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Martensite has a lower density than austenite, so that the martensitic transformation results in a relative change of volume. [4] Of considerably greater importance than the volume change is the shear strain , which has a magnitude of about 0.26 and which determines the shape of the plates of martensite.
In metallurgy, quenching is most commonly used to harden steel by inducing a martensite transformation, where the steel must be rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. Rapid cooling prevents the formation of cementite structure, instead forcibly dissolving carbon atoms in the ferrite ...
When some carbon is present, and if cooling occurs quickly, some of the austenite will transform into martensite. Tempering or annealing will transform the martensitic structure into ferrite and carbides. Above about 17% Cr the steel will have a ferritic structure at all temperatures.
The pearlite takes on longer, deeper scratches, and either appears shiny and bright, or sometimes dark depending on the viewing angle. The martensite is harder to scratch, so the microscopic abrasions are smaller. The martensite usually appears brighter yet flatter than the pearlite, and this is less dependent on the viewing angle. [12]
Acicular ferrite steels: These steels are characterized by a very fine high strength acicular ferrite structure, a very low carbon content, and good hardenability. Dual-phase steels: These steels have a ferrite microstructure that contain small, uniformly distributed sections of martensite. This microstructure gives the steels a low yield ...
This reduces the amount of total martensite by changing some of it to ferrite. Further heating reduces the martensite even more, transforming the unstable carbides into stable cementite. The first stage of tempering occurs between room temperature and 200 °C (392 °F). In the first stage, carbon precipitates into ε-carbon (Fe 2,4 C). In the ...
Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). [1] First described by E. S. Davenport and Edgar Bain, [2] [3] it is one of the products that may form when austenite (the face-centered cubic crystal structure of iron) is cooled past a temperature where it is no longer thermodynamically stable with respect to ferrite ...
The structures form due to the precipitation of a single crystal phase into two separate phases. In this way, the Widmanstätten transformation differs from other transformations, such as a martensite or ferrite transformation. The structures form at very precise angles, which may vary depending on the arrangement of the crystal lattices.