A high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa

Abstract

The present invention discloses a high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, which mainly solves the technical problem of low hole expansion rate of existing hot-rolled pickled steel plates with a yield strength of 600 MPa. The technical solution is as follows: a high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, whose chemical composition by weight percentage is as follows: C: 0.04% to 0.10%, Si≤0.10%, Mn: 0.8% to 1.5%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.05%, N≤0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance is Fe and unavoidable impurity elements; the yield strength R of the hot-rolled pickled steel plate with a thickness of 1.8 to 5.0 mm is 0. p0.2 The hot-rolled pickled steel plate of the present invention is used for manufacturing automobile structural parts.

Description

Technical Field

[0001] The present invention relates to a hot-rolled pickled steel plate, in particular to a hot-rolled pickled steel plate with a yield strength of 600 MPa and a high hole expansion rate and a manufacturing method thereof. Specifically, the present invention relates to a hot-rolled pickled steel plate with a yield strength of 600 MPa and a hole expansion rate λ of 80% to 100% and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Pickled automotive steel plates, with their excellent surface quality and formability, are widely used in automotive chassis and various body structural components. With the trend toward lightweighting, high-strength and thinning steel plates has become a crucial technological approach. Simultaneously, an increasing number of components are employing design features such as flanging and partial hole expansion to enhance their strength and rigidity. However, this increased strength and reduced thickness lead to higher demands on the material's machinability, particularly hole expansion performance.

[0003] The hole expansion performance of steel plates is related to the strength, microstructure and uniformity of the steel plates. The metallographic structures of existing high hole expansion steels with a yield strength of more than 500 MPa are generally divided into two types: one is mainly composed of full ferrite + nano-precipitate phases in different forms, which is generally combined with rapid cooling process and high alloy design; rapid cooling process is difficult to implement on most hot rolling production lines, and the control accuracy requirements are also high, the equipment investment is large, and the production cost is high; the other is mainly composed of ferrite + bainite, and a two-stage or three-stage cooling process is often used. The production of high hole expansion steels with different strength levels is achieved through alloy composition design and different cooling rate control; how to use a reasonable rolling process with appropriate microstructure to achieve a better match between a yield strength of more than 550 MPa and a hole expansion rate of more than 80% is a technical difficulty that the industry urgently needs to overcome, and there is currently no successful technical solution.

[0004] In the prior art, there are several types of composition systems for producing high-hole expansion steel with a yield strength of about 500 MPa using a low alloy system: one is a high-Si design, and the other is a trace Nb and Ti design.

[0005] The Chinese patent application document with application publication number CN107747042A discloses a 690MPa grade economical high surface quality high hole expansion steel and its preparation method, wherein the Si content in the steel is 0.85% to 1.50%, and through two-stage cooling, the steel plate has a yield strength of 470-530MPa, a tensile strength of 710-760MPa, and an elongation of A 80 22-35%, hole expansion rate λ80-105%, but for high-quality pickled automotive steel, too high Si content will significantly affect the pickling surface quality.

[0006] The Chinese patent application document with application publication number CN112779401A discloses a high-expansion hot-rolled pickled steel plate with a yield strength of 550MPa. The hot-rolled pickled steel plate contains Nb: 0.01-0.02%, Ti: 0.04-0.08%. Through three-stage cooling, the metallographic structure of the steel plate is polygonal ferrite + trace bainite + dispersed carbide particles, and the yield strength Rp 0.2 The tensile strength Rm is 550-620MPa, the elongation after fracture A is 650-710MPa, and the 80mm ≥20%, hole expansion performance λ≥70%, but it can be seen from the examples that the hole expansion rate of hot-rolled pickled steel plate does not exceed 80%.

[0007] The Chinese patent application document with application publication number CN110983196A discloses a 600MPa grade hot-rolled galvanized high-expansion steel and its production method, wherein the Nb content of the steel is 0.01-0.05%, the Ti content is 0.03-0.08%, and the metallographic structure of the steel plate is ferrite + bainite through three-stage cooling, with a yield strength of 500-530MPa, a tensile strength of 600-620MPa, and an elongation after fracture of A. 80mm 20-22%, hole expansion rate λ90-105%. The alloy content of this method is not high, but the yield strength is limited to below 550MPa.

