High-strength beam steel series and flexible CSP manufacturing method thereof

Abstract

The invention discloses a high-strength beam steel series which comprises the following chemical components in percentage by weight: 0.04-0.065% of C, less than or equal to 0.2% of Si, 0.9-1.4% of Mn, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.08-0.14% of Ti, 0.005-0.020% of Nb, 0.02-0.05% of Als, less than or equal to 0.006% of N and the balance of Fe and inevitable impurities. A series of high-strength and strong beam steel is divided into different combinations according to performance indexes and thickness specifications, process adjustment and matching are carried out according to components and specifications, a flexible CSP manufacturing method is provided in a targeted mode, and products of different strength grades are produced; while the cost and the production efficiency are ensured, the personalized requirements of users are effectively met; and meanwhile, the belt yield of a CSP production line can be remarkably reduced, and a new thought can be provided for preparation of high-quality girder steel.

Description

Technical Field

[0001] The invention belongs to the field of steel product manufacturing, and in particular relates to a high-strength beam steel series and a flexible CSP manufacturing method thereof. Background Art

[0002] The beam is a very important safety component in the car. The development of lightweight makes the application of high-strength beam steel more and more extensive. The strength level of hot-rolled beam steel is gradually developing towards high strength, from the tensile strength of 610Mpa to 750, or even 800Mpa (non-heat-treated). The forming process mainly includes stamping, rolling, etc. Therefore, while meeting the high strength, the stamping forming performance and economy of the beam steel must also be guaranteed.

[0003] At present, the production process of domestic beam plates mostly adopts the traditional thick slab hot rolling process, but there are problems such as difficulty in producing some extreme width thin plates and long delivery cycle. Conventional hot rolling and CSP processes can usually complement each other to achieve full coverage of specifications and strength. However, the high-strength beam steel of the CSP production line needs to be further developed according to the process characteristics of the production line. At the same time, the smelting and rolling of the CSP production line usually has the process characteristics of rigid connection and continuous large-scale single variety. Although it can reduce costs and shorten delivery time, the contradiction with the diversified and personalized needs of users is becoming more and more obvious and acute. On the basis of expanding the CSP variety structure as a supplement to conventional hot rolling, it is also necessary to research and develop flexible rolling technology for high-strength beam steel, so as to expand CSP single batch production under the same composition, reduce production line costs, and improve production line profitability. Summary of the invention

[0004] The main purpose of the present invention is to provide a series of high-strength beam steels and flexible CSP manufacturing methods thereof. Combining the CSP variety development and process technology characteristics, the high-strength beam steels produced have stable performance and specifications that can be used as a supplement to conventional hot rolling processes. They can meet the personalized needs of different manufacturers of commercial vehicles, modified vehicles, and dump trucks for steel products, and solve the problem of a large number of carry-out products in the production organization process of the CSP production line.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The chemical composition of the high-strength beam steel series is calculated by weight percentage: C 0.04-0.065%, Si≤0.2%, Mn 0.9-1.4%, P≤0.020%, S≤0.008%, Ti 0.08-0.14%, Nb 0.005-0.020%, Als0.02-0.05%, N≤0.006%, and the balance is Fe and unavoidable impurities; and the performance indicators and thickness specifications of this series of hot-rolled high-strength beam steel are divided into the following three combinations:

[0007] ①Rel≥550Mpa, 580Mpa≤Rm<660Mpa, A≥18%, d=a, 180°, cold bending qualified;

[0008] ②Rel≥600Mpa, 660Mpa≤Rm<760Mpa, A≥17%, d=1.5a, 180°, cold bending qualified;

[0009] ③Rel≥700Mpa, 760Mpa≤Rm≤920Mpa, A≥16%, d=1.5a, 180°, cold bending qualified;

[0010] Among them, Rel is the yield strength, Rm is the tensile strength, A is the elongation, d is the bending radius, mm, and a is the plate thickness, mm.

[0011] In the above solution, the thickness a of the hot-rolled substrate is 1.2 to 4.0 mm.

