Martensite


Also found in: Dictionary, Thesaurus, Wikipedia.
Related to Martensite: austenite

martensite

[′mär‚ten‚zīt]
(metallurgy)
A metastable transitional structure formed by a shear process during a phase transformation, characterized by an acicular or needlelike pattern; in carbon steel it is a hard, supersaturated solid solution of carbon in a body-centered tetragonal lattice of iron.

Martensite

 

the structure of crystalline solids arising as the result of a slip, diffusionless polymorphic transformation on cooling. It is named for the German specialist in physical metallurgy A. Martens (1850-1914).

As a result of a lattice deformation, known as cooperative displacement, during the transformation, a relief appears on the surface of the metal. Internal strain arises in the bulk and plastic deformation occurs, which limit crystal growth. The rate of growth reaches 103 m/sec and is independent of temperature. Hence, the rate of martensite formation is usually limited by crystal nucleation. The reaction of the internal strain shifts crystal nucleation greatly below the thermodynamic phase equilibrium point and may stop the transformation at constant temperatures. Thus, the amount of martensite formed usually increases with an increase in supercooling.

Since the elastic energy must be minimal, martensite crystals take the shape of plates (needles in cross section) regularly oriented relative to the initial lattice. The internal strain is also reduced by plastic deformation and thus the crystal contains many dislocations (up to 1012 cm-2) or is split into twins with a thickness of 10-100 nanometers (100-1000 angstroms). Intragranular boundaries and dislocations strengthen martensite.

Martensite is a typical product of low-temperature polymorphic transformations in pure metals such as iron, cobalt, titanium, zirconium, and lithium; in solid solutions based on these metals; and in intermetallic compounds such as CuZn, Cu3Al, NiTi, V3Si, and AuCd.

Martensite in steel is a supersaturated Fe-C solution obtained by hardening from austenite. The ordered position of carbon atoms that results from martensite displacement transforms the body-centered lattice of a-iron from cubic to tetragonal. The distortion of the lattice near the interstitial atoms results in hardness. The tetragonality and the hardness increase with the carbon content. Hardness increases up to 1,000 HV (Vickers hardness).

Carbon martensite is the major structural component of most high-strength steels. The carbon content in the solid solution and the martensite subgranular structure change upon tempering, which is used for increasing the ductility of steel.

Carbon is the most important factor of martensite strength in steel. The strength of noncarbon maraging steel results from the separation of intermetallic compounds upon aging.

The physical characteristics of Fe-C martensite as an interstitial solid solution, the source of its high strength, and the kinetics of martensite formation were established by G. V. Kurdiumov.

M. A. SHTREMEL’

References in periodicals archive ?
The microstructure right in the ball or roller track can be examined under a microscope after etching with an acid solution to check for the presence of untempered martensite (Figure 3).
The only stress-strain curve with distinct linear deformation of stress-induced martensite is found at -20[degrees]C, thus the elasticity modulus for stress-induced martensite, [D.
This process makes your parts very dimensionally stable and allows them to cool at a rate that assists the transformation to martensite.
For comparison, Burstein's group also used the conventional method of removing martensite.
Martensite in quenched Fe-C steels and Engel-Brewer electron theory of crystal structures
The heat treated sintered component was found to have Forward Transition Martensite with rich nickel austenite at its surface.
Austenite morphology feature and nucleation mechanism during intercritical reheating of martensite steel, Jinshu Rechuli/heat Treatment of Metals 40: 68-72.
The strain induced martensite transformation in austenitic stainless steels Part 1- Influence of temperature and strain History.
The last approach focuses on the competing slip and twinning mechanisms during deformation-induced martensite transformation [2].
The resulting product microstructure consists of pure martensite.
The material is heat-treated at 880[degrees]C and oil-quench-hardened and it is tempered at 410[degrees]C for 90 minutes to get tempered martensite structure.
Concluding a comprehensive two-volume reference on phase transformations in steel, scientists and engineers in metals and materials consider such topics as the crystallography of martensite transformations in steels, shape memory in ferrous alloys, phase transformations in quenched and partitioned steels, first principles in modeling phase transformation in steels, the molecular dynamics modeling of martensitic transformations in steels, atom probe tomography for studying phase transformations in steels, and applying synchrotron and neutron scattering techniques for tracking phase transformations in steels.