In this paper, cooling plan is optimized to solve the central porosity problem of 450 mm diameter steel electrode ingot. The central porosity of ingot in corresponding cooling plans is calculated by the finite element analysis software ProCAST. The results show that in the plan of independent riser and strengthened cooling in lower ingot part, the central porosity has been significantly reduced

G. W. Ao

M. G. Shen

R. T. Zhang

Z. S. Zhang

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The simulation study on central porosity of 450 mm diameter steel electrode ingot

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301METALURGIJA 56 (2017) 3-4, 301-303Z. S. ZHANG, R. T. ZHANG, M. G. SHEN, G. W. AOTHE SIMULATION STUDY ON CENTRAL POROSITY OF 450 MM DIAMETER STEEL ELECTRODE INGOTReceived – Primljeno: 2017-02-02Accepted – Prihvaćeno: 2017-05-15Original Scientific Paper – Izvorni znanstveni radZ. S. Zhang, G. W. Ao: Applied Technology College, University of Sci-ence and Technology of Liaoning, Anshan City, ChinaR. T. Zhang: Angang Subsidiary Enterprise Corporation, Liaoning, Anshan City, China M. G. Shen: College of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan City, ChinaIn this paper, cooling plan is optimized to solve the central porosity problem of 450 mm diameter steel electrode ingot. The central porosity of ingot in corresponding cooling plans is calculated by the finite element analysis soft-ware ProCAST. The results show that in the plan of independent riser and strengthened cooling in lower ingot part, the central porosity has been significantly reduced. Key words: steel electrode ingot, heat flux, central porosity, numerical simulationINTRODUCTIONThere is high requirement for internal quality of electrode ingot. And the electrode ingot tends to be larg-er ratio of height to diameter due to the two parameters of the design of the filling ratio and the height to diam-eter ratio of the electro-slag remelting process[1]. In the large ratio of height to diameter electrode ingot produc-tion, there will be prone to central porosity or even con-centrated shrinkage.The internal quality of electrode ingot has great influ-ence to electro-slag remelting production. The central porosity or even shrinkage will cause the fluctuation of current in the end of melting electrode, and that will af-fect the quality of the electro-slag remelting ingot [2].The main influence factors of ingot internal quality is design parameters and heat flux control in solidifica-tion. And for the electrode ingot, the design parameters have been limited. So the only way to improve the inter-nal quality of products is the heat flux control[3].In this paper, the central porosity of the electrode ingot is calculated by ProCAST. And the plan of heat flux control in solidification process of the electrode in-got is optimized based on the comparisons of plans.MATHEMATICAL MODEL ESTABLISHMENTBasic condition settingGeometric model and mesh of 450 mm diameter electrode ingot are showed by Figure 1. ISSN 0543-5846METABK 56(3-4) 301-303 (2017)UDC – UDK 669.18:66.065:621.556:536.235:518.1=111The heat transfer control equation[4]:  (1)Where T is temperature / °C, ρ is steel density / kg/m3, λ is thermal conductivity / W/m/°C, c is specific heat / J/kg/K.The assumptions used for heat transfer simulation are the molten steel is viscous incompressible flow and the thermal conductivity is isotropic, the thermal physi-cal parameters of molten steel is only a function of tem-perature, the boundary is no slip boundary.The study plans are set as follow.Plan 1 is set as air cooling at the outer wall. Plan 2 is set as air cooling at the outer wall and exo-thermic at upper ingot. Plan 3 is set as air cooling at the outer wall. The riser is designed separated from mould and the part contact with mould is refractory. It is set forced cool-Figure 1  The ingot geometry model and mesh of electrode ingot302Z. S. ZHANG et al.: THE SIMULATION STUDY ON CENTRAL POROSITY OF 450 MM DIAMETER STEEL ELECTRODE... METALURGIJA 56 (2017) 3-4, 301-303Figure 2 shows that the heat flow in the upper part of the ingot is large because of the heat absorption by iron mould. And in addition to the heat transfer to the hori-zontal direction, there is lots of heat absorbed by the upper part of iron mould. In the upper area of ingot, the temperature of molten steel