A hot-rolled pipeline steel and a method of manufacturing and use thereof

Abstract

The present application belongs to the technical field of steel preparation, and particularly relates to a hot-rolled pipeline steel and a preparation method and application thereof. The preparation method comprises the following steps: 1) heating a continuous casting blank to a first heating temperature, then continuously heating at a second heating temperature, and then rough rolling to obtain an intermediate blank; the total time of the first heating and the second heating is related to the thickness of the continuous casting blank as follows: t = beta * thickness of the continuous casting blank; the rough rolling comprises R1 stage rolling for at least one pass and R2 stage rolling for at least five passes, the third, fourth and fifth passes of the R2 stage are respectively opened to remove scale water, the roller speed is controlled, and the reduction rate of each pass is controlled, and the thickness is pressed to 42-48 mm; 2) performing finish rolling, super-fast cooling, laminar flow front cooling, and coiling to obtain the hot-rolled pipeline steel. The hot-rolled pipeline steel prepared by the present application has high drop hammer performance, high elongation, and high impact energy.

Description

Technical Field

[0001] This invention belongs to the field of steel preparation technology, specifically relating to a hot-rolled pipeline steel, its preparation method, and its application. Background Technology

[0002] Pipeline steel is mainly used for long-distance transportation of fluids such as oil and natural gas. To ensure the safety and reliability of pipelines during operation, pipeline steel should possess high strength and high toughness. The toughness index of pipeline steel materials can be characterized by the Charpy impact test and the drop hammer tear test. Among them, the drop hammer tear test (DWTT) uses a full-thickness specimen and mainly reflects the fracture toughness of the material in the full thickness direction of the steel plate. Currently, high-grade pipeline steels have strict requirements for drop hammer performance.

[0003] The drop hammer performance of steel plates is closely related to their thickness; the thicker the plate, the more difficult it is to guarantee drop hammer performance. In current technologies, during the production of thick-gauge hot-rolled pipeline steel, the limited compression ratio in the finishing rolling stage makes it difficult for deformation to penetrate to the core of the billet, easily leading to problems such as coarse grains and uneven microstructure along the thickness direction, resulting in unreliable low-temperature drop hammer performance. To ensure the low-temperature drop hammer performance of the steel plate, alloying with Mo or Ni is often used to produce thick-gauge pipelines. Chinese patent application CN109680135A discloses a method for producing X80 hot-rolled coils for pipelines with a thickness ≥22mm. This method uses a C-Mn-Nb-Cr-Ni-Mo alloying design, improving the drop hammer performance of the steel by adding 0.10-0.25% Mo and 0.10-0.25% Ni. However, Mo and Ni are expensive, resulting in high costs. While existing hot-rolled pipeline steels without added Mo and Ni reduce costs, their drop hammer performance, ductility, and impact energy are inferior. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor drop hammer performance, elongation and impact energy of hot-rolled pipeline steel without Mo and Ni addition, thereby providing a hot-rolled pipeline steel, its preparation method and application.

[0005] This invention provides a method for preparing hot-rolled pipeline steel, comprising the following steps:

[0006] 1) Heat the continuous casting billet to the first heating temperature and control the heating time of the continuous casting billet at the first heating temperature to t1. Then, continue to heat the continuous casting billet at the second heating temperature and control the heating time of the continuous casting billet at the second heating temperature to t2. After that, perform rough rolling on the continuous casting billet to obtain an intermediate billet.

[0007] The relationship between the total time t (heating time t1 at the first heating temperature and heating time t2 at the second heating temperature) and the thickness of the continuously cast billet is: t = β * thickness of the continuously cast billet, where β is an adjustment coefficient with a value range of 0.4-0.6 min / mm, t is in min, and the thickness of the continuously cast billet is in mm.

[0008] The roughing process includes at least one pass in the R1 stage and at least five passes in the R2 stage. During the third, fourth, and fifth passes in the R2 stage, descaling water is turned on, and the roll speeds for the third, fourth, and fifth passes are 3.2-4.2 m / s. The reduction rate for each pass in the third, fourth, and fifth passes is 25-30%, and the thickness of the intermediate billet obtained after roughing is controlled to be 42-48 mm.

