Vol. 27 No. 2 2025 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 27 No. 2 2025 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Sundukov S.K., Nigmetzyanov R.I., Prikhodko V.M., Fatyukhin D.S., Koldyushov V.K. Comparison of ultrasonic surface treatment methods applied to additively manufactured Ti-6Al-4V alloy................................................................ 6 Kate N., Kulkarni A.P., Dama Y.B. A comparative evaluation of friction and wear in alternative materials for brake friction composites............................................................................................................................................................... 29 Naumov S.V., Panov D.O., Sokolovsky V.S., Chernichenko R.S., Salishchev G.A., Belinin D.S., Lukianov V.V. Microstructure and mechanical properties of Ti2AlNb-based alloy weld joints as a function of gas tungsten arc welding parameters............................................................................................................................................................................. 43 Jatti V.S., Singarajan V., SaiyathibrahimA., Jatti V.S., KrishnanM.R., Jatti S.V. Enhancement of EDM performance for NiTi, NiCu, and BeCu alloys using a multi-criteria approach based on utility function................................................ 57 Stelmakov V.A., Gimadeev M.R., Nikitenko A.V. Ensuring hole shape accuracy in fi nish machining using boring...... 89 EQUIPMENT. INSTRUMENTS Patil N., Agarwal S., Kulkarni A.P., Saraf A., Rane M., Dama Y.B. Experimental investigation of graphene oxide-based nano cutting fl uid in drilling of aluminum matrix composite reinforced with SiC particles under nano-MQL conditions............................................................................................................................................................................. 103 Gimadeev M.R., Stelmakov V.A., Nikitenko A.V., Uliskov M.V. Prediction of surface roughness in milling with a ball end tool using an artifi cial neural network................................................................................................................. 126 Osipovich K.O., Sidorov E.A., Chumaevskii A.V., Nikonov S.N., Kolubaev E.A. Manufacturing conditions of bimetallic samples based on iron and copper alloys by wire-feed electron beam additive manufacturing......................... 142 Babaev A.S., Savchenko N.L., Kozlov V.N., Semenov A.R., Grigoriev M.V. Performance of Y-TZP-Al2O3 composite ceramics in dry high-speed turning of thermally hardened steel 0.4 C-Cr (AISI 5135)...................................................... 159 MATERIAL SCIENCE Sokolov R.A., Muratov K.R., Mamadaliev R.A. Morphological changes of deformed structural steel surface in corrosive environment......................................................................................................................................................... 174 Chernichenko R.S., Panov D.O., Naumov S.V., Kudryavtsev E.A., Salishchev G.A., Pertsev A.S. Eff ect of heterogeneous structure on mechanical behavior of austenitic stainless steel subjected to novel thermomechanical processing............................................................................................................................................................................. 189 Panov D.O., Chernichenko R.S., Naumov S.V., Kudryavtsev E.A., Salishchev G.A., Pertsev A.S. Eff ect of cold radial forging on structure, texture and mechanical properties of lightweight austenitic steel................................................ 206 Deshpande A., Kulkarni A.P., Anerao P., Deshpande L., Somatkar A. Integrated numerical and experimental investigation of tribological performance of PTFE based composite material.................................................................... 219 Vorontsov A.V., Panfi lov A.O., Nikolaeva A.V., Cheremnov A.V., Knyazhev E.O. Eff ect of impact processing on the structure and properties of nickel alloy ZhS6U produced by casting and electron beam additive manufacturing........ 238 Misochenko A.A. Martensitic transformations in TiNi-based alloys during rolling with pulsed current........................... 