Method for producing a pipeline steel plate with optimized residual stresses

Abstract

The present invention discloses a production method of pipeline steel plate with optimized residual stress. The production method comprises sequentially, heating: soaking T NbC +(50~125)℃ and time ≥25min; first stage rolling, rough rolling T nr +(10~100)℃, finish rolling T nr +(5~50)℃; intermediate slab cooling, slab thickness is 2.5~3.5 times of the target thickness of the steel plate, final cooling A r3 +(0~90)℃, cooling time ≥50s; second stage rolling, rough rolling A r3 +(‑10~80)℃, finish rolling A r3 +(‑50~40)℃ and 8~10s before rolling, the obtained steel plate thickness ≥6mm; controlled water cooling: water inlet A r3 +(‑80~10)℃, water outlet B s +(‑220~100)℃, cooling rate 10~25℃ / s; air cooling self-tempering. Thus, the residual stress of the steel plate is low and uniformly distributed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steel material preparation, and relates to a production method of pipeline steel plate with optimized residual stress. BACKGROUND

[0002] Pipeline steel plays an irreplaceable role in the energy transportation industry such as oil and natural gas. In the production process of pipeline steel plate, due to the comprehensive action of rolling, cooling, heat treatment and other processes, residual stress will be generated inside the steel plate.

[0003] The existence of residual stress has many adverse effects on the performance of pipeline steel and the safety of the pipeline.

[0004] Specifically, in the pipe manufacturing process, the pipeline steel plate generally needs to go through JCO forming, welding and other processes to make steel pipes. Residual stress will 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 is easy to cause the steel pipe end to appear a crooked 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 crooked mouth of the steel pipe, reducing the service life of the steel pipe.

[0005] Therefore, how to control and reduce residual stress and how to make the residual stress of pipeline steel plate uniform become difficult problems to be solved in the field of pipeline steel manufacturing. SUMMARY

[0006] The purpose of the present application is to provide a pipeline steel plate with optimized residual stress and a production method thereof.

[0007] To achieve the above-mentioned purpose of the application, an embodiment of the present application provides a production method of pipeline steel plate. The production method comprises, in sequence,

[0008] The slab heating process: the soaking temperature is T NbC +(50-125)℃, and the soaking time is ≥25min;

[0009] The hot rolling process: having a first stage rolling, intermediate slab cooling and a second stage rolling; in the first stage rolling, the starting rolling temperature is T nr +(10-100)℃, 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 pipeline steel plate, the final cooling temperature is A r3 +(0-90)℃, and the cooling time is ≥50s; in the second stage rolling, the starting rolling temperature is A r3 +(-10-80)℃, and the rolling temperature of the last pass is A r3+(-50~40)℃ and stays for 8~10s before rolling, and the thickness d of the pipeline steel plate obtained is not less than 6mm;

[0010] Control water cooling process: water inlet temperature A r3 +(-80~10)℃, water outlet temperature B s +(-220~100)℃, cooling speed 10~25℃ / s;

[0011] Air cooling self tempering process: air cooling of the steel plate on a cooling bed;

[0012] Wherein, T NbC , T nr , A r3 , B s are calculated by the following formulas respectively, and the element symbols in each formula represent the mass percentage of the corresponding element in the casting blank;

[0013] T NbC =7700 / (3.18-lg(Nb×C 0.87 ))-273.15;

[0014] T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al;

[0015] A r3 =910-203 -11Si-15.2Mn-30Cr-13Ni-40Mo;

[0016] B s =550-160C-10Mn-10Cr-10Ni-5Mo.

[0017] Preferably, in the casting blank heating process, including heat recovery, preheating, first heating, second heating and soaking, the heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the first heating temperature is 970~1030℃, the second heating section temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm casting blank thickness.

[0018] Preferably, in the casting blank heating process, the furnace inlet temperature of the casting blank is ≥M S -350℃, M S is calculated by the following formula, unit: ℃;

[0019] M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo.

[0020] Preferably, the reduction of each pass is ≤20 mm, and the reduction of the last pass is ≤3 mm.

[0021] Preferably, in the air cooling and self-tempering process, the temperature of the upper cooling bed is B s +(-270~100)℃, the temperature of the lower cooling bed is M s -(260~150)℃.

[0022] Preferably, the production method further comprises a stacking process after the air cooling and self-tempering process: the 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 one or more auxiliary steel plates in the lower layer and one or more pipeline steel plates in the upper layer, and n is a positive integer; the stacking temperature of the auxiliary steel plates is M s +(-110~50)℃, and the unstacking temperature of the pipeline steel plates is not higher than M s -(410~250)℃.

[0023] Preferably, the production method further comprises a temperature-controlled cold straightening process after the stacking process: 1~3 passes of cold straightening are performed, the straightening speed is 0.1~0.5 m / s, and the straightening temperature is M s -(420~360)℃, and the maximum reduction is ≤6 mm; M S The following formula is used for calculation:

[0024] M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo.

[0025] Preferably, the production method further comprises a temperature-controlled warm straightening process after the air cooling and self-tempering process: 2~4 passes of warm straightening are performed, the straightening speed is 0.1~0.5 m / s, and the straightening temperature is M s -(270~150)℃, and the maximum reduction is ≤10 mm; M S The following formula is used for calculation:

[0026] M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo.

[0027] Preferably, the production method further comprises a temperature-controlled preheating straightening process between the hot rolling process and the controlled water cooling process: at least 1 pass of preheating straightening is performed, the straightening speed is 0.1~1.5 m / s, and the straightening temperature is A r3 +(-65~25)℃, and the maximum reduction is ≤4 mm.

[0028] Preferably, the production method further comprises a temperature-controlled hot straightening process after the water cooling process: 1-3 passes of hot straightening is performed, the straightening speed is 0.1-1.5 m / s, and the straightening temperature B s +(-230~90)℃, the maximum reduction is ≤4mm.

[0029] Preferably, the production method further comprises a surface treatment process: after the pipeline steel plate is cooled to room temperature, the surface of the steel plate is treated by using the shot blasting or the shot peening.

[0030] Preferably, the thickness d of the pipeline steel plate is 6-20 mm, and the shot blasting or the shot peening uses mixed shot 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;

[0031] Alternatively, the thickness d of the pipeline steel plate is 20-50 mm, and the shot blasting or the shot peening uses mixed shot 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;

[0032] Alternatively, the thickness d of the pipeline steel plate is >50 mm, and the shot blasting or the shot peening uses mixed shot of shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4-6):5.

[0033] Preferably, the time t of the shot blasting or the shot peening and the thickness d of the pipeline 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;

[0034] And / or, the shot blasting amount or the shot peening amount P and the thickness d of the pipeline 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;

[0035] And / or, the speed S of the shot blasting or the shot peening and the thickness d of the pipeline 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.

[0036] Preferably, the production method further comprises a 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, the unit of t1 is min.

[0037] Preferably, the thickness d of the pipeline steel plate is 6-20 mm, and the tempering temperature T is B s +(-65~55)℃.

[0038] Alternatively, the thickness d of the pipeline steel plate is 20-50 mm, and the tempering temperature T is B s +(-85-35)℃;

[0039] Alternatively, the thickness d of the pipeline steel plate is >50 mm, and the tempering temperature T is B s +(-105-15)℃.

[0040] Preferably, the production method further comprises a post-tempering stacking process after the tempering heat treatment process: after the tempering holding time t1 is reached, directly stacking off-line, the stacking temperature B s -(210-110)℃, the cooling rate is 10-30℃ / h, and the unstacking temperature is ≤B s -450℃.

[0041] Preferably, the chemical composition of the pipeline steel plate comprises, in mass percent: C 0.03-0.15%, Si 0.09-0.26%, Mn 1.16-1.69%, Cr 0-0.29%, Ni 0-0.29%, Mo 0-0.18%, Cu 0-0.29%, Nb 0.009-0.066%, 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 unavoidable impurities.

[0042] Preferably, the chemical composition of the pipeline steel plate further satisfies, in mass percent:

[0043] CEV=C+Mn / 6+(Cr+Mo) / 5+(Cu+Ni) / 15 is 0.223-0.571;

[0044] and / or, Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.091-0.294;

[0045] wherein the element symbols in the formulas represent the mass percent of the corresponding elements.

