Abstract
Macrosegregation remains one of main defects affecting metal materials properties, which is mainly caused by interdendritic fluid flow during solidifying. However, as for controlling actual specific segregation, it is still difficult to effectively measure or simulate this kind flow instead of pure fluid flow, especially in complex casting processes of high-grade materials. Herein, a new method for obtaining velocity magnitude and direction of interdendritic fluid flow during metal solidifying is proposed from boundary layer and standard deviation obtained by measuring etched surface heights of the actual ingot and using statistical principles. Taking continuous casting bloom of GCr15 bearing steel as an example, it is indicated that the calculated velocity magnitudes under different sides and superheats can be explained by process features and, hence, solidification mechanism. The velocity magnitude and fluctuation are higher on the inner curve side and under low superheat. Meanwhile, it is found that the fluctuation extent of secondary arm spacing is more relevant with interdendritic fluid flow, although its magnitude is mainly determined by the cooling rate. Moreover, on the basis of the calculated velocity directions and magnitudes, there is a positive correlation between segregation area ratio and the effective ratio between interdendritic flow velocity and growth velocity especially in the equiaxed grain zone, which corresponds with classic macrosegregation formation theory. The above findings and comparison with other results demonstrate the validity of the new approach, which can obtain the magnitude and the direction of interdendritic fluid velocity for two or three-dimensional multiscale velocity distribution by tailoring measuring length and numbers.
Highlights
Macrosegregations are very typical defects in metal materials which can cause performance failures due to nonuniform composition distribution and structure [1,2,3]
Because interdendritic fluid flow exists in three-dimensional space and the calculated velocity magnitude above is a three-dimensional value, in order to compare them the effective ratio between interdendritic flow velocity and growth velocity (Vi f f /Mx )e was calculated as Equation (21) which can contain the influence of velocity direction
We have put forward a full model that can calculate the magnitude and direction of interdendritic fluid flow during solidifying at different positions by measuring the corresponding etched surface heights of casting metal bloom
Summary
Macrosegregations are very typical defects in metal materials which can cause performance failures due to nonuniform composition distribution and structure [1,2,3]. As to the complex solidifying process, it is always difficult to investigate precisely the characteristics of interdendritic liquid flow for the formation mechanism of different actual segregation morphology. An entirely accurate quantitative correlation equation between the etched surface height and the element content at a certain position is difficult to establish, plenty of etched surface heights (abbreviated as hes in this article) may be partly suitable for investigating some segregation formation processes by simultaneously using some statistical methods. The hes values at different surface places are measured firstly in GCr15 bearing steel bloom of continuous casting for the reason that its high-content carbon element (mass fraction, 1.02%) is easy to segregate during solidifying and the fluid flow is strong enough during the continuous casting process [15,19]. This study demonstrates a new approach for measuring the velocity of interdendritic fluid flow during metal solidification, which may provide a unique alternative method for understanding the interdendritic fluid flow, macrosegregation formation, and material properties
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