Haurastumisilmiö

Haurastumisilmiö refers to the phenomenon of embrittlement in materials, particularly metals, where they lose their ductility and become brittle. This can lead to unexpected fracture even under stresses that would normally be well within the material's elastic limit. There are several types of embrittlement, each with its own causes and mechanisms.

One common form is hydrogen embrittlement, which occurs when hydrogen atoms diffuse into the metal lattice. Hydrogen can be introduced during manufacturing processes like pickling or electroplating, or through environmental exposure. These hydrogen atoms can accumulate at grain boundaries or dislocations, weakening the material and promoting crack initiation and propagation.

Another type is strain aging embrittlement, often seen in low-carbon steels. It is caused by the migration of interstitial solute atoms, such as carbon or nitrogen, to dislocations during aging after deformation. This increases the material's yield strength but also reduces its ductility, making it more susceptible to brittle fracture at lower temperatures.

Tempered martensite embrittlement is a concern in hardened and tempered steels. If tempered within specific temperature ranges, typically between 250°C and 400°C, the steel can become brittle. This is often attributed to the segregation of impurities like phosphorus or sulfur to grain boundaries, or the formation of brittle carbides.

Stress-corrosion cracking (SCC) is another related phenomenon where a susceptible material is exposed to a corrosive environment while under tensile stress. The combination of these factors can lead to the initiation and slow growth of cracks, ultimately causing failure. While not strictly embrittlement in the same sense as hydrogen embrittlement, SCC results in brittle-like fracture surfaces. Understanding haurastumisilmiö is crucial for ensuring the safety and reliability of structures and components made from various materials.