A hot-rolled steel sheet for preventing wrinkling of a 590 MPa grade bending pipe in the Si-Cr system and a production method thereof

Abstract

The present invention provides a Si-Cr-based 590MPa grade hot-rolled steel plate for anti-bending pipe wrinkling and a production method thereof. The hot-rolled steel plate comprises the following components by weight: C 0.04% to 0.06%, Si 0.40% to 0.50%, Mn 1.35% to 1.45%, P ≤ 0.020%, S ≤ 0.005%, Nb 0.03% to 0.04%, Cr 0.40% to 0.50%, Als: 0.010% to 0.050%, with the balance being Fe and unavoidable impurities. The production method comprises the following steps: molten iron desulfurization → converter smelting and composite blowing → ... → continuous casting → slab heating → high-pressure water descaling → rough rolling → hot coil box coiling → finishing rolling → laminar cooling → ... → warehousing. Through rational alloy composition and production process design, this invention achieves excellent weldability and anti-bending wrinkling performance while also offering simple production methods, low costs, and excellent overall performance, promising promising applications. The solid solution strengthening effects of Si and Mn, the strong hardenability of Cr, and the grain refinement of Nb contribute to improved strength.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled plate and strip production, and in particular to a Si-Cr series 590MPa grade hot-rolled steel plate for anti-bending pipe wrinkling and a production method thereof. Background Art

[0002] CNC bending control technology for thin-walled tubes (relative diameter greater than 30mm) is an inevitable trend in the development of tube bending technology towards advanced plastic processing technology. This CNC precision bending technology for thin-walled tubes achieves high precision, high efficiency, and advanced technology in the tube plastic bending process, while also meeting the requirements for lightweight products. This technology aligns with the development trend of lightweight automobiles and can be widely used in automotive chassis components and Class B safety parts.

[0003] For example, patent document CN 103572164 B discloses a hot-rolled pickled steel plate and its production method. Its chemical composition by weight is as follows: C 0.08% to 0.12%, Si ≤ 0.15%, Mn 1.20% to 1.40%, P ≤ 0.02%, S ≤ 0.015%, Cr 0.60% to 0.70%, Als ≤ 0.015%, with the remainder being Fe and unavoidable impurities. The product described in this patent can achieve a yield strength of 310 MPa to 360 MPa and a tensile strength of 490 MPa to 540 MPa. However, its yield strength is too low to be suitable for thin-walled tube bending.

[0004] The bending process of thin-walled tubes is prone to unstable wrinkling defects, resulting in substandard forming quality and becoming a key factor restricting the development of this technology. Whether thin-walled tubes wrinkle during bending is influenced by multiple factors, the material being a key factor. The material influences the stress / strain effects of the bent tube under complex loading conditions, directly impacting the part's wrinkle resistance.

[0005] like Figure 3 As shown in the figure, during the bending process of a thin-walled tube, the metal away from the bend center experiences tensile stress in the tangential direction, causing elongation, while the metal closer to the bend center experiences compressive stress in the tangential direction, causing compression. The tangential stress changes along the cross section from tensile stress on the outside of the bend to compressive stress on the inside. Due to the poor stability of the tube wall thickness, when the plastic deformation energy T in the compression deformation zone of the inner shell reaches the critical buckling energy U of the thin shell, the in-plane deformation bifurcates outward under slight perturbations, resulting in buckling.

[0006] These deformation characteristics during the bending process of thin-walled tubes make the bent tubes prone to problems such as outer cracking and inner wrinkling. In particular, as the die gap increases and the material hardening index decreases, the tangential compressive stress on the inner side of the tube wall will greatly increase, reducing the tube blank's ability to resist instability.

[0007] The main factors affecting the instability and wrinkling of thin-walled tube bending are as follows: ① Geometric factors: bending radius, relative tube diameter; ② Material factors: hardening index (or yield strength ratio), hardening coefficient (or strength limit); ③ Process factors: mold gap, friction coefficient, bending speed, etc.

[0008] Currently, researchers at home and abroad have conducted extensive research on the instability wrinkling of thin-walled tubes during bending using experimental, theoretical, and finite element numerical simulation methods. Redd experimentally studied the instability wrinkling process of thin-walled tubes and found that the primary cause of this wrinkling is the "agitation" generated during the bending process. Corona and Vaze used experimental verification methods to study the instability wrinkling phenomenon during the bending of rectangular cross-section tubes and analyzed the collapse and wrinkling behavior of thin-walled tubes during bending. Zhang Jingwen et al. experimentally investigated the effects of relative bending radius and relative tube wall thickness on instability wrinkling in CNC bending and found that the wrinkling tendency decreased with increasing relative bending radius and relative tube wall thickness. Kyriakids et al. used bifurcation theory to study the instability wrinkling of tubes under pure bending conditions. The results showed that the theoretical predictions were generally consistent with the experimental results. Li et al. established a quantitative prediction model for instability wrinkling in the CNC bending process of aluminum alloy thin-walled tubes based on the energy method. Combined with finite element simulation, they clarified the mechanism by which geometric and material parameters influence instability wrinkling during bending. Zhao et al. established a three-dimensional elastic-plastic finite element model for the CNC bending process of thin-walled aluminum alloy rectangular tubes based on the ABAQUS finite element analysis platform. They used this model to study the effect of clearance on the instability and wrinkling of the tube during the bending process. Fang et al. used finite element simulation to study the effects of friction coefficient and geometric parameters on the instability and wrinkling of 21-6-9 high-strength stainless steel tubes during the CNC bending process. Li et al. used numerical simulation to study the effects of clearance and friction on the instability and wrinkling of tubes during the CNC bending process.

