Corten Steel ASTM A709 50W Plates Manufacturer. Marc Steel is a well-known supplier and manufacturer of ASTM A709-50W Corten Steel Plates, which are factory-made by using best quality of steel in dissimilar diameters and wall thickness. ASTM A709 50W Plates These ASTM A709-50W Corten Steel Sheets are as well used in a number of automobile and mechanical industries that are being ASTM A709-50W Weathering Steel Central Steel ServiceASTM A709-50W is a standard specification for structural steel primarily in the fabrication of steel bridges. ASTM A709-50W covers high strength, low allow steel structural shapes, plates and bars. The atmospheric corrosion resistance of this steel in most environments is substantially better than carbon steel with or without copper addition.