TY - JOUR
T1 - Suppression of grain refinement in heat-affected zone of 9Cr-3W-3Co-VNb steels
AU - Matsunaga, Tetsuya
AU - Hongo, Hiromichi
AU - Tabuchi, Masaaki
AU - Sahara, Ryoji
N1 - Funding Information:
The authors appreciate funding support from A-USC technology development, the Ministry of Economy, Trade, and Industry of Japan and the Inamori Foundation .
Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2016/2/8
Y1 - 2016/2/8
N2 - Prompt phase transformations make grains in the heat-affected zone (HAZ) smaller during welding of 9% chromium (9Cr) heat-resistant steels leading to premature failure under creep conditions, which is well known as a type IV fracture. Because the type IV fracture shortens the creep lifetime of the steels, suppressing the fracture is an urgent task in the energy industry. The present study shows that boron addition and nitrogen reduction inhibit grain refinement after welding because of a change in the morphology of the precipitate at prior austenite grain boundaries. In conventional 9Cr steel (ASME Gr. 92 steel), a high amount of MX was unable to pin interface migration of the phase transformation and generated fine grains in the HAZ. In the new B-added steels, B-stabilized M23C6 became the dominant precipitate and showed a larger pinning effect of the phase transformation than MX, which resulted in coarse grains in the HAZ. This suggests that designing stabilized M23C6 forms a superior welded microstructure and results in a longer creep lifetime of 9Cr steels.
AB - Prompt phase transformations make grains in the heat-affected zone (HAZ) smaller during welding of 9% chromium (9Cr) heat-resistant steels leading to premature failure under creep conditions, which is well known as a type IV fracture. Because the type IV fracture shortens the creep lifetime of the steels, suppressing the fracture is an urgent task in the energy industry. The present study shows that boron addition and nitrogen reduction inhibit grain refinement after welding because of a change in the morphology of the precipitate at prior austenite grain boundaries. In conventional 9Cr steel (ASME Gr. 92 steel), a high amount of MX was unable to pin interface migration of the phase transformation and generated fine grains in the HAZ. In the new B-added steels, B-stabilized M23C6 became the dominant precipitate and showed a larger pinning effect of the phase transformation than MX, which resulted in coarse grains in the HAZ. This suggests that designing stabilized M23C6 forms a superior welded microstructure and results in a longer creep lifetime of 9Cr steels.
KW - Ferritic/martensitic steel
KW - Phase transformation
KW - Precipitate
KW - Welding
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U2 - 10.1016/j.msea.2015.12.095
DO - 10.1016/j.msea.2015.12.095
M3 - Article
AN - SCOPUS:84953283613
VL - 655
SP - 168
EP - 174
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
SN - 0921-5093
ER -