Microalloying Carbonitride
Finely dispersed precipitates of carbides and nitrides formed by elements such as titanium, niobium, or vanadium, serving for grain refinement and increased high-temperature strength.
Microalloying elements like titanium, niobium, or vanadium bind carbon and nitrogen in steel. This forms fine carbonitrides that keep the grain fine. This makes the steel stronger and tougher without becoming brittle. When welding, you have to be careful: the fine particles can dissolve or coarsen due to heat. Then you lose grain refinement and impact toughness suffers. The cooling rate and heat input determine whether the particles precipitate finely again or you get coarse structure. In practice, this means: keep the interpass temperature low and don't weld with too much energy. Then the carbonitrides remain and the weld metal doesn't become too soft or too hard.