Incubation Period of Martensitic Transformation
The incubation time of martensitic transformation is the time during which austenite is held below the martensite start temperature before diffusionless lattice shear occurs. It depends on the steel composition.
Physico-Chemical Mechanism of Action
The incubation time refers to the time during which austenite is held below the martensite start temperature (Ms). In this phase, no diffusionless lattice shear of the iron-carbon lattice to a carbon-rich phase occurs. Transformation begins only when the temperature falls below Ms and the material cools slowly.
Metallurgical Relevance & Welding Risks
Too short an incubation time can result in incomplete martensite transformation. This can lead to fine cracks and increased hardness of the material, affecting mechanical properties. Too long an incubation time coarsens the microstructure and reduces steel toughness.
Workshop Practice & Instructions
To ensure optimal martensitic transformation, it is important that the weld cools slowly. This can be achieved by choosing a suitable cooling concept and controlling the ambient temperature. A typical incubation time is about 10-20 seconds, depending on steel composition and desired hardness.