What is the martensitic transformation?

What is the martensitic transformation?

Martensitic transformation of shape memory alloys is a shear-like mechanism which takes place below the transition temperature. The martensitic transformation can be induced by mechanical forces or by temperature changes in a cooling process.

What are the characteristics of martensitic transformation?

2. Characteristics of Martensitic Transformation in Steels:

  • Diffusionless Transformation:
  • Martensite Forms by Shear (or Displacive) Mechanism Indicated by Surface Relief of Polished Surface (Which Indicates Highly Crystallographic Nature of Transformation):
  • Ms Temperature:
  • Athermal Transformation:

What is martensitic transformation in steel?

Martensite is an exceptionally hard phase of steel. To form martensite, steel must first be heated to very high temperatures to form a high-temperature phase called austenite. Martensite forms when austenite is cooled very quickly, for instance, by placing the hot metal in water.

Is martensitic transformation reversible?

Martensitic transformations can be irreversible, as seen in steels upon quenching, or they can be reversible, such as those observed in shape-memory alloys. In the latter case, the microstructures formed on cooling are easily manipulated by loads and disappear upon reheating.

Is martensite FCC or BCC?

Martensite is a metastable interstitial solid solution of carbon in iron. It is formed when austenite is quenched rapidly to room temperature and may have a bcc structure at low carbon concentrations or a body centered tetragonal structure at high carbon concentrations.

What is the meaning of martensitic?

Definition of martensite : the hard constituent that is the chief component of quenched steel.

At what temperature does martensite form?

Martensite, the hardening constituent in quenched steels, is formed at temperatures below about 200°C. The regions of the austenite which have transformed to martensite are lenticular in shape and may easily be recognized by etching or from the distortion they produce on the polished surface of the alloy.

Is martensite FCC or bcc?

Why martensite is so hard?

Because the cooling rate is so sudden, carbon does not have enough time for diffusion. Therefore, the martensite phase consists of a metastable iron phase oversaturated in carbon. Since the more carbon a steel has, the harder and more brittle it is, a martensitic steel is very hard and brittle.

Is martensite a bcc?

What is the fundamental thermodynamic equation for thermoelastic transformation?

A fundamental thermodynamic equation is derived for thermoelastic martensitic transformations. It describes the mutual equilibrium between the two phases at every temperature and applied stress, taking into account internal interaction between domains, the existence of interfaces and dissipative effects associated with motion of boundaries.

What type of calorimeter is used for thermally-induced transformations at constant stress?

For thermally-induced transformations at constant stress (studied in 3.1), a differential heat-flow scan- ning calorimeter [27] should be built around a tensile specimen subjected to a movable constant load.

What is a transformation at constant strain?

A transformation proceeding at constant strain, represented by the vertical solid line, starts with the system strained in the parent phase at high temperatures, proceeds by cooling through the two-phase region and finishes when the whole material is transformed into martensite.