High-strength green surface cleaning steel plate for automobile frame and manufacturing method of high-strength green surface cleaning steel plate

Abstract

The invention relates to the technical field of steel plates for automobile frames, in particular to a high-strength green surface cleaning steel plate for an automobile frame and a manufacturing method of the high-strength green surface cleaning steel plate. The method comprises the following steps: 1) heating process: heating a continuous casting sheet billet to 1200-1260 DEG C in a heating furnace, and keeping the temperature for 1-2 hours; 2) rolling process: the initial rolling temperature of finish rolling is 1020-1080 DEG C, and the final rolling temperature is 800-840 DEG C; (3) a cooling process is carried out, wherein a front-section cooling mode is adopted after finish rolling, and the coiling temperature is 540-580 DEG C; and (4) a wet type sand blasting descaling treatment process is conducted, specifically, the steel coil sand blasting descaling treatment temperature is lower than 60 DEG C, the steel plate advancing speed in the process section is 30-50 m / min, the steel grit mesh number is 30-50, the steel grit hardness is HRC 55-60, and the sand blasting motor rotating speed is 1800-2200 rpm. And the tensile strength is 550MPa or above, the surface quality is high, the rust resistance can be kept for 180 days under the condition that anti-rust oil is not used, the manufacturing cost is low, and environmental protection is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of steel plates for automobile beams, in particular to a high-strength green clean-surface steel plate for automobile beams and a manufacturing method thereof. Background Art

[0002] With the rapid development of the automobile industry, automobile manufacturers have more and more requirements on the surface quality of steel plates and environmental protection factors. Advanced manufacturing technology, reduced structural quality and green new processes are the focus of attention of all parties. The automobile frame is a frame structure that spans the front and rear axles of the car and is the base of the car. It is generally composed of two longitudinal beams and several cross beams, and is supported on the wheels through the suspension device, front axle and rear axle. The frame must have sufficient strength and rigidity to withstand the load of the car and the impact from the wheels. The function of the frame is to support and connect the various assemblies of the car, so that each assembly maintains a relatively correct position and withstands various loads inside and outside the car. As an important component of the car, lightweight and environmentally friendly manufacturing processes have become a new development trend.

[0003] However, the current production process of automobile beams usually uses pickling technology to remove the iron oxide scale on the surface of the steel plate before forming the beam components, but the pickling process has defects such as large acid mist pollution, high cost of waste acid treatment, uneven descaling, and large substrate loss. Alternatively, the method of adding Cr elements is used to obtain dense Fe3O4 iron scale on the surface of the steel plate, which can be directly used in the stamping and rolling process of the beam, but the iron oxide scale occasionally falls off, affecting production and the cost is high.

[0004] Domestic and foreign steel manufacturers attach great importance to and pay attention to the research and development of high-surface quality steel plates for automobile beams with excellent processing performance, environmental protection, corrosion resistance and low cost. The Chinese patent document with announcement number CN107649522A discloses a "hot-rolled steel coil surface quality control method", which uses a cooling rate of 20 to 60 ° C / s to cool the hot-rolled steel to 580 to 660 ° C and then coil it to control the thickness and composition of the oxide layer on the surface of the steel plate. However, the surface of the automobile beam steel still has a thickness of 5 to 8 μm of Fe3O4 oxide scale, which is relatively rough and is not conducive to subsequent painting, stamping and other processes. The Chinese patent document with announcement number CN101906584A discloses a "production method for environmentally friendly high-surface quality pickling-free automobile beam steel". The production process adopts a low-temperature coiling scheme, increases the cooling rate of the rolled steel plate, and adds Cr elements to generate an oxide layer that is closely bonded to the matrix. However, the surface of the automobile beam steel still has black iron oxide Fe3O4, which is rougher than the steel plate of the present invention, which is not conducive to subsequent painting, stamping and other processes. The Chinese patent document with the announcement number CN103320683A discloses the "production process of thin-gauge high-elongation hot-rolled pickled 610L automobile beam steel strip". After the heating, rolling and cooling processes, it must pass through a continuous pickling production line and undergo three-stage continuous hydrochloric acid pickling, which has the disadvantages of high acid solution cost, large acid mist pollution, and high waste acid treatment cost. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a high-strength green clean surface steel plate for automobile beams and a manufacturing method thereof. The tensile strength is above 550MPa, the surface quality is high, and it can remain rust-free for 180 days without using anti-rust oil. The manufacturing cost is low and it is environmentally friendly.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A high-strength green clean surface steel plate for automobile beams, with a tensile strength of 550MPa or above and a surface cleanliness of 3.0 or above, is composed of the following chemical components in percentage by weight:

