No abstract

This paper investigates how the basicity and alumina content in synthetic slags influence the crystallization behavior that takes place in a heat flux simulator for mold slags. The purpose is to elucidate the variation in crystallization behavior for model slags that are expected to be glassy, partly crystalline and fully crystalline in order to correlate the changes in heat flux to the dynamic solid evolution that occurs in the simulator. Three levels of alumina content (3, 15 and 25 wt%) were chosen to investigate the heat transfer behavior through slag film which have different tendency of reaction with molten steel during continuous casting of high aluminum containing Transformation Induced Plasticity (TRIP) steels. A Confocal Scanning Laser Microscopy (CSLM) was used to develop TTT diagrams for the slags. XRD and SEM were also used to analyze the micro-structures of the crystalline phases.The measured heat fluxes through the mold slags tested were found to increase, as the crystallinity of the slag film decreased with decreasing basicity and alumina content. It was found that the crystallization temperature increased, while the incubation time for crystallization decreases with increasing basicity and alumina content. The increase in alumina content induced the precipitation of CaF 2 during cooling process and hence a change in the crystalline phase from Ca 4 Si 2 O 7 F 2 to Ca 2 Al 2 SiO 7 .KEY WORDS: mold slag; TRIP steel; crystallization behavior; heat flux.formance of a mold slag simulator that was developed by Wen 12) by using model mold slags whose crystallization behavior can be predicted. The second purpose was to analyze the heat fluxes with TTT diagrams developed using CSLM method.In recent years, advanced high strength steels (AHSS) have attracted much attention to be used as car bodies due to its excellent combination of high strength and ductility, [13][14][15] which necessitate the development of AHSS steels for continuous production in steel plants. However, there are several problems that need to be overcome and some are related to the high amount of reactive elements in these alloys. 16,17) For example, it is difficult to control the alloy composition during continuously casting of some grades of AHSS, such as TRIP steels, as a result of reactions between the mold slag and the melt, involving the formation of alumina. Critical properties of the mold slag can change during casting as a result of alumina pick-up, 18,19) when casting high aluminum TRIP steel and this could cause surface cracks on the slab or sticker break-outs. It is therefore necessary to study how to suppress the reactions between the mold slag and the melt. One possible method to accomplish this is to increase the alumina content in the mold slag. The details of the incorporation of alumina in slags is however not completely known and depending on this the alumina content in mold slag could result in changes in the key thermophysical properties of mold slag, such as viscosity, crystallization and thermal conductivity. The t...

The viscosity of SiO 2 -30Al 2 O 3 -B 2 O 3 -12Na 2 O-CaO slag system (CaO/SiO 2 52?68-7?35, B 2 O 3 50-9 wt-%) was investigated in the present study. The objective is to study the influence of B 2 O 3 on the viscosity and structure of mould slags containing low silica content. The research of the low silica slag system is meaningful because of it is less reactive with Al during continuous casting of steels containing high amounts of dissolved aluminium, such as transformation induced plasticity assisted steels. The viscosities of these quinternary slags decreased slightly with an increase in the content of additive B 2 O 3 above the break temperature. The apparent activation energy of viscous flow was found to decrease with increasing B 2 O 3 content. The break temperature also decreased with increasing B 2 O 3 content. Based on the experimental data, the decrease in break temperature per mol.-% B 2 O 3 DT br is 15?23 K. An empirical model was then established to predict the break temperature of mould slags containing B 2 O 3 , and the deviation is between 225 and z25 K. Based on the viscosity and Fourier transform infrared analysis, it is proposed that the three-coordinated boron is dominated in these slags over the entire compositional range, and the borosilicate networks are loosened with increasing B 2 O 3 content in the present study. The Riboud model was modified empirically based on the present experimental data, and the mean deviation is ,13%.