Corrosion-resistant steel for sulfuric acid transportation tank truck and manufacturing method of corrosion-resistant steel

Abstract

The invention discloses corrosion-resistant steel for a sulfuric acid transportation tank truck and a manufacturing method of the corrosion-resistant steel. The corrosion-resistant steel comprises the following chemical components in percentage by weight: 0.11-0.13% of C; 0.70% to 0.90% of Si; 0.70% to 1.10% of Mn; p: less than or equal to 0.010%; s: 0.005 to 0.015 percent; 0.60% to 0.80% of Cr; cu: 0.22 to 0.35%; alt: < = 0.005%; 0.025% to 0.045% of Ti; 0.20% or less of Mo; 0.11-0.15% of Sb, and the balance Fe and inevitable inclusions; the steel plate has the advantages of high strength, high toughness, low yield ratio, high acid resistance and the like, and is mainly used in the field of sulfuric acid transportation tank trucks.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion-resistant steel, and in particular relates to corrosion-resistant steel for a sulfuric acid transport tank truck and a manufacturing method thereof. Background Art

[0002] As a common industrial raw material, sulfuric acid is widely used in industries such as batteries, explosives, and pigments. It is highly corrosive and oxidizing. Special materials are usually used for its storage and transportation. At present, most sulfuric acid transport tankers are made of stainless steel, which has high manufacturing costs. The corrosion rate of ordinary acid-resistant steel under different temperatures and different concentrations of sulfuric acid varies significantly. For example, the corrosion rate of sulfuric acid with a concentration of 40-50% is faster in the service temperature range of 50-70℃, which can reach more than 20 times the corrosion rate under 20℃ and 20% sulfuric acid. When the concentration reaches more than 95%, the corrosion rate drops significantly, and the corrosion rate at 40℃ is less than 1mm / a.

[0003] If a relatively low-alloy steel plate with excellent sulfuric acid corrosion resistance under multiple temperature and concentration sulfuric acid service conditions can be manufactured for sulfuric acid transport tank trucks, it will have better economy and use value. At the same time, in view of the high-risk characteristics of sulfuric acid transport tank trucks, it should also have a high strength reserve and a low yield ratio. The low yield ratio can delay its fracture under unexpected loads and improve the safety factor. How to design and develop a corrosion-resistant steel for sulfuric acid transport tank trucks with excellent acid resistance, high strength and low yield ratio is a technical difficulty.

[0004] Chinese patent CN 115011876A discloses a steel resistant to high temperature sulfuric acid dew point corrosion and a manufacturing method thereof, wherein the chemical composition is C: 0.052-0.087%, Si: 0.21-0.63%, Mn: 0.34-1.04%, P≤0.015%, S:≤0.006%, Cr: 0.43-1.23%, Ni: 0.22-0.43%, Cu: 0.17-0.27%, Sb: 0.06-0.13%, Ti: 0.013%-0.043%, Sn: 0.04-0.11%, Nb: 0.012-0.024%, Alt: 0.024-0.054%, N: 0.008-0.014%, Ca: 0.0034%-0.0041%. The ingot is heated at 1183-1203℃, and slowly heated below 1081℃, with a heating rate of 8.2-9.2℃ / min; high-temperature fast firing above 1081℃, with a heating rate of 14.2-15.2℃ / min, and a total furnace time of 202-212min, including a soaking and heat preservation time of 47-57min. The average corrosion rate of this patent is (6.34-7.83) mg / cm under the conditions of medium temperature 70℃, sulfuric acid concentration 50%, and full immersion for 24h. 2.h. The relative corrosion rate of Q235B is 17.74% to 21.91%. Under the conditions of high temperature 130℃, sulfuric acid concentration 80%, and full immersion for 24h, the average corrosion rate is (13.76 to 16.81) mg / cm 2 .h, the corrosion rate of Q235B is 19.62% to 23.97%, which shows that its corrosion rate is relatively high, and its corrosion level under dilute sulfuric acid conditions has not been disclosed. The composition design is also a low-carbon and high-yield ratio acid-resistant steel. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a corrosion-resistant steel for sulfuric acid transport tanker and a manufacturing method thereof. The steel plate has the advantages of high strength, high toughness, low yield ratio, high acid resistance, etc., and is mainly used in the field of sulfuric acid transport tanker.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A corrosion-resistant steel for a sulfuric acid transport tanker, comprising the following chemical components in weight percentage: C: 0.11-0.13%; Si: 0.70-0.90%; Mn: 0.70-1.10%; P: ≤0.010%; S: 0.005-0.015%; Cr: 0.60-0.80%; Cu: 0.22-0.35%; Alt: ≤0.005%; Ti: 0.025-0.045%; Mo≤0.20%; Sb: 0.11-0.15%, with the remainder being Fe and unavoidable inclusions.

