Niobium Carbide Retardation of Recrystallization

Niobium forms fine carbides in steel that inhibit grain growth, resulting in a finer structure. This makes the material tougher and harder. When welding, you need to be careful that the heat input isn't too high and cooling isn't too slow, otherwise the grain coarsens again and the material becomes softer and more crack-sensitive. Keep the interpass temperature within limits and don't let the component cool down unnecessarily when doing multi-pass welds.