[0012] In the above scheme, when producing steel corresponding to combination ①-②, molten steel with the same composition can be used for production, and the first type of composition design can be carried out; when producing steel corresponding to combination ③, the second type of composition design can be carried out.

[0013] Furthermore, in the first type of component design, the Mn content is preferably less than 1.2%, and the Ti content is 0.10-0.12%, which can effectively reduce the cost and produce steels corresponding to the requirements of combinations ① to ②; in the second type of component design, the Mn content is controlled to be 1.2-1.4%, and the Ti content is 0.12-0.14%; the remaining components and their contents are required to be consistent, combined with the dynamic adjustment process, to produce steels corresponding to combinations ① to ③.

[0014] In terms of production organization, if only beam steel below Rel 700Mpa is involved, the first type of composition design is directly adopted, and FT7 and CT are automatically adjusted according to the current actual rolling specifications and actual composition to produce various steel types. When it comes to 700Mpa-level high-strength steel, the plan is optimized according to the production contract structure. There are two ways to optimize: mix two types of steel with different compositions, and change the mixed casting connection billet to roll the corresponding steel materials ①-②; or use the second type of composition design for mixed arrangement, according to the rolling principle and the transition material matching principle, with automatic dynamic process adjustment, to achieve the matching of strength levels of various steel types under the same composition. At the same time, dynamic process adjustment will automatically optimize according to the composition.

[0015] The present invention also provides a flexible CSP manufacturing method of the above-mentioned high-strength beam steel series, including converter smelting, LF furnace refining, slab casting, slab heating, flexible rolling, laminar cooling and coiling processes, wherein each process and key control points include the following:

[0016] 1) Slab casting, the key points of process control are as follows:

[0017] ① The thickness of the casting is 65-85 mm, and the pulling speed is 4.2-4.6 m / min;

[0018] ② Crystallizer cooling water volume, narrow side water volume 200 ~ 245L / min, wide side water volume 5600 ~ 6500L / min; crystallizer taper: 4.5 ~ 6.0mm;

[0019] ③ Secondary cooling water: specific water volume 1.8~1.9L / min, the water volume at the edge is reduced to ensure that the edge temperature of the ingot is ≥800℃ before straightening;

[0020] 2) Slab heating and rolling, the key points of process control are as follows:

[0021] ① Heating process: The slab is in the furnace for 20 to 50 minutes, the furnace temperature is 1200 to 1250°C, the acceleration roller position is ≥50, and the heating speed is controlled at 30 to 50°C / min; the heating furnace gas calorific value is 8300 to 9000 kJ / Nm 3 ; The air-fuel ratio of each section is: heating section 1-2 zone is 1.30-1.35, heating section 3-7 zone is 1.2-1.27, and equalizing section is 1.3-1.38;

[0022] ② Finishing rolling process: No speed increase rolling, final rolling temperature FT7 is controlled at 860-920℃, side spraying between F4-7 stands is disabled, and side guide cooling water of F5-F7 stands is prohibited;

[0023] The convexity target is set to 30μm, and the corresponding convexity control range is 10-50μm; the wedge target range is ±30μm;

[0024] ③Laminar cooling, control the flow ratio of upper and lower laminar cooling water;

[0025] ④ Coiling process: The target value of coiling temperature CT is 570~630℃;

[0026] In addition, dynamic adjustments are made to the finishing and coiling processes, specifically including: setting the corresponding target range of effective Ti content for strip steel with different performance indicators and thickness specifications, where effective Ti content = Ti content - 3.4*N content - 3*S content - 0.006; when the effective Ti content range calculated based on the steel leaving station composition or the tundish composition exceeds the above target range, the finishing and coiling processes are dynamically adjusted in combination with the thickness specifications, and the corresponding final rolling temperature FT7 and coiling temperature CT are adjusted to match the current actual composition with the appropriate process to obtain the required strength range, thereby avoiding degradation and spot goods that do not meet the standards due to composition fluctuations.