[0008] The corrosion-resistant steel also contains 0.08-0.10% Ni by weight, and the edge crack sensitivity coefficient A=(C+Cu+Sb) / Ni≤7. When A≤7, the steel has good edge quality.

[0009] Furthermore, the weight percentage of Mo is preferably 0.01 to 0.20.

[0010] The metallographic structure of the corrosion-resistant steel is ferrite and pearlite.

[0011] The R of the corrosion resistant steel eL ≥420MPa, R m ≥600~750MPa, A≥25%, yield strength ratio less than 0.75; the relative Q345B corrosion rates after immersion in 20℃, 20% H2SO4; 70℃, 50% H2SO4; 40℃, 98% H2SO4 for 24h are ≤2%, ≤20%, ≤80% respectively.

[0012] The present invention also provides a method for manufacturing the corrosion-resistant steel for sulfuric acid transport tanker, wherein the manufacturing method comprises heating, controlled rolling, controlled cooling, coiling and finishing the ingot obtained by continuous casting.

[0013] Furthermore, when the billet width is 2000-2150 mm, the billet pulling speed is 0.95-1.00 m / min; when the billet width is 1500-2000 mm, the billet pulling speed is 1-1.25 m / min; when the billet width is 950-1500 mm, the billet pulling speed is 1.25-1.30 m / min; avoid lifting the billet at 600 and 800°C, and the billet straightening temperature is ≥850°C.

[0014] In the heating step, when the steel does not contain Ni, the temperature at the end of the first heating section is controlled to be ≤1040°C, the temperature at the end of the second heating section is controlled to be between 1160 and 1200°C, the sum of the time of the second heating section and the soaking section is controlled to be ≤110min, and the temperature of the ingot out of the furnace is controlled to be between 1170 and 1210°C, and the low-temperature fast burning process is strictly implemented; when the steel contains Ni, the temperature out of the furnace is controlled to be between 1190 and 1230°C.

[0015] In the controlled rolling step, the starting temperature of the rough rolling is 1020-1080°C; for the hot-rolled plate with a thickness of 3mm≤<8mm, the final rolling temperature is 840-880°C; for the hot-rolled plate with a thickness of 8mm≤<12mm, the final rolling temperature is 820-860°C; for the hot-rolled plate with a thickness of 12mm≤≤16mm, the final rolling temperature is 800-840°C; and laminar cooling is performed after rolling.

[0016] If edge cracks occur during the rolling process, when the edge crack is less than 8mm from the edge, the width of the rolling should be increased by 5 to 10mm; when the edge crack is 8 to 15mm from the edge, the width of the rolling should be increased by 10 to 15mm (not including 10mm).

[0017] In the coiling step, for hot-rolled plates with a thickness of 3 mm ≤ and less than 8 mm, the coiling temperature is 600-640° C.; for hot-rolled plates with a thickness of 8 mm ≤ and less than 12 mm, the coiling temperature is 570-610° C.; for hot-rolled plates with a thickness of 12 mm ≤ and less than 16 mm, the coiling temperature is 540-580° C.

[0018] In the finishing step, the thickness of the steel strip is ≤ 6 mm, the flattening force is 300-400 t, and the bending roller force is 25-35 KN.

[0019] The components of the corrosion-resistant steel for sulfuric acid transport tanker provided by the present invention have the following functions and controls:

[0020] C: One of the main strengthening elements. Low C content affects the strength of steel, especially the tensile strength. Higher C content is conducive to obtaining a low yield strength ratio, but too high C content reduces the plasticity and weldability of the steel plate, and also deteriorates the sulfuric acid corrosion resistance of the steel plate. The cylinder of the transport tank truck needs to be stamped, so based on the dual considerations of good forming performance and corrosion resistance, C is controlled to be ≤ 0.13%. At the same time, based on the safety consideration of low yield strength ratio, C 0.11-0.13% is preferred.

