Steel plate for 555 MPa-grade low-stress pipeline and production method of steel plate

Abstract

The invention discloses a steel plate for a 555 MPa-grade low-stress pipeline and a production method of the steel plate. The Rt0.5 of the steel plate is larger than or equal to 555 MPa, the A50 is larger than or equal to 20%, the residual stress is smaller than or equal to 130 MPa, and the residual stress fluctuation of the whole plate is smaller than or equal to 50 MPa. The method comprises the following steps: heating: soaking TNbC + (50-125) DEG C for more than or equal to 25 minutes; in the first-stage rolling, the initial rolling temperature is Tnr + (10-100) DEG C, and the final rolling temperature is Tnr + (5-50) DEG C; the thickness of an intermediate billet is 2.5-3.5 times of the target thickness of the steel plate, the final cooling temperature is Ar3 + (0-20) DEG C, and the cooling time is longer than or equal to 50 s; in the second-stage rolling, the initial rolling is Ar < 3 + > (-10 <-10 >) DEG C, and the final rolling is Ar < 3-> (50-30) DEG C; water cooling: the inlet water is Ar3-(80-60) DEG C, the outlet water is Bs-(220-180) DEG C, and the cooling speed is 10-25 DEG C / s; and after the temperature reaches the room temperature, shot blasting or shot blasting is conducted.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel material preparation, and relates to a 555MPa-grade low-stress pipeline steel plate and a production method thereof. BACKGROUND

[0002] Pipeline steel plays an irreplaceable role in the energy transportation industry such as petroleum and natural gas. At present, high-strength pipeline steel is used in high-pressure pipelines, which can reduce the thickness and weight of the steel pipe, as well as the workload of transportation and welding, thereby greatly reducing the cost of pipeline construction. However, with the increase of the strength of the pipeline steel, the residual stress in the steel plate increases significantly, thereby affecting the safe operation of the hydrogen transmission pipeline.

[0003] Specifically, in the pipe-making process, the pipeline steel plate generally needs to go through JCO forming, welding and other processes to make a steel pipe. Residual stress can cause uneven deformation of the steel plate during pipe forming, thereby affecting the roundness and dimensional accuracy of the steel pipe. After welding, the existence of residual stress can easily cause the steel pipe end to have a bent mouth phenomenon, which not only makes the roundness of the steel pipe end locally exceed the standard range, causing misalignment during girth welding butt joint at the construction site, but also generates stress concentration at the bent mouth of the steel pipe, thereby reducing the service life of the steel pipe.

[0004] Therefore, the problem of residual stress limits the strength grade of the pipeline steel, and how to balance the mechanical strength and residual stress is also one of the difficult problems to be solved in the field of pipeline steel manufacturing. SUMMARY

[0005] The present application aims to provide a 555MPa-grade low-stress pipeline steel plate and a production method thereof.

[0006] To achieve the above-mentioned application purpose, an embodiment of the present application provides a 555MPa-grade low-stress pipeline steel plate. The chemical composition of the steel plate includes, in terms of mass percentage: C 0.03~0.07%, Si 0.09~0.21%, Mn 1.61~1.69%, Cr 0.11~0.29%, Ni 0.11~0.29%, Mo 0.06~0.18%, Cu 0.11~0.29%, Nb 0.054~0.066%, Ti 0.009~0.021%, Al 0.021~0.049%, P≤0.0150%, S≤0.0040%, O≤0.0025%, N≤0.0048%, H≤0.0002%, and the rest is iron and unavoidable impurities. The thickness d of the steel plate is≥6mm, R m is 625~825MPa, R t0.5 ≥555MPa, A 50 ≥20%, R t0.5 / Rm ≤0.93; The residual stress of the steel plate is ≤130 MPa, and the difference in residual stress between any two of the head, the middle, the tail, the upper portion, and the lower portion is ≤50 MPa.

[0007] As a further improvement of an embodiment, the chemical composition of the steel plate further satisfies, in terms of mass percentage: CEV is 0.354-0.491, and Pcm is 0.135-0.212. CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15; Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 is 0.091-0.294. In the formula, each element symbol represents the mass percentage of the corresponding element.

[0008] As a further improvement of an embodiment, the chemical composition of the steel plate includes, in terms of mass percentage: P 0.0050-0.0100%, S 0.0005-0.0020%, N 0.0022-0.0048%, O 0.0011-0.0025%, and H 0.00005-0.00018%.

[0009] As a further improvement of an embodiment, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite. In the formula, the volume fraction of the polygonal ferrite is 0-5%, the volume fraction of the acicular ferrite is 30-45%, the volume fraction of the tempered bainite is 55-65%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite, and the tempered bainite is 100%.

[0010] As a further improvement of an embodiment, the average grain size of the steel plate is 3-9 μm.

[0011] As a further improvement of an embodiment, the steel plate satisfies any one or several of the following: 0℃ impact energy KV2≥360 J, -20℃ impact energy KV2≥350 J, -40℃ impact energy KV2≥320 J, and -60℃ impact energy KV2≥300 J.

[0012] As a further improvement of an embodiment, the steel plate has a ductile-brittle transition temperature T t50%US ≤-100℃.

[0013] As a further improvement of an embodiment, the steel plate satisfies any one or several of the following: a DWTT drop hammer shearing area fraction of 100% at -10℃, a DWTT drop hammer shearing area fraction ≥ 100% at -20℃, a DWTT drop hammer shearing area fraction ≥ 95% at -30℃, a CTOD crack tip opening displacement ≥ 1.2mm at 0℃, a CTOD crack tip opening displacement ≥ 1.0mm at -20℃, a CTOD crack tip opening displacement ≥ 0.6mm at -40℃.

[0014] As a further improvement of an embodiment, the steel plate has a hardness ≤ 250HV10.

[0015] As a further improvement of an embodiment, the steel plate has a unevenness ≤ 3mm / m.

[0016] Compared with the prior art, the beneficial effects of an embodiment of the present application are that the chemical composition of the steel plate adopts a low alloy design, and on this basis, the problem of being difficult to balance the mechanical properties and residual stress in the prior art is solved, so that the steel plate maintains excellent mechanical properties, and has the advantages of low and uniform residual stress, for example, the steel plate reaches 555MPa grade, and the residual stress is ≤ 130MPa, and the residual stress fluctuation of the whole plate is ≤ 50MPa, so that the steel plate has good processability, safety and service life in the pipeline application scenario.

[0017] To achieve the above-mentioned purposes, an embodiment of the present application provides a production method of a 555MPa grade low stress pipeline steel plate. The production method comprises the following steps in sequence, a slab heating process: the soaking temperature is T NbC +(50~125)℃, and the soaking time is ≥ 25min; a hot rolling process: having a first stage rolling, an intermediate slab cooling and a second stage rolling; in the first stage rolling, the starting rolling temperature is T nr +(10~100)℃, and the final rolling temperature is T nr +(5~50)℃; in the intermediate slab cooling, the intermediate slab thickness is 2.5~3.5 times of the target thickness of the steel plate, and the final cooling temperature is A r3 +(0~20)℃, and the cooling time is ≥ 50s; in the second stage rolling, the starting rolling temperature is A r3 +(-10~10)℃, and the rolling temperature of the last pass is A r3 -(50~30)℃; a controlled water cooling process: the water inlet temperature is A r3 -(80~60)℃, the water outlet temperature is B s -(220~180)℃, and the cooling speed is 10~25℃ / s; an air cooling process: the steel plate is air cooled; The surface treatment process is carried out on the steel plate by means of shot blasting or shot peening after the steel plate is cooled to room temperature. wherein, T NbC , T nr , A r3 , B s are respectively calculated by the following formulas, and the element symbols in each formula represent the mass percentage of the corresponding element in the slab; T NbC =7700 / (3.18-lg(Nb×C 0.87 ))-273.15; T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al; A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo; B s =550-160C-10Mn-10Cr-10Ni-5Mo.

