Optimization of Melt Treatment for Austenitic Steel Grain Refinement

Refinement of the as-cast grain structure of austenitic steels requires the presence of active solid nuclei during solidification. These nuclei can be formed in situ in the liquid alloy by promoting reactions between transition metals (Ti, Zr, Nb, and Hf) and metalloid elements (C, S, O, and N) diss...

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Bibliographic Details
Published in:Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2017-02, Vol.48 (1), p.406-419
Main Authors: Lekakh, Simon N., Ge, Jun, Richards, Von, O’Malley, Ron, TerBush, Jessica R.
Format: Article
Language:English
Subjects:
Austenitic stainless steel
Austenitic stainless steels
Castings
Characterization and Evaluation of Materials
Chemical reactions
Chemistry and Materials Science
Grain refinement
Grain size
Grain structure
Materials Science
Melting
Melts
Metallic Materials
Metals
Nanotechnology
Nuclei
Structural Materials
Structural steels
Surfaces and Interfaces
Thin Films
Titanium nitride
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Summary:Refinement of the as-cast grain structure of austenitic steels requires the presence of active solid nuclei during solidification. These nuclei can be formed in situ in the liquid alloy by promoting reactions between transition metals (Ti, Zr, Nb, and Hf) and metalloid elements (C, S, O, and N) dissolved in the melt. Using thermodynamic simulations, experiments were designed to evaluate the effectiveness of a predicted sequence of reactions targeted to form precipitates that could act as active nuclei for grain refinement in austenitic steel castings. Melt additions performed to promote the sequential precipitation of titanium nitride (TiN) onto previously formed spinel (Al 2 MgO 4 ) inclusions in the melt resulted in a significant refinement of the as-cast grain structure in heavy section Cr-Ni-Mo stainless steel castings. A refined as-cast structure consisting of an inner fine-equiaxed grain structure and outer columnar dendrite zone structure of limited length was achieved in experimental castings. The sequential of precipitation of TiN onto Al 2 MgO 4 was confirmed using automated SEM/EDX and TEM analyses.
ISSN:1073-5615
1543-1916
DOI:10.1007/s11663-016-0832-5