A concept of mechanical stability of structural steels

Abstract

We have developed a new approach to the evaluation of the capability of steels to resist brittle fracture based on the physical ideas concerning the micromechanism of transition of metals from the plastic state into the brittle state. Within the framework of this approach, we propose new microscopic characteristics of stability of the metal, namely, the parameter of mechanical stability and the coefficient of mechanical stability. The procedure of experimental evaluation of these parameters is described and the relationship between the coefficient of mechanical stability and standard characteristics, such as plasticity under uniaxial tension and impact toughness, is analyzed in detail. We introduce a new characteristic called the force equivalent of embrittlement, which enables us to describe, on a single scale, the embrittling action of the following factors of different physical nature: complex stressed state, stress concentration, low temperatures, and dynamical loading. We propose a criterion aimed at the description of stability of the plastic state of the metal at the tip of a macrocrack and develop a procedure of experimental determination of the value of force equivalent of embrittlement for a standard cracked specimen. For the typical representatives of low-, medium-, and high-strength structural steels considered as an example, we study the regularities of the influence of the strength of a steel on the value of the coefficient of mechanical stability. On the basis of these data, we compare structural steels from the viewpoint of their stability under the embrittling action of cracklike defects.