The result of a previous eight-year atmospheric exposure of steels at seven sites in China showed significant effect of variation of Cu, P, and S content within the allowance in carbon steels and copper-free low-alloy steels in corrosive environments. To verify this phenomenon, steels with 0.035% phosphorous and 0.2% copper were prepared and tested. Accelerated corrosion tests and four year, three period atmospheric exposure at Beijing, Qingdao, Wuhan, Jiangjin, Guangzhou, Qionghai and Wanning, seven typical environmental sites in China, were made on these steels together with ordinary mild steels. The results showed that the new steels were more corrosion resistant than ordinary steels at all exposure sites and in the alternating immersion accelerated corrosion tests. The effect is bigger at Qingdao, Jiangjin, characterized by serious pollution of marine salt and acid rain. The effects were most significant at Wanning, a site of high humidity and heat in addition to marine salt pollution. Alternate immersion accelerated corrosion tests showed an obvious advantage of the steels over the common mild steels. Suggestion was made of an introduction of a minimum content of phosphorous and copper in the standard mild steels. Combined with a low sulphur content, the routine request now for steels, it would make any ordinary steel a weathering steel—economic weathering steel—without additional cost, a way of avoiding enormous amounts of corrosion loss for the whole world.