[0018] Preferably, in the surface treatment process: the thickness d of the steel plate is 6-20 mm, and the shot blasting or shot peening uses a mixture of shot with a diameter of 0.5 mm and shot with a diameter of 0.7 mm in a mass ratio of (7-8):5; or, the thickness d of the steel plate is 20-50 mm, and the shot blasting or shot peening uses a mixture of shot with a diameter of 0.7 mm and shot with a diameter of 1.0 mm in a mass ratio of (9-11):5.

[0019] Preferably, in the surface treatment process: the time t of shot blasting or shot peening and the thickness d of the steel plate satisfy t=k×d+C, the unit of t is min, k is 0.1-0.2 min / mm, and C is 5-7 min; and / or, the shot blasting or shot peening amount P and the thickness d of the steel plate satisfy P=k1×d+C1, the unit of P is kg / min, k1 is 0.4-0.6 kg / (min·mm), and C1 is 160-200 kg / min; and / or, the speed S of shot blasting or shot peening and the thickness d of the steel plate satisfy S=k2×d+C2, the unit of S is m / s, k2 is 0.1-0.3 m / (s·mm), and C2 is 65-75 m / s.

[0020] Preferably, the production method further comprises, after the surface treatment process, tempering heat treatment process: heating rate 8~15℃ / min, tempering temperature T is B s +(-105~55)℃, and the tempering holding time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, the unit of t1 is min.

[0021] Preferably, in the tempering heat treatment process: the thickness d of the steel plate is 6~20mm, and the tempering temperature T is B s +(-65~55)℃; Alternatively, the thickness d of the steel plate is 20~50mm, and the tempering temperature T is B s +(-85~35)℃.

[0022] Preferably, the production method further comprises, after the tempering heat treatment process, post-tempering stacking process: stacking temperature B s -(210~110)℃, cooling rate 10~30℃ / h, and unstacking temperature≤B s -450℃.

[0023] Preferably, in the air cooling process: the air cooling is performed on the upper cooling bed, and the upper cooling bed temperature is B s -(270~230)℃, and the lower cooling bed temperature is not more than M s -210℃; M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo, unit: ℃, the element symbols in the formula represent the mass percentage of the corresponding elements in the casting blank.

[0024] Preferably, in the air cooling process: the lower cooling bed temperature is M s -(260~210)℃; the production method further comprises, after the air cooling process, stacking process: n groups of steel plates are stacked in turn from bottom to top, and the top layer is covered with auxiliary steel plates, each group of steel plates is composed of an auxiliary steel plate at the bottom and a steel plate at the top, and n is a positive integer; the stacking temperature of the auxiliary steel plate is M s -(110~10)℃, and the unstacking temperature of the steel plate is not more than M s -(410~310)℃.

[0025] Preferably, the production method further comprises one, two or more of the following four processes, preheating straightening process between the hot rolling process and the controlled water cooling process: at least one pass of preheating straightening is performed, the straightening speed is 0.1~1.5m / s, and the straightening temperature Ar3 -(65~45)℃, maximum reduction ≤4mm; In the hot straightening process between the water cooling and air cooling processes: 1-3 passes of preheating straightening are performed, with a straightening speed of 0.1-1.5 m / s and a straightening temperature of B. s -(230~190)℃, maximum reduction ≤4mm; In the warm straightening process between the air cooling process and the surface treatment process: 2-4 passes of warm straightening are performed, with a straightening speed of 0.1-0.5 m / s and a straightening temperature of M. s -(270~220)℃, maximum reduction ≤10mm; The cold straightening process between the warm straightening process and the surface treatment process: 1-3 passes of cold straightening are performed, with a straightening speed of 0.1-0.5 m / s and a straightening temperature of M. s -(420~360)℃, maximum reduction ≤6mm; Among them, M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo, with units in °C. The element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0026] Preferably, in the hot rolling process: During the first stage of rolling, the reduction of each pass is ≤34mm, and the reduction of the non-widening initial rolling pass is ≥24mm. During the second stage of rolling, the reduction in each pass is ≤20mm, and the reduction in the last pass is ≤3mm.

[0027] Compared with the prior art, the beneficial effects of one embodiment of this application are as follows: by controlling the homogenization temperature, homogenization time, temperature during hot rolling, temperature and cooling rate of water cooling, air cooling, and shot blasting / peening operations, not only can the performance-promoting effect of chemical components be fully utilized to ensure the excellent comprehensive performance of the steel plate, including but not limited to excellent mechanical properties and low-temperature toughness, but also the adverse effects of chemical components or production processes on residual stress can be avoided, that is, the residual stress of the steel plate can be greatly reduced and the uniformity of residual stress distribution of the steel plate can be improved. Attached Figure Description

[0028] Figure 1 This is a metallographic diagram of the steel plate of Experimental Example 4 of the present invention; Figure 2 This is a schematic diagram of the stacking process in one embodiment of the present invention. Detailed Implementation

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely in combination with the specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0030] First embodiment The present embodiment provides a steel plate for pipeline, in particular, a steel plate with high strength and low residual stress.

[0031] The chemical composition of the steel plate includes, in mass percentage, C 0.03-0.07%, Si 0.09-0.21%, Mn 1.61-1.69%, Cr 0.11-0.29%, Ni 0.11-0.29%, Mo 0.06-0.18%, Cu 0.11-0.29%, Nb 0.054-0.066%, Ti 0.009-0.021%, Al 0.021-0.049%, P≤0.0150%, S≤0.0040%, O≤0.0025%, N≤0.0048%, H≤0.0002%, and the rest is iron and inevitable impurities.

[0032] The main effects of each element and the selection of the amount thereof will be described in detail as follows.

[0033] C: Carbon is the most economical strengthening element in steel, which has solid solution strengthening effect, and forms carbide with niobium, titanium, chromium, molybdenum, etc., which has precipitation strengthening effect; the increase of carbon content has obvious effect on improving the strength and hardness of the steel plate, but too high carbon will lead to poor low-temperature toughness and ductility, and reduce the low-temperature drop hammer performance of the steel plate; the formation of carbide and martensite will induce the increase of residual stress. In the present application, the carbon content is controlled to be 0.03-0.07%.

[0034] Preferably, the carbon content can be controlled to be any one of 0.03%, 0.04%, 0.05%, 0.06% and 0.07%.

[0035] Si: Silicon has solid solution strengthening effect in steel, but will increase the grain boundary segregation of phosphorus, sulfur and other elements, reduce the low-temperature toughness and plasticity, and too much silicon is easy to produce Fe2SiO4 on the surface of continuous casting billet, which is not conducive to the control of the surface quality of the steel plate. In an embodiment, the silicon content is controlled to be 0.09-0.21%.

[0036] Preferably, the silicon content can be controlled to be any one of 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20% and 0.21%.

[0037] Mn: Manganese in steel plays a role of solid solution strengthening, improving strength and hardness. Too much manganese will cause center segregation of the casting blank, which is not conducive to toughness. Furthermore, increasing the content of manganese will also cause the level of banded structure to increase, and the higher the level of banded structure, the more uneven the distribution of the structure. In addition, manganese is easy to form manganese sulfide inclusions. Center segregation, banded structure, inclusions and the like will cause the increase of residual stress. In an embodiment, the content of manganese is controlled to be 1.61-1.69%.

