline structure formed by equal-channel angular pressing and in the nanocrystalline α iron.

Keywords

steel, thermal stability, annealing, ultrafine-grained structure, carbides, high-pressure torsion, recrystallization

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Evolution of grain–subgrain structure and carbide subsystem upon annealing of a low-carbon low-alloy steel subjected to high-pressure torsion

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