A gas-collecting hood is arranged over the circular outlet or mouth of a top-blown steel-making converter. This hood comprises a cylindrical tube or duct with a smaller diameter than the mouth coaxial therewith. The tube is fitted with an outer trough which opens downwardly and sustains a crown vortex feeding back into the main stream. This trough has an outer wall or apron whose diameter is greater than that of the mouth and whose lower periphery is positioned below the bottom end of the tube, while being spaced above the converter.