Anthracite Coal

Anthracite Coal Anthracite coal derives its name from the Greek word ‘anthrakít?s’, literally meaning ‘coal-like’.  It is frequently being referred as hard coal and is one of the four types of coals. Other types of coals are lignite coal, sub- bituminous coal and bituminous coal. Since anthracite coal had been subjected to the intense pressure and heat, it is the most compressed and hardest coal available. Being a hard coal, it contains greater potential to produce heat energy than softer, geologically ‘newer’ coal. As per ISO 11760:2005, anthracite coal is defined as the coal, synonymous with high-rank coal, having a mean random vitrinite reflectance, equal to or greater than 2.0 % but less than 6.0 %, or, preferably, a mean maximum reflectance, , less than 8.0 % for geologically unaltered coal. Geology and mining of anthracite coal Anthracite coal was formed from bituminous coal when great pressures had developed in the folded rock. Transformation of the bituminous coal into anthracite is called ‘Anthracitization’. It was formed during the Carboniferous Age, when the dense green vegetation that thrived during the tropical climate of the time fossilized. It is the oldest and cleanest type of coal. It is the rarest and most mature coal. It is a hard, compact variety of coal. It has the highest ranking amongst all the four types of coals. It has undergone the most metamorphosis. It has the highest fixed carbon content and the least impurities. It has the highest energy density amongst all types of coal. The formation of anthracite coal is shown in Fig 1. Fig 1 Formation of anthracite coal Anthracite coal normally occurs in old geological formations which have spent the longest time underground. It is the rarest and most mature coal which accounts for only around 1 % of the world’s total coal reserves. The major reserves of the anthracite coal are...

Tensile Testing of Steel...

Tensile Testing of Steel Sample of steel is subjected to a wide variety of mechanical tests to measure their strength, elastic constants, and other material properties as well as their performance under a variety of actual use conditions and environments. Tensile test is one of them. Other tests are hardness test, impact test, fatigue test, and fracture test. These mechanical tests are used to measure how a sample of steel withstands an applied mechanical force. The results of such tests are used for two primary purposes namely (i) engineering design (e.g. failure theories based on strength, or deflections based on elastic constants and component geometry), and (ii) quality control either by the producer of steel to verify the process or by the end user to confirm the material specifications. Uniaxial tensile test is known as a basic and universal engineering test to achieve material parameters such as ultimate tensile strength (UTS), yield strength (YS), % elongation, % area of reduction and young’s modulus. Tensile testing is done for many reasons. The results of tensile tests are used in selecting materials for engineering applications. Tensile properties are often included in material specifications to ensure quality. Tensile properties are also normally measured during development of new materials and processes, so that different materials and processes can be compared. Also, tensile properties are generally used to predict the behaviour of a material under forms of loading other than uniaxial tension. Safely withstanding the expected maximum load without permanent deformation (or to stay within the specified deflection) is a basic requirement for a steel product. The ‘resistance’ against the load is a function of the cross-section and the mechanical properties (or in other words the ‘strength’) of the steel material. Tensile testing is done to determine the mechanical...

Alloy Cast Irons

Alloy Cast Irons Alloy cast irons are the casting alloys which are based on the iron (Fe) – carbon (C) – silicon (Si) system. They contain one or more alloying elements intentionally added to improve one or more properties. The addition to the ladle of small amounts of substances such as ferrosilicon (Fe-Si), cerium (Ce), or magnesium (Mg)) that are used to control the size, shape, and/or distribution of graphite particles is termed as inoculation. The quantities of material used for inoculation neither change the basic composition of the solidified cast iron nor alter the properties of individual constituents. Alloying elements, including Si when it exceeds about 3 %, are usually added to increase the strength, hardness, hardenability, or corrosion resistance of the basic iron and are often added in quantities sufficient to affect the occurrence, properties, or distribution of constituents in the microstructure. In gray and ductile cast irons, small amounts of alloying elements such as chromium (Cr), molybdenum (Mo), or nickel (Ni) are added primarily to achieve high strength or to ensure the attainment of a specified minimum strength in heavy sections. Otherwise, alloying elements are used almost exclusively to enhance resistance to abrasive wear or chemical corrosion or to extend service life at elevated temperatures. Classification of alloy cast irons Alloy cast irons can be classified as (i) white cast irons, (ii) corrosion resistant cast irons, and (iii) heat resistant cast irons (Fig 1). Fig 1 Classification of alloy cast irons White cast irons White cast irons are so named because of their characteristically white fracture surfaces. They do not have any graphite in their microstructures. Instead, the C is present in the form of carbides, mainly of the types Fe3C and Cr7C3. Frequently, complex carbides such as (Fe,Cr)3C and (Cr,Fe)7C3,...

Cast Steels and Steel Castings...

Cast Steels and Steel Castings Steel casting is a specialized form of casting involving various types of steels. Steel castings are used when cast irons cannot deliver enough strength or shock resistance. A steel casting is the product formed by pouring liquid steel into a mould cavity. The liquid steel cools and solidifies in the mould cavity and is then removed for cleaning. Heat treatment may be needed to meet desired properties. This process provides the near net shape and mechanical properties required for meeting the specifications. The differences between steel castings and wrought steels are principally in the method of production. In the case of wrought steel cast ingots, slabs, blooms, and billets are mechanically worked to produce flat, sectional or tubular products. However, steel castings are produced in the final product (near net shape product) form without any intermediate mechanical working. The making of a steel casting is a long and complex process. A large investment in capital equipment is required for the melting of steel, manufacturing of cores and moulds and the cleaning and heat treating of castings. Additional major investments for support equipment and facilities are required for sand reclamation systems, dust collection devices and bulk material handling systems etc. Steel castings are used for vitally important components in the mining, railways, automotive, construction, military, and various industries including oil and gas industries. Steel castings are specified for applications which require weldability, abrasion resistance, high strength, low and high temperature service and corrosion resistance. Though there are large numbers of steel foundries, yet due to the diversity of market requirements such as size, tolerances, chemistry, volume, etc., a single foundry cannot serve all of the market and each foundry tends to specialize in a portion of the total market. Some of the specialized...

Tool Steels

Tool Steels The term tool steel is a generic description for those steels which have been developed specifically for tooling applications. These steels are used for making tools, punches and dies etc. Tools used for working steels and other metals must be stronger and harder than the steels or the materials they cut or form. Normally tool steels are known for their distinctive toughness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures (red hardness). Some of the operations that tool steels are used for include drawing, blanking, mould inserts, stamping, metal slitting, forming and embossing, although their use is not limited to just these areas. The metallurgical characteristics of various compositions of tool steels are extremely complex. There are hundreds of different types of tool steels available and each may have a specific composition and end use. Tool steels are mainly medium to high carbon steels with specific alloying elements added in different amounts to provide it special characteristics. The carbon in the tool steel is provided to help harden the steel to greater hardness for cutting and wear resistance while alloying elements are added to the tool steel for providing it greater toughness or strength. In some cases, alloying elements are added to retain the size and shape of the tool during its heat treat hardening operation or to make the hardening operation safer and to provide red hardness to it so that the tool retains its hardness and strength when it becomes extremely hot. Various alloying elements in addition to carbon are chromium (Cr), cobalt (Co), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), and vanadium (V). The effect of the alloying elements on the properties of tool steels is as follows. Chromium –...