[0008] The Chinese patent application document with application publication number CN110295325A discloses a Ti microalloyed 540MPa grade high hole expansion steel strip and its production method. The Ti content in the steel strip is 0.02-0.04%. Through three-stage cooling, the steel plate has a yield strength of 365-500MPa, a tensile strength of 540-580MPa, and an elongation after fracture of A 80mm 24-35%, hole expansion rate λ85-110%, and strength is also low. Summary of the Invention

[0009] The purpose of the present invention is to provide a high hole expansion hot-rolled pickled steel plate with a yield strength of 600 MPa and a manufacturing method thereof, mainly to solve the technical problem of low hole expansion rate of existing hot-rolled pickled steel plate with a yield strength of 600 MPa.

[0010] The technical idea of ​​the present invention is that the steel composition is designed as a low alloy, and a trace amount of Nb and Ti is used. The hot rolling laminar cooling process adopts three-stage cooling. By matching the three-stage cooling rate and time, on the one hand, the composite precipitation strengthening of Nb and Ti two-phase particles in different cooling stages is controlled to improve the matrix strength; on the other hand, a high hole expansion rate is achieved through the ferrite morphology and bainite proportion and morphology, thereby improving the strength and hole expansion rate of the steel plate under this low-cost composition system.

[0011] The technical solution adopted by the present invention is a high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, whose chemical composition by weight is as follows: C: 0.04% to 0.10%, Si≤0.10%, Mn: 0.8% to 1.5%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.05%, N≤0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance is Fe and unavoidable impurity elements.

[0012] The metallographic structure of the hot-rolled pickled steel plate of the present invention comprises 70% to 80% of quasi-polygonal ferrite + 20% to 30% of bainite by area fraction, and the grain size of the ferrite in the metallographic structure is 10.0 to 11.0; the yield strength R of the 1.8 to 5.0 mm thick hot-rolled pickled steel plate is p0.2 The tensile strength is 630~670MPa, and the tensile strength R m 680~740MPa, elongation after fracture A 80mm The hole expansion rate is 18% to 25%, and the hole expansion rate λ is 80% to 100%.

[0013] The hot-rolled pickled steel plate of the present invention is used for manufacturing automobile structural parts.

[0014] The reasons why the chemical composition of the 600 MPa yield strength high hole expansion hot-rolled pickled steel plate described in the present invention is limited to the above range are as follows:

[0015] C: The primary strengthening element in steel. In this application, it forms carbide-strengthening phases with Nb and Ti to ensure the strength of the steel plate. Too low a C content will not meet the required strength, while too high a C content will result in coarse carbide precipitation and poor hole expansion performance. Considering both strength and hole expansion requirements, this invention limits the C content to 0.04% to 0.10%.

[0016] Si: Silicon in steel acts as a solid solution strengthener. However, it tends to segregate on the steel plate surface to form Fe₂SiO₄. Once molten during heating, it penetrates into the oxide scale and steel matrix, making descaling incomplete. It also forms strips of red iron scale during subsequent rolling, making it extremely difficult to remove during pickling. Therefore, the Si content in pickled steel plates must be strictly controlled. The present invention limits Si to ≤ 0.10%.

[0017] Mn: Manganese is a solid solution strengthening element that also promotes bainite formation. However, excessive manganese content can easily cause slab composition segregation, affecting the uniformity of the hot-rolled plate structure and adversely affecting the hole expansion rate of the steel plate. The present invention limits the Mn content to 0.8% to 1.5%.

[0018] S and P are impurity elements in steel. The lower the content, the better. S easily forms MnS in steel. The amount and form of sulfides in steel directly affect the hole expansion rate of the steel plate. Considering economy and feasibility, the present invention limits S to ≤ 0.005% and P to ≤ 0.020%.

[0019] Al: A strong oxidizing element, it effectively reduces oxide inclusions in steel, purifies steel quality, and improves the formability of steel plates. However, Al₂O₃ particles are large, and excessive amounts can easily clog the pouring nozzle during continuous casting. Therefore, the present invention limits Al content to 0.01% to 0.05%.

