The focus of this study involved comparative investigations of non-metallic inclusions in 316L stainless steel bars without and with Ca treatments. The inclusions were extracted by using electrolytic extraction (EE). After that, the characteristics of the inclusions, such as morphology, size, number, and composition, were investigated by using a scanning electron microscope (SEM) in combination with an energy dispersive X-ray spectroscopy (EDS). The following four types of inclusions were observed in 316L steels: (1) Elongated MnS (Type I), (2) MnS with hard oxide cores (Type II), (3) Undeformed irregular oxides (Type III), and (4) Elongated oxides with a hard oxide core (Type IV). In the reference sample, only a small amount of the Type III oxides (Al2O3–MgO–MnO–TiOx) existed. However, in Ca-treated 316L steel, about 46% of the observed inclusions were oxide inclusions (Types III and IV) correlated to gehlenite and to a mixture of gehlenite and anorthite, which are favorable for the machinability of steel. Furthermore, untransformed oxide cores (Al2O3–MgO–MnO) were also found in the inclusions of Type IV. The mechanism leading to different morphologies of oxide inclusions is also discussed.

It is well known that inclusions affect the properties of the steel and other alloys. The importance of understanding the behavior of the inclusions during production can never be overstated. This study has examined the main types of big size (>10 μm) inclusions that exist in Ni‐based Alloy at the end of ladle treatment and after casting during industrial production of Ni based Alloys 825. Sources, mechanisms of formation and behavior of different type large size inclusions in Alloy 825 are discussed based on 2 and 3D investigations of inclusion characteristics (such as, morphology, composition, size, and number) and thermodynamic considerations. The large size inclusions found can be divided in spherical (Type I and II) inclusions and in clusters (Type III–V). Type I‐A inclusions (Al2O3–CaO–MgO) originate from the slag. Type I‐B inclusions and Type II inclusions consist of CaO–Al2O3–MgO and Al2O3–TiO2–CaO, respectively. Both types originate from the FeTi70R alloy. Type III clusters (Al2O3–MgO–CaO) are formed during an Al deoxidation of the Ni‐based alloy. Type IV clusters (Al2O3–TiO2–CaO) formed from small inclusions, which are precipitated in local zones which contain high Ti and Al levels. These clusters are transformed to Type III clusters over time in the ladle. Finally, Type V clusters are typical TiN clusters.

It is well known that inclusions affect the properties of alloys. Therefore, the importance of understanding what inclusions exist and how they behave cannot be overstated. This study has examined the behavior of Al 2 O 3 -MgO particles and clusters in the melt during the ladle treatment of Alloy 825, who is a Ni-based Alloy. The effect of different stirring directions of electromagnetic stirring in combination with gas stirring is discussed based on three-dimensional investigations of the clustered particles. More specifically, the composition, size, and number of particles and clusters are determined after electrolytic extraction of metal samples by using SEM in combination with EDS. The results show that the agglomeration of Al 2 O 3 -MgO particles in the melt is faster for an upward induction stirring combined with a gas stirring in comparison to a downward stirring combined with a gas stirring. However, the total removal of clusters from the melt is more effective when using a downward induction stirring compared to when using an upward induction stirring, especially for large size clusters (>11.2 mm). The effect of the different stirring modes on the behavior of the Al 2 O 3 -MgO particles and clusters in the melt for the ladle treatment experiments agree with the theoretical predictions based on Stokes', Brownian, and Turbulent collisions.

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The LSHR sampler is a new development for providing a sample volume large enough to study semi‐macro and macro inclusions in clean steel. During the development of the LSHR sampler it was found that the pin where the steel enters the sampler can be used for the determination of the total oxygen content. Therefore, samples were taken at several different steel plants both in the ladle and the tundish as well as for the following five different steel grades: bearing steel, stainless steel 304L and 316L, DWI steel and ULC steel. The general conclusion regarding the sampling is that it was successful for all conditions and steel grades studied. The sample pins were examined for total oxygen content using both the inert‐gas‐fusion method and the fractional‐gas‐analysis method. Thereafter, the standard deviations with respect to the total oxygen data were used as a measure of the samples reliability. The general conclusion regarding the total oxygen determinations is that they were accurate for the five steel grades studied and the conditions under which the sampling took place.