Effect of New Types of Nonmetallic Inclusions on Continuously-Cast Billets and the Quality of High-Strength Low-Alloy Steel Rolled Product

Resumo

The nature of new types of nonmetallic inclusions (NI) facilitating improvement of a continuously-cast billet (CCB) and rolled product of high-strength low-alloy steels is studied. Contemporary approaches are considered for improving hot-rolled product. It is noted that apart from chemical composition and hot rolling regimes its properties are affected by CCB quality and the degree of different liquation processes. Results are analyzed for previous studies pointing to the fact that liquation inhomogeneity is suppressed in the case when in the concluding stage of steel treatment in a ladle and/or during crystallization there is formation of oxide NI of complex composition, presumably glassy. NI composition, and macro- and microstructure of CCB whose rolled product has a different level of mechanical properties and an axial zone with a different degree of structural inhomogeneity, are studied. It is shown that rolled product with a high level of properties and uniform structure of the axial zone is obtained from a CCB within whose structure there are compound NI of complex composition containing oxides of silicon, iron, and other elements, and also dendrite-like precipitates of carbonitrides (carbides).