Influence of hydrogen saturation on the structure and mechanical properties of Fe-17Cr-13Ni-3Mo-0.01С austenitic steel during rolling at different temperatures

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 plasticity of the steel (Table 3). Depending on processing regime, the values of the yield strengths increase by factor of 2.5–2.6 and ultimate strength by factor of 1.4–1.6, while elongation to fracture decreases drasti- cally (Table 3). When the yield point is reached in specimens subjected to chemical-deformation process- ing with 50% reduction, bands of localized plastic deformation are formed and a neck is formed, in which fracture occurs. Grain refinement, an increase in the linear density of twin boundaries and the formation of deformation martensite all contribute to a significant increase in the strength characteristics of the steel. However, there is a high tendency to macroscopic localization of deformation, which is typical for steels with highly defective grain/subgrain structures of a submicron scale [36]. Despite the differences in the microstructure of the specimens treated in different modes of chemical-deformation processing, no principal differences are found in the mechanical properties of the specimens rolled to the same reduction. Nevertheless, hydrogen saturated and deformed with cooling specimens possess the highest mechanical properties (Table 3). Conclusions Chemical-deformation processing of austenitic stainless Fe-17Cr-13Ni-3Mo-0.01С steel in rolling combined with hydrogen saturation provides the formation of a highly defective grain/subgrain structure. The deformation temperature and hydrogen saturation significantly affect the deformation mechanisms, phase transformations and final microstructure of the specimens in rolling. Preliminary hydrogen saturation and decrease in deformation temperature (due to cooling of specimens before each rolling path) promote mechanical twinning and phase transformations during rolling of the specimens. Despite the formation of a small fraction of ε and α’martensitic phases in the structure, the main deformation mechanisms of the steel during rolling are slip, twinning, and microlocalization of plastic flow, which all assist the formation of the ultrafine-grained structures with various morphologies. Grain refinement, accumulation of the defects of the crystal structure and the increase in internal stresses lead to an increase in the strength characteristics of the steel. Despite the fact that preliminary hydrogen saturation and decrease in temperature significantly affect the morphology of grain/subgrain structure and defective microstructure formed by rolling, they do not cause the significant hardening and plasticity loss of the specimens relative to those rolled at room temperature without preliminary saturation with hydrogen. References 1. Takeichi N., Senoh H., Yokota T., Tsuruta H., Hamada K., Takeshita H.T., Tanaka H., Kiyobayashi T., Takano T., Kuriyama N. “Hybrid hydrogen storage vessel”, a novel high pressure hydrogen storage vessel combined with hydrogen storage material. International Journal of Hydrogen Energy , 2003, vol. 28, iss. 10, pp. 1121–1129. DOI: 10.1016/S0360-3199(02)00216-1. 2. Duschek D., Wellnitz J. High pressure hydrogen storage system based on new hybrid concept. Sustainable Automotive Technologies . Cham, 2013, pp. 27–33. DOI: 10.1007/978-3-319-01884-3_3. 3. MacadreA.,Artamonova M., Matsuoka S., Furtado J. Effects of hydrogen pressure and test frequency on fatigue crack growth properties of Ni-Cr-Mo steel candidate for a storage cylinder of a 70 MPa hydrogen filling station. Engineering Fracture Mechanics , 2011, vol. 78, iss. 18, pp. 3196–3211. DOI: 10.1016/j.engfracmech.2011.09.007. 4. Michler T., Marchi C.S., Naumann J., Weber S., Martin M. Hydrogen environment embrittlement of stable austenitic steels. International Journal of Hydrogen Energy , 2012, vol. 37, pp. 16231–16246. DOI: 10.1016/j. ijhydene.2012.08.071. 5. Perng T.P., Altstetter C.J. Comparison of hydrogen gas embrittlement of austenitic and ferritic stainless steels. Metallurgical Transactions A , 1987, vol. 18, pp. 123–134. DOI: 10.1007/BF02646229. 6. Shakhova I., Dudko V., Belyakov A., Tsuzaki K., Kaibyshev R. Effect of large strain cold rolling and subse- quent annealing on microstructure and mechanical properties of an austenitic stainless steel. Materials Science and Engineering: A , 2012, vol. 545, pp. 176–186. DOI: 10.1016/j.msea.2012.02.101. 7. Wasnik D.N., Gopalakrishnan I.K., Yakhmi J.V., Kain V., Samajdar I. Cold rolled texture and microstructure in types 304 and 316L austenitic stainless steels. ISIJ International , 2003, vol. 43, no. 10, pp. 1581–1589. DOI: 10.2355/ isijinternational.43.1581.