text: The material has a rough surface, so it can hold platings and coatings better than smooth steel. For instance, a galvanic zinc finish applied to wrought iron is approximately 25–40% thicker than the same finish on steel. In Table 1, the chemical composition of wrought iron is compared to that of pig iron and carbon steel. Although it appears that wrought iron and plain carbon steel have similar chemical compositions, that is deceptive. Most of the manganese, sulfur, phosphorus, and silicon in the wrought iron are incorporated into the slag fibers, making wrought iron purer than plain carbon steel.
  Amongst its other properties, wrought iron becomes soft at red heat and can be easily forged and forge welded. It can be used to form temporary magnets, but it cannot be magnetized permanently, and is ductile, malleable, and tough.
  Ductility
  For most purposes, ductility rather than tensile strength is a more important measure of the quality of wrought iron. In tensile testing, the best irons are able to undergo considerable elongation before failure. Higher tensile wrought iron is brittle.
  Because of the large number of boiler explosions on steamboats in the early 1800s, the U.S. Congress passed legislation in 1830 which approved funds for correcting the problem. The treasury awarded a $1500 contract to the Franklin Institute to conduct a study. As part of the study, Walter R. Johnson and Benjamin Reeves conducted strength tests on boiler iron using a tester they had built in 1832 based on a design by Lagerhjelm in Sweden. Because of misunderstandings about tensile strength and ductility, their work did little to reduce failures.
  The importance of ductility was recognized by some very early in the development of tube boilers, evidenced by Thurston's comment: