Changes in the mechanical properties and structural condition of stainless steel AISI 301 caused by the combined effect of impact-oscillatory loading and cryogenic cooling. Effects caused by holding specimens in liquid nitrogen for 1 h

The main patterns of the combined effect of impact-oscillatory loading (IOL) (dynamic non-equilibrium processes (DNP)) and cryogenic cooling on changes in the structural condition and mechanical properties of stainless steel AISI 301 are described. In our experiment, the steel was first immersed in liquid nitrogen for 1 h and then subjected to static tensioning at normal temperature. New structural and mechanical conditions of steel AISI 301 that occurred under DNP (ε_imp = 7.75 … 13.5 %) are scrutinised. In particular, it was found that for ε_imp = 10 … 11.5 %, the ultimate strength of the steel that was further subjected to static tensioning at normal temperature increased appreciably, and the ductility decreased. With ε_imp ∼10 %, the ultimate strength increased by 13.9 % compared to the baseline steel, but the relative strain remained at the level of 3.85 %. The structural conditions of steel AISI 301 and their link to new mechanical properties were studied by physical methods. A physical explanation is given for a rapid decline in steel ductility when ε_imp was in the range from 10.0 % to 11.5 %. With repeated static tensioning, when ε_imp was above 11.5 %, the ultimate strength increased significantly and ductility increased only slightly. When ε_imp was 13.5 %, the ultimate strength increased to 40 % compared to the baseline steel, and strain remained at the level of 7.22 %. Thus, the detected ranges of the intensity of the DNP during cryogenic cooling, at which the mechanical properties of steel, in particular plasticity, are significantly deteriorated, which is dangerous during the operation of aerospace structures.