SS400 is a way of marking Japanese steel material, is a judgment standard, equivalent to the domestic Q235 steel (also known as A3 steel). Foreign standard structural steels are often classified according to tensile strength, such as SS400 (labeled as such in Japan), where 400 means the minimum value of σ B is 400 Mpa. Ultra-high strength steels are those with σ B ≥1373 Mpa.