[0009] 2) The intermediate billet obtained after rough rolling in step 1) is fine rolled, cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel.

[0010] The cooling rate of the ultra-fast cooling section is 50-70℃ / s.

[0011] Preferably, the chemical composition of the continuously cast billet in step 1) does not include Mo and / or Ni.

[0012] Preferably, the chemical composition of the continuously cast billet in step 1) comprises, by mass percentage: C: 0.05-0.07%, Si: 0.16-0.24%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.0050%, Alt: 0.020-0.040%, Nb: 0.05-0.07%, Ti: 0.01-0.02%, with the remainder being iron and unavoidable impurities.

[0013] Preferably, in step 1), the first heating temperature is higher than the second heating temperature;

[0014] In step 1), the first heating temperature is 1180-1220℃, and the second heating temperature is 1170-1210℃;

[0015] The ratio of t1 to t2 is (1.09-1.3):1.

[0016] Preferably, the thickness of the continuously cast billet in step 1) is 200-250 mm;

[0017] The target exit temperature of the roughing mill mentioned in step 1) is 970-1000℃;

[0018] In step 1), the descaling water outlet pressure during the third, fourth, and fifth passes of the R2 stage rolling is 18-20 MPa.

[0019] Preferably, the roughing in step 1) includes one pass of rolling in the R1 stage and five passes of rolling in the R2 stage;

[0020] After the R1 stage rolling in step 1), the exit thickness of the continuously cast billet is 170-190 mm;

[0021] The second pass reduction rate in the R2 stage rolling is 17-19%;

[0022] Optionally, the rough rolling step described in step 1) may include a descaling step.

[0023] Optionally, the rough rolling step described in step 1) may be followed by a descaling step.

[0024] Preferably, the threading speed of the finishing mill in step 2) is 2.0-2.5 m / s, and the finishing mill temperature is 820-840℃;

[0025] The winding temperature mentioned in step 2) is 510-540℃;

[0026] The outlet temperature of the ultra-fast cooling section mentioned in step 2) is 560-590℃, and the cooling water pressure of the ultra-fast cooling section is 7.5-8.5MPa;

[0027] The laminar flow front-end cooling rate is 20-30℃ / s;

[0028] The thickness of the hot-rolled pipeline steel is 15-20mm.

[0029] After finishing, the steel moves from the mill side to the coiler side, and is cooled during the movement. The laminar cooling section has at least 24 sets of cooling manifolds. For laminar front-end cooling, the cooling manifolds are opened sequentially from the mill side to the coiler side until the temperature drops to the coiling temperature, and the cooling water is mainly concentrated at the front end of the laminar cooling. For laminar rear-end cooling, the cooling manifolds are opened sequentially from the coiler side to the mill side until the temperature drops to the coiling temperature, and the cooling water is concentrated at the rear end of the laminar cooling.

[0030] This invention provides a hot-rolled pipeline steel, which is prepared by the above-described method for preparing hot-rolled pipeline steel.

[0031] Preferably, the yield strength R of the hot-rolled pipeline steel t0.5 The tensile strength (Rm) is 520-570 MPa, and the elongation (A) is 620-680 MPa. 50.8 ≥37%, 0℃ impact energy KV2 is 320-450J, -5℃ drop hammer toughness shear area ratio SA single value ≥93%, -5℃ drop hammer toughness shear area ratio SA average value ≥94.3%.

[0032] Preferably, the yield strength R of the hot-rolled pipeline steel t0.5The tensile strength Rm is 620-635 MPa, and the elongation A is 520-535 MPa. 50.8 ≥39%, 0℃ impact energy KV2 is 390-450J, -5℃ drop hammer toughness shear area ratio SA single value ≥98%, -5℃ drop hammer toughness shear area ratio SA average value ≥99%.

