Abstract: Basic monolithic refractories of which the chemical composition consists essentially of, in oxide equivalence, 65%-96% by weight of MgO, 2.6%-20% by weight of ZrO.sub.2, 1.3-10% by weight of SiO.sub.2, 2% or less by weight of CaO, 0.5% or less by weight of Fe.sub.2 O.sub.3 and 1% or less by weight of Al.sub.2 O.sub.3, and with a mineral composition containing periclase as the main component and cubic zirconia and forsterite as sub-components, and with apparent porosity of 7% or less and bulk density of 3.2 g/cm.sup.3 or more.Basic monolithic refractories under this invention possess excellent slaking resistance, slag erosion resistance, slag penetration resistance and spalling resistance. They exhibit an excellent service life, especially as lining material for steel-making furnaces.

Abstract: A treating agent of molten steel according to the present invention is used for desulfurization molten steel for desulfurizing it in a reaction vessel which is lined with a basic refractory containing MgO, and consists of CaO, CaF.sub.2 and MgO and unavoidable impurities contains from 10 to 60% by weight of MgO, and has a weight ratio of {(% CaF.sub.2)/((% CaO)+(% CaF.sub.2))}.times.100(%) of from 20 to 80%.Said agent is injected with the aid of inert carrier gas into the molten steel and floats toward a portion of the molten steel bath essentially free of slag. Another treating agent essentially consisting of CaO and CaF.sub.2 may be also injected prior and/or subsequent to injection of said agent, so as to decrease inclusions. The inert gas may also be injected after injection of said agent(s).