[0027] In the above scheme, the converter smelting step controls the target sulfur content in the molten steel at the end point to be ≤0.025%, and the target steel tapping temperature to be ≥1650°C.

[0028] In the above scheme, the LF furnace refining steps include: desulfurization, controlling the slag basicity (CaO+MgO) / (SiO2+Al2O3)≥3.0, FeO<1.0%.

[0029] In the above scheme, in the laminar cooling step, the flow ratio of upper and lower laminar cooling water is 1:1.1 to 1.3.

[0030] Furthermore, in the dynamic adjustment step of the finishing rolling and coiling process, for the steel corresponding to combination ①, the effective Ti target range is set as: 0.064% ≤ effective Ti < 0.076%; for the steel corresponding to combination ②, the effective Ti target range is set as: 0.0761% ≤ effective Ti < 0.092%; for the steel corresponding to combination ③, the effective Ti target range is set as: 0.092% ≤ effective Ti ≤ 0.11%.

[0031] Furthermore, the dynamic adjustment steps of the finishing rolling and coiling process specifically include:

[0032] When the effective Ti content calculated according to the steel leaving station composition or the tundish composition is less than the lower limit of the effective Ti target range, for steel with a thickness of 2.0 mm < ≤ 4.0 mm, the coiling temperature CT is increased by 10 to 30 ° C; for steel with a thickness of ≤ 2.0 mm, the finishing temperature FT7 is increased by 10 to 30 ° C, and the coiling temperature CT is reduced by 10 to 30 ° C;

[0033] When the effective Ti content calculated based on the steel leaving station composition or the tundish composition is greater than the upper limit of the effective Ti target range, for steel with a thickness of 2.0mm<≤4.0mm, the coiling temperature CT is reduced by 10 to 30°C; for steel with a thickness of ≤2.0mm, the finishing temperature FT7 is increased by 10 to 30°C, and the coiling temperature CT is increased by 20 to 40°C.

[0034] Furthermore, in the coiling step, in order to ensure the uniformity of the performance over the entire length, the steel plate with a thickness of ≤2.0mm adopts a U-shaped cooling process, and the coiling temperature of the head and tail is increased by 20-30°C and 10-20°C respectively on the basis of the coiling temperature of the middle part, and the length is 10-20 meters; after coiling, they are all put into the slow cooling pit for slow cooling for 24-48 hours

[0035] The flexible CSP manufacturing method of the present invention can reasonably arrange plans according to the contract, and roll out products of different strength levels with the same one or two chemical compositions, thereby meeting the diversified product needs of customers while simplifying the operation and management of smelting and continuous casting, which is conducive to continuous and stable process, simplifies management, reduces costs, and improves quality.

[0036] The principles of the present invention include:

[0037] 1) Steel composition design;

[0038] Control of C component: C is the most basic strengthening element, which improves the strength of steel through solid solution strengthening and precipitation strengthening. In the present invention, it forms microalloy carbides with steel grade Ti or Nb; however, too high a carbon content will affect the welding performance and crack sensitivity coefficient. Considering the fact that the continuous casting of the CSP production line cannot cast peritectic steel, the C content of the present invention is controlled to be 0.04-0.065%;

[0039] Si: deoxidation and solid solution strengthening effects, but too high Si content can easily lead to the formation of red iron scale. Considering the cost and quality control, the Si content is controlled to ≤0.2%;

[0040] Control of Mn composition: It is the main strengthening element, which plays a role in solid solution strengthening. At the same time, Mn can form MnS with S to eliminate the harmful effects of S. The present invention adopts a content of 0.9-1.4% to achieve the required performance indicators.