255 EDITORIALMATERIALS 270 FOUNDERS MATERIALS 279 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 Effect of cold radial forging on structure, texture and mechanical properties of lightweight austenitic steel Dmitrii Panov 1, a,*, Ruslan Chernichenko 1, b, Stanislav Naumov 1, s, Egor Kudryavtsev 1, d, Gennady Salishchev 1, e, Alexey Pertsev 2, f 1 Belgorod National Research University, 85 Pobedy Str., Belgorod, 308015, Russian Federation 2 Department Chief Metallurgist, Perm Scientific-Research Technological Institute, 41 Geroev Khasana Str., Perm, 614990, Russian Federation a https://orcid.org/0000-0002-8971-1268, dimmak-panov@mail.ru; b https://orcid.org/0000-0002-8619-0700, rus.chernichenko@mail.ru; c https://orcid.org/0000-0002-4084-8861, NaumovStanislav@yandex.ru; d https://orcid.org/0000-0003-1113-0807, kudryavtsev@bsuedu.ru; e https://orcid.org/0000-0002-0815-3525, salishchev_g@bsuedu.ru; f https://orcid.org/0009-0009-0771-9345, perets_87@mail.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2025 vol. 27 no. 2 pp. 206–218 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2025-27.2-206-218 ART I CLE I NFO Article history: Received: 25 February 2025 Revised: 18 March 2025 Accepted: 27 March 2025 Available online: 15 June 2025 Keywords: Lightweight austenitic steel Cold radial forging Structure Texture Strength Ductility Funding This work was supported by the Russian Science Foundation (grant No. 20-79-10094) using the equipment of BSU Shared Research Facilities “Technologies and Materials”. ABSTRACT Introduction. Lightweight austenitic steels, exhibiting high mechanical properties combined with cost-effective alloying and low density, are promising materials for automotive and airspace industries. The purpose of this work is to study the evolution of the structure and properties of Fe-21Mn-6Al-1C lightweight austenitic steel after cold radial forging (CRF) under various modes. Methods. Microstructural studies were performed using transmission and scanning electron microscopy (TEM) on JEOL JEM-2100 and FEI Nova NanoSEM 450 microscopes, respectively. Microhardness was determined in the cross-section using a Wolpert 402MVD microhardness tester with a load of 200 g and a dwell time of 15 s. Uniaxial tension testing of samples cut from the edge and center was performed on an Instron 5882 machine at room temperature and a strain rate of 1×10-3 s−1. Results and discussion. The stages of structure formation were determined: after deformation (ε) of up to 20 %, the formation of deformation microbands in the center and parallel deformation microbands at the rod edge takes place; after ε = 40–60 %, the formation of single mechanical twins in the center and packets of twins/lamellas at the edge occurs; after ε = 80 %, the intensive twinning in the center and formation of a fragmented structure at the edge takes place. Increasing the degree of CRF leads to the development of a sharp two-component axial texture <111>// rod axis (RA) and <100>//RA in the center, which is blurred towards the edge. At the edge of the rod, a shear texture B/B̅ is observed after CRF with ε = 40 % and higher. After CRF with ε = 20 %, the material in the center of the rod exhibits higher strength and hardness and lower ductility compared to the edge. Further CRF is accompanied by a change in this strength/hardness and ductility ratio between the center and the edge of the rod to the opposite. Thus, CRF is a promising method for producing industrial blanks from lightweight austenitic steels. For citation: Panov D.O., Chernichenko R.S., Naumov S.V., Kudryavtsev E.A., Salishchev G.A., Pertsev A.S. Effect of cold radial forging on structure, texture and mechanical properties of lightweight austenitic steel. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2025, vol. 27, no. 2, pp. 206–218. DOI: 10.17212/1994-6309-2025-27.2-206-218. (In Russian). ______ * Corresponding author Panov Dmitrii D., Ph.D. (Engineering), Belgorod National Research University, 85 Pobedy Str., 308015, Belgorod, Russian Federation Tel.: +7 4722 30-12-11, e-mail: dimmak-panov@mail.ru Introduction Lightweight austenitic steels (LWASs) have recently attracted increasing attention due to their costeffective alloying, high strength, ductility, and impact toughness [1–4]. The presence of such elements as manganese, carbon, aluminum, and silicon in LWASs decreases the density of the material by up to 18 % compared to traditional steels, which further increases the attractiveness of these materials for automotive and airspace industries. However, LWASs require the development of new approaches to fabrication and processing, which is determined by the emergence of a new deformation mechanism ‑ the formation
