The article investigates the effect of combined thermomechanical processing, including pre-heat treatment and radial-shear rolling on the brass microstructure evolution and the microhardness change. The microstructure analysis of heat-treated samples according to various modes showed that the most optimal heat treatment before radialshear rolling for L63 brass is annealing at a temperature of 500 °C. As a result of combined thermomechanical processing, a gradient structure was obtained, so in the resulting rods with a diameter of 16 mm in the surface layer, a structure with an average grain size of 9 μm was obtained. In rods with a diameter of 12 mm, a fine–grained, equalgrained structure of 3 μm was obtained in the surface layer

Belsky, S.

Lezhnev, S.

Naizabekov, A.

Panin, E.

Pishchov, M.

Tolkushkin, A.

Volokitina, I.

English

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283METALURGIJA 63 (2024) 2, 283-286A. NAIZABEKOV, S. LEZHNEV, I. VOLOKITINA, E. PANIN,  A. TOLKUSHKIN, S. BELSKY, M. PISHCHOVINVESTIGATION OF THE EFFECT OF COMBINED THERMOMECHANICAL PROCESSING  ON THE BRASS MICROSTRUCTURE EVOLUTION  AND THE MICROHARDNESS CHANGEReceived – Primljeno: 2023-11-03Accepted – Prihvaćeno: 2023-12-26Preliminary Note – Prethodno priopćenjeThe article investigates the effect of combined thermomechanical processing, including pre-heat treatment and radial-shear rolling on the brass microstructure evolution and the microhardness change. The microstructure analy-sis of heat-treated samples according to various modes showed that the most optimal heat treatment before radial-shear rolling for L63 brass is annealing at a temperature of 500 °C. As a result of combined thermomechanical pro-cessing, a gradient structure was obtained, so in the resulting rods with a diameter of 16 mm in the surface layer, a structure with an average grain size of 9 μm was obtained. In rods with a diameter of 12 mm, a fine–grained, equal-grained structure of 3 μm was obtained in the surface layer.Keywords: brass, radial-shear rolling, heat treatment, microstructure, microhardnessISSN 0543-5846METABK 63(2) 283-286 (2024)UDC – UDK 669.35.5:621.771:621.78:620.18:620.178.1 =111INTRODUCTIONFor more than a decade, scientists around the world have been working to reduce the metal consumption of machines and structures and increase their reliability by improving the quality of metal products. In order to im-prove the quality of metal products and the formation of increased mechanical properties in it, many technolo-gists traditionally use heat treatment, which generates structural and phase transformations in materials. At the same time, one of the most important tasks of heat treat-ment is to obtain an optimal grain structure of the mate-rial, which determines its high structural strength. It is the production of such a structure and fine grain that avoids many disadvantages of alloys associated with its grain-boundary structure. However, it is impossible to achieve an improvement in the quality of metal products by increasing the mechanical and operational properties to the currently required level only by heat treatment.Therefore, much attention is currently being paid to the development of various combined thermomechanical treatments of metals and alloys, including various types of heat treatment and various methods of processing these metals and alloys by pressure in a hot or cold state. And special attention is paid to the methods of metal forming, which make it possible to implement severe plastic deformation (SPD) in metals and alloys [1-2].S. Lezhnev, A. Naizabekov, A. Tolkushkin, Rudny Industrial Institu- te, Rudny, Kazakhstan; I. Volokitina, E. Panin (e-mail: ye.panin@tttu.edu.kz), Karaganda Industrial University, Temirtau, Kazakhstan; S. Belsky, M. Pishchov, Belarusian State Technological University, Minsk, BelarusAmong the many methods of SPD implementing de-veloped to date, the most well-known are high-pressure torsion (HPT) [3] and equal-channel angular pressing (ECAP) [4]. The HPT method makes it possible to ob-tain nanostructures with a grain size of 100 - 200 nm or less [5-7] in small samples suitable for most basic re-search. The ECAP method makes it possible to grind grains in bulk samples of a number of metals and alloys up to 200 nm, and at the same time obtain significantly improved mechanical properties [8-11]. The main dis-advantages of these methods of implementing