Abstract
Heavy gauge line pipe and structural steel plate materials are often rolled in the two-phase region for strength reasons. However, strength and toughness show opposite trends, and the exact effect of each rolling process parameter remains unclear. Even though intercritical rolling has been widely studied, the specific mechanisms that act when different microalloying elements are added remain unclear. To investigate this further, laboratory thermomechanical simulations reproducing intercritical rolling conditions were performed in plain low carbon and NbV-microalloyed steels. Based on a previously developed procedure using electron backscattered diffraction (EBSD), the discretization between intercritically deformed ferrite and new ferrite grains formed after deformation was extended to microalloyed steels. The austenite conditioning before intercritical deformation in the Nb-bearing steel affects the balance of final precipitates by modifying the size distributions and origin of the Nb (C, N). This fact could modify the substructure in the intercritically deformed grains. A simple transformation model is proposed to predict average grain sizes under intercritical deformation conditions.
Highlights
Intercritical rolling is extensively employed in the production of heavy gauge structural plates, with the aim of meeting the increasing material demands of a variety of structural applications
In a recently published work [7], the microstructural evolution during intercritical deformation was explored for low carbon steels, and a methodology capable of differentiating different ferrite populations using electron backscattered diffraction (EBSD) was developed
A completely different substructure is observed inside the deformed ferrite grains for each austenite condition
Summary
Intercritical rolling is extensively employed in the production of heavy gauge structural plates, with the aim of meeting the increasing material demands of a variety of structural applications. In a recently published work [7], the microstructural evolution during intercritical deformation was explored for low carbon steels, and a methodology capable of differentiating different ferrite populations (intercritically deformed and non-deformed ferrite formed during the final cooling) using EBSD was developed This methodology will provide a better understanding of the exact effect of the rolling process parameters on each ferrite population. For this purpose, intercritical deformation simulations were carried out via dilatometry tests using CMn steels with different C content, and an exhaustive EBSD characterization procedure was developed to classify and quantify the different phases obtained after air cooling [7].
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