[0021] Si: An appropriate amount of silicon not only plays the role of deoxidation and solid solution strengthening to improve strength, but also can be used in combination with Cu and P to improve the sulfuric acid corrosion resistance of steel. In the present invention, a relatively high content of Si is added to replace Al for deoxidation. In addition, Si forms a SiO2 film in an oxidizing atmosphere to improve the resistance to sulfuric acid oxidation, especially the acid resistance under high temperature and high concentration sulfuric acid conditions. However, too high a content of Si will produce iron oxide strips that are difficult to remove. This oxygen pressure defect is difficult to remove in the shot blasting or electrophoresis process, so the present invention controls the Si content range to 0.70-0.90%.

[0022] S: Generally, it is a harmful impurity element, which is easy to form inclusions and segregation defects, thus reducing plastic toughness and being unfavorable for processing. However, a high content of S forms a dense Cu2S passivation film in a concentrated sulfuric acid solution with the cooperation of Cu, which adheres to the surface of the steel plate and prevents further corrosion in a sulfuric acid environment. Therefore, the present invention does not limit the S content to an ultra-low level, and controls S0.005-0.015%.

[0023] Cr: by inhibiting Fe 3+ Fe 2+ The reduction reaction of the conversion increases the amount of FeOOH produced and can replace part of the Fe in α-FeOOH. 3+ , forming nano-scale oxide α-FexCr(1-x)OOH, which makes the rust layer obtain cationic selectivity and effectively prevents SO4 2- At the same time, Cr also has a certain self-passivation tendency in steel, which increases the electrode potential of the solid solution. Therefore, a higher content of Cr is used to improve the acid resistance, and the Cr content is controlled at 0.6-0.8%.

[0024] Ni: Ni is added appropriately to improve the low temperature toughness of the steel plate. A high content of Ni has good corrosion resistance to acids and alkalis, but the effect of Ni in low alloy steel on sulfuric acid corrosion resistance is limited, and the cost of Ni content is very high. For every 0.01% Ni added to a ton of steel, the cost increases by about 10 yuan / ton. In the present invention, Ni is controlled at ≤0.10%, and adding 0.08-0.10% Ni can form a Cu-Ni high temperature phase to inhibit the occurrence of copper brittleness. Ni can also be omitted, but a low temperature fast firing process is required to avoid the copper brittleness sensitive temperature zone.

[0025] Cu: A corrosion rust layer rich in oxides will be generated on the surface of the steel, and a thin copper-rich layer will also be generated. A dense thin copper oxide intermediate layer will also be formed between the corrosion rust layer and the copper-rich layer, thus forming a dense double-layer structure corrosion product layer, which effectively isolates the steel matrix from direct contact with the corrosive medium. However, a high content will cause copper brittleness. Therefore, the Cu content is controlled at 0.22-0.35%.

[0026] Sb: An essential element for improving acid resistance. In the initial stage of sulfuric acid corrosion, an inner Sb2O3 film and an outer Sb2O5 film are generated on the steel surface. The film has good stability and density, and effectively blocks the passage of the corrosive medium to the steel matrix. The present invention is not only resistant to dilute sulfuric acid corrosion, but also resistant to 50-98% high concentration concentrated sulfuric acid corrosion. Therefore, the antimony content is designed to be in a higher range relative to ordinary acid corrosion-resistant steel, but antimony, as a low melting point phase (melting point is only 630°C), is easily liquefied at high temperatures and enriched at the austenite grain boundaries to form cracks, so the Sb content should not be too high. Based on the above, the Sb content is controlled at 0.11-0.15%.

[0027] Mo: 1) It has a solid solution strengthening effect on ferrite, improves the stability of carbides, and improves strength, especially thermal strength; 2) It improves the corrosion resistance to sulfuric acid at higher service temperatures and prevents pitting tendency. The present invention is used in sulfuric acid transport tankers, so it is necessary to overcome the high temperature working conditions of 100-200°C under sulfuric acid immersion; 3) It increases hardenability. The thickness span of the present invention is large (3-16mm). In order to ensure the uniformity of F+P type structure in thickness, Mo should be appropriately added. In summary of the above three points, Mo is added, but Mo≤0.20%.

[0028] Alt: Alumina inclusions are prone to undergo redox reactions with dilute sulfuric acid to generate Al2(S04)3 and water, which further dilutes the concentrated sulfuric acid and becomes a pitting source of acid corrosion at the alumina inclusions in the steel, accelerating corrosion. Therefore, in order to reduce sulfuric acid corrosion, especially to reduce corrosion in a dilute sulfuric acid immersion environment, an Al-free design is adopted, with Alt≤0.005%.

