A pipeline steel with excellent toughness for extremely low temperature environment at -45°C and its manufacturing method

Abstract

The invention discloses pipeline steel with excellent toughness for a minus 45 DEG C extremely-low-temperature environment and a manufacturing method thereof. The steel comprises, in percentage by mass, the following chemical elements of 0.030%-0.060% of C, 0.10%-0.30% of Si, 1.30%-1.60% of Mn, less than or equal to 0.0100% of P, less than or equal to 0.0015% of S, 0.40%-0.55% of Ni, 0.05%-0.20% of Cr, 0.050%-0.075% of Nb, 0.008%-0.020% of Ti, 0.0010%-0.0040% of Ca, 0.010%-0.050% of Al, less than or equal to 0.005% of B, 0.0010%-0.0060% of N, less than or equal to 0.0050% of O, and the balanceFe and inevitable impurities, wherein the elements simultaneously meet the following relationship that the Ni is larger than or equal to 1.6*(C+Mn / 6), log (C*Nb) is less than or equal to minus 2.5, Cplus Mn / 6 plus Cr / 5 is larger than or equal to 0.28% and is less than or equal to 0.35%, and Ti / N is larger than or equal to 2.5 and is less than or equal to 5.0. The yield strength of the pipeline steel is larger than or equal to 450 MPa, the tensile strength is larger than or equal to 535 MPa, the elongation rate is larger than or equal to 18%, the Charpy impact power AKV at minus 45 DEG C is larger than or equal to 250J, and the shear area rate Sa% of a DWTT fracture at minus 45 DEG C is larger than or equal to 85%.

Description

technical field [0001] The invention relates to a pipeline steel and a manufacturing method thereof, in particular to a pipeline steel with excellent toughness for an extremely low temperature environment of -45°C and a manufacturing method thereof. Background technique [0002] Oil and natural gas will still account for the main part of the primary energy consumption in the future, and the demand will continue to rise, and the mining area will gradually expand. The service temperature can be as low as -45°C. Although modern controlled rolling and controlled cooling technology has been able to obtain pipeline steel with both strength and toughness, it is still difficult to meet the low temperature toughness requirements of -45°C. Therefore, pipeline steel with extremely low temperature toughness has considerable application prospects. [0003] The low-temperature toughness of pipeline steel usually refers to Charpy impact performance (CVN) and drop weight tear performance (...

AI Technical Summary

Problems solved by technology

[0004] Chinese patent CN106480381A discloses a hot-rolled wide and thick plate with good plasticity and toughness for low-temperature pipelines. This patent adopts the composition design of low Ni (0.06-0.15%) and Mo-containing composition design, the production cost is high, and its DWTT performance is only Satisfy the requirement of -20℃

The technical solution disclosed in this patent is designed with low Ni (0.21-0.35%) and high Nb (0.05-0.08%) composition, the structure is quasi-polygonal ferrite + granular bainite, and its DWTT performance only meets the requirements of -25°C

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