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 of deformation microbands (microband-induced plasticity ‑ MBIP) [5, 6], on the one hand. On the other hand, during heating of such materials, an aging phenomenon is observed ‑ precipitation of nanoparticles of κ’- carbides, B2- and/or DO3- phases [7–10], which is accompanied by significant strengthening and a decrease in ductility. The structure formation of LWASs during cold plastic deformation has currently been studied mainly in cold rolling and uniaxial tension [5, 11–13]. The high stacking fault energy (SFE) of such materials (60‑120 mJ/m2) at room temperature determines dislocation slip as the main mechanism of plastic deformation [1]. In this case, the phenomenon of short-range ordering due to alloying with aluminum causes deformation due to the formation of microbands in the {111} planes. It has been established that at early stages of deformation (ε up to 10 %) in Fe-28Mn-10Al-1C steel a Taylor lattice is formed from dislocation microbands of two different systems [5]. With an increase in the degree of deformation, an accumulation of misorientation occurs between the domains of the Taylor lattice, which after ε = 60 % leads to the fragmentation of initial austenitic grains. Meanwhile, there are other methods of severe plastic deformation without cracking, for example, radial forging [14, 15]. Recently, it has been shown that cold radial forging with high degrees of deformation (to 90 %) resulted in the development of heterogeneous structures in austenitic alloys [16–18]. This phenomenon is caused by the non-uniform distribution of the operating stresses and temperatures across the rod cross-section during deformation processing. Thus, high compressive stresses act in the rod edge, and moderate tensile stresses are predicted in the rod core. In addition, due to external water cooling and deformation-induced internal heating of the rod core, a gradient in the temperature distribution across the cross-section is observed. However, the effect of radial forging on the microstructure and mechanical properties of LWASs requires separate consideration. The purpose of this work is to study the evolution of the microstructure, texture, and mechanical properties of the lightweight austenitic steel Fe-21Mn-6Al-1C subjected to cold radial forging. To achieve this purpose, the following objectives were addressed: - to determine the effect of the degree of deformation on the microstructure in the cross-section of the rod; – to determine the effect of the degree of deformation on the texture in the cross-section of the rod; – to study the distribution of microhardness in the cross-section of the rod after cold radial forging (CRF); – to determine the effect of the degree of deformation on the mechanical properties of the material after cold radial forging (CRF). Methods The object of the study was the lightweight austenitic steel Fe-21Mn-6Al-1C in the form of rods with an experimental composition including the following components (wt. %): 19.76 % Mn; 6.08 % Al; 0.25 % Ni; 1.01 % C; 0.004 % P; 0.004 % S; Fe – balance. The initial ingot was obtained from pure materials by vacuum arc melting. Then, the ingot was subjected to hot working in the temperature range of 900–1,100 °C in order to obtain a rod for subsequent cold radial forging. The rod with a diameter of 39 mm was annealed (austenitized) at 1,050 °C for 2 hours with cooling in water. The rod was subsequently cold radially forged using a radial forging machine with a feed rate of 180 mm/min, a striker frequency of 1,000 strokes per minute (spm), and a rotation speed of 25 rpm. During the deformation process, the rod was water cooled. Four stages of forging were carried out: from ~39 mm to ~34 mm, from ~34 mm to ~29 mm, from ~29 mm to ~24 mm, from ~24 mm to ~18 mm, which amounted to ~20 %, ~40 %, ~60 % and ~80 % of the relative deformation, respectively. The microstructure was examined in the cross section of the rod on thin foils using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Specimens 0.3 mm thick were cut using an electrical discharge machine, thinned to 0.1 mm by grinding on abrasive paper and polished in an electrolyte (electrolyte composition: 5 % perchloric acid, 35 % butanol and 60 % methanol) at room
