martensittisiä

Martensiittiä is a Finnish term referring to martensite, a hard and brittle phase formed in steel during rapid cooling. This transformation occurs when austenite, a high-temperature phase of iron alloys, is cooled so quickly that carbon atoms do not have time to diffuse and form cementite. Instead, the carbon atoms become trapped within the iron lattice, distorting it into a body-centered tetragonal structure.

The formation of martensite is a diffusionless transformation, meaning that the atoms move cooperatively rather than individually. This results in a very fine microstructure characterized by acicular (needle-like) or lath-like appearance. The hardness of martensite is a direct consequence of the trapped carbon atoms, which impede the movement of dislocations within the crystal lattice.

While martensite is highly desirable for its hardness and strength, its inherent brittleness can be a disadvantage. To mitigate this, steel containing martensite is often subjected to a tempering process. Tempering involves reheating the martensitic steel to a lower temperature, allowing some carbon to diffuse and form fine carbides, while also relieving internal stresses. This process reduces hardness and increases toughness, making the material more suitable for various applications. Martensitic transformations are crucial in heat treatment processes for tools, springs, and structural components requiring high wear resistance and strength.