A method for saving low alloy warped steel plates with a thickness of less than 20 mm

Abstract

The present invention relates to a method for saving low-alloy warped steel plates with a thickness of less than 20 mm, and belongs to the technical field of medium and thick plate production in the metallurgical industry. The technical solution is: operate according to the following steps: Step 1: Make a lower template and an upper template according to the initial deflection of the warped steel plate; Step 2: Place the warped steel plate between the lower template and the upper template, and when placing it, make the warping direction of the warped steel plate opposite to that of the lower template and the upper template; Step 3: Place a pressing plate on the upper template, and apply a certain pressure by the pressing plate to correct the deflection of the warped steel plate to within the permitted range. The beneficial effects of the present invention are: there is no need to build a new cold straightening machine or flattening machine, and the production plan of the normalizing furnace and the rolling mill will no longer be disrupted, and the deflection of the low-alloy warped steel plate with a thickness of less than 20 mm can be corrected to within the permitted range.

Description

Technical Field

[0001] The invention relates to a method for saving a low-alloy warped steel plate with a thickness of less than 20 mm, belonging to the technical field of medium and thick plate production in the metallurgical industry. Background Art

[0002] Q355 series low-alloy high-strength structural steel is the mainstream plate material, accounting for a large proportion of medium and thick plate production lines. To increase production and efficiency, a process of micro-alloying, no temperature control, and high-pressure accelerated cooling is adopted for hot rolling, giving full play to the strengthening and toughening effects of micro-alloying elements and achieving excellent comprehensive performance. Although the no-temperature-controlled + DQ rapid cooling process can strongly straighten the steel plate, the residual stress or uneven cooling of the steel plate can easily cause varying degrees of warping, especially for mechanically sheared steel plates with an H of ≤ 20 mm. Under fast-paced mode, warped plates with an unevenness of > 11 mm / 2 m are often produced. For production lines without cold straightening machines or presses, there are generally two ways to save these warped plates: one is to transport them to a normalizing furnace for low-temperature heating and then straighten them, and the other is to hoist them to a hot straightening machine for straightening at room temperature. In long-term production practice, these two recovery methods have revealed several shortcomings. Recovering the plate in a normalizing furnace increases extra transportation and fuel costs, disrupting production schedules. Using a hot straightener for room-temperature straightening can only be performed during the mill's downtime. Furthermore, burrs and sharp corners on the sheared surface of the steel plate must be ground to prevent damage to the straightening rollers, making the entire process cumbersome and inconvenient. Given the small number of warped plates, installing a new cold straightener or press is unnecessary, which would significantly complicate production organization.

[0003] Patent CN102139296B describes a method for rescuing warped pipeline steel plates with a thickness of less than 20 mm by straightening them at room temperature. This method utilizes the mill's downtime to organize straighteners to perform repeated straightening on warped pipeline steel plates with a small reduction and multiple passes on a hot straightening machine, bringing the warped steel plates within the national standard of 11 mm flatness for every 2 meters.

[0004] Patent CN101451184B, a normalizing furnace low-temperature preheating flattening method, adopts a method of heating the room temperature steel plate to a lower heating temperature of 600-650℃ and then straightening it. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for saving low-alloy buckled steel plates with a thickness of less than 20 mm, which can correct the deflection of low-alloy buckled steel plates with a thickness of less than 20 mm to within the permitted range and solve the problems existing in the background technology.

[0006] The technical solution of the present invention is:

[0007] A method for rescuing low-alloy warped steel plates with a thickness of less than 20 mm, which is carried out in accordance with the following steps:

[0008] Step 1: Make a lower template and an upper template according to the initial deflection of the bent steel plate. The deflection calculation formula of the lower template and the upper template is as follows:

[0009] C w =σ s / 250(1+0.008(C o -50))(4.2λ 2 -0.6λ+0.6)

[0010] Where: σ s -Yield strength of curved steel plate N / mm 2 or MPa;

[0011] C o -The initial deflection of the curved steel plate is the curved value (mm);

[0012] λ-Ratio of the width of the curved steel plate to 760mm;

[0013] C w - The deflection of the lower and upper formwork, i.e. the amount of deflection or the amount of bend required to straighten a curved steel plate;

[0014] Step 2: Place the curved steel plate between the lower template and the upper template, making sure that the curved steel plate is in the opposite direction to the lower and upper templates;

[0015] Step 3: Place a pressing plate on the upper template. Apply a certain pressure through the pressing plate to correct the deflection of the bent steel plate to within the permitted range. The pressure calculation formula of the pressing plate is as follows:

[0016] P=3b / 2t×h 2 σ s

[0017] Where: b—width of the pressing plate in mm;

[0018] t—width of the curved steel plate in mm;

[0019] h—platen thickness (mm)

[0020] σ s —Yield strength of curved steel plate N / mm 2 or MPa.

[0021] The outer dimensions of the lower template and the upper template are greater than or equal to the outer dimensions of the curved steel plate.

[0022] The pressing plate in step 3 is 1 to 4 flat steel plates.

[0023] The beneficial effects of the present invention are: without building a new cold straightening machine or flattening machine, and without disrupting the production plan of the normalizing furnace and the rolling mill, the deflection of low-alloy curved steel plates with a thickness of less than 20 mm can be corrected to within the standard allowable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a curved steel plate;

[0025] Figure 2 It is a flattening schematic diagram;

[0026] In the figure: lower template 1, upper template 2, pressing plate 3, curved steel plate 4. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and through examples.