[0046] Compared with the prior art, the embodiment of the application has the beneficial effects that: through the soaking temperature, soaking time, temperature in hot rolling, temperature and cooling rate of controlled water cooling, and the operation of stopping for 8-10s before the last pass of hot rolling, the residual stress of the steel plate can be greatly reduced and the residual stress distribution uniformity of the steel plate can be improved at a low production cost and process cost on the basis of ensuring the performance of the steel plate. For example, the residual stress of the steel plate is ≤130MPa, and the residual stress difference between any two of the head, middle, tail, upper, and lower parts is all ≤50MPa.

[0047] To achieve the above object, one embodiment of the present application provides a pipeline steel plate. The chemical composition of the pipeline steel plate includes, in mass percent: C 0.03-0.15%, Si 0.09-0.26%, Mn 1.16-1.69%, Cr 0-0.29%, Ni 0-0.29%, Mo 0-0.18%, Cu 0-0.29%, Nb 0.009-0.066%, 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.

[0048] As an improved embodiment, the residual stress of the pipeline 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.

[0049] As an improved embodiment, the microstructure of the pipeline steel plate is polygonal ferrite+pearlite+tempered bainite. The volume fraction of the polygonal ferrite is 85-97%, the volume fraction of the pearlite is 3-10%, and the volume fraction of the tempered bainite is 0-10%, and the sum of the volume fractions of the polygonal ferrite, the pearlite and the tempered bainite is 100%.

[0050] As an improved embodiment, the microstructure of the pipeline steel plate is polygonal ferrite+acicular ferrite+tempered bainite. The volume fraction of the polygonal ferrite is 0-10%, the volume fraction of the acicular ferrite is 30-85%, and the volume fraction of the tempered bainite is 10-65%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

[0051] As an improved embodiment, the average grain size of the pipeline steel plate is 3-30 μm.

[0052] As an improved embodiment, the R m of the pipeline steel plate is 415-825 MPa, the R t0.5 ≥245 MPa, the A 50 ≥20%, the R t0.5 / R m ≤0.93.

[0053] As an improved embodiment, the pipeline steel plate has a 0℃ impact energy KV2≥250 J, a -20℃ impact energy KV2≥230 J, a -40℃ impact energy KV2≥200 J, a -60℃ impact energy KV2≥180 J, and a ductile-brittle transition temperature T t50%US ≤-80℃.

[0054] As an improved embodiment, the hardness of the pipeline steel plate is ≤250HV 10 ; 100% of DWTT drop hammer shearing area fraction at -10℃, ≥90% of DWTT drop hammer shearing area fraction at -20℃, ≥85% of DWTT drop hammer shearing area fraction at -30℃; 0℃ CTOD crack tip opening displacement ≥0.6mm, -20℃ CTOD crack tip opening displacement ≥0.4mm, -40℃ CTOD crack tip opening displacement ≥0.2mm.

[0055] As an improved embodiment, the unevenness of the pipeline steel plate is ≤3mm / m.

[0056] Compared with the prior art, the embodiment of the present application has the beneficial effect that the steel plate adopts a low-alloy cost component design and has the advantages of low residual stress and uniform residual stress distribution, which can not only ensure excellent machinability in the subsequent pipe manufacturing process of the pipeline steel, but also improve the service life of the steel pipe. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 is a schematic diagram of stacking in the stacking process in an embodiment of the present application;

[0058] Figure 2 is a metallographic structure diagram of the steel plate of Test Example 1 of the present application;

[0059] Figure 3 is a metallographic structure diagram of the steel plate of Test Example 2 of the present application;

[0060] Figure 4 is a metallographic structure diagram of the steel plate of Test Example 3 of the present application;

[0061] Figure 5 is a metallographic structure diagram of the steel plate of Test Example 4 of the present application;

[0062] Figure 6 is a metallographic structure diagram of the steel plate of Test Example 5 of the present application;

[0063] Figure 7 is a metallographic structure diagram of the steel plate of Test Example 6 of the present application;

[0064] Figure 8 is a metallographic structure diagram of the steel plate of Test Example 7 of the present application. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme 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 part of the embodiments of the present application, not all the embodiments.

[0066] First embodiment

[0067] The present embodiment provides a pipeline steel plate, i.e. a steel plate that can be applied to a pipeline scene.

[0068] The chemical composition of the pipeline steel plate includes, in mass percentage: C 0.03~0.15%, Si 0.09~0.26%, Mn 1.16~1.69%, Cr 0~0.29%, Ni 0~0.29%, Mo 0~0.18%, Cu 0~0.29%, Nb 0.009~0.066%, 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.

[0069] The main role of each element and the selection of its amount are specifically analyzed and explained as follows.

[0070] C: Carbon is the most economical strengthening element in steel, which has a solid solution strengthening effect, and forms carbides with niobium, titanium, chromium, molybdenum, etc., which has a precipitation strengthening effect; the increase of carbon content has a significant 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 carbides and martensite will induce an increase in residual stress. In the present embodiment, the carbon content is controlled to be 0.03~0.15%.

[0071] Preferably, the carbon content can be controlled to be 0.03~0.07%, 0.04~0.08%, 0.05~0.09%, 0.07~0.11% or 0.11~0.15%.

[0072] More preferably, the carbon content can be controlled to be any one of 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%.

[0073] Si: Silicon in steel has a solid solution strengthening effect, but it will increase the grain boundary segregation of phosphorus, sulfur and other elements, reduce the low-temperature toughness and plasticity, and at the same time, 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 0.09~0.26%.

[0074] Preferably, the silicon content can be further controlled to be 0.14~0.26%, 0.12~0.24%, 0.10~0.22% or 0.09~0.21%.

[0075] More preferably, the silicon content can be specifically controlled at 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%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, and 0.26%.

[0076] Mn: Manganese plays a solid solution strengthening role in steel, improving strength and hardness. Excessive manganese can lead to center segregation in the cast billet, which is detrimental to toughness. Furthermore, increased manganese content also leads to a higher level of banded structure, and the higher the level of banded structure, the more uneven the microstructure distribution. In addition, manganese readily forms manganese sulfide inclusions. Center segregation, banded structure, and inclusions all contribute to increased residual stress. In one embodiment, the manganese content is controlled at 1.16~1.69%.

[0077] Preferably, the manganese content can be further controlled at 1.16~1.24%, 1.31~1.39%, 1.46~1.54%, 1.51~1.59%, 1.56~1.64%, or 1.61~1.69%.

[0078] More preferably, the manganese content can be specifically controlled within any one of the following: 1.16%, 1.18%, 1.20%, 1.22%, 1.24%, 1.25%, 1.30%, 1.31%, 1.33%, 1.35%, 1.37%, 1.39%, 1.40%, 1.45%, 1.46%, 1.48%, 1.50%, 1.51%, 1.52%, 1.54%, 1.55%, 1.57%, 1.59%, 1.60%, 1.61%, 1.63%, 1.64%, 1.65%, 1.67%, and 1.69%.

[0079] Cr: Chromium plays a solid solution strengthening role in steel; furthermore, chromium can form stable carbides and improve the stability of martensite, thus generating greater residual stress during rapid cooling. The higher the chromium content, the more complex the distribution of residual stress after cooling. In this application, chromium can be selectively added or selectively omitted. Specifically, the chromium content is controlled at 0~0.29%.

[0080] Preferably, in one embodiment, chromium is not present, that is, the chromium content is 0 or close to 0. For example, chromium alloys are not actively added in the form of alloying during the production process so that the chromium content in the steel is 0, or chromium is introduced as an impurity in the raw materials.

[0081] Preferably, in another embodiment, chromium is added, and the chromium content can be controlled at 0.06~0.24%, 0.09~0.27%, or 0.11~0.29%.

[0082] More preferably, the chromium content can be controlled at any one of 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.15%, 0.20%, 0.22%, 0.25%, 0.27%, 0.29%, respectively.