[0033] Optionally, the microstructure of the hot-rolled pipeline steel includes acicular ferrite, polygonal ferrite, and carbides.

[0034] The present invention also provides an application of the above-described hot-rolled pipeline steel in the preparation of transportation pipelines.

[0035] The technical solution of this invention has the following advantages:

[0036] (1) The method for preparing hot-rolled pipeline steel provided by the present invention includes the following steps: heating a continuous casting billet to a first heating temperature and controlling the heating time of the continuous casting billet at the first heating temperature to be t1; then continuing to heat the continuous casting billet at a second heating temperature and controlling the heating time of the continuous casting billet at the second heating temperature to be t2; and then performing rough rolling on the continuous casting billet to obtain an intermediate billet; the relationship between the total time t of the heating time t1 at the first heating temperature and the heating time t2 at the second heating temperature and the thickness of the continuous casting billet is: t = β * thickness of the continuous casting billet, where β is an adjustment coefficient with a value range of 0.4-0.6 min / mm, and the unit of t is m. In, the unit of thickness of the continuously cast billet is mm; the rough rolling includes at least one pass of rolling in the R1 stage and no less than five passes of rolling in the R2 stage. In the R2 stage, the descaling water is turned on in the third, fourth and fifth passes, and the roll speed of the third, fourth and fifth passes is 3.2-4.2 m / s. The reduction rate of each pass in the third, fourth and fifth passes is 25-30%, and the thickness of the intermediate billet obtained after rough rolling is controlled to be 42-48 mm; 2) The intermediate billet obtained after rough rolling in step 1) is subjected to finish rolling, ultra-fast cooling section, laminar front-end cooling, and coiling to obtain the hot-rolled pipeline steel; the cooling rate of the ultra-fast cooling section is 50-70℃ / s. This invention employs a specific heating method for continuously cast billets, and the relationship between the total heating time at the first and second heating temperatures and the billet thickness. This ensures thorough heating of the steel plate, guarantees smooth rolling, and avoids excessively long high-temperature heating times that could lead to coarse grains and negatively impact pipeline steel performance. In the R2 stage of rough rolling, descaling water is activated in the third, fourth, and fifth passes to lower the steel plate surface temperature. Combined with specific high roll speed settings, rapid rolling accumulates distortion energy, which is beneficial for dynamic recrystallization. Simultaneously, the billet is thick and hot in this stage; the descaling water rapidly lowers the billet surface temperature, resulting in a low surface temperature and high deformation resistance, while the core temperature is high and deformation resistance is low. This, combined with specific settings for each of the third, fourth, and fifth passes... A large reduction rate of 25-30% allows deformation to penetrate into the core of the billet, promoting recrystallization and refining the austenite grains in the core. The intermediate billet thickness obtained after rough rolling in this invention is 42-48 mm. Under the large reduction conditions in the post-rough rolling stage, an intermediate billet thickness of 42-48 mm is obtained, which is beneficial for deformation penetration into the slab core during rough rolling and can also reduce the mill load during subsequent finish rolling, thus reducing the manufacturing difficulty. The cooling described in step 2) includes first performing ultra-fast cooling, followed immediately by laminar front-end water spray cooling. Ultra-fast cooling further prevents the high-temperature precipitation of equiaxed proeutectoid ferrite, while laminar front-end water spray cooling further promotes the formation of polygonal ferrite and acicular ferrite, synergistically improving the drop hammer performance of the steel. Through the control and synergistic cooperation of each step and its parameters, this invention produces hot-rolled pipeline steel with excellent characteristics of high drop hammer performance, high elongation, and high impact energy.

[0037] (2) The hot-rolled pipeline steel preparation method provided by the present invention has the advantages of low preparation cost, no need for large reduction rate and low temperature rolling in the finishing rolling process, moderate intermediate billet thickness and final rolling temperature, low finishing rolling load, fast rolling speed, easy and stable production process.

