Martensitic dislocation structure
Martensite is a hard and crack-prone dislocation structure in steels, formed during rapid cooling. It has low ductility and can cause hot cracking.
Physical-Chemical Mechanism of Action
Martensite forms through rapid cooling of steels, where the grain abruptly transforms into a lath-like structure. This occurs when the temperature drops below the martensite start point and carbon atoms are trapped between the lattice planes of the ferrite structure.
Metallurgical Relevance & Welding Risks
Martensite is hard and has low plasticity, which can lead to hot cracks. It forms when the weld cools too quickly (t8/5 < 5 s). This can be caused by insufficient cooling or too high heat conductivity of the surroundings.
Shop Practice & Action Items
To avoid martensite, it is important to cool the weld slowly and evenly. This can be achieved by sufficient cooling lag or using shielding gas. For high-carbon steels, be especially careful and keep the cooling time at least 25 s.