Aluminum nitride precipitation
Formation of fine aluminum nitride particles through the interaction of dissolved aluminum and nitrogen in steel. They are intentionally used to restrict austenite grain growth at elevated temperatures.
Aluminum nitride forms when the aluminum dissolved in the steel reacts with nitrogen. The fine particles are important because they slow down grain growth in the heat-affected zone. Without these precipitates, the grain grows quickly, and the weld becomes tough and crack-sensitive. So make sure that the nitrogen content in the base material and filler material is right. If you work with higher heat inputs, you have to keep an eye on the weld after welding. If the weld has become coarse-grained, the aluminum-nitrogen balance is off, and you have to adjust the parameters or the filler material.