Grain structures in gas tungsten-arc welds of austenitic stainless steels with ferrite primary phase |
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Authors: | J C Villafuerte H W Kerr |
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Affiliation: | (1) Department of Mechanical Engineering, University of Waterloo, N2L 3G1 Waterloo, ON, Canada |
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Abstract: | The grain structures were investigated in full penetration gas tungsten-arc (GTA) welds in sheets of 304 and 321 austenitic
stainless steels for a range of welding conditions. In type 321 steel welds, fine equiaxed ferrite dendrites were observed
in the ferrite phase. The equiaxed structure was ascribed to heterogeneous nucleation of ferrite on Ti-rich cuboidal inclusions
present in this steel, since these inclusions were observed at the origin of equiaxed dendrites. In type 304 welds, the ferrite
grains were columnar, except in less complete penetration specimens, where a few coarse equiaxed dendrites appeared to originate
from the weld surface. The secondary austenitic grain structure was columnar in both steels. In type 304 steel, the columnar
austenitic grain structure did not necessarily correspond to the primary ferrite grains. In type 321 steel, the secondary
austenite was columnar despite the equiaxed structure of the primary ferrite. Factors which affect the columnar-to-equiaxed
transition (CET) are discussed. The failure to form equiaxed austenitic grains in type 321 steel is ascribed to austenite
growing across the space between ferrite grains instead of renucleating on the primary equiaxed ferrite. |
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