Comparative analysis of the effect of microalloying with niobium, vanadium and titanium on the processes of structure formation in low-alloy low-carbon steels subjected to hot plastic deformation by ...controlled rolling is performed. The concentration and temperature ranges of the influence of these elements on formation of austenite preceding the hot plastic deformation or occurring in the final stage of the controlled rolling before the start of polymorphic γ → α transformation are determined. It is shown that the inhibitory effect of the microalloying elements on the growth of the austenite grains in heating in the γ -range intensifies in the V → Nb → Ti order, and the capacity to retard recrystallization of the hot-deformed austenite intensifies in the V → Ti → Nb order. The microadditions of niobium are shown to have a dual effect on the kinetics of the polymorphic γ → α transformation.
The properties of thick-sheet steels of the 0.09% C – 1.5% Mn – 0.035% Si – (0.04 – 0.09)% Nb system (steel type 09G2B) with low (up to 0.10%) additions of niobium are analyzed. The main mechanisms ...of the influence of microalloying on the microstructure and mechanical properties of the steels are considered, i.e., suppression of the growth of austenite grains in heating for rolling, deceleration of the processes of recrystallization of hot-deformed austenite, refinement of grains, and precipitation hardening with particles of Nb(C, N) carbonitride in cooling after the rolling. The conditions for microalloying with niobium raising the strength properties and lowering the cold shortness threshold or, on the contrary, affecting positively the impact toughness without changing the strength are determined.
The effect of up to 0.18% microadditions of titanium on the structure and mechanical properties of sheet low-carbon (0.07 – 0.09% C) steels with different alloying systems (C – Mn – Ti, C – Mn – V – ...Ti,C – Mn – Nb – Ti) is studied. The phase composition and the structure of the steels are determined. The specimens are tested for static tension and impact toughness. The content of titanium Ti
cr
above which fine particles of TiC carbide precipitate in the structure and elevate the strength properties at simultaneous decrease in the ductility and toughness of the steels is determined.
A favorable effect is established for reducing carbon and manganese content in low-alloy pipe steels of strength categories X56–X65 on the increase in hydrogen-induced cracking (HIC) resistance of ...thick-rolled sheet prepared by a thermomechanical treatment regime. This effect is due to a reduction in segregation structural inhomogeneity in the axial area of sheets in the form of a solid band of high-carbon structures.
The influence of sheet microstructure formed by various thermomechanical processing schedules on sulfide stress cracking (
SSC
) resistance under uniaxial tension for low-alloy pipe steels grades ...X42–X65 is studied. A favorable role is established for substitution of a ferritic-pearlitic by a ferritic-bainitic microstructure and improvement of structural component dispersion is established. The favorable effect is facilitated by using high intensity post-deformation cooling from the austenite region. It is shown that segregation bands and non-metallic inclusions in a sheet axial zone do not affect the duration of specimens withstanding SSC, but they can lead to formation of hydrogen cracks (
HIC
) on a specimen surface that is a defective feature. In order to prevent crack formation in a specimen surface and premature failure it is necessary to lay down high specifications for specimen gauge length and fillet surface quality.
Based on test results for low-alloy steel of strength categories X42–X70 the effect is established of loading and strength properties on sulfide stress corrosion (SSC) cracking resistance with ...uniaxial tension. A favorable effect is demonstrated for a reduction in loading factor and an increase in strength on an increase in steel SSC resistance. The level of steel yield and ultimate strengths providing good SSC resistance is determined.
The effect of molybdenum in an amount of 0.15% on the microstructure and properties of low-alloy pipe steel plate prepared by controlled rolling technology with accelerated cooling is studied. A ...favorable effect is established for molybdenum on increasing strength properties and sheet hydrogen induced cracking resistance.
The effect of accelerated cooling parameters on microstructure and hydrogen initiated cracking (HIC) is studied for thick-walled low-alloy steels of strength categories X52–X65 used for manufacturing ...large diameter pipes intended for operation in hydrogen sulfide media. Optimum accelerated cooling regimes are determined providing formation of a ferrite-bainite microstructure throughout the rolled product’s thickness, exhibiting improved hydrogen cracking resistance.
At the Azovstal Metallurgical Combine together with the Bardin Central Research Institute of Ferrous Metallurgy production of thick plate (3266 × 19.1 mm) is being developed for a large diameter gas ...pipeline of strength category X70. Plates are manufactured using controlled rolling technology with accelerated cooling (CR + AC) instead of previous controlled rolling technology with air cooling. Introduction of CR + AC promotes an increase in average values of energy for failure KV with impact tests on finished metal plate, and also a marked improvement in 3600 rolling mill productivity.
Contemporary controlled rolling technology with accelerated cooling is assimilated at the Azovstal Metallurgical Combine, used in production of plate intended for manufacturing gas and oil pipelines ...of considerable diameter. General characteristics are provided for the SMS-Demag accelerated controlled cooling unit in the plate workshop within the 3600 mill line. Mechanical properties are tested and the microstructure is examined. Batches of pipe steels of various grades satisfy test specifications and are estimated as favorable according to results for pipes manufactured from them.
