CN111378893A

CN111378893A - Hot-rolled steel plate for longitudinal welded pipe with yield strength of 290MPa

Info

Publication number: CN111378893A
Application number: CN201811622425.0A
Authority: CN
Inventors: 徐国利
Original assignee: Shanghai Meishan Iron and Steel Co Ltd
Current assignee: Shanghai Meishan Iron and Steel Co Ltd
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2020-07-07

Abstract

The invention discloses a hot rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength, which mainly solves the technical problem that the product performance of the existing hot rolled steel plate for a pipeline with 290 MPa-grade yield strength cannot meet the requirements of petroleum and natural gas welded pipe manufacturing enterprises. The invention relates to a hot rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength, which comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Si 0.07-0.12%, Mn: 0.60-0.70%, P is less than or equal to 0.018%, S is less than or equal to 0.005%, N is less than or equal to 0.0060%, Al: 0.010-0.045%,ti: 0.010-0.020%, Nb: 0.010-0.020%, and the balance of iron and inevitable impurities. Elongation after fracture of hot rolled steel plate A_50mm35-60% and Akv is not less than 70J at-5 ℃.

Description

Hot-rolled steel plate for longitudinal welded pipe with yield strength of 290MPa

Technical Field

The invention relates to steel for oil and gas pipelines, in particular to a hot-rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength, and specifically relates to a hot-rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength and a manufacturing method thereof, which are used for manufacturing pipelines for conveying oil and gas and belong to the technical field of steel for oil and gas pipelines.

Background

The pipeline transportation is the most economical and safe transportation mode for long-distance petroleum and natural gas transportation, and has the characteristics of high efficiency, economy, safety, no pollution and the like. In order to improve the conveying efficiency, reduce the energy consumption and reduce the investment, the development of long-distance pipelines towards high-pressure and large-caliber conveying is a trend. The development of a newly-built hot continuous rolling unit to a wider specification and higher strength direction is promoted, so that the long-distance and high-pressure requirements of a conveying main line are met. On the other hand, the steel quantity for the small-diameter welding pipe required by pipeline branch engineering and urban pipe networks is also greatly and synchronously improved. In order to produce steel for small-diameter welded pipes required for pipeline branch works and urban pipe networks in wide hot continuous rolling mills, it is necessary to longitudinally cut a wide hot rolled steel strip.

Longitudinal welded pipes are a delicate product among welded pipe products. Compared with a conventional welded pipe which is not longitudinally cut, longitudinally-cut welded steel is manufactured by a HFW method after a hot-rolled coil is longitudinally cut along the longitudinal direction when a user uses the welded pipe. When the slab is solidified, the slab width 1/2 is most prone to generate defects such as component segregation, looseness, cracks and excessive inclusions, and in the HFW welding process, the defect part is extruded and is easily expanded to be a base material defect of the welding part, the defect is represented as defect incompatibility caused by cracks or inclusions, the defect can be discovered only after the defect is detected, and the economic loss caused by the defect is often large. The advantages are wide steel coil, low production cost of hot coil in steel mill, stable performance control, and large coil delivery.

The existing product has relatively high inclusion content due to reasons of unclear component design and continuous casting slab control specification and the like, the center segregation grade can not meet the requirements of longitudinal welded pipes, and flaw detection failure caused by cracks or inclusions after welding can be easily caused.

Chinese patent application publication No. CN106244925A discloses thick X42 pipeline steel and a production method thereof, which comprises the following steps: smelting and continuous casting; rough rolling; fine rolling; and (5) cooling in two sections. The weight percentage of the chemical components is as follows: c: 0.03% -0.07%, Si: 0.10% -0.30%, Mn: 0.70% -1.00%, P: less than or equal to 0.020%, S: less than or equal to 0.010 percent, Nb: 0.015% -0.030%, Ti: 0.008% -0.019%, Cr: 0.15 to 0.30 percent, and the balance of Fe and inevitable impurities. The material of the invention is in the level of 290MPa of yield strength, but the invention is directed to X42 pipeline steel with the specification of 12-22mm thick, and 0.15-0.30% of Cr element is required to be added to improve the strength of the steel and increase the hardenability. However, if too high chromium is added into steel at the same time, low-melting-point Cr-Mn composite oxides are formed, surface cracks are formed in the hot working process, the welding performance is seriously deteriorated, and the defect detection failure of the steel pipe is easily caused. The design does not meet the requirements specific to a longitudinal section line.

