Grain refinement in the coarse-grained region of the heat-affected zone in low-carbon high-strength microalloyed steels

Ran Wei1), Cheng-jia Shang2), and Kai-ming Wu1) 1) International Research Institute for Steel Technology, Wuhan University of Science and Technology, Wuhan 430081, China 2) School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China

摘 要：The microstructural features and grain refinement in the coarse-grained region of the heat-affected zone in low-carbon high-strength microalloyed steels were investigated using optical microscopy, scanning electron microscopy, and electron backscattering diffraction. The coarse-grained region of the heat-affected zone consists of predominantly bainite and a small proportion of acicular ferrite. Bainite packets are separated by high angle boundaries. Acicular ferrite laths or plates in the coarse-grained region of the heat-affected zone formed prior to bainite packets partition austenite grains into many smaller and separate areas, resulting in fine-grained mixed microstructures. Electron backscattering diffraction analysis indicates that the average crystallographic grain size of the coarse-grained region of the heat-affected zone reaches 6-9 μm, much smaller than that of austenite grains.

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