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Open AccessArticle

Large Delta T Thermal Cycling Induced Stress Accelerates Equilibrium and Transformation in Super DSS

1
Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan
2
Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
3
Department of Marine Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan
4
Taiwan Instrument Research Institute, National Applied Research Laboratories, Hsinchu 30076, Taiwan
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(11), 962; https://doi.org/10.3390/cryst10110962
Received: 3 September 2020 / Revised: 18 October 2020 / Accepted: 20 October 2020 / Published: 23 October 2020
(This article belongs to the Special Issue Investigation of Duplex Stainless Steel)
Based on the predicted phase diagram of super duplex stainless steel (DSS) calculated by Thermo-Calc, the maximum peak temperature 1100 °C was selected to ensure no σ phase existence. This target temperature fell into the two-phase solid solution (SS) region. A series of different thermal cycling tests were carried out with the notations of 2SS, 2SS + 3 cycles, 2SS + 7 cycles, 2SS + 13 cycles, and 2SS + 20 cycles. It was found that the trend of two-phase volume ratio variation by thermal cycling followed the predicted thermodynamic equilibrium trend. After 2SS + 7 cycles, the ratio of two-phase δ/γ tended toward the ideal 1:1. According to the electron backscatter diffraction (EBSD) analysis, the δ phase crystal orientation changed from the most frequent directions of <001> and <111> of the as-received sample to the most frequent orientation of <113> after two SS treatments. While the γ phase grain always remained at <101> orientation. The grain boundary misorientation angles of the γ grains were relatively stable, ranging from 53° to 63°, but those of the δ grains were widely distributed actively presuming the lattice rotation. The Kernel Average Misorientation (KAM) value of the local strain in face center cubic (fcc) γ grains was varied and greater than that of the body center cubic (bcc) δ phase, indicating that the former, with a large grain boundary misorientation had larger local deformation than the latter, which possesses wide random misorientation angle distribution. View Full-Text
Keywords: thermal cycling; most frequent orientation; duplex stainless steel; KAM; EBSD thermal cycling; most frequent orientation; duplex stainless steel; KAM; EBSD
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MDPI and ACS Style

Yu, P.-J.; Chen, S.-C.; Yen, H.-W.; Chang, H.-Y.; Yang, J.-R.; Wang, S.-H.; Chiu, P.-K.; Lin, T.-R. Large Delta T Thermal Cycling Induced Stress Accelerates Equilibrium and Transformation in Super DSS. Crystals 2020, 10, 962.

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