A low-carbon aluminum-killed steel and its preparation method

Abstract

This application relates to the technical field of steel rolling production, and in particular to a low-carbon, aluminum-killed steel and its preparation method. The method comprises: obtaining a hot-rolled plate having a predetermined chemical composition; performing tension straightening on the hot-rolled plate according to the thickness of the hot-rolled plate, and controlling the process parameters of the tension straightening; wherein the temperature of the tension straightening machine on the hot-rolled plate is controlled. The hot-rolled plate after tension straightening is pickled to obtain the low-carbon, aluminum-killed steel. This application addresses the technical problem of crease marks appearing on the surface of existing low-carbon, aluminum-killed steel.

Description

Technical Field

[0001] The present application relates to the technical field of steel rolling production, and in particular to a low-carbon aluminum-killed steel and a preparation method thereof. Background Art

[0002] Given the cost pressures faced by the automotive industry for automotive structural parts, air conditioner, and refrigerator compressors, many products have adopted tropical cooling to reduce costs. Consequently, pickled products have become a key focus in recent years. This situation places high demands on the pickled surface, with no surface defects or flaws permitted. With the intensification of competition in the steel market, the demand for high-quality, low-cost steel is becoming increasingly prominent. Hot-rolled pickled steel, a special intermediate product between hot-rolled and cold-rolled steel, is a product that undergoes continuous turbulent pickling, followed by straightening, trimming, oiling, and coiling, resulting in a highly precise surface finish.

[0003] The "crease mark" defect of pickled low-carbon aluminum-killed steel is a common surface quality problem. The existence of a yield platform and obvious upper and lower yield points in the SPHC tensile stress-strain curve of the pickled plate is the internal reason why the "crease mark" defect is easily generated on its surface. The uneven force on the steel plate surface during the uncoiling process is the external reason. At present, the traditional control of the horizontal fold mark defect of low-carbon aluminum pickled plate is eliminated through the leveling process. When eliminating the "crease mark" defect, low-carbon aluminum pickled plate relies on the hot rolling leveling process, which not only increases production costs but also seriously restricts the utilization of production capacity. At present, the pickling production lines are all continuous pickling production lines. The continuous pickling line has its own straightening process. If it is through the offline leveling process, it will increase the cost. Although the "crease mark" defect is eliminated when the strip passes through the offline leveling process, other defects are prone to occur. Summary of the Invention

[0004] The present application provides a low-carbon aluminum-killed steel and a preparation method thereof to solve the technical problem of crease marks appearing on the surface of existing low-carbon aluminum-killed steel.

[0005] In a first aspect, the present application provides a method for preparing low-carbon aluminum-killed steel, the method comprising:

[0006] obtaining a hot-rolled plate having a set chemical composition;

[0007] According to the thickness of the hot rolled plate, the hot rolled plate is tension-leveled and the process parameters of the tension-leveling are controlled; wherein the temperature of the tension-leveling machine on the hot rolled plate is controlled;

[0008] The hot-rolled plate after tensioning and straightening is pickled to obtain low-carbon aluminum-killed steel.

[0009] Optionally, the set chemical composition includes: C, Si, Mn, P, S, Alt, N, Ti and Fe; wherein the Ti content is 0.015 wt%-0.025 wt%.

[0010] Optionally, the Ti content is 0.0178 wt%-0.0225 wt%.

[0011] Optionally, in the set chemical composition, the C content is 0.025 weight%-0.05 weight%, the Si content is ≤0.05 weight%, the Mn content is 0.18 weight%-0.25 weight%, the P content is ≤0.02 weight%, the S content is ≤0.015 weight%, the Alt content is 0.02 weight%-0.05 weight%, and the N content is ≤0.005 weight%.

[0012] Optionally, the step of performing tension straightening on the hot-rolled plate according to the thickness of the hot-rolled coil and controlling the process parameters of the tension straightening comprises:

[0013] If the thickness of the hot-rolled plate is less than or equal to 3 mm, performing a first straightening process on the hot-rolled plate and controlling process parameters of the first straightening process;

[0014] If the thickness of the hot-rolled plate is 3 mm < h ≤ 5 mm, performing a second straightening operation on the hot-rolled plate and controlling the process parameters of the second straightening operation;

[0015] If the thickness of the hot-rolled plate is greater than 5 mm, the hot-rolled plate is subjected to a third straightening process, and the process parameters of the third straightening process are controlled.

