A method for stably producing low-carbon drawing steel based on a continuous casting and rolling production line

Abstract

The present invention discloses a method for stably producing low-carbon drawing steel based on a continuous casting and rolling production line, belonging to the field of iron and steel production. The continuous rolling includes finish rolling, and the finish rolling adopts five-stand rolling. F5 adopts different-diameter rolling and roll misalignment rolling. The different-diameter rolling means that the roll diameter of the upper roll < the roll diameter of the lower roll, and the linear speed of the upper roll < the linear speed of the lower roll. The roll misalignment rolling means that the lower roll is misaligned towards the direction in which the strip steel enters. Compared with the prior art, the present invention improves the uneven deformation, structure and performance of the strip steel by adopting different-diameter misalignment rolling in finish rolling F5.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel, and relates to a rolling method and process for improving the uneven deformation, structure and properties of strip steel by using different-diameter offset rolling in finishing stand F5. Background Art

[0002] At present, in the finishing area of the continuous casting and rolling production line, the cumulative deformation of low-carbon soft steel series of drawing steels with a thickness specification of 1.2 - 2.5 mm cannot reach 90%, resulting in a small central deformation of the rolled piece, leading to problems such as uneven deformation, structure and properties between the surface and the center of the rolled piece, and excessive residual stress of the rolled piece, seriously affecting the performance of the rolled piece.

[0003] Through the detection of existing symmetrically rolled pieces, it is found that the reason lies in that the existing process increases the proportion of the {001} cube texture that is not conducive to stamping deformation in the texture components, resulting in a reduction in the proportion of the {111} texture that is conducive to stamping deformation in the structure, thus seriously affecting the r value, and further affecting the stamping performance of the rolled piece, resulting in a low stamping forming rate of the rolled piece. Summary of the Invention

[0004] The technical task of the present invention is to overcome the above deficiencies of the prior art, and provide a method for stably producing low-carbon soft steel series of drawing steels based on the continuous casting and rolling production line, and improving the uneven deformation, structure and properties of strip steel by using different-diameter offset rolling in finishing stand F5.

[0005] The technical solution for the present invention to solve its technical problems is: A method for stably producing low-carbon drawing steels based on the continuous casting and rolling production line, characterized in that: the continuous rolling includes finishing rolling, and the finishing rolling adopts five-stand rolling, and F5 adopts different-diameter rolling and roll offset rolling; the different-diameter rolling is that the upper roll diameter < the lower roll diameter, and the linear speed of the upper roll < the linear speed of the lower roll; the roll offset rolling is that the lower roll is offset towards the strip steel entry direction.

[0006] Further, the above-mentioned low-carbon is a steel grade with C ≤ 0.05%.

[0007] Further, the above-mentioned drawing means that the drawing depth does not exceed 30 mm.

[0008] Further, in the above-mentioned different-diameter rolling, the upper roll diameter: the lower roll diameter = 1:1.06 - 1:1.1.

[0009] Further, the rotational speed difference in the above-mentioned different-diameter rolling is between 6% - 10%.

[0010] Further, the offset amount of the above-mentioned roll offset rolling is 10 - 15 mm.

[0011] Compared with the prior art, the present invention has the following prominent beneficial effects:

[0012] 1. In the present invention, the finishing rolling F5 of the continuous casting and rolling production line adopts the process of unequal diameter rolling combined with misalignment amount, which causes strong shear strain in the rolled piece, thereby increasing the total strain of the rolled piece, making the strain penetrate into the center of the rolled piece, promoting the formation of {111} texture, improving the tissue uniformity of the rolled piece and enhancing the stamping performance of the rolled piece (the r value is increased from 0.8 to 1.2).

[0013] 2. By designing an online F5 stand, F5 can not only adopt the new rolling process but also avoid the risk of scrap steel during threading of thin gauge products, ensuring stable threading in finishing rolling.

[0014] 3. The present invention is used to produce low-carbon soft steel series of shallow drawing steels, which can further expand the shallow stamping market. The estimated price difference between the market shallow stamping steel and ordinary low-carbon soft steel is 30 yuan per ton. Calculated according to a performance non-conforming rejudgment rate of 1.5% and an annual output of 1 million tons, the benefit can be increased by 450,000 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of the online F5 stand of the present invention.

