Generation Transport and Uses of Mill Scale Sep23

Generation Transport and Uses of Mill Scale...

Generation Transport and Uses of Mill Scale  Mill scale is the flaky surface of hot worked steel and is formed by the oxidation of the steel surface during reheating, conditioning, hot rolling, and hot forming operations. It is one of the wastes generated in steel plants and represents around 2 % of the produced steel. It is a hard brittle coating of several distinct layers of iron oxides formed during the processing of steel and composed mainly of iron oxides and may contain varying amounts of other oxides and spinels, elements and trace compounds. It flakes off the steel easily. Characteristics of mill scale Mill scale is normally present on rolled steel and is frequently mistaken for a blue coloured primer. The very high surface temperature combined with high rolling pressures result in a smooth, bluish grey surface. Under visual inspection, mill scale appears as a black metal powder made up of small particles and chips. Its physical state is solid and powdered. The specific gravity of mill scale is in the range of 5.7 to 6.2. Mill scale’s melting point is around 1370 deg C and boiling point is around 2760 deg C. It has a stable state and is insoluble in water and alkalis but soluble in most of strong acids. It is normally classified as non dangerous waste material. Fig 1 shows a small pile of mill scale. Fig 1 Small pile of mill scale  The size of the mill scale normally varies from dust size in microns up to usually 6 mm. The average mill scale obtained during the hot working of steels has iron content ranging from 68 % to 72 %. The iron in the mill scale is present in different chemical forms as given below. Magnetite, Fe3O4,...

Phosphorus in Steels

Phosphorus in Steels  Phosphorus (P) (atomic number 15 and atomic weight 30.974) has density of 1.82 gm/cc. It has a melting point of 44.1 deg C and boiling point of 280 deg C. The iron (Fe) – P phase diagram is shown in Fig 1. Fig 1 Fe- P phase diagram P is normally considered an undesirable impurity in steels. It is present in varying concentrations in iron ore, is retained in hot metal, but is eliminated early in the steelmaking process. P oxidizes readily and is removed from steel as P2O5, which is taken up by the oxidizing slag, before the oxidation of carbon takes place. Carryover of any P2O5 containing oxidizing slag can result in P reversion to the steel in subsequent steelmaking operations. In normal commercial steels, residual P content is usually  at a level of 0.05 % max, but concentrations as low as 0.005 % are not unusual. P is readily removed only in basic steelmaking processes. Acidic processes must therefore begin with low P raw materials. It was the ability to remove this element that led to the widespread adoption of the steelmaking by the basic open hearth, electric arc furnace, basic Bessemer converter and subsequently basic oxygen furnace (BOF) processes. P is sometimes added intentionally to the steel to improve strength, machinability and atmospheric corrosion resistance. P is added to the steel in the form of ferro-phosphorus (Fe-P), containing 23 % to 26 % P. Fe-P fines are usually briquetted, after using a binder. Fe-P is capable of oxidizing the residual silicon to silica, thus enabling it to float out to the ladle slag during steel making. The intent is to reduce the concentration of residual siliceous inclusions, which are detrimental to machinability. Fe-P is normally added to the...

A Learning Organization and its Characteristics...

A Learning Organization and its Characteristics  A learning organization is the term given to an organization which facilitates the learning of its employees so that the organization can continuously transforms itself. Learning organization develops as a result of the pressures which are being faced by the organizations these days for enabling them to remain competitive in the present day business environment. The learning organization concept was coined through the work and research of Peter Senge and his colleagues. The learning organization encourages to a more interconnected way of thinking. Such organization becomes more like a community for which employees feel a commitment to. Employees work harder for the organization since they are committed to it. The concept of the learning organization is commonly hailed as panacea for organizational success in a dynamic global economy. The concept of learning organization is increasingly relevant given the increasing complexity and uncertainty of the organizational environment. In the words of Senge: “The rate at which organizations learn may become the only sustainable source of competitive advantage”. People have found the idea of a learning organization to be inspiring, yet difficult to implement. It frequently involves deep change in the mind sets of employees as well as the culture of the organization and the society. Such change does not occur overnight. Definitions of learning organization The following are some of the available definitions of the learning organization. Peter Senge has defined the learning organization as the organization “in which you cannot not learn because learning is so insinuated into the fabric of life.” According to him the learning organizations are “ …organizations where people continually expand their capacity to create the results they truly desire, where new and expansive patterns of thinking are nurtured, where collective aspiration is set free, and where people are continually learning to see the...

Metal Coatings of Steels Sep18

Metal Coatings of Steels...

Metal Coatings of Steels  Metallic coated steels are defined as a steel substrates coated with a layer of zinc, Zn/Al (zinc/aluminum) alloy, Zn/Si (zinc/silicon) alloy, or pure Al etc. The schematic arrangements of metal coating structure with and without passivation is shown in Fig 1, Fig 1 Metal coating structure with and without passivation  Metal coatings of steels enhance the life and the performance of the steels. They provide the most effective and economical way of protecting steels against corrosion. Metal coated steels offer unique combination of properties which include high strength, formability, light weight, corrosion resistance, aesthetics, recyclability and low cost. There are several processes for metal coating of steels as given below. The hot dip coating process, whereby the steel strip is immersed in a bath of molten metal. The composition of the molten metal (Zn, Zn/Al, Al/Si, or pure Al etc.) determines the nature of the metal coating. The electro-galvanizing process, in which metal is deposited electrolytically on the cold steel strip. Coating under vacuum, such as PVD (physical vapour deposition), CVD (chemical vapour deposition) etc. Hot dip coating processes are the most popular processes for the metal coating of steel strips. Normally continuous coating lines are employed for the production of the metal coated steel products. Metallic coated steels produced in continuous coating lines have experienced a remarkable growth and continues to be used in increasingly varied new fields. This is due to their outstanding economic, technological and environmental advantages. .The wide range of metallic coated steel products available today meets the requirements of all sectors. The following are the parameters which govern the choice of the metal coated steel material. Quality or grade of the steel substrate Type of metal coating Mass or thickness of the metal coating Surface...

Copper in Steels

Copper in Steels  Copper (Cu) provides interesting alloying advantages to steel and steel welds. Cu (atomic no. 29 and atomic weight 63.54) has a density of 8.96 gm/cc. The melting point of Cu is 1083 deg C while the boiling point is 2570 deg C. Cu is normally added to steel to increase corrosion resistance. Experimentation with the addition of Cu to structural steels for its ability to impart good atmospheric corrosion resistance properties began in the year 1916 in the USA. The first commercial use of Cu bearing steel as atmospheric corrosion resistant steel was during the period 1933 to 1935. Cu is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20 %. The atmospheric corrosion resistance steels are also called weathering steels. Addition of Cu in steelmaking Cu is added to steel in the form of pigs, refined ingots or as copper and nonferrous alloy scrap. Any Cu already present in the steel scrap charge is carried over into the liquid steel with little or no loss. Scrap electric motors containing usually 10-15 % Cu are often used as a source of Cu during steelmaking. Cu can be added either in the steelmaking furnace or in the teeming ladle. Both techniques of Cu addition give very high recoveries. Losses, if any, are due to the mechanical reasons. When addition of Cu is made in the steelmaking furnace, it should be done before the end of decarburization. Effects of copper on steels The ability of Cu bearing steel to withstand atmospheric corrosion is not the major reason which provides the impetus for the development of Cu bearing steels today. Until recently, it was not fully recognized that along with the improved corrosion resistance, the precipitation of Cu can make a significant...