[0083] Ni: Nickel can improve the strength of the steel by solid solution strengthening, and does not significantly increase the hardness of the steel. Nickel can expand the austenite phase region, thereby reducing residual stress; and nickel can also improve the toughness of the steel and reduce stress concentration. In the present application, nickel can be selectively added or not added. Specifically, the nickel content is controlled at 0-0.29%.

[0084] Preferably, in one embodiment, nickel is not contained, i.e. the nickel content is 0 or close to 0, for example, no nickel alloy is actively added in the form of alloying during the production process, so that the nickel content in the steel is 0, or only the nickel introduced as an impurity in the raw material.

[0085] Preferably, in another embodiment, nickel is added, and the nickel content can be controlled at 0.02-0.18%, 0.06-0.24% or 0.11-0.29%.

[0086] More preferably, the nickel content can be controlled at any one of 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.10%, 0.11%, 0.12%, 0.16%, 0.18%, 0.20%, 0.22%, 0.24%, 0.27%, 0.29%, respectively.

[0087] Mo: Molybdenum can significantly improve the hardenability of the steel, and improve the strength, toughness, and can also refine the grain and improve the corrosion resistance. Molybdenum can improve the tempering stability of the steel and reduce the increase of residual stress. In the present application, molybdenum can be selectively added or not added. Specifically, the molybdenum content is controlled at 0-0.18%.

[0088] Preferably, in one embodiment, molybdenum is not contained, i.e. the molybdenum content is 0 or close to 0, for example, no molybdenum alloy is actively added in the form of alloying during the production process, so that the molybdenum content in the steel is 0, or only the molybdenum introduced as an impurity in the raw material.

[0089] Preferably, in another embodiment, molybdenum is added, and the molybdenum content can be controlled at 0.02-0.14% or 0.06-0.18%.

[0090] Preferably, the molybdenum content can be controlled to be any one of 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.12%, 0.14%, 0.16%, 0.18%.

[0091] Cu: Copper can promote the precipitation of niobium and make up for the loss of strength caused by the decrease of carbon content. Adding a certain amount of nickel while adding copper can effectively inhibit surface cracks. In an embodiment, copper can be selectively added or not added in the present application. Specifically, the copper content is controlled to be 0-0.29%.

[0092] Preferably, in an embodiment, copper is not contained, that is, the copper content is 0 or close to 0, for example, copper alloy is not actively added in the form of alloying during the production process, so that the copper content in the steel is 0, or only the copper introduced as an impurity in the raw material.

[0093] Preferably, in another embodiment, copper is added, and the copper content can be controlled to be 0.11-0.29%.

[0094] Preferably, the copper content can be controlled to be any one of 0, 0.005%, 0.01%, 0.015%, 0.02%, 0.03%, 0.04%, 0.05%, 0.08%, 0.11%, 0.15%, 0.20%, 0.21%, 0.23%, 0.25%, 0.29%.

[0095] Nb: Niobium is an important grain refining element in steel. In the hot rolling process, niobium strongly inhibits austenite recrystallization and its precipitation in austenite, pins austenite grain boundaries, and refines recrystallized grains. During cooling, the solid-soluble niobium can continue to precipitate in the form of niobium carbonitride, significantly refining the structure of the material after phase transformation, 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 to be 0.009-0.066%.

[0096] Preferably, the niobium content can be further controlled to be 0.009-0.021%, 0.014-0.026%, 0.019-0.031%, 0.024-0.036%, 0.034-0.046%, 0.044-0.056% or 0.054-0.066%.

[0097] More preferably, the niobium content can be controlled to be any one of 0.009%, 0.010%, 0.014%, 0.015%, 0.018%, 0.019%, 0.021%, 0.024%, 0.026%, 0.030%, 0.031%, 0.034%, 0.036%, 0.038%, 0.040%, 0.042%, 0.044%, 0.046%, 0.048%, 0.050%, 0.054%, 0.056%, 0.060%, 0.062%, 0.064%, 0.066%, respectively.

[0098] Ti: Titanium is a nitrogen-fixing element in steel, which can form carbonitride dispersedly distributed, inhibits austenite grain coarsening and refines grains during the process of slab heating and hot rolling, thereby reducing residual stress. However, when the titanium content is high, coarse carbonitride precipitates are easily formed in the center of the slab, which affects the low-temperature toughness of the steel plate. And large-particle TiN easily leads to stress concentration. In the present application, the titanium content is controlled to be 0.009-0.021%.

[0099] Preferably, the titanium content can be controlled to be any one of 0.009%, 0.010%, 0.014%, 0.015%, 0.016%, 0.018%, 0.020%, 0.021%, respectively.

[0100] Al: Aluminum is a deoxidizing element in steel, and excessive aluminum easily increases Al2O3 inclusions in steel, affecting the low-temperature toughness of the steel, and coarse inclusions cause discontinuous structure, causing stress concentration. In the present application, the aluminum content is controlled to be 0.021-0.049%.

[0101] Preferably, the aluminum content can be controlled to be 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%, respectively.

[0102] 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%.

[0103] Preferably, the P content is controlled to be 0.0120% or less, 0.0100% or less, and can also be controlled to be 0.0050% or more.

[0104] Preferably, the S content is controlled to be 0.0030% or less, 0.0020% or less, and can also be controlled to be 0.0005% or more.

[0105] Preferably, the N content is controlled at 0.0022% or more.

[0106] Preferably, the O content is controlled at 0.0011% or more.

[0107] Preferably, the H content is controlled at 0.00018% or less, and can also be controlled at 0.00005% or more.

[0108] Further, the chemical composition of the pipeline steel plate, in terms of mass percentage, also satisfies any one or both of the following ① and ②: ① CEV is 0.223-0.571, and ② Pcm is 0.091-0.294.

[0109] Here, the CEV and Pcm can be calculated by the following two formulas respectively:

[0110] CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15;

[0111] Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15.

[0112] 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 the C element in the pipeline steel plate is 0.03%, then "C" in the formula represents the mass percentage of 0.03.

[0113] Further, the residual stress of the pipeline steel plate is ≤130 MPa.

[0114] More preferably, the residual stress of the pipeline 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.

[0115] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0116] For example, the residual stress difference between any two of the head, the middle, the tail, the upper part, and the lower part is ≤50 MPa.

[0117] 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.

[0118] In this application, the steel material can be sampled and tested for residual stress according to GB / T 31310-2014 "Metallic Materials - Determination of Residual Stresses - Hole Drilling Strain Gage Method".

[0119] In the embodiment, the thickness of the pipeline steel plate is ≥ 6 mm.

[0120] Furthermore, the pipeline steel plate has excellent mechanical properties:

[0121] R m is 415-825 MPa;

[0122] R t0.5 ≥ 245 MPa;

[0123] A 50 ≥ 20%;

[0124] R t0.5 / R m ≤ 0.93.

[0125] In the present application, the steel material can be sampled and tested for mechanical properties in accordance with GB / T 2975-2018 “Steel and Steel Products Mechanical Properties Test Sampling Position and Sample Preparation” and GB / T 228.1-2021 “Metallic Materials Tensile Test Part 1: Room Temperature Test Method”.

[0126] The pipeline steel plate has excellent toughness, satisfying any one or any combination of the following:

[0127] 0℃ impact energy KV2≥ 250J;

[0128] -20℃ impact energy KV2≥ 230J;

[0129] -40℃ impact energy KV2≥ 200J;

[0130] -60℃ impact energy KV2≥ 180J;

[0131] ductile-to-brittle transition temperature T t50%US ≤ -80℃;

[0132] -10℃ DWTT drop hammer shear area fraction 100%;

[0133] -20℃ DWTT drop hammer shear area fraction ≥ 90%;

[0134] -30℃ DWTT drop hammer shear area fraction ≥ 85%;

[0135] 0℃ CTOD crack tip opening displacement ≥ 0.6mm;

[0136] -20℃ CTOD crack tip opening displacement ≥ 0.4mm;

[0137] -40℃ CTOD crack tip opening displacement ≥ 0.2mm.

[0138] 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 Mechanical Property Testing Sampling Position and Sample Preparation” and GB / T 229-2020 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0139] The hardness of the pipeline steel plate is ≤250HV 10 .

