Evaluation and Repair of Wrought Iron and - Purdue e-Pubs ...

80The carbon content present in the wrought iron was similar to the carbon contentin some, low carbon steels. Even though the wrought iron contained the same amount ofcarbon as some low carbon steel, the properties of wrought iron are much different to thatof steel. This is due to the manufacturing process of wrought iron. In this manufacturingprocess the iron ore is not completely heated until it is fluid in nature and completelyabove the eutectoid transition temperature needed for pearlite to form and impurities toseparate. Instead, the iron is heated until it achieves a pasty condition at a lowertemperature; at this temperature pearlite is not able to be formed and impurities are noteasily or fully removed. Therefore, wrought iron consists mainly of ferrite which hasbody-centered cubic (BCC) structure and a low solubility for carbon. Because of this andthe existence of many impurities throughout the iron, the strength of the wrought iron islower than common steel.A greater amount of phosphorous and sulfur was found in the wrought iron thanwhat is found in common steels. The amount of phosphorous in the wrought iron wasbetween 0.25 and 0.36 percent by weight and the amount of sulfur in the material wasbetween 0.062 and 0.072 percent by weight. The high amounts of phosphorous andsulfur in the wrought iron decreases the overall strength of the material.Ferrite iron can hold approximately 0.1 percent phosphorous in solution at roomtemperature. Phosphorous in excess of this amount exists as Fe 3 P particles embedded inthe structure of ferrite. Phosphorous tends to decrease the fracture toughness in steelespecially if the steel is to be heat treated, where the amount of phosphorous is usuallylimited to 0.04% (Linnert, 1994). The addition of phosphorous increases themachinability of iron and was commonly added in low carbon steels for this reason.The presence of sulfur in the metal also affects the overall tensile strength of themetal. Sulfur creates hot shortness which creates cracks dispersed though out the metal.Sulfur has a relatively low melting point and is insoluble in molten iron. When present inmolten iron, sulfur creates iron sulfide which also solidifies at a lower temperature than