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 temperature and a voltage of 26 V. SEM studies were carried out using a FEI Nova NanoSEM 450 scanning electron microscope equipped with an EDAX Hikari electron backscatter diffraction (EBSD) camera. EBSD analysis was performed with a scanning step of 100 nm. For subsequent texture evaluation, only results with a confidence index (CI) of more than 0.1 were used, which improved the quality of the EBSD analysis results. TEM studies were conducted using a JEOL JEM-2100 microscope at an accelerating voltage of 200 kV. Vickers microhardness was determined using a Wolpert 402MVD hardness tester using a diamond pyramid with an angle of 136° at the apex. The tests were carried out in the cross section of the rods along two mutually perpendicular diameters. The indentation step was calculated for each diameter separately, taking into account 70 measurements per diameter. The load applied to the indenter was 200 g with an indentation time of 15 s. The results of microhardness measurements obtained along two mutually perpendicular diameters in the cross-section of the specimen were averaged. Tensile tests were carried out at room temperature and a strain rate of 1×10−3 s−1 using an Instron 5882 electromechanical testing machine. Specimens were cut from the center and subsurface layers of the rod in the axial direction. The dimensions of the gauge of the specimen were 6×3×1.5 mm3. Mechanical properties (yield strength, ultimate tensile strength, elongation to failure) were determined according to GOST 1497-23. The elongation of specimens during testing was measured using the VIC-3D system. For this purpose, one of the side surfaces of the specimens was first coated with white paint, followed by the application of small drops of black paint. The VIC 2D program was used to process the obtained data. At least two specimens were tested at each point. Results and discussion Austenitization of Fe-21Mn-6Al-1C steel produced a fully austenitic, face-centered cubic (FCC) structure (Fig. 1, a). The microstructure, phase, and chemical composition were uniform across the cross section of the rod. The average size of austenite grains was 150 µm (Fig. 1, b), but annealing twins further fragmented the grains, reducing the average distance between high-angle grain boundaries to 55 µm. The fraction of twinned boundaries (Σ3) did not exceed 34 %. The direct and reverse pole figures show a weak two-component axial texture <111>// rod axis (RA) and <100>//RA (Fig. 1, c and d). The results of the study of the microstructure evolution during the CRF process are shown in Fig. 2. 20 % CRF causes microbanding along various systems. It should be noted that in the direction from the center to the edge, the deformation microbands become more pronounced (Fig. 2, a1 and a2). According to diffraction c a b d Fig. 1. X-ray diffraction pattern (a), grain misorientation map (b), direct pole figure (c), and inverse pole figure (d) of the Fe-21Mn-6Al-1C steel in the initial state c
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 analysis, the misorientation between adjacent regions separated by microbands is negligible (<2°). With an increase in the CRF reduction to 40 %, mechanical twins appear (Fig. 2, b1 and b2). Microdiffraction and EBSD analysis indicated that the mechanical twins are located in the {111} planes and are misoriented by approximately 60° relative to the parent austenite (Σ3 boundary). In this case, parallel primary mechanical twins of one plane set meet in the center of the rod (Fig. 2, b1), and packets of parallel mechanical twins are formed at the edge of the rod (Fig. 2, b2). A further increase in the CRF reduction to 60 % is accompanied by the development of