[0140] In addition, the pipeline steel plate has excellent flatness, with unevenness ≤3mm / m.

[0141] Further, the microstructure of the pipeline steel plate is polygonal ferrite + pearlite + tempered bainite.

[0142] Among them, the volume fraction of polygonal ferrite is 85-97%, the volume fraction of pearlite is 3-10%, and the volume fraction of tempered bainite is 0-10%, and the sum of the volume fractions of polygonal ferrite, pearlite and tempered bainite is 100%.

[0143] The average grain size of the pipeline steel plate is 3-30μm. Preferably, it is 12-30μm.

[0144] Second embodiment

[0145] The present embodiment provides a pipeline steel plate.

[0146] The difference between this embodiment and the aforementioned first embodiment is only in the microstructure of the pipeline steel plate. Only this difference will be introduced below; the rest is the same as the aforementioned first embodiment, and all can be referred to the introduction of the first embodiment, which will not be repeated.

[0147] In the present embodiment, the microstructure of the pipeline steel plate is polygonal ferrite + acicular ferrite + tempered bainite.

[0148] Among them, the volume fraction of polygonal ferrite is 0-10%, the volume fraction of acicular ferrite is 30-85%, and the volume fraction of tempered bainite is 10-65%, and the sum of the volume fractions of polygonal ferrite, acicular ferrite and tempered bainite is 100%.

[0149] The average grain size of the pipeline steel plate is 3-30μm. Preferably, it is 3-12μm.

[0150] Third embodiment

[0151] The present embodiment provides a pipeline steel plate, specifically a BM / 245MPa grade pipeline steel plate.

[0152] The chemical composition of the pipeline steel plate includes, in mass percentage, C 0.11-0.15%, Si 0.14-0.26%, Mn 1.16-1.24%, Nb 0.009-0.021%, 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.

[0153] For the main role of each element and the selection of its amount, reference can be made to the specific analysis in the first embodiment, which will not be repeated here.

[0154] Preferably, the content of P is controlled to be 0.0050-0.0150%.

[0155] Preferably, the content of S is controlled to be 0.0005-0.0040%.

[0156] Preferably, the content of N is controlled to be 0.0022-0.0048%.

[0157] Preferably, the content of O is controlled to be 0.0011-0.0025%.

[0158] Preferably, the content of H is controlled to be 0.00005-0.00018%.

[0159] Further, the chemical composition of the pipeline steel plate, in mass percentage, further satisfies any one or both of the following ① and ②: ① CEV is 0.303-0.357, and ② Pcm is 0.173-0.221.

[0160] Wherein, the calculation formula of CEV and Pcm is as described in the first embodiment, which will not be repeated.

[0161] Further, the residual stress of the pipeline steel plate is ≤50MPa.

[0162] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0163] For example, the residual stress difference of any two of the head, the middle, the tail, the upper part and the lower part is ≤25MPa.

[0164] Further, the thickness of the pipeline steel plate is ≥6mm.

[0165] Excellent mechanical properties: R m is 415-655MPa; R t0.5 ≥245MPa; A 50 ≥32%; R t0.5 / R m ≤0.87.

[0166] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2≥250J; -20℃ impact energy KV2≥230J; -40℃ impact energy KV2≥200J; -60℃ impact energy KV2≥180J; toughness transition temperature T t50%US ≤-80℃; -10℃ DWTT drop hammer shearing area fraction 100%; -20℃ DWTT drop hammer shearing area fraction≥90%; -30℃ DWTT drop hammer shearing area fraction≥85%; 0℃ CTOD crack tip opening displacement≥0.6mm; -20℃ CTOD crack tip opening displacement≥0.4mm; -40℃ CTOD crack tip opening displacement≥0.2mm.

[0167] The pipeline steel plate has a hardness of ≤200HV 10 .

[0168] In addition, the pipeline steel plate has excellent flatness, and unevenness≤1mm / m.

[0169] Further, the pipeline steel plate has a microstructure of polygonal ferrite+pearlite+tempered bainite.

[0170] The volume fraction of the polygonal ferrite is 85~95%, the volume fraction of the pearlite is 5~10%, the volume fraction of the tempered bainite is 0~5%, and the total volume fraction of the polygonal ferrite, the pearlite and the tempered bainite is 100%.

[0171] The pipeline steel plate has an average grain size of 20~30μm.

[0172] Fourth embodiment

[0173] The present embodiment provides a pipeline steel plate, in particular to a X42M / 290MPa grade pipeline steel plate.

[0174] The chemical composition of the pipeline steel plate includes, in mass percentage: C 0.07~0.11%, Si 0.14~0.26%, Mn 1.31~1.39%, Nb 0.014~0.026%, 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.

[0175] For the main role of each element and the selection of its amount, please refer to the specific analysis in the first embodiment, which will not be repeated here.

[0176] Preferably, the P content is controlled to be 0.0050~0.0150%.

[0177] Preferably, the S content is controlled to be 0.0005-0.0040%.

[0178] Preferably, the N content is controlled to be 0.0022-0.0048%.

[0179] Preferably, the O content is controlled to be 0.0011-0.0025%.

[0180] Preferably, the H content is controlled to be 0.00005-0.00018%.

[0181] Further, the chemical composition of the pipeline steel plate, in terms of mass percentage, further satisfies any one or both of the following ① and ②: ① CEV is 0.288-0.342, and ② Pcm is 0.140-0.188.

[0182] Wherein, the calculation formulas of CEV and Pcm are as described in the first embodiment, which will not be repeated.

[0183] Further, the residual stress of the pipeline steel plate is ≤60 MPa.

[0184] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0185] For example, the residual stress difference of any two of the head, the middle, the tail, the upper portion, and the lower portion is ≤25 MPa.

[0186] Further, the thickness of the pipeline steel plate is ≥6 mm.

[0187] Excellent mechanical properties: R m is 415-655 MPa; R t0.5 ≥290 MPa; A 50 ≥30%; R t0.5 / R m ≤0.88.

[0188] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2≥260 J; -20℃ impact energy KV2≥250 J; -40℃ impact energy KV2≥220 J; -60℃ impact energy KV2≥200 J; ductile-to-brittle transition temperature T t50%US ≤-80℃; -10℃ DWTT drop hammer shear area fraction is 100%; -20℃ DWTT drop hammer shear area fraction is ≥95%; -30℃ DWTT drop hammer shear area fraction is ≥85%; 0℃ CTOD crack tip opening displacement is ≥0.8 mm; -20℃ CTOD crack tip opening displacement is ≥0.6 mm; -40℃ CTOD crack tip opening displacement is ≥0.3 mm.

[0189] The hardness of the pipeline steel plate is ≤200HV 10 .

[0190] In addition, the pipeline steel plate has excellent plate shape, and the unevenness is ≤1mm / m.

[0191] Further, the microstructure of the pipeline steel plate is polygonal ferrite+pearlite+tempered bainite.

[0192] The volume fraction of the polygonal ferrite is 90-97%, the volume fraction of the pearlite is 3-8%, and the volume fraction of the tempered bainite is 0-2%, and the sum of the volume fractions of the polygonal ferrite, the pearlite and the tempered bainite is 100%.

[0193] The average grain size of the pipeline steel plate is 18-28μm.

[0194] Fifth embodiment

[0195] The present embodiment provides a pipeline steel plate, in particular to a pipeline steel plate of X52M / 360MPa grade.

[0196] The chemical composition of the pipeline steel plate includes, in terms of mass percentage, C 0.05-0.09%, Si 0.12-0.24%, Mn 1.46-1.54%, Cr 0.06-0.24%, Nb 0.019-0.031%, 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.

[0197] For the main role of each element and the selection of its amount, please refer to the specific analysis in the first embodiment, which will not be repeated here.

[0198] Preferably, the content of P is controlled to be 0.0050-0.0120%.

[0199] Preferably, the content of S is controlled to be 0.0005-0.0030%.

[0200] Preferably, the content of N is controlled to be 0.0022-0.0048%.

[0201] Preferably, the content of O is controlled to be 0.0011-0.0025%.

[0202] Preferably, the content of H is controlled to be 0.00005-0.00018%.