Chinese patent application publication No. CN101928877A discloses a steel for oil casing pipes, which can be used for manufacturing J55 grade high frequency oil casing pipes, and a high frequency welding oil casing pipe, and a manufacturing method thereof, and a longitudinal section thereof is suitable for manufacturing J55 grade high frequency welding oil casing pipes having an outer diameter of 244.48mm or less. The chemical components of the alloy are 0.13-0.18% of C, 0.15-0.25% of Si, 0.60-1.00% of Mn, less than or equal to 0.005% of S, less than or equal to 0.015% of P, 0.008-0.020% of Nb, 0.0010-0.0045% of Ca, 0.010-0.040% of Al, and the balance of iron and inevitable impurities. The material can meet the requirements of longitudinal section, but has higher carbon content and low impact toughness, and can not meet the requirements of manufacturing welded pipes for conveying petroleum and natural gas.

Therefore, the chemical components and the product performance of the existing hot rolled steel plate for the pipeline with the yield strength of 290MPa cannot meet the requirements of oil and gas welded pipe manufacturing enterprises on the longitudinal cutting process quality of the steel plate.

Disclosure of Invention

The invention aims to provide a hot rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength and a manufacturing method thereof, and mainly solves the technical problem that the product performance of the existing hot rolled steel plate for a pipeline with 290 MPa-grade yield strength cannot meet the requirements of petroleum and natural gas welded pipe manufacturing enterprises.

According to the invention, the Nb and Ti are adopted for alloying, key solid solution strengthening elements such as carbon and manganese which guarantee the final performance of the longitudinal-cutting product are strictly controlled, the Mn/Si ratio is strictly controlled to be 5-10, and the proper steel-making, continuous casting and hot rolling process design is combined, so that the product is guaranteed to have good mechanical properties and process properties such as cold bending and welding, and the processing requirements such as longitudinal-cutting, welding and forming are met.

The invention adopts the technical scheme that a hot rolled steel plate for longitudinal welded pipes with yield strength of 290MPa is prepared from the following chemical components in percentage by weight: c: 0.06-0.08%, Si 0.07-0.12%, Mn: 0.60-0.70 percent of Fe, less than or equal to 0.018 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0060 percent of N, 0.010-0.045 percent of Al, 0.010-0.020 percent of Ti, 0.010-0.020 percent of Nb, 5-10 percent of Mn/Si, and the balance of Fe and inevitable impurities.

The metallographic structure of the hot-rolled steel plate is ferrite and pearlite, and the grain size of the ferrite in the metallographic structure is 8-12 grades; the hot rolled steel sheet having a thickness of 6.0 to 12.0mm has a yield strength Rt0.5 of 290 to 475MPa and a tensile strength R_m415 to 560MPa, elongation after break A_50mm35-60%, the impact work value Akv at-5 ℃ is more than or equal to 70J, and d is qualified as 2a in a 180-degree bending test.

The hot rolled steel plate is suitable for manufacturing longitudinal welded pipes for petroleum and natural gas transportation.

The reason why the chemical composition of the hot rolled steel sheet having a yield strength of 290MPa grade according to the present invention is limited to the above range is as follows:

carbon: carbon is the most basic strengthening element, carbon is dissolved in steel to form an interstitial solid solution and plays a role in solid solution strengthening, and carbon forms carbide precipitation with strong carbide elements and plays a role in precipitation strengthening. The component system makes full use of the strengthening effect of C. However, it is an easily segregating element, and the high content of the easily segregating element increases the center segregation of the continuous casting slab, is not beneficial to the welding of longitudinal steel, and simultaneously reduces the toughness and deteriorates the performance of the material. Meanwhile, carbon is too high to enter the peritectic region of the low-carbon steel. Too low carbon reduces the strength of the steel grade. Therefore, the strengthening effect of C and Mn is comprehensively considered, and the set C content is 0.06-0.08%.