[0041] Control of P component: P is a harmful element that increases the risk of cracking during cold bending. For high-strength cold-bent steel, its content should be strictly controlled. In the present invention, the P content is controlled to ≤0.020%;

[0042] Control of S and N components: S is a harmful element in steel, which reduces the zero plasticity temperature of steel, and N promotes the aging effect of steel; at the same time, in Ti-containing steel, S and N will seriously reduce the effective content of Ti, thereby reducing the precipitation strengthening effect of TiC; the present invention controls the content of the two to S≤0.008%, N≤0.006%;

[0043] Als component control: Aluminum is a strong deoxidizing element. Using aluminum deoxidation can not only effectively reduce the oxygen in the steel, but also refine the grains, improve toughness, and prevent aging. The present invention controls the Als content range to 0.02-0.05%;

[0044] Ti and effective Ti: The use of Ti in the present invention is one of the keys to the entire composition design. It utilizes its good precipitation strengthening effect and low cost advantage to promote the production of low-cost high-strength steel; the present invention controls the Ti content to 0.08-0.15%. At the same time, according to the Ti precipitation strengthening mechanism, Ti will preferentially form compounds with S, N, etc. in molten steel, reducing the TiC content of dispersion precipitation strengthening; in addition, the concept of effective Ti is further introduced and combined with the thickness specification (Ti = Ti-3.4*N-3*S-0.006) to further ensure that the precipitation strengthening effect is achieved, so as to promote the dynamic adjustment of the CSP production line.

[0045] Nb: In the present invention, Nb is another key element in the composition design. In addition to precipitation strengthening, the fine grain strengthening effect of Nb is also utilized (due to the limited compression ratio of the CSP production line) to improve the impact energy of thick-gauge high-strength beam steel, better meet the plastic-toughness matching of the beam steel, and ensure the forming performance.

[0046] 2) Process design;

[0047] The basicity of LF furnace refining slag is controlled to produce white slag and better exert the desulfurization effect.

[0048] Continuous casting mold cooling water and taper control, secondary cooling water ratio control: on the one hand, it is to reduce the longitudinal crack defects of niobium-containing low-carbon alloy steel during the casting process and improve plastic toughness; secondary cooling water ratio control, based on the measurement of the thermoplastic temperature of the slab, ensures the plastic toughness of the slab edge and reduces the occurrence of edge crack defects.

[0049] Control of the accelerating roller and furnace temperature: The heating temperature used causes most of the existing carbonitrides to dissolve again, and then precipitate during the coiling process to achieve grain refinement and precipitation strengthening; in addition, by controlling the accelerating roller, slow and uniform heating can be effectively guaranteed (avoiding the operator from forcibly burning the steel quickly), which on the one hand strengthens the dissolution of micro-alloying elements, and on the other hand reduces thermal stress and improves the plastic toughness of the slab edge.

[0050] Atmosphere control in the heating furnace: strong oxidizing atmosphere in the front section (air-fuel ratio of 1.3-1.35) allows the slab to be fully heated; weak oxidizing atmosphere in the middle section (air-fuel ratio of 1.2-1.27) reduces the thickness of the iron sheet; strong oxidizing atmosphere in the last section (air-fuel ratio of 1.3-1.38) makes the iron sheet loose.

[0051] Finishing rolling temperature: comprehensively consider the effects of grain refinement strengthening (lower rolling temperature is conducive to grain refinement strengthening) and precipitation strengthening (high rolling temperature can reduce the precipitation of elements such as Ti in the finishing rolling stage, ensuring the precipitation strengthening effect of the ferrite zone in the subsequent cooling process), and determine the finishing rolling temperature range in combination with the strength level requirements and usage requirements; and dynamically adjust the finishing rolling temperature in combination with the effective Ti content and thickness specifications.

[0052] Finishing rolling crown control: can better meet the requirements of plate shape control.

[0053] The side spraying between F4-7 stands is stopped during finishing rolling, and the side guide plate cooling water of F5-F7 stands is prohibited: this is to avoid overcooling of the edge and entering the two-phase zone prematurely, which may cause edge defects due to uneven deformation.

