L485M pipeline steel excellent in low-temperature toughness and manufacturing method of pipeline steel

Abstract

The invention discloses L485M pipeline steel excellent in low-temperature toughness and a manufacturing method of the pipeline steel. The steel comprises 0.045%-0.065% of C, 0.10%-0.25% of Si, 1.55%-1.65% of Mn, 0.055%-0.075% of Nb, 0.010%-0.025% of Ti, 0.10%-0.15% of Mo, 0.20%-0.30% of Cr, 0.015%-0.045% of Als, smaller than or equal to 0.015% of P, smaller than or equal to 0.003% of S, smaller than or equal to 0.006% of N, and the balance Fe and inevitable impurities, and Pcm is smaller than or equal to 0.18%. The continuous cast blank thickness is smaller than or equal to 170 mm, hot charging is performed at 500-850 DEG C, heating is performed to 1160-1200 DEG C, the rough rolling final rolling temperature is larger than or equal to 980 DEG C, the finish rolling final rolling temperatureis 780-820 DEG C, the finish rolling total downward pressing rate is larger than or equal to 65%, then cooling is firstly performed at the speed of 40-60 DEG C/s till 550-600 DEG C is achieved, and then final cooling is performed at 10-25 DEG C/s till reeling is performed at 400-500 DEG C. A plate coil has excellent low temperature toughness, and using in extremely cold zones and regions harsh incondition is achieved.

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 L485M grade pipeline steel with excellent low-temperature toughness and its hot-rolled coil. 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, major domestic and foreign main pipelines basically use L485M and L555M steel grades. [0003] When the pipeline is located in an extremely cold region or the transport medium is low-temperature liquefied natural gas, from the perspective of operational stability and safety, higher requirements are put forward ...

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Problems solved by technology

[0013] The L485M grade pipeline steel disclosed in the above documents can meet the strength index requirements, but it is basically difficult to meet the low-temperature fracture toughness requirements below -30°C. Conventional laminar flow cooling cannot fully and effectively refine the grains and control the uniformity of the structure, and some components are added with precious alloying elements such as Ni and Cu, and the cost is high

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