Low-alloy low-yield-ratio steel for oceaneering structure and production method thereof

Abstract

Provided are a low-alloy low-yield-ratio steel for an oceaneering structure and a production method thereof. The steel contains the following chemical components by mass: 0.09-0.13% of C, 0.15-0.40% of Si, 0.80-1.50% of Mn, 0.01-0.04% of Alt, 0.02-0.04% of Nb, 0.008-0.018% of Ti, less than 0.015% of P, less than 0.005% of S and the balance, Fe and unavoidable impurities. The production method includes that thick plate slabs of 250-400mm are heated before being rolled with heating temperature as 1180-1260 DEG C, rolling is divided into two stages, start rolling temperature at an austenite recrystallization area is 1000-1100 DEG C, start rolling temperature at an austenite non-recrystallization area is 850-950 DEG C, finishing rolling temperature is 790-820 DEG C, the thick plate slabs enter a water cooling area after being rolled with cooling speed as 9-12 DEG C / s and fishing cooling temperature as 450-500 DEG C, and steel plates are cooled in heap for more than 12 hours after being taped out. The steel has the advantages of good strength, low yield ratio, good toughness and good lamellar tearing resistant performance, thereby being capable of being used in oceaneering structure construction under severe conditions.

Description

technical field [0001] The invention belongs to the technical field of marine engineering, in particular to a low-alloy low-yield-strength-ratio marine engineering structural steel and a production method thereof. Background technique [0002] Offshore engineering structure is an important super-large welded steel structure for offshore platforms. It is used in severe marine working environments such as waves, tides, storms and cold drift ice, supporting platforms and drilling equipment with a total weight of more than hundreds of tons. The test of severe natural disasters such as earthquakes and tsunamis. These use characteristics determine that the steel used in offshore engineering structures must have high strength, high toughness, low yield ratio and anti-lamellar tearing properties. [0003] However, due to the properties of the steel, the low temperature toughness of the steel sheet generally decreases as the strength of the steel sheet increases. At the same time, ...

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Problems solved by technology

[0005] The invention patent with the publication number CN101358320A proposes controlled rolling and controlled cooling offshore platform steel and its production method. It needs to add V and higher than 0.03% Nb, but its tensile strength is lower than 610MPa, and it does not involve the yield strength ratio and the low temperature of the steel plate core. Measured value of impact energy

[0006] The publication number is CN101906591A. The invention patent adopts the controlled rolling and controlled cooling + tempering process to produce 460MPa grade marine engineering structural steel, but it needs subsequent heat treatment, adding alloy elements such as Ni, Cr, Cu, Mo, etc., which increases the cost while increasing the cost. Welding performance is adversely affected, there is no explanation for the low temperature toughness of the core, and the yield ratio is high

[0007] The publication number is CN101868560A. The invention patent proposes a production method of high-strength and low-yield-ratio structural steel with excellent low-temperature toughness. It needs to add precious alloy elements such as Cr, Mo, Ni, Cu, V, etc., and its production process is complicated to control. The narrow window is not conducive to large-scale industrial production, and does not involve the research and description of the low-temperature toughness and lamellar tear resistance of the core

[0008] Publication No. CN101255528A invention patent proposes a production method of niobium-containing steel with excellent ultra-low temperature toughness. The content of C is extremely low, and it is difficult to control during smelting. The content of Nb is 0.04-0.10%, which is high, and its tensile strength is not stable. It reaches 610MPa, and the thickness of the steel plate is 20-30mm, and does not involve the description of the low-temperature impact toughness of the core of the steel plate

[0009] At present, there is no precedent for producing steel with low yield ratio, high strength and high toughness for marine engineering structures by using low alloy

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