martensitic

Martensitic is an adjective used in materials science to describe a material that has undergone a martensitic transformation, a diffusionless, solid-state phase change from a high-temperature phase known as austenite to martensite. This transformation is typically rapid and can be induced by quenching or by mechanical deformation. It is characterized by a coordinated displacive shift of atoms, resulting in a lattice distortion with little atomic diffusion.

In steel, martensite forms when austenite is cooled quickly enough to pass below the Ms temperature. The resulting martensite is a body-centered tetragonal phase that is often supersaturated with carbon and other alloying elements. The microstructure commonly appears as needle-like or plate-like regions and is associated with markedly increased hardness and strength but reduced toughness. The extent of transformation and the final properties depend on carbon content, alloying elements, and the heat-treatment sequence, including tempering to improve toughness and reduce brittleness. Transformation temperatures are described by Ms, Mf (cooling), and As, Af (heating).

Martensitic transformations also occur in other alloys and are central to the behavior of certain shape memory alloys, such as nickel-titanium (Nitinol), where reversible martensitic changes enable shape memory and superelastic effects. Martensitic stainless steels are another class that can form martensite through heat treatment, offering high hardness and strength with specific corrosion resistance.

Overall, the term martensitic describes materials whose properties and microstructure have been shaped by diffusionless martensitic transformations, influencing hardness, strength, and toughness in applications ranging from tools to medical devices.