Effects of Nucleus Density and Dendritic Growth Influenced by Ti and Nb on Solidification Structure of Fe-18 Pct Cr Ferritic Stainless Steel

The effects of nucleus density and dendritic growth influenced by Ti and Nb on the solidification structure of Fe-18 pct Cr ferritic stainless steel (FSS) ingots were investigated. The equiaxed zone ratios (EZR) were 8.5, 28.8, 67.5, and 57.3 pct in the blank, Nb-bearing, Ti-bearing, and Ti-Nb-beari...

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Published in:Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2019-06, Vol.50 (3), p.1322-1333
Main Authors: Hou, Yuyang, Cheng, Guoguang
Format: Article
Language:English
Subjects:
Bearing
BULK DENSITY
Cellular automata
Characterization and Evaluation of Materials
Chemistry and Materials Science
Chromium
CRYSTAL GROWTH
DENDRITES
Dendritic structure
Ferritic stainless steel
Ferritic stainless steels
FERRITIC STEELS
FINITE ELEMENT METHOD
GRAIN SIZE
Ingots
Iron
KINETICS
MATERIALS SCIENCE
Mathematical analysis
Metallic Materials
Nanotechnology
NIOBIUM
NUCLEATION
Nuclei (cytology)
Phase transitions
SILICON OXIDES
SOLIDIFICATION
STAINLESS STEELS
STATISTICS
Structural Materials
Surfaces and Interfaces
THERMODYNAMICS
Thin Films
TITANIUM
TITANIUM NITRIDES
TITANIUM OXIDES
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Summary:The effects of nucleus density and dendritic growth influenced by Ti and Nb on the solidification structure of Fe-18 pct Cr ferritic stainless steel (FSS) ingots were investigated. The equiaxed zone ratios (EZR) were 8.5, 28.8, 67.5, and 57.3 pct in the blank, Nb-bearing, Ti-bearing, and Ti-Nb-bearing FSS ingots, respectively. The grain size was the smallest in the Ti-Nb-bearing ingot. Silicon oxide was present in the blank sample and Nb-bearing ingot, but the complex nuclei that were composed of TiO x -Ti(C, N) and TiO x -(Ti, Nb) x (C, N) y existed in the Ti-bearing and Ti-Nb-bearing ingots, respectively. The bulk density of the complex nucleus decreased by 70 pct when the Ti content decreased from 0.16 to 0.14 mass pct. Thermodynamic calculations indicate that the phase transformation from Ti 3 O 5 to Ti 2 O 3 was delayed in the ingot with a lower Ti content and that the Ti 2 O 3 shows more potential for TiN nucleation compared with Ti 3 O 5 according to the disregistry theory. The increased EZR mechanism was illustrated by a cellular-automaton–finite-element method with actual distribution statistics of the complex nucleus and dendritic-growth-kinetic analysis. The heterogeneous nucleation effect of the complex nucleus by Ti addition and the variations in dendritic-growth kinetics by Ti and Nb contribute to the EZR increase of FSS.
ISSN:1073-5615
1543-1916
DOI:10.1007/s11663-019-01557-5