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

Abstract

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.%).

Effect of heat treatments on 316 stainless steel parts fabricated by wire and arc additive manufacturing : Microstructure and synchrotron X-ray diffraction analysis

“…The probe has a needle spacing of 635 µm, and a current of 80 mA was imposed between the external needles. Typically, layers comprise skeletal-type ferrite in the non-remelted area and lathy-ferrite in the remelted area between layers [23,39], which is explained by the higher cooling rates in the remelted zone, since it is the first portion of volume to solidify [40].…”

Investigation of the Effect of Thermal Limiters on the Change in the Structure Formation of Deposited Multilayer Specimens from Steel AISI 308LSi

“…Due to the fact that the metal of sample № 1 is at temperatures higher than the metal of sample № 2, then the process of diffusion of δ-ferrite into austenite takes place in it. Similar changes in the phase composition were established in [20], where the authors subjected the samples obtained by electron-beam surfacing from AISI 304 steel, followed by heat treatment followed by quenching in water.…”

The Effect of Thermo-Mechanical Processing Regime on High-Temperature Tensile Properties of V-Alloyed High-Nitrogen Steel

“…9b). Results of mechanical tests for MTMT specimens show that in temperature interval from 850 to 1000 °C and for strain rate interval from 4.2×10 -4 to 6.3×10 -3 s -1 value of strain rate sensitivity coefficient m varies from 0.4 to 0.49 [22]. Microstructural analysis showed that proposed multistage thermo-mechanical treatment assists to refinement and redistribution of disperse particles of carbonitrides of vanadium and chromium and produces the deformation microstructure in austenite.…”

“…7b) that MTMT procedure does not allow to produce well-developed ultrafine-grained structure. Instead, a highly defective microstructure with high density of deformation-assisted defects was produced [22].…”