Hot rolled corrosion resistant steel plate and manufacturing method thereof

Abstract

The invention provides a hot-rolled corrosion-resistant steel plate and a manufacturing method thereof. The steel plate comprises the following components: C: 0.015%-0.050%, Si: 0.15%-0.35%, Mn: 0.60%-0.90%, P: ≤0.015%, S: ≤0.0020%, Cr: 2.0%-3.5%, Ni: ≤0.10%, Cu: 0.15%-0.30%, Als: 0.015%-0.035%, Ca: 0.0010%-0.0035%, N≤0.0050%, H≤1.5ppm, and the remainder is Fe and unavoidable impurity elements; the weathering index I≥8.0; 1≤Ca / S≤5; compared with the prior art, the steel plate developed by the invention has excellent atmospheric corrosion resistance and H2S corrosion resistance through the coordinated design of alloy components and the whole-process manufacturing process of smelting, continuous casting, controlled rolling and controlled cooling.

Description

Technical Field

[0001] The invention belongs to the field of steel material manufacturing, and specifically relates to a hot-rolled corrosion-resistant steel plate with excellent atmospheric corrosion resistance and H2S corrosion resistance and a manufacturing method thereof. Background Art

[0002] Compared with ordinary carbon steel, corrosion-resistant steel has excellent corrosion resistance, which can effectively extend the service life of materials, reduce the consumption of steel materials throughout their life cycle, save energy and resources, and reduce carbon emissions. Corrosion-resistant steel is a green steel material with more and more applications.

[0003] Corrosion-resistant steel can be divided into atmospheric corrosion-resistant steel (also known as weathering steel), marine corrosion-resistant steel, industrial medium corrosion-resistant steel, etc. according to the characteristics of the use environment. Among them, weathering steel is widely used in the manufacture of outdoor equipment and components such as railway vehicles, containers, bridges, and towers. Marine corrosion-resistant steel is used in the manufacture of coastal cities and island reef infrastructure, offshore platforms, etc. Industrial medium corrosion-resistant steel includes different types of corrosive media such as acid, alkali, H2S, and CO2.

[0004] In actual use, steel materials are often exposed to corrosion from multiple media at the same time, and the requirements for their resistance to multiphase corrosion are getting higher and higher. For example, oil production platforms and chemical petroleum equipment are often exposed to atmospheric corrosion and H2S corrosion at the same time, and they need to have excellent atmospheric corrosion resistance and H2S corrosion resistance. Hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSC) are the main forms of H2S corrosion.

[0005] At present, the domestic patents on corrosion-resistant steel mainly focus on improving the corrosion resistance of materials in a single corrosion environment. For example, the weathering steel disclosed in patents with publication numbers CN 102409253 A, CN 102127717 A, CN103074548 A, CN105296885A, CN111996451 A, etc., for atmospheric environment, improves atmospheric corrosion resistance. Invention patents with publication numbers CN102260834A, CN110306103A, CN113943889A, etc. disclose methods for manufacturing pipeline steel resistant to H2S corrosion, targeting H2S-rich environments, and only for pipeline steel manufacturing.

[0006] Currently, there are few hot-rolled corrosion-resistant steel plates that have both excellent atmospheric corrosion resistance and H2S corrosion resistance. Summary of the invention

[0007] The object of the present invention is to provide a hot-rolled corrosion-resistant steel plate and a method for manufacturing the same. The steel plate developed by the coordinated design of alloy composition and the whole-process manufacturing process of smelting, continuous casting, controlled rolling and controlled cooling has excellent atmospheric corrosion resistance and H2S corrosion resistance, as well as good strength and toughness, and can meet the long life requirements of materials in atmospheric environment and H2S-rich service environment, and can be used for the manufacture of equipment and components serving in atmospheric environment and H2S-rich environment.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A hot-rolled corrosion-resistant steel plate comprises the following components in percentage by mass:

[0010] C: 0.015%-0.050%, Si: 0.15-0.35%, Mn: 0.60%-0.90%, P: ≤0.015%, S: ≤0.0020%, Cr: 2.0%-3.5%, Ni: ≤0.10%, Cu: 0.15%-0.30%, Als: 0.015%-0.035%, Ca: 0.0010%-0.0035%, N≤0.0050%, H≤1.5ppm, the rest are Fe and unavoidable impurity elements.

