Ferroalloys have become increasingly important due to their indispensable role in steelmaking. In addition, the demand for improved steel qualities has increased considerably, which in turn highlights the quality of ferroalloys. This is due to the fact that the impurities in ferroalloys directly and significantly influence the quality of steel products. To gain a better understanding of the main trace elements and inclusions in ferroalloys (such asFeSi, FeMn, SiMn, FeTi, FeCr, FeMo, FeNb, FeV, FeB, FeP, some complex ferroalloys) and their behaviours after the additions of ferroalloys in steel melt, information from a large number of previous results on this topic was extensively reviewed in this work. The applications of different ferroalloys and their production trends were discussed. In addition, the effects of some trace elements from ferroalloys on the inclusion characteristics in steel were also discussed. The possible harmful inclusions in different ferroalloys were identified. Overall, the results showed that the inclusions present in ferroalloys had the following influence on the final steel cleanliness: 1) MnO, MnS and MnO-SiO2-MnS inclusions from FeMn and SiMn alloys have a temporary influence on the steel quality;2) the effect of large size SiO2 inclusions (up to 200 μm) in FeSi and FeMo alloys on the steel cleanliness is not fully understood. The effect of Al, Ca contents should be considered before the addition of FeSi alloys. Also, Al2O3 inclusions and relatively high Al content are commonly found in FeTi, FeNb and FeV alloys due to the production process. This information should be paid more attention to when these ferroalloys are added to steel.3) except for the existing inclusions in these alloys, the Ti-rich, Nb-rich, V-rich carbides and nitrides, which have important effects on the steel properties also should be studied further; and 4) specific alloys containing REMoxides, Cr-C-N, Cr-Mn-O, Al2O3, Al-Ti-O, TiS and Ti(C, N) have not been studied enough to enable a judgement on their influence on the steel cleanliness. Finally, some suggestions were given for further studies for the development of ferroalloy productions 

Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, morphology, size, and composition) in different industrial ferroalloys (FeV, FeMo, FeB, and FeCr) were investigated using the electrolytic extraction (EE) technique. After extraction from the ferroalloy samples and filtration of the solution, the inclusions were investigated on a film filter. The three-dimensional (3D) investigations were conducted using a scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). The characteristics of inclusions observed in the ferroalloys were compared with previous results and discussed with respect to their possible behaviors in the melt and their effects on the quality of the cast steels. The particle size distributions and floatation distances were plotted for the main inclusion types. The results showed that the most harmful inclusions in the ferroalloys investigated are the following: pure Al2O3 and high Al2O3-containing inclusions in FeV alloys; pure SiO2 and high SiO2-containing inclusions in FeMo alloys; Al2O3 and SiO2-containing inclusions in FeB alloys; and MnO-Cr2O3, Al2O3, and Cr2O3-based inclusions in FeCr alloys.

 Ferroalloys are one of the most important raw materials widely used in the steelmaking processes. Depending on the cleanliness of used ferroalloys, they can be an inevitable source of impurities and non-metallic inclusions (NMIs) in steelmaking products. In this study, the inclusions in five different industrial ferroalloys (FeTi, FeMo, FeW, MnN and FeCrN) were investigated. This was done by using two-dimensional (2D) investigations on polished crosssections of ferroalloy samples and by using three-dimensional (3D) investigations of NMIs on film filters and metal surfaces after electrolytic extraction (EE) using scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). Moreover, the characteristics of the main types of inclusions presented on film filters and metal surfaces afterEE were compared and their possible transformations in Al-killed steel were evaluated. The results showed that the main inclusions were more likely the oxidization products of the reductant and some unreduced ore during the ferroalloy production process. The 3Dinvestigations of inclusions on metal surfaces after extraction were found to be very useful in detection and evaluation of larger sized inclusions. Overall, this study helps to better understand the impurities in different ferroalloys and their possible effect on the steel cleanliness. 

The characteristics of different shapes of nonmetallic inclusions (NMIs) aredetermined using different methods. In this respect, various shapes of NMIs,including spherical, octahedral, elongated, bar-like, plate-like, polyhedral, andirregular inclusions, are observed in different steels and ferroalloys. The inclu-sions are investigated using three methods: 1) 2D investigations on a polishedcross section (2D method); 2) 3D investigations on afilmfilter after electrolyticextraction andfiltration (EE method); and 3) 3D investigations on a metal surfaceafter electrolytic extraction (MS method). In addition, scanning electron micro-scopy (SEM) with an energy-dispersive spectrometer (EDS) is used for thedetermination of the chemical composition of inclusions. The advantages andlimitations of different methods for investigations of different shaped inclusionsare discussed. The results show that the 2D method is less precise to detectthe morphology, size, and number of inclusions; however, the EE and MSmethods are used to determine a more accurate morphology. Furthermore, theMS method is found to be more advantageous in detecting large-sized inclusions.This study also shows that the results on both thefilmfilter and metal surfaceshould be grouped together to obtain more comprehensive information of theinclusion characteristics.

