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16Journal of Siberian Federal University. Engineering & Technologies, 2017, 10(3), 346-351
УДК 669.11/621.746
Simulation of a Continuous Ingots Structure Formation Process
Oleg A. Kovalenko* and Vladimir I. Dozhdikov
Lipetsk State Technical University 30 Moscovskaya Str., Lipetsk, 398600, Russia
Received 09.09.2016, received in revised form 20.11.2016, accepted 10.01.2017
The presented results demonstrate the possibility of mathematical complex model in research of the temperature characteristics pattern changes in polymorphic transformations, isotherms of liquidus and solidus, and other parameters depending on the cooling conditions of the ingot. Shown the possibility of predicting parameters of a continuous ingot microstructure (distance between dendrites, size of the austenite and ferrite grains). Were made microstructure parameter calculations of the continuous steel ignot containing 0.17 % C, 0.62 % Si, 1.4 % Mn at various secondary cooling modes.
Keywords: continuous casting of steel, dendrite, austenite, grain size, structure formation.
Citation: Kovalenko O.A., Dozhdikov V.I. Simulation of a continuous ingots structure formation process, J. Sib. Fed. Univ. Eng. technol., 2017, 10(3), 346-351. DOI: 10.17516/1999-494X-2017-10-3-346-351.
Моделирование процесса формирования структуры непрерывного слитка
О.А. Коваленко, В.И. Дождиков
Липецкий государственный технический университет Россия, 398600, Липецк, ул. Московская, 30
В статье представлены результаты применения разработанной комплексной математической модели в исследовании закономерностей изменения характерных температур полиморфных превращений, изотерм ликвидуса и солидуса, а также других параметров в зависимости от условий охлаждения слитка. Показана возможность прогнозирования параметров микроструктуры непрерывного слитка (междендритноерасстояния, размер зерна аустенита и феррита). Произведен расчёт параметров микроструктуры стального непрерывного слитка с содержанием 0,17 % С, 0,62 % Si, 1,4 % Мп при различных режимах вторичного охлаждения.
Ключевые слова: непрерывная разливка стали, дендрит, аустенит, диаметр зерна, структурообразование.
© Siberian Federal University. All rights reserved
* Corresponding author E-mail address: [email protected]
Introduction
The development of measurements aimed at improving the quality of continuously cast billets involves the use of mathematical modeling of the ingot formation. This can be achieved by minimizing the defects formed during solidification of the ingot at continuous casting machine (CC machine), and by ongoing research of metal structure management capabilities.
Results and discussion
As a tool for implementing this approach, a mathematical model can be used to determine the temperature field and structure parameters of a continuous ingot [1, 2]. Features of this model can be seen quite clearly from the results of the analysis. For example, formation process of a continuous ingot steel containing 0.17 % C, 0.62 % Si, 1.4 % Mn with various secondary cooling modes. The main parameters used in computational experiments are: casting steel temperature - 1535 °C, casting speed - 1 m/min, ingot thickness - 0, 250 m.
Fig. 1 shows one of the modules interface of the program used to determine liquidus and solidus temperatures according to the method used in the model [1]. For the case in question, they were as follows: - 1514.28 °C liquidus, solidus - 1479.76 °C. This module alsodetermines the temperature of polymo ^luc tranefermetions.
Changes in the surface temperature of the ingot in crystallizer were set using the experimental vnluei of the lieat flux Ihruughcrystalllzii wailo °3] (Fig. 24.
Boundary tondilconi of uhangei mar surfeco temperature gunctions atlhera condarg eoeling zone over timewereuredasbatiec haracteeihtico od rhosecoadaty eoo33zgmod3 [41:
C \\-+1
~ V c-T+m
T(t) = (TH-TK)• 1--^ ' +TK, (1)
V koo J
TH - TK - temperature difference at the beginning of the cooling process and at the end; °C; Tkon -cooling time of the ingot;n, m, c -parametersdefiningthe type of dependence T (t).
Concentration C, %
Fig. 1. The andsolidus
The effect of secondary cooling intensity on the parameters of the ingot was examined by comparing the simulation of the formation process results of a continuous ingot using two cooling modes: intense and soft. For the first mode ingot surface after exiting the crystallizer was quenched to 700 °C followed by cooling to 600 °C. In the second mode, the surface temperature decreased gradually up to 600 ° as soon as the ingot was taken out of the crystallizer (Fig. 3).
The results of computational experiments are presented in Fig. 4. A characteristic feature of the first mode is smaller length zone of molten steel, two-phase region, of the growth zone of an austenitic-ferritic pearlitic structure. These results also follow the change in the cross section of the ingot structure as shown, for example, for coordinates processing of 10 meters from the axis of the meniscus (Fig. 5). So at a distance of 5 mm from the surface of ingot billet ferrite-pearlite structure already formed with a size of 21.36 microns ferrite grains at the surface and 26.93 mm at a distance of 5 mm. Deeper you can find austenite grains and ferritic grains formed at their boundaries. Austenite grain size at that portion (5-18 mm from the surface) is 1250-1480 microns. At a distance of 18-95 mm from the ingot surface is a zone with austenitic structure, the grain size gradually increases to 2368 micron at a distance of 60 mm
2 1,8 'P 1.6
5 1.4 2 1,2
i 1 0.8
« 06
SC 0,4
0.2
0
0 0,2 0,4 0,6 0,8 1
Meniscus distance , m
Fig. 2. The density distribution of the heat flow adjustment in the wide side of the crystallizers at a distance of 0.16 m from itscenter [2] (Pulling speed: 1- 0.4m/min,2 -0.6 m/min,3- 0.8 m/min, 4- 1.0m/min,5-l,2 m/min)
1600 1500 1400 y 1300 y 1200 3 1100 h iooo g 900 £ 800 700 600 500
Fig. 3. Changes ofthe ingot temperature: 1,3- ingot surfaceandcentertemperaturefor thelst cooling mode; 2, 4 - ingotsurface andcenter temperature forthe 2nd coolingmode
_____
\ \
\ X.
