The book covers the interaction of gas strings with a molten bath during blowing, the regularity of heat and mass exchange in the gas - slag - metal - solid material system, the hydrodynamics of the steel-making bath and its impact on the transfer processes. Considerable attention is paid to the peculiarities of the mechanism and kinetics of oxidation of elements in the conditions of blowing the bath with oxygen, the kinetics of gas absorption, the justification for the choice of a rational blow mode and the design of the tuyeres. The basics of aerohydrodynamics and heat and matter transfer processes are presented. The book is intended for scientific and engineering workers involved in steelmaking and the theory of metallurgical processes. It can be useful for university students of the corresponding specialty.