Abstract: The main factors affecting the properties of agglomerated flux, such as the basicity of flux, quantity of additive, form of CaO and amounts of CaF₂ and SiO₂, have been studied. The authors have developed a new SJ102 flux which has high basicity and belongs in the CaO-MgO-SiO₂-CaF₂ fluoride-basic type slag system. The SJ102 flux is for low hydrogen and high toughness welds, and is suitable for welding of HSLA steels of σ_b=500~800MPa.