Low-temperature L450M pipeline steel and manufacturing method thereof

Abstract

The invention discloses low-temperature L450M pipeline steel and a manufacturing method thereof. The low-temperature L450M pipeline steel comprises, by weight, 0.050-0.070% of C, 0.10-0.25% of Si, 1.61-1.70% of Mn, 0.056-0.070% of Nb, 0.21-0.30% of Cr, 0.008-0.020% of Ti, 0.015-0.045% of Al, no more than 0.020% of P, no more than 0.006% of S, no more than 0.008% of N, and the balance iron and inevitable impurities, and the cold crack sensitivity coefficient Pcm is smaller than or equal to 0.18%. The thickness of a casting blank is smaller than or equal to 200 mm; the casting blank is subjectedto direct hot charge at the temperature of 500-850 DEG C and heated to be 1140-1200 DEG C, the rough rolling finished rolling temperature is larger than or equal to 970 DEG C, the finish rolling inlet temperature is smaller than or equal to 970 DEG C, and the finish rolling outlet temperature is 790-830 DEG C; then a steel plate is cooled in ultra fast cooling and laminar cooling modes, the cooling speed is higher than or equal to 15 DEG C / s, and low-temperature coiling is conducted under the temperature of 450-550 DEG C. The produced steel plate has good low-temperature performance.

Description

technical field [0001] The invention belongs to the field of high-strength low-alloy steel for metal materials, and in particular relates to a method for manufacturing pipeline steel for oil and gas transportation pipelines, in particular to a method for manufacturing hot-rolled coils of L450M steel grade pipeline steel for low temperature in the API SPEC 5L specification . Background technique [0002] In recent years, the construction of energy transmission pipelines has developed rapidly. In order to improve transmission efficiency and operational safety, the requirements for the strength and toughness of the selected steel raw materials are getting higher and higher. At present, the major main pipelines at home and abroad basically use L485M and L555M steel grades, and the branch lines and urban pipe networks mostly use L450M steel grades. [0003] When the pipeline is located in an extremely cold region or the transport medium is low-temperature liquefied natural gas, ...

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Problems solved by technology

The weight percentage of the patented ingredients is C0.02%~0.08%, Si 0.01%~0.5%, Mn 0.5%~1.8%, P≤0.01%, S≤0.002%, Nb0.005%~0.05%, Mo 0.005% ~0.5%, Ti 0.005%~0.04%, N 0.002%~0.007%, Al≤0.07%, Mg 0.0005%~0.005%, the composition of this steel contains Mo and Mg, and the cost is high

[0011] Hou Qingping, Wang Xusheng and others published "Benxi Iron and Steel Thin Slab Continuous Casting to Produce API X65 Pipeline Steel" in "Benxi Iron and Steel Technology", 2007 (4): 21-23. The composition of the steel grade disclosed in the article is designed to be low Mn (1.38%) , containing V (0.038%) and Ni (0.12%), the cost of the alloy is high, the temperature of the final rolling (840°C) and coiling process (600°C) is obviously high, and the role of the water-substituted alloy cannot be fully exerted

[0012] Although most of the L450M steel grade pipeline steels disclosed in the above documents have achieved high strength and high toughness, there are not many used for low temperature resistance. The alloy design contains many precious elements such as V, Mo, Ni, Cu, etc., and the cost is relatively high.

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