Effect of Bubbles on Crystallization Behavior of CaO–SiO2 Based Slags

Shaopeng Gu,Qiang Liu,Zequan Ding,Guanghua Wen,Junli Guo,Ping Tang

doi:10.3390/met9020193

Abstract

Surface longitudinal cracks are a serious problem and particularly prevalent in the casting of peritectic steel (carbon content between 0.10%C and 0.18%C, non-alloyed). It is usually alleviated by controlling the horizontal heat transfer from the steel shell to the mold through increasing the crystallization performance of slags. In the actual continuous casting process, a large number of bubbles are formed in the molten slags, and the crystallization properties of the mold fluxes are affected by bubbles. Therefore, an investigation of the influence of bubbles on the crystallization performance of mold fluxes was carried out by applying the hot thermocouple technique and it is hoped that surface longitudinal cracks can be solved in this way in the peritectic steel casting process. The continuous cooling transformation (CCT) diagrams and time–temperature transformation (TTT) diagrams were constructed for an analysis of the crystallization kinetics. The results showed that the crystallization ability of mold fluxes was enhanced by adding bubbles through shortening the incubation time of crystallization, increasing the critical cooling rate, and decreasing the activation energy of crystallization. As a result, the crystalline fraction, slag film thickness, and surface roughness of the slag films were improved, but the crystalline phase was not affected by bubbles. With an increase of the bubble content remaining in the molten slag, the growth mechanism of the cuspidine crystal phase changed from a low dimension to a high dimension, and the content of the molten slag’s structure unit (Q1) needed for cuspidine in the molten slag was markedly increased.

Highlights

Mold fluxes are vital functional materials in the continuous casting process and play an indispensable role for preventing oxidation of molten steel, lubricating the steel shell, adsorbing non-metallic inclusions, moderating mold heat transfer, and insulating the molten steel free surface [1,2]
Previous studies on the crystallization property of mold fluxes in the laboratory always eliminated the influence of bubbles, which is inconsistent with the actual continuous casting process [3]
The composition of the mold flux used in the present study is given in Table 1. 50 g in Table 1. 50 g and 350 g samples were prepared and mixed according to the proportions shown and 350 g samples were prepared and mixed according to the proportions shown in Table 1 and in Table 1 and calcined in a muffle furnace at 373 K to remove moisture

Summary

Introduction

Mold fluxes are vital functional materials in the continuous casting process and play an indispensable role for preventing oxidation of molten steel, lubricating the steel shell, adsorbing non-metallic inclusions, moderating mold heat transfer, and insulating the molten steel free surface [1,2]. Longitudinal cracks have always been a serious problem that influences the steel shell quality in the continuous casting of peritectic steels (carbon content between 0.10%C and 0.18%C, non-alloyed). It is caused by the releasing of thermal stresses formed through the volumetric shrinkage during the δ/γ phase transformation [4]. Previous studies on the crystallization property of mold fluxes in the laboratory always eliminated the influence of bubbles, which is inconsistent with the actual continuous casting process [3]. Mills et al [10]

Methods

Results

Conclusion