Analysis of thin-slab casting by the compact-strip process: Part I. Heat extraction and solidification

Abstract

This article reports on an extensive experimental and modeling study undertaken to elucidate the thermal evolution of thin slabs during their passage through the mold and secondary cooling system of a compact-strip process (CSP) caster. In industrial trials covering a wide range of casting conditions, temperature measurements were carried out at (1) the copper plates of an operating mold and (2) the stainless steel frame of an operating grid. Separately, water-flux and heat-flux distributions generated by the several water and air-mist sprays produced by the different nozzles used in the process were determined in the laboratory. The analysis of these pieces of information, together with a detailed consideration of the geometry of the mold and the arrangement of the rolls and spray nozzles, were used to establish appropriate boundary conditions for a two-dimensional, curvilinear-coordinate, unsteady-state heat-conduction model for predicting the solidification rate of thin slabs. The predicted slab surface temperatures show very good agreement with corresponding measured values taken in plant tests at several locations along and across the secondary cooling system. The validation trials involved a wide range of low-and medium-carbon steel grades, casting speeds, slab widths, and secondary cooling strategies. The second part of this article combines the solidification model with a creep model of the shell to yield useful information about design parameters and casting conditions associated with undesirable bulging behavior of the slab after the last support roll, which causes stoppage of the process by slab clogging at the pinch rolls.

Study of Shell-Mold Thermal Resistance: Laboratory Measurements, Estimation from Compact Strip Production Plant Data, and Observation of Simulated Flux-Mold Interface

“…[37,38] Thus, in the present study, it is conjectured that observation of the motion of a slag surface, devitrifying at those temperatures, in relation to a stationary surface parallel to it would shed light on the formation of the gap-due to shrinkage-that has been claimed so profusely in the literature. To carry out these observations, glass samples in the form of parallelepipeds 2 9 6 9 4 mm 3 (thickness 9 width 9 height) are prepared.…”

“…To compare the total effective thermal resistance, R T , determined in the laboratory with values estimated from industrial trials involving CSP molds, computational calculations reported by the authors [37] are used. The mold studied is straight in the casting direction and has a funnel-shaped section across its central upper part.…”

“…The mold studied is straight in the casting direction and has a funnel-shaped section across its central upper part. The main characteristics and operating conditions of the mold employed are given in detail elsewhere, [37] and although in the present operation the mold has been widened to adapt it to a liquid core reduction machine, the mold powders selected continue in use.…”

“…Temperature measurements over steady-state operation periods were used to determine the mold hot-face temperature, T m , and heat flux, q m , distributions by solving iteratively the direct steady-state two-dimensional heat conduction problem using the control volume method. [37] The temperature distribution in the strand is determined by solving the heat conduction conservation equation for a steel slice moving at the casting speed. While the slice is in the mold, the boundary conditions at its faces are specified according to the q m distributions estimated by the procedure described in the previous paragraph.…”

“…The solution of the energy conservation equation for the slice allows calculation of, among other parameters, the slab surface temperature T sh . [37] Hence, from the difference in local surface temperatures between the strand and the mold and from the local heat flux transferred between the two, the overall effective thermal resistance is estimated as…”