Manganese: manganese is also the main element of the composition system, can play a role in solid solution strengthening, and is the most main and economic strengthening element for compensating strength loss caused by carbon reduction in steel. However, Mn is an easily segregated element, and the high content of Mn increases the center segregation of the continuous casting slab, which is not favorable for welding longitudinal steel. Mn is a strictly controlled element in the component system, and the content of Mn is further limited to be 0.60-0.70%.

Carbon and manganese are key elements for ensuring the final performance of longitudinal-section products, and the range is strictly controlled in order to ensure the stable performance of the hot-rolled steel plates.

Silicon: silicon suitably increases the strength of steel by solid solution strengthening in steel, too high a content of Si lowers the Mn/Si ratio, adversely affects the surface quality of a slab and the weldability of a welded pipe, and the weld toughness increases with the increase in the Mn/Si ratio. However, too low Si will affect the casting quality of Ca-treated steel. According to the test, the Mn/Si is optimal between 5 and 10, and the Si content is limited to be 0.07 to 0.12 percent.

Sulfur and phosphorus: too high sulfur and phosphorus adversely affect the toughness and plasticity of the material, while too low sulfur and Lin increase the cost of desulfurization and dephosphorization in steel making. The invention limits S to be less than or equal to 0.005 percent and P to be less than or equal to 0.018 percent.

Nitrogen: the plasticity and toughness of the material are seriously deteriorated if the nitrogen content is too high, and N is limited to be less than or equal to 0.0060 percent.

Aluminum: the aluminum plays a role in deoxidation in the present invention, and is a strong oxidizing forming element, and forms Al with oxygen in steel₂O₃Is removed during steel making. Too high an aluminum content can lead to excessive Al formation₂O₃And the pouring nozzle is easy to block during continuous casting. The invention limits the Al content to be 0.010-0.045%.

Titanium: is a strong solid N element, the stoichiometric ratio of Ti/N is about 3.42, about 0.02% of Ti can be used for fixing N in the steel below 60ppm, and a fine TiN precipitated phase which is stable at high temperature can be formed during slab continuous casting. The trace amount of titanium plays a strengthening role, and the influence of the trace amount of titanium is that fine TiN particles can effectively prevent austenite grains from growing when the plate blank is reheated, so that the fine TiN particles have a positive effect on improving the toughness of a final product. A very small amount of Ti gives a significant strengthening effect. In addition, the TiN particles can also avoid the growth of crystal grains in a welding heat affected zone during welding, and improve the impact toughness of the welding heat affected zone. The invention limits the Ti content to 0.010-0.020%.

Niobium: is the main microalloying element of the low-alloy high-strength steel and mainly plays a role in fine grain strengthening. NbC strain is induced and precipitated in the hot rolling process to hinder recovery and recrystallization of the deformed austenite, and the deformed austenite structure rolled in a non-recrystallization region is converted into a fine phase change product during phase change through controlled rolling and controlled cooling, so that the steel has high strength and high toughness. In order to achieve the strength required by the steel grade, the strength is improved by increasing the niobium content to compensate for the strength loss caused by reducing the manganese and silicon contents. According to the test result, the content of Nb is limited to 0.010-0.020%.

A manufacturing method of a hot rolled steel plate for a longitudinal welded pipe with a yield strength of 290MPa comprises the following steps:

a hot rolled steel plate for longitudinal welded pipes with yield strength of 290MPa comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Si 0.07-0.12%, Mn: 0.60-0.70 percent of Fe, less than or equal to 0.018 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0060 percent of N, 0.010-0.045 percent of Al, 0.010-0.020 percent of Ti, 0.010-0.020 percent of Nb, 5-10 percent of Mn/Si, and the balance of Fe and inevitable impurities; controlling the grade of inclusions in the continuous casting slab, and testing according to the Standard test method for determining the content of inclusions in steel by ASTM E45-13 of American society for testing and materials, by adopting a method A, wherein the A is below 0.5 grade, the C is 0, and the B and D are below 1.5 grade; controlling the center segregation grade of the continuous casting slab to be below the Mannesmann standard grade 2;

heating the continuously cast plate blank at 1160-1200 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at the temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 960-1020 ℃; the thickness of the intermediate blank is 34-49 mm, the finish rolling is 7-pass continuous rolling, the inlet temperature of the finish rolling is 940-1000 ℃, and the finish rolling finishing temperature is 800-840 ℃; after finish rolling, the thickness of the steel plate is controlled to be 6.0-12.0 mm, front-end cooling is adopted for laminar cooling, the laminar cooling speed is 15-35 ℃/s, and when the coiling temperature is 520-600 ℃, the hot rolled steel coil is coiled.

