Optimization of Melt Treatment for Austenitic Steel Grain Refinement

Abstract

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 (Al2MgO4) 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 Al2MgO4 was confirmed using automated SEM/EDX and TEM analyses.

Department(s)

Materials Science and Engineering

Research Center/Lab(s)

Peaslee Steel Manufacturing Research Center

Keywords and Phrases

Aluminum; Austenite; Austenitic steel; Crystal microstructure; Grain refinement; Grain size and shape; Niobium; Stainless steel; Titanium; Titanium castings; Titanium compounds; Titanium nitride; Transition metals; As-cast structures; Columnar dendrites; Fine equiaxed grains; Heavy sections; Liquid alloy; Melt treatments; TEM analysis; Thermodynamic simulations; Steel castings

International Standard Serial Number (ISSN)

1073-5615

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2017 Springer Boston, All rights reserved.

Publication Date

01 Feb 2017

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