Conceptually, corrosion refers to the chemical or electrochemical degeneration of construction materials under environmental impacts. Corrosion is a characteristic of each material. In the case of steel, we generally speak of rust. The rusting behaviour of steel depends on its chemical composition, the environment, structural considerations and an appropriate design of the construction. In order to control the corrosion behaviour, weathering steels are alloyed with small amounts of chromium, nickel, copper and phosphorus. The environment, too, has a signi cant eect on the corrosion behaviour.
When the surface of weathering steel is exposed to outdoor air, the oxygen and moisture in the air produce a compact oxide layer, patina, developing on the surface, thus preventing the further propagation of corrosion. The graph in Fig. 1 illustrates the dierence between the corrosion rates of general structural steels and weathering steels.
Weathering steels can be cold formed the same as general structural steels of the corresponding grades. For strip rolled products, bending with the axis transverse to the major rolling direction is preferred. The suggested minimum bending radii for bending longitudinal to the rolling direction are given in Table 3. For applications calling for better forming properties, steels in accordance with Standard EN 10155 can be supplied with guaranteed angeability, or the COR-TEN AF grade can be used. Exacting forming operations are easier to carry out either by warm forming at a temperature under 600°C, or by hot forming at 800 – 1050°C.
Weathering steels are suitable for welding by all welding procedures. Elevated working temperatures are not needed when using dry welding consumables under favourable conditions. Although the recommended working temperature for welding weathering steels of over 15 mm thickness is 100 – 200°C, this preheating can be omitted in the case of steel grades S235J0W and S235J25W of any thickness. Capacitor Discharge (CD) stud welding can be used with copper coated steel studs, TIG welding with a corten welding wire is used to form a weld that oxidised in a similar manner. MIG welding for speed or to form a stitch weld for a structural application.