[0038] (3) The method for preparing hot-rolled pipeline steel provided by the present invention, wherein the chemical composition of the continuously cast billet in step 1) does not include Mo and / or Ni, and further, the chemical composition of the continuously cast billet in step 1), by mass percentage, includes: C: 0.05-0.07%, Si: 0.16-0.24%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.0050%, Alt: 0.020-0.040%, Nb: 0.05-0.07%, Ti: 0.01-0.02%, with the remainder being iron and unavoidable impurities. This invention employs a C-Mn-Nb-Ti composition system with a specific content, without the addition of expensive metal elements Mo and Ni, and requires no equipment modification or alteration of existing processes and production techniques. By adjusting the heating, rolling, and cooling processes, and in conjunction with the specific preparation process of this invention, the drop hammer performance, elongation, and impact energy of steel plates are further improved, thus solving the problem of low drop hammer performance of thick-gauge hot-rolled pipeline steel. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 Metallographic image of a quarter section of the cross-section of the hot-rolled pipeline steel prepared in Example 1 of this invention;

[0041] Figure 2 Metallographic image of the core of the cross-section of the hot-rolled pipeline steel prepared in Example 1 of this invention. Detailed Implementation

[0042] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0043] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0044] Example 1

[0045] This embodiment provides a method for preparing hot-rolled pipeline steel, including the following steps:

[0046] 1) A 220mm thick continuously cast billet is heated in a heating furnace to a first heating temperature of 1200℃, and the heating time at the first heating temperature is controlled as t1. Then, the billet is further heated at a second heating temperature of 1190℃, and the heating time at the second heating temperature is controlled as t2. The relationship between the total heating time t (t1 at the first heating temperature and t2 at the second heating temperature) and the billet thickness is: t = 0.5min / mm * billet thickness, i.e., t = 110min, where t1 is 60min and t2 is 50min. Afterwards, the billet is descaled and then rough rolled, including the R1 stage rolling. The rolling process consists of one pass and five passes in the R2 stage. The exit thickness of the first pass in the R1 stage is 170 mm. The reduction rate of the second pass in the R2 stage is 18%, the roll speed of the third pass is 3.6 m / s and the reduction rate is 30%, the roll speed of the fourth pass is 3.8 m / s and the reduction rate is 28%, and the roll speed of the fifth pass is 4.2 m / s and the reduction rate is 27%. At the same time, the V2 stand turns on the descaling water during the third, fourth and fifth passes of the R2 stage to reduce the surface temperature of the steel plate. The descaling water outlet pressure of the third, fourth and fifth passes is 19 MPa. The target exit temperature of the roughing mill is 985℃, and an intermediate billet with a thickness of 46 mm is obtained.

[0047] The chemical composition of the continuous casting billet without added Mo and Ni, by mass percentage, includes: C: 0.06%, Si: 0.19%, Mn: 1.55%, P: 0.010%, S: 0.003%, Alt: 0.030%, Nb: 0.060%, Ti: 0.015%, with the remainder being iron and unavoidable impurities;

[0048] 2) The intermediate billet after rough rolling is descaled and finished rolled at a strip threading speed of 2.5 m / s and a finishing rolling temperature of 820℃. Then, it is sequentially cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel with a thickness of 17.5 mm. The cooling rate of the ultra-fast cooling section is 50℃ / s, the outlet temperature of the ultra-fast cooling section is 590℃, the cooling water pressure of the ultra-fast cooling section is 8 MPa, the cooling rate of the laminar flow front end is 25℃ / s, and the coiling temperature is 540℃.

