High-strength corrosion-resistant steel and method for manufacturing same

Abstract

The application provides a high-strength corrosion-resistant steel and a manufacturing method thereof, and the composition of the high-strength corrosion-resistant steel comprises the following components: Cr 1.3-2.0%; Ni 0.07-0.15%; Cu 0.25-0.40%; W 0.05-0.15%; Alt 0.040-0.070%; Sb 0.05-0.10%; Ti 0.010-0.025%; Nb 0.020-0.040%; Ca 0.0010-0.0035%; C 0.05-0.08%; Si 0.15-0.35%; Mn 0.50-0.70%; P≤0.012%; S≤0.002%; N≤40ppm; O≤30ppm, and the balance is Fe and inevitable inclusions. Through the process design of controlled rolling + staged cooling + holding pit slow cooling, the product has high strength, high toughness and excellent corrosion resistance to strong acid and strong alkali, and the cost is greatly reduced compared with stainless steel and aluminum alloy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steel materials and its production technology, and particularly relates to a high-strength corrosion-resistant steel and a manufacturing method thereof. BACKGROUND

[0002] Chemical raw materials such as strong acid and strong base have strong corrosiveness. When a chemical liquid tank semi-trailer is used for transporting strong acid and strong base, the tank body is usually made of stainless steel or aluminum alloy material. However, the price of stainless steel and aluminum alloy is high, resulting in high manufacturing cost of the chemical liquid tank semi-trailer. Low-alloy corrosion-resistant steel material has excellent corrosion resistance, and its manufacturing cost is significantly lower than that of stainless steel and aluminum alloy, so it is widely used. In order to improve the transportation efficiency of the chemical liquid tank semi-trailer, a high-strength thinning lightweight design is often used, but thinning makes the corrosion problem of the material more prominent. Therefore, it is necessary to develop a low-alloy high-strength corrosion-resistant steel material with excellent acid and alkali corrosion resistance and high strength and ductility to meet the requirements of low-cost manufacturing and high transportation efficiency of the chemical liquid tank semi-trailer.

[0003] A corrosion-resistant steel for a coal open wagon with a yield strength of 550 MPa and a manufacturing method thereof are disclosed in Chinese Patent No. CN109628842A published on April 16, 2019. The chemical composition thereof is C: 0.049-0.072%, Si: 0.21-0.29%, Mn: 1.05-1.39%, P: ≤0.018%, S: ≤0.006%, Als: 0.015-0.045%, Cr: 0.45-0.91%, Ni: 0.11-0.19%, Cu: 0.27-0.41, Nb: 0.018-0.039%, Ti: 0.015-0.035%, Sb: 0.046-0.099%, Sn: 0.034-0.079%, Mo: 0.11-0.19%, B: 0.0008-0.0019%, Ca: 0.0008-0.0030%; the rest is Fe and unavoidable impurities. The R eL of the steel plate is ≥550 MPa, the R m of the steel plate is ≥650 MPa, A ≥18%, and the impact toughness at -40℃ is ≥60 J. Although the strength of the material is high, the elongation is insufficient. The steel plate has excellent corrosion resistance under the condition of "room temperature, 20% H2SO4+3.5 NaCl solution, immersion for 24 h", and the relative corrosion rate of Q345B is <4%, but it is only suitable for dilute H2SO4 and Cl - environment.

[0004] The invention patent with the patent publication number CN 107868919A published on April 3, 2018 discloses a kind of corrosion-resistant steel to hydrochloric acid and sulfuric acid and preparation method thereof, its chemical composition C:0.02-0.04%, Si:0.2-0.4%, Mn:0.8-1.0%, P≤0.01%, S:0.005-0.015%,

[0005] Cu:0.25-0.35%,Cr:0.3-0.4%,Ni:0.1-0.2%,Sb:0.05-0.15%,Sn:0.05-0.15%,Mo:0.05-0.15%。The yield strength of the material is greater than or equal to 245 MPa, the tensile strength is greater than or equal to 400 MPa, and the strength is lower. And under the condition of "70℃, 50%H2SO4 solution, immersion for 24h", the corrosion rate is 55.1-60.2g / m 2 ·h(61.5-67.2mm / a), the corrosion rate of the material in concentrated sulfuric acid environment is faster. SUMMARY

[0006] The purpose of the present application is to provide a kind of high-strength corrosion-resistant steel and its manufacturing method, for the complex corrosion environment in chemical liquid tank semi-trailer tank body and the development demand of lightweight, from chemical composition system design, steelmaking and controlled rolling process design, a kind of high-strength corrosion-resistant steel material is prepared, which has excellent acid and alkali corrosion resistance and high strength and toughness, and can be used for the manufacture of chemical liquid tank semi-trailer, instead of stainless steel and aluminum alloy.

