This is a good article. Follow the link for physical properties of steel pdf information. Iron is the base metal of steel.
In the body-centred cubic arrangement, there is an iron atom in the centre of each cube, and in the face-centred cubic, there is one at the center of each of the six faces of the cube. The carbon in typical steel alloys may contribute up to 2. Today, steel is one of the most common man-made materials in the world, with more than 1. 6 billion tons produced annually. The carbon content of steel is between 0. Plain carbon-iron alloys with a higher than 2.
With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. The excess carbon and other impurities are removed in a subsequent step. Even in a narrow range of concentrations of mixtures of carbon and iron that make a steel, a number of different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. It is a fairly soft metal that can dissolve only a small concentration of carbon, no more than 0. The inclusion of carbon in gamma iron is called austenite.
The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2. When steels with exactly 0. The carbon no longer fits within the FCC austenite structure, resulting in an excess of carbon. BCC iron called ferrite with a small percentage of carbon in solution. For steels that have less than 0.
No large inclusions of cementite will form at the boundaries in hypoeuctoid steel. The above assumes that the cooling process is very slow, allowing enough time for the carbon to migrate. Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on the carbon content, the martensitic phase takes different forms. Moreover, there is no compositional change so the atoms generally retain their same neighbors. In this case, expansion occurs.
If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. It is common for quench cracks to form when steel is water quenched, although they may not always be visible. Hypoeutectoid steel does not benefit from heat treatment. Annealing is the process of heating the steel to a sufficiently high temperature to relieve local internal stresses. It does not create a general softening of the product but only locally relieves strains and stresses locked up within the material. The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents. This rapid cooling results in a hard but brittle martensitic structure.