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In-Situ Observation of Acicular Ferrite Transformation in High-Strength Low-Alloy Steel Using Confocal Laser Scanning Microscopy

Lee Sang-In, Shin Seung-Hyeok, Park Hyeonwoo, Kim Hansoo, Lee Joonho, Hwang Byoungchul

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 4

1497--1501

EN

In-situ observation of the transformation behavior of acicular ferrite in high-strength low-alloy steel using confocal laser scanning microscopy was discussed in terms of nucleation and growth. It is found that acicular ferrite nucleated at dislocations and slip bands in deformed austenite grains introduced by hot deformation in the non-recrystallization austenite region, and then proceeded to grow into an austenite grain boundary. According to an ex-situ EBSD analysis, acicular ferrite had an irregular shape morphology, finer grains with sub-grain boundaries, and higher strain values than those of polygonal ferrite. The fraction of acicular ferrite was affected by the deformation condition and increased with increasing the amount of hot deformation in the non-recrystallization austenite region.

2

Effects of the Coiling Temperature and Anisotropy on the Tensile Properties of High-Strength API X70 Linepipe Steel

Oh Dong-Kyu, Shin Seung-Hyeok, Lee Sang-Min, Hwang Byoungchul

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 4

1487--1490

EN

In this study, the effect of the coiling temperature on the tensile properties of API X70 linepipe steel plates is investigated in terms of the microstructure and related anisotropy. Two coiling temperatures are selected to control the microstructure and tensile properties. The API X70 linepipe steels consist mostly of ferritic microstructures such as polygonal ferrite, acicular ferrite, granular bainite, and pearlite irrespective of the coiling temperature. In order to evaluate the anisotropy in the tensile properties, tensile tests in various directions, in this case 0° (rolling direction), 30°, 45° (diagonal direction), 60°, and 90° (transverse direction) are conducted. As the higher coiling temperature, the larger amount of pearlite is formed, resulting in higher strength and better deformability. The steel has higher ductility and lower strength in the rolling direction than in the transverse direction due to the development of γ-fiber, particularly the {111}<112> texture.

3

Application of Artificial Neural Network to Predict the Tensile Properties of Dual-Phase Steels

Shin Seung-Hyeok, Kim Sang-Gyu, Hwang Byoungchul

Archives of Metallurgy and Materials

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2021

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Vol. 66, iss. 3

719--723

EN

An artificial neural network (ANN) model was developed to predict the tensile properties of dual-phase steels in terms of alloying elements and microstructural factors. The developed ANN model was confirmed to be more reasonable than the multiple linear regression model to predict the tensile properties. In addition, the 3D contour maps and an average index of the relative importance calculated by the developed ANN model, demonstrated the importance of controlling microstructural factors to achieve the required tensile properties of the dual-phase steels. The ANN model is expected to be useful in understanding the complex relationship between alloying elements, microstructural factors, and tensile properties in dual-phase steels.