Based on the temperature dependences of mechanical properties of steels for standard specimens and specimens with stress raisers (SR) of different sharpness the effect of ductility $\psi_{K}$ (reduction in area) on the critical temperature of brittleness is analysed under the various stress-strain state (SSS)—for thin plates (biaxial stress state—BSS), for specimens with circular notches (triaxial stress state—TSS) at tension and for prismatic pre-cracked specimens at three-point bending. As ascertained, embrittlement of steel due to SR is caused by the local ductility near SR via the strain hardening of metal, which is characterized by the parameter of break resistance $B_{\textrm{r}}$. Critical value of break resistance $B_{\textrm{rc}}$ at temperature $T_{\textrm{C}}$ depends on SR sharpness, SSS mode, and on ductility characterizing by the coefficient of break resistance, i.e., accounting for the influence of strain hardening. The effect of ductility is most vividly manifests itself for BSS, so, the sharpest SR (cracks) embrittle metal to maximum extent in thin plates, not in bars (plates of moderate thickness). As shown, structural reliability of steel products with SR ($k_{\textrm{s}}$) is governed by ductility (via $B_{\textrm{r}}$) by a different way for various SSS.