[0020] Ti: This is the primary strengthening alloying element in this invention. Its alloy price is lower than that of niobium alloys. The addition of some Ti facilitates the formation of compounds with carbon, nitrogen, oxygen, and sulfur in the steel. This, combined with the cooling rate and temperature settings, promotes the precipitation of dual-phase particles, improving matrix strength. However, due to the large size of TiN particles, there is a risk of cracking and reduced hole expansion. Therefore, the Ti content must be effectively controlled. This invention limits the Ti content to 0.05% to 0.10%.

[0021] Nb: It is an important strengthening element. When heated at high temperatures, niobium combines with carbon and nitrogen to form smaller carbonitrides. During cooling after rolling or after coiling, it precipitates finely in the form of carbides, which plays a good precipitation strengthening role. At the same time, it also promotes the formation of bainite. The target structure of this application is a metallographic structure including 70% to 80% quasi-polygonal ferrite and 20% to 30% bainite by area fraction. The ferrite grain size is 5 to 10 μm and the grain size is 10.0-11.0. Because Nb significantly delays recrystallization and precipitates a second phase during deformation during rolling to inhibit the recrystallization of deformed austenite, in order to control the ferrite grain size, the Nb content cannot be set too high. Therefore, the present invention limits Nb to 0.01% to 0.02%, and it precipitates together with Ti to play a strengthening role.

[0022] N: is an inclusion element. Nitrogen easily reacts with titanium under high temperature conditions to form TiN particles. Excessively large titanium nitride particles will become inducing points for local deformation and microcracks in the steel plate, affecting the hole expansion rate. Therefore, the nitrogen content of the molten steel must be controlled. Therefore, the present invention limits N to 0.006%.

[0023] A method for manufacturing a high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, the method comprising the following steps:

[0024] The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows by weight: C: 0.04% to 0.10%, Si≤0.10%, Mn: 0.8% to 1.5%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.05%, N≤0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance is Fe and unavoidable impurity elements;

[0025] The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1220-1260°C and the heating time is 180-240 minutes. The hot rolling is a two-stage rolling process. The rough rolling is a 6-pass continuous rolling process, which is rolled above the austenite recrystallization temperature. The rough rolling end temperature is 1080-1120°C. After rough rolling, the intermediate slab thickness is controlled to be 38-42 mm. The finishing rolling is a 7-pass continuous rolling process, which is rolled in the austenite non-recrystallization zone. The finishing temperature is 900-930°C. After finishing rolling, the steel plate thickness is controlled to be 1 .8~5.0mm, laminar cooling adopts three-stage cooling method, the first stage is water cooling, the first stage cooling rate is 40~50℃ / s, the first stage cooling end temperature is 680~720℃; the second stage is air cooling, the second stage cooling rate is 5~10℃ / s, the second stage air cooling time is 4~8s; the third stage is water cooling, the third stage cooling rate is 20~30℃ / s, the third stage cooling end temperature is 440~480℃; the coiling temperature is 430~460℃, and the hot rolled steel plate is coiled by a rolling line coiler to obtain hot rolled steel coils;

[0026] The hot rolled steel coil is unwound again on the unwinding machine, and is subjected to drawing and straightening and pickling to obtain a finished hot rolled pickled steel plate. The drawing and straightening elongation is 0.8% to 1.2%.

[0027] Through calculation, the composition system A3 of the present invention is 864.5℃, and A1 is 692.2℃. The hot rolling process adopted by the present invention is based on the composition system of the present invention and the calculated phase transition point. The reasons for the production process adopted by the present invention are as follows:

[0028] 1. Setting of continuous casting slab heating temperature and heating time

[0029] As the heating temperature increases and the holding time increases, the second-phase elements gradually dissolve, and the slab composition becomes uniform. Since the present application adopts a trace amount of Nb and Ti composite addition, the solid solution temperature of Nb is further increased. Therefore, a certain lower limit of the heating temperature needs to be guaranteed. In addition, sufficient second-phase solid solution can also ensure that the two-phase particles are fully precipitated during the subsequent coiling and cooling process, thereby ensuring the precipitation strengthening effect. At the same time, the slab heating temperature should not be too high, otherwise the pinning effect of the two-phase particles on the austenite grain boundary will decrease, and the austenite grain size will be too large, which is not conducive to strength assurance. The heating time should not be too long, otherwise the slab surface will be severely oxidized, which is not conducive to the surface quality of the steel plate. Therefore, the present invention sets the continuous casting slab heating temperature to 1220-1260°C and the heating time to 180-240min.

