Abstract: The liquid steel slag (2) is poured in at least four successive layers (6-8), comprising a lowermost layer (6), an uppermost layer (7) and at least two intermediate layers (8), in a reservoir (3) and the layers of liquid steel slag are allowed to solidify. After having applied the uppermost layer (7), the solidified steel slag is cooled down more quickly by means of water. The average temperature of each of the intermediate layers (8) is kept at least until the start of the water cooling step, and this for at least one hour, above a minimum temperature which is equal to or higher than the temperature at which ?-dicalcium silicate is formed. In this way, more crystalline phases different from dicalcium silicates are formed so that the formation of fines by the transition of ? into ?-dicalcium silicates can be considerably reduced. A glassy material and/or a phosphorus containing compound is preferably added to the liquid slag to further reduce the formation of fines.