Hideaki Yamamura

Effect of Molten Steel Flow on Nonuniformity of Initially Solidified Shell

The effect of swirling flow in the horizontal direction on the nonuniform growth of a solidified shell was investigated by dip testing the rotating cylindrical chill block. The thickness nonuniformity of the solidified shell decreases with increasing flow velocity of the molten steel. The forced flow of the molten steel increases the average heat transfer coefficient between the molten steel and the solidified shell, equalizes the growth directions of the dendrites, stabilizes the direction and intensity of the heat flux, and evens the formation of solidification nuclei.

Study of hot tearing and macrosegregation through ingot bending test and its numerical simulation

Ingot bending tests are performed on the already formed solid shell of a 450 kg solidifying ingot. It is designed in order to be representative of two defects occurring during secondary cooling in steel continuous casting: hot tearing and macrosegregation. Ingots show the defects which result from the application of bending. In order to understand the different physical phenomena, finite element numerical modelling of the test has been developed, using two different approaches. A first approach consists of a 3D finite element thermomechanical simulation. Hot tearing criteria, based on strain, strain rate and two values for solid fraction are then evaluated. It is demonstrated that such a strain based criterion has an excellent capability to predict the formation of hot tears. A second approach consists of a 2D planar finite element simulation in the median section of the ingot. A two-phase formulation is used, in which the velocity of the liquid and solid phases are distinguished. The simulation shows how solutes are redistributed through the ingot under the effect of bending. Solute-depleted and enriched regions are well reproduced, but peak values of macrosegregation are underestimated.