[0011] In order to further improve the atmospheric corrosion resistance and H2S corrosion resistance of the hot-rolled corrosion-resistant steel plate, the composition design of the hot-rolled corrosion-resistant steel plate must also meet the following requirements:

[0012] Weather resistance index I≥8.0, I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)×(%Ni)-9.10(%Ni)×(%P)-33.39(%Cu) 2 ; In the formula, each chemical element is substituted into the value before the percentage sign of its mass percentage content.

[0013] The composition design of the hot-rolled corrosion-resistant steel plate also needs to meet: 1≤Ca / S≤5, so as to reduce the long strip MnS inclusions, and combine the crystallization steel smelting technology to make the coarse and fine MnS inclusions both level 0, thereby improving the H2S corrosion resistance.

[0014] The metallographic structure of the hot-rolled corrosion-resistant steel plate is quasi-polygonal ferrite and fine granular pearlite, without banded pearlite structure, and the average grain size of ferrite is 5 μm-7 μm. There is no long pearlite banded structure, so the H2S corrosion resistance is improved.

[0015] Mechanical properties of the hot-rolled corrosion-resistant steel plate: yield strength R eL ≥350MPa, tensile strength R m≥500MPa, elongation A≥26%, -40℃ KV2≥140J (impact specimen size: 10×10×55mm), with excellent plastic toughness. After 180° cold bending (d=a) and double cold bending, no cracks appear on the outer side of the specimen, with good cold bending forming performance, which is convenient for downstream users to manufacture and process.

[0016] The hot-rolled corrosion-resistant steel plate has excellent atmospheric corrosion resistance, with a relative corrosion rate of Q345B less than 40%; the hot-rolled corrosion-resistant steel plate also has excellent H2S corrosion resistance, with the crack length rate (CLR%), crack thickness rate (CTR%) and crack sensitivity rate (CSR%) of the HIC test being all 0; in the SSC test, the loading stress is 90% of the actual stress, and no cracks appear on the sample.

[0017] The design principle of the present invention is as follows:

[0018] C (carbon): C is the most economical element for improving the strength of steel and has a significant interstitial solid solution strengthening effect. However, too high a C content will deteriorate the atmospheric corrosion resistance and H2S corrosion resistance of the steel, and will also reduce plasticity, toughness and welding performance. Therefore, the present invention designs the C content to be 0.015-0.050%.

[0019] Si (silicon): Si is beneficial to refine corrosion products and promote the formation of a dense protective rust layer on the surface of steel, thereby improving atmospheric corrosion resistance. However, too high a Si content will deteriorate the welding performance and surface quality of the steel. Therefore, the present invention designs the Si content to be 0.15-0.35%.

[0020] Mn (Manganese): Mn is one of the important solid solution strengthening elements in steel and is also an important deoxidizing element in the steelmaking process. However, too high a Mn content will not only increase the manufacturing cost and deteriorate the welding performance of the steel, but also promote the formation of pearlite banded structure and deteriorate the steel's resistance to H2S corrosion. Therefore, its content is designed to be 0.60-0.90%.

[0021] Als (aluminum): Al is the main deoxidizing element added to steel. It can also combine with N to precipitate AlN at high temperature, refining the austenite grain size. However, too high Al content will increase the inclusion of aluminum oxide in the steel, reducing the atmospheric corrosion resistance and H2S corrosion resistance of the steel. Therefore, its content is designed to be 0.015-0.035%.

[0022] Cr (chromium): Cr is an important alloying element that improves the atmospheric corrosion resistance of steel. It accumulates on the surface of steel to promote the formation of a dense protective rust layer with good adhesion to the substrate, preventing corrosive media such as oxygen and water from diffusing into the metal substrate. Cr can also improve the resistance to H2S corrosion. Too high Cr content will deteriorate the welding performance of steel, so the Cr content is designed to be 2.0-3.5%.

[0023] Cu (copper): Cu can significantly improve the atmospheric corrosion resistance of materials, and the effect of improving atmospheric corrosion resistance is better when combined with Cr. However, the melting point of Cu is relatively low, only 1083°C. Too high a content can easily lead to continuous casting leakage, edge cracks and warping and other surface defects during hot rolling, so the Cu content is designed to be 0.15-0.30%.

