Iron-carbon phase diagram, showing the conditions under which austenite (γ) is stable in carbon steel. QtubIronPillarJPG|thumb|right| Iron pillar at Delhi India containing 98% wrought iron]] Wrought iron is commercially pure Iron. Ductile iron, also called ductile cast iron, spheroidal graphite iron, or nodular cast iron, is a type of Cast iron invented in 1943 by In Physical chemistry, Mineralogy, and Materials science, a phase diagram is a type of graph used to show the equilibrium conditions

Austenite (or gamma phase iron) is a metallic non-magnetic solid solution of iron and an alloying element. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (about 727 °C); other alloys of steel have different eutectoid temperatures. Carbon steel, also called plain carbon steel, is Steel where the main alloying constituent is Carbon. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 It is named after Sir William Chandler Roberts-Austen (1843-1902). William Chandler Roberts-Austen, ( March 3, 1843 in Kennington - November 22, 1902

Behavior in Plain-Carbon Steel

As austenite cools, it often transforms into a mixture of ferrite and cementite as dissolved carbon falls out of solution. Ferrite or alpha iron ( α-Fe) is a Materials science term for Iron, or a Solid solution with iron as the main constituent with a Cementite or iron carbide is a Chemical compound with the formula Fe3C (or Fe2CFe and an Orthorhombic crystal structure Depending on alloy composition and rate of cooling, pearlite may form. Pearlite is a two-phased, lamellar (or layered structure composed of alternating layers of alpha-ferrite (88 wt% and Cementite (12% that occurs If the rate of cooling is very fast, the alloy may experience a slight lattice distortion known as martensitic transformation, instead of transforming into a mixture. Steel 035 water quenchedpng|thumb|200px|035%C Steel water-quenched from 870°C]] Martensite, named after the German metallurgist Adolf Martens (1850–1914 In this industrially very important case, the carbon is not allowed to blend out in the remaining melt due to the cooling speed, but is captured inside the FCC-structure of austenite, creating tension in the crystal when the alloy cools. The result is hard martensite. Steel 035 water quenchedpng|thumb|200px|035%C Steel water-quenched from 870°C]] Martensite, named after the German metallurgist Adolf Martens (1850–1914 The rate of cooling determines the relative proportions of these materials and therefore the mechanical properties (e. g. hardness, tensile strength) of the steel. Hardness refers to various properties of Matter in the Solid phase that give it high resistance to various kinds of shape change when Force Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms Quenching (to induce martensitic transformation), followed by tempering will transform some of the brittle martensite into bainite. A quench refers to a rapid Cooling. In Polymer chemistry and Materials science, quenching is used to prevent low-temperature processes such as phase Tempering is a Heat treatment technique for metals and Alloys In Steels tempering is done to "toughen" the metal by transforming brittle Bainite is a Phase that exists in Steel Microstructures after certain Heat treatments First described by Davenport E If a low-hardenability steel is quenched, a significant amount of austenite will be retained in the microstructure.

Stabilization

The addition of certain alloying elements, such as manganese and nickel, can stabilize the austenitic structure, facilitating heat-treatment of low-alloy steels. Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 In the extreme case of austenitic stainless steel, much higher alloy content makes this structure stable even at room temperature. In Metallurgy, stainless steel is defined as a Steel Alloy with a minimum of 11 On the other hand, such elements as silicon, molybdenum, and chromium tend to de-stabilize austenite, raising the eutectoid temperature. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24

Austenite transformation and Curie point

In many magnetic alloys, the Curie point, the temperature at which magnetic materials cease to behave magnetically, occurs at nearly the same temperature as the austenite transformation. The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906 This behavior is attributed to the paramagnetic nature of austenite, while both martensite and ferrite are strongly ferromagnetic. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it

Thermo-optical emission

A blacksmith causes phase changes in the iron-carbon system in order to control the material's mechanical properties, often using the annealing, quenching, and tempering processes. blacksmith is a person who creates objects from Iron or Steel by Forging the Metal; i In this context, the color of light emitted by the workpiece is an approximate gauge of temperature, with the transition from red to orange corresponding to the formation of austenite in medium- and high-carbon steel. In Physics, a black body is an object that absorbs all light that falls on it

Maximum carbon solubility in austenite is 2. 03% C at 1420 K (1147 °C).

References

"Physical Metallurgy Principles". Reed-Hill, Robert. 3rd. Edition. PWS Publishing. Boston. 1991.

See also

• Cementite
• Eutectoid
• Ferrite (iron)
• Martensite

External links

• Fe-Fe₃C phase diagram