[0016] Optionally, the process parameters of the first straightening process include: a first elongation, a first insertion amount of the bending roller #1 of the straightening machine, a first insertion amount of the bending roller #2 of the straightening machine, and a first insertion amount of the straightening roller of the straightening machine; wherein,

[0017] The first elongation is 2.3%-2.7%, the first insertion amount of the bending roller of the straightening machine 1# is 17mm-19mm, the first insertion amount of the bending roller of the straightening machine 2# is 17mm-19mm, and the first insertion amount of the straightening roller of the straightening machine is 31mm-33mm.

[0018] Optionally, the process parameters of the second straightening process include: a second elongation, a second insertion amount of the bending roller #1 of the straightening machine, a second insertion amount of the bending roller #2 of the straightening machine, and a second insertion amount of the straightening roller of the straightening machine; wherein,

[0019] The second elongation is 2.3%-2.7%, the second insertion amount of the bending roller of the straightening machine 1# is 19mm-21mm, the second insertion amount of the bending roller of the straightening machine 2# is 19mm-21mm, and the second insertion amount of the straightening roller of the straightening machine is 29mm-31mm.

[0020] Optionally, the process parameters of the third straightening include: a third elongation, a third insertion amount of the bending roller #1 of the straightening machine, a third insertion amount of the bending roller #2 of the straightening machine, and a third insertion amount of the straightening roller of the straightening machine; wherein,

[0021] The third elongation is 2.3%-2.7%, the third insertion amount of the bending roller of the straightening machine 1# is 16mm-18mm, the third insertion amount of the bending roller of the straightening machine 2# is 18mm-20mm, and the third insertion amount of the straightening roller of the straightening machine is 29mm-31mm.

[0022] Optionally, the temperature of the hot-rolled plate straightening machine is ≤40°C.

[0023] In a second aspect, the present application provides a low-carbon aluminum killed steel, which is prepared by the method described in any embodiment of the first aspect.

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The preparation method of the low-carbon aluminum-killed steel provided in the embodiments of this application controls the chemical composition of the killed steel to keep the difference between the upper and lower yield points within a certain range; controls the straightening process to achieve scale removal, accelerate pickling speed, improve strip shape, and control crease marks; and controls the temperature of the upper straightening machine of the steel plate to avoid transverse fold defects on the steel plate surface. In summary, this method solves the technical problem of crease marks on the surface of existing low-carbon aluminum-killed steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 A schematic flow chart of a method for preparing low-carbon aluminum-killed steel provided in an embodiment of the present application;

[0029] Figure 2 A surface morphology of a low-carbon aluminum-killed steel provided as a comparative example of this application;

[0030] Figure 3 A yield curve diagram of adding microalloyed Ti provided in an embodiment of the present application;

[0031] Figure 4 This is a surface morphology of a low-carbon aluminum-killed steel provided in Example 1 of the present application;

[0032] Figure 5 This is a surface morphology of a low-carbon aluminum-killed steel provided in Example 2 of the present application;

[0033] Figure 6 This is a surface morphology diagram of a low-carbon aluminum-killed steel provided in Example 3 of the present application. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0036] In this application, unless otherwise specified, the directional words used, such as "upper" and "lower", refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application specification, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0037] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0038] In the first aspect, the present application provides a method for preparing low carbon aluminum killed steel, see Figure 1 , the method comprising:

[0039] S1. Obtaining a hot-rolled plate with a set chemical composition;

[0040] S2. performing tensioning and straightening on the hot-rolled plate according to the thickness of the hot-rolled plate, and controlling the process parameters of the tensioning and straightening; wherein the temperature of the tensioning and straightening machine on the hot-rolled plate is controlled;

[0041] S3. Pickling the hot-rolled plate after tension straightening to obtain low-carbon aluminum-killed steel.

[0042] In the embodiments of the present application, the chemical composition of the killed steel is controlled to control the difference between the upper and lower yield points within a certain range; the straightening process is controlled to achieve scale breaking, accelerate the pickling speed, improve the strip shape and control crease defects; and the temperature of the upper straightening machine of the steel plate is controlled to avoid transverse folding defects on the surface of the steel plate.

