Influence of hydrogen-charging on microstructure and microhardness of high-nitrogen austenitic steel processed by high-pressure torsion

Maier, Galina; Астафурова, Е. Г.; Moskvina, Valentina; Melnikov, E.; Астафуров, С. В.; Fortuna, A. S.; Galchenko, N. K.; Smirnov, A. I.; Батаев, В. А.

doi:10.1063/1.5083425

Cited by 1 publication

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“…Therefore, multistep thermal-mechanical treatment provided the formation of a composite microstructure characterized by a severely deformed misoriented austenitic structure with a high volume fraction of precipitates. This structure was a characteristic of severely deformed austenitic steels with high interstitial content [32,33]. During heating of the specimens to the test temperature, this structure recrystallized into fine-grained austenitic one, which was stabilized by numerous precipitates.…”

Section: Resultsmentioning

confidence: 93%

On the Superplastic Deformation in Vanadium-Alloyed High-Nitrogen Steel

Астафурова¹,

Moskvina²,

Panchenko³

et al. 2019

Metals

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The experimental evidence for the realization of a superplastic behavior with 900% elongation in V-alloyed high-nitrogen austenitic Fe-19Cr-22Mn-1.5V-0.3C-0.6N steel was proposed. Using thermomechanical processing, a misoriented grain/subgrain austenitic microstructure with a high density of deformation-assisted defects and precipitates was developed in the steel. During high-temperature tensile deformation in a temperature interval from 850 to 1000 • C and strain-rate range from 4 × 10 −4 s −1 to 6 × 10 −3 s −1 , this microstructure demonstrated the characteristics of superplastic flow: elongation in the interval 400-900%, strain-rate sensitivity exponent m = 0.40-0.49, grain boundary sliding mechanism. The maximum elongation to failure (900%) was reached at deformation temperature 950 • C and strain rate 4 × 10 −4 s −1 .precipitation hardening [24][25][26][27]. Despite the visible advantages of the high-nitrogen austenitic steels as a construction material, there is limited data related to the possibility of realization of superplastic flow in them. Padmanabhan [1] mentioned a result of N. Narkevich, who reported 239% elongation in Fe-20Cr-20Mn-4.7V-1.14N (mass.%) steel tested at temperature 950 • C and strain-rate 4.6 × 10 −4 s −1 . Such relatively high elongation was obtained for the steel after a solid-solution treatment followed by 50% cold-rolling and age-hardening at 700 • C for 1 h. The microstructure of the steel during high-temperature tests, probably, was not strictly single-phase austenitic but also contained Cr-based and V-based nitrides. This result lied in line with those for single-phase austenitic stainless steels, in which the superplastic-assisted elongation does not exceed 280% [1,28]. Mineura [29] reported much higher elongation (527%) for Fe-20Cr-10Ni-0.7N (mass.%) steel at temperature 800 • C and strain rate 8 × 10 −4 s −1 . They used two-step cold rolling with intermediate anneal at 1000 • C for obtaining fine-grained austenitic structure stabilized by fine chromium nitrides. Vanadium-alloying promotes a homogeneous (continuous) reaction of precipitate hardening in austenitic CrMn steels [24], and this fact could provide higher stability of the fine-grained structure during high-temperature tests as compared to chromium nitrides. Therefore, there is a potential for improvement of the values for the superplastic elongation obtained by Mineura [29].This paper aimed to find out the superplastic characteristics in high-nitrogen V-alloyed austenitic steel Fe-19Cr-22Mn-1.5V-0.3C-0.6N (mass.%).

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Section: Resultsmentioning

confidence: 93%