The Spontaneous Emulsification of Entrained Inclusions During Casting of High Aluminum Steels

Abstract

Mold slag entrainment during the continuous casting process presents a late stage source of non-metallic inclusions (NMI) with a high likelihood of ending up in the final product. The reaction between the entrained slag phase and surrounding liquid steel in the continuous casting mold affects the inclusion morphology and properties. However, there is a lack of information on the kinetics of the NMI-steel reaction. A novel approach, utilizing controlled synthetic inclusion/metal samples, has been developed to study the reactions between free inclusion-slag droplets and steel. The technique combines High-Temperature Confocal Scanning Laser Microscopy (HT-CSLM), X-ray Computed Tomography (XCT) and advanced electron microscopy techniques offering rapid controlled heating performance and extensive characterization of the samples. This method offers the ability to observe the size, shape and composition of an unconstrained reacting inclusion and to investigate the interface between the materials with respect to reaction time. This study interrogates a low aluminum steel (0.04 wt pct) and a high aluminum steel (1 wt pct) in contact with an inclusion-slag phase with a starting composition aligned to a typical mold slag. It was found that the reaction between silica and aluminum across the interface of the two phases provided a driving force for spontaneous emulsification to occur. Products of such emulsification will have a significant effect on the inclusion size distribution and potentially the prevalence of inclusion retention in molten steels solidifying in the continuous caster (for example if emulsified buoyancy forces are reduced to near zero) and hence in the subsequent solid product.

Artificial Inclusion Environments—Replicating Industry in the Laboratory

“…This test method provided unique information on the inclusion-steel reaction behaviour, where it was observed that the inclusion's surface area increased by a factor of 13 times its original size when the reaction occurred due to spontaneous emulsification occurring. Further information on this phenomena can be found in our published work (Raviraj et al, 2021).…”

“…The principles of operation for the HT-CLSM are described in (Raviraj et al, 2021) and the equipment can be used for a variety of experiments with direct observation of the sample. In this work the HT-CLSM is used for two types of tests, described in Experimental Techniques with the general principles covered here (and described in more detail in Samples of a maximum size of 1 cm diameter are placed into an alumina crucible which is then loaded into the HT-CLSM chamber.…”

“…The various test methods have allowed detailed investigation into the reaction between a high aluminium steel and an inclusion with the chemical any physical changes and their implications discussed elsewhere in the literature (Raviraj et al, 2021). Each test method has its own advantages and disadvantages as shown in Table 6 and summarised below.…”