[0038] Preferably, the content of manganese can be specifically controlled to be any one of 1.61%, 1.63%, 1.64%, 1.65%, 1.67%, 1.69%.

[0039] Cr: Chromium in steel plays a role of solid solution strengthening; and chromium can form stable carbides and improve the stability of martensite, so that a greater residual stress will be generated during rapid cooling. The higher the content of chromium, the more complex the distribution of residual stress after cooling. In the present application, the content of chromium is controlled to be 0.11-0.29%.

[0040] Preferably, the content of chromium can be specifically controlled to be any one of 0.11%, 0.12%, 0.15%, 0.20%, 0.22%, 0.25%, 0.27%, 0.29%.

[0041] Ni: Nickel in steel plays a role of solid solution strengthening, improving the strength of steel and not significantly increasing the hardness of steel. Nickel will expand the austenite phase region, thereby reducing residual stress; and nickel can also improve the toughness of steel and reduce stress concentration. In the present application, the content of nickel is controlled to be 0.11-0.29%.

[0042] Preferably, the content of nickel can be specifically controlled to be any one of 0.11%, 0.12%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.27%, 0.29%.

[0043] Mo: Molybdenum can significantly improve the hardenability of steel, improve strength and toughness, and also play a role in refining grains and improving corrosion resistance. Molybdenum can improve the tempering stability of steel and reduce the increase of residual stress. In the present application, the content of molybdenum is controlled to be 0.06-0.18%.

[0044] Preferably, the content of molybdenum can be specifically controlled to be any one of 0.06%, 0.08%, 0.12%, 0.14%, 0.16%, 0.18%.

[0045] Cu: Copper can promote the precipitation of niobium and make up for the loss of strength caused by the decrease of carbon content, and adding a certain amount of nickel at the same time can effectively inhibit surface cracks. In an embodiment, the content of copper in the present application is controlled to be 0.11-0.29%.

[0046] Preferably, the copper content can be controlled at any one of 0.11%, 0.13%, 0.15%, 0.17%, 0.19%, 0.21%, 0.23%, 0.25%, 0.29% in particular.

[0047] Nb: Niobium is an important grain refining element in steel. In the process of hot rolling, niobium strongly inhibits austenite recrystallization and its precipitation in austenite, pins austenite grain boundaries, and refines recrystallized grains. During the cooling process, the dissolved niobium can continue to precipitate in the form of niobium carbonitride, significantly refining the structure of the material after phase transition, further improving the strength and toughness of the steel. Niobium can reduce residual stress through grain refinement and precipitation strengthening. In the present application, the niobium content is controlled at 0.054-0.066%.

[0048] Preferably, the niobium content can be controlled at any one of 0.054%, 0.056%, 0.060%, 0.062%, 0.064%, 0.066% in particular.

[0049] Ti: Titanium is a nitrogen-fixing element in steel, which can form a dispersed distribution of carbonitride, inhibit austenite grain coarsening during slab heating and hot rolling, and refine grains, thereby reducing residual stress. However, when the titanium content is high, coarse carbonitride precipitates can form in the center of the slab, affecting the low-temperature toughness of the steel plate. And large particle TiN can easily cause stress concentration. In the present application, the titanium content is controlled at 0.009-0.021%.

[0050] Preferably, the titanium content can be controlled at any one of 0.009%, 0.010%, 0.014%, 0.015%, 0.016%, 0.018%, 0.020%, 0.021% in particular.

[0051] Al: Aluminum is a deoxidizing element in steel. Excessive aluminum can increase Al2O3 inclusions in steel, affecting the low-temperature toughness of the steel, and coarse inclusions can cause discontinuous structure and stress concentration. In the present application, the aluminum content is controlled at 0.021-0.049%.

[0052] Preferably, the aluminum content can be controlled at any one of 0.021%, 0.025%, 0.028%, 0.030%, 0.033%, 0.035%, 0.038%, 0.040%, 0.042%, 0.045%, 0.047%, 0.049% in particular.

[0053] P, S, N, O, H: All are impurity elements in steel, which can cause deterioration of the performance of the steel plate, including but not limited to increasing residual stress. In the present application, P≤0.0150%, S≤0.0040%, O≤0.0025%, N≤0.0048%, H≤0.0002%.

[0054] Preferably, the content of P is controlled to be 0.0120% or less, 0.0100% or less, and can also be controlled to be 0.0050% or more.

[0055] Preferably, the content of S is controlled to be 0.0030% or less, 0.0020% or less, and can also be controlled to be 0.0005% or more.

[0056] Preferably, the content of N is controlled to be 0.0022% or more.

[0057] Preferably, the content of O is controlled to be 0.0011% or more.

[0058] Preferably, the content of H is controlled to be 0.00018% or less, and can also be controlled to be 0.00005% or more.

[0059] Further, the chemical composition of the steel plate also satisfies any one or both of the following ① and ② in terms of mass percentage: ① CEV is 0.223-0.571, and ② Pcm is 0.091-0.294.

[0060] Wherein, the CEV and Pcm can be calculated by the following two formulas respectively: CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15; Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 is 0.091-0.294.

[0061] Here, in the formulas of CEV and Pcm, each element symbol represents the mass percentage of the corresponding element. For example, if the content of C element in the steel plate is 0.03%, then "C" in the formula represents the mass percentage of 0.03.

[0062] In this application, the thickness d of the steel plate is ≥6mm.

[0063] The steel plate has excellent mechanical properties: R m is 625-825MPa, R t0.5 ≥555MPa, A 50 ≥20%, R t0.5 / R m ≤0.93.

[0064] In this application, the steel material can be sampled and tested for mechanical properties in accordance with GB / T 2975-2018 “Steel and Steel Products Mechanical Property Test Sampling Position and Sample Preparation” and GB / T 228.1-2021 “Metallic Materials Tensile Test Part 1: Room Temperature Test Method”.

[0065] In addition, the steel plate has the advantage of low residual stress.

[0066] Specifically, the residual stress of the steel plate is ≤130 MPa.

[0067] More preferably, the residual stress of the steel plate is not more than 120 MPa, or not more than 110 MPa, or not more than 90 MPa, or not more than 70 MPa, or not more than 60 MPa, or even 50 MPa.

[0068] In addition, the steel plate has small residual stress fluctuation and uniform distribution.

[0069] For example, the residual stress difference between any two of the head, middle, tail, upper, and lower portions is ≤50 MPa.

[0070] Preferably, the residual stress difference is not more than 40 MPa, or not more than 35 MPa, or not more than 30 MPa, or even not more than 25 MPa.

[0071] In the present application, the steel material can be sampled and tested for residual stress in accordance with GB / T 31310-2014 “Metallic Materials - Determination of Residual Stresses - Hole Drilling Strain Method”.

[0072] In addition, the steel plate has excellent low-temperature toughness, and satisfies any one or any combination of the following: 0 ℃ impact energy KV2≥360 J, -20 ℃ impact energy KV2≥350 J, -40 ℃ impact energy KV2≥320 J, -60 ℃ impact energy KV2≥300 J, ductile-brittle transition temperature T t50%US ≤-100 ℃, -10 ℃ DWTT drop hammer shear area fraction 100%, -20 ℃ DWTT drop hammer shear area fraction ≥100%, -30 ℃ DWTT drop hammer shear area fraction ≥95%, 0 ℃ CTOD crack tip opening displacement ≥1.2 mm, -20 ℃ CTOD crack tip opening displacement ≥1.0 mm, -40 ℃ CTOD crack tip opening displacement ≥0.6 mm.