[0016] Figure 2 is a schematic diagram of unequal diameter misaligned rolling of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be further described below in conjunction with the drawings of the specification and the specific embodiments.

[0018] For the purposes of the following detailed description, it should be understood that, unless explicitly stated to the contrary, the present invention may assume various alternative variations and step sequences. In addition, except in any operating examples or where otherwise indicated, all numbers representing the amounts of ingredients used in the specification and claims should be understood to be modified in all cases by the term "about". At the very least, and without attempting to limit the application of the principle of equivalents to the scope of the claims, each numerical parameter should be understood at least in accordance with the number of significant figures reported and by applying ordinary rounding techniques.

[0019] Although the numerical ranges and parameters setting forth the broad scope of the present invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviations found in their respective test measurements.

[0020] It should also be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0021] In this application, unless otherwise specifically stated, the use of the singular includes the plural and the plural encompasses the singular. Additionally, in this application, unless otherwise clearly stated, the use of "or" means "and / or", even though in some cases "and / or" may be explicitly used. Further, in this application, unless otherwise specifically stated, the use of "a" or "an" means "at least one". For example, "a" first material, "a" coating composition, etc. refer to one or more of any of these items.

[0022] For better description, taking the direction of the strip entering as the front, that is Figure 1 、 2 the left direction is the front, and vice versa. It should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", "end", "side", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present invention application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation on the embodiments of the present invention application.

[0023] The present invention is a method for stably producing low-carbon shallow-drawing steel based on a continuous casting and rolling production line, and is used to produce low-carbon soft steel series shallow-drawing steel. The low-carbon soft steel series shallow-drawing steel specifically refers to low-carbon (C ≤ 0.05%) steel grades with a stamping depth not exceeding 30 mm, a yield strength ≤ 260 MPa, a tensile strength ≤ 350 MPa, and an elongation ≥ 38%.

[0024] The present invention is based on a continuous casting and rolling production line, and the continuous casting and rolling production line includes: converter smelting → continuous caster casting → rough rolling → induction heating → descaling → finish rolling → laminar cooling → coiling.

[0025] Among them, finish rolling uses five-stand rolling, and F5 uses different-diameter rolling and roll misalignment rolling: For the different-diameter misalignment rolling of the present invention, the linear speed of the upper roll < the linear speed of the lower roll, the rotational speed difference is between 6% - 10%, the roll diameter of the upper roll < the roll diameter of the lower roll, the roll diameter ratio is 1:1.06 to 1:1.1, the lower roll is misaligned towards the strip entering direction, and the misalignment amount between the upper and lower rolls is 10 - 15 mm.

[0026] Considering that currently the upper / lower rolls of the F5 rolling mill on the continuous casting and rolling production line use split gearboxes for transmission, and the surface linear speeds of the upper and lower rolls are basically the same. For the transformation of the F5 roll form, the risk of scrap steel during threading is high. To ensure smooth threading in finish rolling, after threading with four stands at the start of casting, the F5 stand is put into use online.

[0027] The F5 stand was put into use online, specifically: 4.0 / 3.5mm specifications were cast at the start, four stands (i.e. F1-F4 stands) were used for finishing and threading, the specifications were transitioned to 2.5mm specifications, the next piece of steel was put into use of the F5 stand, and the reduction rate was adjusted to ≤10%.

[0028] In the optimization plan, when the F5 frame is put into use, it is combined with the 4# looper second flow control technology and the speed cascade technology of the subsequent finishing rolling equipment. The technology is the first-level automation function of the rolling mill, which uses the pressure closed loop of looper detection to adjust the speed of the front and rear rolling mills to ensure the stability of logistics between the frames. It is an existing technology.

[0029] The F5 stand is put into use online to ensure tension and speed matching. The thickness is detected by instruments and THC control technology (a rolling mill's own thickness control technology that detects the thickness of the rolled piece and controls the mill roll gap in a closed loop) is used to ensure that the thickness meets the requirements.

