A hot-rolled steel plate for preventing wrinkling of 800 MPa grade bending pipes in Si-Cr system and its production method

Abstract

The present invention provides a hot-rolled steel sheet for anti-buckling of 800 MPa grade bending pipes in the Si-Cr system and a production method thereof. Among them, the hot-rolled steel sheet is composed of the following components by weight percentage: C 0.02% - 0.04%, Si 0.60% - 0.70%, Mn 1.50% - 1.60%, P ≤ 0.020%, S ≤ 0.003%, Nb 0.030% - 0.040%, Ti 0.055% - 0.080%, Cr 0.55% - 0.65%, Als: 0.010% - 0.050%, N ≤ 0.0035%, O ≤ 0.0020%, and the balance is Fe and inevitable impurities. The production method is to carry out hot metal desulfurization → converter smelting combined blowing →... → continuous casting → slab heating → high-pressure water descaling → rough rolling → coiling in a hot coil box → finish rolling → laminar flow cooling →... → warehousing in sequence. Through reasonable alloy composition and production process design, the present invention realizes excellent welding performance and anti-buckling performance of the product, while the production method is simple, the cost is low, and the comprehensive performance is excellent, having good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of hot continuous rolling strip production, and in particular, to a hot-rolled steel plate for bending pipe wrinkling of 800 MPa grade in Si-Cr system and its production method. Background Art

[0002] For thin-walled pipes (relative pipe diameter greater than 30 mm), numerical control bending control technology is an inevitable trend in the development of pipe bending technology towards advanced plastic processing technology. The numerical control precise bending technology of thin-walled pipes can achieve high precision, high efficiency, high technology in the plastic bending forming process of pipes and meet the requirements of product lightweight, which is consistent with the development trend of automotive lightweight, and can be widely used in automotive chassis parts and Class B safety parts.

[0003] Patent document CN 105154769 B: C 0.03% - 0.07%, Si ≤ 0.2%, Mn 1.0% - 2.0%, Al 0.02% - 0.05%, Mo 0.15% - 0.25%, Nb 0.032% - 0.045%, P ≤ 0.02%, S ≤ 0.005%, N ≤ 0.005%, Ti 0.08% - 0.20%, and the balance is iron and unavoidable impurities. The microstructure of the product described in this patent can achieve a hot-rolled high-strength and high-expansion steel with a tensile strength of 780 MPa grade, which is a fully ferrite-based microstructure composed of fine equiaxed or needle-like ferrite and nano-carbides. The size of the ferrite grains in the microstructure is <5 μm, and the size of the nano-carbides is <10 nm. If the coiling temperature is too high, it is easy to cause abnormal growth of the precipitation phase size of Ti.

[0004] Patent document CN 105671427 A discloses a titanium-chromium pickled plate and its preparation method. Its chemical composition by weight percentage is as follows: C 0.01% - 0.03%, Si 0.01% - 0.03%, Mn 0.14% - 0.30%, P 0.012% - 0.015%, S 0.003% - 0.005%, Cr 0.1% - 0.6%, Ti 0.012% - 0.023%, and the rest is Fe and unavoidable impurities. The product described in this patent can achieve a tensile strength of 270 MPa - 350 MPa, but its yield strength is too low and is not suitable for the bending forming process of thin-walled pipes.

[0005] During the bending forming process of thin-walled pipes, instability wrinkling defects are extremely likely to occur, resulting in unqualified forming quality, which has become a key factor restricting the development of this technology. Whether wrinkling occurs during the bending forming of thin-walled pipes is affected by various factors, and the material is one of the important factors. The material affects the stress / strain effect of the bent pipe under complex loading conditions and directly affects the anti-wrinkle ability of the part itself.

[0006] Such as Figure 3As shown in the figure, during the bending process of the thin-walled tube, the metal on the side far from the bending center is subjected to tensile stress in the tangential direction and undergoes elongation deformation, while the metal on the side close to the bending center is subjected to compressive stress in the tangential direction and undergoes compression deformation. The tangential stress varies from tensile stress on the outer side of the bend to compressive stress on the inner side along the cross-section. Due to the poor stability of the tube blank in the wall thickness direction, when the plastic deformation energy T in the compression deformation zone of the inner shell of the tube blank reaches the critical buckling wrinkling energy U of the thin shell, under a small perturbation, the in-plane deformation bifurcates to the out-of-plane, that is, the instability wrinkling phenomenon occurs.

