Estimation of Non-Metallic Inclusions in Industrial Ni Based Alloys 825

Abstract

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.

TiN Particles and Clusters during Ladle Treatments of Ni-based Alloy 825 using Different Stirring Modes

“…An earlier study showed that harmful Al 2 O 3 -MgO and TiN clusters exist in Alloy 825 after casting. 15) It was found that the upwards stirring (EMS/U + GS) promote a faster agglomeration of Al 2 O 3 -MgO clusters. The numbers of these clusters for upwards stirring were found to decrease for small and medium size inclusions and to increase for large size inclusions.…”

“…The most harmful non-metallic inclusions in the Alloy 825 during ladle treatment are Al 2 O 3 -MgO and TiN, which can form large size clusters that can remain after casting. 15) The behaviors of Al 2 O 3 -MgO clusters in the melt for dif-ferent stirring modes during ladle treatment were discussed in separate article. 13) However, the formation and behavior of TiN inclusions and clusters in the melt of Ni-base alloys have not been considered up to now.…”

“…However, the Ti content in the Alloy 825 grade is high enough (up to 1.2%) to enable a precipitation of primary TiN in the melt before solidification. 15) By using the TERMOCALC v3.1 software and the TFC7 database (with elements; Fe, Ni, Cr, Cu, Mo, Ti, Al, N, O), the weight fraction of TiN inclusions in the melt of the Alloy 825 grade were calculated depending on the temperature. It can be seen in Fig.…”

An Investigation of Non-Metallic Inclusions in Different Ferroalloys using Electrolytic Extraction

“…where n is the number of inclusions in the appropriate size interval, A f ilter is the area of the film filter with inclusions (1200 mm 2 ), A observed is the total observed area on film filter, ρ f erroalloy is the density of the ferroalloy matrix, and W dissolved is the dissolved weight of the ferroalloy during extraction. The floatation velocity of inclusions was estimated using Stokes' law [14], as expressed by Equation (3).…”

“…where V is the flotation velocity of the inclusion, g is the gravitational acceleration (9.81 m s −2 ), µ is the dynamic viscosity of liquid steel (0.005 m Pa s) [14], d is the diameter of the spherical inclusion, and ρ Fe (7000 kg m −3 ) and ρ NMI are the densities of liquid steel and inclusion, respectively. In this study, the ρ NMI values were taken as 3950 kg m −3 for Al 2 O 3 [15], 2648 kg m −3 for SiO 2 [16], 4930 kg m −3 for Cr-Mn-O [17], 2190 kg m −3 for Si-Al-Mg-O, 2500 kg m −3 for Al-Si-Ca-Mg-O and 2700 kg m −3 for Si-Al-O [18].…”