1. The carrying capacity in terms of permissible stress (σ0, 2) of steels Kh18N10T and Kh21N5AG7 under conditions of uniaxial static tension increases 50% down to −253° as the result of surface hardening. 2. For hardened steels Kh18N10T and Kh21N5AG7 σ b n /σn > 1 and σ b n /σ0.2 > 1 with Kt=3.0 in the range of 20 to −253° C. 3. With static loading and bulk stress conditions (notch root radius 0.25 mm) steel Kh18N10T can be used down to −253° C and steel Kh21N5AG7 down to −196° C in the hardened condition. 4. Under dynamic bending conditions steels Kh18N10T and Kh21N5AG7 can be used in the hardened condition down to −253° C in the presence of a stress concentrator (Kt=3.4).