[0054] Coil temperature: mainly consider to give full play to the precipitation strengthening effect of TiC and other materials. Because the CSP coiling line is relatively short and the cooling intensity is large, the coiling temperature is set to the precipitation peak area of ​​TiC; when the effective Ti changes, the CT temperature is adjusted in a targeted manner in combination with the performance requirements to match the precipitation of Ti and strength control. At the same time, considering the composition, strength and user needs, the coiling temperature value is flexibly adjusted to obtain a reasonable match between strength and plastic toughness.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1) The hot-rolled high-strength beam steel produced by the present invention has a relatively thin specification (1.5-4.0 mm), and can be used as a supplement to conventional hot-rolled high-strength beam steel, achieving full specification coverage and wide applicability;

[0057] (2) The present invention uses the same casting or even the same furnace of molten steel to adjust and match the process according to the composition and specifications (thickness), and produces products of different strength levels through flexible rolling technology, thereby effectively meeting the personalized needs of users while ensuring cost and production efficiency;

[0058] (3) The flexible CSP manufacturing method adopted can significantly reduce the output of the CSP production line and provide a new idea for the preparation of high-quality beam steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is the metallographic structure diagram of the steel obtained in Example 2;

[0060] Figure 2 This is the metallographic structure diagram of the steel obtained in Example 8;

[0061] Figure 3 This is the metallographic structure diagram of the steel obtained in Comparative Example 3;

[0062] Figure 4 This is the metallographic structure diagram of the steel obtained in Comparative Example 4. DETAILED DESCRIPTION

[0063] The technical solution of the present invention will be fully and clearly described below in conjunction with embodiments, but the described embodiments are only some embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0064] In the following embodiments, the chemical composition of the hot-rolled high-strength beam steel series is calculated by weight percentage: C 0.04-0.065%, Si≤0.2%, Mn 0.9-1.4%, P≤0.020%, S≤0.008%, Ti 0.10-0.14%, Nb0.005-0.020%, Als0.02-0.05%, N≤0.006%, and the balance is Fe and unavoidable impurities; the thickness of the hot-rolled base plate is 1.2-4.0 mm.

[0065] The flexible CSP manufacturing method of hot-rolled high-strength beam steel comprises the following steps:

[0066] (1) Converter smelting: Control the final sulfur content in molten steel to ≤0.025% and the tapping temperature to ≥1650°C;

[0067] (2) LF furnace refining: desulfurization, slag basicity (CaO+MgO) / (SiO2+Al2O3)≥3.0, FeO<1.0%;

[0068] (3) Slab casting, key points of process control:

[0069] ①. The thickness of the casting is 65-85 mm, and the pulling speed is 4.2-4.6 m / min;

[0070] ②. Crystallizer cooling water volume, narrow side water volume 200 ~ 245l / min, wide side water volume 5600 ~ 6500l / min; crystallizer taper: 4.5 ~ 6.0mm;

[0071] ③ Secondary cooling water: specific water volume 1.8~1.9l / min, the water volume at the edge is reduced to ensure that the edge temperature of the ingot is ≥800℃ before straightening;

[0072] (4) Slab heating and rolling, key points of process control:

[0073] ①. Heating process: The slab is in the furnace for 20 to 50 minutes, the furnace temperature is 1200 to 1250°C, the acceleration roller position is ≥50, and the heating speed is controlled at 30-50°C / min; the heating furnace gas calorific value range is 8300 to 9000KJ / Nm 3 ; The air-fuel ratio of each section is: heating section 1-2 zone is 1.30-1.35, heating section 3-7 zone is 1.2-1.27, and equalizing section is 1.3-1.38;

[0074] ② Finishing rolling process: no speed increase, no manual speed increase, temperature control, FT7 control at 860-920℃, F4-7 inter-stand side spraying disabled, F5-F7 side wall cooling water prohibited; convexity target: 30μm, range 10-50μm; wedge target range: ±30μm;

[0075] ③. Laminar cooling, the upper and lower laminar cooling water flow ratio is 1:1.1~1.3;

[0076] ④. Coiling process: Coiling temperature target value 570~630℃;

[0077] In addition, dynamic adjustments are made to the finishing and coiling processes, including: setting the corresponding target range of effective Ti content for strip steel with different performance indicators and thickness specifications, where effective Ti content = Ti content - 3.4*N content - 3*S content - 0.006; when the effective Ti content range calculated based on the steel leaving station composition or the tundish composition exceeds the above target range, the finishing and coiling processes are dynamically adjusted in combination with the thickness specifications, and the corresponding final rolling temperature FT7 and coiling temperature CT are adjusted.

