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

metals Article Influence of Al on Evolution of the Inclusions in Ti-Bearing Steel with Ca Treatment Yandong Li 1 , Tongsheng Zhang 2, * and Huamei Duan 3 1 2 3 * College of Materials Science and Engineering, Yangtze Normal University, Chongqing 408000, China; School of Metallurgy and Environment, Central South University, Changsha 410083, China College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; Correspondence: ; Tel.: +86-139-7498-2473 Received: 29 December 2018; Accepted: 18 January 2019; Published: 21 January 2019



 Abstract: Experimental simulations of steelmaking with different amounts of aluminum were achieved in the tube furnace at 1873 K and field scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM and EDX) were employed to explore the characteristics of the inclusions in Ti-bearing steel during the calcium treatment process. It was found that morphologies, chemical compositions, and the size distribution of the inclusions were obviously different before and after calcium treatment. The calcium addition need be carefully considered regarding the mass fraction of aluminum with the purpose of modifying the solid inclusions to liquid phases. The thermodynamic analysis of inclusion formation in the Al–Ti–Ca–O system at 1873 K was conducted, as well as transformation behaviors of inclusions including all types of solid inclusions and liquid phases during solidification. The thermodynamic equilibrium calculations are in good agreement with experimental data, which can be used to estimate inclusion formation in Ti-bearing steel. Keywords: deoxidation; inclusions; thermodynamics; Ti-bearing steel; Ca treatment 1. Introduction The quality of steel products can be effectively increased after being treated with the element titanium [1–4]. Titanium oxides and titanium carbides can be generated during the deoxidation process, which can promote the mechanical properties around the region of welded steels by improving the nucleation ratio of intragranular bainite [5–9]. However, TiOx inclusions have a high probability of being agglomerate and subsequently form clusters, which results in the serious clogging issue of submerged entry nozzle and, consequently, lower the productivity of the continuous casting process as well [9–11]. Owing to the importance of Ti-containing inclusions, scholars have conducted a number of studies on inclusion control in Ti-bearing Al-killed steel, such as on thermodynamic computation and analysis [12–22], size distribution statistics [23–26], precipitation mechanisms [10,11, 16,20], reaction kinetics, and evolution trajectory [14], mostly within the alumina and titanate system. In other words, it is usually difficult to keep the Al–Ti–O system inclusions as liquid phases during the production process at the present period. 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 [27–37]. However, the research involving the calcium treatment process of Ti-bearing Al-killed steel have been limited, until now [38–42]. In addition, the types of Metals 2019, 9, 104; doi:10.3390/met9010104 www.mdpi.com/journal/metals Metals Metals2018, 2018,8,8,x xFOR FORPEER PEERREVIEW REVIEW Metals 2019, 9, 104 2 2ofof1111 2 of 11 types typesofofinclusions inclusionsatatthe thesolidification solidificationtemperature temperatureare aredirectly directlyrelated relatedtotothe theproperties propertiesofofthe the inclusions in the final product. inclusions the final product. inclusions atin the solidification temperature are directly related to the properties of the inclusions in the InInthis thiswork, work,the thelaboratory-scale laboratory-scalemelts, melts,with withdifferent differentmass massfractions fractionsofofcalcium calciumand andaluminum, aluminum, final product. were prepared in order to clarify the influence of aluminum element on inclusion properties during were order to clarify the melts, influence aluminum element on of inclusion during In prepared this work,inthe laboratory-scale withofdifferent mass fractions calciumproperties and aluminum, the calcium treatment process of Ti-bearing Al-killed steels. Then, FE-SEM and EDX were employed the calcium process Ti-bearing steels.element Then, FE-SEM and EDX were employed were preparedtreatment in order to clarifyofthe influenceAl-killed of aluminum on inclusion properties during totoobserve morphologies, chemical compositions, and number and size ofofinclusions inin observeand andanalyze analyze morphologies, chemical compositions, and number and sizewere inclusions the calcium treatment process of Ti-bearing Al-killed steels. Then, FE-SEM and EDX employed steel cylinder before after calcium treatment. InInaddition, steel cylinder sampledfrom fromhigh-temperature high-temperature melts beforeand and after calcium treatment. addition, to observe andsampled analyze morphologies, chemicalmelts compositions, and number and size of inclusions in equilibrium phases of inclusions at smelting temperature were calculated, and the transformation equilibrium phases offrom inclusions at smeltingmelts temperature were calculated, and the transformation steel cylinder sampled high-temperature before and after calcium treatment. In addition, behaviors inclusions during process ofofsolidification behaviorsofof inclusions duringthe processtemperature solidification wereestimated estimated bythe thecommercial commercial equilibrium phases of inclusions atthe smelting werewere calculated, and by the transformation software FactSage. Present works will lay the experimental and thermodynamic foundation on softwareofFactSage. will of laysolidification the experimental and thermodynamic foundation on behaviors inclusionsPresent during works the process were estimated by the commercial software expanding the combined treatment of titanium and calcium to industrial-scale production, and expanding the combined treatment of titanium and to industrial-scale and FactSage. Present works will lay the experimental and calcium thermodynamic foundationproduction, on expanding suggest an totoeliminate the casting suggest analternative alternative way eliminate thenozzle nozzle cloggingissue issueduring during thecontinuous continuous casting the combined treatmentway of titanium andthe calcium toclogging industrial-scale production, and suggest an process of Ti-bearing Al-killed steel. process of way Ti-bearing Al-killed alternative to eliminate thesteel. nozzle clogging issue during the continuous casting process of Ti-bearing Al-killed steel. 2.2.Experimental ExperimentalMethods Methods 2. Experimental Methods Three Threesets setsofofexperiments experimentswere werecond (...truncated)