[0073] In the present application, the steel material can be sampled and tested for low-temperature performance in accordance with GB / T 2975-2018 “Steel and Steel Products - Location and Preparation of Samples for Mechanical Testing” and GB / T 229-2020 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0074] The hardness of the steel plate is ≤250 HV10.

[0075] In addition, the steel plate has excellent flatness, and the unevenness is ≤3 mm / m.

[0076] Further, the microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite.

[0077] The volume fraction of the polygonal ferrite is 0-5%, the volume fraction of the acicular ferrite is 30-45%, the volume fraction of the tempered bainite is 55-65%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

[0078] The average grain size of the steel plate is 3-9 μm.

[0079] Compared with the prior art, the present embodiment has at least the following beneficial effects: the chemical composition of the steel plate adopts a low-alloy design, and on this basis, the problem of being difficult to balance the mechanical properties and the residual stress in the prior art is solved, so that the steel plate maintains excellent mechanical properties, and has the advantages of low and uniform residual stress, for example, the steel plate reaches the level of 555 MPa, and the residual stress is ≤130 MPa, and the residual stress fluctuation of the whole plate is ≤50 MPa, so that the steel plate has good machinability, safety and service life in the pipeline application scenario.

[0080] The basic situation of the present embodiment is introduced above. Several test examples are provided below, of course, these test examples are only a part of the numerous changed embodiments of the present application, not all.

[0081] As shown in Table 1, the chemical composition of the steel plate of several test examples provided. Among them, "-" in the table indicates that the corresponding element is not added.

[0082] [Table 1]

[0083] The microstructure and performance of the steel plate of each test example were detected, and the results are shown in Tables 2 and 3. In addition, the metallographic structure of test example 4 is shown in Figure 1 .

[0084] In addition, the steel plate of all test examples: 0℃ impact energy KV2≥360J, -20℃ impact energy KV2≥350J, -40℃ impact energy KV2≥320J, -60℃ impact energy KV2≥300J, ductile-brittle transition temperature T t50%US ≤-100℃, -10℃ DWTT drop hammer shear area fraction 100%, -20℃ DWTT drop hammer shear area fraction ≥100%, -30℃ DWTT drop hammer shear area fraction ≥95%, 0℃ CTOD crack tip opening displacement ≥1.2mm, -20℃ CTOD crack tip opening displacement ≥1.0mm, -40℃ CTOD crack tip opening displacement ≥0.6mm.

[0085] [Table 2]

[0086] [Table 2]

[0087] Second embodiment The present embodiment provides a production method of a steel plate for pipelines.

[0088] The production method can be used to prepare a steel plate with low residual stress and excellent mechanical properties, such as a 555 MPa grade steel plate for pipelines.

[0089] The production method can also be used to prepare the steel plate provided in the first embodiment.

[0090] In the present embodiment, the production method comprises, in sequence, a slab heating process, a hot rolling process, a controlled water cooling process, an air cooling process, and a surface treatment process, to process the slab into a steel plate.

[0091] Each process will be described in detail below in sequence.

[0092] <Slab heating process> In this process, the slab is sent into a heating furnace for heating.

[0093] The slab can be a continuous casting slab or a mold casting slab, which is not limited in the present application.

[0094] The thickness of the slab is preferably above 200 mm, such as 220-320 mm.

[0095] The chemical composition of the slab is consistent with that of the prepared steel plate. For example, when preparing the steel plate provided in the first embodiment, the chemical composition of the slab is also the same as that of the steel plate in the first embodiment.

[0096] In this process, the soaking temperature is T NbC +(50-125)℃, and the soaking duration is ≥25 min.

[0097] T NbC is the onset precipitation temperature of NbC, which is calculated by the formula T NbC =7700 / (3.18-lg(Nb×C 0.87 ))-273.15, wherein the element symbols represent the mass percentage of the corresponding elements in the slab.

[0098] In this way, by controlling the soaking temperature and the soaking duration, on the one hand, the austenite grains can be prevented from growing too much, preparing for the subsequent precipitation in the hot rolling process, thereby ensuring the mechanical properties and low temperature toughness of the final steel plate, and on the other hand, more importantly, the precipitates of Nb can be completely dissolved, thereby reducing the residual stress while ensuring the mechanical properties.

[0099] Preferably, the soaking temperature is T NbC +50℃, and TNbC +55℃, T NbC +60℃, T NbC +70℃, T NbC +80℃, T NbC +90℃, T NbC +100℃, T NbC +110℃, T NbC +115℃, T NbC +120℃, T NbC +125℃.

[0100] Preferably, the process can adopt segmented heating, for example including heat recovery, preheating, first heating, second heating and soaking. But not limited thereto.

[0101] Wherein, the heat recovery temperature ≤800℃, the preheating temperature ≤900℃, the first heating temperature 970~1030℃, the second heating temperature 1070~1130℃, and the total heating time 0.019~0.023h / mm slab thickness. In this way, by segmented heating and controlling the temperature of each segment, the slab can be slowly and uniformly heated, reducing the temperature difference of the head, middle, tail, surface and center of the slab, and further avoiding cracking caused by thermal stress.

[0102] Further, the slab entering the furnace temperature ≥M S -350℃.

[0103] M S is the start temperature of austenite to martensite phase transition, calculated by the formula M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo, unit ℃, and the element symbol in the formula represents the mass percentage of the corresponding element in the slab.

[0104] <Hot rolling process> In this process, the slab is rolled into a steel plate with a thickness d not less than 6mm through first stage rolling, intermediate slab cooling and second stage rolling.

[0105] In the first stage rolling, the opening temperature T nr +(10~100)℃, and the finishing temperature T nr +(5~50)℃.

[0106] Wherein, T nr is the minimum temperature of austenite recrystallization, calculated by the formula T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al, and the element symbol in each formula represents the mass percentage of the corresponding element in the slab.

[0107] Through the first stage rolling, the thickness of the intermediate blank is 2.5-3.5 times of the target thickness of the steel plate.

[0108] Thus, rolling in the higher temperature range can reduce the rolling deformation resistance and increase the rolling reduction, which is beneficial to the penetration of deformation into the core of the blank and the improvement of the core segregation, porosity and banded structure and other defects; secondly, it ensures that the blank can be rolled in the recrystallization zone to avoid mixed crystals, and at the same time, the precipitation of Nb compounds prevents the growth of recrystallized grains, thereby refining the recrystallized grains and ensuring the performance of the final steel plate.

[0109] In this process, the target thickness of the steel plate is the thickness d of the final steel plate.

[0110] Preferably, the opening rolling temperature in the first stage rolling is T nr +10℃, T nr +20℃, T nr +30℃, T nr +40℃, T nr +50℃, T nr +60℃, T nr +70℃, T nr +80℃, T nr +90℃, T nr +100℃.

[0111] Preferably, the finishing rolling temperature in the first stage rolling is T nr +5℃, T nr +10℃, T nr +15℃, T nr +20℃, T nr +25℃, T nr +30℃, T nr +35℃, T nr +40℃, T nr +45℃, T nr +50℃.

[0112] Preferably, the reduction of each pass in the first stage rolling is ≤34mm, and the reduction of the initial rolling pass in the non-expanding passes is ≥24mm.

[0113] That is, the first stage rolling includes a plurality of passes, one part of which is the expanding pass and the other part is the non-expanding pass. The reduction of each pass is not more than 34mm; and the reduction of the initial rolling pass (i.e. the first non-expanding pass) in the plurality of non-expanding passes is ≥24mm.

[0114] Thus, it can not only fully break up the as-cast structure to obtain refined recrystallized grains, which lays a foundation for subsequent excellent mechanical properties, but also can avoid the rapid increase of internal stress.

