Abstract: Installation according to the invention comprising a desilication and dephosphorization stage (A), followed by a decarburization stage and in which the pig iron to be pre-smelted is intended to form a bath whose free surface is maintained at a predetermined level (N.sub.1).The dephosphorization comprises a reactor (1) comprising means (5, 6, 8) respectively for introducing the pig iron to be pre-smelted, for adding desilication and dephosphorization agents, and for creating an oxidizing atmosphere, as well as rabbling means (9). It also comprises a decanter (2) separated from the reactor (1) by a partition (3) having an opening (4) below the level (N.sub.1) and whose upper end is above the latter. The decanter comprises an immersed outlet opening (10) connected to the decarburization stage and an overflow (12) for evacuating the slag. The slag formed in the reactor (1) flows out in the decanter (2), overflows above the partition (3), and moves toward the overflow (12) which evacuated it.

Abstract: In the production of steel from pig iron melted and refined in a vessel, the pig iron is preheated in two phases. In the first preheating phase, the cold pig iron and hot gases recovered from the melting and refining vessel are moved simultaneously through a first and higher rotary tubular furnace whose lower open end is in communication with an upper open end of a second and lower rotary tubular furnace constituting a second preheating phase. The second furnace is heated from the outside to regulate the temperature of the pig iron to a desired value before it is introduced into the vessel from the second furnace.