intensive plastic deformation, which prevent their widespread in-dustrial introduction into production, are also well known, these are limitations in the size of the initial samples and extremely low manufacturability of the production itself.These disadvantages can be eliminated by using a method of radial-shear rolling [12], which also allows obtaining an ultrafine-grained (UFG) state in metals and alloys with some structural distribution features, but al-ready due to the implementation of severe plastic defor-mation in long round bars. The main feature of radial-shear rolling is the non-monotonicity and turbulence of deformation, as well as differences in the plastic flow and the study of the structure of different zones of the work-piece due to the trajectory-velocity features of the pro-cess [12-13]. A significant advantage of this method of deformation is that in the deformation zone during radial-shear rolling, a stress-strain state scheme is implemented that is close to comprehensive compression with large shear deformations, which is favorable for the formation of the UFG structure. But at the same time, pre-heat treat-284  METALURGIJA 63 (2024) 2, 283-286A. NAIZABEKOV et al.: INVESTIGATION OF THE EFFECT OF COMBINED THERMOMECHANICAL PROCESSING…ment is one of the promising ways to obtain a pre-regu-lated microcrystalline structure in various metals and al-loys, including copper and its alloys [14].The purpose of this work is to study the effect of combined thermomechanical processing, including pre-heat treatment (PHT) and radial-shear rolling (RSR), on the evolution of the microstructure and the change in the microhardness of brass.MATERIALS AND METHODSTo achieve this goal, a laboratory experiment using a Nabertherm tubular resistance furnace and a radial-shear rolling mill RSR 10-30 was conducted.The material of the study was L63 brass. The choice of L63 brass is justified by the fact that it is one of the most popular brasses, due to the high Zn content, good mechanical performance and low cost, compared with alloys containing more Cu. Two-component alloys, in-cluding L63, mainly belong to single-phase structures. When the second phase appears, the mechanical charac-teristics of the products fall: the brittleness, hardness increases, the plasticity of the products decreases. For this reason, two-phase brass is difficult to process by pressure. Single-phase alloys are well processed by pressure, as well as cast into ingots. L63 contains a small amount of substance in the β-phase, therefore, it lends itself well to pressure treatment: rolling, deep drawing, chasing, drawing, bending without serious consequences, while observing the processing mode even in a cold state.Bars with a diameter of 30 mm and a length of 200 mm were prepared as initial blanks for conducting stud-ies on the effect of combined thermomechanical pro-cessing, including preliminary heat treatment and radi-al-shear rolling, on the brass microstructure evolution.At the first stage of the research, the task was to de-termine the optimal mode of preliminary heat treatment of L63 brass, which ensures both obtaining a fine-grained structure and the possibility of further worka-bility on a radial-shear rolling mill without destruction.To solve this problem, based on the Cu-Zn state dia-gram, the following types of PHT were selected and implemented in practice:1) annealing at a temperature of 500 °C;2) annealing at a temperature of 800 °C;3) quenching at a temperature of 400 °C;4) quenching at a temperature of 500 °C;5) quenching at a temperature of 800 °C.Samples were cut from all the blanks for metallo-graphic studies and microhardness studies.RESULTS AND DISCUSSIONThe analysis of the microstructure of L63 brass ob-tained after annealing and quenching from various tem-peratures is shown in Figure 1.Figure 1  Microstructure of brass after preliminary heat treatment: a – annealing 500 °C; b – annealing  800 °C; c – quenching 400 °C; d – quenching 500 °C; e – quenching 800 °CAs is known from the Cu-Zn state diagram, the structure of brass consists of α or α + β’ phases, where α-phase is a solid solution of zinc substitution in copper having a HCC lattice, high plasticity, low strength and a)b)c)d)e)285A. NAIZABEKOV et al.: INVESTIGATION OF THE EFFECT OF COMBINED THERMOMECHANICAL PROCESSING…METALURGIJA 63 (2024) 2, 283-286hardness values; β’–phase is an ordered solid solution based on an