This European Standard specifies the characteristics of railway wheels for use on European networks. Four steel grades, ER6, ER7, ER8 and ER9 are defined in this standard; for European freight wagon interoperability purposes only grades ER6, ER7 and ER8 are applicable. NOTE 1 Grade ER6 is not normally fit for the duty of application to freight wagons; it is normally applied in low axleload situations. Certain characteristics are defined according to a category 1 or a category 2. Category 1 is generally chosen when the train speed is higher than 200 km/h. Freight vehicles running at speeds lower than 200 km/h generally use wheels of Category 2. These categories can sometimes be subdivided, depending upon the characteristics. This standard is applicable to solid forged and rolled wheels which are made from vacuum degassed steel and have a chilled rim. They are to have already been used in commercial conditions on a European network in a significant quantity, or to have satisfied a technical approval procedure according to EN 13979-1 for their design. NOTE 2 The definition of other wheels may be found in other documents, such as UIC leaflets or ISO standards. NOTE 3 The technical approval procedure is not within the scope of this standard. NOTE 4 "Rim-chilled" describes heat treatment of the rim, the aim of which is to harden the rim and to create compressive residual stresses in the rim.