Obtaining microstructures of hot-rolled dual-phase steel plates

This work presents a novel methodology for directly obtaining dual-phase (DP) steels from the hot rolling process. The effect of chemical composition on the behavior of continuous cooling transformation diagrams was investigated using JMatPro software. The results of the computational study were validated experimentally. These results were used to obtain a DP steel from AISI-1018 steel, which was processed by hot rolling at 1,000°C and rolling finishing temperatures ranging from 953 to 744°C, with deformation degrees of 10–40%, and controlled cooling at a rate of 30°C s⁻¹. The microstructure was characterized using scanning electron microscopy, and the mechanical properties were evaluated through microhardness measurements, uniaxial tension tests, and impact tests. Results show that the percentage of the phases strongly depended on the processing conditions: finishing temperatures T > Ac₃, and deformations of 10–20%, and they promote microstructures composed of ferrite and martensite, predominantly with α′ > 63%. In contrast, with deformations of 30–40% and finishing temperatures close to Ac₁, a better phase equilibrium (55%α–45%α′) results, which generates ultimate tensile strength values greater than 930 MPa and elongation of 32%. The proposed methodology represents a low-cost alternative processing route for obtaining DP steels without the heat treatment stage after hot rolling, compared to those produced with a large amount of microalloying and high processing. This methodology yields significant energy and cost savings, making it an attractive manufacturing option for in-line steel production, which can be utilized for the manufacture of automotive components.