High-formability boron-containing steel with tensile strength higher than or equal to 320 MPa and production method

Abstract

The invention discloses high-formability boron-containing steel with tensile strength higher than or equal to 320 MPa. The high-formability boron-containing steel is prepared from the following components in percentage by weight (wt%): 0.03-0.07% of C, 0.01-0.3% of Si, 0.4-0.9% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 0.006% of N, 0.0005-0.003% of B, and 0.03-0.08% of Ti. A production method comprises the following steps: continuously casting to form blank after smelting; heating in stages; roughly rolling; performing fine rolling; performing laminar cooling; and rolling. The high-formability boron-containing steel has yield strength of 250-350 MPa, tensile strength of 320-460 MPa, and ductility higher than or equal to 32%; moreover, cast blank does not need to cut corner after being unloaded if a secondary cooling water ratio is not reduced and N content is not strictly limited; and hot rolling can be directly performed, so that a product defect rate can be controlled to be lower than 0.5%.

Description

technical field [0001] The invention relates to a hot-rolled steel and a production method thereof, and specifically belongs to a high-formability boron-containing steel with a tensile strength ≥ 320 MPa and a production method thereof. Background technique [0002] Boron-containing steel is a low-alloy structural steel based on manganese and boron, in which boron can significantly improve the hardenability of steel, and is often used to replace precious metals such as Cr and Ni. The comprehensive performance and organization and performance uniformity of the product. 320-460MPa grade high formability boron-containing steel is mainly used to manufacture parts such as structural pipes, fluid conveying pipes and pressure pipes. It has a wide range of uses and the annual demand is ≥ 10 million tons. [0003] It is worth noting that the addition of boron will increase the crack sensitivity of the steel, which manifests as corner cracks on the slab, and edge cracks and warped sk...

AI Technical Summary

Problems solved by technology

Its disadvantage is that the low water ratio of the secondary cooling will increase the segregation of the slab, which is not conducive to improving the uniformity of the structure and properties of the product

The disadvantage is that the elongation of the product is low and it is easy to crack when forming

The disadvantage of this invention is that the N content is strictly limited, and a long time of vacuum treatment is required, which increases the production cost.

After adding titanium to the hot-rolled boron-added steel of the present invention, the billet quality has been significantly improved, and the off-line cleaning rate has dropped to 15.06%. The statistical results show that although the defect rate has been reduced to 1.39%, there are disadvantages in that, 15.06% of the slabs still need to be cleaned after they come off the assembly line

Its disadvantage is that if the amount of secondary cooling water is too low, it will increase the segregation of the billet, which is not conducive to improving the uniformity of the structure and properties of the product.

The disadvantage is that the elongation of the product is low and it is easy to crack when forming

[0013] 1. Reduce the specific water volume of the continuous casting secondary cooling and increase the straightening temperature. The disadvantage of this measure is that the low specific water volume of the secondary cooling will increase the segregation of the billet, which is not conducive to improving the uniformity of the structure and performance of the product

[0014] 2. Control the N content in the steel to ≤28ppm. The disadvantage of this measure is that it requires a long time of vacuum treatment, which significantly increases the production cost

[0015] 3. A pulse current is applied to the boron-containing steel slab before the straightening area. The disadvantage of this measure is that it needs to be equipped with a device for applying pulse current during industrial implementation, which increases the manufacturing cost.

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