Keyword: «low-alloy steel»

The changes of microstructure and resistance of steel 09G2S to brittle fracture after the "cold" (at room temperature) equal channel angular pressing (ECAP) were investigated. It is shown that getting of the nano and submicrocrystalline microstructures has provided a technically significant improvement in the mechanical and operational properties of the steel (strength, toughness), including at fall of tests temperature to –40 °C. The qualitative analysis of features of crack formation processes in nanostructured metal under dynamic loading was conducted. It was revealed that the high values of impact toughness are due to the implementation of energy–intensive micromechanisms of fracture – ductile dimpled fracture and dispersed quasi- cleavage, intensive branching of micro- and macrocracks, what caused the slowing of their velocity and the formation of a developed relief.

The article studies the influence of low-frequency modulated current welding modes on the structure of welded joints of structural low-alloy steels. The welding process takes place in low climatic temperatures. For a comparative analysis of the structure, DC welding was also carried out. The structure was characterized by optical and scanning electron microscopy. The features of the influence of the modulation frequency of the welding current and the ambient temperature on the microstructure of welded joints have been revealed. Comparative structural analysis showed that the low-frequency range of pulsed changes in the energy parameters of the mode provides the most favorable structure of welded joints made of low-alloy steels. The optimal pulse repetition frequency (1.67 Hz) was revealed when welding with modulated current in a low-temperature environment (up to -45°C), at which the most favorable dispersed structure of the welded joint is formed.

The paper provides a brief overview of the technological methods studied at the Institute of Physics and Technical of the Siberian Branch of the Russian Academy of Sciences. Impact-mechanical treatment is proposed as one of the promising methods for hardening surfaces and reducing residual welding stresses. The development of fundamental research in the field of development and improvement of technological methods of post-weld processing to improve the physical and mechanical properties of welded joints of metal structures operated at low climatic temperatures is an important area with high opportunities for their intro-duction into production.

The study is devoted to the urgent problem of residual welding stress management in welded joints made of low-alloy steel 10XSD. The effect of ultrasonic shock treatment (UO) on the redistribution of HP after welding at room and subzero temperatures has been experimentally studied. It is established that after welding, significant tensile stresses are formed in the seam area, the level of which increases during low-temperature welding. It is shown that UO effectively transforms tensile stresses into compressive stresses, which contributes to an increase in the fatigue life of joints.

Ensuring the reliability of welded structures in Arctic conditions is a critical issue, as extremely low temperatures intensify heat dissipation during welding. This increases the cooling rate and the risk of forming quenched structures, which reduces resistance to brittle fracture. The article describes a methodology for measuring thermal cycles using thermocouples at sub-zero temperatures and presents the data in the form of a graph. It is shown that in multi-pass welding, the self-heating of the metal reduces the cooling rate of subsequent layers.