Grain refiner
Alloying elements like titanium, vanadium, or niobium that form fine precipitates and restrict grain growth. They yield a fine-grained microstructure, enhancing both toughness and strength.
Grain refiners ensure that the steel remains fine-grained during welding. They form tiny particles that stop grain growth in the heat-affected zone. This is important because coarse grain makes the weld tough and prone to fracture, especially in cold conditions. But be careful: too much is also not good, then the particles become too coarse and make the steel brittle. And if you weld too hot, the particles dissolve again and are useless. So it's best to use base material with guaranteed fine-grain treatment and keep heat input low. Also control the interpass temperature, it must not rise too high. And with the filler metal, you have to make sure it matches your base material.