[0007] These deformation characteristics during the bending process of the thin-walled tube make it easy for the bent tube to have problems such as outer side tensile cracking and inner side wrinkling. Especially with the increase of the die gap and the decrease of the material hardening index, the tangential compressive stress on the inner side of the tube wall will increase significantly, reducing the anti-instability ability of the tube blank.

[0008] The main factors affecting the instability wrinkling of the thin-walled tube bending are as follows: ① Geometric factors: bending radius, relative pipe diameter; ② Material factors: hardening index (or yield strength ratio), hardening coefficient (or ultimate strength); ③ Process factors: die gap, friction coefficient, bending speed, etc.

[0009] At present, domestic and foreign research scholars have conducted a large number of studies on the instability wrinkling during the bending process of thin-walled tubes using experimental, theoretical analysis, and finite element numerical simulation methods. Redd's experimental study on the instability wrinkling process of thin-walled tubes found that the main cause of the instability wrinkling of thin-walled tubes is the "flutter" generated during the bending process of thin-walled tubes. Corona and Vaze used the method of experimental verification to study the instability wrinkling phenomenon during the bending process of rectangular-section tubes and analyzed the collapse and wrinkling behaviors of thin-walled tubes during the bending process. Zhang Jingwen et al. experimentally studied the influence of the relative bending radius and relative wall thickness on the instability wrinkling of numerically controlled rotary draw bending, and found that with the increase of the relative bending radius and relative wall thickness, the wrinkling trend decreases. Kyriakids et al. used the bifurcation theory to conduct relevant research on the instability wrinkling of tubes under pure bending conditions, and the results showed that the theoretical prediction results are basically consistent with the experimental results. Li et al. established a quantitative prediction model for the instability wrinkling during the numerically controlled bending process of aluminum alloy thin-walled tubes based on the energy method, and combined with finite element simulation to clarify the influence mechanism of geometric parameters and material parameters on bending instability wrinkling. Zhao et al. established a three-dimensional elastoplastic finite element model for the numerically controlled rotary draw bending process of aluminum alloy thin-walled rectangular tubes based on the ABAQUS finite element analysis platform, and used this model to study the influence of the gap on the instability wrinkling during the rotary draw bending process of the bent tube. Fang et al. used the finite element simulation method to study the influence of the friction factor and geometric parameters on the instability wrinkling during the numerically controlled rotary draw bending process of 21-6-9 high-strength stainless steel tubes. Li et al. used the numerical simulation method to study the influence of the gap and friction on the instability wrinkling during the numerically controlled rotary draw bending process of tubes.

[0010] Most of the above research is about the influence of process parameters and geometric parameters on the instability and wrinkling of tube bending forming. However, the research on the influence of material parameters on the instability and wrinkling of tube bending forming is relatively less, and the research on low-alloy high-strength steel for anti-wrinkle of bent tubes is less. Therefore, it is necessary to propose a hot-rolled high-strength steel for anti-wrinkle of bent tubes and its production method to solve the above problems from the aspect of material parameters. Summary of the Invention

[0011] According to the above-mentioned lack of a solution for anti-wrinkle of bent tubes in terms of material parameters, a hot-rolled steel plate of Si-Cr series with a yield strength of 800 MPa for anti-wrinkle of bent tubes and its production method are provided.

[0012] The technical problem to be solved by the present invention is to ensure meeting the performance requirements. The present invention mainly utilizes the proportion of alloy components of the steel plate to achieve excellent welding performance and anti-wrinkle performance of bent tubes.

[0013] The technical means adopted by the present invention are as follows:

[0014] A hot-rolled steel plate of Si-Cr series with a yield strength of 800 MPa for anti-wrinkle of bent tubes, characterized in that it consists of the following components by weight percentage:

[0015] C 0.020% - 0.040%, Si 0.60% - 0.70%, Mn 1.50% - 1.60%, P ≤ 0.020%, S ≤ 0.003%, Nb 0.030% - 0.040%, Ti 0.055% - 0.080%, Cr 0.40% - 0.65%, Als: 0.010% - 0.050%, N ≤ 0.0035%, O ≤ 0.0020%, and the balance is Fe and unavoidable impurities.