[0008] C: 0.06%~0.08%, Si: 0.05%~0.15%, Mn: 1.50%~1.65%, Als: 0.015%~0.045%, Nb: 0.045%~0.060%, Ti: 0.025%~0.040%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the yield strength of the steel plate is higher than 500 MPa, and the elongation A is ≥ 24%.

[0010] Furthermore, the roughness of the steel plate is less than 2.5 μm.

[0011] Furthermore, the final structure of the steel plate is ferrite and pearlite, with ferrite accounting for 85%.

[0012] A method for manufacturing a high-strength green clean surface steel plate for an automobile beam, the manufacturing method specifically comprising the following steps:

[0013] 1) Heating process:

[0014] The continuous casting slab is heated to 1200-1260°C in a heating furnace and kept warm for 1-2 hours;

[0015] 2) Rolling process:

[0016] The starting temperature of finishing rolling is 1020~1080℃, and the final rolling temperature is 800~840℃;

[0017] 3) Cooling process:

[0018] After final rolling, the front-stage cooling method is adopted, and the coiling temperature is 540-580℃;

[0019] 4) Wet sandblasting descaling process:

[0020] The sandblasting descaling treatment temperature of steel coil is less than 60℃, the steel plate travel speed in the process section is 30-50m / min, the steel grit mesh number is 30-50, the steel grit hardness is HRC55-60, the sandblasting motor speed is 1800-2200rpm, and the medium is water-based rust inhibitor.

[0021] Furthermore, in the step 2), the thickness of the finished product is 2 to 12 mm.

[0022] Furthermore, in the step 4), straightening is performed after uncoiling.

[0023] Furthermore, in the step 4), the hardness of the steel sand is HRC57.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. Based on the C-Mn steel composition, a low-silicon, low-carbon, composite Nb and Ti component system is adopted. The hot rolling process is controlled by using the solid solution strengthening and fine grain strengthening principles, and the surface is wet-blasted for descaling to obtain a green and clean surface steel plate for automobile structure with a tensile strength of 510MPa or above and an elongation of A ≥ 24%.

[0026] 2. Conventional pickling processes are strong acids with high pollution, which will produce a lot of pollution during the pickling process, posing a threat to the environment and the health of operators. The wet sandblasting descaling process of the present invention uses a physical method to remove iron scale. Compared with chemical pickling, there is no waste acid discharge, and it has the advantages of being clean and pollution-free.

[0027] 3. Compared with the pickling process, the process of removing iron oxide scale from the surface of the steel plate produced by the present invention can process steel plates with a thickness exceeding 6 mm, thereby expanding the product range.

[0028] 4. Compared with the pickling products, the products produced by the present invention can be adjusted according to the requirements of users by adjusting the steel sand particle size and adjusting the steel plates with different surface roughness, so as to better match the requirements of subsequent processing procedures for the surface quality of the steel plates.

[0029] 5. In the process of wet sandblasting descaling in the present invention, the medium is a water-based rust inhibitor, and the sandblasting liquid has an anti-corrosion function, which can ensure that the steel plate will not rust when stored for 180 days without oiling.

[0030] 6. The traditional pickling process requires the treatment of waste acid. The steel sand in the wet sandblasting descaling process of the present invention can be recycled. Compared with the traditional pickling process, the present invention reduces production costs and reduces the generation of process waste.

