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What is Normalizing?

Normalizing is a defined as softening process in which iron base alloys are heated 40 to 50°C above the upper-critical limit for both hypo and hyper eutectoid steels and held there for a specified period and followed by cooling in still air up to room temperature. Fig 1 shows the heating temperature ranges for normalizing process of both hypo and hyper carbon steel. Fig. 2 shows the structure obtained after normalizing of medium carbon steel. Objectives of Normalizing 1. To soften metals 2. Refine grain structure 3. Improve machinability after forging and rolling 4. improve grain size 5. Improve structure…

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Objectives of Heat Treatment

The major objectives of heat treatment are given as under 1. It relieves internal stresses induced during hot or cold working. 2. It changes or refines grain size. 3. It increases resistance to heat and corrosion. 4. It improves mechanical properties such as ductility, strength, hardness, toughness, etc. 5. It helps to improve machinability. 6. It increases wear resistance 7. It removes gases. 8. It improves electrical and magnetic properties. 9. It changes the chemical composition. 10. It helps to improve shock resistance. 11. It improves weldability. The above objectives of heat treatment may be served by one or more…

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Iron-Carbon Equilibrium Diagram

Fig. 1 shows, the Fe-C equilibrium diagram in which various structure (obtained during heating and cooling), phases and microscopic constituents of various kinds of steel and cast iron are depicted. The main structures, significance of various lines and critical points are discussed as under. Structures in Fe-C-diagram The main microscopic constituents of iron and steel are as follows: 1. Austenite 2. Ferrite 3. Cementite 4. Pearlite Austenite Austenite is a solid solution of free carbon (ferrite) and iron in gamma iron. On heating the steel, after upper critical temperature, the formation of structure completes into austenite which is hard, ductile…

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Transformation of Steel During Heating and Cooling Process

When a steel specimen is heated, its temperature rises unless there is change of state or a change in structure. Fig. 1 shows heating and cooling curve of steel bearing different structures. Similarly, if heat is extracted, the temperature falls unless there is change in state or a change in structure. This change of structure does not occur at a constant temperature. It takes a sufficient time a range of temperature is required for the transformation. This range is known as transformation range. For example, the portion between the lower critical temperature line and the upper critical temperature line with hypo and hyper eutectoid steels,…

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Allotropy Of Iron

In actual practice it is very difficult to trace the cooling of iron from 1600°C to ambient temperature because particular cooling rate is not known. Particular curve can be traced from temperature, time and transformation (TTT) curve. However allotropic changes observed during cooling of pure iron are depicted in Fig. 1. When iron is cooled from molten condition up to the solid state, the major allotropic changing occurs which are: 1539-1600°C Molten-Fe (Liquid state of iron) 1400-1539°C Delta-Fe (Body centered) 910-1400°C Gamma-Fe (FCC atomic arrangement and austenite structure) 770- 910°C Beta-Fe (Body centered-nonmagnetic) Up to 770°C Alpha-Fe (BCC atomic arrangement and ferrite structure) (i)…

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Micro structure of mild steel, pearlite eutectoid steel & high carbon steel

Fig. 1 shows micro structure of mild steel (0.2-0.3% C). White constituent in this figure is very pure iron or having very low free carbon in iron in form of ferrite and dark patches contain carbon in iron is chemically combined form known as carbide (Cementite). Cementite is very hard and brittle. Now if the dark patches of the above figure are further observed, a substance built up of alternate layer of light and dark patches is reflected in Fig. 2. These layers are alternatively of ferrite and cementite. This substance is called as pearlite and is made up of 87% ferrite and 13% cementite. But…

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Various Types of Heat Treatment Furnaces

What is Heat Treatment? Heat treatment is a heating and cooling process of a metal or an alloy in the solid state with the purpose of changing their properties. It can also be said as a process of heating and cooling of ferrous metals especially various kinds of steels in which some special properties like softness, hardness, tensile-strength, toughness etc, are induced in these metals for achieving the special function objective. It consists of three main phases namely; (i) heating of the metal (ii) soaking of the metal and (iii) cooling of the metal. The theory of heat treatment is based on the fact that a…

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Various Types of Testing of Metals

Metal testing is accomplished for the purpose of for estimating the behavior of metal under loading (tensile, compressive, shear, tortion and impact, cyclic loading etc.) of metal and for providing necessary data for the product designers, equipment designers, tool and die designers and system designers. The material behavior data under loading is used by designers for design calculations and determining weather a metal can meet the desired functional requirements of the designed product or part. Also, it is very important that the material shall be tested so that their mechanical properties especially their strength can be assessed and compared. Therefore…

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Metal Equilibrium Approach Through Recovery, Recrystallisation and Grain Growth Process

When metal is subjected to hot working and cold working processes, plastic deformation occurs which is an important phenomenon. Plastic deformation of metal distorts the crystal lattice. It breaks up the blocks of initial equiaxed grains to produce fibrous structure and  increases the energy level of metal. Deformed metal, during comparison with its un-deformed state, is in non-equilibrium, thermodynamically unstable state. Therefore, spontaneous processes occur in strain-hardened metal, even at room temperature that brings it into a more stable condition. When the temperature of metal is increased, the metal attempts to approach equilibrium through three processes: (i) recovery, (ii) recrystallisation,…

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Various Types of Properties of Engineering Material

Properties of Metals The important properties of an engineering material determine the utility of the material which influences quantitatively or qualitatively the response of a given material to imposed stimuli and constraints. The various engineering material properties are given as under. 1. Physical properties 2. Chemical properties 3. Thermal properties 4. Electrical properties 5. Magnetic properties 6. Optical properties, and 7. Mechanical properties These properties of the material are discussed as under. Physical Properties The important physical properties of the metals are density, color, size and shape (dimensions), specific gravity, porosity, luster etc. Some of them are defined as under. 1. Density: Mass…