Abstract
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.
Highlights
FERRITIC stainless steel (FSS) grades are essentiallyFe–Cr binary alloys containing 12 to 30 mass pct Cr
It can be seen that the initial Cr content before FeCr addition was about 16 mass pct, which corresponds to time 0
The Ti content was about 0.21 mass pct at the beginning of the experiment, it drastically decreased to 0.15 mass pct after 8 minutes from FeCr addition and thereafter had an almost constant value
Summary
Fe–Cr binary alloys containing 12 to 30 mass pct Cr. Recently, ferritic stainless steels containing chromium up to 30 mass pct with ultra-low carbon and nitrogen contents have been developed for good corrosion resistance and high formability to replace austenitic stainless steels.[1,2] Titanium has been widely used as an alloying element in stainless steel to suppress chromium nitride precipitations at grain boundaries by stabilizing. The effects of Al and Ca in FeSi alloys on the composition evolution of inclusions in different steel melt have been well investigated by several researchers.[12,13,14,15,16,17] They reported that the high Al-containing FeSi alloys can significantly increase the formation of pure Al2O3 and/or MgAl2O4 spinel inclusions in liquid steel. They studied the influence of impurities in FeTi70 and FeTi35 alloys on steel cleanliness in an industrial process Their results showed that the number of generated inclusions was higher for a FeTi35 addition compared to a FeTi70 addition, which was attributed to the presence of larger contents of impurities in the FeTi35 alloys.[21] Dorrer et al.[22] reported that the FeTi75 additions can cause the formation of a new population of Ti-containing alumina inclusions which increased clogging tendency. The aim is to investigate the effects of FeCr additions on the inclusion transformation thermodynamics and kinetics in steel
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