[0043] In some embodiments, the set chemical composition includes: C, Si, Mn, P, S, Alt, N, Ti and Fe; wherein the content of Ti is 0.015 wt%-0.025 wt%.

[0044] The positive effect of controlling the Ti content to 0.015 wt%-0.025 wt% is that, through thermodynamic calculations, the addition of Ti completely dissolves N, thereby controlling the difference between the upper and lower yield points within 10 MPa. This completely fixes the C and N elements, thereby achieving the purpose of controlling the "crease mark" defect. If the Ti content is too high, the yield strength will increase to a certain extent, failing to meet the stamping requirements of low-carbon aluminum customers; if the Ti content is too low, the purpose of controlling the "crease mark" defect will be achieved to a certain extent. Specifically, the Ti content can be 0.015 wt%, 0.020 wt%, 0.025 wt%, etc.

[0045] In some embodiments, the Ti content is 0.0178 wt % to 0.0225 wt %.

[0046] Preferably, in the embodiment of the present application, the Ti content can be controlled to be 0.0178 wt %-0.0225 wt %.

[0047] In some embodiments, in the set chemical composition, the C content is 0.025 wt%-0.05 wt%, the Si content is ≤0.05 wt%, the Mn content is 0.18 wt%-0.25 wt%, the P content is ≤0.02 wt%, the S content is ≤0.015 wt%, the Alt content is 0.02 wt%-0.05 wt%, and the N content is ≤0.005 wt%.

[0048] The positive effect of controlling the C content to 0.025% to 0.05% by weight: Carbon, as a strengthening element, can improve the strength of low-carbon aluminum products. Specifically, the C content can be 0.025%, 0.030%, 0.035%, 0.04%, 0.045%, 0.05%, etc.

[0049] The positive effect of controlling the Si content to ≤ 0.05 wt% is that silicon is a residual element and is removed as much as possible during the steelmaking process. Specifically, the Si content can be 0.05 wt%, 0.04 wt%, 0.03 wt%, etc.

[0050] Controlling the Mn content to 0.18% to 0.25% by weight has the following positive effects: Manganese, as a primary strengthening element, improves the strength of low-carbon aluminum steels. Manganese combines with sulfur in the steel to form MnS, thereby eliminating the adverse effects of sulfur. Mn dissolves in ferrite and austenite, expanding the austenite region. Specifically, the Mn content can be 0.18%, 0.20%, 0.22%, 0.25%, etc.

[0051] The positive effect of controlling the P content to ≤ 0.02 wt% is that harmful elements are removed as much as possible during the steelmaking process. Specifically, the P content can be 0.02 wt%, 0.15 wt%, etc.

[0052] The positive effect of controlling the S content to ≤ 0.015 wt% is that it is a harmful element and should be removed as much as possible during the steelmaking process. Specifically, the S content can be 0.015 wt%, 0.014 wt%, 0.013 wt%, etc.

[0053] Controlling the Alt content to 0.02-0.05% by weight has the positive effects of refining grain size and fixing nitrogen in the steel, thereby significantly improving the steel's impact toughness and reducing its tendency to cold brittleness and aging. Specifically, the Alt content can be 0.02, 0.03, 0.04, 0.05, etc.

[0054] The positive effect of controlling the nitrogen content to ≤ 0.005 wt% is that Ti is added to form TiN, thereby fixing the nitrogen. If the nitrogen content is high, more Ti needs to be added to improve the strength of the low-carbon aluminum, but this will cause cracking and earing defects during stamping. Specifically, the nitrogen content can be 0.05 wt%, 0.04 wt%, 0.03 wt%, etc.

[0055] In some embodiments, the stretching and straightening of the hot-rolled plate according to the thickness of the hot-rolled coil and controlling the process parameters of the stretching and straightening include:

[0056] If the thickness of the hot-rolled plate is less than or equal to 3 mm, performing a first straightening process on the hot-rolled plate and controlling process parameters of the first straightening process;

[0057] If the thickness of the hot-rolled plate is 3 mm < h ≤ 5 mm, performing a second straightening operation on the hot-rolled plate and controlling the process parameters of the second straightening operation;

[0058] If the thickness of the hot-rolled plate is greater than 5 mm, the hot-rolled plate is subjected to a third straightening process, and the process parameters of the third straightening process are controlled.

