[en] The behaviour of solid silicon monoxide in deoxidation of molten iron, carbon steel and 40Kh and 30KhN3 alloyed steels as well as its effect on the crystallized metal structure have been studied. The metallographic analysis of ingots and phase X-ray spectrometric analysis of silicon and oxygen impurities are reported. The possibility of the presence in solid steel of silicon monoxide in the form of a special phase is experimentally assessed. Small silica globules are formed in the central ingot zones during crystallization. Single silica globules up to 50 mcm have been found in 30KhN3 steel. It is shown that addition of silicon monoxide to a melt causes overcooling in crystallization and the formation of the Vindmanstett structure