[0007] The specific technical scheme of the present application is as follows:

[0008] The present application provides a kind of high-strength corrosion-resistant steel, including the following mass percentage chemical composition:

[0009] Cr: 1.3-2.0%;Ni: 0.07-0.15%;Cu: 0.25-0.40%;W: 0.05-0.15%;Alt: 0.040-0.070%;Sb: 0.05-0.10%;Ti: 0.010-0.025%;Nb: 0.020-0.040%;Ca: 0.0010-0.0035%;C: 0.05-0.08%;Si: 0.15-0.35%;Mn: 0.50-0.70%;P: ≤0.012%;S: ≤0.002%;N: ≤40ppm;O: ≤30ppm, the balance is Fe and unavoidable inclusions.

[0010] The microstructure of the high-strength corrosion-resistant steel is uniform and fine polygonal ferrite and pearlite structure; the average grain size of ferrite is 5.6-7.0 μm, and the volume fraction of ferrite is 90-95%.

[0011] The non-metallic inclusion diameter of the high-strength corrosion-resistant steel is 0.77-6.6 microns, and the average diameter is 1.5-2.4 microns, wherein the number of non-metallic inclusions with a diameter of less than 5 microns accounts for 96-98%.

[0012] The thickness of the high-strength corrosion-resistant steel is less than 10 mm.

[0013] The high-strength corrosion-resistant steel has high strength and high plasticity, and the R eL ≥450 MPa, R m ≥550 MPa, A≥25%.

[0014] The high-strength corrosion-resistant steel has excellent low-temperature toughness: KV2≥120 J at-60℃ (size 10*10*55mm), the present application adopts Al-Cu-Cr-Ni-Sb-W multi-element composite design, through the synergistic effect of multi-element alloy, the high-strength corrosion-resistant steel has excellent corrosion resistance: the corrosion rate is 0.2-0.4 mm / a in 40℃, 98% H2SO4 solution immersion for 24h; the corrosion rate is 10-20 mm / a in 70℃, 50% H2SO4 solution immersion for 24h; the corrosion rate is 0.01-0.02 mm / a in 40℃, 40% NaOH solution immersion for 24h.

[0015] The present application provides a manufacturing method of high-strength corrosion-resistant steel, comprising the following process flow:

[0016] hot metal pretreatment→ converter smelting→ refining→ continuous casting→ slab heating→ controlled rolling→ controlled cooling→ coiling.

[0017] The refining adopts LF+RH double treatment, the total weak stirring time of the LF furnace is ≥13 min, which promotes the floating of non-metallic inclusions in the molten steel, and the RH vacuum degassing time is ≥15 min. Through the above rewards, the non-metallic inclusion diameter is 0.77-6.6 microns, and the average diameter is 1.5-2.4 microns, wherein the number of non-metallic inclusions with a diameter of less than 5 microns accounts for 96-98%.

[0018] The continuous casting controls the tundish temperature of the molten steel to be 1530-1550℃, and the casting blank speed is 1.1-1.4 m / min, the thickness of the continuous casting slab is 230 mm, and the casting blank is slowly cooled to below 100℃ in the holding pit after cutting, and the cooling rate is ≤15℃ / h.

[0019] The slab heating controls the casting blank discharge temperature in the slab heating process to be 1180-1230℃, and the furnace time is 160-220 min, which promotes the full solid solution of alloy elements, especially titanium carbonitride. The heating furnace adopts a weak reducing atmosphere, and the air excess coefficient is 0.9-1.0, which reduces the oxidation burning loss of the slab surface Fe in the heating process.

[0020] After the billet is discharged from the heating furnace, it is subjected to high-pressure water descaling and then is rolled.