[0028] Refer to the attached Figure 1-2 A method for saving low-alloy warped steel plates with a thickness of less than 20 mm is to follow the steps below:

[0029] Step 1: Make a lower template and an upper template according to the initial deflection of the bent steel plate. The deflection calculation formula of the lower template and the upper template is as follows:

[0030] C w =σ s / 250(1+0.008(C o -50))(4.2λ 2 -0.6λ+0.6)

[0031] Where: σ s -Yield strength of curved steel plate N / mm 2 or MPa;

[0032] C o -The initial deflection of the curved steel plate is the curved value (mm);

[0033] λ-Ratio of the width of the curved steel plate to 760mm;

[0034] C w - The deflection of the lower and upper formwork, i.e. the amount of deflection or the amount of bend required to straighten a curved steel plate;

[0035] Step 2: Place the curved steel plate between the lower template and the upper template, making sure that the curved steel plate is in the opposite direction to the lower and upper templates.

[0036] Step 3: Place a pressing plate on the upper template. Apply a certain pressure through the pressing plate to correct the deflection of the bent steel plate to within the permitted range. The pressure calculation formula of the pressing plate is as follows:

[0037] P=3b / 2t×h 2 σ s

[0038] Where: b—width of the pressing plate in mm;

[0039] t—width of the curved steel plate in mm;

[0040] h—platen thickness (mm)

[0041] σ s —Yield strength of curved steel plate N / mm 2 or MPa.

[0042] Example 1: Follow the steps below:

[0043] (1) The size of the curved steel plate is 20×2200×12000mm, and the initial deflection C o 20mm / 2m, yield strength σ s 400N / mm 2 ,λ=2200mm / 760mm=2.89;

[0044] Calculate the amount of rebend required to straighten the bent steel plate according to the formula

[0045] h'=C w =σ s / 250(1+0.008(C o -50))(4.2λ 2 -0.6λ+0.6)

[0046] =400 / 250(1+0.008(20-50))(4.2×2.89 2 -0.6×2.89+0.6)

[0047] =8 / 5(1-0.24)×33.95 =1.6×0.76×33.95=41mm

[0048] (2) Customize two lower templates 1 and upper templates 2 with a thickness of 30 mm, a width of 2500 mm, and a length of 12000 mm, and the deflection of each template is 41 mm / 2 m.

[0049] (3) Customized flat plate: 20mm thick × 2500mm wide × 12000mm long. Each flat plate weighs 7 tons, which means the pressure of each plate is 70KN. The flattening force is calculated according to the formula:

[0050] P=3b / 2t×h 2 σ s =(3×2500 / 2×2200)×20 2 ×400=273KN

[0051] Therefore, a total of 4 pressing plates were customized.

[0052] (4) Refer to the attached Figure 2 , place the lower template opening downward, place the curved steel plate opening upward on the lower template, place the upper template opening downward on the curved steel plate, and finally place four pressing plates on the upper template. Press for 5 to 10 seconds and then lift it away. The curved steel plate with a deflection of 20mm / 2m can be pressed into a deflection of ≤10mm / 2m, which meets the requirements of Article 7.1 of the national standard GBT 709-2019.

[0053] Example 2:

[0054] The size of the curved steel plate is 16×2500×12000mm, and the initial deflection C o 16mm / 2m, yield strength σ s 400 N / mm 2 ;

[0055] Calculate the required backbend h'=400 / 250(1+0.008(16-50))(4.2×3.29 2 -0.6×3.29+0.6)=1.6×0.728×44.09=51mm;

[0056] Pressure p = (3 × 2500 / 2 × 2500) × 16 2 ×400=154KN, 3 pressing plates in total, and the rest are the same as in Example 1.

[0057] Example 3:

[0058] The size of the curved steel plate is 14×2000×8000mm, and the initial deflection C o 14mm / 2m, yield strength σ s 400 N / mm 2 ;

[0059] Calculate the required backbend h'=400 / 250(1+0.008(14-50)) (4.2×2.63 2 -0.6×2.63+0.6)=32mm;

[0060] Pressure p = (3 × 2500 / 2 × 2000) × 14 2 ×400=192 KN, there are 3 pressing plates in total, and the rest are the same as in Example 1.

Claims

1. A method for rescuing low-alloy warped steel plates with a thickness of less than 20 mm, characterized by: Follow these steps: Step 1: Make a lower template and an upper template according to the initial deflection of the bent steel plate. The deflection calculation formula of the lower template and the upper template is as follows: C w =s s / 250(1+0.008(C o -50))(4.2l 2 -0.6λ+0.6) Where: σ s -Yield strength of curved steel plate N / mm 2 or MPa; C o -The initial deflection of the curved steel plate is the curved value (mm); λ-Ratio of the width of the curved steel plate to 760mm; C w - The deflection of the lower and upper formwork, i.e. the amount of deflection or the amount of bend required to straighten a curved steel plate; Step 2: Place the bent steel plate between the lower template and the upper template, making sure that the bent direction of the bent steel plate is opposite to that of the lower template and the upper template; Step 3: Place a pressing plate on the upper template. Apply a certain pressure through the pressing plate to correct the deflection of the bent steel plate to within the permitted range. The pressure calculation formula of the pressing plate is as follows: P=3b / 2t×h 2 s s Where: b—width of the pressing plate in mm; t—width of the curved steel plate in mm; h—platen thickness (mm) σ s —Yield strength of curved steel plate N / mm 2 or MPa.

2. The method for rescuing a low-alloy warped steel plate with a thickness of less than 20 mm according to claim 1, characterized in that: The outer dimensions of the lower template and the upper template are greater than or equal to the outer dimensions of the curved steel plate.

3. The method for salvaging low-alloy warped steel plates with a thickness of less than 20 mm according to claim 1, characterized in that: The pressing plate in step 3 is 1 to 4 flat steel plates.

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