[0024] Ni (nickel): Ni can increase the self-corrosion potential of the material, reduce the corrosion tendency, and improve the atmospheric corrosion resistance; it can also react with Cu to form a high melting point Cu-Ni binary alloy phase, effectively preventing copper embrittlement caused by Cu; but Ni is a precious metal element, and excessive content significantly increases the cost of steel manufacturing. Therefore, the Ni content is controlled at ≤0.10%.

[0025] Ca (calcium): Ca has a strong binding force with O in molten steel to form CaO, which then reacts with Al2O3 to form low-melting-point calcium-aluminate composite inclusions, promoting the floating of non-metallic inclusions and improving the cleanliness of molten steel; Ca easily reacts with S in molten steel to form spherical CaS, reducing MnS non-metallic inclusions; reducing crack sensitivity and improving the material's resistance to H2S corrosion. Therefore, the Ca content is controlled at 0.0010%-0.0035%.

[0026] P (Phosphorus): P is a harmful residual element in steel. It is easy to segregate at the grain boundary, reduce the low-temperature toughness of steel, increase welding crack sensitivity, and deteriorate H2S corrosion resistance. Therefore, the P content is controlled to ≤0.015%.

[0027] S (sulfur): S is a harmful residual element in steel, which is easy to react with Mn to form long strips of MnS non-metallic inclusions. Hydrogen atoms in steel gather in MnS inclusions, leading to sulfide stress cracking, which significantly deteriorates the steel's H2S corrosion resistance and also reduces atmospheric corrosion resistance. Therefore, the present invention controls the S content to ≤0.0020%.

[0028] N (nitrogen): N is a harmful residual element in steel, which increases the aging resistance of steel and deteriorates the low-temperature toughness. Therefore, the present invention controls the N content to ≤0.0050%.

[0029] H (hydrogen): H is a harmful residual element in steel. The H atoms dissolved in the steel tend to gather at defects such as inclusions and dislocations to form hydrogen molecules, which significantly increase the internal stress of the steel and initiate internal cracks. Therefore, the present invention controls the H content to ≤1.5ppm.

[0030] The invention provides a method for manufacturing a hot-rolled corrosion-resistant steel plate, comprising the following process flow: deep desulfurization of molten iron pretreatment → composite blowing at top and bottom of converter → refining outside the furnace → continuous casting → heating → rolling → laminar cooling → coiling → cooling to room temperature.

[0031] The converter top and bottom composite blowing: molten steel is smelted according to the above chemical composition, and the converter terminal temperature is 1650-1700°C.

[0032] The out-of-furnace refining adopts LF+RH treatment, LF slag desulfurization, promotes the floating of non-metallic inclusions, and improves the cleanliness of molten steel; RH vacuum treatment degassing time is ≥12min, and the H content is controlled to be ≤1.5ppm.

[0033] The continuous casting adopts electromagnetic stirring and dynamic light pressure to improve the internal quality of the continuous casting billet and control the center segregation of the casting billet ≤ Class C 1.0 level; the temperature of the molten steel casting ladle is controlled at 1530-1560°C, and special protective slag is used for protective casting; the continuous casting billet drawing speed is controlled at 1.0-1.5m / min; the thickness of the continuous casting slab is 230mm.

[0034] The heating method is as follows: after the billet is cut, it is directly loaded into the furnace. The billet that does not meet the direct loading conditions enters the insulation pit for slow cooling, and the temperature entering the heating furnace is ≥500°C; the slab is first heated in a walking beam heating furnace, the heating temperature of the first heating section is ≤1050°C, the total time of the second heating section and the soaking section is ≤90min, the heating time is 120-170min, and the furnace temperature is 1180°C-1230°C, which promotes the homogenization of austenite and the full solid solution of alloy elements in austenite; at the same time, avoid the heating time being too long, the low melting point Cu element is enriched at the austenite grain boundary, and crack defects are generated in the hot rolled curling part. The heating furnace adopts a reducing atmosphere, and the air excess coefficient is less than 0.9-1.0, which reduces the oxidation and burning of Fe on the surface of the slab during the heating process and inhibits Cu enrichment.