The reason of the production process system adopted by the invention is as follows:

1. setting of center segregation of continuous casting slab and setting of level of inclusions in continuous casting slab

The control of the center segregation of the continuous casting slab and the control of molten steel inclusions are the technical key for realizing the method, and in order to ensure that when a longitudinal welded pipe is produced, a user longitudinally cuts a hot-rolled coil along the longitudinal direction and then manufactures the pipe; the method is characterized in that the method sets and controls the grade of inclusions in the continuous casting slab, and the grade of the inclusions in the continuous casting slab is tested by adopting a method A according to the standard test method for measuring the content of the inclusions in steel by American society for testing and materials (ASTM E45-13), wherein the A is below 0.5, the C is below 0, and the B and D are below 1.5; and controlling the center segregation grade of the continuous casting slab to be below the Mannesmann standard grade 2.

2. Setting of heating temperature and heating time of continuous casting slab

The heating temperature and time of the continuous casting slab are set to ensure that niobium carbide and niobium carbonitride in the continuous casting slab are fully dissolved and the original crystal grains are not grown too large. Therefore, the heating temperature is very important for the technical scheme of the invention, the temperature is too low or the heating time is too short, and niobium carbide and niobium carbonitride in the continuous casting plate blank can not be fully dissolved; and the temperature is too high, the heating time is too long, the original structure of the plate blank is thick, and the final performance and the surface quality of the steel plate are not facilitated. The heating temperature of the continuous casting plate blank is set to be 1160-1200 ℃, and the heating time is set to be 150-240 min.

3. Roughing finish temperature setting

The rough rolling process is controlled to be rolled above the austenite recrystallization temperature, so that uniform and fine austenite grains are ensured to be obtained. Therefore, the rough rolling finishing temperature is set to be 960-1020 ℃.

4. Intermediate billet thickness and finish rolling entry temperature settings

In order to obtain good impact toughness, particularly for hot continuous rolled steel sheets with a thickness of 8mm or more, it is necessary to control the effective reduction ratio at the finish rolling stage. The effective reduction rate is the reduction rate of deformation occurring in the temperature range of the austenite non-recrystallization region in the finish rolling stage, and is related to the thickness and temperature of the intermediate billet at the finish rolling inlet. The compression ratio of finish rolling is controlled to be more than 4, so that the thickness of the intermediate blank is set to be 34-49 mm according to the thickness of the finished product, and the temperature of a finish rolling inlet is 940-1000 ℃.

5. Finish rolling finish temperature setting

The setting of the finishing rolling temperature is to obtain flat austenite grains with deformation zones inside through rolling in an austenite non-recrystallization region, and the flat austenite grains are converted into fine ferrite grains in the subsequent laminar cooling process to play a role of fine grain strengthening. Therefore, the finish rolling finishing temperature is set to be 800-840 ℃.

6. Laminar cooling rate setting

The set laminar cooling speed after finish rolling is very critical, and the rapid cooling speed is adopted to inhibit the growth of ferrite grains and the precipitation of TiC at a high-temperature stage. The rapid cooling makes it possible to precipitate fine and dispersed particles of TiC and the like in the ferrite at a lower temperature. The cooling speed is too slow, and the advance precipitation of TiC in high-temperature deformation austenite cannot be inhibited; the steel plate is cooled too fast, the toughness of the steel plate is unfavorable, and the plate shape is greatly influenced. The laminar cooling adopts front-section cooling, and the cooling speed is 15-35 ℃/s.