[0030] 2. Setting of rough rolling end temperature

[0031] During the rough rolling stage, the billet is generally rolled to approximately 60% reduction before entering the finishing stage to achieve the target thickness. Since the rough rolling end temperature affects the final rolling temperature and thickness control during finishing, the rough rolling end temperature is set between 1080°C and 1120°C to ensure the accuracy of the finishing rolling inlet temperature.

[0032] 3. Setting of finishing temperature

[0033] The finishing temperature of finishing rolling is generally set to ensure that the entire slab is fully rolled in the austenite region, and to avoid the mixed crystals caused by rolling in the two-phase region at the end of rolling, which is not conducive to the hole expansion rate. The finishing temperature of the present application is set relatively high. This is because it has been found through experiments that under the same subsequent cooling process, a higher finishing temperature can obtain larger blocky ferrite grains, which can significantly improve the hole expansion rate. However, the temperature cannot be set too high, otherwise the phase-transformed ferrite grains will be too large, which is not conducive to the guarantee of strength. Therefore, the present invention sets the finishing temperature of finishing rolling to 900-930°C.

[0034] 4. Setting of laminar cooling mode, cooling speed and cooling time after finishing rolling

[0035] This application adopts a three-stage cooling method. The first stage is water cooling, cooling to 680-720℃ at a cooling rate of 40-50℃ / s. The second stage is air cooling, with a cooling rate of generally 5-10℃ / s and an air cooling time of 4-8s. The setting of the cooling rate in the first stage is mainly based on the actual cooling capacity of most units to use a higher cooling rate as much as possible to promote the nucleation of ferrite and the precipitation of two-phase particles. The setting of the cooling temperature and air cooling time is, on the one hand, to promote the growth of ferrite after nucleation, close to the grain size of the target structure, to ensure the realization of a high hole expansion rate, and on the other hand, to facilitate the precipitation of Nb\Ti two-phase particles to ensure strength requirements. The third stage is water cooling, cooling to 440-480℃ at a cooling rate of 20-30℃ / s. The setting of the cooling process in this stage is mainly based on the requirements of bainite formation. Under this process, the proportion of bainite can be increased to 20-30%. Under normal circumstances, due to the performance differences between the two-phase structures, it is difficult to achieve synchronous deformation, resulting in a decrease in plasticity. However, through research, it was found that under this process, although bainite accounts for a high proportion, it is evenly distributed around the ferrite. At the same time, the carbides inside the bainite are distributed in a dot-line manner, which greatly reduces the performance difference between bainite and ferrite, thereby better ensuring the realization of a high hole expansion rate.

[0036] 5. Setting of hot rolling coiling temperature

[0037] After laminar cooling, the steel plate enters the rolling line coiler for coiling. Combined with the cooling end temperature, the present invention sets the hot rolling coiling temperature to 430-460°C.

[0038] 6. Setting of elongation of tension straightening

[0039] The setting of the pickling straightening rate is generally mainly for breaking the iron oxide scale to facilitate pickling, and at the same time can better flatten the plate shape; the present invention sets the straightening elongation to 0.8-1.2%.

[0040] The metallographic structure of the hot-rolled pickled steel plate produced by the method of the present invention comprises 70% to 80% of quasi-polygonal ferrite + 20% to 30% of bainite in terms of area fraction, and the grain size of the ferrite in the metallographic structure is 10.0 to 11.0; the yield strength R of the 1.8 to 5.0 mm thick hot-rolled pickled steel plate is p0.2 The tensile strength is 630~670MPa, and the tensile strength R m 680~740MPa, elongation after fracture A 80mm The hole expansion rate is 18% to 25%, and the hole expansion rate λ is 80% to 100%.

[0041] Compared with the existing technology, the present invention has the following positive effects: 1. The composition of the present invention adopts low carbon, low Si + trace Nb, Ti design, combined with hot rolling process design, can achieve micro alloy design while achieving high strength and high hole expansion rate requirements, the yield strength R of 1.8 ~ 5.0mm thick hot rolled pickled steel platep0.2 The tensile strength is 630~670MPa, and the tensile strength R m 2. The present invention achieves a yield strength greater than 630 MPa while maintaining a hole expansion ratio of λ of 80% to 100% by controlling the ferrite grain size and the proportion of bainite in the metallographic structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a metallographic photograph of the hot-rolled pickled steel plate according to Example 3 of the present invention.

