Rolling method of low-compression-ratio high-deformation-penetration extra-thick plate

Abstract

The invention discloses a rolling method of a low-compression-ratio high-deformation-permeability extra-thick plate, which comprises the following steps: 1) heating: heating a plate blank at the heating temperature of 1000-1250 DEG C for 4-8 hours in a furnace, and keeping the thickness of the plate blank at 300-400 mm; (2) rolling is conducted, specifically, rolling is conducted at the high temperature that the slab temperature is larger than or equal to 850 DEG C, the pass rolling reduction is controlled to range from 40 mm to 45 mm, along with the rolling process, the pass rolling reduction of the next pass is not reduced compared with the pass rolling reduction of the previous pass, and a steel plate with the thickness ranging from 125 mm to 167 mm is obtained after rolling; by adopting the small compression ratio of 2.4-3.0, effective deformation permeation of the core part of the steel plate is realized, the production of the thick steel plate (with the thickness of 125-167mm) can be realized, the production cost is reduced compared with the existing process, and the method is more suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of carbon steel thick plate production technology, specifically relating to a rolling method for extra-thick plates with low compression ratio and high deformation penetration. Background Technology

[0002] Currently, the production of carbon steel thick plates generally uses continuously cast billets as raw material slabs. After being heated in a furnace, these billets undergo a specific reduction process on a thick plate rolling mill to produce carbon steel thick plate products of a certain thickness. Because continuously cast billets are prone to developing specific defects at certain locations along the thickness direction, such as half-thickness or quarter-thickness, these defects can affect the performance of the rolled thick plate products. Therefore, carbon steel thick plate product standards generally have performance requirements for specific locations along the thickness direction, such as half-thickness or quarter-thickness. Thus, during the subsequent heating and rolling process of the continuously cast billet, it is necessary to eliminate these defects through reasonable heating and reduction processes to ensure that the product performance meets user requirements.

[0003] With the increasing market demand for thicker carbon steel plates, steel manufacturers generally use thicker carbon steel slabs and roll them on thick plate mills at a certain compression ratio to produce thicker carbon steel plates. As the thickness of the carbon steel slab increases, so do the internal defects, requiring a higher compression ratio to eliminate them. It is generally believed that a compression ratio of no less than 3.0 is necessary to produce carbon steel plates with acceptable performance. However, when the slab thickness reaches a certain range, some defects may arise inside the slab that cannot be eliminated during the thick plate rolling process. Even with a high compression ratio during rolling, effective deformation penetration into the core of the steel plate cannot be achieved, resulting in unsatisfactory performance in the thickness direction after rolling.

[0004] Chinese patent CN101773931A discloses a method for vacuum composite rolling of extra-thick plates, comprising the following steps: 1. Stacking billets with their surfaces to be composited facing each other horizontally, ensuring complete overlap, and then lifting the billets using a mechanical lifting device; 2. Performing vacuum electron beam welding around the perimeter of the joint surfaces of the two billets under vacuum conditions; 3. Rolling the welded billets. The extra-thick plates obtained by this patent have no inclusions in the composite surface. By pre-setting the spacing between the surfaces to be composited before vacuuming, some air is prevented from being trapped within the composite surfaces before welding, thus preventing oxidation. Simultaneously, by moving the billets to ensure the two composite surfaces are aligned, the two surfaces are kept parallel, preventing uneven ends from affecting electron beam welding. This patent obtains extra-thick plates with a thickness exceeding 100mm through composite billet assembly.

[0005] Chinese patent CN104962814A discloses a normalized high-strength and high-toughness 150mm extra-thick plate and its production method. The chemical composition of the extra-thick plate, by weight percentage, is: C: 0.14%–0.19%; Si: 0.20%–0.50%; Mn: 1.40%–1.70%; Ni: 0.30%–0.40%; Cu: 0.10%–0.30%; Nb: 0.035%. ~0.050%; V: 0.030%~0.050%; Ti: 0.010%~0.020%; Alt: 0.015%~0.050%; P≤0.015%; S≤0.0050%; Carbon equivalent Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni / +Cu) / 15: 0.41%~0.53%; the remainder is Fe and unavoidable impurities. This patent solves the problems of poor low-temperature impact and insufficient strength after normal normalizing in extra-thick plates through reasonable alloy composition design, strict controlled rolling and cooling, and normalizing + water cooling process.