[0078] Furthermore, the dynamic adjustment step of the finishing rolling and coiling process specifically includes: under normal circumstances, when the effective Ti content calculated from the leaving station composition or the tundish composition of the molten steel is within the effective Ti target range, for steel with a thickness of ≤2.0mm, the coiling temperature CT is 610-630°C, and the final rolling temperature FT7 is 860-890°C; and for steel with a thickness of 2.0mm<thickness≤4.0mm, taking into full consideration the fine grain strengthening and impact energy matching, CT is 570-600°C, and the final rolling temperature FT7 is 890-910°C;

[0079] Among them, for the steel corresponding to combination ①, the effective Ti target range set is: 0.064% ≤ effective Ti < 0.076%; for the steel corresponding to combination ②, the effective Ti target range set is: 0.0761% ≤ effective Ti < 0.092%; for the steel corresponding to combination ③, the effective Ti target range set is: 0.092% ≤ effective Ti ≤ 0.11%;

[0080] When the effective Ti content calculated according to the steel leaving station composition or the tundish composition is less than the lower limit of the effective Ti target range, for steel with a thickness of 2.0 mm < ≤ 4.0 mm, the coiling temperature CT is increased by 10 to 30 ° C; for steel with a thickness of ≤ 2.0 mm, the finishing temperature FT7 is increased by 10 to 30 ° C, and the coiling temperature CT is reduced by 10 to 30 ° C;

[0081] When the effective Ti content calculated based on the steel leaving station composition or the tundish composition is greater than the upper limit of the effective Ti target range, for steel with a thickness of 2.0 mm < ≤ 4.0 mm, the coiling temperature CT is reduced by 10 to 30 ° C; for steel with a thickness of ≤ 2.0 mm, the finishing temperature FT7 is increased by 10 to 30 ° C, and the coiling temperature CT is increased by 20 to 40 ° C;

[0082] At the same time, in the coiling step, in order to ensure the uniformity of performance over the entire length, a U-shaped cooling process is adopted for specifications with a thickness of ≤2.0mm. The CT targets at the head and tail are increased by 20-30°C and 10-20°C respectively on the basis of the middle target, and the length is 10-20 meters. After coiling, they are all put into a slow cooling pit for 24-48 hours to ensure the uniformity of performance over the entire length of the steel coil.

[0083] Example 1

[0084] A series of customized high-strength steel beams with a width of 1480-1500mm. The specific performance and specification requirements are shown in Table 1;

[0085] Table 1 Customization requirements for high strength beam steel

[0086]

[0087] In view of the above-mentioned customized requirements, conventional preparation methods are adopted. Except for steel #6 which can be normally produced in conventional hot rolling, the other specifications are beyond the scope of conventional hot rolling and cannot be produced. If CSP production is adopted, it is necessary to organize production in two small batches according to the strength grades of 700Mpa and 620-550MPa, and the production furnaces are 2 and 3 respectively. Among them, because there are no other transition materials with thicknesses of 1.6-2.0mm and 4.0-2.5mm between 620-550Mpa, transition materials with other thickness specifications such as 3.0mm and 1.8mm will be produced in stock. At the same time, the 700MPa and 620-550Mpa levels will each produce about 100 tons of excess molten steel.