[0203] Further, the chemical composition of the pipeline steel plate satisfies any one or both of the following ① and ② in terms of mass percentage: ① CEV is 0.305-0.395, and ② Pcm is 0.130-0.187.

[0204] The calculation formulas of CEV and Pcm are as described in the first embodiment.

[0205] Further, the residual stress of the pipeline steel plate is ≤70 MPa.

[0206] In addition, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0207] For example, the residual stress difference between any two of the head, the middle, the tail, the upper portion, and the lower portion is ≤30 MPa.

[0208] Further, the thickness of the pipeline steel plate is ≥6 mm.

[0209] The pipeline steel plate has excellent mechanical properties: R m is 460-760 MPa; R t0.5 ≥360 MPa; A 50 ≥28%; R t0.5 / R m ≤0.89.

[0210] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2≥280 J; -20℃ impact energy KV2≥270 J; -40℃ impact energy KV2≥240 J; -60℃ impact energy KV2≥220 J; ductile-to-brittle transition temperature T t50%US ≤-100℃; -10℃ DWTT drop hammer shear area fraction is 100%; -20℃ DWTT drop hammer shear area fraction is ≥98%; -30℃ DWTT drop hammer shear area fraction is ≥90%; 0℃ CTOD crack tip opening displacement is ≥1.0 mm; -20℃ CTOD crack tip opening displacement is ≥0.8 mm; -40℃ CTOD crack tip opening displacement is ≥0.4 mm.

[0211] The pipeline steel plate has hardness ≤210 HV 10 .

[0212] In addition, the pipeline steel plate has excellent flatness, and unevenness is ≤2 mm / m.

[0213] Further, the microstructure of the pipeline steel plate is polygonal ferrite + pearlite + tempered bainite.

[0214] The volume percentage of the polygonal ferrite is 85-92%, the volume percentage of the pearlite is 3-5%, the volume percentage of the tempered bainite is 5-10%, and the volume percentage of the polygonal ferrite, the pearlite and the tempered bainite is 100%.

[0215] The average grain size of the pipeline steel plate is 12-20 μm.

[0216] Sixth embodiment

[0217] The embodiment provides a pipeline steel plate, and particularly relates to an X60M / 415 MPa grade pipeline steel plate.

[0218] The pipeline steel plate comprises the following chemical components in percentage by mass: C 0.04-0.08%, Si 0.10-0.22%, Mn 1.51-1.59%, Cr 0.06-0.24%, Ni 0.02-0.18%, Nb 0.024-0.036%, 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.

[0219] The main roles of the various elements and the selection of the amounts thereof can be referred to the specific analysis in the first embodiment, and will not be repeated here.

[0220] Preferably, the content of P is controlled to be 0.0050-0.0120%.

[0221] Preferably, the content of S is controlled to be 0.0005-0.0030%.

[0222] Preferably, the content of N is controlled to be 0.0022-0.0048%.

[0223] Preferably, the content of O is controlled to be 0.0011-0.0025%.

[0224] Preferably, the content of H is controlled to be 0.00005-0.00018%.

[0225] Further, the chemical components of the pipeline steel plate satisfy the following ① and ② or both in percentage by mass: ① CEV is 0.305-0.405, and ② Pcm is 0.122-0.182.

[0226] The calculation formulae of CEV and Pcm are the same as those in the first embodiment, and will not be repeated here.

[0227] Further, the residual stress of the pipeline steel plate is ≤90 MPa.

[0228] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0229] For example, the residual stress difference between any two of the head, the middle, the tail, the upper portion and the lower portion is less than or equal to 35 MPa.

[0230] Further, the thickness of the pipeline steel plate is greater than or equal to 6 mm.

[0231] Excellent mechanical properties: R m is 520-760 MPa; R t0.5 is greater than or equal to 415 MPa; A 50 is greater than or equal to 26%; R t0.5 / R m is less than or equal to 0.90.

[0232] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2 is greater than or equal to 300 J; -20℃ impact energy KV2 is greater than or equal to 290 J; -40℃ impact energy KV2 is greater than or equal to 260 J; -60℃ impact energy KV2 is greater than or equal to 240 J; ductile-to-brittle transition temperature T t50%US is less than or equal to -100℃; -10℃ DWTT drop hammer shear area fraction is 100%; -20℃ DWTT drop hammer shear area fraction is greater than or equal to 100%; -30℃ DWTT drop hammer shear area fraction is greater than or equal to 90%; 0℃ CTOD crack tip opening displacement is greater than or equal to 1.0 mm; -20℃ CTOD crack tip opening displacement is greater than or equal to 0.8 mm; -40℃ CTOD crack tip opening displacement is greater than or equal to 0.4 mm.

[0233] The hardness of the pipeline steel plate is less than or equal to 220 HV 10 .

[0234] In addition, the pipeline steel plate has excellent flatness, and the unevenness is less than or equal to 2 mm / m.

[0235] Further, the microstructure of the pipeline steel plate is polygonal ferrite + acicular ferrite + tempered bainite.

[0236] The volume fraction of the polygonal ferrite is 5-10%, the volume fraction of the acicular ferrite is 70-85%, the volume fraction of the tempered bainite is 10-20%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

[0237] The average grain size of the pipeline steel plate is 4-12 μm.

[0238] Seventh embodiment

[0239] The present embodiment provides a pipeline steel plate, in particular, a X65M / 450 MPa grade pipeline steel plate.

[0240] The chemical composition of the pipeline steel plate includes, in mass percentage, C 0.04~0.08%, Si 0.10~0.22%, Mn 1.51~1.59%, Cr 0.09~0.27%, Ni 0.02~0.18%, Nb 0.034~0.046%, 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.

[0241] The main role of each element and the selection of its amount can refer to the specific analysis in the first embodiment, which will not be repeated here.

[0242] Preferably, the content of P is controlled to be 0.0050~0.0120%.

[0243] Preferably, the content of S is controlled to be 0.0005~0.0030%.

[0244] Preferably, the content of N is controlled to be 0.0022~0.0048%.

[0245] Preferably, the content of O is controlled to be 0.0011~0.0025%.

[0246] Preferably, the content of H is controlled to be 0.00005~0.00018%.

[0247] Further, the chemical composition of the pipeline steel plate, in mass percentage, also satisfies any one or both of the following ① and ②: ① CEV is 0.311~0.411, and ② Pcm is 0.124~0.183.

[0248] Wherein, the calculation formula of CEV and Pcm is in the first embodiment, which will not be repeated.

[0249] Further, the residual stress of the pipeline steel plate is ≤100MPa.

[0250] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0251] For example, the residual stress difference of any two of the head, the middle, the tail, the upper part and the lower part is ≤35MPa.

[0252] Further, the thickness of the pipeline steel plate is ≥6mm.

[0253] Excellent mechanical properties: R m is 535~760MPa; R t0.5 ≥450MPa; A 50 ≥24%; R t0.5 / Rm ≤0.91.

[0254] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2≥320J; -20℃ impact energy KV2≥310J; -40℃ impact energy KV2≥280J; -60℃ impact energy KV2≥260J; ductile-brittle transition temperature T t50%US ≤-100℃; -10℃ DWTT drop hammer shearing area fraction 100%; -20℃ DWTT drop hammer shearing area fraction≥100%; -30℃ DWTT drop hammer shearing 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.

[0255] The pipeline steel plate has a hardness≤230HV 10 .

[0256] In addition, the pipeline steel plate has excellent flatness, and unevenness≤2mm / m.

[0257] Further, the pipeline steel plate has a structure of polygonal ferrite + acicular ferrite + tempered bainite.

[0258] The volume fraction of the polygonal ferrite is 5-10%, the volume fraction of the acicular ferrite is 65-80%, the volume fraction of the tempered bainite is 15-25%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

[0259] The pipeline steel plate has an average grain size of 3-11μm.

[0260] Eighth embodiment

[0261] The embodiment provides a pipeline steel plate, and particularly relates to an X70M / 485MPa-grade pipeline steel plate.

[0262] The pipeline steel plate has a chemical composition containing, in mass percentage, C 0.03-0.07%, Si 0.09-0.21%, Mn 1.56-1.64%, Cr 0.09-0.27%, Ni 0.06-0.24%, Mo 0.02-0.14%, Nb 0.044-0.056%, 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 being iron and inevitable impurities.