7. Coiling temperature setting

The coiling temperature mainly affects the structure and performance of the strip steel. The high coiling temperature is beneficial to the precipitation of secondary phases of particles of Ti, Nb alloy carbon and nitrogen, but easily causes the growth of a matrix ferrite structure, coarsens precipitates of Nb, Ti microalloy carbon and nitride, and reduces the toughness of the steel plate; when the coiling temperature is too low, secondary phase precipitation of Ti, Nb alloy carbon and nitrogen particles is suppressed, and the precipitation strengthening effect of improving the strength of the steel sheet is not good. Comprehensively, the hot rolling coiling temperature is set to be 520-600 ℃.

The metallographic structure of the hot-rolled steel plate produced by the method is ferrite and pearlite, and the grain size of the ferrite in the metallographic structure is 8-12 grades; yield strength R of hot rolled steel plate with thickness of 6.0-12.0 mm_t0.5 is 290-475 MPa, tensile strength R_m415 to 560MPa, elongation after break A_50mm35-60%, the impact work value Akv at-5 ℃ is more than or equal to 70J, and d is qualified as 2a in a 180-degree bending test. The hot rolled steel plate is suitable for manufacturing longitudinal welded pipes for petroleum and natural gas transportation.

Compared with the prior art, the invention has the following positive effects: 1. according to the invention, Nb and Ti are alloyed, key solid solution strengthening elements of carbon and manganese are strictly controlled to ensure the final performance of a longitudinal-section product, Mn/Si is controlled to be 5-10, and the composition design is ensured to meet the requirement of stable performance of a longitudinal-section hot-rolled steel plate. 2. The invention requires that the center segregation of the continuous casting slab is controlled to be below the Mannesian standard 2 grade, and the inclusion control is performed according to the Standard test method for measuring the content of the inclusions in steel of ASTM E45-13 of the American society for testing materials, wherein the A class is below 0.5 grade, the C class is 0, and the B class and the D class are below 1.5 grade, so that the method can meet the requirement of producing the longitudinal welded pipe after longitudinally cutting the hot rolled coil by a user along the longitudinal direction. 3. Through the design of longitudinal section material components and the design of a manufacturing process, the wide hot continuous rolling unit can be satisfied to produce a wide-specification hot rolled steel strip, and the steel strip is longitudinally cut, so that the steel requirements for small-pipe-diameter welded pipes required by production pipeline branch line engineering and urban pipe networks are satisfied. The wide hot continuous rolling unit can improve the productivity and fully exert the capacity of the wide hot continuous rolling unit on the premise of ensuring the quality of finished products. 4. The hot rolled steel plate for the longitudinal welded pipe with the yield strength of 290MPa grade obtained by combining the component system with proper steel-making, continuous casting and hot rolling process designs has stable structure and performance compared with other steel plates with the same strength grade, can better meet the process requirements of longitudinal cutting, welding, forming and the like, and reduces the manufacturing cost of small-caliber welded pipes required by pipeline branch line engineering and urban pipe networks. 5. The hot rolled steel plate meets the requirements of welded pipe manufacturing enterprises on mechanical property and technological property of the longitudinal steel plate, and fills the industrial blank.

Drawings

FIG. 1 is a metallographic structure photograph of a hot-rolled steel sheet according to example 1 of the invention.

Detailed Description

The present invention is further described below with reference to examples 1 to 4, which are shown in tables 1 to 3.

Table 1 shows the chemical composition (in weight percent) of the steels of the examples of the invention, with the balance being iron and unavoidable impurities.

Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.

The continuous casting method comprises the steps of smelting in a converter, carrying out desulfurization treatment in an LF ladle refining furnace refining procedure, carrying out vacuum circulating degassing treatment in an RH furnace, finely adjusting components to obtain molten steel meeting the component requirements, and continuously casting to obtain a continuous casting slab. The thickness of the continuous casting plate blank is 210-230 mm, the width is 900-1600 mm, and the length is 8000-11700 mm.

And (3) conveying the fixed-length plate blanks produced in the steelmaking process to a heating furnace for heating, discharging and descaling, and conveying to a hot continuous rolling unit for rolling. And controlling rolling by a rough rolling and finish rolling continuous rolling unit, coiling after laminar cooling, and carrying out front-section cooling on the laminar cooling to produce a qualified hot-rolled steel coil. The thickness of the hot rolled steel plate is 6.0-12.0 mm. The hot rolling process control parameters are shown in Table 2.