[0006] Chinese patent CN108034897A discloses an extra-thick plate produced under low compression ratio conditions and its production method. The weight percentage of the alloy composition of the extra-thick plate is as follows: C: 0.16%~0.18%, Si: 0.15%~0.25%, Mn: 1.40%~1.50%, P: ≤0.015%, S: ≤0.0050%, Nb: 0.020%~0.025%, Ti: 0.010%~0.015%, Alt: 0.020%~0.050%, with the remainder being Fe. The sum of all the above alloy components is 100%, and the chemical composition of each alloy element satisfies the following: carbon equivalent Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.43. This patent, through the setting of composition and rolling process, has obtained Q390 extra-thick plates with a thickness of more than 150mm. The longitudinal impact energy at -40℃ and -60℃ is above 138J, and the cross-sectional shrinkage rate in the thickness direction meets the Z35 requirements.

[0007] Chinese patent CN108034898A discloses a 160mm thick extra-thick plate produced under low compression ratio conditions and its production method. The weight percentage of the alloy composition of the extra-thick plate is as follows: C: 0.14%~0.16%, Si: 0.15%~0.25%, Mn: 1.45%~1.55%, P: ≤0.015%, S: ≤0.0020%, Nb: 0.030%~0.035%, V: 0.050%~0.055%, Ti: 0.010%~0.020%, Ni: 0.22%~0.25%, Alt: 0.040%~0.060%, with the remainder being Fe. The sum of all the above alloy components is 100%, and the chemical composition of each alloy element satisfies the carbon equivalent Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.43. This patented technology utilizes a compositional design and a continuous casting billet process involving a four-stage rolling process, ultra-fast cooling, and heat treatment to produce extra-thick plates. It yields Q345D extra-thick plates with a thickness exceeding 160mm, exhibiting a longitudinal impact energy of over 161J at -20℃ and a thickness reduction in area meeting Z35 requirements.

[0008] In summary, the current methods for producing extra-thick plates are: First, using composite billet assembly technology, where continuously cast billets are assembled to prepare thicker slabs, which are then rolled into even thicker steel plates using a rolling mill. However, this leads to a significant increase in steel plate production costs. Second, by adjusting the carbon steel alloy composition, the internal microstructure of the rolled steel plate can be controlled under low compression ratio conditions through alloy composition or heat treatment, enabling the production of thicker steel plates. However, this method is only effective for steel plates that meet certain alloy composition requirements, and cannot produce thicker steel plates for grades with specific user needs. Summary of the Invention

[0009] The purpose of this invention is to provide a rolling method for extra-thick plates with low compression ratio and high deformation penetration. By using a small compression ratio, effective deformation penetration of the steel plate core can be achieved, enabling the production of thick steel plates (thickness 125-167mm). Compared with existing processes, this method reduces production costs and is more suitable for large-scale production.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A rolling method for extra-thick plates with low compression ratio and high deformation penetration includes the following steps:

[0012] 1) Heating

[0013] The slab heating temperature is 1000-1250℃, the heating time in the furnace is 4-8 hours, and the slab thickness is 300-400mm;

[0014] 2) Rolling

[0015] The slab is rolled at a high temperature of ≥850℃, with the reduction per pass controlled at 40-45mm. As the rolling process progresses, the reduction of the subsequent pass does not decrease compared to the previous pass, resulting in a steel plate with a thickness of 125-167mm.

[0016] Preferably, the steel plate compression ratio is 2.4-3.0.

[0017] Preferably, in step 2), the slab is first rolled in forming passes.

[0018] Preferably, in step 2), rolling is performed on a thick plate rolling mill.

[0019] Preferably, the thickness-direction properties of the rolled steel plate meet the GB / T 5313-2010 standard "Steel Plates with Thickness-Direction Properties".

[0020] Research has revealed that in current carbon steel plate production, when the slab thickness is ≥300mm, the mainstream rolling process suffers from insufficient core deformation due to amplified dimensional effects. Figure 1 The figure shows the distribution of reduction in the thickness direction of a 300mm thick slab after rolling with a reduction of 20mm per pass. It can be seen that the deformation is greatest in the near-surface area (about 30mm from the top and bottom surfaces), while the deformation is negligible in the interior (more than 60mm from the surface).

