OBRABOTKAMETALLOV Vol. 25 No. 4 2023 technology Fig. 2. Technologies for manufacturing welded steel pipes (a) and conventional electric resistance welded (ERW) pipes (b) а b relationships of third-generation alloys are also discussed. Finally, the prospects and problems of future applications are studied. It isnoted in [27] that themost important phenomena in this context are themartensiticphase transformation and the associated effects of accommodation plasticity (TRIP) and twinning-induced plasticity (TWIP) that can occur, both of which are possible due to the presence of thermodynamically metastable austenite. The paper [28] provides an overview of the technology for manufacturing high-strength pipeline steels. The microstructure and mechanical properties of sheets and pipes made of steel grades X80, X100 and X120 are analyzed and discussed. The microstructure of steel X80 consists of needle ferrite containing the M/A phase (martensite/austenite component). The X80 steel sheets and pipes tested were found to exhibit superior performance in the Drop Weight Tensile Test (DWTT). The DWTT of 85 % SATT of X80 steel in the pipe was about -40 °C. The deformation capacity of the X80 pipeline was evaluated on a large-sized deforming machine operating under the load of bending and axial compression forces. The developed X80 pipeline was found to meet DNV and API bending resistance requirements. In the case of X100 steel, the main phase was bainitic ferrite, which has a lath and granular morphology, and M/A existed as the second phase. It was shown that the developed steel X100 can be implemented with the appropriate properties for UOE pipes. DWT 85 % SAT of steel pipe X00 was shown at temperatures below -40 °C. The development of pipeline steel of the X120 grade was also tested. The microstructure of steel X120 consists of bainitic ferrite and needle ferrite. The tensile strength of the developed steel sheets and pipes X120 fully meets the target properties required in the current study. The DWTT of 75 % SATT of the developed X120 sheet steel
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