Oxygen Deoxidation

Oxygen in the weld pool is poison for the seam – it binds during solidification and causes pores. To prevent that, you need deoxidizers like silicon or aluminum. They catch the oxygen and bind it as slag that floats to the top. If you don't do that, you get a porous, crack-prone seam. So always make sure there's enough deoxidizer in the filler or in the pool, and don't let the melt pick up unnecessary oxygen.