TABLE 2 Hot Rolling Process control parameters of the inventive examples

Referring to fig. 1, the hot-rolled steel plate obtained by the method has a metallographic structure of ferrite and pearlite, the grain size of the ferrite in the metallographic structure is 8-12 grade, and the yield strength R of the hot-rolled steel plate with the thickness of 6.0-12.0 mm_t0.5 is 290-475 MPa, tensile strength R_m415 to 560MPa, elongation after break A_50mm35-60%, the impact work value Akv at-5 ℃ is more than or equal to 70J, and d is qualified as 2a in a 180-degree bending test.

The hot rolled steel plate obtained by the invention is sampled, a transverse sample is obtained by tensile and bending tests, a longitudinal sample is obtained by impact tests, and the tensile test is carried out according to the part 1 of the GB/T228.1-2010 metal material tensile test: room temperature test method for tensile test; performing a bending test according to GB/T232-2010 metal material bending test method; the impact test is carried out according to GB/T229-2007 method for testing charpy pendulum impact of metal materials, and the mechanical properties are shown in Table 3.

The hot rolled steel plate obtained by the invention has good strength and toughness, weldability and bending formability.

TABLE 3 mechanical Properties of Hot rolled Steel sheets according to examples of the present invention

As seen from Table 3, the hot rolled steel sheet obtained by the present invention has good toughness, weldability and bending formability.

In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.

Claims

1. A hot rolled steel plate for longitudinal welded pipes with yield strength of 290MPa comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Si 0.07-0.12%, Mn: 0.60-0.70 percent of Fe, less than or equal to 0.018 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0060 percent of N, 0.010-0.045 percent of Al, 0.010-0.020 percent of Ti, 0.010-0.020 percent of Nb, 5-10 percent of Mn/Si, and the balance of Fe and inevitable impurities; the metallographic structure of the hot-rolled steel plate is ferrite and pearlite, and the grain size of the ferrite in the metallographic structure is 8-12 grades.

2. A hot-rolled steel sheet for a longitudinal welded pipe having a yield strength of 290MPa according to claim 1, wherein the hot-rolled steel sheet has a yield strength Rt0.5 of 290 to 475MPa and a tensile strength R of 6.0 to 12.0mm_m415 to 560MPa, elongation after break A_50mm35-60%, the impact work value Akv at-5 ℃ is more than or equal to 70J, and d is qualified as 2a in a 180-degree bending test.

3. A manufacturing method of a hot rolled steel plate for a longitudinal welded pipe with 290 MPa-grade yield strength is characterized by comprising the following steps of:

a hot rolled steel plate for longitudinal welded pipes with yield strength of 290MPa comprises the following chemical components in percentage by weight: c: 0.06-0.08%, Si 0.07-0.12%, Mn: 0.60-0.70 percent of Fe, less than or equal to 0.018 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0060 percent of N, 0.010-0.045 percent of Al, 0.010-0.020 percent of Ti, 0.010-0.020 percent of Nb, 5-10 percent of Mn/Si, and the balance of Fe and inevitable impurities; controlling the grade of inclusions in the continuous casting slab, and testing the grade of the inclusions in the continuous casting slab by adopting a method A according to the Standard test method for determining the content of the inclusions in steel by ASTM E45-13 of the American society for testing and materials, wherein the class A is below 0.5, the class C is 0, and the class B and the class D are below 1.5; controlling the center segregation grade of the continuous casting slab to be below the Mannesmann standard grade 2;

heating the continuously cast plate blank at 1160-1200 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at the temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 960-1020 ℃; the thickness of the intermediate blank is 34-49 mm, the finish rolling is 7-pass continuous rolling, the inlet temperature of the finish rolling is 940-1000 ℃, and the finish rolling finishing temperature is 800-840 ℃; and after finish rolling, performing front-stage cooling by adopting laminar cooling, wherein the laminar cooling speed is 15-35 ℃/s, and the hot-rolled steel coil is obtained by coiling when the coiling temperature is 520-600 ℃.

4. A method for producing a hot-rolled steel sheet for a longitudinal welded pipe having a yield strength of 290MPa according to claim 3, wherein the thickness of the steel sheet after the hot rolling and the finish rolling is controlled to be 6.0 to 12.0 mm.