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Abstract
The production of high-toughness jumbo structural sections remains a significant challenge in heavy section mills due to low reduction ratios, heterogeneous microstructure, and inconsistent mechanical properties across thick flange regions. These challenges are particularly critical for offshore grades (JR, J0, J2), which require strict toughness compliance according to standard.
In this work, a thermo-mechanically controlled processing (TMCP) method is developed for the production of high-toughness steel jumbo beams using a direct reduced iron (DRI)-based steelmaking route. The process is applied to beam blank rolling in a heavy section mill, producing universal columns with flange thicknesses up to 77 mm.
An integrated metallurgical model is established to predict and control microstructure evolution during reheating, rolling, and cooling stages. The model incorporates key process parameters including deformation temperature, reduction per pass, strain accumulation, strain rate, and precipitation behavior of microalloying elements (Nb, Ti, V), with particular emphasis on the determination of the non-recrystallization temperature (Tnr).
A two-stage controlled rolling strategy combining recrystallization controlled rolling (RCR) and conventional controlled rolling (CCR) is implemented to achieve effective austenite grain refinement under limited reduction conditions. The model further predicts ferrite grain size as a function of accumulated strain and cooling rate, enabling optimization of final mechanical properties without reliance on intensive cooling systems.
Industrial application demonstrates improved microstructural homogeneity and enhanced toughness performance while maintaining weldability and reducing alloying requirements.