Comparison of Steel with Aluminum...

Comparison of Steel with Aluminum Steel is an alloy of iron and other elements, primarily carbon. It is most commonly produced by reduction of iron ore. Carbon, the most common alloying material in steel, acts as a hardening agent, preventing any dislocations within the iron atom crystal lattice from separating and sliding past each other thus making steel more durable. By varying the amount of alloying elements and the form of their presence in the steel, one can control qualities such as hardness, ductility, and tensile strength of steel. Though, steel has been known to be around since 4,000 years ago, it was not widely produced until the 17th century. Its mass production started due to the introduction of the Bessemer process during 1850s. This process made steel production cheaper, efficient and easier. Production of steel is a two stage process. First iron is produced by reduction of iron ore. This iron is then converted into steel by oxidizing the impurities. (Fig 1) Fig 1 Production process of steel Steel is widely used in construction and other applications because of its high tensile strength and low cost. Iron is the basic component of steel. Composition of steel mainly consists of iron and other elements such as carbon, manganese, silicon, phosphorus, sulphur, and alloying elements. A large number of elements in wide ranging percentages are used for the purpose of alloying of steels. Variations in chemical composition of steels are responsible for a great variety of steel grades and steel properties. Each element that is added to the basic steel composition has some effect on the properties of the steel and how that steel reacts to the processes of working and fabrication of steels. The chemical composition of steel also determines the behaviour of steel in...

Steels as a Material for Rail Tracks...

Steels as a Material for Rail Tracks Railways were originally uniquely identified with the material of their initial construction and now are technically identified by the characteristic contact of ?steel wheel on steel rail?. The phrase ?Railways need steel ? steel needs railways?, defines the relationship between steel industry and the railways. Presently railways rely on a wide variety of steels for its materials requirement. It is since steel meets the requirements of cost, weight, reliability, crashworthiness, maintainability and inspection required by the railways. Large varieties of steels are used by railways for its requirement for (i) rolling stock (locomotives, coaches, and wagons), (ii) rail tracks (permanent way), (ii) electric traction, and (iv) infrastructure. A wide variety of steels is needed by railways. These include flat products, structural products, bar and wire products, special products like rails, wheels and axles, tubular products and steels for reinforcement. Steels required by railways are in the form of castings, rolled products and fabricates products. The quality of steels needed by railways varies with the application. The quality of steels used are mild steel, other plain carbon steels, alloy steels, high strength steels, wear resistant steels, corrosion resistant steels, spring steels, electrical steels, and stainless steels etc. Further some steels need special processing to meet the specific requirements of railways. The requirement of various steels is getting updated on a continuous basis with the advancement of rail engineering. For this, railways and the steel industry work in close co-ordination with each other. The rail track is known as a stable structure. It ensures the transportation of trains through providing a dependable surface for their wheels. As to the development of rail track, it has a long history. The first rail track was made of wood and had continued...

Oxygen and Steels

Oxygen and Steels  Oxygen (O) (atomic number 8 and atomic weight 15.999) has density of 1.429 gm/litre at standard temperature and pressure. Melting point of oxygen is -218.79 deg C and boiling point is – 182.96 deg C. It is a colourless gas but the colour of liquid oxygen is pale blue. The phase diagram of the Fe-O binary system is at Fig 1. Fig 1 Fe- O binary phase diagram  There is a very strong relationship between oxygen  and steel. Oxygen is first used in the steel making process which is a controlled oxidation process. Excess oxygen going to steel during steel  making process,  if not properly taken care of, is source of many steel defects like porosity, inclusions etc. Oxygen is used in the processes of cutting, lancing, scarfing and welding of steels. Oxygen is also the cause of steel destruction by the processes of rusting, scaling and corrosion. Further transport of oxygen takes place in cylinders, tanks and pipelines made of steel. Oxygen is also used (oxy-fuel process) for heating of the steel. During steel making process, the main sources of oxygen in steel are as follows. Oxygen used for blowing in the steel making process Use of oxidizing slags and oxidizing materials ( ores, sinter etc.) during steel making processes Atmospheric oxygen dissolves in the liquid steel during steel tapping and casting operations Oxidizing refractories used in various vessels for holding liquid steel in the process of steel making Rusted and wet scrap Solubility of oxygen in liquid steel is 0.23 % at the steel making temperatures ( 1600 – 1700 deg C). However it decreases during cooling down and then drops sharply during solidification of steel reaching a level of 0.003 % in solid steel. Solubility of oxygen in steel...

Sulphur in Steels

Sulphur in Steels  Sulphur (S) (atomic number 16 and atomic weight 32.066) has density of 2.05 gm/cc. Monoclinic S melts at 119.25 deg C and boils at 444.6 deg C. However, S and iron (Fe) are miscible, and Fe-S binary system at one atmosphere of pressure forms a liquid at temperatures as high as 1800 deg C, far above the boiling point of S alone. Fig 1 is the phase diagram of the Fe-S binary system at 1 atmosphere of pressure.  Fig 1 Fe-S phase diagram S is an element which is always present in steel in small quantities. S in steel is introduced through iron ore and fuel (coal and coke). The removal of S during steel making is a tedious and difficult process. S is normally regarded as an impurity in steel and is required to be reduced to the limits of practicality. However steels which are to be machined need a certain minimum S content for proper chip formation. Where machining constitutes a major fraction of the end products cost, many types of steel (carbon, alloy, and less often stainless) are intentionally resulphurized just for this reason. (refer http://ispatguru.com/free-cutting-steels/) Except in those cases where it is added for machinability, or where residual S content of around 0.040 % maximum is tolerable, the usual aim during iron and steel making is to reduce S to low levels, consistent with mechanical property requirements. For high strength (HS) steel plates and for some special bar quality (SBQ) steel products, this may mean removing the S to a level of 0.005 % maximum. There are several methods which are widely used for achieving this level of S. Further, efficient removal of S from liquid steel or iron depends on specific metallurgical and thermodynamic conditions. Though...

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,...