[0016] Further, it consists of the following components by weight percentage:

[0017] C 0.025% - 0.035%, Si 0.62% - 0.68%, Mn 1.42% - 1.58%, P ≤ 0.018%, S ≤ 0.004%, Nb 0.032% - 0.038%, Ti 0.055% - 0.078%, Cr 0.40% - 0.50%, Als: 0.017% - 0.048%, N ≤ 0.0035%, O ≤ 0.0020%, and the balance is Fe and unavoidable impurities.

[0018] Further, it consists of the following components by weight percentage:

[0019] C 0.025% - 0.030%, Si 0.64% - 0.66%, Mn 1.54% - 1.58%, P ≤ 0.014%, S ≤ 0.002%, Nb 0.034% - 0.036%, Ti 0.068% - 0.078%, Cr 0.40% - 0.45%, Als: 0.025% - 0.035%, N ≤ 0.0035%, O ≤ 0.0020%, the balance being Fe and unavoidable impurities.

[0020] Further, the thickness of the hot-rolled steel plate is 1.8 mm - 6.0 mm.

[0021] Further, the thickness of the hot-rolled steel plate is 2.5 mm - 6.0 mm.

[0022] Further, the thickness of the hot-rolled steel plate is 4.0 mm - 6.0 mm.

[0023] Further, for the hot-rolled steel plate used for anti-bending pipe wrinkling, the yield strength ≥ 600 MPa, the tensile strength ≥ 800 MPa, the elongation after fracture ≥ 20%, and the 180° bending test D = 0a.

[0024] The present invention also discloses a production method of a hot-rolled steel plate for anti-bending pipe wrinkling of the Si-Cr series 800 MPa grade, which is characterized by including the following steps: preparing raw materials according to the composition of the hot-rolled steel plate for anti-bending pipe wrinkling of the Si-Cr series 800 MPa grade as described above, and successively carrying out hot metal desulfurization → converter smelting combined blowing → deoxidation and alloying → feeding Al wire at the small platform after the furnace → LF refining heating → RH vacuum cyclic degassing refining → continuous casting → slab heating → high-pressure water descaling → rough rolling → coiling in the hot coil box → finish rolling → laminar flow cooling → coiling → (welding the head and tail → pickling → oiling → coiling →) warehousing.

[0025] Further, heat the slab obtained by continuous casting to 1220 - 1250 °C for heat preservation and rough rolling. According to the different finished product thicknesses, the continuous casting billet undergoes at least 3 passes of rough rolling, with the deformation per pass ≥ 20%. According to the different finished product thicknesses, the thickness of the intermediate billet is different and is between 36 mm and 45 mm.

[0026] Further, after the intermediate billet is coiled in the hot coil box, it is immediately uncoiled for displacement and enters the finish rolling area for finish rolling. The finish rolling adopts constant speed rolling, the entrance temperature of the finish rolling is 1020 - 1070 °C, and the final rolling temperature range is 860 °C - 900 °C; after finish rolling, the laminar flow cooling adopts a segmented cooling method, the final temperature of the first stage of cooling is 690 °C - 730 °C, then air-cool for 5 s - 7 s, and then quickly cool to 530 °C - 570 °C.

[0027] Compared with the prior art, the present invention utilizes the solid solution strengthening effects of Si and Mn, the strong hardenability of Cr, and the precipitation of the second phase of Ti at low temperatures to improve the strength of the material, and designs reasonable controlled rolling and controlled cooling process parameters to obtain an ideal microstructure, and finally obtains a hot-rolled steel plate or pickled steel plate product with the ability to resist bending pipe wrinkling.

[0028] Through reasonable alloy composition and production process design, the present invention realizes excellent welding performance and bending pipe wrinkling performance of the product, while the production method of the product is simple, the production cost is low, and the comprehensive performance is excellent, having good application prospects.

[0029] Based on the above reasons, the present invention can be widely promoted in the field of hot strip mill production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 It is a schematic diagram of the microstructure in Example 3 of a hot-rolled steel plate with 800 MPa grade for resisting bending pipe wrinkling of the Si-Cr system of the present invention.

[0032] Figure 2 It is a schematic diagram of the limiting microstructure of Comparative Example 1 of a hot-rolled steel plate with 800 MPa grade for resisting bending pipe wrinkling of the Si-Cr system of the present invention.

[0033] Figure 3 It is a schematic diagram of the principle during the bending forming process of a thin-walled pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail the present invention.

