Author: Haroon Khalil
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NORMALIZING
Normalizing is a process of heating about 30–50°C above higher critical point for the time duration of 15 min and cooling in still air. The purposes of the process normalizing are: (a) to reduce grain size of steel, (b) to remove internal stress caused by working, and (c) to improve some of the mechanical properties.…
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TTT (TIME–TEMPERATURE–TRANSFORMATION) DIAGRAM
The time–temperature–transformation curves correspond to the start and finish of transformations which extend into the range of temperatures where austenite transforms to pearlite (Figure 24.2). Above 550°C, austenite transforms completely to pearlite. Below 550°C, both pearlite and bainite are formed and below 450°C, only bainite is formed. The horizontal dotted line that runs between the two…
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IRON–CARBON PHASE DIAGRAM
Iron–carbon (Fe–C) phase diagram shows the solubility of carbon in iron at different temperatures and corresponding structure of the steel. For describing the Fe–C phase diagram, the equilibrium between Fe and Fe–C is considered as metastable. The larger phase field of γ-iron (austenite) compared with that of α-iron (ferrite) reflects the greater solubility of carbon, with a…
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INTRODUCTION
Heat treatment is a process to control the mechanical properties of engineering materials by heating, cooling, and alloying the metal as per requirement. It deals with change in properties by alloying different elements to the metal at various temperatures. The various mechanical properties such as hardness, toughness, ductility, machinability, and grain refinement are controlled by…
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PLASMA ARC MACHINING (PAM)
Plasma arc can produce a temperature as high as 33,000°°C. Plasma refers to a gas which has been raised to such a high temperature that it gets ionized and becomes electrically conductive. The plasma torch consists of a conversed focus of arc that operates between tungston electrode and workpiece. The torch is directed onto the…
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Principle of Electro-discharge Machining
When a discharge takes place between two points of the anode and the cathode, the intense heat generated near the zone melts and evaporates the materials. For improving the effectiveness, the workpiece and tool are submerged in a dielectric fluid as shown in Figure 23.9. It has been observed that both the electrodes are made of…
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ELECTRO-DISCHARGE MACHINING
In this machining process, metal removal takes place due to erosion caused by electric spark. This process may be used for machining any material, irrespective of its hardness, which is an electrical conductor. The rate of metal removal and the resulting surface finish can be controlled by proper variations in the energy and the duration…
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LASER BEAM MACHINING
Laser (Light Amplification by Stimulated Emission of Radiation) is a highly coherent (in space and time) beam of electromagnetic radiation with wavelength varying from 0.1 to 70 mm. However, the power requirement for a machining operation restricts the effectively usable wavelength ranges to 0.4–0.6 mm. Because of the fact that the rays of a laser…
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ELECTRON BEAM MACHINING (EBM)
Electron beam machining is also a thermal process of material removal. Here, a stream of high-speed electrons impinges on the work surface whereby the kinetic energy, transferred to the work material, produces intense heating. Depending on the intensity of the heat thus generated, the material can melt or vaporize. Very high velocity of electron beam…