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Kawatek A.., Dyja H.
a higher rotational speed of the lower and the upper rolls in successive passes, which will cause the rolls to be alternately driving and driven rolls, whereby their excessive overloading will be prevented.
References
1. Dyja H., Satganik A. M., Piesin A. M., Kawatek A. Asymetryczne walcowanie blach cienkich Teoria, technologia i nowe rozwi^zania [M]. Wydawnictwo Politechniki Cz^stochowskiej, (Poland), 2008. 345.
2. Kawatek A., Dyja H., Knapinski M. Wptyw asymetrycznego walcowania na popraw^ wskaznikow techniczno-ekonomicznych procesu walcowania blach na gor^co [J]. Hutnik Wiadomosci Hutnicze. 2008, 6: 266-270 (in Polish).
3. Markowski J., Dyja H., Knapinski M., Kawatek A. Theoretical analysis of
the asymmetric rolling of sheets on leader and finishing stands [J]. Journal of Materials Processing Technology, 2003, 183-188.
4. Sinicyn V.G. Nesimmetrichnaja prokatka listov i lent [M]. Metallurgja, Moskva, 1984, 165 (in Russian).
5. Kawatek A. Analiza pol pr^dkosci i pr^dkosci odksztatcenia w
asymetrycznej kotlinie walcowniczej [J]. Hutnik Wiadomosci Hutnicze. 2002, 12: 485-488, (in Polish).
6. Dyja H., Wilk K. Asymetryczne walcowanie blach i tasm [M]. Wydawnictwo WMilM Politechniki Cz^stochowskiej, (Poland), 1998. 268.
7. Gorelik V.S., Nalcha G.I., Rudnev A.E., Klimenko I.V., Feofilaktov A.V. Uluchshenie sluzhebnykh svojstv tolstykh listov putem osvoenija tekhnologii asimmetrichnoj prokatki [J]. Stal', 11, 1991, 41-44 (in Russian).
8. Forge3® Reference Guide Release 6.2, Sophia-Antipolis, 2002.
9. Kawatek A. Asymetryczne walcowanie blach grubych w walcarce
wykanczajqcej [J]. Hutnik Wiadomosci Hutnicze, 2006, 6: 266-270, (in Polish).
Chukin M.V., Korchunov A.G., Gun G.S., Polyakova M.A., Koptseva N.V.
NANODIMENTIONAL STRUCTURAL PART FORMATION IN HIGH CARBON STEEL BY THERMAL AND DEFORMATION PROCESSING
Abstract. On the example of high carbon steel of grade 80, updated by boron, the ability of forming nanodimensional structural constituents has been proved. Special types of thermal and deformation processing are used. The thin- plate pearlite structure, obtained in this way, according to modern material science concept is considered to be a nanomaterial where interlamellar spacing in a ferrite-carbide mixture is a nanodimensional element. It is experimentally proved that interlamellar spacing decreasing takes place in steel, being investigated after heat treatment and further cold plastic deformation. The rate of interlamellar spacing, after heat treatment, and cold plastic deformation is 1,66, the rate of billet geometrical dimensions, before and after deformation, is 1,6. The results obtained are used to achieve desired properties of high-tensile reinforcing bars of 9,6 mm in diameter for the new generation of concrete sleepers.
Keywords: Nanodimensional structural constituents, high carbon steel, pearlite structure, interlamellar spacing, thermal processing, deformation processing
Achievement of high quality and field reliability of metallic constructions is possible on the basis of knowledge-intensive technologies of getting materials with a new unique property package. Nowadays such technologies are those, which allow obtaining ultrafine and nanostructures, which considerably affect metal and alloy mechanical properties during the production of hardware items of different purpose [1]. This investigation actuality is stipulated by searching of an effective complex of impacts on billet microstructure with major diameters (more than 10,0 mm) made from high carbon steel to get the highest strength and ductility.