[0021] The rolling is controlled, and the rolling is divided into two stages of rough rolling and finish rolling. The rough rolling stage adopts two four-roll reversible rolling mills to roll back and forth, and is rolled for 3 passes and 5 passes respectively. The rolling temperature is controlled to be above 1050 DEG C. The cumulative reduction is greater than or equal to 80%. The multi-pass large deformation is carried out at high temperature, so as to promote the grain recovery and recrystallization of the deformed austenite, and refine the austenite grain size. The finish rolling stage adopts seven four-roll rolling mills to carry out continuous rolling. The finish rolling starting temperature is less than or equal to 1030 DEG C. The cumulative deformation is greater than or equal to 85%. Through the cumulative large deformation, the deformation band and dislocation density in the deformed austenite are increased, the ferrite phase nucleation points are increased, and the ferrite grain after phase transformation is refined. The finish rolling temperature is controlled to be 840-890 DEG C.

[0022] The cooling is controlled by adopting the sectional cooling. The coiling temperature of the tail part of the hot-rolled coil within 50m is controlled to be 640-660 DEG C. The coiling temperature of the head part of the hot-rolled coil within 20m is controlled to be 650-680 DEG C. The coiling temperature of the middle part of the hot-rolled coil is controlled to be 590-630 DEG C. After coiling, the steel coil is placed in the heat preservation pit and is slowly cooled to be less than or equal to 450 DEG C at a cooling rate of less than or equal to 0.2 DEG C / min. Then, the steel coil is taken out and is air-cooled to room temperature. The cooling speed of the head part and the tail part of the hot-rolled coil is avoided to be fast, so as to generate the bainite structure, and the strength of the head part and the tail part of the hot-rolled coil is high, and the plasticity and toughness are reduced.

[0023] The design idea of the present application is as follows:

[0024] C: The radius of C atom is small, and the strong lattice distortion is caused by the interstitial solid solution, so that the strength of the material can be significantly improved. However, if the content of C is too high, the plasticity and toughness of the steel and the welding performance will be deteriorated, and the crack sensitivity of the casting blank will be increased. In the present application, the content of C is controlled to be 0.05-0.08% considering the manufacturing cost and the strength and toughness requirements.

[0025] Si: Si is often used for deoxidation of molten steel, and can also improve the strength of the steel through solid solution strengthening. However, if the content of Si is too high, the iron oxide scale which is difficult to remove will be generated on the surface of the steel strip, and the surface quality of the steel will be deteriorated. Therefore, the content of Si is controlled to be 0.15-0.35% in the present application.

[0026] Mn: Mn is one of the important deoxidizing elements in steel, and can also improve the strength through the replacement solid solution strengthening effect. However, if the content of Mn is too high, the stability of austenite will be enhanced, the bainite structure will be easily generated, the manufacturing cost will be increased, and the welding performance will be deteriorated. Therefore, the content of Mn is controlled to be 0.50-0.70% in the present application.

[0027] Alt (Al): Al has a strong binding force with oxygen and is the most important deoxidizing element added during the smelting of steel materials, with a stronger deoxidizing ability than Si and Mn. It can also form a dense alumina film on the steel surface, inhibiting the corrosion of the substrate by acids and alkalis. However, excessive Al content will lead to an increase in the content of alumina inclusions in the steel, deteriorating the toughness of the steel. Therefore, this invention controls the Alt content at 0.040–0.070%.

[0028] Cr: Cr can promote the formation of α-FeOOH and replace some of the Fe in α-FeOOH. 3+ This forms nano-sized oxide α-FexCr1-xOOH, effectively preventing SO42-. 2- Corrosion. Meanwhile, Cr in steel also has a certain tendency for self-passivation, increasing the electrode potential of the solid solution; therefore, a higher Cr content is used to improve acid resistance. However, excessively high Cr content significantly increases the hardenability of the material, easily forming bainitic structures and deteriorating weldability. Therefore, the Cr content is controlled between 1.3% and 2.0%.

[0029] Ni can significantly improve the resistance of materials to hydrochloric acid and alkali corrosion, and can also form high-temperature binary alloys with Cu, inhibiting copper embrittlement on the surface of steel; however, Ni is an expensive alloy, significantly increasing the manufacturing cost of materials. Therefore, its content is controlled at 0.07–0.15%.

[0030] Cu reacts with Sb to form Cu₂Sb, inhibiting cathodic reactions and improving acid corrosion resistance. Cu can also react with hydroxide ions to form a dense passivation layer on the steel surface, thereby improving alkali corrosion resistance. However, Cu has a low melting point of only 1073℃, and high content can cause copper embrittlement defects on the surface of hot-rolled coils. Therefore, the Cu content should be controlled between 0.25% and 0.40%.