[0115] Further, when the intermediate billet is cooled, the intermediate billet is cooled to a finish cooling temperature A r3 + (0~20) ℃, and the cooling time is ≥ 50 s.

[0116] Wherein, A r3 is the temperature at which austenite (γ-Fe) begins to precipitate ferrite (α-Fe) when cooled, calculated using the formula A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo, wherein the element symbols in the formula represent the mass percentage of the corresponding element in the cast billet.

[0117] In this way, by controlling the finish cooling temperature and the cooling time, not only can the production efficiency be ensured, but also the recrystallized grains can be prevented from growing rapidly during the temperature holding process, thereby avoiding deterioration of the low-temperature toughness, and more importantly, the recrystallization can be fully achieved, and a certain internal stress can be released at high temperature.

[0118] Preferably, the finish cooling temperature is any value in the range of A r3 , A r3 +10 ℃, or A r3 +20 ℃.

[0119] Preferably, the cooling time is ≥ 70 s.

[0120] More preferably, the intermediate billet can be cooled by air cooling.

[0121] Next, during the second stage rolling, the starting rolling temperature A r3 + (-10~10) ℃, and the finishing rolling temperature A r3 - (50~30) ℃.

[0122] In this way, not only can the microstructure be controlled, but also the comprehensive performance of the steel plate, including the mechanical properties and the low-temperature toughness, can be improved.

[0123] Preferably, during the second stage rolling, the reduction amount of each pass is ≤ 20 mm, and the reduction amount of the finishing pass is ≤ 3 mm.

[0124] In this way, by means of the small reduction amount deformation, fine microstructure can be obtained during the subsequent cooling process, thereby improving the low-temperature toughness of the steel plate, and in addition, the plate shape can be improved, the temperature difference between the plates can be reduced, and the residual stress can be further reduced.

[0125] Preferably, during the second stage rolling, the starting rolling temperature is any value in the range of A r3 -10 ℃, A r3 , or A r3 +10 ℃.

[0126] Preferably, the rolling temperature of the last pass is A r3 -50℃, A r3 -40℃, A r3 -30℃.

[0127] <Controlled water cooling process> In this process, the hot-rolled steel plate is water-cooled.

[0128] In this process, the water inlet temperature A r3 -(80~60)℃, the water outlet temperature B s -(220~180)℃, the cooling speed is 10~25℃ / s.

[0129] Wherein, B s is the temperature at the beginning of the bainite phase transformation, which is calculated by the formula B s =550-160C-10Mn-10Cr-10Ni-5Mo, wherein the element symbols in the formula represent the mass percentage of the corresponding elements in the casting blank.

[0130] In this way, by controlling the temperature and cooling speed, the supercooled austenite phase in the steel plate can be cooled to cause phase transformation, and weak water and slow cooling speed can be used to transform to ferrite / bainite, so as to ensure that the strength and toughness are well matched and evenly developed; avoid forming martensite, and ensure that the residual stress is low and evenly distributed.

[0131] Preferably, the water inlet temperature is A r3 -80℃, A r3 -70℃, A r3 -60℃.

[0132] Preferably, the water outlet temperature is B s -220℃, B s -210℃, B s -200℃, B s -190℃, B s -180℃.

[0133] Preferably, the cooling speed is any value in 10℃ / s, 12℃ / s, 14℃ / s, 15℃ / s, 16℃ / s, 18℃ / s, 20℃ / s, 22℃ / s, 23℃ / s, 25℃ / s.

[0134] Preferably, in this process, the steel plate is water-cooled on a super-fast cooling system.

[0135] The roller speed of the super-fast cooling system is preferably controlled at 0.8~2.0m / s.

[0136] Further, in an optional embodiment, the control of the cooling headers on the ultrafast cooling system can be performed in an intermittent manner or a head-tail shielding manner. Of course, the present application is not limited thereto.

[0137] The intermittent manner specifically includes, for example, that the ultrafast cooling system includes 24 or more groups of cooling headers distributed along the roller bed, and the control manner of the cooling headers is that: Along the roller bed, 1-2 groups of cooling headers are opened, and 1-2 groups of cooling headers are closed in between.

[0138] The head-tail shielding manner specifically includes, for example, that the steel plate is divided into Xn head low-temperature zones, a middle zone, and Xm tail low-temperature zones from the head to the tail, Xn and Xm are each a positive integer greater than 1; taking the unit length cooling water quantity Q of the middle zone as a standard, the unit length cooling water quantity of the Xn head low-temperature zones is controlled to be k X1 ~k Xn times Q from the head to the tail, and the unit length cooling water quantity of the Xm tail low-temperature zones is controlled to be K X1 ~K Xm times Q from the tail to the head; wherein k X1 ~k Xn , K X1 ~K Xm are each a value in a range from 0.55 to 0.85 and from 0.50 to 0.80, respectively.

[0139] For example, Xn and Xm can each be 3, and k X1 , k X2 , k X3 , K X1 , K X2 , K X3 are each a value in a range from 0.55 to 0.65, from 0.65 to 0.75, and from 0.75 to 0.85, and from 0.50 to 0.60, from 0.60 to 0.70, and from 0.70 to 0.80, respectively.

[0140] <Air cooling process> In this process, the steel plate is air-cooled, and self-tempering occurs during the cooling.

[0141] In this way, by air-cooling self-tempering after water cooling, in combination with the temperature control of the cooling bed, on the one hand, the steel plate can release phase transformation stress and thermal stress during air-cooling self-tempering; on the other hand, air-cooling self-tempering can decompose the bainite or MA generated in the phase transformation, improve the toughness and local hard spots, and further release internal stress.

[0142] Preferably, in an embodiment, in this process, the steel plate can be air-cooled on the cooling bed.

[0143] Specifically, the temperature Bs - (270 ~ 230) °C.

[0144] the upper cooling bed temperature is B s - 270 °C, B s - 260 °C, B s - 250 °C, B s - 240 °C, B s - 230 °C.

[0145] Further, in the process, the lower cooling bed temperature of the steel plate is not more than M s - 210 °C.

[0146] Preferably, the lower cooling bed temperature is M s - (260 ~ 210) °C.

[0147] More preferably, the lower cooling bed temperature of the steel plate is M s - 260 °C, M s - 250 °C, M s - 240 °C, M s - 230 °C, M s - 220 °C, M s - 210 °C.

[0148] <surface treatment process> In the present embodiment, after the steel plate is cooled to room temperature, the steel plate is subjected to surface treatment by means of shot blasting or grit blasting.

[0149] In this way, by shot blasting or grit blasting the steel plate cooled to room temperature, surface compressive stress can be achieved, which counteracts the residual tensile stress inside the steel plate, thereby reducing the residual stress and improving the distribution of the residual stress.

[0150] Preferably, in one embodiment, for a steel plate with a thickness d of 6 ~ 20 mm, the shot used for shot blasting or grit blasting is a mixture of shot with a diameter of 0.5 mm and shot with a diameter of 0.7 mm in a mass ratio of (7 ~ 8) : 5.

[0151] For a steel plate with a thickness d of 20 ~ 50 mm, the shot used for shot blasting or grit blasting is a mixture of shot with a diameter of 0.7 mm and shot with a diameter of 1.0 mm in a mass ratio of (9 ~ 11) : 5.

[0152] More preferably, the time t of shot blasting or grit blasting and the thickness d of the steel plate can satisfy t = k x d + C.

[0153] wherein the unit of t is min, k is 0.1 ~ 0.2 min / mm, and C is 5 ~ 7 min.

