Yield strength 500mpa grade high crack arrest toughness steel plate and production method thereof

Abstract

The invention provides a high crack-arresting toughness steel plate with yield strength of 500MPa and a production method thereof. The chemical components of steel comprises the following components in percentage by weight: 0.04-0.08% of C, 0.10-0.5% of Si, 0.8-1.6% of Mn, not more than 0.02% of P, not more than 0.01% of S, 0.03-0.065% of Al, not more than 0.005% of N, 0.005-0.05% of Nb, 0.005-0.03% of Ti, 0.0005-0.003% of B, not more than 0.004% of Ca, and the balance of Fe and avoidless impurities. The preparation method comprises the steps of roughing in an austenite re-crystalline region in a first stage, wherein the rolling temperature is 1000-1130 DEG C, the total reduction rate in the re-crystalline region is greater than or equal to 50%; cooling a rolled steel plate quickly to 580-530 DEG C at a rate of 10 DEG C / s; rolling in a non-re-crystalline region in a second stage when the temperature of the surface of the steel plate is 720-770 DEG C, wherein the accumulated deformation is greater than or equal to 50%, the finish rolling temperature is 700-740 DEG C; and water-cooling after rolling, wherein the cooling rate is 5-15 DEG C / s, and the final cooling temperature is 460-560 DEG C. The high crack-arresting toughness steel plate provided by the invention has the characteristics of high strength, high toughness, inhibition of crack formation and expansion and the like, and meets the performance requirements of special part members of large container ships.

Description

technical field [0001] The invention relates to a steel plate with ultra-high strength and excellent low-temperature toughness produced by micro-alloy + controlled rolling and controlled cooling technology, especially its high crack arrest toughness can be used to manufacture steel for container hull structures in low-temperature environments. Background technique [0002] With the enlargement of ships, the steel plates for shipbuilding are also developing in the direction of thicker plates. Especially for container ships, due to the requirements of the hull structure, thick plates with a thickness of 40-80 mm have been used as high-strength components in hatch coamings, upper decks and other parts. On the other hand, from the perspective of ensuring the safety of ships and preventing brittle fractures, ship steels are required to have a fracture toughness value above a certain level. In parts where cracks are expected to occur and in important parts where large-scale fract...

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Problems solved by technology

[0005] CN200710011724.6 discloses a mechanical treatment method through high-speed plastic deformation at room temperature or low temperature to refine the micron-scale coarse grain structure on the surface of the metal material into a nearly equiaxed submicron grain or nano-grain structure, Its strain rate > 100s -1 , total shear deformation > 2.9 and other high-speed processing methods are difficult to achieve in industrial production

[0006] Patents such as CN200910075647.X, CN200910038833.6, and CN200710046298.X respectively disclose several methods for preparing ultra-fine-grained low-carbon steel plates, whose toughness is difficult to meet the requirements for the use of structural steel in low-temperature environments

[0007] CN200910063768.2, CN200810012977.X and CN200810038047.1 and other low-welding crack-sensitive high-strength steel plates have applied for patents. The composition is designed with a low Pcm (≤0.26%) system, combined with controlled rolling or post-rolling normalizing, quenching and tempering treatment, to obtain B+F or tempered troostite and tempered sorbite structure, normalizing and quenching and tempering treatment cannot guarantee the continuity of on-line production, which not only increases the production process and cost, but also obtains relatively coarse surface and matrix structures, which do not have Excellent crack arrest

[0008] Marine steels with excellent low-temperature toughness such as WO2009 / 072753, CN200810033765.X and CN200810119506.9 adopt the traditional TMCP process or combined with post-rolling normalizing treatment to eliminate banded structure, coarse Widmanstatten structure and refine grains, although to a certain extent However, the low-temperature toughness is improved, but the strength of the steel plate is low, the matrix structure is F+P, and the surface structure is not deeply refined, which has no significant effect on improving the crack arrest performance, so it is not suitable for use as super-large container ship hull to hatch coaming , upper deck and other components manufacturing

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