[0049] Example 2

[0050] This embodiment provides a method for preparing hot-rolled pipeline steel, including the following steps:

[0051] 1) A 220mm thick continuously cast billet is heated in a heating furnace to a first heating temperature of 1180℃, and the heating time at the first heating temperature is controlled as t1. Then, the billet is further heated at a second heating temperature of 1170℃, and the heating time at the second heating temperature is controlled as t2. The relationship between the total heating time t (t1 at the first heating temperature and t2 at the second heating temperature) and the billet thickness is: t = 0.4min / mm * billet thickness, i.e., t = 88min, where t1 is 46min and t2 is 42min. Afterwards, the billet is descaled and then rough rolled, including the R1 stage rolling. The rolling process consists of one pass and five passes in the R2 stage. The exit thickness of the first pass in the R1 stage is 180 mm. The reduction rate of the second pass in the R2 stage is 19%, the roll speed of the third pass is 3.4 m / s and the reduction rate is 29%, the roll speed of the fourth pass is 3.6 m / s and the reduction rate is 28%, and the roll speed of the fifth pass is 4.0 m / s and the reduction rate is 26%. At the same time, the V2 stand turns on the descaling water during the third, fourth and fifth passes of the R2 stage to reduce the surface temperature of the steel plate. The descaling water outlet pressure of the third, fourth and fifth passes is 20 MPa. The target exit temperature of the roughing mill is 970℃, and an intermediate billet with a thickness of 42 mm is obtained.

[0052] The chemical composition of the continuous casting billet without added Mo and Ni, by mass percentage, includes: C: 0.05%, Si: 0.16%, Mn: 1.50%, P: 0.008%, S: 0.0010%, Alt: 0.020%, Nb: 0.050%, Ti: 0.010%, with the remainder being iron and unavoidable impurities;

[0053] 2) The intermediate billet after rough rolling is descaled and finished rolled at a strip threading speed of 2.3 m / s and a finishing rolling temperature of 830℃. Then, it is sequentially cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel with a thickness of 15.9 mm. The cooling rate of the ultra-fast cooling section is 60℃ / s, the outlet temperature of the ultra-fast cooling section is 580℃, the cooling water pressure of the ultra-fast cooling section is 8.5 MPa, the cooling rate at the laminar flow front end is 20℃ / s, and the coiling temperature is 520℃.

[0054] Example 3

[0055] This embodiment provides a method for preparing hot-rolled pipeline steel, including the following steps:

[0056] 1) A 220mm thick continuously cast billet is heated in a heating furnace to a first heating temperature of 1220℃, and the heating time at the first heating temperature is controlled as t1. Then, the billet is further heated at a second heating temperature of 1210℃, and the heating time at the second heating temperature is controlled as t2. The relationship between the total heating time t (t1 at the first heating temperature and t2 at the second heating temperature) and the billet thickness is: t = 0.6min / mm * billet thickness, i.e., t = 132min, where t1 is 74min and t2 is 58min. Afterwards, the billet is descaled and then rough rolled, including the R1 stage rolling. The rolling process consists of one pass and five passes in the R2 stage. The exit thickness of the first pass in the R1 stage is 190 mm. The reduction rate of the second pass in the R2 stage is 18%, the roll speed of the third pass is 3.2 m / s and the reduction rate is 28%, the roll speed of the fourth pass is 3.4 m / s and the reduction rate is 27%, and the roll speed of the fifth pass is 3.6 m / s and the reduction rate is 25%. At the same time, the V2 stand turns on the descaling water during the third, fourth and fifth passes of the R2 stage to reduce the surface temperature of the steel plate. The descaling water outlet pressure of the third, fourth and fifth passes is 18 MPa. The target exit temperature of the roughing mill is 1000℃, and an intermediate billet with a thickness of 48 mm is obtained.

[0057] The chemical composition of the continuously cast billet without added Mo and Ni, by mass percentage, includes: C: 0.07%, Si: 0.24%, Mn: 1.60%, P: 0.015%, S: 0.005%, Alt: 0.040%, Nb: 0.070%, Ti: 0.020%, with the remainder being iron and unavoidable impurities;

[0058] 2) The intermediate billet after rough rolling is descaled and finished rolled at a strip threading speed of 2 m / s and a finishing rolling temperature of 840℃. Then, it is sequentially cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel with a thickness of 20 mm. The cooling rate of the ultra-fast cooling section is 70℃ / s, the outlet temperature of the ultra-fast cooling section is 560℃, the cooling water pressure of the ultra-fast cooling section is 7.5 MPa, the cooling rate at the laminar flow front end is 20℃ / s, and the coiling temperature is 510℃.