[0009] Most of the above studies are about the influence of process parameters and geometric parameters on the unstable wrinkling of tube bending forming, while there are relatively few studies on material parameters and low-alloy high-strength steel that resists tube bending wrinkling. Therefore, it is necessary to propose a hot-rolled high-strength steel for resisting tube bending wrinkling and its production method to solve the above problems from the perspective of material parameters. Summary of the Invention

[0010] According to the above proposal that there is a lack of solutions to combat pipe wrinkling in terms of material parameters, a Si-Cr series 590MPa grade hot-rolled steel plate for combating pipe wrinkling and a production method thereof are provided.

[0011] The technical problem to be solved by the present invention is to ensure that the performance requirements are met, and the present invention mainly utilizes the ratio of the alloy components of the steel plate to achieve excellent welding performance and anti-bending wrinkling performance.

[0012] The technical means adopted in the present invention are as follows:

[0013] A Si-Cr 590 MPa grade hot-rolled steel plate for anti-bending pipe wrinkling, characterized by being composed of the following components in percentage by weight:

[0014] C 0.04% to 0.06%, Si 0.40% to 0.50%, Mn 1.35% to 1.45%, P ≤ 0.020%, S ≤ 0.005%, Nb 0.03% to 0.04%, Cr 0.40% to 0.50%, Als: 0.010% to 0.050%, and the balance is Fe and unavoidable impurities.

[0015] Furthermore, it is composed of the following ingredients in percentage by weight:

[0016] C 0.045% to 0.055%, Si 0.41% to 0.48%, Mn 1.37% to 1.43%, P ≤ 0.018%, S ≤ 0.004%, Nb 0.032% to 0.038%, Cr 0.41% to 0.48%, Als: 0.017% to 0.048%, and the balance is Fe and unavoidable impurities.

[0017] Furthermore, it is composed of the following ingredients in percentage by weight:

[0018] C 0.048% to 0.052%, Si 0.45% to 0.47%, Mn 1.39% to 1.42%, P ≤ 0.015%, S ≤ 0.003%, Nb 0.034% to 0.036%, Cr 0.45% to 0.48%, Als: 0.027% to 0.034%, and the balance is Fe and unavoidable impurities.

[0019] Furthermore, the hot-rolled steel plate has a thickness of 1.8 mm to 6.0 mm.

[0020] Furthermore, the hot-rolled steel plate has a thickness of 2.5 mm to 6.0 mm.

[0021] Furthermore, the hot-rolled steel plate has a thickness of 4.0 mm to 6.0 mm.

[0022] Furthermore, the hot-rolled steel plate for resisting bending pipe wrinkling has a yield strength of ≥460 MPa, a tensile strength of ≥590 MPa, an elongation after fracture of ≥24%, and a 180° bending test D=0a.

[0023] The present invention also discloses a production method of a Si-Cr-based 590MPa-grade hot-rolled steel plate for anti-bending pipe wrinkling, which is characterized by comprising the following steps: preparing raw materials according to the composition of the above-mentioned Si-Cr-based 590MPa-grade hot-rolled steel plate for anti-bending pipe wrinkling, 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 →) and storage.

[0024] Furthermore, the slab obtained by continuous casting is heated to 1220-1250°C and rough rolled. Depending on the thickness of the finished product, the continuous casting slab undergoes at least 3 rough rolling passes, with a deformation of ≥20% in each pass. Depending on the thickness of the finished product, the thickness of the intermediate slab varies, ranging from 36mm to 45mm.

[0025] Furthermore, 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 520℃~560℃.

[0026] Compared with the existing technology, the present invention utilizes the solid solution strengthening effect of Si and Mn and the strong hardenability of Cr to improve the strength of the material. At the same time, the added niobium can pin the austenite grain boundaries, thereby preventing grain growth and ultimately refining the grains, which is beneficial to improving strength, plasticity, yield point elongation and impact toughness. In addition, reasonable controlled rolling and controlled cooling process parameters are designed to obtain an ideal microstructure, ultimately resulting in a hot-rolled steel plate or pickled steel plate product with anti-bending wrinkling ability.

[0027] The present invention realizes excellent welding performance and anti-bending wrinkling performance of the product through reasonable alloy composition and production process design. At the same time, the product has a simple production method, low production cost, and excellent comprehensive performance, and has a good application prospect.