N
. 2 \
s V
i A
K -
..... ____... _
10 20 30 40 50 60 Technology axis distance, m
Ingot thickness, mm 0 20 SO 60 80 100 120
b Ingot thickness, mm
0 20 so «o »o loo 120
o
Fig. 4. Basic forming parameters of a continuous ingot: a - mode 1; b - mode 2
2500 j---j----- !
\
i i
3° td -------—
^ -to
Fig. 5. Ingotchangeof structureparameterswith thickness for the second mode
anda 95mm-750mm. The sharp increase in the grain size to 60 mm is associated with the processes of recrystallization occurring at high temperatures. Two-phase zone plot: 95-110 mm is characterized with a dendritic structure by dispersion of 700-745 microns, respectively.
The change of the microstructure of the ingot along the continuous casting machine for the first mode shown in Fig. 6.
MPH a
W
720 00
Fig. 6. Changing of the structure parameters along a vertical cross section of the ingot at a distance of 100 mm from the surface for the first cooling mode
Thus, ata distanceoflOOmm from the surface of the ingot, the liquid phase is maintained up to 9.55 m. Thenthheecs theeeiU aeeiatud-solidpitase, weretheformfeionof fdeadfcCicatructure htppens, which has an impact on the size of the austenite grains, formed below the peritectic transformation temperature. For the current regime at a distance of 100 mm from the surface of the ingot, magnitude of interdendritic distance at the beginning of austenitic structure formation was 750 microns. Further, tWs eizt taken os an intiM sustanice gram in simutetion dueing growth of austenite. Tte rlet 11.8 m-40g mm t0e tn^cfnulo|rf exis n au ^rea ug cu sten^c itcrui^t^i^ni. TWs rapid growtn cr nnsienite graine dears ^(cniimhi^h; op t9.7 mof the te^n-lon nuis,en^lifrTOd^]iug daes noc sian^i^tiuntiy affect thr irsrehse ingsain rze. Bciowthe ACC tf^r£^ratore sieee (8fO°C), which
coi^tesi^^i^ds^ci arounn 40^]cm, ferriteraieasee l:^cttUcbouns^;a]rg t ofthee adrtemte graianPiefirsi stage of see ermiurosrructureformation irentectoidtrancformationcf auotn nite intr5e ferriteecementite mix at720SU (56 nee lcru5icn)( FemCe htuiв nize odSUe 6naieirncture tr a givan sec5rfn is 60 miinons.
Cine l-SWai
Bhe6reren5edrrsurCs domc>nstrat( nhu po ssiMtiy of mathematical complex model in research of the temperature characteristics pattern changes in polymorphic transformations, isotherms of liquidus and solidus, and other parameters depending on the cooling conditions of the ingot. All this makes it possible to obtain the microstructure characteristics, and with presence of contact functions at different points in the cross section and the mechanical properties of the ingot at a particular time. An extensive
set of input data (structural and technological parameters of casting, steel thermal parameters) used in the implemented model, allow user to get a set of quality characteristics of the structure and properties of continuous ingot needed to select the optimal conditions for the formation of the ingot in the casting of steel on a particular CC-machine.
References
[1] Коваленко О.А., Дождиков В.И. Влияние параметров процесса формирования структуры непрерывного слитка на образование трещин. Научно-технический вестник Поволжья. Казань. 2012, 6, 271-274 [Kovalenko O.A., Dozhdikov V.I. Influence of the process parameters forming the structure of a continuous ingot to cracking. Scientific and Technical Gazette Volga. Kazan, 2012, 6, 271-274 (in Russian)]
[2] Коваленко О.А. Информационная система прогнозирования микроструктуры непрерывнолитого слитка. Всероссийский конкурс научно-исследовательских работ студентов и аспирантов в области информатики и информационных технологий: сб. науч. работ: в 3 т. Белгород: ИД «Белгород», 2012, 3, 245-250 [Kovalenko O.A. Information system of microstructure prediction in continuous casting ingot. All-Russian Contest ofresearch works of students and graduate students in computer science and information technologies: Sat. scientific. papers: 3 tons. Belgorod:. ID "Belgorod", 2012, 3, 245-250 (in Russian)]
[3] Дождиков В.И. Теплофизические особенности формирования непрерывного слитка в кристаллизаторе МНЛЗ. Липецк: ЛГТУ, 2007. 184 с. [Dozhdikov V.I. Thermal features of formation of a continuous ingot mold in a continuous casting machine. Lipetsk: Lipetsk State Technical University, 2007. 184 p. (in Russian)]
[4] Порядин С.В., Дождиков В.И. Определение параметров процесса управления охлаждением непрерывного слитка. Образование, наука, производство и управление сб. науч. и научно-методических. докладов всероссийской. Старый Оскол: СТИ НИТУ МИСиС, 2011, 1, 5963 [Poryadin S.V., Dozhdikov V.I. Defining the parameters of the cooling control process of continuous ingot. Education, science, production and management of sb. scientific. scientific and methodical. All-Russia reports. Stary Oskol: STI NUST MISA, 2011, 1, 59-63 (in Russian)]
