Effect of Continuous Casting Technology on Low-Alloy Steel Structure in Different Production Stages

Resumo

The effect of “soft reduction” technology on chemical inhomogeneity of a continuously-cast slab, and also on the structure and properties of finished rolled product made of low-carbon microalloyed steel is studied. In slabs prepared without soft reduction, a defect is often observed in the form of white bands leading to a reduction in the proportion of ductile component in low-standard rolled product. In a slab transverse section, from the surface into the depth there are coarse grains with ferrite over boundaries and bainite within grains. A white band is formed by fine polyhedral ferrite grains with a small amount of finely acicular bainite. In this case, the microhardness of ferrite and bainite in the axial zone, and in a white band is considerably higher than in other slab zones. Also within the limits of a white band there is formation of an increased amount of sulfides and carbonitrides. It is demonstrated that as a result of liquation processes there is an increase in carbon, manganese, sulfur, and phosphorus, and also microalloying element content within a white band.