High Purity, Low Residual, and Clean Steels

The term “clean steel” is commonly used to describe steels that have low levels of the solute elements sulfur, phosphorus, nitrogen, oxygen, and hydrogen; controlled levels of the residual elements copper, lead, zinc, nickel, chromium, bismuth, tin, antimony, and magnesium; and a low frequency of product defects that can be related to the presence of oxides created during the act of steelmaking, ladle metallurgy, casting, and rolling. This last part of the definition causes extreme problems to the steel manufacturer, as the definition of “clean” is not absolute but is based on the product formed from the casting and the in-service use or life of the product. In addition, the definition “clean” is comparative, as each customer of a steel producer has the ability to buy steel from around the world and compare the performance levels of a given product obtained from various suppliers. In this system, as steel is a commodity, the best steel producer defines the level of quality that is expected by a customer, and as steel producers are continually striving to produce “cleaner” steels, the cleanliness standard desired by the customer is continuously changing as a function of time and technological improvements. The term “clean steel” is therefore continually variable depending on the application and the competition between steel suppliers.