[0029] Ti: Adding an appropriate amount of Ti can increase the electrode potential of ferrite, which is beneficial to improving the acid corrosion resistance. The bonding force between Ti and C is much greater than that between Cr and C. Therefore, Ti is used to eliminate the depletion of Cr at the grain boundary and improve the resistance to intergranular corrosion. In the present invention, a relatively high content of Cr is added, so an appropriate amount of Ti is also added to eliminate the depletion of Cr. At the same time, Ti is a strong carbonitride forming element, which significantly improves the strength of acid-resistant steel. When the Ti content is low, it can also inhibit the coarsening of austenite grains in the coarse grain zone. In summary, the Ti content is strictly controlled at 0.025% to 0.045%.

[0030] In the manufacturing method of corrosion-resistant steel for sulfuric acid transport tankers provided by the present invention, antimony block alloy is added during the LF refining process, and the total weak stirring time before and after the calcium line is fed is guaranteed to be ≥11min. The steel grade of the present invention belongs to a high crack sensitivity steel grade, and the high temperature plasticity in the range of 600-850°C shows a phenomenon of first increasing and then decreasing. In the low temperature plasticity trough area of ​​600 and 800°C, the present invention avoids hoisting the ingot in the low plasticity area of ​​600 and 800°C. And a high straightening temperature of ≥850°C is used to reduce the risk of cracks in the ingot. If edge cracks occur during the rolling process, when the edge crack is less than 8mm from the edge, the widening rolling is 5-10mm; when the edge crack is 8-15mm from the edge, the widening rolling is 10mm﹤≤15mm.

[0031] The present invention adopts "controlled S + medium Si + no Al + medium Sb + Mo-Ti microalloying" to form passivation films such as Cu2S and Sb2O3 and Mo-Ti's ability to resist intergranular corrosion and prevent pitting corrosion, so that the sulfuric acid corrosion resistance is excellent. In particular, the innovative design of "medium Si + no Al" makes it have good acid corrosion resistance under both dilute sulfuric acid and concentrated sulfuric acid service conditions; and in steelmaking and continuous casting, high straightening temperature + pulling speed-width gradient matching is adopted to reduce the risk of edge cracking of corrosion-resistant steel containing Sb-Cu low-melting point elements; in controlled rolling and controlled cooling, the final rolling / coiling-thickness gradient matching system is adopted to achieve the purpose of excellent performance stability at different thicknesses. In addition, combined with the 0.11-0.13% C design, a low yield ratio 420MPa grade high-strength corrosion-resistant steel for the manufacture of sulfuric acid transport tankers is obtained.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The corrosion-resistant steel provided by the present invention has high strength plasticity and low yield strength ratio. eL ≥420MPa, R m ≥600~750MPa, A≥25%, yield strength ratio is less than 0.75.

[0034] The corrosion-resistant steel provided by the present invention has high sulfuric acid corrosion resistance: when immersed in 20% H2SO4 at 20°C for 24 hours, the corrosion rate is ≤0.17 mg / (cm 2 *h), relative corrosion rate of Q345B ≤2%; 70℃, 50% H2SO4 immersion for 24h, corrosion rate ≤2.8mg / (cm 2 *h), relative corrosion rate of Q345B ≤20%; 40℃, 98% H2SO4 immersion for 24h, corrosion rate ≤0.055mg / (cm 2 *h), relative corrosion rate of Q345B ≤80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the metallographic structure diagram of the corrosion-resistant steel in Example 1;

[0036] Figure 2 is the metallographic structure diagram of the corrosion-resistant steel in Example 3;

[0037] Figure 3 The surface morphology of the rust layer of the corrosion-resistant steel in Example 1 after being immersed in 50% H2SO4 at 70°C for 24 hours. The rust layer contains enriched Cu, S, Sb, etc., forming a dense passivation film of Cu2S, Sb2O3, etc., which hinders further corrosion in the sulfuric acid service environment;

[0038] Figure 4 The edge quality of the corrosion-resistant steel in Comparative Example 5 has similar "serrated edge" defects;

[0039] Figure 5 The corrosion-resistant steel in Comparative Example 10 did not use a suitable billet drawing speed and straightening temperature, which resulted in billet cracks;

[0040] Figure 6 It is a comparison diagram of the plate shapes of comparative example 11 and embodiment 3. There is an obvious double wave shape in comparative example 11, while the plate shape in embodiment 3 is good. DETAILED DESCRIPTION

[0041] The invention provides a corrosion-resistant steel for a sulfuric acid transport tanker. The main chemical components of the corrosion-resistant steel and their weight percentage contents (wt%) are C: 0.11-0.13%; Si: 0.70-0.90%; Mn: 0.70-1.10%; P: ≤0.010%; S: 0.005-0.015%; Cr: 0.60-0.80%; Ni: ≤0.10%; Cu: 0.22-0.35%; Alt: ≤0.005%; Ti: 0.025-0.045%; Mo≤0.20%, Sb: 0.11-0.15%, and the balance is Fe and inevitable inclusions.

