Weathering steels (WS), also known as low‐alloy steels, are steels with a carbon content of less than 0.2 wt. % to which mainly Cu, Cr, Ni, P, Si and Mn are added as alloying elements to a total of no more than 3‐5 wt. % . The enhanced corrosion resistance of WS in relation to mild steel or plain carbon steel (CS) is due to the formation in low aggressive atmospheres of a compact and well‐adhering corrosion product layer known as patina. This definition, however, has not remained unchanged but has evolved as new WS compositions have been developed to achieve improved mechanical properties and/or withstand increasingly aggressive atmospheric conditions from the corrosion point of view, especially in marine environments. The American Society for Testing and Materials (ASTM) has standardised different alloy compositions for WS, from an initial 1.5% total weight of alloying elements added in the first standardised WS A‐242 , to 5% in the last standardised WS A 709‐HPS 100W , which is at the limit of the composition of intermediate alloy steels.