[0028] Based on the above reasons, the present invention can be widely promoted in the field of hot strip production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention 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, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 This is a schematic diagram of the microstructure of Example 2 of a Si-Cr 590MPa grade hot-rolled steel plate for anti-bending pipe wrinkling according to the present invention.

[0031] Figure 2 This is a schematic diagram of the limiting structure of comparative example 1 of a Si-Cr 590MPa grade hot-rolled steel plate for anti-bending pipe wrinkling of the present invention.

[0032] Figure 3 This is the principle diagram of the thin-walled tube bending process.

[0033] Figure 4 This is an actual product diagram of the present invention. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within 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 according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" 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 arrangement of the parts and steps, numerical expressions and numerical values described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted 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 numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0038] The present invention provides a hot-rolled steel plate for resisting wrinkling of bending pipes, which is composed of the following components in percentage by weight:

[0039] C 0.04% to 0.06%, Si 0.40% to 0.50%, Mn 1.35% to 1.45%, P ≤ 0.020%, S ≤ 0.005%, Nb 0.03% to 0.04%, Cr 0.40% to 0.50%, Als: 0.010% to 0.050%, and the balance is Fe and unavoidable impurities.

[0040] The production process of the present invention is: 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 →) storage.

[0041] The slab obtained by continuous casting is heated to 1220-1250℃ and then rough rolled. Depending on the thickness of the finished product, the continuous casting slab undergoes 5 rough rolling passes. The deformation of each pass must be ≥20%. Depending on the thickness of the finished product, the thickness of the intermediate slab is different: 36mm-45mm.

[0042] After rough rolling, the steel billet is then coiled in a hot coil box to ensure uniform temperature throughout the billet length; at the same time, the secondary iron oxide scale is removed to ensure a smooth surface of the billet.

[0043] 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 520℃~560℃.

[0044] After laminar cooling, the coils are taken up and put into storage; when the finished product is in the pickling state, the hot rolled coils should be sent to the pickling production line, uncoiled, laser welded at the head and tail of the two steel coils, pickled, oiled, coiled and stored.

[0045] The specific embodiments of the present invention are further described below in conjunction with examples, but the present invention is not limited to the scope of the examples.

[0046] Examples 1-4

[0047] Table 1 shows the chemical composition of the molten steel in the embodiment of the present invention, Table 2 shows the hot rolling process control values, and Table 3 shows the mechanical properties of the steel coil, wherein the yield strength (R eL or R p0.2 ), tensile strength (R m ) and elongation (A%) were tested according to the method specified in GB / T228.1-2010. The microstructure of the obtained product is F+P+B, and its grain size is 11.0 to 13.0.

[0048] Comparative Example

[0049] The production process of Comparative Examples 1 and 2 is the same as that of the embodiment. The 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]

[0052]

[0053] Table 2 Hot rolling process control values of Examples and Comparative Examples

[0054]

[0055] Table 3 Mechanical properties of the steel coils obtained in the examples and comparative examples

[0056]

[0057] In summary, if Figure 1 and Figure 2 As shown, the present invention utilizes the solid solution strengthening effect of Si and Mn and the strong hardenability of Cr, with a tensile strength of 590MPa 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 the following Figure 4 Hot rolled steel plate or pickled steel plate product with the ability to resist wrinkling during bending.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Si-Cr 590MPa 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 0.04% to 0.06%, Si 0.40% to 0.50%, Mn 1.35% to 1.45%, P ≤ 0.020%, S ≤ 0.005%, Nb 0.03% to 0.04%, Cr 0.40% to 0.50%, Als: 0.010% to 0.050%, the balance is Fe and unavoidable impurities; In the specific production process, 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 three rough rolling passes, with the deformation of each pass being ≥20%. Depending on the thickness of the finished product, the thickness of the intermediate slab varies, ranging from 36mm to 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 520℃~560℃.

2. The Si-Cr 590 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 0.045% to 0.055%, Si 0.41% to 0.48%, Mn 1.37% to 1.43%, P ≤ 0.018%, S ≤ 0.004%, Nb 0.032% to 0.038%, Cr 0.41% to 0.48%, Als: 0.017% to 0.048%, and the balance is Fe and unavoidable impurities.

3. The Si-Cr based 590 MPa grade hot rolled steel plate for anti-bending pipe wrinkling according to claim 2, characterized in that: It is composed of the following ingredients in percentage by weight: C 0.048% to 0.052%, Si 0.45% to 0.47%, Mn 1.39% to 1.42%, P ≤ 0.015%, S ≤ 0.003%, Nb 0.034% to 0.036%, Cr 0.45% to 0.48%, Als: 0.027% to 0.034%, and the balance is Fe and unavoidable impurities.

4. The Si-Cr based 590 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 590 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 590 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 590 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 ≥460 MPa, a tensile strength of ≥590 MPa, an elongation after fracture of ≥24%, and a 180° bending test D=0a.

8. A method for producing Si-Cr 590MPa 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 590MPa 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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