These days, ensuring the high quality of thin products (0,6 – 2,0 mm) is the most promising direction for the development of hot-rolled strip production. Hot-rolled strips can be used in place of a more expensive cold-rolled strip. The effect of cooling modes on quality of hot-rolled metal was observed heating at different temperature, the degree of deformation was observed after cooling by water-air mixture. It was observed that the micro hardness of the samples decreases and the amount of structurally free ferrite increases by decreasing the cooling time and increasing the temperature

A. Bukayeva

A. Zhauyt

G. Bulekbayeva

G. Mambetaliyeva

M. Chazhabayeva

Z. Tursymbekova

Zh. Begendikova

English

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387METALURGIJA 60 (2021) 3-4, 387-390A. ZHAUYT, A. BUKAYEVA, Z. TURSYMBEKOVA, G.BULEKBAYEVA, ZH. BEGENDIKOVA, G.MAMBETALIYEVA, M. CHAZHABAYEVADEVELOPMENT OF HOT ROLLING TECHNOLOGY  USING THE METHOD OF PHYSICAL MODELINGReceived – Primljeno: 2021-02-12Accepted – Prihvaćeno: 2021-04-10Preliminary Note – Prethodno priopćenjeA. Zhauyt, (a.zhauyt@aues.kz), Almaty University of Power Engineer-ing and Telecommunictions, Almaty, KazakhstanA. Bukayeva, G. Bulekbayeva, Zh. Begendikova, G. Mambetaliyeva, M. Chazhabayeva, Yessenov University, Aktau, KazakhstanZ. Tursymbekova, Kazakh University Ways of Communications, Al-maty, KazakhstanThese days, ensuring the high quality of thin products (0,6 – 2,0 mm) is the most promising direction for the devel-opment of hot-rolled strip production. Hot-rolled strips can be used in place of a more expensive cold-rolled strip. The effect of cooling modes on quality of hot-rolled metal was observed heating at different temperature, the de-gree of deformation was observed after cooling by water-air mixture. It was observed that the micro hardness of the samples decreases and the amount of structurally free ferrite increases by decreasing the cooling time and increas-ing the temperature.Key words: Gleeble-3800, rolling, sheet, structure, temperatureINTRODUCTIONNumerous schemes of Thermo mechanical process-ing (TMP) rolled products have been developed and are being actively used [1]. In the production of carbon sheets, it is great interest to provide a scheme for forma-tion of perlite, based on the plastic deformation of steel in austenite state and subsequent isothermal transfor-mation of austenite in the pearlite region [2]. Other things being equal, an increase in cooling rate leads to an increase in strength properties of the rolled metal. This reduces the plastic properties. At a very high cool-ing rate, a padded layer of metal forms on the surface strip. To the discrepancy between mechanical properties of hot-rolled steel and the requirements of standards, i.e. to get a marriage can lead to heterogeneity of the microstructure along the thickness of strip, increased hardness and “brittleness” of the incandescent surface. Thus, the microstructure of hot-rolled thin strips pro-duced on known mills is often characterized by consid-erable grain size (large grain on the surface), which leads to the formation of various defects when using such metal for cold stamping. Thus, the microstructure of hot-rolled thin strips produced on known mills is of-ten characterized by considerable grain size (large grain on the surface), which leads to the formation of various defects when using such metal for cold stamping.The main reason for the heterogeneity of thin strips is incorrect assignment of temperature deformation ISSN 0543-5846METABK 60(3-4) 387-390 (2021)UDC – UDK 539.5.001.4:621.771:621.41:620.18:536.5=111modes of rolling and cooling. Technological solutions are effective for one mill is often unacceptable for an-other [3]. Therefore, the study of the influence of tem-perature regimes rolling and quenching, as well as the cooling of strips on quality of hot-rolled steel, rolled and chilled in a new mill and a retractable roller table is great importance [4]. The plastic deformation of sam-ples from steel A1 was carried out on the “tension-com-pression” module. The samples were heated at a rate of 100 °C / s to a temperature of 1 100 °C and held at these temperatures 1 h. Further, each heated sample was cooled to temperatures of 800, 900 and 1 000 °C, de-formed by cyclic compression at the rolling speeds of the longitudinal wedge mill (LWM).MATERIALS AND METHODSFor the purpose of rolling high-quality sheets of met-als and alloys, it offers a LWM and a new design of the diverting roller. The work investigated the effect of cool-ing with a water-air mixture on the structure and proper-ties of rolled sheets of steel А1 having the following chemical composition / wt. %: C 0,15, Mn 0,95, Si 0,29, Р 0,011, S 0,012, V 0,11, Тi  0,012, Сu 0,20, Аs 0,020. The analogue of the experimental steel A1 is the steel St3Gsp of the CIS countries (C 0,14 - 0,2, Mn 0,8 - 1,1, Si 0,15 - 0,3, Р 0,04, S 0,05, Ni 0,3, Сr 0,3, N 0,008, Сu 0,3, Аs 0,08). To determine the effect degree of deforma-tion and subsequent water-air cooling on the structure of steel A1, Samples with a size of Ø 10,0 × 15,0 mm were tested by compression on the Gleeble-3800 test complex. The Gleeble-3500 is a fully digital closed-loop thermo mechanical testing system. It is based on software based on easy-to-use Windows operating systems and a block of powerful processors that provide an interface for