[0263] The main role of each element and the selection of its amount can refer to the specific analysis in the first embodiment, which will not be repeated here.

[0264] Preferably, the content of P is controlled at 0.0050~0.0100%.

[0265] Preferably, the content of S is controlled at 0.0005~0.0020%.

[0266] Preferably, the content of N is controlled at 0.0022~0.0048%.

[0267] Preferably, the content of O is controlled at 0.0011~0.0025%.

[0268] Preferably, the content of H is controlled at 0.00005~0.00018%.

[0269] Further, the chemical composition of the pipeline steel plate, in terms of mass percentage, further satisfies any one or both of the following ① and ②: ① CEV is 0.316~0.441, and ② Pcm is 0.118~0.186.

[0270] Wherein, the calculation formula of CEV and Pcm is as described in the first embodiment, which will not be repeated.

[0271] Further, the residual stress of the pipeline steel plate is ≤120MPa.

[0272] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0273] For example, the residual stress difference of any two of the head, the middle, the tail, the upper part and the lower part is ≤40MPa.

[0274] Further, the thickness of the pipeline steel plate is ≥6mm.

[0275] Excellent mechanical properties: R m is 570~760MPa; R t0.5 ≥485MPa; A 50 ≥22%; R t0.5 / R m ≤0.92.

[0276] The pipeline steel plate has excellent toughness, and satisfies any one or any combination of the following: 0℃ impact energy KV2≥340J; -20℃ impact energy KV2≥330J; -40℃ impact energy KV2≥300J; -60℃ impact energy KV2≥280J; ductile-brittle transition temperature T t50%US≤-100℃; -10℃ DWTT drop weight shear area fraction 100%; -20℃ DWTT drop weight shear area fraction ≥100%; -30℃ DWTT drop weight 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.

[0277] The hardness of the pipeline steel plate is ≤240HV 10 .

[0278] In addition, the pipeline steel plate has excellent flatness, and the unevenness is ≤3mm / m.

[0279] Further, the microstructure of the pipeline steel plate is polygonal ferrite + acicular ferrite + tempered bainite.

[0280] The volume fraction of the polygonal ferrite is 0-5%, the volume fraction of the acicular ferrite is 55-70%, the volume fraction of the tempered bainite is 30-40%, and the sum of the volume fractions of the polygonal ferrite, the acicular ferrite and the tempered bainite is 100%.

[0281] The average grain size of the pipeline steel plate is 3-9μm.

[0282] Ninth embodiment

[0283] The present embodiment provides a pipeline steel plate, in particular to a X80M / 555MPa grade pipeline steel plate.

[0284] The chemical composition of the pipeline 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 inevitable impurities.

[0285] For the main role of each element and the selection of its amount, refer to the specific analysis in the first embodiment, which will not be repeated here.

[0286] Preferably, the content of P is controlled to be 0.0050-0.0100%.

[0287] Preferably, the content of S is controlled to be 0.0005-0.0020%.

[0288] Preferably, the N content is controlled to be 0.0022-0.0048%.

[0289] Preferably, the O content is controlled to be 0.0011-0.0025%.

[0290] Preferably, the H content is controlled to be 0.00005-0.00018%.

[0291] Further, the chemical composition of the pipeline steel plate, in terms of mass percentage, further satisfies any one or both of the following ① and ②: ① CEV is 0.354-0.491, and ② Pcm is 0.135-0.212.

[0292] Wherein, the calculation formulas of CEV and Pcm are as described in the first embodiment, which will not be repeated.

[0293] Further, the residual stress of the pipeline steel plate is ≤130 MPa.

[0294] And, the pipeline steel plate has small residual stress fluctuation and uniform distribution.

[0295] For example, the residual stress difference between any two of the head, the middle, the tail, the upper portion and the lower portion is ≤50 MPa.

[0296] Further, the thickness of the pipeline steel plate is ≥6 mm.

[0297] Excellent mechanical properties: R m is 625-825 MPa; R t0.5 ≥555 MPa; A 50 ≥20%; R t0.5 / R m ≤0.93.

[0298] The pipeline steel plate has excellent 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-to-brittle transition temperature T t50%US ≤-100℃; -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; -40℃ CTOD crack tip opening displacement is ≥0.6 mm.

[0299] The hardness of the pipeline steel plate is ≤250 HV 10 .

[0300] In addition, the pipeline steel plate has excellent flatness, and unevenness is less than or equal to 3 mm / m.

[0301] Further, the pipeline steel plate has a microstructure of polygonal ferrite + acicular ferrite + tempered bainite.

[0302] 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%.

[0303] The pipeline steel plate has an average grain size of 3-9 μm.

[0304] Tenth embodiment

[0305] The embodiment provides a production method of a pipeline steel plate.

[0306] The production method can be used to prepare a pipeline steel plate with low and uniform residual stress.

[0307] Further, the production method can also be used to prepare the pipeline steel plate provided in any one of the first to ninth embodiments.

[0308] In the embodiment, the production method comprises a casting blank heating process, a hot rolling process, a controlled water cooling process and an air cooling self-tempering process in sequence, so as to process the casting blank into a pipeline steel plate.

[0309] The processes are described in detail below in sequence.

[0310] <casting blank heating process>

[0311] In the process, the casting blank is sent into a heating furnace for heating.

[0312] The casting blank can be a continuous casting blank or a die casting blank, which is not limited in the application.

[0313] The thickness of the casting blank is preferably greater than or equal to 200 mm, for example, 220-320 mm.

[0314] The chemical composition of the casting blank is consistent with that of the prepared pipeline steel plate. For example, when the pipeline steel plate provided in any one of the first to ninth embodiments is prepared, the chemical composition of the casting blank is also the same as the chemical composition described in the first to ninth embodiments.

[0315] In the process, the soaking temperature is T NbC +(50-125) ℃, and the soaking time is greater than or equal to 25 min.

[0316] T NbC is the starting precipitation temperature of NbC, and the formula T NbC=7700 / (3.18-lg(Nb×C 0.87 The formula ))-273.15 is used for calculation, where the element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0317] Thus, by controlling the homogenization temperature and duration, on the one hand, excessive growth of austenite grains can be avoided, preparing for precipitation in subsequent hot rolling processes; on the other hand, and more importantly, it can ensure that Nb precipitates are completely dissolved, reducing residual stress.

[0318] Preferably, the heat spreader temperature is T. NbC +50℃, T NbC +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 Any value of +125℃.

[0319] Preferably, this process can employ segmented heating, such as including heat recovery, preheating, primary heating, secondary heating, and homogenization. However, it is not limited to this.

[0320] The heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the first heating temperature is 970~1030℃, the second heating temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm billet thickness. In this way, by segmenting the heating process and controlling the temperature of each segment, the billet can be heated slowly and uniformly, reducing the temperature difference between the beginning, middle, and end of the billet, as well as the surface and center, thereby avoiding cracking caused by thermal stress.

[0321] Furthermore, the furnace entry temperature of the billet is ≥ M S -350℃.

[0322] M S The starting temperature for the austenite-to-martensite phase transformation is given by formula M. S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo, calculated in °C. The element symbols in the formula represent the mass percentage of the corresponding element in the billet.

[0323] <Hot Rolling Process>

[0324] In this process, the billet is rolled into a pipeline steel plate with a thickness d of not less than 6 mm through the first stage rolling, intermediate billet cooling and the second stage rolling.

[0325] The thickness d of the steel plate is, for example, specifically 6-60 mm.

[0326] In the first stage rolling, the starting rolling temperature T nr +(10-100)℃, the finishing rolling temperature T nr +(5-50)℃.

[0327] Wherein, T nr is the lowest temperature of austenite recrystallization, calculated by the formula T nr =887+464C-357Si+6445Nb-644 +890Ti+363Al, and the element symbols in each formula represent the mass percentage of the corresponding element in the casting blank.

[0328] Through the first stage rolling, the intermediate blank thickness is 2.5-3.5 times the target thickness of the pipeline steel plate.

