Development of Steel Microalloying System for Cold-Resistant Coiled Product Designated for Pipes Under CRC Conditions

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Results

are provided for a study of the effect of microalloying steel with niobium, titanium,, and vanadium on the level of mechanical properties and cold resistance of coiled rolled product for pipe purposes produced under conditions of the OMK-Stal casting and rolling complex (CRC). It is shown that with a standard nitrogen content in steel (less than 0.008%) under CRC conditions introduction into pipe steel of microadditions of vanadium does not provide strengthening for coiled rolled product by a precipitation hardening mechanism. Precipitation of vanadium carbide phase is difficult as a result accelerated strip cooling on the run-out table before winding strip on a coil and use of relatively low coiling temperatures under CRC conditions. Separation of VC particles after tempering at 650°C confirms retention of vanadium in solid solution. The presence of fine VN particles in steel with an increased nitrogen content may be explained by the fact the vanadium nitride phase may precipitate at higher temperatures compared with carbide. Research work has made it possible to assimilate production of cold-resistant coiled rolled product more than 10 mm thick of strength class up to K60 under CRC conditions without microalloying steel with vanadium.