[0035] To make the purpose, technical solutions, and advantages of the embodiments of the present invention clearer, the following will combine the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the authorized specification. In all the examples shown and discussed herein, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0038] The present invention provides a hot-rolled steel sheet for preventing bending pipe from wrinkling, which is composed of the following components by weight percentage:

[0039] C 0.020% - 0.040%, Si 0.60% - 0.70%, Mn 1.50% - 1.60%, P ≤ 0.020%, S ≤ 0.003%, Nb 0.030% - 0.040%, Ti 0.055% - 0.080%, Cr 0.40% - 0.65%, Als: 0.010% - 0.050%, N ≤ 0.0035%, O ≤ 0.0020%, and the balance is Fe and inevitable impurities.

[0040] The production process flow of the present invention is: hot metal desulfurization → converter smelting combined blowing → deoxidation and alloying → feeding Al wire on the small platform after the furnace → LF refining heating → RH vacuum circulation degassing refining → continuous casting → slab heating → high-pressure water descaling → rough rolling → coiling in the hot coil box → finishing rolling → laminar flow cooling → coiling → (welding the head and tail → pickling → oiling → coiling →) warehousing.

[0041] Specifically, the slab obtained by continuous casting is heated to 1220 - 1250 °C for heat preservation and rough rolling. According to the different thicknesses of the finished products, the continuous casting billets are rough rolled through 5 passes, and the deformation amount of each pass must be ≥ 20%. According to the different thicknesses of the finished products, the thickness of the intermediate billets is different: 36 mm - 45 mm.

[0042] The billet after rough rolling is then coiled by a hot coil box to ensure uniform temperature throughout the billet; at the same time, secondary scale is removed to ensure a smooth surface of the billet.

[0043] After the intermediate billet is coiled by the hot coil box, it is then uncoiled and shifted, and enters the finishing rolling area for finishing rolling. The finishing rolling is carried out at a constant speed. The entry temperature for finishing rolling is 1020 - 1070 °C, and the final rolling temperature range is 860 °C - 900 °C; after finishing rolling, laminar cooling is adopted in a segmented cooling mode. The final temperature of the first cooling stage is 690 °C - 730 °C, followed by air cooling for 5 s - 7 s, and then quickly cooled to 530 °C - 570 °C.

[0044] After laminar cooling, coiling and merging are carried out; when the finished product is in pickled state, the hot rolled coil should be sent to the pickling production line, where it is uncoiled, the head and tail of two coils are laser welded, pickled, oiled, coiled and stored in the warehouse.

[0045] The following further describes the specific implementation manners of the present invention in conjunction with embodiments, and the present invention is not thereby limited to the scope of the described embodiments.

[0046] Examples 1 - 4

[0047] Table 1 shows the chemical composition of the molten steel in the examples of the present invention, Table 2 shows the hot rolling process control values, and Table 3 shows the mechanical properties of the steel coils. Among them, the yield strength (R eL or R p0.2 ), tensile strength (R m ), and elongation (A%) of the steel coils are all detected according to the methods specified in GB / T228.1 - 2010. The obtained product has a microstructure of F + B + P, and its grain size is 11.0 - 13.0 grades.

[0048] Comparative examples

[0049] The production process flows of Comparative Examples 1 and 2 are the same as those of the examples. Their chemical compositions are shown in Table 1, the hot rolling process parameters are shown in Table 2, and the mechanical properties of the obtained hot rolled steel coils are shown in Table 3.

[0050] Table 1 Chemical compositions of examples and comparative examples

[0051] C Si Mn P S Nb Ti Cr Mo Als N O Example 1 0.025 0.66 1.55 0.011 0.002 0.036 0.078 0.43 / 0.025 0.0021 0.0015 Example 2 0.032 0.65 1.49 0.009 0.003 0.033 0.069 0.41 / 0.044 0.00 0.0012 Example 3 0.038 0.63 1.46 0.015 0.002 0.038 0.057 0.49 / 0.028 0.00 0.0015 Example 4 0.021 0.68 1.52 0.018 0.001 0.038 0.064 0.43 / 0.032 0.00 0.0017 Comparative Example 1 0.063 0.10 1.83 0.015 0.002 0.042 0.098 0.01 0.18 0.020 0.0038 0.0021 Comparative Example 2 0.077 0.08 1.78 0.008 0.001 0.038 0.092 0.04 0.22 0.018 0.0046 0.0016