Nb is an important microalloying element in steelmaking. Its interaction with liquid Fe during an early stage of the alloying process has a considerable influence on the Nb recovery. In the present work, the inclusions in FeNb alloys were characterized using the electrolytic extraction method combined with SEM-EDS. The interfacial reactions between FeNb alloy and liquid Fe, as well as inclusion formations, were studied during an early stage of an alloy addition using a liquid-metal-suction method. The results revealed that a diffusion zone consisting of different regions of Fe-Nb phases was formed and that the thickness of the zone increased with time. Based on the experimental findings, the mechanism of the early dissolution process of FeNb alloys in liquid Fe was discussed. Moreover, the Nb rich regions formed after the alloy contacted with liquid Fe could modify the existing inclusions in the alloy, also their evolution mechanisms were studied. The addition of FeNb alloys can introduce inclusions, such as Al-O and Al-Ti-Nb-O inclusions to the liquid steel. Overall, this study has contributed to the understanding the behaviour of impurities from the FeNb source at the early dissolution process during the microalloying process of steels containing Nb.

 Chromium is normally added to liquid steel in the form of different grades of ferrochromium (FeCr) alloys for the requirement of different alloy grades, such as stainless steels, high Cr cast iron, etc.. In this work, inclusions in two commercially produced alloys, i.e. high-carbon ferrochromium (HCFeCr) and low-carbon ferrochromium (LCFeCr) alloys were investigated. The FeCr alloy/liquid iron interactions at an early stage were investigated by inserting solid alloy piece into contact with the liquid iron for a predetermined time using the liquid-metal-suction method. After quenching these samples, a diffusion zone between the alloys and the liquid was studied based on the microstructural characterizations. It was observed that Cr-O-(Fe) inclusions were formed in the diffusion zone, FeOx inclusions were formed in the bulk Fe and an “inclusion-free” zone was detected between them. Moreover, it was found that the HCFeCr was slowly dissolved but LCFeCr alloy was rapidly melted during the experiment. The dissolution and melting behaviours of these two FeCr alloys were compared and the mechanism of the early stage dissolution process of FeCr alloys in the liquid Fe was proposed. 

The influence of commercial low carbon ferrochromium (LCFeCr) additions on the inclusion characteristics in Ti-containing ferritic stainless steel was studied by laboratory experiment in this work. The inclusions in steel before and after the FeCr alloy additions were investigated through systematic samplings of the liquid steel. Different types of inclusions in the FeCr alloy and the steel were detected and the evolution of inclusion characteristics (e.g. composition, size, morphology and number density) were investigated. The results showed that the Ti content decreased after the FeCr alloy additions. MnCr2O4 spinel inclusions originated from the FeCr alloys transformed into Ti2O3-Cr2O3 based liquid inclusions and Ti2O3-rich solid inclusions. They were formed due to the reactions between MnCr2O4 and TiN or dissolved Ti in molten steel. The ratio of Ti/Al in the steel melt has a direct influence on the evolution of inclusions from thermodynamic calculations. The addition of FeCr alloys caused an increased number density of these Ti2O3-containing inclusions and TiN inclusions up to 8 minutes from the time for the alloy addition. The increased Cr content by the FeCr additions from 16 to 24 mass pct can increase the critical N content to form TiN inclusions at a specific Ti content. It is concluded that the inclusions in FeCr alloys can be inherited to the steel and undergo some evolutions depending on the inclusions in steel as well as the steel compositions.  

 Laboratory experiment and thermodynamic calculation for the Ti-containing 24 mass pct Cr ferriticstainless steel with a CaO-SiO2-Al2O3-MgO system slag were performed to investigate the effect of slagaddition on the inclusion characteristics in molten steel. The morphology, composition, and size evolution of inclusions in steel samples were analyzed in three-dimensional by the electrolytic extraction method and in two-dimensional by the automatic analysis method. The results showed that the Ti content significantly decreased after the slag addition. However, the change of the Si content showed an opposite tendency. The decrease of the Ti content in steel was due to the reduction of SiO2and Al2O3 in the slag by dissolved Ti in steel. An increase of the TiO2 content in the slag can decrease the Ti loss in steel based on the slag-steel kinetic analysis. The total O content in the steel melt decreased from 62 ppm to 26 ppm, and the steel cleanliness was improved, since the number density of inclusions decreased after the slag refining. The results of a kinetic analysis showed that the rate-determining step of the oxidation of Ti in the steel and the reduction of SiO2 in the slag were the mass transfer on the slag side. Also, high Ti2O3-containing inclusions were found to be transformed to Cr2O3-Ti2O3-Al2O3and Cr2O3-Ti2O3-SiO2 system inclusions after the slag addition. The Al2O3 contents in inclusions increased while the Ti2O3 contents decreased with time. However, there were some amount of high-melting-point inclusions with high Al2O3 content, which were not what we expected. When plotted on logarithmic scales, the mole ratio values of the inclusions were expressed as a linear function of the values of the steel melts with a slope of unity, which was theoretically expected.