[0059] Example 4

[0060] This embodiment provides a method for preparing hot-rolled pipeline steel, which differs from Embodiment 1 in that the chemical composition of the continuously cast billet without Mo and Ni additives described in step 1) includes, by mass percentage: C: 0.06%, Si: 0.19%, Mn: 1.70%, P: 0.010%, S: 0.003%, Alt: 0.030%, Nb: 0.100%, Ti: 0.03%, with the remainder being iron and unavoidable impurities.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that t is 176 min in step 1), where t1 is 96 min and t2 is 80 min.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that descaling water is turned on during the first, second, and fourth passes of the R2 stage in step 1).

[0065] Comparative Example 3

[0066] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that the reduction rate of the third pass in the R2 stage in step 1) is 24%, the reduction rate of the fourth pass is 23%, and the reduction rate of the fifth pass is 22%, and the thickness of the intermediate billet after rough rolling is controlled to be 58 mm.

[0067] Comparative Example 4

[0068] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that the rolling speed of the third pass in step 1) of the R2 stage is 2.5 m / s, the rolling speed of the fourth pass is 2.7 m / s, and the rolling speed of the fifth pass is 3.0 m / s.

[0069] Comparative Example 5

[0070] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that the cooling rate of the ultra-fast cooling section in step 1) is 40°C / s.

[0071] Comparative Example 6

[0072] This comparative example provides a method for preparing hot-rolled pipeline steel, which differs from Example 1 only in that laminar back-end cooling is used instead of laminar front-end cooling in step 2).

[0073] Comparative Example 7

[0074] This embodiment provides a method for preparing hot-rolled pipeline steel, including the following steps:

[0075] 1) A 220mm thick continuously cast billet is heated in a heating furnace to a first heating temperature of 1200℃, and the heating time at the first heating temperature is controlled as t1. Then, the billet is further heated at a second heating temperature of 1190℃, and the heating time at the second heating temperature is controlled as t2. The relationship between the total heating time t (t1 at the first heating temperature and t2 at the second heating temperature) and the billet thickness is: t = 0.5min / mm * billet thickness, i.e., t = 110min, where t1 is 60min and t2 is 50min. Afterwards, the billet is descaled and then rough rolled, including the R1 stage rolling. The rolling process consists of one pass and five passes in the R2 stage. The exit thickness of the first pass in the R1 stage is 170 mm. The reduction rate of the second pass in the R2 stage is 18%, the roll speed of the third pass is 2.5 m / s and the reduction rate is 24%, the roll speed of the fourth pass is 2.7 m / s and the reduction rate is 23%, and the roll speed of the fifth pass is 3.0 m / s and the reduction rate is 22%. At the same time, the V2 stand turns on the descaling water during the first, second, and fifth passes of the R2 stage to reduce the surface temperature of the steel plate. The descaling water outlet pressure of the first, second, and fifth passes is 19 MPa. The target exit temperature of the roughing mill is 985℃, and an intermediate billet with a thickness of 50 mm is obtained.

[0076] The chemical composition of the continuously cast billet without added Mo and Ni, by mass percentage, includes: C: 0.06%, Si: 0.19%, Mn: 1.55%, P: 0.010%, S: 0.003%, Alt: 0.030%, Nb: 0.060%, Ti: 0.015%, with the remainder being iron and unavoidable impurities.

[0077] 2) The intermediate billet after rough rolling is descaled and finished rolled at a strip threading speed of 1.8 m / s and a finishing rolling temperature of 820℃. Then, it is sequentially cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel with a thickness of 17.5 mm. The cooling rate of the ultra-fast cooling section is 50℃ / s, the outlet temperature of the ultra-fast cooling section is 590℃, the cooling water pressure of the ultra-fast cooling section is 8 MPa, the cooling rate of the laminar flow front end is 25℃ / s, and the coiling temperature is 540℃.