The aim of this work is to study peculiarities of getting nanodimensional structural constituents in the billet from high carbon eutectoid steel of grade 80, updated by boron, after special types of thermal and deformation processing. The thin- plate pearlite structure, obtained in this way, according to modern material science concept is considered to be a nanomaterial with structural constituents of plate form. Interlamellar spacing in a ferrite-carbide mixture is a nanodimensional element of steel structure.
The subject matter of the chosen thermal processing lies in heating and isothermal holding in the field of minimal stability of overcooled austenite with further cooling in lead hot melt. The thermal processing task is formed, in major diameter billets, steel structure, providing the capability of the highest hardening during the following deformation effect with large total deformation degrees.
The history of steel structural constituent fine crushing is known to be determined mainly by accumulation of sharing deformation in processing. Considerable steel structure fine crushing is achieved by large degrees of plastic deformation close to 1. To provide such processing conditions, repetitive cold plastic deformation was used. The differential characteristic of offered deformation effect is that operation modes are appointed in such a way, that each deformation cycle initiates active dislocations sliding and it provides additional fragmentation of microstructure and the highest hardening of thermally processed steel.
The billet of diameter 16,0 mm from high carbon steel with carbon content of 0.8 % was used to carry out the experiments. Thermal processing was realized with the following parameters: reheat temperature range was 930°C to 970°C; isothermal holding temperature range was 4700°C to 550°C. Ageing time was chosen that way to provide finishing diffusional decay of overcooled aus-tenite in the preset temperature. Cold plastic deformation was carried out with total deformation degree up to 60%. Herewith the billet diameter decreased from 16,0 mm to 10,0 mm. Scanning electron-microscope analysis of the bars was done on the electron microscope JEOL JSM-6490 LV with accelerating voltage 30 kW in modes of secondary and temporary reflected electrons in conditions of Nano Steel Research Studies Institute of Nosov Magnitogorsk State Technical University. Quality and quantity microanalysis was carried out on the metallographic mi-
Nanodimentional structural part formation in high carbon steel by thermal and deformation processing
croscope Meiji Techno using computer system of images analysis Thixomet Pro.
A steel structure in its initial state represents a ferrite-carbide mixture with interlamellar spacing from 0,22 pm to 0,28 pm (Fig. 1, a). Small sections of structurally free ferrite are presented in microstructure (Fig. 1, b).
b
Fig. 1. Steel microstructure in its initial state
After thermal processing the microstructure consisted of a ferrite-carbide mixture and some quantity of structurally free ferrite as small islands on grain junction lines (Fig. 2, a) with interlamellar spacing of ferrite-carbide mixture from 0,12 pm to 0,16 pm (Fig. 2, b).
b Fig. 2. Steel microstructure after thermal processing
Previous cold plastic deformation experiments showed that heat treated steel with interlamellar spacing in a ferrite-carbide mixture from 0,12 pm to 0,16 pm demonstrates the highest treatment and hardening capability [2]. Further decrease of interlamellar spacing in a ferrite-carbide mixture is observed in repetitive deformation processing for heat-treated steel with such structure parameters (Fig. 3).
e f
Fig. 3. Heat-treated steel microstructure at different total degree of cold plastic deformation:a - 21,8 %; b - 34,0 %; c - 43,3 %; d - 58,8 %; e - 56,3 %; f - 60,9 %
In Fig. 4 one can see interlamellar spacing value change in a ferrite-carbide mixture depending on total deformation degree.
Deformation degree ?%
Fig. 4. Total deformation degree effect on interlamellar spacing value in a ferrite-carbide mixture
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Vestnik of Nosov Magnitogorsk State Technical University 2013. №5.
Chukin M.V., KorchunovA.G., Gun G.S., Polyakova M.A., Koptseva N.V
From the obtained data one can see that decrease of interlamellar spacing which is proportional to a diameter decrease of the billet, being processed, happens in the steel, being investigated, after heat treatment and further cold plastic deformation. The rate of interlamellar spacing after heat treatment and cold plastic deformation is 1,66, the rate of billet geometrical dimensions before and after deformation is 1,6. Thickness of cementite and ferrite plates in cold plastic deformation also decreases.