[0154] Preferably, the shot or blast amount P and the thickness d of the steel plate satisfy P = k1 x d + C1.

[0155] wherein the unit of P is kg / min, k1 is 0.4-0.6 kg / (min mm), and C1 is 160-200 kg / min.

[0156] Preferably, the shot or blast speed S and the thickness d of the steel plate satisfy S = k2 x d + C2.

[0157] wherein the unit of S is m / s, k2 is 0.1-0.3 m / (s mm), and C2 is 65-75 m / s.

[0158] Thus, the time t, the shot or blast amount P, and the speed S of the present embodiment are jointly controlled with the thickness d of the steel plate, so that a uniform compressive stress layer can be formed on the surface of the steel plate, and the formed compressive stress can greatly eliminate the residual tensile stress, achieving the effect of reducing the residual stress and improving the distribution of the residual stress.

[0159] Optionally, the shot used is cast steel shot with a hardness of 35-50 HRC. The specific material of the cast steel shot is not limited in the present application.

[0160] In summary, in the present embodiment, through the soaking temperature, soaking time, temperature in hot rolling, temperature and cooling speed of water cooling, air cooling, and shot or blast operation, not only the performance promoting effect of the chemical composition can be fully played to ensure excellent comprehensive performance of the steel plate, including but not limited to excellent mechanical properties and low-temperature toughness, but also the adverse effects of the chemical composition or production process on the residual stress can be avoided, i.e., the residual stress of the steel plate can be greatly reduced, and the uniformity of the residual stress distribution of the steel plate can be improved.

[0161] For example, in terms of mechanical properties, the steel plate has R m of 625-825 MPa, R t0.5 ≥555 MPa, A 50 ≥20%, R t0.5 / R m ≤0.93.

[0162] For another example, in terms of residual stress, the residual stress of the steel plate is ≤130 MPa, and the difference in residual stress between any two of the head, the middle, the tail, the upper portion, and the lower portion is ≤50 MPa.

[0163] Evenly, the residual stress of the steel plate can be reduced to not more than 100 MPa, 90 MPa, or 80 MPa, more evenly not more than 70 MPa, more or not more than 60 MPa, or even 50 MPa.

[0164] The difference between the residual stress of the middle part, the tail part, the upper part and the lower part can be less than 40 MPa, or less than 35 MPa, or less than 30 MPa, or even less than 25 MPa.

[0165] Next, as a further optimization of the embodiment, the production method can further comprise, after the surface treatment process: a tempering heat treatment process, a post-tempering stacking process. Details of the two processes are described below.

[0166] <tempering heat treatment process> In this process, the steel plate after shot blasting or grit blasting is subjected to a tempering heat treatment.

[0167] In this process, the heating rate is 8-15℃ / min.

[0168] In addition, the tempering temperature T is B s +(-105-55)℃, and the tempering holding time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, and the unit of t1 is min.

[0169] That is, not only is the tempering temperature T controlled within a certain range, but the tempering temperature T and the tempering holding time t1 are also synergistically controlled according to the formula. In this way, not only can the structure and properties, including mechanical properties, plasticity and toughness, hardness, and plate shape, be optimized, but the residual stress can also be greatly reduced and the residual stress distribution can be improved, and deformation and cracking during subsequent pipe processing can be prevented.

[0170] Preferably, for a steel plate with a thickness d of 6-20 mm, the tempering temperature T is B s +(-65-55)℃.

[0171] For a steel plate with a thickness d of 20-50 mm, the tempering temperature T is B s +(-85-35)℃.

[0172] In this way, while the tempering temperature T and the tempering holding time t1 are synergistically controlled, the tempering temperature T is precisely controlled according to the different thicknesses. On the one hand, this can effectively reduce the residual stress, and on the other hand, it can avoid a decrease in material properties, especially strength and toughness, and on the third hand, it can also avoid the problem of excessive energy consumption and production cost caused by the introduction of the tempering heat treatment.

[0173] Preferably, in this process, the tempering heat treatment can be carried out in a tempering furnace, and the nitrogen atmosphere can be maintained in the tempering furnace.

[0174] In this way, under the nitrogen atmosphere, not only can the steel plate be prevented from oxidizing or decarburizing during the tempering heat treatment process, but the surface quality of the steel plate can also be protected. It has been found through research that this can further optimize the uniformity of the residual stress.

[0175] <Stacking process after tempering> In this process, after reaching the tempering holding time t1, the pipeline steel plate is directly discharged (i.e. leaving the tempering furnace) and stacked.

[0176] In this process, the stacking temperature B s - (210~110) ℃, cooling rate 10~30 ℃ / h, and the unstacking temperature ≤B s - 450 ℃.

[0177] In this way, by quickly discharging and stacking, and controlling the cooling rate, not only the excellent structure and performance can be maintained, but also the uniform distribution of residual stress is helped.

[0178] Preferably, the stacking time is 12~24 h.

[0179] The above introduces the basic situation of the embodiment. Below, several test examples are provided, of course, these test examples are only part of the numerous variation embodiments contained in the present application, not all.

[0180] Specifically, four test examples are provided here, using the production method introduced in the embodiment, respectively for preparing test examples 1-4 shown in the above Table 1. Some important parameters in the production process are shown in Table 4 and Table 5. Among them, " / " in the table indicates that the corresponding process is not performed.

[0181] [Table 4]

[0182] [Table 5]

[0183] Third embodiment The present embodiment provides a production method of a pipeline steel plate.

[0184] The difference between this embodiment and the aforementioned second embodiment is only that a stacking process is added between the air cooling process and the surface treatment process. Below, only this difference is introduced; the rest is the same as the aforementioned second embodiment, all can be referred to the introduction of the second embodiment, and will not be repeated here.

[0185] <Stacking process> In this process, the pipeline steel plate is combined and stacked with the auxiliary steel plate.

[0186] Specifically, as shown in Figure 2 A group of steel plates 21 is composed of the auxiliary steel plate 20 in the lower layer and the steel plate 10 in the upper layer.

[0187] The n groups of steel plates 21 are stacked from bottom to top, and the top layer is covered by the auxiliary steel plate 20, where n is a positive integer.

[0188] Figure 2 Two groups of steel plates 21 are shown in the above example, but in practice, there can be one, three or more groups of steel plates 21.

[0189] The stacking temperature of the auxiliary steel plate is M s - (110~10) ℃.

[0190] The stacking temperature of the auxiliary steel plate is M s -210℃, the unstacking temperature is not more than M s - (410~310) ℃.

[0191] In this way, the stacking temperature of the steel plate is less than the stacking temperature of the auxiliary steel plate, which can utilize the heat of the auxiliary steel plate to produce tempering effect on the steel plate, on the one hand, to improve the uniformity of the structure and performance of the steel plate, on the other hand, to further release internal stress, reduce the residual stress of the steel plate, and improve the distribution uniformity of the residual stress.

[0192] Preferably, the stacking temperature of the steel plate is less than M s -260℃, M s -250℃, M s -240℃, M s -230℃, M s -220℃, M s -210℃.

[0193] The unstacking temperature of the steel plate is not more than M s -410℃, M s -400℃, M s -390℃, M s -380℃, M s -370℃, M s -360℃, M s -350℃, M s -340℃, M s -330℃, M s -320℃, or M s -310℃.

[0194] Further, the length, width and thickness of the steel plate are all less than the length, width and thickness of the auxiliary steel plate.

[0195] Furthermore, in the process, the stacking time is preferably 12~18h.

[0196] Further, the basic situation of the present embodiment is introduced above. Next, several test examples are provided, of course, these test examples are only a part of numerous variation embodiments contained in the present application, not all.

