Steel for longitudinal resistance welded pipe with low yield ratio and manufacturing method thereof

Abstract

The invention discloses steel for a longitudinal resistance welded pipe with a low yield ratio and a manufacturing method thereof. The steel comprises the following chemical components in percentage by weight: 0.15 to 0.22 percent of C, 0.10 to 0.30 percent of Si, 1.20 to 1.60 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.008 percent of S, 0.005 to 0.025 percent of Ti, 0.20 to 0.30 percent of Cr, 0.010 to 0.045 percent of Als, less than or equal to 0.008 percent of N and the balance of Fe and inevitable impurities. The manufacturing method comprises molten iron pretreatment, molten steel smelting, external refining and slab continuous casting, and heating, rolling, cooling and reeling of a continuous cast slab, wherein the continuous cast slab is heated to between 1,180 and 1,280 DEG C in a heating furnace, and then rolled into a hot rolled strip; the finishing temperature of the strip is between 760 and 820 DEG C; the rolled strip is rapidly cooled at a speed of between 9 and 14 DEG C per minute; and the strip is rolled into a coiled sheet at the temperature of between 560 and 620 DEG C. The problem that industrial production cannot be realized due to a slow cooling speed after rolling and the problem that the requirement of a user on the impact toughness of the coiled sheet cannot be met in the prior art are solved.

Description

technical field [0001] The invention relates to the product design and manufacture of a steel for straight seam electric resistance welded pipes, in particular to the product design and manufacture of a steel for API Spec 5CT standard low yield ratio K55 steel grade ERW oil casing. Background technique [0002] Petroleum casing is one of the most commonly used petroleum-specific pipes in oil fields. It is an indispensable construction material in oil and gas field drilling and production operations, and occupies a very prominent position in the production and development of oil and gas fields. According to the API Spec 5CT standard, the seamless process and the ERW straight seam welding process can be used to manufacture oil casing. [0003] ERW oil casing, also known as high-frequency straight seam resistance welding casing. ERW oil casing is a new type of oil pipe with uniform wall thickness, high dimensional accuracy, good perforation performance, strong collapse resista...

AI Technical Summary

Problems solved by technology

[0015] The purpose of the present invention is to provide a kind of ERW welding process to manufacture K55 steel grade straight seam welded oil casing hot-rolled coils and its manufacturing method, to solve the problem that the cooling speed after rolling in the prior art is too slow to realize industrialized production, and at the same time, the user cannot be guaranteed Problems with impact toughness requirements for coils

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