In this case, an additional final deoxidizer was needed.
The 0.05% titanium and 0.02% aluminum combination was used as a final deoxidizer, and then gradually aluminum was excluded completely.
Once the foundry switched to titanium as its final deoxidizer, the tensile and yield strength and elongation measurements improved, eliminating this problem.
However, the final deoxidizer, whether titanium or aluminum, is only a part of the solution.
Charges consist of 40-60% foundry returns with the balance made up of low carbon iron or 1010 steel, ferroalloys and deoxidizers. All foundry-generated returns are color coded and segregated, while purchased scrap is not used in recipes.
Aluminum, Fe-Si, and Fe-Mn, which have a high affinity with oxygen, are used as deoxidizers
. The steel by-product of this process is refining slag (STS-refining slag (SRS)).
The corrosion numbers at 1000 hr were also close to values reported by Mol where a similar pretreatment, deoxidizer
, and chromate conversion coating were used.
Content, chemical-mineralogical composition, and dimensions of non-metal inclusions depend upon a number of the following priority factors: thermodynamic activity of used deoxidizers and their composition, temperature-time conditions of deoxidation and ladle treatment of the metal, methods of steel casting, limitation of secondary oxidation, quality of bottom-pouring refractories (high heat resistance and low erosion), weight of the ingots (duration of the metal crystallization), and geometrical dimensions of sectioned rolled stock, which effects deformability of inclusions.
Theoretical analysis of the processes and material balance of the steel deoxidizers (calcium and aluminium) at all stages of ladle treatment showed that although << excessive >> amount of calcium during casting and crystallization of metal in the mould (weight of the ingot equaled 3.6 t) ensures with residual (dissolved) aluminium a relatively low content of the dissolved (active) oxygen, at the same time it is to a significant degree responsible for formation of increased amounts and dimensions of both globular inclusions in steel on basis of CaO-[Al.sub.2][O.sub.3] and heterogeneous inclusions on basis of CaO-[Al.sub.2][O.sub.3]-MgO-Si[O.sub.2] (Figure 2, Table 1).
Crystal-chemical structure of multiphase oxide inclusions is determined by physical-chemical state of the pool, sequence of introduction of the deoxidizers, and interaction of dissolved in the metal elements.
It should be noted that according to valid normative-technical documentation addition of deoxidizers
and modifiers without limitation of their kinds and residual contents is allowed in melting of the 20GL steel for transport machine building.