[0059] In the embodiment of the present application, a scale breaking and straightening machine is used to realize the straightening process, and its working principle is: the strip is repeatedly bent by the bending roller under the action of front and rear tension, so that the neutral layer of the strip deviates and the center layer undergoes plastic deformation to achieve a certain elongation, ultimately achieving the purpose of scale breaking, accelerating the pickling speed and improving the strip shape.

[0060] The positive effect of setting different tensile straightening processes according to the thickness of hot rolled plates is to control the precise elongation.

[0061] The positive effects of the above numerical ranges are as follows: by controlling the different thicknesses, the plate shape and transverse fold defects can be controlled, and the purpose of breaking the scale and removing the iron oxide can be achieved, thereby controlling the surface quality after pickling.

[0062] In some embodiments, the process parameters of the first straightening process include: a first elongation, a first insertion amount of the bending roller #1 of the straightening machine, a first insertion amount of the bending roller #2 of the straightening machine, and a first insertion amount of the straightening roller of the straightening machine; wherein,

[0063] The first elongation is 2.3%-2.7%, the first insertion amount of the bending roller of the straightening machine 1# is 17mm-19mm, the first insertion amount of the bending roller of the straightening machine 2# is 17mm-19mm, and the first insertion amount of the straightening roller of the straightening machine is 31mm-33mm.

[0064] In some embodiments, the process parameters of the second straightening process include: a second elongation, a second insertion amount of the bending roller #1 of the straightening machine, a second insertion amount of the bending roller #2 of the straightening machine, and a second insertion amount of the straightening roller of the straightening machine; wherein,

[0065] The second elongation is 2.3%-2.7%, the second insertion amount of the bending roller of the straightening machine 1# is 19mm-21mm, the second insertion amount of the bending roller of the straightening machine 2# is 19mm-21mm, and the second insertion amount of the straightening roller of the straightening machine is 29mm-31mm.

[0066] In some embodiments, the process parameters of the third straightening process include: a third elongation, a third insertion amount of the bending roller #1 of the straightening machine, a third insertion amount of the bending roller #2 of the straightening machine, and a third insertion amount of the straightening roller of the straightening machine; wherein,

[0067] The third elongation is 2.3%-2.7%, the third insertion amount of the bending roller of the straightening machine 1# is 16mm-18mm, the third insertion amount of the bending roller of the straightening machine 2# is 18mm-20mm, and the third insertion amount of the straightening roller of the straightening machine is 29mm-31mm.

[0068] In the embodiment of the present application, a variable tension control mode under a constant insertion amount state is adopted, that is, under a constant elongation control mode, as the insertion amount continues to increase, the straightening tension tends to decrease.

[0069] The above positive effects on controlling the elongation according to different thicknesses of hot-rolled plates, the insertion amount of the bending roller of the straightening machine 1#, the insertion amount of the bending roller of the straightening machine 2#, and the insertion amount of the straightening roller of the straightening machine: the purpose of controlling the precise elongation.

[0070] If the elongation is too high, or the first insertion amount of the bending roller #1 of the straightening machine is too high, or the first insertion amount of the bending roller #2 of the straightening machine is too high, or the first insertion amount of the straightening roller of the straightening machine is too high, it will cause strip performance loss to a certain extent; if the elongation is too high, or the first insertion amount of the bending roller #1 of the straightening machine is too low, or the first insertion amount of the bending roller #2 of the straightening machine is too low, or the first insertion amount of the straightening roller of the straightening machine is too high. If the first insertion amount of the bending roller #1 of the straightening machine is too low, it will fail to achieve the effect of eliminating wave shape, transverse folding and scale breakage to a certain extent.

[0071] In some embodiments, the temperature of the hot rolled plate straightening machine is ≤40°C.

[0072] Controlling the temperature of the hot-rolled plate straightening machine to 40°C or less has the positive effect of preventing transverse folding defects on the strip surface. If the temperature is too high, the metal molecules become more active, and the strip is subjected to combined stresses, easily shifting from the elastic deformation zone to the plastic deformation zone. This creates slip lines on the strip surface, resulting in transverse folding defects. Specifically, the temperature can be 40°C, 39°C, 38°C, etc.