[0042] When Ni is added, the weight percentage of Ni is 0.08-0.10%, and the edge crack sensitivity coefficient A=(C+Cu+Sb) / Ni≤7.

[0043] The manufacturing method of the corrosion-resistant steel for sulfuric acid transport tanker comprises the following steps: molten iron pretreatment→converter smelting→LF refining→continuous casting→slab heating→controlled rolling→controlled cooling→coiling→finishing.

[0044] 1) Smelting, refining and continuous casting process

[0045] Antimony block alloy is added during the LF refining process, and the total weak stirring time before and after feeding the calcium wire is ensured to be ≥11min.

[0046] The high-temperature plasticity of the steel grade of the present invention increases first and then decreases in the range of 600-850°C. In the low-temperature plasticity valley area of ​​600 and 800°C, the present invention avoids hoisting the billet in the low plasticity area of ​​600 and 800°C. And the high straightening temperature of >850°C is used to reduce the risk of billet cracks. When the billet width is 2000-2150mm, the billet pulling speed is 0.95-1.00m / min, when the billet width is 1500-2000mm, the billet pulling speed is 1-1.25m / min, and when the billet width is 950-1500mm, the billet pulling speed is 1.25-1.30m / min.

[0047] 2) Slab heating, controlled rolling and controlled cooling processes

[0048] The present invention adopts the method of rolling after the casting is inspected and cleaned after falling to the ground. In the slab heating process, ① when no Ni is added: the temperature at the end of the first heating section is controlled to be ≤1040°C; the temperature at the end of the second heating section is controlled to be 1160-1200°C; the sum of the time of the second heating section and the soaking section is controlled to be ≤110min, and the casting temperature out of the furnace is controlled to be 1170-1210°C; ② if Ni alloy is added, it is preferably added at 0.08-0.10%, and the furnace temperature is controlled to be 1190-1230°C.

[0049] The steel billet is rolled into a hot-rolled plate with a thickness of 3 to 16 mm in two stages of rough rolling and finish rolling. The starting temperature of rough rolling is 1020 to 1080°C, and the finish rolling adopts large reduction. When H≥12mm, the thickness of the intermediate billet is 58 to 60mm; the finishing temperature and coiling temperature of the finish rolling are set according to the thickness gradient. When 3≤H<8mm, the finishing temperature is 840 to 880°C; when 8≤H<12, the finishing temperature is 820 to 860°C; when 12≤H≤16, the finishing temperature is 800 to 840, and laminar cooling is carried out after rolling. When H<8mm, the coiling temperature is 600 to 640°C; when 8≤H<12, the coiling temperature is 570 to 610°C; when 12≤H≤16, the coiling temperature is 540 to 580°C.

[0050] If edge cracks occur during the rolling process, when the edge crack is less than 8mm from the edge, the width of the rolling should be increased by 5 to 10mm; when the edge crack is 8 to 15mm from the edge, the width of the rolling should be increased by 10 to 15mm (not including 10mm).

[0051] 3) Finishing

[0052] For steel strips ≤6mm, large rolling force is used for flattening, the flattening force is 300~400t, and the bending roll force is 25~35KN.

[0053] The present invention is described in detail below with reference to the embodiments.

[0054] The chemical composition and weight percentage of the steel in each embodiment and comparative example are shown in Table 1, and the balance is iron and inevitable impurities. Among them, comparative example 5 only adds 0.05% Ni, the edge crack sensitivity coefficient A value is 10.8, and the low-temperature fast heating process is not performed, so the quality of the hot rolled edge is poor.

[0055] Table 1 Chemical compositions of the embodiments and comparative examples

[0056]

[0057] The main rolling process parameters of the steel in each embodiment and comparative example are shown in Table 2, the mechanical properties are shown in Table 3, and the sulfuric acid corrosion resistance is shown in Table 4.

