Low-yield-ratio high-tenacity steel plate and manufacture method thereof

Abstract

The invention relates to a low-yield-ratio high-tenacity steel plate. The steel plate comprises the following chemical constituents in percentage by weight: 0.05 to 0.08 percent of C, 0.15 to 0.30 percent of Si, 1.55 to 1.85 percent of Mn, smaller than or equal to 0.015 percent of P, smaller than or equal to 0.005 percent of S, 0.015 to 0.04 percent of Al, 0.015 to 0.025 percent of Nb, 0.01 to 0.02 percent of Ti, 0.20 to 0.40 percent of Cr, 0.20 to 0.30 percent of Mo, smaller than or equal to 0.006 percent of N, smaller than or equal to 0.004 percent of O, smaller than or equal to 0.005 percent of Ca, smaller than or equal to 0.40 percent of Ni, and the balance of iron and inevitable impurities, wherein Ca / s is larger than or equal to 1.5. The steel plate is manufactured through the following method: heating a continuous casting or steel billet at 1150 to 1220 DEG C and performing multi-pass rolling, wherein the total reduction rate is larger than or equal to 80 percent, and the finish rolling temperature is larger than or equal to 850 DEG C; performing rapid water cooling on a rolled steel plate at the speed of 15 to 50 DEG C / s to a temperature range from Bs-60 DEG C to Bs-100 DEG C, and then performing air cooling for 5 to 60 seconds; and heating the cooled steel plate in an on-line induction heating furnace to Bs plus 20 DEG C at the speed of 1 to 10 DEG C / s, tempering for 40 to 60 seconds, then discharging from the furnace and performing air cooling. The thickness of the steel plate is 10 to 25mm, the yield strength is larger than or equal to 500MPa, the yield ratio is smaller than or equal to 0.75, the ductility A50 is larger than or equal to 20 percent, and Akv at minus 60 DEG C is larger than or equal to 200J.

Description

technical field [0001] The invention relates to a high-toughness hot-rolled steel plate and a manufacturing method thereof, in particular to a high-toughness steel plate with a yield strength of 500 MPa and a low yield ratio and a manufacturing method thereof. The steel plate of the invention has a relatively low yield strength ratio, and the transportation pipeline made of the steel plate is suitable for use in high-earthquake-prone areas and can resist large deformation. Background technique [0002] Nb alloying and controlled rolling are often used in traditional oil and gas pipeline transportation steel, resulting in a relatively high yield strength of pipeline steel, usually greater than or equal to 0.85. This type of pipeline steel is not suitable for production of transmission pipelines in earthquake-prone areas. [0003] CN101962733A discloses a low-cost, high-strength X80-grade large-deformation-resistant pipeline steel and its production method, wherein C: 0.02-0.0...

AI Technical Summary

Problems solved by technology

Its properties such as yield strength ratio and elongation rate cannot meet the requirements of high-earthquake areas, and can resist large deformation of the transmission pipeline.

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