[0030] The method of the present invention is used to produce low-carbon mild steel series shallow punching steel with a thickness specification of 1.2-2.5 mm. The present invention will be further described below by taking the production of 1.8 mm product as an example in conjunction with the accompanying drawings.

[0031] The overall process is: converter smelting → continuous casting → rough rolling → induction heating → descaling → finishing rolling → laminar cooling → coiling. Except for the finishing rolling process, other process parameters are only examples and have no limiting meaning.

[0032] The composition of molten steel is limited (wt%): C≤0.05%, Si≤0.05%, Mn≤0.1%, P≤0.030%, S≤0.0030%; the rest are Fe elements and unavoidable impurities.

[0033] Early conventional rolling:

[0034] (1) The continuous casting machine produces 105 mm × 1250 mm billets at a casting speed of 5.0 m / min and a temperature of 950-990 °C.

[0035] (2) The ingot is rolled into a 15 mm intermediate plate (980-1010°C) through R1-R2-R3 rolling, and the intermediate plate is heated to 1100-1120°C in an induction heating furnace;

[0036] (3) After the middle plate is descaled, Figure 1 As shown in Figure 1-a, the finishing rolling and threading adopts four stands (i.e., F1-F2-F3-F4 stands, with F5 being empty) to roll the strip into 4.0mm strip steel; the strip steel is layer-cooled to 660-680℃ and then coiled.

[0037] Different diameter offset rolling:

[0038] (4) F5 racks put into use online:

[0039] The 4.0 specification gradually decreases to the 2.5 mm specification.

[0040] The next roll with a specification of 2.5 mm is rolled to 2.0 mm, and F5 is put into use online at the end of the 2.0 mm roll (as shown in 1-b). Figure 1 as shown in 1-b

[0041] The specific process is as follows: When the tail is 2.2 - 2.5 s away from the center line of the F4 rolling mill, the F5 stand is lowered to the set roll gap h (h = 1.8 mm - predicted rolling force / mill stiffness). Within 1.5 - 2 s:

[0042] ① The reduction rate of F5 increases from 0 to 10% to complete the online commissioning.

[0043] ② Between F4 and F5, it is set at 20 - 22 N / mm after the instant increase in the rolling force of F5 to ensure the stable material flow of the rolled piece between F4 and F5. 2 Set to ensure the stable material flow of the rolled piece between F4 and F5.

[0044] The reason for the above operations is as follows: Due to the change in the roll diameter and structure of F5, there is a risk of scrap steel during threading of F5 finish rolling. By threading the steel with a four-stand 4.0 / 3.5 mm specification and then putting F5 into use online after adopting the 2.5 mm specification, the risk of scrap steel can be effectively avoided.

[0045] (5) Different-diameter misaligned rolling of the F5 stand:

[0046] As Figure 2 shown: 2a is synchronous rolling, ω1 = ω2, d1 = d2; 2b is misaligned rolling, ω1 < ω2, d1 = d2, S > 0; 2c is the different-diameter misaligned rolling of F5 in the present invention, ω1 < ω2, d1 < d2, S = 10 - 15 mm.

[0047] Among them: ω1 / ω2 are the linear speeds of the upper and lower rolls (unit: m / s); d1 / d2 are the roll diameters of the upper and lower rolls (unit: mm); S is the misalignment amount of the upper and lower rolls (unit: mm).

[0048] The upper and lower rolls of the F5 stand adopt different roll diameters (roll diameter ratio 1:1.06 - 1:1.1), and the rolls are matched according to a specific roll diameter ratio to achieve different linear speeds of the upper and lower rolls. In the present invention, the center of the lower roll is forward, and the misalignment amount of the upper and lower rolls is 10 - 15 mm, which can generate a "shearing" effect on the rolled piece, increase the desired strip deformation form, be conducive to introducing orientation, be easier to bite into the rolling mill, and have no obvious impact on the bending of the rolled piece. In the optimized solution, the original working roll window size is not adjusted, and the misalignment amount of the upper and lower rolls is achieved by thinning the thickness of the wear-resistant lining on one side and increasing the thickness of the wear-resistant lining on the other side (the original thickness of the single-sided lining is 20 mm), which is more cost-saving and transformation-cost-saving.