[0197] Specifically, 2 test examples are provided here, using the production method introduced in the present embodiment, that is, by casting billet heating process, hot rolling process, controlled water cooling process, air cooling process, stacking process, surface treatment process, (optional) tempering heat treatment process, (optional) post-tempering stacking process, respectively for preparing test examples 5 and 6 shown in Table 1 above. Some important parameters in the production process are shown in Tables 6-8. Among them, " / " in the table means that the corresponding process is not carried out.

[0198] [Table 6]

[0199] [Table 7]

[0200] [Table 8]

[0201] Fourth embodiment The present embodiment provides a production method of a steel plate for pipeline.

[0202] As a further optimization of the aforementioned second or third embodiment, the present embodiment further adds any one or several of the following four processes: preheating straightening process, hot straightening process, warm straightening process, cold straightening process.

[0203] Next, only the four processes that can be selectively added are introduced in detail. And the casting billet heating process, hot rolling process, controlled water cooling process, air cooling process, continuous casting process, surface treatment process, tempering heat treatment process, post-tempering stacking process, etc. can refer to the detailed introduction in the second or third embodiment.

[0204] <Preheating straightening process> This process is located between the hot rolling process and the controlled water cooling process, and at least one pass of preheating straightening is performed on the steel plate obtained by hot rolling.

[0205] Among them, the straightening speed is 0.1-1.5 m / s, and the straightening temperature A r3 -(65-45) ℃, maximum reduction ≤4 mm.

[0206] Thus, the high-temperature steel plate after hot rolling and before water cooling control is straightened, at this time the deformation resistance of the steel plate is small, and the problems of poor flatness such as head warping, head buckling, edge wave, and middle wave caused by the hot rolling process can be greatly eliminated, and the high flatness of the steel plate before the water cooling control process is ensured. Moreover, straightening before the phase change in the water cooling control process can release part of the internal stress generated by rolling deformation, thereby finally reducing the residual stress of the steel plate product.

[0207] Preferably, in this process, the straightening temperature is A r3 -65℃, A r3 -60℃, A r3 -55℃, A r3 -50℃, A r3 -45℃.

[0208] Optionally, the preheating straightening machine used is 11 rollers, the upper straightening rollers are 6, the lower straightening rollers are 5, the roller diameter is 300mm, and the straightening force is 28000kN. These are only examples, and the application is not limited thereto.

[0209] <Hot straightening process> This process is located between the water cooling control process and the air cooling process, and 1-3 passes of preheating straightening are performed on the steel plate after water out in the water cooling control process.

[0210] Wherein, the straightening speed is 0.1-1.5m / s, and the straightening temperature is B s -(230-190)℃, the maximum reduction is ≤4mm.

[0211] Thus, the steel plate after water cooling and before air cooling self-tempering is still in the ferrite or bainite phase change region, at this time, through straightening, the phase change stress and thermal stress can be released to finally reduce the residual stress of the steel plate product.

[0212] Preferably, in this process, the straightening temperature is B s -230℃, B s -220℃, B s -210℃, B s -200℃, B s -190℃.

[0213] Optionally, the hot straightening machine used is 11 rollers, the upper straightening rollers are 5, the lower straightening rollers are 6, the roller diameter is 285mm, and the straightening force is 32000kN. These are only examples, and the application is not limited thereto.

[0214] <Warm straightening process> This process is located between the air cooling process and the surface treatment process, and when the stacking process is added between the air cooling process and the surface treatment process, the warm straightening process is located between the air cooling process and the stacking process.

[0215] Specifically, the steel plate is subjected to 2-4 passes of warm straightening after being discharged from the air cooling process to the cooling bed.

[0216] wherein the straightening speed is 0.1-0.5 m / s and the straightening temperature is M s - (270-220) °C, and the maximum reduction is ≤10 mm.

[0217] Thus, during the air cooling and self-tempering process, certain residual stress is still generated and may cause the steel plate to be warped. Straightening the steel plate after air cooling and self-tempering can further release the phase transformation stress and thermal stress, so as to finally reduce the residual stress of the finished steel plate.

[0218] Preferably, in this process, the straightening temperature is M s - 270 °C, M s - 260 °C, M s - 250 °C, M s - 240 °C, M s - 230 °C, M s - 220 °C.

[0219] Optionally, the warm straightening machine used is a 9-roller machine, the upper straightening rollers are 4 in number, the lower straightening rollers are 5 in number, the roller diameter is 320 mm, and the straightening force is 48000 kN. These are only examples, and the application is not limited thereto.

[0220] <cold straightening process> This process is located between the warm straightening process and the surface treatment process. When a stacking process is added between the air cooling process and the surface treatment process, the cold straightening process is located between the stacking process and the surface treatment process.

[0221] The steel plate is subjected to 1-3 passes of cold straightening.

[0222] wherein the straightening speed is 0.1-0.5 m / s and the straightening temperature is M s - (420-360) °C, and the maximum reduction is ≤6 mm.

[0223] Thus, the phase transformation stress and thermal stress are further released, so as to finally reduce the residual stress of the finished steel plate.

[0224] Preferably, in this process, the straightening temperature is M s - 420 °C, M s - 410 °C, M s - 400 °C, M s - 390 °C, M s - 380 °C, M s - 370 °C, M s - 360 °C.

[0225] Optionally, the cold straightener used is a 11-roller one, with 5 upper straightening rollers and 6 lower straightening rollers, each having a diameter of 220 mm, and a straightening force of 35000 kN. These are only examples, and the present application is not limited thereto.

[0226] Further, the basic situation of the present embodiment is introduced above. Several test examples are provided below, which are only a part of the numerous varied embodiments of the present application, not all.

[0227] Specifically, two test examples are provided herein, which are prepared by using the production method introduced in the present embodiment, i.e. by casting slab heating process, hot rolling process, preheating straightening process, controlled water cooling process, hot straightening process, air cooling process, warm straightening process, stacking process, cold straightening process, surface treatment process, (optional) tempering heat treatment process, (optional) post-tempering stacking process, respectively for preparing test examples 7 and 8 shown in Table 1 above. Some important parameters in the production process are shown in Tables 9-11. In the tables, “ / ” indicates that the corresponding process is not performed, and the numerical value and “√” indicate that the corresponding process is performed.

[0228] [Table 9]

[0229] [Table 10]

[0230] [Table 11]

Claims

1. A 555 MPa grade low stress pipeline steel plate characterized in that, The chemical composition of the steel plate includes, in mass percent: C 0.03-0.07%, Si 0.09-0.21%, Mn 1.61-1.69%, Cr 0.11-0.29%, Ni 0.11-0.29%, Mo 0.06-0.18%, Cu 0.11-0.29%, Nb 0.054-0.066%, Ti 0.009-0.021%, Al 0.021-0.049%, P≤0.0150%, S≤0.0040%, O≤0.0025%, N≤0.0048%, H≤0.0002%, and the balance being iron and inevitable impurities; The thickness d of the steel sheet is ≥ 6 mm, R m 625 ~ 825 MPa, R t0.5 ≥ 555 MPa, A 50 ≥ 20%, R t0.5 / R m ≤ 0.93; The residual stress of the steel plate is ≤130 MPa, and the residual stress difference between any two of the head, the middle, the tail, the upper portion and the lower portion is ≤50 MPa.

2. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by The chemical composition of the steel plate further satisfies, in mass percent: CEV is 0.354-0.491, and Pcm is 0.135-0.212; CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15; Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 is 0.091-0.294; In the formula, each element symbol represents the mass percent of the corresponding element.

3. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by, The chemical composition of the steel plate includes, in mass percent: P 0.0050-0.0100%, S 0.0005-0.0020%, N 0.0022-0.0048%, O 0.0011-0.0025%, and H 0.00005-0.00018%.

4. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by, The microstructure of the steel plate is polygonal ferrite + acicular ferrite + tempered bainite; In the formula, the volume fraction of the polygonal ferrite is 0-5%, the volume fraction of the acicular ferrite is 30-45%, the volume fraction of the tempered bainite is 55-65%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

5. The 555 MPa grade low-stress pipe line steel plate according to claim 4, characterized in that, The average grain size of the steel plate is 3-9 μm.

6. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by The steel plate satisfies any one or several of the following: 0 ℃ impact energy KV2≥360 J, -20 ℃ impact energy KV2≥350 J, -40 ℃ impact energy KV2≥320 J, and -60 ℃ impact energy KV2≥300 J.

7. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by The steel sheet has a brittle-ductile transition temperature T t50%US ≤ -100 °C.

8. The 555 MPa grade low-stress pipe line steel plate according to claim 1, characterized by, The steel plate satisfies any one or several of the following: -10 ℃ DWTT drop hammer shear area fraction is 100%, -20 ℃ DWTT drop hammer shear area fraction is ≥100%, -30 ℃ DWTT drop hammer shear area fraction is ≥95%, 0 ℃ CTOD crack tip opening displacement is ≥1.2 mm, -20 ℃ CTOD crack tip opening displacement is ≥1.0 mm, and -40 ℃ CTOD crack tip opening displacement is ≥0.6 mm.

9. A method of producing a 555 MPa grade low-stress pipe line steel sheet as claimed in any one of claims 1 to 8, characterized in that, comprising, in sequence, The slab heating process: soaking temperature is T NbC + (50~125) ℃, soaking time is ≥25 min; Hot rolling process: with first stage rolling, intermediate slab cooling and second stage rolling; in the first stage rolling, the starting rolling temperature T nr +(10~100)℃, the final rolling temperature T nr +(5~50)℃; in the intermediate slab cooling, the thickness of the intermediate slab is 2.5~3.5 times of the target thickness of the steel plate, the final cooling temperature A r3 +(0~20)℃, the cooling time is ≥50s; in the second stage rolling, the starting rolling temperature A r3 +(-10~10)℃, the rolling temperature of the last pass A r3 -(50~30)℃; Controlled water cooling process: water inlet temperature A r3 - (80~60) °C, water outlet temperature B s - (220~180) °C, cooling rate 10~25 °C / s; an air cooling process, in which the steel plate is air cooled; a surface treatment process, in which the steel plate is subjected to surface treatment by means of shot blasting or shot peening after the steel plate is cooled to room temperature; wherein, T NbC , T nr , A r3 , B s are calculated using the following equations, respectively, and the element symbols in each equation represent the mass percentage of the corresponding element in the slab. T NbC = 7700 / (3.18-lg(Nb x C 0.87 ))-273.15; T nr = 887 + 464C - 357Si + 6445Nb - 644 + 890Ti + 363Al; A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo; B s = 550 - 160 C - 10 Mn - 10 Cr - 10 Ni - 5 Mo.

10. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, in the surface treatment process: The thickness d of the steel plate is 6-20 mm, and the shot material used for the shot blasting or the shot peening is a mixture of shot material with a diameter of 0.5 mm and shot material with a diameter of 0.7 mm in a mass ratio of (7-8):5; Or, the thickness d of the steel plate is 20-50 mm, and the shot material used for the shot blasting or the shot peening is a mixture of shot material with a diameter of 0.7 mm and shot material with a diameter of 1.0 mm in a mass ratio of (9-11):

5.

11. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, In the surface treatment process: The time t of the shot blasting or the shot peening and the thickness d of the steel plate satisfy t=k×d+C, the unit of t is min, k is 0.1-0.2 min / mm, and C is 5-7 min; And / or, the shot blasting amount or the shot peening amount P and the thickness d of the steel plate satisfy P=k1×d+C1, the unit of P is kg / min, k1 is 0.4-0.6 kg / (min·mm), and C1 is 160-200 kg / min; And / or, the speed S of the shot blasting or the shot peening and the thickness d of the steel plate satisfy S=k2×d+C2, the unit of S is m / s, k2 is 0.1-0.3 m / (s·mm), and C2 is 65-75 m / s.

12. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, Further comprising, after the surface treatment process, tempering heat treatment process: the heating rate is 8~15℃ / min, the tempering temperature T is B s +(-105~55)℃, and the tempering holding time t1 is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, and the unit of t1 is min.

13. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 12, characterized in that, In the tempering heat treatment process: The thickness d of the steel plate is 6-20 mm, and the tempering temperature T is B s +(-65~55)℃; Alternatively, the thickness d of the steel sheet is 20 to 50 mm, and the tempering temperature T is B s +(-85 to 35) °C.

14. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 12, characterized in that, Further comprising, after the tempering heat treatment process, Stacking after tempering: stacking temperature B s - (210-110) °C, cooling rate 10-30 °C / h, unstacking temperature ≤ B s - 450 °C.

15. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, In the air cooling step: air cooling on the cooling bed, the temperature of the cooling bed B s - (270 ~ 230) °C, the temperature of the lower cooling bed is not more than M s - 210 °C; M S = 539 - 423C - 11Si - 30.4Mn - 12.1Cr - 17.7Ni - 7.5Mo, in °C, where the element symbols in the formula represent the mass percent of the respective element in the strand.

16. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 15, characterized in that, In the air cooling step: lower bed temperature M s - (260-210) °C; The production method further comprises, after the air cooling process, Stacking process: stacking in the order of n groups of steel plates from bottom to top, with the top layer covered by an auxiliary steel plate, each group of steel plates consisting of an auxiliary steel plate at the bottom and a steel plate at the top, n being a positive integer; the stacking temperature of the auxiliary steel plate is M s -(110~10)℃, the unstacking temperature of the steel plate does not exceed M s -(410~310)℃.

17. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, Further comprising one, two or more of the following four processes, Preheating straightening process between hot rolling process and controlled water cooling process: at least 1 pass preheating straightening is performed at a straightening speed of 0.1-1.5 m / s and a straightening temperature A r3 - (65-45) °C, maximum reduction ≤ 4 mm; In the heat straightening process between the water cooling process and the air cooling process: 1-3 passes of preheating straightening is performed, the straightening speed is 0.1-1.5 m / s, and the straightening temperature B is 650-750°C s - (230-190) °C, maximum reduction ≤ 4 mm; In the warm straightening process between the air cooling process and the surface treatment process: 2-4 passes of warm straightening, straightening speed 0.1-0.5 m / s, straightening temperature M s - (270-220) °C, maximum reduction ≤ 10 mm; Cold straightening process between the warm straightening process and the surface treatment process: 1-3 passes of cold straightening, straightening speed 0.1-0.5 m / s, straightening temperature M s - (420-360) °C, maximum reduction ≤ 6 mm; where M S = 539 - 423C - 11Si - 30.4Mn - 12.1Cr - 17.7Ni - 7.5Mo, in °C, where the element symbols in the formula represent the mass percent of the corresponding element in the strand.

18. The method of producing a 555 MPa grade low-stress pipe line steel plate according to claim 9, characterized in that, In the hot rolling process: In the first stage rolling, the reduction of each pass is ≤34 mm, and the reduction of the non-breadth-expanding roughing pass is ≥24 mm; In the second stage rolling, the reduction of each pass is ≤20 mm, and the reduction of the last pass is ≤3 mm.

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