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

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.

Evolution of the Non-metallic Inclusions Influenced by Slag-Metal Reactions in Ti-Containing Ferritic Stainless Steel

“…To get stable TiO x and TiO x -CrO x based inclusions, FeCr alloys were added into the Ti-containing steels. The inclusion characteristics can be found from previous work, [31] where Ti In sample S1 taken after 5 min of the slag addition, the number of inclusions significantly increased due to the slag-steel reactions. A relatively larger amount of inclusions were located together on the film filters, as shown in Figure 2 In sample S2 taken after 15 min of the slag addition, the number of inclusions significantly reduced, which is discussed in detail in Figure 5 software using the FactPS and FToxid databases at 1873 K (1600°C) and p(O 2 )=10 -15 atm, which was calculated based on the measured oxygen content.…”

“…The details of the calculation to determine the oxygen partial pressure in the present system is given elsewhere. [31] It can be seen from Figure 4(a) that the main compositions of inclusions are concentrated in the single liquid and Ti 2 O 3 +liquid regions before the slag addition. After 5 min of the slag addition (S1), the number of inclusions significantly increases, as shown in Figure 4 .…”

“…Several steel samples were taken after the FeCr addition, and the inclusion characterization results were reported elsewhere. [31] After 30 min of the alloy addition, sample S0 was taken from the molten steel using a quartz tube (ID=4 mm). Thereafter, 50 g slag was added on the surface of molten steel under an Ar-3 pct H 2 atmosphere.…”

“…The effect of the activity of alumina in the slag on the mole fraction of alumina in the inclusions is shown in Figure 13 This might be due to the fact that they were reduced by dissolved Al in the steel melts based on Eqs. [29] and [31]. [39,40,42] Thus, the composition of inclusions can be deduced as a function of the activities of Al, Ti, Cr and O as given in Eq.…”

“…In terms of the multiphase inclusions, they can be divided into two groups: type 1 containing Ti [29], [31] and [37]. [38,40,42]…”