decreases rapidly. And thus, a solid bridge is formed at 1 843 s from end of filling. Then, the steel feeding channel disappeared, eventually led to the formation of the ingot central porosity. The simulation results are shown in Figure 3. In the Figure 3, it can be seen that the central shrinkage poros-ity is very serious. And as being shown in (b), the area of shrinkage porosity above 30 % level is very large. The main reason is that the “solid bridge” hinders the upper molten steel feeding.Result of plan 2The simulation results of solid phase rate and heat flux of ingot in plan 2 are shown in Figure 4. And the ingot shrinkage simulation result is shown in Figure 5.ing to mould at the region of the 1 / 5 mould height from bottom. Initial conditions and boundary conditionsHeat flux calculation is : q=h×(Tm - Tc) (2)Where q is heat flux / W/m2, Tm is mould surface temperature / °C, Tc is environmental temperature / °C, h is comprehensive heat transfer coefficient / W/m2 /°C. Initial conditions are:Liquid steel:  T = Tst0,  mould: T = Tm0.Composition of steel: C is 0,16 %, Si is 0,33 %, Mn is 1,5 %, S is 0,03 %, P is 0,03 %.THE ANALYSIS OF CALCULATION RESULTSResult of plan 1The simulation results of solid phase rate and heat flux of ingot in plan 1 are shown in Figure 2. Figure 2 The solid phase rate and heat flux of ingot in plan 1Figure 3  The ingot shrinkage solidification simulation result in plan1 Figure 4 The solid phase rate and heat flux of ingot in plan 2 Figure 5 The ingot shrinkage simulation result of plan 2303Z. S. ZHANG et al.: THE SIMULATION STUDY ON CENTRAL POROSITY OF 450 MM DIAMETER STEEL ELECTRODE...METALURGIJA 56 (2017) 3-4, 301-303In the small diameter electrode ingot cooling pro-cess, heat flux of the upper ingot cannot be decreased significantly in traditional electrode ingot mould be-cause of the strong endothermic effect of iron mould. And thus solid bridging is formed quickly which will leads to a wide range of central porosity in ingot.Heat flux in upper ingot is significantly limited by independent riser. The solid bridging formation is de-layed. And enhance cooling in lower ingot part acceler-ates the solidification of molten steel. The central po-rosity of electrode ingot can be significantly diseased due to the comprehensive effect in plan 3.REFERENCES[1]  T. L. Shui, General situation of overseas electroslag remel-ting and developing direction of electroslag remelting in China, Journal of Materials and Metallurgy 10(2011)3, 21-28.[2]  Z. Q. Huo, S. X. Liang, The reasons and preventing mea-sure of hot crack in electrode ingot products, Heavy Ca-sting and Forging (2011)11, 36-38.[3]  Z. B. Li, A New Advance Electroslag Metallurgy in the 21th Century, Special Steel 25(2004)9, 1-5.[4]  X. H. ZHan, J. H. Mao, Z. W. Yan, Selection and layout of nozzle for ultra-thick slab continuous caster, Iron and Steel 49(2014)5, 42-43.Note:  The responsible for English is Yan Wu, University of Science and Technology Liaoning, Anshan, ChinaThe simulation results show that the exothermic keep the molten steel temperature in riser at a high lev-el, move the solid bridging position down slightly. But it do not disease large heat flux in upper ingot, and de-lay the solid bridging time to 1 847 s from end of filling. This is because a lot of heat of the molten steel is main-ly absorbed by the iron mould, exothermic cannot change this situation.Result of plan 3The simulation results of solid phase rate and heat flux of ingot in plan 2 are shown in Figure 6. And the ingot shrinkage simulation result is shown in Figure 7.The simulation results show, in plan 3, the heat flux in upper ingot is significantly limited due to the inde-pendent riser. The solid bridging moment is delayed to 1 947 s. And the solidification rate of molten steel in the lower ingot part is higher because of the enhancement cooling.CONCLUSIONThe solid bridge in upper part of traditional 450 mm steel electrode ingot is formed because the heat flux in upper part of ingot is large. The reason is in addition to the horizontal heat flux, there are a lot of heat flow to the riser part.Figure 6 The solid phase rate and heat flux of ingot in plan 3 Figure 7 The ingot shrinkage simulation result of plan 3

The simulation study on central porosity of 450 mm diameter steel electrode ingot

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