A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot

doi:10.1007/s40195-015-0303-z

Abstract

Abstract:

In present paper, a ladle-tundish-mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring (MP) process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring (SP) and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.

Key words: Multiple pouring process, Macrosegregation, Numerical simulation, Large steel ingot

Zhen-Hu Duan, Hou-Fa Shen, Bai-Cheng Liu. A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(9): 1123-1133.

Figures/Tables 15

Fig. 1 Schematic of MP process: a the filling stage; b the holding stage; c the draining stage

Table 1 Conservation equations used in mathematical model for the mixing in tundish.

Mass	ρ∂a q ∂t +ρu ¯ ⋅? 0 ⋅a p =0	(1)
Momentum	∂ρ m u∂t +?⋅(ρ m uu)=-?p+?⋅(μ eff ?u)+ρ m g	(2)
Realizable k-ε	∂ρ m k∂t +?⋅(ρ m uk)∂ρ m ε∂t +?⋅(ρ m uε) =?⋅(u+u eff σ k )?k+G k -ρ m =? 0 ⋅(u+u t σ ε )?ε 0 +ρ m C 1 Eε-ρ m C 2 ε 2 k+νε - - √	(3)
Energy	∂ρ m T∂t +?⋅(ρ m uT)=?⋅(k eff c p ?T)	(4)
Species	∂ρ m C∂t +?⋅(ρ m uC)=?⋅(D eff ?C)	(5)

Table 2 Conservation equations used in the mathematical model for the macrosegregation in the mold.

Mass	?⋅u	(6)
Momentum	ρ∂u∂t +ρ?⋅(uu)=-?p+μ 1 ? 2 u-μ 1 K -1 u+ρ b g g	(7)
Density in buoyancy term	ρ b =ρ[1-β T (T-T 0 )-β C (C 1 -C 0 )]	(8)
Energy	∂T∂t +?⋅(uT)=kρC p ? 2 T+Lc p ∂g s ∂t	(9)
Species	∂C∂t +?⋅(uC)=?⋅(g 1 D 1 ?C)+?⋅[g 1 D 1 ?(C 1 -C)]-?⋅[u(C 1 -C)].	(10)
Permeability	K=λ 2 180 g 3 1 (1-g 1 ) 2	(11)
Temperature and liquid concentration	T=T m +m 1 C 1	(12)
Solid volume fraction and temperature	g s =11-k p T-T 1 T-T m	(13)

Table 3 Thermophysical properties of the steel ingot and mold materials

Material	ρ (kg m^-3)	k (W m^-1 K^-1)	c _p (J kg^-1 K^-1)
Steel ingot	6990	38.3	520
Mold	7100	26.3	540
Insulation sleeve	180	1.2	1020

Table 4 Steel properties used in the simulation

k _p	m _l (K wt%^-1)	β _C (wt%^-1)	β _T (K^-1)	L (kJ·kg^-1)	μ _l (Pa·s)	λ ₂ (μm)	D _l (m²·s^-1)
0.314	-80.45	1.4164 × 10^-2	1.07 × 10^-4	271	0.0042	500	2 × 10^-8

Fig. 2 Sketch of 438-ton steel ingot system.

Fig. 3 Carbon concentration variation through the outlet of the tundish.

Fig. 4 Fluid flow and carbon distribution in the mold during MP process: a at 1.3 h; b at 4.2 h; c at 20 h; d at final solidification.

Fig. 5 Comparison of carbon concentration between the predicted and experimental results: a section A; b section B; c section C; d section D.

Fig. 6 Fluid flow and carbon distribution with SP process at different times: a 1.3 h; b 4.2 h; c 20 h; d final solidification.

Fig. 7 Comparison of the carbon distribution along the ingot centerline between the SP and MP processes: a at 1.3 h; b at 4.2 h; c at 20 h; d at final solidification.

Fig. 8 Comparison of final macrosegregation with different riser insulating times: a 0 h (traditional mold riser); b insulating 10 h; c insulating 20 h; d insulating 30 h.

Fig. 9 Predicted solidification sequence of 438-ton steel ingot with riser insulating time of 30 h, the left part shows the solid volume fraction (g s), while the right shows the macrosegregation and liquid velocity: a at 1.7 h; b at 10 h; c at 30 h; d at 60 h.

Fig. 10 Comparison of the carbon distribution along the ingot centerline: a at 1.7 h; b at 10 h; d at 30 h; d at final moment.

Fig. 11 Time evolution of the carbon concentration and liquid velocity at the position P in case 1 and case 4: a carbon concentration, b velocity in horizontal; c velocity in vertical.

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