Influence of heat treatment on the structure and corrosion properties of microalloyed pipe steels with a chromium content of up to 1 %

The service life of oil pipelines has recently decreased significantly due to severe operating conditions and the increased aggressiveness of the environment, caused by the simultaneous presence of dissolved hydrogen sulfide, carbon dioxide, chlorides, and a high water phase content. Conventional corrosion mitigation methods typically address only one of these factors and therefore fail to provide adequate protection under such combined conditions. This limitation necessitates the use of multiple complementary approaches for corrosion control. This paper proposes microalloying systems for low-carbon steels of grades 10KhB, 10F, 10B, and 15KhF (with chromium content up to 1 %) for seamless pipes, along with optimized heat treatment regimes that provide increased strength, cold resistance, and corrosion resistance in CO2- and H2S-containing environments. Mechanical testing after heat treatment demonstrated that the proposed chemical compositions ensure strength classes K52–K56, while also providing high low-temperature toughness. The morphology of carbides in the microstructure depends on the chemical composition and determines the steel’s strength, though it does not affect corrosion resistance. The investigated steels showed high resistance to hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC). After exposure to CO2–H2S media, a protective iron sulfide film formed on the surface, indicating uniform sulfide corrosion. The corrosion rate and mechanism were found to be governed by the medium composition and the kinetics of iron sulfide film formation. The obtained results allow expanding the scope of application of the proposed steels in multicomponent aggressive environments regardless of the type of microalloying.