Martensite

What is MARTENSITE? What does MARTENSITE mean? MARTENSITE meaning, definition & explanation

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What is MARTENSITE? What does MARTENSITE mean? MARTENSITE meaning -MARTENSITE pronunciation - MARTENSITE definition - MARTENSITE explanation - How to pronounce MARTENSITE? Source: Wikipedia.org article, adapted under https://creativecommons.org/licenses/by-sa/3.0/ license. Martensite, named after the German metallurgist Adolf Martens (1850–1914), most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by diffusionless transformation. It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in cross section, the lenticular (lens-shaped) crystal grains may be incorrectly described as acicular (needle-shaped). Martensite is formed in carbon steels by the rapid cooling (quenching) of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe3C). Austenite is ?-Fe, (gamma-phase iron), a solid solution of iron and alloying elements. As a result of the quenching, the face-centered cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon. The shear deformations that result produce a large number of dislocations, which is a primary strengthening mechanism of steels. The highest hardness of a pearlitic steel is 400 Brinell whereas martensite can achieve 700 Brinell. The martensitic reaction begins during cooling when the austenite reaches the martensite start temperature (Ms) and the parent austenite becomes mechanically unstable. As the sample is quenched, an increasingly large percentage of the austenite transforms to martensite until the lower transformation temperature Mf is reached, at which time the transformation is completed. For a eutectoid steel (0.78% C), between 6 and 10% of austenite, called retained austenite, will remain. The percentage of retained austenite increases from insignificant for less than 0.6% C steel, to 13% retained austenite at 0.95% C and 30–47% retained austenite for a 1.4% carbon steels. A very rapid quench is essential to create martensite. For a eutectoid carbon steel of thin section, if the quench starting at 750 °C and ending at 450 °C takes place in 0.7 seconds (a rate of 430 °C/s) no pearlite will form and the steel will be martensitic with small amounts of retained austenite. For steel 0-0.6% carbon the martensite has the appearance of lath, and is called lath martensite. For steel greater than 1% carbon it will form a plate like structure called plate martensite. Between those two percentages, the physical appearance of the grains is a mix of the two. The strength of the martensite is reduced as the amount of retained austenite grows. If the cooling rate is slower than the critical cooling rate, some amount of pearlite will form, starting at the grain boundaries where it will grow into the grains until the Ms temperature is reached then the remaining austenite transforms into martensite at about half the speed of sound in steel. In certain alloy steels, martensite can also be formed by the working and hence deformation of the steel at temperature, while it is in its austenitic form, by quenching to below Ms and then working by plastic deformations to reductions of cross section area between 20% to 40% of the original. The process produces dislocation densities up to 1013/cm2. The great number of dislocations, combined with precipitates that originate and pin the dislocations in place, produces a very hard steel (this property is frequently used in toughened ceramics like yttria-stabilized zirconia and in special steels like TRIP steels).

What is MARTENSITE? What does MARTENSITE mean? MARTENSITE meaning, definition & explanation

• Report rights infringement
• published: 14 Apr 2017
• views: 412

What is MARTENSITE? What does MARTENSITE mean? MARTENSITE meaning -MARTENSITE pronunciation - MARTENSITE definition - MARTENSITE explanation - How to pronounce MARTENSITE? Source: Wikipedia.org article, adapted under https://creativecommons.org/licenses/by-sa/3.0/ license. Martensite, named after the German metallurgist Adolf Martens (1850–1914), most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by diffusionless transformation. It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in cross section, the lenticular (lens-shaped) crystal grains may be incorrectly described as acicular (needle-shaped). Martensite is formed in carbon steels by the rapid cooling (quenching) of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe3C). Austenite is ?-Fe, (gamma-phase iron), a solid solution of iron and alloying elements. As a result of the quenching, the face-centered cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon. The shear deformations that result produce a large number of dislocations, which is a primary strengthening mechanism of steels. The highest hardness of a pearlitic steel is 400 Brinell whereas martensite can achieve 700 Brinell. The martensitic reaction begins during cooling when the austenite reaches the martensite start temperature (Ms) and the parent austenite becomes mechanically unstable. As the sample is quenched, an increasingly large percentage of the austenite transforms to martensite until the lower transformation temperature Mf is reached, at which time the transformation is completed. For a eutectoid steel (0.78% C), between 6 and 10% of austenite, called retained austenite, will remain. The percentage of retained austenite increases from insignificant for less than 0.6% C steel, to 13% retained austenite at 0.95% C and 30–47% retained austenite for a 1.4% carbon steels. A very rapid quench is essential to create martensite. For a eutectoid carbon steel of thin section, if the quench starting at 750 °C and ending at 450 °C takes place in 0.7 seconds (a rate of 430 °C/s) no pearlite will form and the steel will be martensitic with small amounts of retained austenite. For steel 0-0.6% carbon the martensite has the appearance of lath, and is called lath martensite. For steel greater than 1% carbon it will form a plate like structure called plate martensite. Between those two percentages, the physical appearance of the grains is a mix of the two. The strength of the martensite is reduced as the amount of retained austenite grows. If the cooling rate is slower than the critical cooling rate, some amount of pearlite will form, starting at the grain boundaries where it will grow into the grains until the Ms temperature is reached then the remaining austenite transforms into martensite at about half the speed of sound in steel. In certain alloy steels, martensite can also be formed by the working and hence deformation of the steel at temperature, while it is in its austenitic form, by quenching to below Ms and then working by plastic deformations to reductions of cross section area between 20% to 40% of the original. The process produces dislocation densities up to 1013/cm2. The great number of dislocations, combined with precipitates that originate and pin the dislocations in place, produces a very hard steel (this property is frequently used in toughened ceramics like yttria-stabilized zirconia and in special steels like TRIP steels).