Lattice Shear Distortion
Shear distortion of the lattice is a lattice deformation where atoms shift cooperatively without diffusion. It occurs in martensite formation and leads to high stress buildup.
Physical-chemical Mechanism of Action
In shear transformation of the lattice, atoms within the crystal lattice shift parallel to the lattice direction. This occurs without diffusion and through cooperative movement of atoms, leading to a rapid transformation.
Metallurgical Relevance & Risks in Welding
Shear transformation is characteristic of martensite formation during rapid cooling. It causes high stresses in the material, which can lead to crack-sensitive microstructures and increases the risk of hot cracking. Excessive shear transformation can make the material glass-hard.
Workshop Practice & Instructions
To minimize shear transformation, ensure controlled cooling after welding. Use appropriate cooling agents and avoid rapid cooling rates. For high-strength steels, slow cooling (t8/5 > 25 s) is recommended to avoid martensite formation.