[0043] Figure 2 This is a scanning electron microscope (SEM) photograph of the metallographic structure of the hot-rolled pickled steel plate of Example 3 of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below with reference to Examples 1-5, as shown in Table 1-3.

[0045] Table 1 shows the chemical composition (by weight percentage) of the steel according to the embodiment of the present invention, with the remainder being Fe and unavoidable impurities.

[0046] Table 1 Chemical composition of steel according to the embodiment of the present invention, unit: weight percentage.

[0047]

[0048]

[0049] The molten steel meeting the chemical composition requirements is obtained through converter smelting, the molten steel is subjected to Ar blowing treatment in the LF ladle refining furnace refining process, the molten steel is subjected to vacuum circulation degassing treatment and composition fine-tuning in the RH furnace, and the molten steel is continuously cast under Ar blowing protection throughout the process to obtain continuous casting slabs; the continuous casting slabs have a thickness of 210 to 230 mm, a width of 800 to 1300 mm, and a length of 5000 to 10000 mm.

[0050] The cut-to-length slabs produced during steelmaking are then sent to a reheating furnace for reheating. After removal from the furnace and dephosphorization, they are then sent to a continuous hot rolling mill for rolling. The rolling process is controlled by a roughing mill and a finishing mill. After laminar cooling using a three-stage cooling method, the slabs are coiled to produce qualified hot-rolled coils. The thickness of the hot-rolled steel plates ranges from 1.8 to 5.0 mm. The hot rolling process control parameters are shown in Tables 2 and 3.

[0051] Table 2 Hot rolling process control parameters of the embodiment of the present invention (I)

[0052]

[0053] Table 3 Hot rolling process control parameters of the embodiment of the present invention (II)

[0054]

[0055] The hot rolled steel coil is unwound on an unwinder, straightened and pickled to obtain a finished hot rolled pickled steel plate. The straightening elongation is 0.8% to 1.2%. The straightening elongation used in the embodiment of the present invention is shown in Table 4.

[0056] Table 4 Elongation of tensile straightening in the embodiment of the present invention

[0057] Hot rolling parameters Thickness of hot rolled pickled steel plate / mm Tensile elongation / % The present invention 1.8-5.0 0.8-1.2 Example 1 1.8 1.2 Example 2 3.5 0.9 Example 3 5.0 0.8 Example 4 2.0 1.15 Example 5 3.0 1.02

[0058] The hot-rolled pickled steel plate obtained by the above method is shown in FIG. Figure 1 、 Figure 2 The metallographic structure of the hot-rolled pickled steel plate includes 70% to 80% quasi-polygonal ferrite + 20% to 30% bainite by area fraction, and the grain size of the ferrite in the metallographic structure is 10.0 to 11.0; the yield strength R of the 1.8 to 5.0 mm thick hot-rolled pickled steel plate is p0.2 The tensile strength is 630~670MPa, and the tensile strength R m 680~740MPa, elongation after fracture A 80mm The hole expansion rate is 18% to 25%, and the hole expansion rate λ is 80% to 100%.

[0059] The hot-rolled pickled steel plate obtained in the present invention was subjected to a tensile test according to GB / T 228.1-2010 Tensile tests on metallic materials - Part 1: Room temperature test methods, and a hole expansion test was performed according to GB / T 24524-2009 Test methods for hole expansion of metallic materials - Sheet and strip. The mechanical properties are shown in Table 5.

[0060] Table 5 Mechanical properties of hot-rolled pickled steel plates according to the present invention

[0061]

[0062] In Table 5, when testing the elongation after fracture of hot-rolled pickled steel plates, when the thickness of the hot-rolled pickled steel plates is less than 3mm, the gauge length is 80mm; when the thickness of the hot-rolled pickled steel plates is ≥3mm, the gauge length is 80mm. S0 is the cross-sectional area of ​​the steel plate.

