Low yield strength ratio structural steel with yield strength ≥ 690mpa and production method thereof

Abstract

Steel for a low-yield-ratio structure with the yield strength larger than or equal to 690MPa comprises, by weight, 0.01-0.05% of C, 0.41-0.60% of Si, 2.10-3.50% of Mn, less than 0.010% of P, less than 0.005% of S, 0.10-0.50% of Mo, 0.51-0.80% of Cr, 0.10-0.80% of Cu, 0.05-0.50% of Ni, 0.052-0.11% of Nb, 0.053-0.10% of V, 0.008-0.025% of Ti, 0.015-0.060% of Als, 0.0010-0.0080% of Ca, 0.0005-0.0050% of Mg, 0.0010-0.0030% of N and 0.0005-0.0025% of O. A production method includes the steps of steel making, continuous casting for billet formation, heating of cast billets, temperature preservation, rough rolling, fine rolling, relaxing and slow cooling of a steel plate, and straightening. The mechanical properties of the steel include RP0.2 is larger than or equal to 690MPa, Rm is larger than or equal to 800MPa, the ductility A is larger than or equal to 22%, KV2 at the temperature of -20 DEG C is larger than or equal to 180J, and RP0.2 / Rm is smaller than or equal to 0.83. The steel after welding is not preheated or the preheating temperature is not higher than 50 DEG C, heating processing is not carried out after welding, welding efficiency is greatly improved, and the steel has good cold and hot machining performance and high deformation resistance.

Description

technical field [0001] The invention relates to a steel for engineering structure and a production method thereof, in particular to structural steel with a yield strength ≥ 690 MPa and a production method thereof. Background technique [0002] Traditional high-strength steel is generally produced by quenching + tempering. While the strength is increasing, the yield ratio is also increasing. Especially when the tensile strength reaches 600MPa or more, the yield ratio has reached more than 0.90, and the plasticity index is also high. drop to below 20%. Based on safety considerations, bridges, pipelines, and construction steel all have restrictions on the yield strength ratio of steel plates, especially high-rise buildings and public large buildings must have good earthquake resistance, that is, the use of steel The yield ratio (less than 0.85) and plasticity index (above 20%) are strictly limited. Obviously, the higher yield ratio and lower elongation of traditional high-s...

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Problems solved by technology

[0004] The patent document with Chinese patent application number 201010599469.3 discloses a 800MPa grade low yield ratio structural steel plate and its production method. The steel must contain more Cu and Ni elements, the alloy cost is high, and the steel plate must be tempered. , increasing the production cost of the process

[0005] Patent No. EP20010930007 discloses "THICK STEEL PLATE BEING EXCELLENT IN CTOD CHARACTERISTIC IN WELDING HEAT AFFECTED ZONE AND HAVING YIELD STRENGTH OF 460MPa OR MORE". Only some of the steel plates produced by direct quenching + tempering have a yield strength above 550MPa, and the yield strength ratio is between 0.84-0.90, which does not have seismic performance and the production process cost is relatively high; the yield strength of steel plates produced by TMCP is all between Below 550MPa, the strength level is low, and its yield ratio is between 0.79-0.88, the seismic performance is poor

The steel plates produced by the above two processes both limit the number of Mg and Al oxide particles per unit area, which is difficult to control and is not conducive to the promotion of production in various metallurgical industries

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