Reoxidation of Ni‐ and Ni‐Fe‐Alloys by Al₂O₃‐SiO₂ Refractory Materials

Abstract

Reactions at the refractory/melt interface during ingot casting of Ni-and Ni-Fe-alloys were studied. The casts were performed using different alumino-silicate bricks as refractory materials. Samples taken from the casting channel before and after casting were investigated using light and scanning electron microscopy with XPS. Thermodynamic calculations were performed with FactSage and the results were compared with the results from industrial tests. After the melt has infiltrated the surface layer of the bricks, refractory corrosion starts with an attack of Mn and Mg of the melt on Si0 2 and Fe203 of the refractory bonding matrix. Despite the presence of elements with higher oxygen affinity in the melt, low-melting alumino-silicate phases are predominantly built by the reaction with Mn and Mg. In a second step this liquid phase either traps non-metallic inclusions from the melt or, at higher contents of Zr, Ti, Mg, Y etc. in the melt, causes massive reoxidation and inclusion formation. The refractory materials investigated show an increasing trend for reoxidation with an increasing amount of Si0 2 in glassy phases of the refractory bonding matrix. By the use of a refractory material with higher mullite content in the bonding matrix or by use of alumina bricks a strong reoxidation of the melt and intense inclusion formation can be avoided. These observations are also valid for other alloys with higher contents of elements with high affinity to oxygen.

Experiment Research on Argon Shroud for the Protection of Steel Casting

“…A number of potential sources can lead to generation of new inclusions, such as reoxidation [1,2] , reaction between steel and runner refractory [3,4], While a number of sources could supply oxygen for reoxidation, the pickup of oxygen by the steel stream from the surrounding atmosphere is one of the most important. [5][6][7] Industrial studies have evidently shown that using a protective shroud of inert gas such as argon can reduce the number of inclusions and lower the nitrogen as well as hydrogencontents in the steel [8,9] . Some efforts have been made to understand and describe the oxygen pickup around the teeming steel stream.…”

Inclusions Generated during Ingot Casting of Tool Steel

“…A number of studies 3–22 were carried out to find the possible sources for non‐metallic inclusions. Inclusions were also found to be generated in the casting process.…”

“…Inclusions were also found to be generated in the casting process. For example, reoxidation during transfer from the ladle to the runner system 3–9, interaction between the steel and the refractory material in the runner system 5–7, 10, 11, 22, reoxidation inside the mould 3, 5, 6, 19 and the mould powder 4, 5, 12, 13 were all been reported the sources of non‐metallic inclusions.…”

Oxygen Penetration in the Protection Shroud in Steel Casting

“…A number of potential sources can lead to generation of new inclusions, such as reoxidation, 1–2 reaction between steel and runner refractory 3–7, flushing‐off of refractory and entrainment of casting powder 6, 8–10. While a number of sources could supply oxygen for reoxidation, the pickup of oxygen by the steel stream from the surrounding atmosphere is one of the most important 6, 8, 11, 12.…”