Heating and melting furnaces, smelting and refining furnaces, and the vessels used to carry hot metal and molten steel are all lined with refractories. The main reason why these furnaces and vessels cannot be used continuously is the need for repair and replacement as a result of wear of the refractory lining. In other words, the life of the refractories determines the life of furnaces and vessels. Refractories for iron and steel production are used under very severe conditions, which include not only elevated temperatures, but also thermal shock caused by abrupt temperature changes. Further, they must possess high-temperature strength and wear resistance to the large momentum of impinging and turbulent metal flow. Refractories must also have the chemical stability to withstand attack by hot metal, molten steel, slag, and various fluxes. Refractories have a high melting point and good heat-insulating properties. Their basic composition comprises chemically stable substances such as magnesia, alumina, and silica which do not easily react with steel slags or fluxes. When binders are mixed with these refractories, the mixture, when used as it is, is called a monolithic refractory; when pressurized, compacted, and fired, it is called firebrick. The figure shows the progress in the unit consumption of refractories (weight of refractories consumed to produce one ton of crude steel) in Japan. Unit consumption decreased by as much as 60% from 1970 onwards for two main reasons: (i) changes in blowing and casting processes, which are typified by the change from the open hearth furnace to the BOF, and the replacement of ingot casting by the continuous casting process; and (ii) the extension of the life of refractories by improvement in their quality as well as progress in application techniques. An example of quality improvement of the furnace-bottom carbon brick in the BF is a decrease in the penetration of slag and iron achieved by adding silicon and a reduction in wear damage, by adding alumina. These measures have contributed greatly to extending the furnace life. At present, the BOF and EAF are lined mainly with fired magnesia-carbon brick which is a composite material that maintains the high corrosion resistance to basic slag and molten metal of magnesia, while enhancing thermal shock resistance, which was the weak point of magnesia brick, by adding carbon. Porosity is reduced by firing this brick at high temperatures in reducing atmosphere to prevent penetration by slag and molten steel. In the BOF, progress in related techniques, together with the above-mentioned improvements in quality, has also contributed to the extension of the life of refractories. Typical examples are, (i) zone lining, in which a brick of optimum composition is used for each zone of the furnace; (ii) slag-coating of the inner walls of the vessel; and (iii) decreasing thermal shock to the refractories by eliminating tilting of the vessel for reblowing, which has become possible due to the improved hit ratio achieved through improved BOF operation. At the continuous caster, the ladle and tundish are lined with a powdery monolithic refractory material which is applied by stamping or gunning. The consumption of monolithic refractories has been increasing because mechanization and automatization have made production and application easier, and since 1988, the use of monolithic materials has exceeded that of firebrick. Repeated use of ladles and tundishes while still hot from previous use has also extended their service life substantially because the thermal stress arising from cooling and reheating is minimized and hence resulting spalling of the refractories can be avoided. This repeated "as-hot" use has been made possible by the development of robotized automation of repair and maintenance of hot tundishes in combination with advanced hot gunning of refractories to points where damage is observed. Submerged entry nozzles used to deliver molten steel from the tundish into the mold are made of alumina-graphite refractories of higher corrosion resistance, which have replaced fused-silica refractories. Carefully thought-out refractory development for other equipment has also resulted in higher-quality refractories suitable for specific service environments.