In the manuscript the problem of brittleness of metals and alloys, and in particular products from them, is considered as a problem of the effect of essential inhomogeneities of stresses in a specimen with the stress raiser (cracks) on stability of saving of basic strength of metal ($\sigma_{0.2}$—yield strength) in the ultimate strength of specimen with stress raiser ($\sigma_{\textrm{NF}}$). The condition of stability of the strength of specimen with stress raiser is $\sigma_{\textrm{NF}}$ > $\sigma_{0.2}$, of instability—$\sigma_{\textrm{NF}}$ < $\sigma_{0.2}$. The literature experimental results of bending tests of specimens with a crack made of steels in a wide range of strength ($\sigma_{0.2}$ = 200–2200 МPа) and ductility ($\psi_{\textrm{K}}$ = 10–85%) characteristics are analysed. A technique for determining the critical parameters of ductility is suggested, which ensure the stability of fracture strength of specimens with stress raisers ($\sigma_{\textrm{NF}}$) at room temperatures ($\sigma_{\textrm{NF}}$ > $\sigma_{0.2}$) in the specified strength range of tested steels It is concluded that to certify steels for the possibility of their brittle fracture, it is sufficient to ascertain the degree of the strength stability at the actual operating temperature of product without the need to determine the critical brittleness temperature of steel, $T_C$, on specimens with the stress raiser (crack).