intermetallic compound with a crystal lat-tice BCC. This phase is characterized by higher hard-ness than the α-phase and brittleness.Analysis of Figures 2a and 2b showed that slow cooling during annealing forms an equilateral structure and ensures maximum transition of the β-phase to the α-phase. An increase in the annealing temperature to 800°C leads to grain growth.Thus, at a temperature of 500 °C, a grain with a size of 40 μm was obtained (Figure 1a), and at a temperature of 800 °C, a grain with a size of 60 μm was obtained (Figure 1b).After quenching from 400 °C, a predominantly sin-gle-phase structure with a certain amount of β-phase was obtained, which is characterized by heterogeneity due to the formation of a zone of very small grains of this phase and inclusions of the β-phase along the boundaries of the α-phase grains (Figure 1c). Quench-ing from 500 °C due to rapid cooling ensured the pro-duction of a homogeneous martensitic-type structure from α-phase crystals and β-phase residues. The crys-tals of the α-phase have the shape of plates, at the boundaries of these crystals, the remnants of the β-phase (dark areas) are observed (Figure 1d). When quenching from 800 °C, a structure consisting of the remains of the initial α-phase and sections of a two-phase structure is observed, which includes crystals of a metastable β-phase with dispersed alpha-phase secretions in the middle of these sections. Since the etcher tints the β-phase in a dark color, it can be seen how much the amount of the β-phase increases (Figure 1e).After the heat treatment, measurements of the mi-crohardness of the obtained samples were also per-formed. The microhardness of the brass samples after annealing was 560 MPa at a temperature of 500 °C and 485 MPa at a temperature of 800 °C. After quenching from 400 °C, the hardness of the alloy was 960 MPa. Quenching from 500 °C provided a hardness of 1 100 MPa. Quenching from 800 °C with the rapid cooling provided an increase in hardness up to 1 120 MPa due to increased β-phase separation.Since the β-phase embrittles the brass alloy, it is un-desirable for further deformation of the samples. There-fore, annealing is the most suitable PHT for L63 brass. In order to save energy and obtain a fine-grained struc-ture after deformation by radial-shear rolling, annealing at a temperature of 500 °C was chosen as a PHT for brass.At the second stage of the research, the task was to identify the effect of radial shear rolling on the evolu-tion of the microstructure of L63 brass, previously sub-jected to the most optimal (of the above) heat treatment, namely annealing at a temperature of 500 °C.To solve this problem, a physical experiment was carried out on the deformation of brass samples sub-jected to annealing at a temperature of 500 °C on a radi-al-shear rolling mill. This experiment was as follows. Rods with a diameter of 30 mm and a length of 200 mm were preheated to a temperature of 500 °C with expo-sure in a Nabertherm tubular furnace to equalize the temperature along the cross-section of the samples be-fore deformation. After that, the deformation of these samples was carried out on the radial-shear rolling mill RSR 10-30 up to a diameter of 16 mm and 12 mm with an absolute compression step of 2,0 mm in diameter.Samples from all deformed workpieces for metallo-graphic studies and microhardness measurements were cut. The microstructure analysis after deformation at the radial-shear rolling mill (Figure 2) showed that the mi-crostructure in the surface layers of the bars, both with a diameter of 16 mm and a diameter of 12 mm, differs significantly from the microstructure in the central part of the bar.Figure 2  Microstructure of L63 brass formed on a radial-shear rolling mill (cross section): a – 16 mm diameter (surface); b – 16 mm diameter (center); c – 12 mm diameter (surface); d – 12 mm diameter (center)a)b)c)d)286  METALURGIJA 63 (2024) 2, 283-286A. NAIZABEKOV et al.: INVESTIGATION OF THE EFFECT OF COMBINED THERMOMECHANICAL PROCESSING…Thus, in rods with a diameter of 16 mm in the sur-face layer, a structure with an average grain size of 9 μm was obtained, and in the center of the rod a multi-grained structure with an average grain size of 35 μm was obtained. After RSR up to a diameter of 12 mm, a fine–grained, equal-grained structure of 3 μm was ob-tained in the surface layer, and 20 μm in the center. in both cases, the gradient nature of the