Interfacial Reactions and Inclusion Formations at an Early Stage of FeNb Alloy Additions to Molten Iron

Kim

et al. 2021

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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 and microscopy investigations of the liquid steel. Different types of inclusions in the FeCr alloy and steel were detected and the evolution of the 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. Furthermore, MnCr2O4 spinel inclusions originating 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 inclusions 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 of alloy addition. The increased Cr content from 16 to 24 mass pct due to the FeCr additions can increase the critical N content to form TiN inclusions at a specific Ti content. Overall, this study has contributed to the understanding the behavior of inclusions from LCFeCr alloy during the alloying process in Ti-containing steel.

Section: Evolution Mechanism Of the Inclusions In Steelmentioning

confidence: 99%

Effect of LCFeCr Alloy Additions on the Non-metallic Inclusion Characteristics in Ti-Containing Ferritic Stainless Steel

Kim

et al. 2021

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“…It means that they were not significantly melted or dissolved, which was similar to what was found for FeNb alloys. [9] On the contrary, the LCFeCr alloy was melted since their sizes decreased significantly, which is discussed in detail later. According to the Fe-Cr-C phase diagram calculated using Factsage 7.2 with databases of FactPS and FSstel (Figure 4), the approximate melting point of the investigated HCFeCr alloy is above 1873 K (1600°C), which indicates that the alloy piece cannot melt at the given experimental conditions.…”

Section: B Macroscopic Observations Of the Qt Samplesmentioning

confidence: 99%

“…[5] Several researchers have investigated the early stage dissolution behavior of different ferroalloys. [4,[6][7][8][9] However, not enough attention has been paid to the interfacial processes between FeCr alloys and liquid iron and steel so far. In stainless steelmaking process, comparatively cheap HCFeCr alloys are added initially before decarburization.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Phenomena and Inclusion Formation Behavior at Early Melting Stages of HCFeCr and LCFeCr Alloys in Liquid Iron

Karasev

Park

et al. 2021

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Chromium is normally added to liquid alloy 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 Fe 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 behaviors 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.

Non-metallic Inclusions in Different Ferroalloys and Their Effect on the Steel Quality: A Review

Karasev

Park

et al. 2021

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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 as FeSi, FeMn, SiMn, FeTi, FeCr, FeMo, FeNb, FeV, FeB, some complex ferroalloys) and their behaviours in steel melt after the additions of these ferroalloys, 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 element impurities 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. In addition, Al2O3 inclusions and relatively high Al content are commonly found in FeTi, FeNb and FeV alloys due to their 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 REM oxides, 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.