Dislocated martensite
Dislocated martensite is a subtype of martensite with a high number of dislocations in low-carbon steels. It offers a good combination of strength and formability.
Physical-Chemical Mechanism of Action
Dislocated martensite forms by rapid cooling of low-carbon steels, transforming the atomic structure into a glass-hard, highly dislocated form. These dislocations are line defects in the crystal lattice that impede the movement of atoms, thereby increasing strength.
Metallurgical Relevance & Risks in Welding
Dislocated martensite can form in low-carbon steels during rapid cooling, leading to increased hardness and reduced formability. This can cause cracks or fractures in the workpiece, especially if the weld is under mechanical stress. Additionally, high hardness can make welding difficult and reduce the weld's service life.
Workshop Practice & Action Guidelines
To avoid dislocated martensite, controlled cooling should be applied to low-carbon steels. This can be achieved by using cooling water or special cooling media. The cooling rate should be set so that the critical temperature window (t8/5) is between 10 and 20 seconds. This prevents too rapid cooling and the formation of dislocated martensite.