The proof strength, tensile strength and notch impact toughness of plain C steel and low (alloy) steel is improved by the addn. of: 20 - 35wt.% Si, pref. in the form of Ca-Si and/or Zr-Si; 15 - 35 wt.% Ca or an equiatomic amt. of another alkali(ne earth) metal pref. in the form of Ca-Si and/or Ca cyanamide; 0.5 - 5wt.% N, pref. in the form of Ca cyanamide; 15 - 25 wt.% Nb, pref. in the form of ferroniobium; 8.2 wt.% Al, pref. in the form of powder or fine cuttings; 0-25 wt.% Zr, pref. in the form of Zr-Si; and 0 - 2wt.% Be. These elements are added in the form of a finely ground mixt. to the liq. steel in the ladle. The addn. has the effect in that special nitrides, such as Al or Nb nitride, are formed by N, which is liberated and reactive at the temp. of the liq. steel, while harmful Fe nitrides are not formed.
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