Crystallographic orientation relationship

The orientation relationship tells you how the lattice of a new phase – for example martensite – attaches to the old structure, such as austenite. If the alignment is good, there's less stress at the phase boundary. In welding, this is crucial because poor lattice matching creates internal stresses and can cause cracks in the weld. You want to keep cooling uniform and controlled so the structure transforms cleanly. The right filler material and a clean weld area also prevent structural problems.