Diffusionless martensitic transformation
Diffusionless martensitic transformation is a rapid transformation of austenite to martensite upon very fast cooling, without atomic movement.
Physical-Chemical Mechanism of Action
In diffusionless martensitic transformation, the crystal lattice remains unchanged. Rapid cooling (supersonic speed) moves atoms so fast that they cannot take their normal positions and instead are rolled into a new order.
Metallurgical Relevance & Welding Risks
This transformation can lead to very hard and crack-sensitive steels. Too rapid cooling can alter the microstructure so that it becomes susceptible to hot cracking. This increases stress in the weld and can lead to fracture points.
Workshop Practice & Action Instructions
To achieve controlled diffusionless martensitic transformation, the cooling rate must be precisely controlled. This often requires special welding processes such as high-frequency welding or laser welding. The optimal cooling time is typically between 0.1 and 1 second, depending on the steel and desired properties.