creat-388A. ZHAUYT et al.: DEVELOPMENT OF HOT ROLLING TECHNOLOGY USING THE METHOD OF PHYSICAL MODELING METALURGIJA 60 (2021) 3-4, 387-390ing, conducting and processing programs for physical modeling and thermo mechanical tests. The heating sys-tem of the Gleeble-3500 unit allows direct current trans-mission to heat samples at a speed of up to 10 000 °C / s and maintain a constant equilibrium temperature. Thanks to high thermal conductivity of grippers that hold the samples Gleeble-3500 complex can cool the samples at high speed. The additional cooling system allows you to achieve a cooling rate of more than 10 000 °C / s on the sample surface. Thermocouples and an optional infrared pyrometer transmit signals for precise temperature con-trol of the samples. The Gleeble-3500 mechanical system is a closed, fully integrated servo hydraulic system capa-ble of developing a force of up to 100 kN, the maximum speed of mobile traverse: 1 000 mm / s. LVDT sensors / force sensors (strain gauges) or non-contact laser exten-someters provide feedback for the precise implementa-tion of the mechanical test program. All tests can be car-ried out under reduced pressure or in a protective atmo-sphere. Plastic deformation of samples made of A1 steel was performed on the «tension-compression» module. The samples were heated at a rate of 100 °C / s to tem-peratures of 1 100 °C and maintained at these tempera-tures of 1 h. Further, each heated sample was cooled to temperatures of 800, 900 and 1 000 °C, deformed by cy-clic compression at rolling speeds of a LWM. When drawing up the experiment plan, time of the inter-forma-tion pause was determined basis law of the constancy of the second volumes during rolling in a five-cell LWM [5]. In intervals of cyclic deformation after switching off electric drive of installation, the sample remained clamped by strikers and active loading was replaced by a relaxation stage. Subsequently, the samples were cooled with air, water-air mixture and naturally to room temper-ature. The sections for metallographic research were pre-pared according to the traditional method on grinding and polishing wheels. A solution of nitric acid in ethyl alcohol was used to etch the samples.Metallographic analysis was performed using a uni-versal microscope Neophot 32 (Carl Zeiss, Jena) (Ger-many). The Neophot 32 microscope is designed for me-tallographic microscopy and creation of photographs. The observation can be made by the light and dark field method, in polarized light, with a change in magnifica-tion multiplicities. Magnification of microscope, multi-ple: from 10 to 2 000. The microscope is equipped with an Olympus digital SLR camera with output of the re-sulting image and saving images to a computer. Using above method, the influence of temperature, compres-sion, deformation rate and inter formational pause on the deformation resistance of A1 steel was studied. It is known that speed effect at high temperature is deter-mined by the speed of such processes as hardening and softening. An increase in rate of deformation corre-sponds to a more hardened state, since probability of partial softening of metal during plastic deformation decreases. The data available in various monographs on rate dependence of the deformation resistance of steels are in many cases contradictory and do not always al-low us to definitely judge the influence of this factor on the deformation resistance. In most studies, there is an increase in the values of deformation resistance with an increase in the deformation rate.RESULTS AND DISCUSSIONIt should be noted that in our experiments, with an increase in the rate of deformation in cyclic compres-sion, value of the deformation resistance decreases in magnitude. Figures 1-3 show laws of variation of the strain resistance σ as a function of cyclic deformation with different compressions ε and deformation rates. From  analysis and comparison of the hardening curves of A1 steel, it follows that the deformation resistance of this steel at temperatures of 800, 900 and 1 000 °C in-creases in the initial deformation cycle and decreases in the last cycles. In our opinion, dynamic and static softening and the thermal effect of deformation have a significant impact on the deformation resistance curves. Thus, with increasing compression and thus the rate of deformation, character of the hardening curves changes. At low deformation rates, there is a monoto-nous hardening of the metal, i.e., the deformation resis-tance increases at the end of the sample compression process [6]. During transition from one precipitation cycle to another precipitation cycle, the maximum val-ues of the strain resistance decrease. The presence of such a feature of the rheological behavior of steel under study can be explained by the course of dynamic and static recrystallization during precipitation and in the inter-formation pauses. If we compare the maximum values of the deformation resistance of samples depos-ited at different temperatures, we can see that the value of the deformation resistance is significantly affected by temperature. When the temperature increases, the value of the deformation resistance decreases. At the same time, difference in strain resistances increases in the first and fifth cycles of deformation, i.e., the value increases Ds = s1 – s2, residual hardening decreases, as the return and recrystallization processes have