[0035] The rolling process is divided into two stages: rough rolling and finishing rolling. The rolling temperature in the rough rolling stage is controlled above 1050°C, the cumulative reduction rate is ≥80%, and multiple large deformations are performed at high temperature to promote the recovery and recrystallization of the deformed austenite grains and refine the austenite grain size. The finishing rolling stage adopts 7-stand continuous rolling, the finishing rolling start temperature is ≤1030°C, and the cumulative deformation amount is ≥85%. Through cumulative large deformation, the deformation band and dislocation density in the deformed austenite are increased, the deformation nucleus points of the ferrite phase are increased, and the ferrite grains after phase transformation are refined. In order to ensure the grain refinement effect, the finishing rolling final rolling temperature is controlled to be 840-890°C.

[0036] After finishing rolling, laminar cooling is carried out, with a cooling rate of 20℃ / s-40℃ / s and a coiling temperature of 620-660℃. If the coiling temperature is too low, bainite or martensite will be generated, which will reduce the plasticity and toughness of the material and deteriorate the H2S corrosion resistance; if the coiling temperature is too high, the ferrite grain structure will coarsen and reduce the strength of the material.

[0037] The present invention adopts the conventional hot continuous rolling plate and strip process for production, adopts the design of low C, low Mn and a small amount of multi-component composite components of Cr, Cu and Ni, so as to improve the atmospheric corrosion resistance and H2S corrosion resistance of the material.

[0038] Further improve the cleanliness of molten steel, control S≤0.0020%, H≤1.5ppm, N≤0.0050%, and both coarse and fine MnS inclusions are level 0, improve HIC and SSC resistance, thereby improving H2S corrosion resistance; reduce pitting caused by non-metallic inclusions and improve atmospheric corrosion resistance.

[0039] Pearlite bands in steel materials are prone to become fast channels for crack expansion; martensite and bainite, as hard phases, are prone to cause sulfide stress corrosion and reduce plastic toughness. The present invention controls the central segregation of the ingot to ≤C class 1.0, improves the internal quality of the ingot, combines controlled rolling and controlled cooling process control to obtain fine-grained ferrite and a small amount of granular pearlite structure without pearlite bands, and further improves the material's SSC resistance and plastic toughness.

[0040] The present invention also reduces the amount of precious alloy Ni in Cu-containing steel and reduces manufacturing costs by controlling the heating time, heating temperature and atmosphere in the heating furnace. The present invention adopts a hot-rolling process to reduce the energy consumption of the heating furnace and the oxidation and burning loss of the casting billet, improve production efficiency and yield rate, and reduce manufacturing costs. The mechanical properties of the steel plate finally obtained: yield strength R eL ≥350MPa, tensile strength R m ≥500MPa, elongation A≥26%, -40℃ KV2≥140J (impact specimen size: 10×10×55mm), with excellent plastic toughness. No cracks appeared on the outer side of the specimen after 180° cold bending (d=a) and double cold bending, with good cold bending forming performance, which is convenient for downstream users to manufacture and process. The obtained steel plate has excellent atmospheric corrosion resistance, with a relative corrosion rate of Q345B <40%. The steel plate of the present invention also has excellent H2S corrosion resistance, and the crack length rate (CLR%), crack thickness rate (CTR%) and crack sensitivity rate (CSR%) of the HIC test are all 0; in the SSC test, the loading stress is 90% of the actual stress, and no cracks appear in the specimen. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The microstructure morphology of the hot-rolled corrosion-resistant steel plate produced by the present invention under an optical microscope and a scanning electron microscope is quasi-polygonal ferrite and fine granular pearlite structure, and the average grain size of the ferrite is about 5.5 μm. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below through specific embodiments.

[0043] Example 1-Example 5

[0044] A hot-rolled corrosion-resistant steel plate comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and inevitable impurity elements.

[0045] Comparative Example 1-Comparative Example 3

[0046] A hot-rolled corrosion-resistant steel plate comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and inevitable impurity elements.

[0047] Table 1 Chemical composition of hot-rolled corrosion-resistant steel sheets of various embodiments and comparative examples (wt%)

[0048]

[0049]

[0050] The manufacturing method of the hot-rolled corrosion-resistant steel plate of the above embodiments and comparative examples includes the following process flow:

[0051] Hot metal pretreatment and deep desulfurization → top and bottom composite blowing in converter → refining outside the furnace → continuous casting → heating → rolling → laminar cooling → coiling → cooling to room temperature.