mechanical twinning in secondary systems in the center of the rod (Fig. 2, c1). Towards the edge of the rod, a pronounced lamellar structure is observed to form, resulting frommechanical twinning on a single system (Fig. 2, c2). In addition, shear bands are formed across the twin lamellas (Fig. 2, c2). After 80 % CRF, an increase in the number of twins in the center of the rod is detected (Fig. 2, d1). In turn, at the edge of the rod, the structure is fragmented due to the formation of shear bands in the original lamellar microstructure (Fig. 2, d2). CRF ε = 20 % CRF ε = 40 % CRF ε = 60 % CRF ε = 80 % Center a1 b1 c1 d1 Edge a2 b2 c2 d2 Fig. 2. Fine structure of the Fe-21Mn-6Al-1Csteel after CRF with ε = 20% (a1, a2), ε = 40% (b1, b2), ε = 60% (c1, c2), and ε = 80% (d1, d2) in the center and at the edge of the rod The results of the quantitative analysis of the density of deformation microbands (ρdm) and mechanical twins (ρt) after CRF with different degrees are shown in Fig. 3. The results indicate that CRF leads to an increase in the density of deformation microbands, beginning at 20 % deformation (Fig. 3, a), and mechanical twins, beginning at 40 % deformation (Fig. 3, b). It should be noted that after 60 % CRF, the density of crystal structure defects in both cases is higher in the rod center than that at the rod edge. 80 % CRF causes, on the one hand, a further increase in the density of both deformation microbands and mechanical twins in the center. On the other hand, a decrease in the density of these defects occurs at the edge, apparently due to fragmentation of the microstructure during the formation of shear bands. After 80 % CRF, the average size of the elements of the fragmented structure at the edge of the rods of the studied steels is 200‑250 nm, and in the center ‑ 300‑350 nm (Fig. 2, d1 and d2). The maps of the distribution of austenite crystal orientations and the direct pole figures of the center and edge of the rod after CRF with different reductions are shown in Fig. 4. The direct pole figures of the rod center demonstrate a pronounced axial two-component texture <111>//rod axis (RA) and <100>//RA (Fig. 4, a1-d1), which in the subsurface layer is replaced by the simple shear texture B/B ̅(Fig. 4, a2-d2). It is worth noting that increasing the CRF reduction enhances the intensity of these texture patterns on the corresponding pole figures. A further increase in the CRF reduction to 80 % in the center of the rod develops the sharp axial texture <111>//RA (Fig. 4, a1-d1), while the fraction of austenite grains with such an orientation reaches 70 %. At the same time, after 80 % CRF, the volume fraction of austenite grains with
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 a b Fig. 3. Density of deformation microbands (ρdm) and mechanical twins (ρt) as a function of the degree of CRF in Fe-21Mn-6Al-1C steel rod at various distances from the rod center CRF ε = 20 % CRF ε = 40 % CRF ε = 60 % CRF ε = 80 % Center a1 b1 c1 d1 Edge a2 b2 c2 d2 Fig. 4. Orientation maps of austenitic grains and direct pole figures (111) from the center and edge of the rod after CRF with ε = 20% (a1, a2), ε = 40% (b1, b2), ε = 60% (c1, c2), and ε = 80% (d1, d2) the <100>//RA orientation in the center does not exceed 18 %. In this case, the fraction of austenite grains with the <111>//RA orientation in the direction from the center to the edge decreases to 20 %, whereas the fraction of grains with the <100>//RA orientation in the subsurface layer does not exceed 3 %. The distribution of microhardness along the rod diameter depending on the degree of CRF of Fe-21Mn6Al-1C steel is shown in Fig. 5. In the initial state, the uniform distribution of microhardness is observed over the rod cross section. The microhardness of the initial rod is at the level of 230 HV0.2. 20 % CRF causes an increase in the microhardness of the rod periphery to a greater extent compared to the center, which leads to the formation of a gradient of microhardness distribution from the center to the edge of the rod. Subsequent CRF is accompanied by a further increase in the overall level of microhardness. However, after a deformation of 60 %, the pronounced peak of microhardness appears in the core of the rod. At the same time, in the direction from the center to the edge of the rod, the microhardness smoothly decreases, i.e. the microhardness gradient changes its direction from the edge to the center. After 80 % CRF this peak reaches
