Effect of Al Content on the Characteristics of Inclusions in Al–Ti Complex Deoxidized Steel with Calcium Treatment

Abstract

To improve the effect of calcium treatment and the cleanliness of steel and to make use of fine TiOx to refine the microstructure of steel, the effect of aluminum content on inclusion characteristics of aluminum-titanium complex deoxidized and calcium treated steel is investigated based on the experiment with SEM/EDS, Image Pro-Plus 6.0 and FactSage 6.1 softwares and thermodynamic calculation in the present work. The results show that the inclusions in two steels with different aluminum content are obviously spherical composite inclusions with a two-layer complex structure, consisting of an Al2O3-CaO-TiOX core surrounded by MnS. In low aluminum steel, the oxide core of inclusions contains much TiOx and CaO, and their composite structure is mosaic compared with bundle in high aluminum steel, the number of inclusions is 2.5 times more than that in high aluminum steel, the thickness of MnS on oxides surface is also thinner. In addition, melting point of the inclusions in low aluminum steel is lower, the cleanliness of the steel is relatively improved because of the inclusions floating up, and the deformation aspect ratio of calcium aluminate inclusions with a certain amount of Ti2O3 is effectively improved, which is about 1-2 while the composition of oxide core is xAl 2 O 3 = 35-55%, xTi 2 O 3 = 15-35%, and xCaO = 10-25%. As a result, less calcium is needed to modify the alumina inclusions to liquid calcium aluminate in the case of lower aluminum deoxidized steel, thus the calcium treatment effect can be improved. The low aluminum in steel is more effective to control the inclusion characteristics to reduce the harm of MnS and to improve the cleanliness of steel.

Influence of Al on Evolution of the Inclusions in Ti-Bearing Steel with Ca Treatment

“…It is noticeable that the stability region of liquid calcium aluminate is located in a common calcium content range. As the compositions of the steel samples in the current work (based on the content of the calcium and titanium) and experimental results introduced from Seo and Zheng [38,39] were marked in the phase diagrams, a good consistency in the above data is conspicuous, as shown in Figure 6b,c. Consequently, the calculated phase diagrams of Al-Ca-Ti-O system are reliable for effectively estimating the evolution behavior of inclusions at steelmaking temperature.…”

“…It is generally the technique of calcium treatment that has been introduced to get liquid phases of calcium aluminate at casting temperature, which relieves the nozzle clogging issue during continuous process of steels, especially of grades of Al-killed steel, and also has benefits for the mechanical performance of final steel products [27][28][29][30][31][32][33][34][35][36][37]. However, the research involving the calcium treatment process of Ti-bearing Al-killed steel have been limited, until now [38][39][40][41][42]. In addition, the types of inclusions at the solidification temperature are directly related to the properties of the inclusions in the final product.…”

Effect of Ti Content on the Characteristics of Inclusions in Al–Ti–Ca Complex Deoxidized Steel

“…7. It can be easily seen that the equilibrium relation calculation in the present work shows a good agreement with the experimental data of Seo et al, 33) Zheng et al, 34) Kimura et al 63) and Inoue et al 64) in the previous work. Therefore, Al-Ti-Ca-O phase diagram can be used to evaluate the change process of oxide inclusion effectively.…”

“…[25][26][27][28][29][30][31][32] However, few systematic reports have been published on the deoxidization, especially inclusion evolution by calcium and titanium complex treatment yet. [33][34][35] Besides, the evolution process and phase stability of the inclusions in the melts are not clarified due to lack of exact thermodynamic calculation. Thus, it is of interest to explore the formation and evolution of Al-Ti-Ca-O complex inclusions in detail.…”

Effect of Sulphur Concentration on Precipitation Behaviors of MnS-containing Inclusions in GCr15 Bearing Steels after LF Refining

“…And the growth rate of MnS was determined by the diffusion of manganese and sulphur in the liquid steel. Zheng et al 6) found that not only the precipitation rate but also the thickness of MnS on the oxides increased with the increase of sulphur concentration…”