[0052] Table 2 Hot rolling process control values of examples and comparative examples

[0053]

[0054] Table 3 Mechanical properties of steel coils obtained from examples and comparative examples

[0055]

[0056] In summary, asFigure 1 and Figure 2 As shown, the present invention utilizes the solid solution strengthening effect of Si and Mn, the strong hardenability of Cr, and the precipitation of the second phase of Ti at low temperature, with a tensile strength of 800 MPa level, in order to improve the strength of the material, and designs reasonable controlled rolling and controlled cooling process parameters to obtain an ideal microstructure, and finally obtains a hot-rolled steel plate or pickled steel plate product with the ability to resist bending pipe wrinkling.

[0057] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Si-Cr 800MPa grade hot-rolled steel plate for anti-bending pipe wrinkling, characterized in that: It is composed of the following ingredients in percentage by weight: C 0.020% to 0.040%, Si 0.60% to 0.70%, Mn 1.50% to 1.60%, P ≤ 0.020%, S ≤ 0.003%, Nb 0.030% to 0.040%, Ti 0.055% to 0.080%, Cr 0.40% to 0.65%, Als: 0.010% to 0.050%, N ≤ 0.0035%, O ≤ 0.0020%, the balance being Fe and unavoidable impurities; The slab obtained by continuous casting is heated to 1220-1250℃ and then subjected to rough rolling. Depending on the thickness of the finished product, the continuous casting slab undergoes at least 3 rough rolling passes, with the deformation of each pass being ≥20%. The thickness of the intermediate slab varies depending on the thickness of the finished product and is between 36mm and 45mm. After the intermediate billet is coiled in the hot coil box, it is shifted and uncoiled and enters the finishing rolling area for finishing rolling. The finishing rolling adopts constant speed rolling, the finishing rolling inlet temperature is 1020~1070℃, and the final rolling temperature range is 860℃~900℃; after finishing rolling, the laminar cooling adopts a segmented cooling method, the end temperature of the first cooling stage is 690℃~730℃, followed by air cooling for 5s~7s, and then rapid cooling to 530℃~570℃.

2. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 1, characterized in that: It is composed of the following ingredients in percentage by weight: C 0.025%~0.035%, Si 0.62%~0.68%, Mn 1.42%~1.58%, P≤0.018%, S≤0.004%, Nb 0.032%~0.038%, Ti 0.055%~0.078%, Cr 0.40%~0.50%, Als: 0.017%~0.048%, N≤0.0035%, O≤0.0020%, and the balance is Fe and unavoidable impurities.

3. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 2, characterized in that: C 0.025% ~ 0.030%, Si 0.64% ~ 0.66%, Mn 1.54% ~ 1.58%, P ≤ 0.014%, S ≤ 0.002%, Nb 0.034% ~ 0.036%, Ti 0.068% ~ 0.078%, Cr 0.40% ~ 0.45%, Als: 0.025% ~ 0.035%, N ≤ 0.0035%, O ≤ 0.0020%, the balance is Fe and unavoidable impurities.

4. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 1, characterized in that: The hot-rolled steel plate has a thickness of 1.8 mm to 6.0 mm.

5. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 2, characterized in that: The hot-rolled steel plate has a thickness of 2.5 mm to 6.0 mm.

6. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 3, characterized in that: The thickness of the hot-rolled steel plate is 4.0 mm to 6.0 mm.

7. The Si-Cr based 800 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 1, characterized in that: The hot-rolled steel plate for anti-bending pipe wrinkling has a yield strength of ≥600 MPa, a tensile strength of ≥800 MPa, an elongation after fracture of ≥20%, and a 180° bending test D=0a.

8. A method for producing Si-Cr 800MPa grade hot rolled steel plate for anti-bending pipe wrinkling, characterized in that The method comprises the following steps: preparing raw materials according to the composition of the Si-Cr series 800 MPa grade hot-rolled steel plate for anti-bending pipe wrinkling according to any one of claims 1 to 7, and sequentially carrying out molten iron desulfurization → converter smelting and composite blowing → deoxidation and alloying → Al wire feeding on a small platform behind the furnace → LF refining and heating → RH vacuum cycle degassing and refining → continuous casting → slab heating → high-pressure water descaling → rough rolling → hot coil box coiling → finishing rolling → laminar cooling → coiling → welding head and tail → pickling → oiling → coiling → warehousing.

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