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 Fig. 5. Microhardness distribution in the crosssection of rods after various degrees of CRF 600 HV0.2 and becomes even more pronounced. In this case, the highest overall level of microhardness is observed – 500-600 HV0.2. Fig. 6 and Table 1 show the tensile stress-strain diagrams and mechanical properties of Fe-21Mn-6Al1C steel in the initial state (after preliminary quenching to the austenite structure) and after CRF with different degrees. In the initial state, the steel under study demonstrates pronounced strain hardening, as well as a high level of ductility (elongation to failure (δ) = 56-58 %; uniform elongation (δu) = 48-50 %) and good strength properties (ultimate tensile strength (σu) = 830 MPa; yield strength (σ0.2) = 460 MPa). Tensile testing of the cold-forged Fe-21Mn-6Al-1C steel specimens showed that the material of the center and edge of the rod demonstrates significantly different mechanical behavior (Fig. 6) and, consequently, mechanical properties (Table). Thus, the specimen cut from the center of the rod subjected to 20 % CRF possesses high ductility (δ = 51.4 %; δu = 37.9 %) along with pronounced strain hardening (Fig. 6). At a b c d e Fig. 6. Uniaxial tensile stress-strain curves of Fe-21Mn-6Al-1C steel in the initial state (a) and after CRF with ε = 20% (b), ε = 40% (c), ε = 60% (d), and ε = 80% (e)
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 Mechanical properties of Fe-21Mn-6Al-1C steel samples in the initial state and steel samples cut from the center and edge of rods after various CRF reductions ε 0 % 20 % 40 % 60 % 80 % Position Center Edge Center Edge Center Edge Center Edge σu, MPa 818 1,009 1,133 1,505 1,381 1,853 1,621 2,062 1,741 σ0.2, MPa 459 705 1,028 1,499 1,303 1,838 1,531 2,062 1,626 δ, % 55.6 51.4 32.7 18.6 20.3 10 16.9 5.7 15.4 δu, % 47.9 37.9 10 0.3 1.8 0.3 1.4 0.2 1.2 the same time, an increase in the yield strength to 705 MPa and ultimate tensile strength to 1,009 MPa is observed (Table). The ductility of the edge of the rod is noticeably lower (δ = 32.7%; δu = 10%), while the strength characteristics are higher (σu = 1,133 MPa; σ0.2 = 1,028 MPa). Further CRF is accompanied by a change in the above-mentioned ratio of strength and plasticity between the center and the edge of the rod to the opposite: the strength becomes higher at the central part of the rod, and plasticity ‑ at the edge. For example, after 80 % CRF, the uniform elongation (δu) of the center and edge material decreases to 0.2 % and 1.2 %, respectively. In this case, the elongation to failure of the center material is 5.7 %, and of the edge material – 15.4 %, which is mainly determined by concentrated deformation. The strength properties, in turn, of the center in the rod (σu = 2,062 MPa; σ0.2 = 2,062 MPa) exceed these characteristics of the edge (σu = 1,741 MPa; σ0.2 = 1,626 MPa) by 18-27 %. With an increase in the degree of CRF, the strain-hardening rate decreases (Fig. 7). a b с Fig. 7. True stress and strain-hardening coefficient (SHC) as a function of true strain during uniaxial tensile testing of samples cut from the center and edge of the rod after CRF with ε = 20% (a), ε = 40% (b), and ε = 80% (c) Previously, using finite element modeling, it was predicted that in CRF, moderate tensile/compressive stresses act at the center of the rod, and high compressive stresses operate at the edge of the rod [16, 17]. Such a non-uniform stress condition leads to the accumulation of greater plastic deformation at the rod edge compared to the core. TEM methods have shown that in the studied steel, during CRF, various deformation mechanisms are activated, resulting in a whole spectrum of structural states along the rod radius. Thus, in the Fe-21Mn-6Al-1C steel, the following stages of microstructure formation are observed (Fig. 2): after low degrees of deformation (ε = 20 %) – formation of deformation microbands along various systems in the center and parallel deformation microbands at the rod edge; after medium degrees of deformation (ε = 40-60 %) – formation of single mechanical twins of various systems in the center and parallel packets of twins at the edge; after high degrees of deformation (ε = 80 %) – twinning according to various systems in the center and formation of a fragmented microstructure at the edge. The results of EBSD analysis show
