Discovering HD Characteristics with HT Flow Behavior of Nb/B Low-Carbon Steel Using Gleeble Thermomechanical Simulations

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Abstract High-temperature deformation behavior and hot ductility characteristics of Nb/B microalloyed low carbon steel were examined using Gleeble thermomechanical simulation. The study emphasizes the role of niobium (Nb) and boron (B) additions in modifying embrittlement zones, precipitation kinetics, and recrystallization behavior during thermomechanical processing (TMP). Three distinct steel compositions, produced via compact strip production (CSP) technology, were subjected to controlled deformation and cooling regimes using the Gleeble 3500 simulator. Mechanical testing, including high-temperature tensile tests, was conducted, while microstructural evolution was examined using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Th findings revealed that adding 0.015% Nb to low-carbon steel increases the non-recrystallization temperature, promoting grain boundary pinning and elevating flow stress by 29 ~ 49 MPa at temperatures of 800 ~ 1050°C. Also, the addition of 0.015% Nb leads to a decline in hot ductility at temperatures above 1150°C by ~ 8% and below 1000°C by ~ 6%. On the other hand, incorporating 30 ppm B counteracts this embrittlement by facilitating BN precipitation, which reduces Nb(C,N) formation and minimizes excessive grain boundary strengthening effects. Assessment of the Zener–Hollomon (Z-H) parameter further establishes a strong correlation between strain rate, deformation resistance, and microalloy precipitation behavior. These results provide insights into optimizing industrial rolling schedules. This study bridges the gap between industrial CSP processing conditions and controlled laboratory simulations for understanding hot rolling deformation mechanics.

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