The results obtained are used in the established manufacturing for obtaining necessary properties for high-tensile reinforcing bars of 9,6 mm in diameter for concrete sleepers of new generation [3, 4]. Thermal and deformation processes combine, firstly, the special kind of thermal treatment of carbon steel, ensured the obtainment of nanostructured materials, possessed of high strength and ability to the subsequent deformation with high total deformation. For the purpose of producing nanostructured parts in the primary blank structure it intends to use the special kind of thermal treatment with mentioned above heating temperature and further isothermal holding. And secondly, highly productive constituent deformation process, activating free glide planes in every deformation cycle is used, which leads to additional fragmentation of material structure and provides maximal strengthening of the processed fittings. Deformation treatment modes set to activate new free glide planes in every deformation cycle which leads to additional dispersion of ultrafine grained stricture and fragmentation of ferrite solder pads in pearlite.
In Fig. 5 you can see the structure of quality indices of a high-tension reinforcement for armoring concrete sleepers.
maintains sufficiently high ultimate elongation before rupture (not less than 4 %). Stress relaxation in reinforcement reduces sharply and do not exceeds 2 % at 1000 h under 20°C and accounts for 75% of tensile strength. Such complex of consumer attributes for end production diam. 9,6 mm is a conceptually new kind of product which cant be obtained by using tradition approaches to manufacture fittings for various applications.
Combination of mentioned treatment methods opens up high technological possibilities for enhancement of strength and special reinforcement properties keeping their high uniformity without steel alloying. The established high-technology production of high-tensile reinforcement with diameter of 9,6 mm for reinforcing of concrete sleepers for modern highways possesses the necessary characteristics of innovation technology. It’s the first time of complex usage of modern science intensive thermal and deformation processes for influence on carbon steel structure with forming nanostructured state.
Post graduate students Gulin A., Dolgiy D., Constan-tinov D., Lysenin A. took part in the presented investigations.
The research corresponds to the realization of complex project for high-technology production development. This project is performed with participation of Russian higher education institute (contract 13.G25.31.0061), the program of the strategic development of the university 2012—2016years (the competitive support of The Ministry of Education and Science of the Russian Federation the
strategic development of SEI HPE) and Grant in the form of subsidy to support scientific researches (agreement № 14.B37.21.0068).
References
Chukin M., Koptseva N., Ba-rushnikov M., Efimova Y., Nosov A., Noskov S., Kolomiets B. Innovative potential of new ware production technologies from nanostructured steels. Vestnik Magnitogorskogo gosu-darstvennogo tehnicheskogo universteta im. G.l. Nosova. [Vestnik of Nosov Magnitogorsk State Technical University]. 2009, no. 2, pp. 64-68.
Lebedev V., Chukin M., Gun G., Korchunov A., Polyakova M. Prospects of high-tensile in manufacturing of large diameter wire rod at «MMK-Metiz» -Magnitigorsk Hardware and Sizing Works / CIS Iron and Steel Review, 2011. pp. 18-21.
Chukin M., Gun G., Korchunov A., Polyakova M. Manufacturing prospects of high-tension reinforcement from high carbon steel. Iron and Steel. 2012. December. pp. 8-15.
Ushakov S., MB. Chukin M., Gun G., Korchunov A., Polyakova M. High-tension reinforcement for armoring new age concrete sleepers. The path and track facilities. 2012. no. 11. P. 25-27.
Fig. 5. Structure of quality indices of a high-tension reinforcement
Using such thermal and deformation processes in manufacturing of reinforcement for prestressed concrete constructions with enhanced apparent elastic limit and conventional yield strength enables to reach these values respectively not less than 80 and 90 % of sorting ultimate strength minimum. In these conditions reinforcement