[0088] In view of the above problems, the present invention provides a flexible CSP manufacturing method for a high-strength beam steel series. The production can be organized according to one casting, and the number of furnaces is reduced to 4. At the same time, in order to ensure the continuity and stability of production, rolling should be carried out according to the principle of transition materials. Therefore, the production is organized according to the composition of 700MPa level. However, due to the difference in actual control on site, there are differences in composition control; the specific composition control is shown in Table 2:

[0089] Table 2 Composition control of high strength beam steel

[0090]

[0091]

[0092] According to the composition design of the above hot-rolled substrate and various parameters of the production process, a casting (the above 4 heats of steel were continuously cast) hot-rolled substrate was prepared, and all hot-rolled substrate samples were subjected to relevant performance tests; the hot rolling process and performance of the above substrate are shown in Table 3 and Table 4 respectively.

[0093] Table 3 Hot rolling process of various embodiments of the present invention

[0094]

[0095]

[0096] Table 4 Mechanical properties data of hot-rolled substrate obtained in Example

[0097]

[0098] The products obtained in Example 2 and Example 8 were subjected to metallographic examination respectively, and the results are as follows: Figure 1 and Figure 2 As shown; the metallographic examination results are all ferrite + pearlite structure, and the overall size is relatively uniform.

[0099] Comparative Example

[0100] The composition, process and properties of the 550-700Mpa grade strip steel are shown in Tables 5, 6 and 7 respectively. Because the composition control exceeded the expected strength range and the dynamic adjustment process was not used, the strength did not meet the standard requirements. Metallographic examination was carried out on Comparative Examples 3 and 4, and the results are as follows Figure 3 and Figure 4 The metallographic results show Figure 3 There are some carbides in the organization. Figure 4 It is ferrite + pearlite, some grains are coarse and do not meet the strength requirements.

[0101] Table 5 Comparative composition control and rolling grade control

[0102]

[0103] Table 6 Hot rolling process of each comparative example

[0104]

[0105]

[0106] Table 7 Mechanical properties data of hot-rolled substrate obtained in comparative example

[0107]

[0108] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and its improved conception within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. High strength beam steel series, characterized by: Its chemical composition is calculated by weight percentage: C 0.04-0.065%, Si≤0.2%, Mn 0.9-1.4%, P≤0.020%, S≤0.008%, Ti 0.08-0.14%, Nb 0.005-0.020%, Als 0.02-0.05%, N≤0.006%, and the balance is Fe and unavoidable impurities.

2. The high-strength beam steel series according to claim 1 is characterized in that: The following combinations are divided according to performance indicators and thickness specifications: ①Rel≥550Mpa, 580Mpa≤Rm<660Mpa, A≥18%, d=a, 180°, cold bending qualified; ②Rel≥600Mpa, 660Mpa≤Rm<760Mpa, A≥17%, d=1.5a, 180°, cold bending qualified; ③Rel≥700Mpa, 760Mpa≤Rm≤920Mpa, A≥16%, d=1.5a, 180°, cold bending qualified; Among them, Rel is the yield strength, Rm is the tensile strength, A is the elongation, d is the bending radius, mm, and a is the plate thickness, mm.

3. The high-strength beam steel series according to claim 2 is characterized in that: When producing steel corresponding to combination ①-②, molten steel with the same composition is used for production and the first type of composition design is carried out; when producing steel corresponding to combination ③, the second type of composition design is carried out.

4. The high strength beam steel series according to claim 3 is characterized in that: In the first type of component design, the Mn content is less than 1.2%, and the Ti content is 0.10-0.12%; in the second type of component design, the Mn content is controlled to be 1.2-1.4%, and the Ti content is 0.12-0.14%.