[0031] Sb: Sb is one of the key elements for improving the acid corrosion resistance of steel. In acidic environments, it accumulates on the steel surface, forming a dense rust layer of Sb₂O₃ and Sb₂O₅, which blocks the corrosion of the substrate by the corrosive medium. As the antimony content increases, the improvement in acid corrosion resistance weakens, and since Sb is a low-melting-point alloying element, excessively high content increases the slab's susceptibility to cracking. Therefore, this invention controls the Sb content to be between 0.05% and 0.10%.

[0032] W: Inhibits anodic reactions and reduces localized corrosion in steel. The effect of adding W and Ni simultaneously on improving the acid and alkali corrosion resistance of steel is even more significant. However, W is expensive and significantly increases the hardenability of the material, easily forming bainitic structures. Therefore, its content is controlled at 0.05–0.15%.

[0033] Ti: Ti is a strong nitride forming element, and has a high solid solution temperature. In the welding process, Ti can inhibit the growth of the austenite grains in the heat affected zone, and improve the low temperature toughness of the heat affected zone. Moreover, the binding force between Ti and C is much greater than that between Cr and C, which can reduce the content of Cr-containing carbide, eliminate the depletion of Cr at the grain boundaries, and improve the intergranular corrosion resistance. However, if the content of Ti is too high, large particles of titanium nitride inclusions are likely to be precipitated, which can reduce the low temperature toughness of the material. Therefore, the content of Ti is controlled to be 0.010% to 0.025%.

[0034] Nb: Nb has a strong grain refinement and precipitation strengthening effect. In the high temperature stage, Nb can precipitate niobium carbonitride to pin dislocations, inhibit the recovery and recrystallization of deformed austenite, increase the dislocation density, improve the nucleation rate, and refine the grains. In the low temperature stage, Nb can precipitate carbonitride particles to improve the strength of the material. However, the alloy price of Nb is relatively high, which can significantly increase the manufacturing cost of the material. Therefore, the content of Nb is controlled to be 0.020% to 0.040%.

[0035] Ca: Ca can promote the spheroidization of non-metallic inclusions, and improve the low temperature toughness and corrosion resistance of the material. The content of Ca is controlled to be 0.0010% to 0.0035%.

[0036] P: P is a common residual element in steel, which is easy to enrich at the grain boundaries and reduce the low temperature toughness of the material. However, if the content of P is controlled at a very low level, the smelting cost will be increased. Therefore, the content of P is controlled to be ≤0.012% in the present application.

[0037] S: Although S can form a dense Cu2S passivation film with Cu to improve the corrosion resistance, S is easy to form MnS inclusions with Mn, which can deteriorate the plasticity and toughness of the steel, especially as the strength increases, the influence on the plasticity and toughness of the steel is more significant. Moreover, S is easy to react with Ti to precipitate coarse Ti4C2S2 two-phase particles at high temperature, which can weaken the effect of the micro-alloying element Ti. Therefore, S is controlled as a harmful element in the present application, and the content of S is controlled to be ≤0.002%.

[0038] N and O: N and O are residual harmful gas elements in steel. If the content of N is too high, coarse TiN particles are likely to be precipitated at high temperature, which can reduce the toughness of the material. O can form oxide inclusions in steel, which can reduce the toughness and corrosion resistance of the material. Therefore, the content of N is controlled to be ≤0.0040%, and the content of O is controlled to be ≤0.0030% in the present application.

[0039] Compared with the prior art, the application is aimed at strong acid and strong alkali corrosive medium in a chemical liquid tank semi-trailer tank body, and the acid and alkali corrosion resistance of the material is improved through a small amount of multi-element interaction of Al-Cu-Cr-Ni-Sb-W. The strength of the material is improved through single Ti micro-alloying. The LF+RH double refining treatment is adopted to reduce the content of gas and non-metallic inclusions and improve the cleanliness of the molten steel. A small amount of Ca is added to promote the spheroidization of non-metallic inclusions, reduce the non-metallic inclusions as a source of pitting corrosion, and improve the toughness of the material. Aiming at the characteristics of high strength corrosion-resistant steel containing Cu, Cr, Ni, W and other alloy elements, high hardenability and narrow hot rolling process control window, a uniform and fine ferrite+pearlite structure is obtained through controlled rolling+staged cooling+holding pit slow cooling process design. The steel plate provided by the application has high strength, high toughness and excellent strong acid and strong alkali corrosion resistance, and the cost is greatly reduced compared with stainless steel and aluminum alloy. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The microstructure morphology of Example 2 of the application under an optical microscope is shown in the figure. A uniform and fine ferrite+pearlite structure is obtained, the average ferrite grain size is 6.1 μm, and the ferrite volume fraction is 92%. DETAILED DESCRIPTION

[0041] To make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below in combination with the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0042] Examples 1-4

[0043] A high-strength corrosion-resistant steel includes the following mass percentage chemical components: as shown in Table 1, the balance of Table 1 is Fe and unavoidable impurities.