[0031] In summary, the steel plate of the present invention has excellent comprehensive performance, yield strength ≥500MPa, tensile strength ≥550MPa, elongation ≥24%, roughness less than 2.5μm, surface cleanliness reaching level 3.0, and good formability. It can be applied to the manufacture of automobile beam parts, with obvious weight reduction effect, and can remain rust-free for 180 days without using anti-rust oil. Moreover, the manufacturing method of the present invention has the characteristics of zero pollution, low cost, and green and clean. DETAILED DESCRIPTION

[0032] The present invention discloses a high-strength green clean surface steel plate for automobile beams and a method for manufacturing the same. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0033] A high-strength green clean surface steel plate for automobile beams, with a tensile strength of 550MPa or above, a surface cleanliness of 3.0 or above, a yield strength of the steel plate higher than 500MPa, an elongation A ≥ 24%, a steel plate roughness less than 2.5μm, a final structure of the steel plate of ferrite and pearlite, ferrite accounting for 85%, and composed of the following chemical components in weight percentage:

[0034] C: 0.06%~0.08%, Si: 0.05%~0.15%, Mn: 1.50%~1.65%, Als: 0.015%~0.045%, Nb: 0.045%~0.060%, Ti: 0.025%~0.040%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurities.

[0035] C: It is a strong solid solution strengthening element, which can significantly improve the strength of steel. If the C content in steel is too low, the content of other elements that increase the strength of the steel plate will increase accordingly, which is not conducive to reducing the cost of the steel plate. If the C content is too high, the strength of the steel plate will increase, but the elongation will decrease, which is not conducive to the forming of the steel plate. Taking comprehensive considerations, the C content in steel is limited to between 0.06% and 0.08%.

[0036] Si: replaces solid solution alloy elements, promotes C enrichment in austenite and increases the stability of austenite. At the same time, it can play a deoxidation role and reduce impurities in steel. Too low Si content is not conducive to deoxidation and increasing the stability of austenite. Too high Si content will reduce the surface quality of the steel plate. Therefore, the present invention limits the content of Si element in steel to 0.05% to 0.15%.

[0037] Mn: Improves the hardenability of steel plates and helps obtain martensite structure under controlled cooling rate. Too low content has little effect, while too high content increases production cost. Therefore, its content is limited to 1.50% to 1.65%

[0038] S, P: harmful elements, the lower the content, the better. Too low content will increase production cost. Under the premise of not affecting the performance of steel plate, the content is limited to p≤0.020%, S≤0.010%.

[0039] Nb: Niobium can refine ferrite grains. At the same time, niobium combines with carbon and nitrogen to form small carbonitrides, which can also delay recrystallization, prevent austenite grain growth, and have a significant precipitation strengthening effect. However, too high a niobium content will have an adverse effect on ferrite phase transformation, so the optimal range of niobium content in the present invention is Nb: 0.045% to 0.060%.

[0040] Ti: Titanium has the effects of precipitation strengthening, fine grain strengthening and inhibiting austenite recrystallization. Adding niobium and titanium elements in steel can effectively increase the precipitation of carbonitrides and significantly improve the strength and cold forming performance of the steel plate through precipitation strengthening. The optimal range of titanium content in the present invention is between 0.025% and 0.040%.

[0041] Als: Aluminum is a deoxidizing element in steel, which reduces oxide inclusions in steel, purifies steel, and is beneficial to improving the formability of steel plates. At the same time, aluminum can form AlN precipitation, which plays a certain role in grain refinement. The optimal range of aluminum is between 0.015 and 0.045%.

[0042] The present invention adopts the above chemical composition to produce a green and clean surface automobile structural steel plate through smelting, hot rolling and wet sandblasting descaling treatment processes. The specific manufacturing method includes the following steps:

[0043] (1) Heating process: The continuous casting slab is heated to 1200-1260°C in a heating furnace and kept warm for 1-2 hours to allow the alloy elements in the slab to be completely dissolved and the composition of the slab to be uniform.

[0044] (2) Rolling process: controlled rolling is adopted, the starting temperature of finishing rolling is 1020-1080℃, the final rolling temperature is 800-840℃, and the finished product thickness is 2-12mm.

[0045] (3) Cooling process: After final rolling, the front-end cooling method is adopted, and the coiling temperature is 540-580℃.

[0046] (4) Wet sandblasting descaling process: The sandblasting descaling temperature of the steel coil is less than 60°C, and the coil is straightened after unwinding. The steel plate travel speed in the process section is 30-50 m / min, the steel grit number is 30-50, the hardness is HRC57, and the sandblasting motor speed is 1800-2200 rpm.

