Low-compression-ratio and thick-specification X70-grade gas transmission pipeline steel and production method

Abstract

Low-compression-ratio and thick-specification X70-grade gas transmission pipeline steel is prepared from, by weight percent, 0.03-0.075% of C, 0.15-0.35% of Si, 1.30-1.90% of Mn, not larger than 0.015% of P, not larger than 0.002% of S, not larger than 0.006% of N, 0.035-0.065% of Nb, 0.025-0.05% of V, 0.015-0.025% of Ti, 0.1-0.40% of Cr, 0.1-0.2% of Ni and 0.10-0.25% of Mo. Production steps include heating of casting blanks with the thickness ranging from 225 mm to 235 mm, rough rolling, high-pressure water descaling, fine rolling, cooling, straightening and standby application. According to the low-compression-ratio and thick-specification X70-grade gas transmission pipeline steel, the X70-grade pipeline steel with the thickness being 30 mm or above can be produced through the continuous casting blanks with the thickness being 230 mm, the Rt0.5 of the product ranges from 500 MPa to 580 MPa, the Rm of the product ranges from 600 MPa to 650 MPa, the ratio of the Rt0.5 to the Rm is not larger than 0.90, and the elongation A50 is not smaller than 24%; at -20 DEG C, the impact energy KV2 is not smaller than 250 J; at -15 DEG C, the DWTT fracture surface shear rate SA is not smaller than 95%; and HV10 <=235.

Description

technical field [0001] The invention relates to a pipeline steel and a production method thereof, in particular to a gas transmission pipeline steel of low compression ratio thickness specification X70 grade and a production method thereof. Background technique [0002] Almost all of China's natural gas resources are concentrated in the western region, which is inversely proportional to China's population density distribution. The burning of a large amount of fossil fuels such as coal and oil has brought serious smog problems to China's environment. The Chinese economy must solve the energy crisis while maintaining high-speed growth. To this end, the country has vigorously developed clean natural gas in the west. The first and second lines of the West-East Gas Pipeline have been built. The third line is currently under construction, and the fourth, fifth, and sixth lines have been planned. . High-grade steel, large diameter, large wall thickness, and high-pressure transmiss...

AI Technical Summary

Problems solved by technology

Although its compression ratio is relatively low, the purity of molten steel is too strict, in which the S content is less than 6ppm, and the P content is less than 70ppm, which is impossible for most iron and steel smelting enterprises.

At the same time, there are few domestic production lines for 150mm continuous casting slabs, and the production equipment is different from conventional production lines. The product thickness is within the range of conventional products, which cannot meet the needs of pipeline engineering for large wall thickness (≥30mm).

[0007] Judging from the existing literature reports on the production of thick-gauge high-grade pipeline steel through low compression ratio, there are deficiencies in thick-gauge high-grade pipeline steel achieved by adding a large amount of expensive alloys and sacrificing impact and drop hammer performance; For rolling with too thin continuous casting slab, although high-grade pipeline steel is produced under the condition of low pressure ratio, the maximum thickness is only 22mm, and the contradiction of insufficient thickness is highlighted

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