Steel for n80 grade electric resistance welding petroleum casing and its manufacturing method

Abstract

The invention discloses N80-grade electric resistance welding steel for oil casings and a method for manufacturing the N80-grade electric resistance welding steel. The N80-grade electric resistance welding steel is characterized by comprising, by weight, from 0.05% to 0.09% of C, from 0.15% to 0.35% of Si, from 1.70% to 1.95% of Mn, lower than or equal to 0.020% of P, lower than or equal to 0.008% of S, from 0.010% to 0.050% of Ti, from 0.02% to 0.06% of Als, from 0.05% to 0.08% of Nb, from 0.20% to 0.30% of Cr, lower than or equal to 0.008% of N, the balance Fe and inevitable elements. The N80-grade electric resistance welding steel is excellent in weldability and good in impact toughness [under conditions that the temperature is 0 DEG C, the Akv is higher than 200J, and the SA (shear area) is larger than 90%]. Besides, after a steel strip made of the N80-grade electric resistance welding steel is made into a casing, only weld joints and heat affected zones need to be subjected to heat treatment, heat treatment for the integral casing is omitted, accordingly, a heat treatment process is simple, and the steel casing is low in production cost.

Description

technical field [0001] The invention relates to a steel for straight seam electric resistance welded pipe (ERW / HFW for short) and a manufacturing method thereof, in particular to a high-strength N80 steel grade 1 class ERW oil casing steel with excellent weldability and impact toughness in APISPEC5CT and its method of manufacture. Background technique [0002] Oil casing is one of the most commonly used petroleum-specific pipes in oil fields. It consumes a lot of money and costs a lot. It is an indispensable construction material in oil and gas field drilling operations. Compared with seamless pipes, HFW casings have significant advantages such as uniform wall thickness, high dimensional accuracy, good perforation performance, strong collapse resistance, and low cost, and are gradually replacing traditional seamless steel pipes. [0003] The APISpec5CT standard stipulates that seamless pipes and longitudinal welded pipes can be used to manufacture oil casings. As far as th...

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Problems solved by technology

The content of C in this paper is low, in order to improve the strength, it is necessary to add precious alloying elements Mo, Ni, and the cost of the alloy is high

[0014] In the published patents and documents, the C content is high, and the weldability of the steel strip is average; some add precious alloying elements Mo, Ni, Cu, etc., and the alloy cost is high; some require heat treatment of the whole tube

[0015] The steel for straight seam welding oil casing disclosed above meets the requirements of N80 steel pipe specified by the American Petroleum Institute APISpec5CT, but the carbon content is relatively high, and the weldability and toughness are average; the alloy elements Mo, Ni, Cu are added, and the alloy cost is high; the heat treatment of the whole pipe , complex process

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