Thermomechanical controlled processing of high strength low alloy steel: Constitutive and finite element modeling

The thermomechanical control processing of high-strength low-alloy (HSLA) steels is of critical importance for optimizing microstructural evolution and mechanical performance in industrial applications. In this research, the hot deformation behavior of a low carbon bainitic HSLA steel was systematically studied through a combination of experimental testing, constitutive modeling, and finite element (FE) simulations. Uniaxial compression tests (UCT) were carried out on a Gleeble machine within the temperature range of 800 –1100 ℃ and strain rates of 0.01–10 s⁻¹, up to a true strain of 0.6. The experimental results were employed to develop a modified hyperbolic sine-type constitutive model capable of incorporating strain-dependent material constants. The modified model demonstrated superior predictive performance, achieving a correlation coefficient of 0.98 and an average absolute relative error of 5%, thereby confirming its reliability in capturing the flow stress behavior. At higher temperatures, the activation energy decreased due to enhanced dislocation mobility, while with increasing strain, a progressive reduction was observed because of dynamic recrystallization. Processing maps were constructed at various strain levels, highlighting the development of instability zones with increasing strain. The optimal hot deformation domain was identified in the range of 960 –1080 ℃ at strain rates between 0.02– 0.12 s⁻¹, conditions that are expected to promote dynamic recrystallization and yield a uniformly refined microstructure. To complement these uniaxial tests, multi-pass plane strain compression (PSC) tests were also performed at 800 –1100 ℃ and a constant strain rate of 0.1 s⁻¹, with individual pass strains of 15–30%. FE simulations conducted using Abaqus for both uniaxial and plane strain compression tests revealed significant strain inhomogeneity due to frictional effects, with higher strain concentrated at the specimen center and reduced strain near the top and bottom surfaces. The microstructural analysis, including grain size spatial variation across the UTC specimen, its correlation with plastic strain distribution was also performed. These combined experimental, modeling, and simulation results provide a comprehensive understanding of the hot deformation behavior of a HSLA steel and offer valuable insights for designing optimized thermomechanical processing routes. Importantly, the outcomes of this research can support the upscaling of HSLA steels for support structures.

Publisher

University of Galway

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CC BY-NC-ND

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University of Galway Theses (Research Masters Theses)