time to pass more completely. All this indicates the passage of dynamic and static recrystallization at elevated tem-peratures. Figures 4 show the microstructure of A1 steel samples obtained under the temperature-strain conditions of rolling thin sheets on a LWM.An increase in precipitation temperature to 1 000 °С leads to an overall coarsening of grain (see Figure 4a). Thus, the samples, upset and cooled according to vari-ant 1, 2 and 3, have the structure of coarse ferrite with dimensions of 84 - 97 µm, thick-plate pearlite, consist-ing of alternating plates of ferrite and cementite, with an average inter-plate distance n=0,82 – 0,91 µm. The size of the coarse-lamellar pearlite colonies reaches 66 - 83 µm, while the size of excess cementite corresponds to 3 - 4 points (see Figure 4b and 4c). The formation of such a coarse-grained structure during upsetting and cooling 389A. ZHAUYT et al.: DEVELOPMENT OF HOT ROLLING TECHNOLOGY USING THE METHOD OF PHYSICAL MODELINGMETALURGIJA 60 (2021) 3-4, 387-390according to variant 1, 2 and 3 can be explained by the creation of conditions for the passage of complete pri-mary recrystallization in the deformed austenite matrix during high-temperature upsetting, as well as by an in-crease in the size of austenite grains at high tempera-tures. It is known that larger initial austenite grain size, larger inherited ferrite + pearlite structure.The presence of such large grains during upsetting and cooling according to variant 1 can be explained by the gradient of work hardening of austenite and ferrite grains over entire section of the strip at a low deforma-tion temperature. Upon slow cooling, recrystallization under conditions of such a gradation of work hardening causes enhanced grain growth over the sample cross section. It should be noted that the reason for formation of an uneven-grained structure over cross-section of the sample at a temperature of 800 ° C may also be non-uniformity of deformation.Since at low rolling temperatures, austenitic and fer-rite grains may undergo deformation to a lesser or great-er extent. Thus, from analysis of the microstructure of A1 steel, it can be concluded that a uniform structure, fine-grained over the thickness of the samples, is ob-tained upon deformation and cooling with a water-air mixture according to option 1 (Figure 4a). According to the results of the study of structure, it was found that with late cooling modes, internal structure of A1 steel is formed according to the same regularities.CONCLUSIONS1 Heating to temperatures of 800 °C and deforma-tion with a degree of 65 – 70 % when cooling with a water-air mixture of 3 and 6 s does not always ensure the formation of a fine-grained ferritic-sorbitol structure in high-carbon samples;2 Heating of the samples to temperatures of 900 and 1 000 °C, deformation with a degree of 65 – 70 %, and cooling by a water-air mixture 3 and 6 s leads to the formation of a sorbitol structure in samples of high-carbon steel with an inter plastic distance of 0,23 – 0,62 μm.(а) variant 1 rolling according to LWM(b) variant 2 rolling according to LWM(c) variant 3 rolling according to LWMFigure 1  Change in resistance to deformation at temperature 800 °С(а) variant 1 rolling according to LWM(b) variant 2 rolling according to LWM(c) variant 3 rolling according to LWMFigure 2  Change in resistance to deformation at temperature 900 °С390A. ZHAUYT et al.: DEVELOPMENT OF HOT ROLLING TECHNOLOGY USING THE METHOD OF PHYSICAL MODELING METALURGIJA 60 (2021) 3-4, 387-390(а) variant 1 rolling according to LWM(b) variant 2 rolling according to LWM(c) variant 3 rolling according to LWMFigure 3  Change in resistance to deformation at temperature 1 000 °С(а) variant 1 rolling according to LWM(b) variant 2 rolling according to LWM(c) variant 3 rolling according to LWMFigure 4  Microstructure of A1 steel deposited at a temperature of 1 000 °С × 500REFERENCES[1] B. T. Kaliyev, B. T Kopenov, et al. Stady on physical and chemical properties of eteel 60C2XA on a retractable roll-er conveyor, Metalurgija 59 (2020) 3, 377-380.[2] X. Zhang, T. Jiang, X. Xue, et al. Influence of MgO/Al2O3 ratio on viscosity of blast furnace slag with high Al2O3 con-tent, Steel Research International 87 (2016), 87-94.[3] K. V. Sudhakar, Metallurgical investigation of failure in 316L stainless steel orthopaedic implant, Eng. Fail. Anal. 12 (2005), 249-256.[4] T. Sahin, H. Kockar, M. Alper, Properties of electrodepos-ited CoFe/Cu multilayers: The effect of Cu layer thickness, J. Mag. Mag. Mater. 373 (2015), 128-131.[5] S. Roy, S. Subodh, S. Kumar, K. Chattopadhyay, Accumu-lative roll bonding of aluminum alloys 2219/5086 lami-nates: Microstructural evolution and tensile properties, Materials and design 36 (2012), 529-539.[6] A. Wierzba, S. Mroz, P. Szota, A. Stefanik, R. Mola, The influence of the asymmetric ARB process on the properties of Al-Mg-Al multi-layer sheets, Archives of Metallurgy and Materials, N. Heeren and T. Fishman, A database seed for a community-driven material intensity research platform 60 (2015) 4, 2821-2825.Note:  The responsible for England language is L. D. Sergeeva, Almaty, Kazakhstan

Development of hot rolling technology using the method of physical modeling

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Development of hot rolling technology using the method of physical modeling

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