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Microstructure Evolution during Controlled Rolling of an Nb–Ti Microalloyed Steel
Author(s) -
Rezayat Mohammad,
Mohebbi Mohammad Sadegh,
Parsa Mohammad Habibi,
Nagy Stefan,
Nosko Martin
Publication year - 2021
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.202000487
Subject(s) - materials science , microstructure , recrystallization (geology) , metallurgy , transmission electron microscopy , grain size , ferrite (magnet) , microalloyed steel , strengthening mechanisms of materials , composite material , austenite , nanotechnology , paleontology , biology
The microstructural evolution of an Nb–Ti microalloyed steel with the application of coiled tubing is studied in detail during hot rolling followed by accelerated cooling and simulated coiling by means of optical microscopy complemented with electron backscattered diffraction and transmission electron microscopy. It is found that the main microstructural characteristics, i.e., grain size, grain morphology, and texture, vary during different thermomechanical steps, largely in finish rolling. Finish rolling at 850 °C, in the nonrecrystallization region, activates the deformation‐induced ferrite transformation (DIFT) mechanism and leads to the appearance of γ‐fiber, and {332}<113> and {113}<110> components. Decreasing the finish rolling temperature to 750 °C promotes this mechanism and results in finer final microstructure consisting of low angle grain boundaries. However, it is found that to obtain a homogenous microstructure with γ‐fiber texture, the final rolling temperature should be high enough for the sufficient occurrence of static recrystallization in ferrite just after finish rolling. More deformation in the nonrecrystallization region, especially for the last rolling steps, strongly affects the DIFT mechanism and leads to fine‐grained microstructure. Refining of ferrite to the grain size of 3.5 ± 0.5 μm results in 65% enhancement of yield strength and reduction of strain hardening by 25%.