TY - JOUR
T1 - Suppression of Coarsening of Upper Bainite at Prior Austenite Grain Boundaries by Intra-granular Bainite Nucleated on Inclusions in Steel Welds
AU - Nakanishi, Daiki
AU - Uchiyama, Tetsuya
AU - Shirahata, Hiroyuki
AU - Takahashi, Manabu
N1 - Publisher Copyright:
© 2024 The Iron and Steel Institute of Japan.
PY - 2024
Y1 - 2024
N2 - The microstructures of intra-granular bainite nucleated on Ti-oxide particles (IGB) and grain boundary upper bainite (GBB) in Ti-deoxidized steel (Fe-0.1mass%C-1.5mass%Mn-2mass%Ni-1mass%Cu) were investigated by EBSD analysis and 3-dimentional observation. The steel was austenitized at 1 673 K for 23 s, held at 803 K for 7 s-20 ks and then quenched to room temperature. 803 K is just below the bainite transformation start temperature. IGB and GBB were observed at 5% bainite transformation. Despite the formation of IGB, part of GBB grew to a size of 100 μm at 17% bainite transformation, and coarsened to 130–200 μm at 85% bainite transformation. Mechanism of the GBB coarsening is discussed in terms of differences in (1) the microstructures and (2) the nucleation site of IGB and GBB. A single packet with many blocks was observed in GBB nucleated at whole surface of austenite grain boundaries with a size of 400–500 μm, while multiple packets with two blocks were observed in IGB nucleated on Ti-oxide particles with a size of 1–2 μm. IGB suppressed the growth of GBB by impingement. However, as the GBB was much larger than IGB, part of the GBB was not impinged by the IGB and continued to grow. GBB grew until all blocks of GBB were impinged by IGB and/or transformation was finished, resulted in GBB coarsening.
AB - The microstructures of intra-granular bainite nucleated on Ti-oxide particles (IGB) and grain boundary upper bainite (GBB) in Ti-deoxidized steel (Fe-0.1mass%C-1.5mass%Mn-2mass%Ni-1mass%Cu) were investigated by EBSD analysis and 3-dimentional observation. The steel was austenitized at 1 673 K for 23 s, held at 803 K for 7 s-20 ks and then quenched to room temperature. 803 K is just below the bainite transformation start temperature. IGB and GBB were observed at 5% bainite transformation. Despite the formation of IGB, part of GBB grew to a size of 100 μm at 17% bainite transformation, and coarsened to 130–200 μm at 85% bainite transformation. Mechanism of the GBB coarsening is discussed in terms of differences in (1) the microstructures and (2) the nucleation site of IGB and GBB. A single packet with many blocks was observed in GBB nucleated at whole surface of austenite grain boundaries with a size of 400–500 μm, while multiple packets with two blocks were observed in IGB nucleated on Ti-oxide particles with a size of 1–2 μm. IGB suppressed the growth of GBB by impingement. However, as the GBB was much larger than IGB, part of the GBB was not impinged by the IGB and continued to grow. GBB grew until all blocks of GBB were impinged by IGB and/or transformation was finished, resulted in GBB coarsening.
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U2 - 10.2355/isijinternational.ISIJINT-2023-381
DO - 10.2355/isijinternational.ISIJINT-2023-381
M3 - Article
AN - SCOPUS:85191399669
SN - 0915-1559
VL - 64
SP - 126
EP - 133
JO - isij international
JF - isij international
IS - 1
ER -