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 that with increasing degree of CRF, pronounced textural gradients develop. These texture gradients are due to the fact that a sharp two-component axial texture <111>//RA and <100>//RA, is formed in the center of the rods, which weakens towards the edge. It should be noted that the shear texture B/B ̅develops at the edge of the rod after 40 % CRF and higher [19, 20]. The distribution of microhardness in the cross section of the rods shows the development of a gradient structure during CRF (Fig. 5). In the case of the initial state with a homogeneous structure, a uniform distribution of microhardness is observed across the cross-section of the rods of both steels. 20 % CRF is accompanied by a general increase in the hardness of the program steel. However, the hardness of the rod edge increases to a greater extent. Texture analysis showed a relatively uniform distribution of grains with <111>//RA and <100>//RA orientations across the section after 20 % CRF, i.e. this factor does not have a significant effect. Meanwhile, the increased density of microbands and mechanical twins is observed at the edge (Fig. 3), which is due to high strain accumulation in this place and determines an increased level of hardness. These structural changes also affect the results of uniaxial tensile tests of samples cut from the center and edge of rods of both steels. At the same time, the strength of the edge material of the rods was significantly higher than that of the material from the center (Table). Plasticity at the edge was lower mainly due to a decrease in uniform elongation due to the accumulation of a higher density of crystalline structure defects (Fig. 3). Further 40-85 % CRF is accompanied by an increase in the microhardness of the rods. After 40 % CRF, the previously obtained microhardness gradient is smoothed out (Fig. 5). Subsequent 60-85 % CRF leads to the formation of the microhardness peak in the center of the studied rod. The results of the quantitative analysis of the microstructure of the studied steels showed that after 40-60 % CRF, an increased density of lattice defects is still observed at the edge of the rod compared to the core (Fig. 3). Additionally, a pronounced gradient of the volume fraction of austenite grains with the <111>//RA orientation is formed across the rod cross-section (Fig. 4). Thus, in the center of the rod, a high proportion (up to 70 %) of grains with the <111>//RA orientation is observed. Due to the active development of shear bands at the edge of the rod, the shear texture B/B ̅is formed. In this case, the determining factor in the occurrence of a microhardness gradient is the texture gradient, since such grains with the orientation <111>//RA perform a low value of the Schmid factor for mechanical twinning and dislocation slip (Fig. 8). The highest level of the Schmid factor is observed in grains with the orientation <100>//RA, however, the proportion of such crystals in the center of the rod does not exceed 18 %. The observed changes in the microstructure and texture during CRF of the studied steels to 40-85 % deformation are accompanied by a change in the ratio between the strength and ductility of the center and edge of the rod (Fig. 6). In this case, the highest strength and the lowest ductility are found in the material from the center of the rod. Following CRF to a b с Fig. 8. Orientation map of austenitic grains with orientations <111>//BA and <100>//BA (a), grain distribution based on Schmid factor for dislocation slip (b) and mechanical twinning (c) of Fe-21Mn-6Al-1C steel after CRF with ε = 60% in the center of the rod