[0052] Specifically: molten steel is smelted according to the above chemical composition, and the final temperature of the converter is 1650-1700℃. LF+RH treatment is used for refining, LF slag desulfurization promotes the floating of non-metallic inclusions and improves the cleanliness of molten steel; RH vacuum treatment degassing time is ≥12min, and the H content is controlled to be ≤1.5ppm. Continuous casting adopts electromagnetic stirring and dynamic light pressure to improve the internal quality of continuous casting billets and control the center segregation of billets to ≤C class 1.0 level. The temperature of the molten steel casting ladle is controlled at 1530-1560℃, and special protective slag is used for protective casting. The continuous casting billet pulling speed is controlled at 1.0-1.5m / min. The thickness of the continuous casting slab is 230mm. After the billet is cut, it is directly loaded into the furnace. The billet that does not meet the conditions for direct loading enters the insulation pit for slow cooling, and the temperature entering the heating furnace is ≥500℃. The present invention adopts the traditional hot continuous rolling process for rolling. First, the slab is heated, the first stage heating temperature is ≤1050℃, the second stage heating + soaking time is ≤90min, the heating time is 120-170min, the furnace temperature is 1180℃-1230℃, the heating furnace adopts a reducing atmosphere, and the air excess coefficient is less than 0.9-1.0. The rolling is carried out in two stages: rough rolling and finishing rolling. The rolling temperature in the rough rolling stage is controlled at above 1050℃, and the cumulative reduction rate is ≥80%. The finishing rolling stage adopts 7-stand continuous rolling, the finishing rolling start temperature is ≤1030℃, the cumulative deformation is ≥85%, and the finishing rolling final rolling temperature is controlled to be 840-890℃. After the finishing rolling is completed, laminar cooling is carried out, the cooling rate is 20℃ / s-40℃ / s, and the coiling temperature is 620-660℃.

[0053] The main process parameters of the rolling process of each embodiment and comparative example are shown in Table 2.

[0054] Table 2 Main process parameters of rolling and cooling process of each embodiment and comparative example

[0055]

[0056]

[0057] The mechanical properties of each embodiment and comparative example are shown in Table 3. The tensile performance test is carried out according to GB / T 228.1-2010 "Tensile test of metallic materials Part 1: Room temperature test method", the impact performance test is carried out according to GB / T229-2020 "Charpy pendulum impact test method for metallic materials", and the cold bending performance test is carried out according to GB / T 232-2010 "Bending test method for metallic materials".

[0058] Table 3 Properties of steel plates in various embodiments and comparative examples

[0059]

[0060]

[0061] Note: According to GB / T 229, the size of the standard impact pattern is 10×10×55mm. For thin steel plates, 7.5×10×55mm or 5×10×55mm impact patterns can be processed. The corresponding impact absorption energy is 75% or 50% of the standard pattern. The data in the table are converted into a standard impact pattern of 10×10×55mm according to the proportion, and the impact absorption energy is greater than 140J.

[0062] According to TB / T 2375, a 72h periodic immersion corrosion test was carried out, with Q345B low alloy steel as a comparative sample, and the test results are shown in Table 4. The corrosion weight loss rate of each embodiment is reduced by nearly 1 times compared with that of Q345B ordinary weathering steel, and has good atmospheric corrosion resistance.

[0063] Table 4 Atmospheric corrosion resistance of various embodiments and comparative samples

[0064] Average corrosion weight loss rate, (g / (m2·h)) Relative corrosion rate, % Example 1 1.68 38 Example 2 1.58 36 Example 3 1.59 36 Example 4 1.62 37 Example 5 1.65 37 Comparative Example 1 2.66 60 Comparative Example 2 1.95 44 Comparative Example 3 1.61 36 Q345B 4.43 100

[0065] The anti-H2S corrosion performance of the embodiments and comparative examples was evaluated by anti-HIC test and anti-SSC test. Each embodiment was tested for anti-HIC according to NACE TM0284-2016, the test solution was solution A, the sample size was 100×20×5mm, the crack length rate (CLR%), crack thickness rate (CTR%) and crack sensitivity rate (CSR%) of the material were all 0; the anti-SSC test was carried out according to NACETM0177-2016, the test solution was solution A, the sample size was 115×15×5mm, the loading stress was 90% of the actual stress, and no cracks appeared in the sample. Each embodiment has good anti-HIC and anti-SSC performance, that is, good anti-H2S corrosion performance.