[0047] [Example]

[0048] The chemical composition (wt%) of the steel plate of the embodiment of the present invention is shown in Table 1; the main production process parameters of the steel plate of the corresponding embodiment are shown in Table 2; and the mechanical properties of the steel plate of the corresponding embodiment are shown in Table 3.

[0049] Table 1 Chemical composition of the present invention (wt, %)

[0050] C Si Mn P S Als Nb Ti N Example 1 0.080 0.14 1.50 0.013 0.002 0.036 0.023 0.022 0.002 Example 2 0.060 0.05 1.52 0.018 0.003 0.044 0.030 0.015 0.003 Example 3 0.075 0.15 1.61 0.011 0.005 0.038 0.016 0.030 0.004 Example 4 0.061 0.07 1.64 0.010 0.001 0.027 0.022 0.023 0.001 Example 5 0.073 0.08 1.58 0.012 0.009 0.015 0.019 0.019 0.003

[0051] Table 2 Production process of the embodiment of the present invention

[0052]

[0053] Table 3 Organization and mechanical properties parameters of the embodiments of the present invention

[0054]

[0055] As shown in Table 3, the steel plate of the present invention has excellent comprehensive performance, yield strength ≥ 500MPa, tensile strength ≥ 550MPa, elongation ≥ 24%, roughness less than 2.5μm, surface cleanliness reaching level 3.0, and good forming performance. It can be applied to the manufacture of automobile beam parts, with obvious weight reduction effect, high surface quality, and can remain rust-free for 180 days without using anti-rust oil, and has low manufacturing cost and is beneficial to environmental protection. It has the advantages of zero pollution, low cost, and green cleaning.

[0056] The above description is only a preferred specific implementation manner 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 scheme and inventive concept of the present invention 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 green clean surface steel plate for automobile beams, characterized in that: The steel plate has a tensile strength of 550 MPa or above, a surface cleanliness of 3.0, and is composed of the following chemical components in percentage by weight: C: 0.06%~0.08%, Si: 0.05%~0.15%, Mn: 1.50%~1.65%, Als: 0.015%~0.045%, Nb: 0.045%~0.060%, Ti: 0.025%~0.040%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurities.

2. The high-strength green clean surface steel plate for automobile beams according to claim 1, characterized in that: The steel plate has a yield strength higher than 500 MPa and an elongation A≥24%.

3. The high-strength green clean surface steel plate for automobile beams according to claim 1, characterized in that: The steel plate has a roughness less than 2.5 μm.

4. The high-strength green clean surface steel plate for automobile beams according to claim 1, characterized in that: The final structure of the steel plate is ferrite and pearlite, with ferrite accounting for 85%.

5. A method for manufacturing a high-strength green clean surface steel plate for automobile beams as claimed in any one of claims 1 to 4, characterized in that: The manufacturing method specifically comprises the following steps: 1) Heating process: The continuous casting slab is heated to 1200-1260°C in a heating furnace and kept warm for 1-2 hours; 2) Rolling process: The starting temperature of finishing rolling is 1020~1080℃, and the final rolling temperature is 800~840℃; 3) Cooling process: After final rolling, the front-stage cooling method is adopted, and the coiling temperature is 540-580℃; 4) Wet sandblasting descaling process: The sandblasting descaling treatment temperature of steel coil is less than 60℃, the steel plate travel speed in the process section is 30-50m / min, the steel grit mesh number is 30-50, the steel grit hardness is HRC55-60, the sandblasting motor speed is 1800-2200rpm, and the medium is water-based rust inhibitor.

6. The method for manufacturing a high-strength green clean surface steel plate for automobile beams according to claim 5, characterized in that: In the step 2), the thickness of the finished product is 2 to 12 mm.

7. The method for manufacturing a high-strength green clean surface steel plate for automobile beams according to claim 5, characterized in that: In the step 4), straightening is performed after uncoiling.

8. The method for manufacturing a high-strength green clean surface steel plate for automobile beams according to claim 5, characterized in that: In the step 4), the hardness of the steel sand is HRC57.

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