Improving the reliability of metal structures of transport and technological machines during operation in the Arctic

Abstract

In the course of the study, we analyzed the main factors affecting the brittle fracture of the elements of welded structures made of structural steels, associated with its unexpectedness and the absence of noticeable plastic deformations at metal stresses much lower than the yield point. During experiments, the relationship between the magnetic parameter Hp and the structure of structural steels during thermal cycling was revealed. This became possible due to the high sensitivity of passive magnetic flux leakage testing when monitoring the structural transformations of metal during cyclic heating and cooling. We provide examples of the formation of ultrafine-grain structures in industrial structural steels based on the results of thermal cycling and analyze factors affecting the final grain size. It is shown that the degree of steel microstructure refinement depends on the chemical composition and initial structure of steels as well as the number of thermal cycling cycles. It was established that an increase in the number of thermal cycling cycles and the degree of steel alloying, the presence of a finer-grain initial structure, and preliminary cold plastic deformation during stage-by-stage monitoring using passive magnetic flux leakage testing contribute to the formation of a finer-grain structure. A decrease in the average grain size shifts the temperature of metal transition from ductile to brittle fracture to the region of lower temperatures, which increases the reliability of welded metal structures of transport and technological machines used in the Arctic.