[0058] Although the mechanical properties of Comparative Examples 8 and 9 can also have the advantages of high strength and plasticity in the present invention, the mechanical properties of different thicknesses vary greatly due to the lack of final rolling / coiling-thickness gradient matching system. eL The difference is 83MPa, the tensile strength R m The difference is 80MPa, which makes it difficult to achieve stability control of mechanical properties at different thicknesses.

[0059] Table 2 Main process parameters of rolling process of embodiment and comparative example

[0060]

[0061] Table 3 Mechanical properties and corrosion properties of examples and comparative examples

[0062]

[0063]

[0064] Table 4 Corrosion performance of examples and comparative examples

[0065]

[0066]

[0067] The detailed description of a corrosion-resistant steel for a sulfuric acid transport tanker and a method for manufacturing the same with reference to the above-mentioned embodiment is illustrative rather than restrictive, and several embodiments may be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A corrosion-resistant steel for a sulfuric acid transport tanker, characterized in that: The corrosion-resistant steel includes the following chemical components in weight percentage: C: 0.11-0.13%; Si: 0.70~0.90%; Mn: 0.70~1.10%; P: ≤0.010％； S: 0.005~0.015%; Cr: 0.60~0.80%; Cu: 0.22~0.35%; Alt: ≤0.005%; Ti: 0.025~0.045%; Mo≤0.20%; Sb: 0.11~0.15%, the balance is Fe and inevitable inclusions.

2. The corrosion-resistant steel for sulfuric acid transport tanker according to claim 1, characterized in that: The corrosion-resistant steel also contains 0.08-0.10% Ni by weight, and A=(C+Cu+Sb) / Ni≤7.

3. The corrosion-resistant steel for sulfuric acid transport tanker according to claim 1 or 2, characterized in that: The metallographic structure of the corrosion-resistant steel is ferrite and pearlite.

4. The corrosion-resistant steel for sulfuric acid transport tanker according to claim 1 or 2, characterized in that: The R of the corrosion resistant steel eL ≥420MPa, R m 600~750MPa, A≥25%, yield ratio less than 0.75; the relative corrosion rates of Q345B after immersion in 20℃, 20% H2SO4; 70℃, 50% H2SO4; 40℃, 98% H2SO4 for 24h are ≤2%, ≤20%, ≤80% respectively.

5. The method for manufacturing corrosion-resistant steel for sulfuric acid transport tanker according to any one of claims 1 to 4, characterized in that: The manufacturing method is to obtain the ingot by continuous casting through heating, controlled rolling, controlled cooling, coiling and finishing.

6. The manufacturing method according to claim 5, characterized in that: When the billet width is 2000-2150mm, the billet pulling speed is 0.95-1.00m / min; when the billet width is 1500-2000mm, the billet pulling speed is 1-1.25m / min; when the billet width is 950-1500mm, the billet pulling speed is 1.25-1.30m / min; avoid lifting the billet at 600 and 800℃, and the billet straightening temperature is ≥850℃.

7. The manufacturing method according to claim 5, characterized in that: In the heating step, when the steel does not contain Ni, the temperature at the end of the first heating section is controlled to be ≤1040°C, the temperature at the end of the second heating section is controlled to be between 1160 and 1200°C, the sum of the time of the second heating section and the soaking section is controlled to be ≤110min, and the temperature of the cast billet out of the furnace is controlled to be between 1170 and 1210°C; when the steel contains Ni, the temperature out of the furnace is controlled to be between 1190 and 1230°C.

8. The manufacturing method according to claim 5, characterized in that: In the controlled rolling step, the starting temperature of the rough rolling is 1020-1080°C; for the hot-rolled plate with a thickness of 3mm≤<8mm, the final rolling temperature is 840-880°C; for the hot-rolled plate with a thickness of 8mm≤<12mm, the final rolling temperature is 820-860°C; for the hot-rolled plate with a thickness of 12mm≤≤16mm, the final rolling temperature is 800-840°C; and laminar cooling is performed after rolling.

9. The manufacturing method according to claim 5, characterized in that: In the coiling step, for hot-rolled plates with a thickness of 3 mm ≤ and less than 8 mm, the coiling temperature is 600-640° C.; for hot-rolled plates with a thickness of 8 mm ≤ and less than 12 mm, the coiling temperature is 570-610° C.; for hot-rolled plates with a thickness of 12 mm ≤ and less than 16 mm, the coiling temperature is 540-580° C.

10. The manufacturing method according to claim 5, characterized in that: In the finishing step, the thickness of the steel strip is ≤ 6 mm, the flattening force is 300-400 t, and the bending roller force is 25-35 KN.

Images