Effect of M-EMS current intensity on the subsurface segregation and internal solidification structure for bloom casting of 42CrMo steel

Abstract

As-cast inherited defects are usually observed especially in quenched and tempered (QT) steels, such as 42CrMo due to macro-segregation. A three-dimensional numerical model has been presented to reveal the heat mass transportation and solidification behaviour of the molten steel in a 250 mm × 280 mm continuously cast bloom with and without M-EMS application. The reliability of the coupled model was proved by comparing the measured data of magnetic flux density with the calculated one along the centreline. The research indicates that the phenomena of a decrease in the solidification rate and an increase in molten steel washing velocity are observed as the current intensity increases from 0 to 450 A, which leads to a decrease of the minimum segregation degree by 0.039 and an increase of the width of the harmful negative segregation band by 3.6 mm. The washing effect that increases with the current intensity can reinforce the heat transfer between molten steel and solidification front and stimulate the formation of the equiaxed crystal. Accordingly, the average, local temperature gradient, and the superheat degree at the centre of mould exit decrease by 0.12, 2.62 K•mm −1 , and 2.9 K, respectively, together with an increase of the equiaxed crystal ratio by about 9.44%. It suggests that the M-EMS may lead to the more serious subsurface negative segregation but can improve the equiaxed crystal ratio of bloom castings, which influences the heat treatment performance and flaw detection pass rate of subsequent rolled products.

Numerical Simulation of the Effect of Solidified Shell Conductivity and Billet Sizes on the Magnetic Field with Final Electromagnetic Stirring in Continuous Casting

“…Due to the complex, high-temperature, and physical processes of the continuous casting process, the model of F-EMS and the heat transfer partial differential solidification mathematical model are simplified by the following assumptions [ 18 , 19 , 20 ]: Ignoring the displacement current, the electromagnetic field is considered as the magnetic quasi-static field in the low-frequency stirring condition; During electromagnetic stirring, molten steel is regarded as stationary, and the influence of the steel movement on the electromagnetic field is neglected; The steel is assumed to be an incompressible conductive fluid; In the model of F-EMS, the steel of the liquid core is seen as a circular platform body, while the length of the steel of the liquid core and the thickness of the billet solidified shell are calculated by ProCAST 2018 software; Since the heat transfer in the cross-section direction of the continuous casting round billet is much greater than the heat transfer along the drawing direction, the heat transfer along the drawing direction of the casting round billet can be neglected; In the continuous casting second cooling zone, the surface of the round billet cooled uniformly; The effect of the steel flow on the internal heat transfer is not considered; Ignoring the influence of the crystallizer vibration and other factors, the casting temperature is equal to the tundish temperature of the crystallizer; The contact heat transfer and the surface radiation between the round billet and the support rolls are used for the integrated thermal conductivity. …”

“…The electromagnetic field distribution is described by Maxwell’s system of equations, which is simplified in this study by neglecting the effect of displacement currents with the following equations [ 18 , 19 ]. where is the magnetic field intensity in A·m −1 ; is the current density in A·m −2 ; E is the electric field intensity in V·m −1 ; is the magnetic induction intensity in T; t is the time in seconds; is Magnetic permeability in H·m −1 ; is the electric conductivity in S·m −1 .…”

Effect of Magnet Alternate Stirring on the Internal Quality of Sn-Pb Alloy

“…As is known, increasing the intensity of electromagnetic stirring in the mold can accelerate the superheat dissipation of high-temperature molten steel, thereby increasing the proportion of equiaxed grain in the core of the billet [24,25]. Theoretically, the greater the magnetic intensity in the mold, the better the internal quality of the billet.…”

Behavior of Mold Electromagnetic Stirring for Round Bloom Castings and Its Eccentric Stirring Problem

“…The electromagnetic characteristics judged at room temperature are different from the real situation [34,35], so the magnetic field measurement was performed when the copper tube was at online temperature during multiple periodic stages at the interval between two castings. The HT-201 Gauss meter for measuring magnetic flux density and the CEDARDIS-RL electromagnetic torque meter for measuring torque values are shown in Figure 3.…”