[0021] To produce qualified thick plates, after increasing the slab thickness, the compression ratio of the steel plate is often increased significantly to eliminate internal defects. However, simply increasing the compression ratio without adopting a high deformation penetration process in the rolling process will not result in effective core deformation of the rolled piece in each rolling pass. After the rolling process is completed, the total amount of deformation accumulated inside the slab (at a distance greater than 60mm from the surface) is insufficient to effectively eliminate internal defects.

[0022] This invention implements a complete large reduction rolling process for slabs with a thickness ≥300mm at a high temperature stage of ≥850℃. Large reduction at high temperature is conducive to deformation penetration into the core, thereby improving the deformation penetration effect inside the steel plate.

[0023] During the rolling process, a large reduction is used in each pass, with the reduction in each pass controlled within the range of 40-45mm. This allows for the accumulation of deformation in the core of the slab (i.e., at half the thickness) in each pass. Although the total number of passes is relatively small, the deformation reduction efficiency of each pass is high. The entire rolling process brings a large amount of deformation to the core of the slab, which can better improve the internal properties of the steel plate. Thus, under the condition of a low compression ratio of 2.4-3.0, thicker steel plates with qualified performance can be produced.

[0024] Furthermore, as the rolling process proceeds, the reduction in each subsequent pass does not decrease compared to the previous pass. There is a logical relationship here: the closer to the target rolling thickness, the greater the deformation distribution. The larger the reduction in each pass should be placed in the last pass, so that the deformation penetration effect is optimal.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention targets slabs with a thickness of 300-400mm. During the rolling process, a large reduction of 40-45mm per pass is employed. Under low compression ratios of 2.4-3.0, this achieves the production of high-performance extra-thick plates with thicknesses of 125-167mm and a thickness-direction reduction of ≥50%. The thickness-direction properties of the rolled steel plates meet the GB / T 5313-2010 standard for "Steel Plates with Through-Thickness Properties". In contrast, existing technologies often employ composite billet assembly and rolling processes with compression ratios greater than 3.0 to obtain qualified extra-thick plates, leading to a significant increase in production costs. Alternatively, optimized alloy composition and offline heat treatment can be used to produce thicker steel plates, but this method only enables the production of specific thickness specifications and further increases production costs. Attached Figure Description

[0027] Figure 1 The distribution of reduction in the thickness direction of the intermediate rolled piece after rolling a 300mm thick slab with a reduction of 20mm per pass. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0029] Table 1 shows the number of passes and the reduction amount in each pass during the rolling process of this invention. Table 2 shows the properties of the steel plate obtained by this invention.

[0030] The steel plates obtained in the embodiments and comparative examples of this invention were tested for their thickness direction properties in accordance with GB / T 5313-2010 standard.

[0031] As can be seen from Tables 1 and 2, the steel plate prepared in the embodiment of the present invention has the thickness direction properties that meet the GB / T 5313-2010 standard, while the core deformation and thickness direction section reduction rate of the steel plate obtained in the comparative example are lower than those of the embodiment of the present invention.

[0032]

[0033]

Claims

1. A rolling method for extra-thick plates with low compression ratio and high deformation penetration, characterized in that, Includes the following steps: 1) Heating The slab heating temperature is 1000-1250℃, the heating time in the furnace is 4-8 hours, and the slab thickness is 300-400mm; 2) Rolling The slab is rolled at a high temperature of ≥850℃, with the reduction per pass controlled at 40-45mm. As the rolling process progresses, the reduction of the subsequent pass does not decrease compared to the previous pass, resulting in a steel plate with a thickness of 125-167mm.

2. The rolling method as described in claim 1, characterized in that, The compression ratio of the steel plate is 2.4-3.

0.

3. The rolling method as described in claim 1, characterized in that, In step 2), the slab is first rolled in forming passes.

4. The rolling method as described in claim 1 or 3, characterized in that, In step 2), rolling is carried out on a thick plate rolling mill.

5. The rolling method as described in claim 1, characterized in that, The thickness properties of the rolled steel plate meet the GB / T 5313-2010 standard for steel plates with thickness properties.

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