Martensitic tempering stage
Martensitic tempering stage: Rapid cooling of high-temperature weld regions creates a hard, crack-prone structure. This can lead to hot cracks and low toughness.
Physical-Chemical Mechanism of Action
Martensite forms by rapid cooling of high-temperature weld zones. Here, the ferrite remains in a tetragonal supersaturated state and transforms into a cubic structure type, while carbides remain finely dispersed.
Metallurgical Relevance & Welding Risks
Martensite is very hard and prone to cracking. This can lead to hot cracks in the weld, especially if cooling is too fast. The toughness of the material decreases, affecting mechanical strength.
Shop Practice & Action Guidelines
To avoid martensite, it is important to ensure controlled cooling of the weld. This can be achieved using cooling water or special cooling mats. The cooling rate should be set so that the critical temperature window (t8/5) is between 5 and 25 seconds.