Martensitisk

Martensitisk (martensitic) refers to the martensite phase observed in steels and some other alloys. It forms through a diffusionless solid-state transformation from austenite when the material is cooled rapidly, or quenched, from temperatures where the steel is fully austenitic. The rapid quench traps carbon and other alloying elements in place, preventing their diffusion and resulting in a metastable, supersaturated structure.

The martensite lattice is body-centered tetragonal and typically appears as plate- or needle-like features within the prior austenite grains. It is usually very hard and strong due to the distorted lattice and carbon atoms locked into interstitial sites. However, martensite is also relatively brittle compared with other microstructures such as pearlite or bainite, which is why further heat treatment is often used to tailor properties.

Heat treatment involves tempering the quenched steel. Tempering allows carbon to diffuse and precipitate as carbides, relieving internal stresses and increasing toughness, at the expense of some hardness. The exact balance of hardness, strength, and ductility depends on alloy composition and tempering temperature.

Applications of martensitisk steels are broad. They are central to tool steels and many martensitic stainless steels used for knives, surgical instruments, and certain gears and turbine components. Common martensitic stainless grades include alloys such as 410, 420, and 440C, which combine corrosion resistance with varying levels of hardness depending on heat treatment.