[0078] Comparative Example 8

[0079] This embodiment provides a method for preparing hot-rolled pipeline steel, including the following steps:

[0080] 1) A 220mm thick continuously cast billet is heated in a heating furnace to a first heating temperature of 1200℃, and the heating time at the first heating temperature is controlled as t1. Then, the billet is further heated at a second heating temperature of 1190℃, and the heating time at the second heating temperature is controlled as t2. The relationship between the total heating time t (t1 at the first heating temperature and t2 at the second heating temperature) and the billet thickness is: t = 0.5min / mm * billet thickness, i.e., t = 110min, where t1 is 60min and t2 is 50min. Afterwards, the billet is descaled and then rough rolled, including the R1 stage rolling. The rolling process consists of one pass and five passes in the R2 stage. The exit thickness of the first pass in the R1 stage is 170 mm. The reduction rate of the second pass in the R2 stage is 18%, the roll speed of the third pass is 3.6 m / s and the reduction rate is 30%, the roll speed of the fourth pass is 3.8 m / s and the reduction rate is 28%, and the roll speed of the fifth pass is 4.2 m / s and the reduction rate is 27%. At the same time, the V2 stand turns on the descaling water during the third, fourth and fifth passes of the R2 stage to reduce the surface temperature of the steel plate. The descaling water outlet pressure of the third, fourth and fifth passes is 19 MPa. The target exit temperature of the roughing mill is 985℃, and an intermediate billet with a thickness of 46 mm is obtained.

[0081] The chemical composition of the continuous casting billet without added Mo and Ni, by mass percentage, includes: C: 0.06%, Si: 0.19%, Mn: 1.55%, P: 0.010%, S: 0.003%, Alt: 0.030%, Nb: 0.060%, Ti: 0.015%, with the remainder being iron and unavoidable impurities;

[0082] 2) The intermediate billet after rough rolling is descaled and finished rolled at a strip threading speed of 2.5 m / s and a finishing rolling temperature of 820℃. Then, it is sequentially cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel with a thickness of 17.5 mm. The cooling rate of the ultra-fast cooling section is 45℃ / s, the outlet temperature of the ultra-fast cooling section is 630℃, the cooling water pressure of the ultra-fast cooling section is 8 MPa, the cooling rate at the laminar flow front end is 25℃ / s, and the coiling temperature is 550℃.

[0083] Test case

[0084] Metallographic images of a quarter section of the cross-section of the hot-rolled pipeline steel obtained in Example 1 were obtained by metallographic analysis (e.g., Figure 1 (as shown) and metallographic diagram of the core section of the cross section (as shown) Figure 2 As shown in the figure, the microstructure of pipeline steel includes acicular ferrite, polygonal ferrite and carbides.

[0085] The hot-rolled pipeline steels obtained in Examples 1-4 and Comparative Examples 1-8 were tested for tensile properties (including yield strength, tensile strength, and elongation) and impact properties (impact energy at 0°C) at room temperature according to ASTM A370 method, and for drop weight properties at -5°C according to API RP 5L3 method. The test results are shown in Table 1. The impact energy, elongation, and drop weight properties of Examples 1-4 of the present invention are significantly better than those of Comparative Examples 1-8.

[0086] Table 1

[0087]