[0329] In this way, rolling in the higher temperature range can reduce the rolling deformation resistance, increase the rolling reduction, facilitate the penetration of deformation to the core of the blank, and improve the core segregation, porosity and banded structure 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 and refines the recrystallized grains.

[0330] Wherein, the target thickness of the pipeline steel plate is the thickness d of the finally obtained steel plate.

[0331] Preferably, in the first stage rolling, the starting rolling temperature is any value in 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℃.

[0332] Preferably, in the first stage rolling, the finishing rolling temperature is any value in 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 nrany value in the range of +50°C.

[0333] Further, when the intermediate billet is cooled, the intermediate billet is cooled to a finish cooling temperature A r3 + (0~90) °C, and the cooling time is ≥ 50s.

[0334] wherein A r3 is the temperature at which austenite (γ-Fe) begins to precipitate ferrite (α-Fe) upon cooling, and is 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.

[0335] In this way, by controlling the finish cooling temperature and the cooling time, not only can the production efficiency be ensured, but also the low-temperature toughness can be avoided from being deteriorated due to the rapid growth of recrystallized grains during the temperature holding, and more importantly, the recrystallization can be fully achieved, and certain internal stress can be released at high temperature.

[0336] Preferably, the finish cooling temperature is any value in the range of A r3 , A r3 + 10°C, A r3 + 20°C, A r3 + 30°C, A r3 + 40°C, A r3 + 50°C, A r3 + 60°C, A r3 + 70°C, A r3 + 80°C, A r3 + 90°C.

[0337] Preferably, the cooling time is ≥ 70s.

[0338] More preferably, the cooling of the intermediate billet can be air cooling.

[0339] Next, during the second stage rolling, the starting rolling temperature A r3 + (-10~80) °C, and the finishing rolling temperature A r3 + (-50~40) °C and the pre-rolling dwell time is 8~10s.

[0340] In this way, not only can the microstructure be controlled, but also by pre-rolling dwell for 8~10s in the finishing pass, the stress accumulated in the steel can be fully released, so as to ensure that the low residual stress is finally obtained.

[0341] Preferably, during the second stage rolling, the reduction amount of each pass is ≤ 20mm, and the reduction amount of the finishing pass is ≤ 3mm.

[0342] Thus, through the deformation of small reduction, the fine structure can be obtained in the subsequent cooling process, the low temperature toughness of the steel plate is improved, the shape of the plate is improved, the temperature difference of the same plate is reduced, and the residual stress is further reduced.

[0343] Preferably, in the second stage rolling, the opening rolling temperature is A r3 -10℃, A r3 , A r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃, A r3 +50℃, A r3 +60℃, A r3 +70℃, A r3 +80℃.

[0344] Preferably, in the second stage rolling, the rolling temperature of the last pass is A r3 -50℃, A r3 -40℃, A r3 -30℃, A r3 -20℃, A r3 -10℃, A r3 , A r3 +10℃, A r3 +20℃, A r3 +30℃, A r3 +40℃.

[0345] <Control water cooling process>

[0346] In this process, the pipeline steel plate obtained by rolling is water-cooled.

[0347] In this process, the water inlet temperature A r3 +(-80~10)℃, the water outlet temperature B s +(-220~100)℃, and the cooling speed is 10~25℃ / s.

[0348] Wherein, B s is the temperature at the beginning of the bainite phase transition, 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.

[0349] Thus, through the control of temperature and cooling speed, the supercooled austenite phase in the steel plate can be cooled to cause phase transition, the weak water slow cooling speed is adopted to transform to ferrite / bainite, so that the strength and toughness are well matched and balanced, the formation of martensite is avoided, and the residual stress is low and uniformly distributed.

[0350] Preferably, the water inlet temperature is any value in the range of A r3 -80℃, A r3 -70℃, A r3 -60℃, A r3 -50℃, A r3 -40℃, A r3 -30℃, A r3 -20℃, A r3 -10℃, A r3 , A r3 +10℃.

[0351] Preferably, the water outlet temperature is any value in the range of B s -220℃, B s -200℃, B s -180℃, B s -160℃, B s -140℃, B s -120℃, B s -100℃, B s -80℃, B s -60℃, B s -40℃, B s -20℃, B s , B s +20℃, B s +40℃, B s +60℃, B s +80℃, B s +100℃.

[0352] Preferably, the cooling speed is any value in the range of 10℃ / s, 12℃ / s, 14℃ / s, 15℃ / s, 16℃ / s, 18℃ / s, 20℃ / s, 22℃ / s, 23℃ / s, 25℃ / s.

[0353] Preferably, in the process, the pipeline steel plate is water-cooled on the ultrafast cooling system.

[0354] The roller speed of the ultrafast cooling system is preferably controlled in the range of 0.8~2.0m / s.

[0355] Further, in an optional embodiment, the control of the cooling manifold on the ultrafast cooling system can be in an intermittent manner or a head-tail shielding manner. Of course, the present application is not limited thereto.

[0356] The intermittent manner specifically includes, for example, that the ultrafast cooling system includes 24 groups or more of cooling manifolds distributed along the roller, and the control manner of the cooling manifolds is:

[0357] Along the roller, every 1~2 groups of cooling headers are opened, and 1~2 groups of cooling headers are closed.

[0358] The head-tail shielding mode specifically includes, for example, dividing the steel plate 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 positive integers 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 of 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 of Q from the tail to the head; wherein, k X1 ~k Xn , K X1 ~K Xm are all in a range of 0.55~0.85 and 0.50~0.80, respectively.

[0359] <Air-cooling self-tempering process>

[0360] In the process, the pipeline steel plate is air-cooled on a cooling bed, and self-tempering occurs during the cooling.

[0361] In this way, by air-cooling self-tempering after water cooling, combined 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.

[0362] Preferably, in the process, the temperature of the cooling bed is B s +(-270~50)℃.

[0363] The temperature of the cooling bed is B s -270℃, B s -250℃, B s -240℃, B s -220℃, B s -200℃, B s -180℃, B s -160℃, B s -140℃, B s -120℃, B s -100℃, B s -80℃, B s -60℃, B s -50℃, B s -40℃, B s -10℃, B s , B s+10°C, B s +30°C, B s any value in the range of +50°C.

[0364] Further, in the process, the temperature of the steel sheet on the down coiler is not more than M s -150°C.

[0365] Preferably, the temperature of the steel sheet on the down coiler is M s -(260-150) °C.

[0366] More preferably, the temperature of the steel sheet on the down coiler 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, M s -200°C, M s -190°C, M s -180°C, M s -170°C, M s -160°C, M s -150°C.

[0367] In the production method of the present embodiment, in the whole, in one preferred embodiment, when the intermediate billet is cooled, the final cooling temperature is A r3 +(70-90) °C; in the second stage rolling, the starting rolling temperature is A r3 +(60-80) °C, and the rolling temperature of the last pass is A r3 +(20-40) °C; in the controlled water cooling process, the water inlet temperature is A r3 +(-10-10) °C, and the water outlet temperature is B s +(60-100) °C; in the air cooling self-tempering process, the temperature of the up coiler is B s +(10-50) °C, and the temperature of the down coiler is M s -(200-150) °C.

[0368] In another preferred embodiment, when the intermediate billet is cooled, the final cooling temperature is A r3 +(60-80) °C; in the second stage rolling, the starting rolling temperature is A r3 +(50-70) °C, and the rolling temperature of the last pass is A r3 +(10-30) °C; in the controlled water cooling process, the water inlet temperature is A r3 +(-20-0) °C, and the water outlet temperature is B s +(20-60) °C; in the air cooling self-tempering process, the temperature of the up coiler is B s+(30~50)℃; the second stage rolling is started at A s -(210~160)℃.

[0369] In another preferred embodiment, the intermediate billet is cooled to a finish cooling temperature A r3 +(40~60)℃; the second stage rolling is started at A r3 +(30~50)℃; the second stage rolling is started at A r3 +(-10~10)℃; the controlled water cooling process is started at A r3 -(40~20)℃, B is the water outlet temperature s +(-10~30)℃; the air cooling and self-tempering process is started at B s -(60~20)℃, M is the lower cooling bed temperature s -(220~170)℃.

