Diffusionless Shear Strain
Diffusionless shear distortion is a rapid shape change by atomic displacements over short distances, typical for martensitic transformation.
Physical-Chemical Mechanism of Action
Diffusionless shear distortion occurs during rapid cooling. Atomic nuclei change positions within the crystal lattice over distances less than an atomic spacing, without atoms fully exchanging (diffusion). This leads to a sudden distortion of the lattice.
Metallurgical Relevance & Welding Risks
This shape change can lead to strong martensite, which is glass-hard and crack-sensitive. With too rapid cooling (t8/5 < 5 s), high hardness develops, making the material more susceptible to cracks. This increases the risk of hot cracks and reduces mechanical toughness.
Workshop Practice & Action Instructions
To control diffusionless shear distortion, a careful cooling strategy is required. Use a slow cooling process (t8/5 > 25 s) and avoid rapid cooling after welding. This reduces hardness and lowers the risk of cracks.