The Synergistic Effects among Crystal Orientations, Creep Parameters, Local Strain, Macro–Microdeformation, and Polycrystals’ Hardness of Boron Alloyed P91 Steels

• Published in: Steel research international 2022-09, Vol.93 (9), p.n/a
• Main Authors: Akhtar, Modassir, Khajuria, Akhil
• Format: Article
• Language: English
• Subjects: Activation energy; Base metal; Boron; Chromium molybdenum steels; creep; Creep (materials); crystal orientations; Crystal structure; Deformation resistance; Electron backscatter diffraction; Ferritic stainless steels; grain reference orientation deviation; Hardness; Homogeneity; Impression creep; kernel average misorientation; Microstructure; Misalignment; Polycrystals; Reciprocity; Steel; Stiffness; Strain; Synergistic effect; Taylor factor; Threshold stress
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202100819

This article induces proficient microstructure––creep reciprocity by electron backscatter diffraction (EBSD) and impression creep measurements (ICM). The article has further contributed to understanding the synergistic effects of boron in extenuating microstructural degradation. Herein, 22 and 100 ppm boron alloyed P91 steels (P91 and P91B steels, respectively) are subjected to ICM, assessing stress exponent (n), threshold stress (σTh), effective activation volume (Veff), and activation energy. Base metal and narrowed crept realm of each steel are measured by employing EBSD. ICM results are correlated with crystal orientations and 1) strain accumulation, 2) macroscopic and 3) microscopic deformation resistance, and 4) hardness of grain in polycrystals by calculating kernel average misorientation (KAM), elastic stiffness, grain reference orientation deviation (GROD), and Taylor factor (M) within microstructure before and after ICM. Measurements of P91B steel show a small value of n and Veff and a high value of σTh and activation energy as regards P91 steel. Lower KAM and stiffness before and after creep, higher GROD in base metal, and lower GROD in the crept realm in P91B steel as regards P91 steel corroborate microstructural homogeneity. M indicates both steels are hard before creep, while ICM moderates hardness. Finally, this study reveals synergistic effects of crystal orientations, KAM, stiffness, GROD, M, and creep. This study helps to understand the perplexing nature of boron effects in 9Cr steels through creep and microstructural measurements. These provide an in‐depth understanding of creep–microstructural mechanisms that help to elucidate synergistic effects.