A steel production method in the steel and iron industry involves dividing a vertically falling solid slag stream which flows from a steelmaking furnace into individual streams, forcedly cooling the individual streams, dividing the individual streams into parts by cutting across the movement thereof, forcedly cooling the parts and transferring them to a belt conveyor on which the separate parts are forcedly cooled and transported away from the vessel. A shaped conveyor belt, on which the slag parts are crushed by means of a cylindrical roll, is used for additional crushing.