[0044] Comparative Examples 1-4

[0045] A high-strength corrosion-resistant steel includes the following mass percentage chemical components: as shown in Table 1, the balance of Table 1 is Fe and unavoidable impurities.

[0046] Table 1 Chemical composition of the embodiments and comparative examples of the application (O and N are ppm, and the rest are wt%)

[0047]

[0048] The production method of each of the above examples and comparative examples includes the following process flow: hot metal pretreatment → converter smelting → refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling.

[0049] The molten steel is smelted according to the above chemical composition, and the refining is treated by LF+RH duplex, the total weak stirring time of the LF furnace is ≥13 min, the non-metallic inclusions in the molten steel are promoted to float up, and the RH vacuum degassing time is ≥15 min. The tundish temperature of the molten steel casting is controlled at 1530-1550℃, the casting blank speed is 1.1-1.4 m / min, the thickness of the continuous casting slab is 230 mm, and the casting blank is slowly cooled to below 100℃ in the holding pit after cutting, and the cooling rate is ≤15℃ / h.

[0050] The casting blank discharge temperature is controlled at 1180-1230℃ in the slab heating process, the furnace time is 160-220 min, the heating furnace adopts a weak reducing atmosphere, and the air excess coefficient is 0.9-1.0. After the steel blank is discharged from the heating furnace, it is rolled after high-pressure water descaling, and the rolling is carried out in two stages of rough rolling and finish rolling. The rolling temperature in the rough rolling stage is controlled at above 1050℃, and the cumulative reduction is ≥80%. The finish rolling adopts 7-stand four-roll rolling, the finish rolling opening rolling temperature is ≤1030℃, the cumulative deformation is ≥85%, and the finish rolling final rolling temperature is 840-890℃. After the finish rolling, the steel coil is coiled by section cooling, the coiling temperature of the tail 50 m of the hot-rolled coil is controlled at 640-660℃, the coiling temperature of the head 20 m is 650-680℃, and the coiling temperature of the middle part of the hot-rolled coil is 590-630℃, and then the steel coil is placed in the holding pit for slow cooling to ≤450℃, the cooling rate is ≤0.2℃ / min, and then it is taken out for air cooling to room temperature.

[0051] The main process parameters of the smelting and rolling process of the examples and comparative examples are shown in Table 2.

[0052] Table 2 Main process parameters of smelting and rolling process of examples and comparative examples

[0053]

[0054] The tensile test and impact test are carried out according to GB / T 228.1 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method" and GB / T229 "Metallic Materials Charpy Pendulum Impact Test Method", the non-metallic inclusion detection is carried out by using ASPEX inclusion analyzer, and the mechanical properties, low temperature toughness and non-metallic inclusions of the examples and comparative examples are shown in Table 3.

[0055] Table 3 Mechanical properties, toughness, non-metallic inclusions of examples and comparative examples

[0056]

[0057]

[0058] The corrosion test was carried out according to JB / T 7901 "Metal Material Laboratory Uniform Corrosion Immersion Test Method", the test period was 24 h, the sample size was 25 mm x 50 mm x 3.5 mm, and the sample surface was treated by a grinding machine. The corrosion resistance of the examples and the comparative examples in strong acid and strong alkali environments is shown in Table 4.

[0059] Table 4 Corrosion resistance of examples and comparative examples

[0060]

[0061] Comparative Example 1 did not add W and Sb elements, so that the material had insufficient corrosion resistance to strong acid and strong alkali;

[0062] Comparative Example 2 had insufficient content of Al, Cr, Ni and Cu elements, so that the material had reduced corrosion resistance to strong acid and strong alkali;

[0063] Comparative Example 3 had high content of C, Mn, P and S, and short LF and RH refining treatment time, so that the material had high content of large-size non-metallic inclusions, high strength, and reduced low-temperature toughness and corrosion resistance.

