Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction
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Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction J.B. WISKEL, X. LI, D.G. IVEY, and H. HENEIN Quantitative X-ray diffraction characterization of four (4) X80 and three (3) X100 microalloyed steels was undertaken. The effect of through-thickness position, processing parameters, and composition on the measured crystallite size, microstrain, and J index (relative magnitude of crystallographic texture) was determined. Microstructure analysis using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-backscattered diffraction was also undertaken. The measured value of microstrain increased with increasing alloy content and decreasing cooling interrupt temperature. Microstructural features corresponding to crystallite size in the X80 steels were both above and below the detection limit for quantitative X-ray diffraction. The X100 steels consistently exhibited microstructure features below the crystallite size detection limit. The yield stress of each steel increased with increasing microstrain. The increase in microstrain from X80 to X100 is also associated with a change in microstructure from predominantly polygonal ferrite to bainitic ferrite. https://doi.org/10.1007/s11663-018-1298-4 The Minerals, Metals & Materials Society and ASM International 2018
I.
INTRODUCTION
MICROSTRUCTURAL characterization of a microalloyed pipeline steel can take many forms,[1–10] including optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron-backscattered diffraction (EBSD). Due to the complexity of the microstructure inherent in microalloyed steels, most, if not all, of these techniques are used in a complimentary way to characterize this material. Microstructural features in microalloyed steels can include the presence of several co-existing complex phases (e.g., ferrite, acicular ferrite, or bainite),[3,4,11,12] dislocation density variations associated with the different phases,[4,13] preferred orientation,[10] and variations in grain size and/or subgrain size.[3] These microstructural features are directly related to the composition of the steel[5–8,13] and to the thermomechanical controlled processing (TMCP) conditions employed, including finish rolling temperature (FRT) and coiling interrupt temperature (CIT),[3,4] and ultimately with the mechanical properties of the material.[14]
J.B. WISKEL, X. LI, D.G. IVEY, and H. HENEIN are with the Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 1H9, Canada. Contact e-mail: [email protected]. Manuscript submitted January 29, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Previous work by the authors[15] used quantitative X-ray diffraction (QXRD) to quantify the mean size and atomic composition of nanosize precipitates in microalloyed steels. This paper focuses on applying the general QXRD technique to the characterization of microstructure, specifically crystallite size (Dv), microstrain (eo), and
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