5. The method for manufacturing the flexible CSP of the high-strength beam steel series according to any one of claims 1 to 4, characterized in that: It includes converter smelting, LF furnace refining, slab casting, slab heating, flexible rolling, laminar cooling and coiling process. The key control points of heating, flexible rolling and coiling process are as follows: ① Slab heating process: Slab in furnace time is 20-50min, furnace temperature is 1200-1250℃, acceleration roller position is ≥50, heating speed is 30-50℃ / min; heating furnace gas calorific value is 8300-9000kJ / Nm 3 ; The air-fuel ratio of each section is: heating section 1-2 zone is 1.30-1.35, heating section 3-7 zone is 1.2-1.27, and equalizing section is 1.3-1.38; ② Finishing rolling process: No speed increase rolling, final rolling temperature FT7 is controlled at 860-920℃, side spraying between F4-7 stands is disabled, and side guide cooling water of F5-F7 stands is prohibited; The set convexity target is 30μm, and the corresponding convexity control range is 10-50μm; wedge target range: ±30μm; ③Laminar cooling, control the flow ratio of upper and lower laminar cooling water; ④ Coiling process: The target value of coiling temperature CT is 570~630℃; At the same time, dynamic adjustments are made to the finishing rolling and coiling processes, specifically including: setting the corresponding target range of effective Ti content for strip steel with different performance indicators and thickness specifications, where effective Ti content = Ti content - 3.4*N content - 3*S content - 0.006; when the effective Ti content range calculated based on the steel leaving station composition or the tundish composition exceeds the above target range, the finishing rolling and coiling processes are dynamically adjusted in combination with the thickness specifications, and the corresponding final rolling temperature FT7 and coiling temperature CT are adjusted.

6. The method for manufacturing a flexible CSP according to claim 5, characterized in that: In the dynamic adjustment step of the finishing rolling and coiling process, for the steel corresponding to combination ①, the effective Ti target range is set as: 0.064% ≤ effective Ti < 0.076%; for the steel corresponding to combination ②, the effective Ti target range is set as: 0.0761% ≤ effective Ti < 0.092%; for the steel corresponding to combination ③, the effective Ti target range is set as: 0.0921% ≤ effective Ti ≤ 0.11%.

7. The method for manufacturing a flexible CSP according to claim 6, characterized in that: The dynamic adjustment steps of the finishing rolling and coiling process specifically include the following: When the effective Ti content calculated according to the steel leaving station composition or the tundish composition is less than the lower limit of the effective Ti target range, for steel with a thickness of 2.0 mm < ≤ 4.0 mm, the coiling temperature CT is increased by 10 to 30 ° C; for steel with a thickness of ≤ 2.0 mm, the finishing temperature FT7 is increased by 10 to 30 ° C, and the coiling temperature CT is reduced by 10 to 30 ° C; When the effective Ti content calculated based on the steel leaving station composition or the tundish composition is greater than the upper limit of the effective Ti target range, for steel with a thickness of 2.0mm<≤4.0mm, the coiling temperature CT is reduced by 10 to 30°C; for steel with a thickness of ≤2.0mm, the finishing temperature FT7 is increased by 10 to 30°C, and the coiling temperature CT is increased by 20 to 40°C.

8. The method for manufacturing a flexible CSP according to claim 7, characterized in that: In the coiling step, the steel plate with a thickness of ≤2.0mm adopts a U-shaped cooling process, and the coiling temperatures of the head and tail are increased by 20-30°C and 10-20°C respectively on the basis of the coiling temperature of the middle part, and the length is 10-20 meters; after coiling, they are all put into a slow cooling pit for slow cooling for 24-48 hours.

9. The method for manufacturing a flexible CSP according to claim 5, characterized in that: The LF furnace refining steps include: desulfurization, controlling slag basicity (CaO+MgO) / (SiO2+Al2O3)≥3.0, and FeO<1.0%.

10. The method for manufacturing a flexible CSP according to claim 5, characterized in that: The key control points of slab casting process are as follows: ① The thickness of the casting is 65-85 mm, and the pulling speed is 4.2-4.6 m / min; ② Cooling water volume of crystallizer: 200~245L / min for narrow side and 5600~6500L / min for wide side; crystallizer taper 4.5~6.0mm; ③ Secondary cooling water: specific water volume is 1.8~1.9L / min, and the water volume at the edge is reduced to ensure that the edge temperature of the ingot is ≥800℃ before straightening.

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