[0073] In a second aspect, the present application provides a low-carbon aluminum killed steel, which is prepared by the method described in any embodiment of the first aspect.

[0074] The low-carbon aluminum-killed steel is realized based on the preparation method of the low-carbon aluminum-killed steel mentioned above. The specific steps of the preparation method of the low-carbon aluminum-killed steel can refer to the above embodiments. Since the low-carbon aluminum-killed steel adopts part or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0075] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0076] Table 1 Chemical composition of low carbon aluminum killed steel (wt%)

[0077]

[0078]

[0079] Table 2 Preparation process parameters of low carbon aluminum killed steel

[0080]

[0081] By the method of the embodiment of the present application, a steel plate with good surface quality can be obtained. Specifically, the morphology after pickling in Example 1 is as follows Figure 4 As shown, the morphology of Example 2 after pickling is as follows Figure 5 As shown, the morphology of Example 3 after pickling is as follows Figure 6 As shown, the surface is good, no "crease mark" defect occurs, and it meets the requirements according to the judgment standard. In the comparative example, the Ti content is too low, the straightening process parameters are not within the set range, and the upper straightening machine temperature is too high, resulting in Figure 2 The crease mark defect shown.

[0082] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing low-carbon aluminum-killed steel, characterized in that: The method comprises: obtaining a hot-rolled plate having a set chemical composition; According to the thickness of the hot rolled plate, the hot rolled plate is straightened and the straightening process parameters are controlled; wherein the temperature of the straightening machine on the hot rolled plate is controlled; The hot rolled plate after tension leveling is pickled to obtain low carbon aluminum killed steel; According to the thickness of the hot rolled plate, the hot rolled plate is straightened and the straightening process parameters are controlled, including: If the thickness of the hot-rolled plate is ≤3 mm, the hot-rolled plate is subjected to the first tension leveling, and the process parameters of the first tension leveling are controlled as follows: the first elongation is 2.3%-2.7%, the first insertion amount of the first bending roller of the tension leveler is 17 mm-19 mm, the first insertion amount of the second bending roller of the tension leveler is 17 mm-19 mm, and the first insertion amount of the straightening roller of the tension leveler is 31 mm-33 mm; If the thickness of the hot-rolled plate is 3mm<h≤5mm, the hot-rolled plate is subjected to a second tension leveling, and the process parameters of the second tension leveling are controlled as follows: the second elongation is 2.3%-2.7%, the second insertion amount of the bending roller of the tension leveler 1# is 19mm-21mm, the second insertion amount of the bending roller of the tension leveler 2# is 19mm-21mm, and the second insertion amount of the straightening roller of the tension leveler is 29mm-31mm; If the thickness of the hot-rolled plate is greater than 5mm, the hot-rolled plate is subjected to the third straightening, and the process parameters of the third straightening are controlled as follows: the third elongation is 2.3%-2.7%, the third insertion amount of the bending roller of the straightening machine 1# is 16mm-18mm, the third insertion amount of the bending roller of the straightening machine 2# is 18mm-20mm, and the third insertion amount of the straightening roller of the straightening machine is 29mm-31mm.

2. The method according to claim 1, characterized in that The set chemical composition includes: C, Si, Mn, P, S, Alt, N, Ti and Fe; among them, The Ti content is 0.015 wt % to 0.025 wt %.

3. The method according to claim 2, characterized in that The Ti content is 0.0178 wt % to 0.0225 wt %.

4. The method according to claim 2 or 3, characterized in that In the set chemical composition, the C content is 0.025 wt%-0.05 wt%, the Si content is ≤0.05 wt%, the Mn content is 0.18 wt%-0.25 wt%, the P content is ≤0.02 wt%, the S content is ≤0.015 wt%, the Alt content is 0.02 wt%-0.05 wt%, and the N content is ≤0.005 wt%.

5. The method according to claim 1, characterized in that The temperature of the hot rolled plate straightening machine is ≤40℃。 6. A low carbon aluminum killed steel, characterized in that: The killed steel is prepared by the method according to any one of claims 1 to 5.

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