[0063] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, wherein the chemical composition by weight is as follows: C: 0.04% to 0.10%, Si ≤ 0.10%, Mn: 0.8% to 1.5%, P ≤ 0.020%, S ≤ 0.005%, Al: 0.01% to 0.05%, N ≤ 0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance being Fe and unavoidable impurity elements; Yield strength R of 1.8~5.0mm thick hot rolled pickled steel plate p0.2 The tensile strength is 630~670MPa, and the tensile strength R m 680~740MPa, elongation after fracture A 80mm is 18% to 25%, and the hole expansion rate λ is 80% to 100%; the manufacturing method of the hot-rolled pickled steel plate is characterized in that, The following steps are involved: The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows by weight: C: 0.04% to 0.10%, Si≤0.10%, Mn: 0.8% to 1.5%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.05%, N≤0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance is Fe and unavoidable impurity elements; The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1220-1260°C and the heating time is 180-240 minutes. The hot rolling is a two-stage rolling process. The rough rolling is a 6-pass continuous rolling process, which is rolled above the austenite recrystallization temperature. The rough rolling end temperature is 1080-1120°C. After rough rolling, the intermediate slab thickness is controlled to be 38-42 mm. The finishing rolling is a 7-pass continuous rolling process, which is rolled in the austenite non-recrystallization zone. The finishing temperature is 900-930°C. After finishing rolling, the thickness of the steel plate is controlled to be 1.8-5.0 mm. The laminar cooling adopts a three-stage cooling method. The first stage The method comprises the following steps: water cooling, a first-stage cooling rate of 40-50°C / s, and a first-stage cooling end temperature of 680-720°C; air cooling, a second-stage cooling rate of 5-10°C / s, and a second-stage air cooling time of 4-8s; water cooling, a third-stage cooling rate of 20-30°C / s, and a third-stage cooling end temperature of 440-480°C; a coiling temperature of 430-460°C, and a hot-rolled steel coil is obtained by using a rolling line coiler to coil the hot-rolled steel plate; the hot-rolled steel coil is re-coiled on a decoiler, and is subjected to drawing, straightening, and pickling to obtain a finished hot-rolled pickled steel plate, wherein the drawing and straightening elongation is 0.8%-1.2%.

2. The high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa according to claim 1, characterized in that: The metallographic structure of the hot-rolled pickled steel plate includes 70% to 80% of quasi-polygonal ferrite and 20% to 30% of bainite in terms of area fraction, and the grain size of the ferrite in the metallographic structure is 10.0 to 11.

0.

3. A method for manufacturing a high-expansion hot-rolled pickled steel plate with a yield strength of 600 MPa, characterized in that: The following steps are involved: The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows by weight: C: 0.04% to 0.10%, Si≤0.10%, Mn: 0.8% to 1.5%, P≤0.020%, S≤0.005%, Al: 0.01% to 0.05%, N≤0.006%, Ti: 0.05% to 0.10%, Nb: 0.01% to 0.02%, and the balance is Fe and unavoidable impurity elements; The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1220-1260°C and the heating time is 180-240 minutes. The hot rolling is a two-stage rolling process. The rough rolling is a 6-pass continuous rolling process, which is rolled above the austenite recrystallization temperature. The rough rolling end temperature is 1080-1120°C. After rough rolling, the intermediate slab thickness is controlled to be 38-42 mm. The finishing rolling is a 7-pass continuous rolling process, which is rolled in the austenite non-recrystallization zone. The finishing temperature is 900-930°C. After finishing rolling, the steel plate thickness is controlled to be 1 .8~5.0mm, laminar cooling adopts three-stage cooling method, the first stage is water cooling, the first stage cooling rate is 40~50℃ / s, the first stage cooling end temperature is 680~720℃; the second stage is air cooling, the second stage cooling rate is 5~10℃ / s, the second stage air cooling time is 4~8s; the third stage is water cooling, the third stage cooling rate is 20~30℃ / s, the third stage cooling end temperature is 440~480℃; the coiling temperature is 430~460℃, and the hot rolled steel plate is coiled by a rolling line coiler to obtain hot rolled steel coils; The hot rolled steel coil is unwound again on the unwinding machine, and is subjected to drawing and straightening and pickling to obtain a finished hot rolled pickled steel plate. The drawing and straightening elongation is 0.8% to 1.2%.

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