[0049] The unequal-diameter offset rolling of the present invention introduces strong shear strain to form a {111} texture, improving the tissue uniformity of the rolled piece and enhancing the stamping performance of the rolled piece. The equivalent strain of the rolled piece in the thickness direction during rolling is higher than that of synchronous rolling, and the minimum equivalent strain in the middle of the rolled piece is 13% higher than that of synchronous rolling.

[0050] In order to better compare the method of this application with the prior art, a comparative test was carried out.

[0051] Using molten steel with the same composition for production, the overall process is: converter smelting → continuous casting machine casting → rough rolling → induction heating → descaling → finish rolling → laminar flow cooling → coiling.

[0052] Example 1 uses the technology of this application, with unequal-diameter offset rolling on the F5 stand, directly producing a 2.5 mm specification.

[0053] Examples 2-4 use the technology of this application, with online commissioning of the F5 stand + unequal-diameter offset rolling on the F5 stand, producing thickness specifications of 1.2-2.5 mm.

[0054] The control group is the prior art, using equal-diameter synchronous rolling on the F5 stand to produce a 1.8 mm thickness specification.

[0055] The process parameters are as follows:

[0056]

[0057] The yield strength of the products obtained in Examples 1-4 and the control group is ≤260 MPa, the tensile strength is ≤350 MPa, and the elongation is ≥34%, meeting the performance requirements of the steel grade.

[0058] The other performance results are shown in the following table:

[0059] Example Target Specification (mm) Cumulative Deformation (%) r value Elongation (%) Stamping Forming Rate (%) Example 1 2.5 91.5 1.204 42.1 97.1 Example 2 1.2 92.9 1.225 43.1 98.3 Example 3 1.8 91.9 1.211 42.3 97.5 Example 4 2.2 91.3 1.201 41.5 96.9 Control Group 1.8 86.3 0.798 37.5 90.3

[0060] It can be seen from the above results that in Examples 1-4 of the present invention, by using unequal-diameter rolling combined with the misalignment amount process in the finish rolling F5 of the continuous casting and rolling production line, strong shear strain is generated in the rolled piece, thereby increasing the total strain of the rolled piece, enabling the strain to penetrate into the center of the rolled piece, promoting the formation of a {111} texture, improving the tissue uniformity of the rolled piece and enhancing the stamping performance of the rolled piece: the cumulative deformation amount is greater than 96%, the r value is increased from 0.8 to 1.2, and the elongation and stamping forming rate are significantly higher than those of the control group.

[0061] It should be noted that specific embodiments of the present invention have been described in detail for the present invention. For those skilled in the art, various obvious changes made without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A method for stably producing low-carbon mild steel in a continuous casting and rolling production line, characterized in that: The thickness specification of the low-carbon shallow drawing steel is 1.2 - 2.5 mm; the continuous rolling includes finish rolling, and the finish rolling adopts five-stand rolling, and F5 adopts different-diameter rolling and roll misalignment rolling; the different-diameter rolling means that the roll diameter of the upper roll < the roll diameter of the lower roll, and the linear speed of the upper roll < the linear speed of the lower roll; the roll misalignment rolling means that the lower roll is misaligned towards the strip entering direction; the low-carbon shallow drawing steel is a low-carbon steel type with a stamping depth not exceeding 30 mm, and in the low-carbon steel type, C ≤ 0.05%, yield strength ≤ 260 MPa, tensile strength ≤ 350 MPa, elongation ≥ 38%; among them; after the four-stand casting and threading in the finish rolling, the F5 stand is put into use online. Specifically, for the casting of 4.0 / 3.5 mm specification, the finish rolling threading adopts F1 - F4 stands, and the specification is transitioned to 2.5 mm specification, and the F5 stand is put into use for the next slab, and the reduction ratio adjustment ≤ 10%; in the different-diameter rolling, the roll diameter ratio of the upper roll to the lower roll = 1:1.06 - 1:1.1; the rotational speed difference in the different-diameter rolling is between 6% - 10%; the misalignment amount in the roll misalignment rolling is 10 - 15 mm.

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