Abstract
The results of experimental studies on the kinetics of crack growth, its relationship with the parameters of crack resistance and long-term strength of pipe steels of different service life and their structural and phase composition are presented. It was found that the value of the critical stress SK for all test steels increases with the increase in the service life, and the impact viscosity decreases, which indicates the structural embrittlement of the pipe steels associated with their sudden flooding. It is shown that the new 06G2BA steel, which is economically modified with a carbide-forming element (vanadium) and has a fine-grained structure and a low content of harmful impurities (sulfur, phosphorus), has the highest visco-plastic properties and resistance to brittle fracture. The microstrain of the α-Fe crystal lattice, as well as the quantitative decay of cementite and the redistribution of carbon between ferrite and pearlite, were evaluated by X-ray structural methods. 06G2BA steel is recommended for use in the construction of pipelines and, for example, bridge structures, which are constantly under cyclic loads with simultaneous contact with a corrosive-aggressive environment. The influence of the service life of water pipes on the hydrogen content and microcracks in pipe steels was determined. A diagram of the relationship between long-term and static strength depending on the hydrogen content in steels is recommended, which can be used by designers to rationally choose the type of steels with high crack resistance in aggressive technological environments. In order to extend the service life of pipe structures, it is necessary to use economically modified steels.
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