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing hot-rolled pipeline steel, characterized in that, Includes the following steps: 1) Heat the continuous casting billet to the first heating temperature and control the heating time of the continuous casting billet at the first heating temperature to t1. Then, continue to heat the continuous casting billet at the second heating temperature and control the heating time of the continuous casting billet at the second heating temperature to t2. After that, perform rough rolling on the continuous casting billet to obtain an intermediate billet. The relationship between the total time t (heating time t1 at the first heating temperature and heating time t2 at the second heating temperature) and the thickness of the continuously cast billet is: t = β * thickness of the continuously cast billet, where β is an adjustment coefficient with a value range of 0.4-0.6 min / mm, t is in min, and the thickness of the continuously cast billet is in mm. The roughing process includes at least one pass in the R1 stage and at least five passes in the R2 stage. During the third, fourth, and fifth passes in the R2 stage, descaling water is turned on, and the roll speeds for the third, fourth, and fifth passes are 3.2-4.2 m / s. The reduction rate for each pass in the third, fourth, and fifth passes is 25-30%, and the thickness of the intermediate billet obtained after roughing is controlled to be 42-48 mm. 2) The intermediate billet obtained after rough rolling in step 1) is fine rolled, cooled in an ultra-fast cooling section, cooled at the laminar flow front end, and coiled to obtain the hot-rolled pipeline steel. The cooling rate of the ultra-fast cooling section is 50-70℃ / s.

2. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, The chemical composition of the continuously cast billet described in step 1) does not include Mo and / or Ni.

3. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, The chemical composition of the continuously cast billet described in step 1), by mass percentage, includes: C: 0.05-0.07%, Si: 0.16-0.24%, Mn: 1.50-1.60%, P: ≤0.015%, S: ≤0.0050%, Alt: 0.020-0.040%, Nb: 0.05-0.07%, Ti: 0.01-0.02%, with the remainder being iron and unavoidable impurities.

4. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, In step 1), the first heating temperature is higher than the second heating temperature; In step 1), the first heating temperature is 1180-1220℃, and the second heating temperature is 1170-1210℃; The ratio of t1 to t2 is (1.09-1.3):

1.

5. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, The thickness of the continuously cast billet mentioned in step 1) is 200-250 mm; The target exit temperature of the roughing mill mentioned in step 1) is 970-1000℃; In step 1), the descaling water outlet pressure during the third, fourth, and fifth passes of the R2 stage rolling is 18-20 MPa.

6. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, The roughing process described in step 1) includes one pass of rolling in the R1 stage and five passes of rolling in the R2 stage; After the R1 stage rolling in step 1), the exit thickness of the continuously cast billet is 170-190 mm; The second pass reduction rate in the R2 stage rolling is 17-19%; Optionally, the rough rolling step described in step 1) may include a descaling step. Optionally, the rough rolling step described in step 1) may be followed by a descaling step.

7. The method for preparing hot-rolled pipeline steel according to claim 1, characterized in that, In step 2), the threading speed of the finishing mill is 2.0-2.5 m / s, and the final rolling temperature is 820-840℃. The winding temperature mentioned in step 2) is 510-540℃; The outlet temperature of the ultra-fast cooling section mentioned in step 2) is 560-590℃, and the cooling water pressure of the ultra-fast cooling section is 7.5-8.5MPa; The laminar flow front-end cooling rate is 20-30℃ / s; The thickness of the hot-rolled pipeline steel is 15-20mm.

8. A hot-rolled pipeline steel, characterized in that, It is prepared by the method for preparing hot-rolled pipeline steel according to any one of claims 1-7.

9. The hot-rolled pipeline steel according to claim 8, characterized in that, The yield strength R of the hot-rolled pipeline steel t0.5 The tensile strength (Rm) is 520-570 MPa, and the elongation (A) is 620-680 MPa. 50.8 ≥37%, 0℃ impact energy KV2 is 320-450J, -5℃ drop hammer toughness shear area ratio SA single value ≥93%, -5℃ drop hammer toughness shear area ratio SA average value ≥94.3%.

10. The hot-rolled pipeline steel according to claim 9, characterized in that, The yield strength R of the hot-rolled pipeline steel t0.5 The tensile strength Rm is 620-635 MPa, and the elongation A is 520-535 MPa. 50.8 ≥39%, 0℃ impact energy KV2 is 390-450J, -5℃ drop hammer toughness shear area ratio SA single value ≥98%, -5℃ drop hammer toughness shear area ratio SA average value ≥99%.

11. The application of the hot-rolled pipeline steel according to claim 9 or 10 in the preparation of transportation pipelines.

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