[0064] Comparative Example 4 had a composition meeting the requirements of the present application, but had low finish rolling reduction, so that the dislocation density in the deformed austenite grains before phase transition was reduced, the ferrite nucleation rate was reduced, and the coiling temperature of the middle part of the hot-rolled coil was high, so that the ferrite grains were coarsened, the material strength was reduced, and the low-temperature toughness was insufficient.

[0065] In summary, the high-strength corrosion-resistant steel plate obtained according to the chemical composition and controlled rolling and controlled cooling process control technology of the present application has a yield strength of ≥450 MPa, a tensile strength of ≥550 MPa, an elongation of ≥25%, and a KV2 of ≥120 J at -60°C, has excellent acid and alkali corrosion resistance, and can be applied to the manufacture of chemical liquid tank semi-trailers.

[0066] The above underlined data do not meet the requirements of the present application.

[0067] The above description of the embodiments is to facilitate the understanding and use of the present application by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above-described embodiments, and improvements and modifications made by those skilled in the art without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A high-strength corrosion-resistant steel, characterized in that, The high-strength corrosion-resistant steel comprises the following chemical composition by weight percentage: Cr：1.3~2.0％； Ni: 0.07~0.15%; Cu: 0.25~0.40%; W: 0.05~0.15%; Alt: 0.040~0.070%; Sb: 0.05~0.10%; Ti: 0.010~0.025%; Nb: 0.020~0.040%; Ca: 0.0010~0.0035%; C: 0.05~0.08%; Si: 0.15~0.35%; Mn: 0.50~0.70%; P：≤0.012％； S: ≤0.002%; N: ≤40ppm; O: ≤30ppm, balance being Fe and unavoidable inclusions; The microstructure of the high-strength corrosion-resistant steel consists of polygonal ferrite and pearlite, wherein the average grain size of the ferrite is 5.6~7.0μm, and the volume fraction of ferrite is 90~95%; the diameter of the non-metallic inclusions is 0.77~6.6μm, with an average diameter of 1.5-2.4μm, and the proportion of non-metallic inclusions with a diameter of less than 5μm is 96-98%. The high-strength corrosion-resistant steel R eL ≥450MPa, R m ≥550MPa, A≥25%; Low temperature toughness: KV2≥120J at -60℃; Corrosion rate 0.2~0.4mm / a after immersion in 98%H2SO4 solution at 40℃ for 24h; Corrosion rate 10~20mm / a after immersion in 50%H2SO4 solution at 70℃ for 24h; Corrosion rate 0.01~0.02mm / a after immersion in 40%NaOH solution at 40℃ for 24h.

2. A method for manufacturing the high-strength corrosion-resistant steel according to claim 1, characterized in that, The manufacturing method includes the following process flow: Hot metal pretreatment → converter smelting → refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling.

3. The manufacturing method according to claim 2, characterized in that, The refining process employs a dual LF+RH treatment, with a total weak stirring time of ≥13 min in the LF furnace to promote the flotation of non-metallic inclusions in the molten steel, and a vacuum degassing time of ≥15 min in the RH furnace.

4. The manufacturing method according to claim 2, characterized in that, In the continuous casting process, the ladle temperature is controlled at 1530℃~1550℃, the billet casting speed is 1.1~1.4m / min, and after the billet is cut, it is slowly cooled to below 100℃ in the heat preservation pit, with a cooling rate ≤15℃ / h.

5. The manufacturing method according to claim 2, characterized in that, The slab heating process involves controlling the slab exit temperature at 1180~1230℃ and the furnace dwell time at 160~220min.

6. The manufacturing method according to claim 2, characterized in that, The controlled rolling process is divided into two stages: roughing and finishing. In the roughing stage, the rolling temperature is controlled above 1050℃ and the cumulative reduction rate is ≥80%. In the finishing stage, a 7-stand four-high rolling mill is used for continuous rolling. The starting temperature of the finishing rolling is ≤1030℃, the cumulative deformation is ≥85%, and the finishing rolling temperature is controlled at 840~890℃.

7. The manufacturing method according to claim 2, characterized in that, The controlled cooling adopts segmented cooling, controlling the coiling temperature within 50m of the tail of the hot-rolled coil at 640~660℃, the coiling temperature within 20m of the head of the hot-rolled coil at 650~680℃, and the coiling temperature in the middle of the hot-rolled coil at 590~630℃; then the steel coil is placed in an insulated pit for slow cooling to ≤450℃, with a cooling rate ≤0.2℃ / min, and then taken out and air-cooled to room temperature.

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