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 2 2025 60 % or higher reductions, the material from the rod center exhibits a decrease in uniform elongation to 0.2-0.3 % and a relative elongation of less than 10 % (Table). The material of the edge of the rod demonstrates a uniform elongation at the level of 1.2-1.7 %, and a relative elongation of about 14-17 %. Conclusion Based on the results of the study of the evolution of the microstructure, texture and mechanical properties of the lightweight austenitic steel Fe-21Mn-6Al-1C after various cold radial forging (CRF) modes, the following conclusions can be drawn: – During CRF, the following stages of the microstructure formation are observed: low degrees of deformation (ε up to 20 %) – formation of deformation microbands of various systems in the center and parallel deformation microbands at the edge of the rod; medium degrees of deformation (ε = 40-60 %) – formation of single mechanical twins of various systems in the center and parallel packets of twins at the edge; high degrees of deformation (ε = 80 %) – twinning according to various systems in the center and formation of a fragmented microstructure at the edge. – With an increase in the degree of CRF, pronounced texture gradients are formed in the rod. The twocomponent axial texture <111>// rod axis (RA) and <100>//RA develops in the center of the rod, which is weakened towards the edge. Meanwhile, the pronounced shear texture B/B ̅is found at the edge of the rod after 40 % CRF and higher. – 20 % CRF causes an increase in microhardness of the rod edge to a greater extent compared to the center. Subsequent CRF is accompanied by a further increase in the overall level of microhardness. After a deformation of 60%, a pronounced peak of microhardness appears in the core of the rod. After 80 % CRF, this peak reaches 600 HV0.2. – After 20 % CRF, the material of the rod center exhibits higher strength and lower ductility compared to the material of the rod edge. With further CRF, the strength becomes higher at the center of the rod, whereas the ductility is higher at the edge. Thus, after 80 % CRF, elongation to failure is δ ≈ 6 % at the center and δ ≈ 15 % at the edge. The strength properties of the central part of the rod (σu = ,2062 MPa; σ0.2 = 2,062 MPa) exceed these characteristics of the edge (σu = 1,741 MPa; σ0.2 = 1,626 MPa) by 20-30 %. References 1. Chen S., Rana R., Haldar A., Ray R.K. Current state of Fe-Mn-Al-C low density steels. Progress in Materials Science, 2017, vol. 89, pp. 345–391. DOI: 10.1016/j.pmatsci.2017.05.002. 2. Raabe D., Springer H., Gutierrez-Urrutia I., Roters F., Bausch M., Seol J.B., Koyama M., Choi P.P., Tsuzaki K. Alloy design, combinatorial synthesis, and microstructure–property relations for low-density Fe-Mn-Al-C austenitic steels. Jom, 2014, vol. 66, pp. 1845–1856. DOI: 10.1007/s11837-014-1032-x. 3. Ding H., Liu D., Cai M., Zhang Y. Austenite-based Fe-Mn-Al-C lightweight steels: research and prospective. Metals, 2022, vol. 12 (10), p. 1572. DOI: 10.3390/met12101572. 4. Kim H., Suh D., Kim N.J., Kim H., Suh D., Kim N.J. Fe–Al–Mn–C lightweight structural alloys: a review on the microstructures and mechanical properties. Science and Technology of Advanced Materials, 2013, vol. 14 (1), p. 014205. DOI: 10.1088/1468-6996/14/1/014205. 5. Yoo J.D., Hwang S.W., Park K.T. Origin of extended tensile ductility of a Fe-28Mn-10Al-1C steel. Metallurgical and Materials Transactions: A, 2009, vol. 40 (7), pp. 1520–1523. DOI: 10.1007/s11661-009-9862-9. 6. Moon J., Park S.J., Jang J.H., Lee T.H., Lee C.H., Hong H.U., Han H.N., Lee J., Lee B.H., Lee C. Investigations of the microstructure evolution and tensile deformation behavior of austenitic Fe-Mn-Al-C lightweight steels and the effect of Mo addition. Acta Materialia, 2018, vol. 147, pp. 226–235. DOI: 10.1016/j.actamat.2018.01.051. 7. Chen P., Zhang F., Zhang Q.C., Du J.H., Shi F., Li X.W. Precipitation behavior of κ-carbides and its relationship with mechanical properties of Fe–Mn–Al–C lightweight austenitic steel. Journal of Materials Research and Technology, 2023, vol. 25 (12), pp. 3780–3788. DOI: 10.1016/j.jmrt.2023.06.212. 8. Harwarth M., Chen G., Rahimi R., Biermann H., Zargaran A., Duffy M., Zupan M., Mola J. Aluminumalloyed lightweight stainless steels strengthened by B2-(Ni,Fe)Al precipitates. Materials & Design, 2021, vol. 206, p. 109813. DOI: 10.1016/j.matdes.2021.109813.
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