Influence of Cast Structure Parameters on Ductility Properties of Low-Carbon Microalloyed Steels

On the example of industrial continuously-cast slabs 355 mm thick of two steels of different chemical compositions recommended for the production of thick heavy plates of quality categories S355ML according to EN 10025-4:2019 and S355NL according to EN 10025-3:2019 features of structure formation and their potential effect on low-temperature impact energy of a continuously cast slab are studied. Macro-and microstructural conditions are studied, the quantitative composition of structural components is calculated, the point of the ternary junction is determined, and values of low-temperature impact energy at 1/8, 1/4 and 1/2 of the slab thickness, 1/4 and 1/2 of the slab width are obtained, and the transition temperature for entirely brittle failure is established. Fractographic analysis is conducted, fracture structure is described, and non-metallic inclusions are identified. Individual examples of the possible inheritance of structural inhomogeneity from slab to thick sheet are illustrated.