[0066] The test results of the specific embodiments and comparative examples are shown in Table 5.

[0067] Table 5 HIC and SSC test results of various examples and comparative examples

[0068]

[0069] In summary, the metallographic structure of the corrosion-resistant steel plate produced in the above embodiment is quasi-polygonal ferrite and fine granular pearlite, without banded pearlite structure, and the average ferrite grain size is 5μm-7μm; the coarse and fine MnS inclusions are both level 0; its yield strength is ≥350MP, tensile strength is ≥500MPa, elongation is ≥26%, -40℃ KV2 is ≥140J, impact specimen size: 10×10×55mm), and it has excellent plastic toughness; after 180° cold bending (d=a) and double cold bending, no cracks appear on the outer side of the specimen, and it has good cold bending forming performance. It has excellent atmospheric corrosion resistance, H2S corrosion resistance and plastic toughness, and can be used in the manufacture of containers, railway vehicles, towers, oil and gas pipelines, oil production platforms, etc. to improve service life.

Claims

1. A hot-rolled corrosion-resistant steel plate, characterized in that: The hot-rolled corrosion-resistant steel plate comprises the following components in percentage by mass: C: 0.015%-0.050%, Si: 0.15-0.35%, Mn: 0.60%-0.90%, P: ≤0.015%, S: ≤0.0020%, Cr: 2.0%-3.5%, Ni: ≤0.10%, Cu: 0.15%-0.30%, Als: 0.015%-0.035%, Ca: 0.0010%-0.0035%, N≤0.0050%, H≤1.5ppm, the rest are Fe and unavoidable impurity elements; The composition of the hot-rolled corrosion-resistant steel plate satisfies: weathering index I≥8.0; The composition of the hot-rolled corrosion-resistant steel plate satisfies: 1≤Ca / S≤5; The metallographic structure of the hot-rolled corrosion-resistant steel plate is quasi-polygonal ferrite and fine granular pearlite, without banded pearlite structure, and the average ferrite grain size is 5 μm-7 μm; Mechanical properties of the hot-rolled corrosion-resistant steel plate: yield strength R eL ≥350MPa, tensile strength R m ≥500MPa, elongation A≥26%, -40℃KV2≥140J; The hot-rolled corrosion-resistant steel plate has a relative corrosion rate of <40% relative to Q345B; at the same time, the crack length rate, crack thickness rate and crack sensitivity rate of the HIC resistance test are all 0; in the SSC resistance test, the loading stress is 90% of the actual stress, and no cracks appear on the sample.

2. A method for manufacturing the hot-rolled corrosion-resistant steel sheet according to claim 1, characterized in that: The manufacturing method comprises the following process flow: deep desulfurization of molten iron pretreatment → composite blowing at top and bottom of converter → refining outside the furnace → continuous casting → heating → rolling → laminar cooling → coiling → cooling to room temperature; The converter top and bottom composite blowing: molten steel is smelted according to the above chemical composition, and the converter end temperature is 1650-1700°C; For the out-of-furnace refining, the RH vacuum treatment degassing time is ≥12min, the H content is controlled to be ≤1.5ppm, and the center segregation of the ingot is controlled to be ≤C class 1.0; The heating method includes: the temperature of the steel billet entering the heating furnace is ≥500°C; the steel billet is heated in a walking beam heating furnace, the heating temperature of the first heating section is ≤1050°C, the total time of the second heating section and the soaking section is ≤90min, the time in the furnace is 120-170min, and the temperature out of the furnace is 1180°C-1230°C; the heating furnace adopts a reducing atmosphere, and the excess air coefficient is less than 0.9-1.0; The rolling process: the final rolling temperature is 840-890°C; After finishing rolling, laminar cooling is carried out with a cooling rate of 20℃ / s-40℃ / s and a coiling temperature of 610-650℃.

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