microstructure dis-tribution over the cross section of the workpieces is ob-served.After deformation of the brass on the radial-shear rolling mill, as well as after the PHT, measurements of the microhardness were performed. These measure-ments also confirmed the gradient nature of the micro-structure distribution over the cross section after radial-shear rolling. Thus, the microhardness of brass rods after RSR up to a diameter of 16 mm in the surface layer was 980 MPa, and in the center of the rod – 650 MPa. The microhardness of the brass rods after their RSP to a di-ameter of 12 mm was 1225 and 730 MPa, respectively.CONCLUSIONSBased on the results obtained, it can be concluded that combined thermomechanical processing, including preliminary heat treatment and radial-shear rolling, al-lows to obtain a gradient fine-grained structure in brass. At the same time, it was proved that the most suitable pre-heat treatment for brass of the L63 brand is anneal-ing at a temperature of 500 °C, since in this case both the maximum complete transition of the β-phase to the α-phase and the production of a uniform fine-grained structure is ensured.AcknowledgmentsThis research was funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant № AP14869128).REFERENCES[1] R.Z. Valiev, B. Straumal, T.G. Langdon, Using Severe  Plastic Deformation to Produce Nanostructured Materials with Superior Properties, Annu. Rev. Mater. Res. 52 (2022), 357-382.[2] R.Z. Valiev, A.V. Korznikov, R.R. Mulyukov, Structure and properties of ultrafine-grained materials produced by severe plastic deformation, Mater. Sci. Eng. A 168 (1993), 141-148.[3] T. Masuda, Y. Tang, I. Fadhlina Mohamed, Z. Horita, Ul-trafine-grained AZ61 alloy produced by high-pressure tor-sion: Advent of superplasticity and effect of anisotropy, Materials Science and Engineering: A 879 (2023), 145240.[4] A.B. Naizabekov, Z.A. Ashkeev, S.N. Lezhnev, A.R. To-leuova, Billet deformation in uniform-channel stepped die, Steel in Translation, 35 (2005), 37-39.[5] P.H.R. Pereira, P. Bazarnik, Y. Huang, M. Lewandowska, T.G. Langdon, Flow behaviour and microstructural stabili-ty in an Al–3Mg-0.2Sc alloy processed by high-pressure torsion at different temperatures, Materials Science and Engineering: А 887 (2023), 145766.[6] T.S. Orlova, A.M. Mavlyutov, D.I. Sadykov, N.A. Enikeev, M.Y. Murashkin, Effect of Deformation-Induced Plasticity in Low-Alloyed Al-Mg-Zr Alloy Processed by High-Pres-sure Torsion, Metals 13 (2023), 1570.[7] A. Volokitin, I. Volokitina, E. Panin, A. Naizabekov, S. Lezhnev, Strain state and microstructure evolution of AISI-316 austenitic stainless steel during high-pressure torsion (HPT) process in the new stamp design, Metalurgi-ja 60 (2021), 325-328.[8] H.B. Ji, J.M. Wang, Z.Y. Wang, Y. Li, X.H. Cheng, The effect of high-temperature ECAP on dynamic recrystalli-zation behavior and material strength of 42CrMo steel, Materials Science and Engineering A 887 (2023), 145732.[9] A. Korchef, I. Souid, Grain Refinement and Strengthening of an Aluminum Alloy Subjected to Severe Plastic Defor-mation through Equal-Channel Angular Pressing, Crystals 13 (2023), 1160.[10] H.N. Radhi, A.M. Aljassani, M.T. Mohammed, Effect of ECAP on microstructure, mechanical and tribological pro-perties of aluminum and brass alloys: A review, Mater. To-day Proc. 26 (2020), 2302-2307.[11] S.N. Lezhnev, I.E. Volokitina, D.V. Kuis, Evolution of mi-crostructure and mechanical properties of composite alu-minum-based alloy during ECAP, Physics of Metals and Metallography 119 (2018), 810-815.[12] S.P. Galkin, Radial shear rolling as an optimal technology for lean production, Steel in Translation 44 (2014), 61-64.[13] D.V. Troitskii, Yu.V. Gamin, S.P. Galkin, A.S. Budnikov, Pa-rametric model of a three-roll unit of radial-shear rolling mini-mill, Izvestiya Ferrous Metallurgy 66 (2023), 376-386.[14] S. Lezhnev, I. Volokitina, T. Koinov, Research of influence equal channel angular pressing on the microstructure of copper, Journal of Chemical Technology and Metallurgy 49 (2014), 621-630.Note: Translated by D. Rahimbekova, Temirtau, Kazakhstan

Investigation of the effect of combined thermomechanical processing on the brass microstructure evolution and the microhardness change

Investigation of the effect of combined thermomechanical processing on the brass microstructure evolution and the microhardness change

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