[0370] In another preferred embodiment, the intermediate billet is cooled to a finish cooling temperature A r3 +(30~50)℃; the second stage rolling is started at A r3 +(20~40)℃; the second stage rolling is started at A r3 -(20~0)℃; the controlled water cooling process is started at A r3 -(50~30)℃, B is the water outlet temperature s -(40~0)℃; the air cooling and self-tempering process is started at B s -(100~50)℃, M is the lower cooling bed temperature s -(230~180)℃.

[0371] In another preferred embodiment, the intermediate billet is cooled to a finish cooling temperature A r3 +(20~40)℃; the second stage rolling is started at A r3 +(10~30)℃; the second stage rolling is started at A r3 -(30~10)℃; the controlled water cooling process is started at A r3 -(60~40)℃, B is the water outlet temperature s -(70~30)℃; the air cooling and self-tempering process is started at B s -(120~80)℃, M is the lower cooling bed temperature s -(240~190)℃.

[0372] In another preferred embodiment, the intermediate billet is cooled to a finish cooling temperature A r3 +(10~30)℃; the second stage rolling is started at A r3 +(0~20)℃; the second stage rolling is started at Ar3 -(40~20)℃; control water cooling process, water temperature A r3 -(70~50)℃, water temperature B s -(140~100)℃; air cooling self-tempering process, upper cooling bed temperature B s -(190~150)℃, lower cooling bed temperature M s -(250~200)℃.

[0373] In another preferred embodiment, the intermediate blank is cooled to a final cooling temperature A r3 +(0~20)℃; the second stage rolling, the rolling temperature A r3 +(-10~10)℃, the last pass rolling temperature A r3 -(50~30)℃; control water cooling process, water temperature A r3 -(80~60)℃, water temperature B s -(220~180)℃; air cooling self-tempering process, upper cooling bed temperature B s -(270~230)℃, lower cooling bed temperature M s -(260~210)℃.

[0374] In summary, in one embodiment of the present application, by soaking temperature, soaking time, temperature in hot rolling, temperature and cooling rate of controlled water cooling, and 8~10s operation before the last pass of hot rolling, 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. For example, the residual stress of the steel plate is ≤130MPa, and the residual stress difference between any two of the head, middle, tail, upper and lower parts is ≤50MPa.

[0375] Even, the residual stress of the steel plate can be reduced to not more than 100MPa, 90MPa or 80MPa, more even not more than 70MPa, more or not more than 60MPa, even 50MPa.

[0376] The residual stress difference between any two of the middle, tail, upper and lower parts can be not more than 40MPa, or not more than 35MPa, or not more than 30MPa, or even not more than 25MPa.

[0377] Eleventh embodiment

[0378] The embodiment provides a production method of a pipeline steel plate.

[0379] The difference between the embodiment and the tenth embodiment is only that a stacking process is added after the air cooling self-tempering process. Only the difference will be introduced below; the rest is the same as the tenth embodiment, and all can be referred to the introduction of the tenth embodiment, and will not be repeated here.

[0380] Specifically, in the embodiment, the production method comprises sequentially a casting slab heating process, a hot rolling process, a controlled water cooling process, an air cooling self-tempering process, and a stacking process, so as to process the casting slab into the pipeline steel plate.

[0381] <Stacking process>

[0382] In the process, the pipeline steel plate is combined and stacked with the auxiliary steel plate.

[0383] Specifically, as shown in the figure, a group of steel plates 21 is composed of the auxiliary steel plate 20 in the lower layer and the pipeline steel plate 10 in the upper layer. Figure 1

[0384] The stacking is performed in the manner that n groups of steel plates 21 are sequentially stacked from bottom to top, and the auxiliary steel plate 20 covers the top layer, where n is a positive integer.

[0385] Figure 1 In the figure, two groups of steel plates 21 are shown, but in the specific implementation, there can be one group, three groups, or more groups of steel plates 21.

[0386] In the process, the stacking temperature of the auxiliary steel plate is M s +(-110~50)℃.

[0387] The stacking temperature of the pipeline steel plate is ≤M s -150℃, and the unstacking temperature is not more than M s -(410~250)℃.

[0388] In this way, the stacking temperature of the pipeline steel plate is less than the stacking temperature of the auxiliary steel plate, so that the pipeline steel plate can be tempered by the heat of the auxiliary steel plate, on the one hand, to improve the uniformity of the structure and performance of the pipeline steel plate, and on the other hand, to further release the internal stress, reduce the residual stress of the pipeline steel plate, and improve the distribution uniformity of the residual stress.

[0389] Preferably, the stacking temperature of the pipeline steel plate is less than any of M s -260℃, M s -250℃, M s -240℃, M s -230℃, M s -220℃, M s -210℃, M s -200℃, M s -190℃, M s -180℃, M s -170℃, M s -160℃, M s -150℃.

[0390] ​The unstacking temperature of the pipeline 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℃, M s -310℃, M s -300℃, M s -290℃, M s -280℃, M s -270℃, M s -260℃, or M s -250℃.

[0391] Further, the length, width and thickness of the pipeline steel plate are all less than those of the auxiliary steel plate.

[0392] Furthermore, the stacking time in the process is preferably 12-18h.

[0393] Twelfth embodiment

[0394] The embodiment provides a pipeline steel plate production method.

[0395] As further optimization of the foregoing tenth or eleventh embodiment, the embodiment further adds any one or several of the following four processes: temperature-controlled preheating straightening process, temperature-controlled hot straightening process, temperature-controlled warm straightening process, and temperature-controlled cold straightening process.

[0396] That is, in the embodiment, the production method comprises, in sequence, the slab heating process, the hot rolling process, the temperature-controlled preheating straightening process (optional), the controlled water cooling process, the temperature-controlled hot straightening process (optional), the air cooling self-tempering process, the temperature-controlled warm straightening process (optional), the stacking process (optional), and the temperature-controlled cold straightening process (optional).

[0397] The following will be described in detail only for the four processes that can be selectively added. The slab heating process, the hot rolling process, the controlled water cooling process, and the air cooling self-tempering process can be referred to the description of the tenth embodiment, and the stacking process can be referred to the description of the eleventh embodiment.

[0398] <temperature-controlled preheating straightening process>

[0399] In the process, the pipeline steel plate obtained by the hot rolling process is subjected to at least one pass of preheating straightening.

[0400] wherein the straightening speed is 0.1-1.5 m / s and the straightening temperature is A r3 +(-65-25)℃, the maximum reduction is ≤4 mm.

[0401] In this way, 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, so as to ensure that the steel plate maintains high flatness before the water cooling control process. Moreover, straightening is performed before the phase change in the water cooling control process, which can release part of the internal stress generated by rolling deformation, thereby finally reducing the residual stress of the pipeline steel plate product.

[0402] Preferably, in this process, the straightening temperature is A r3 -65℃, A r3 -60℃, A r3 -55℃, A r3 -50℃, A r3 -45℃, A r3 -40℃, A r3 -35℃, A r3 -30℃, A r3 -25℃, A r3 -20℃, A r3 -15℃, A r3 -10℃, A r3 -5℃, A r3 , A r3 +5℃, A r3 +10℃, A r3 +15℃, A r3 +20℃, A r3 +25℃.

[0403] <temperature-controlled hot straightening process>

[0404] In this process, the steel plate after water out in the water cooling control process is subjected to 1-3 passes of hot straightening.

[0405] wherein the straightening speed is 0.1-1.5 m / s and the straightening temperature is B s +(-230-90)℃, the maximum reduction is ≤4 mm.

[0406] In this way, 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, by straightening, the phase change stress and thermal stress can be released, so as to finally reduce the residual stress of the pipeline steel plate product.

[0407] Preferably, in this process, the straightening temperature is B s -230℃, B s -200℃, Bs -190℃, B s -180℃, B s -150℃, B s -120℃, B s -110℃, B s -80℃, B s -50℃, B s -40℃, B s -20℃, B s -10℃, B s , B s +10℃, B s +20℃, B s +50℃, B s +90℃.

[0408] <temperature-controlled straightening process>

[0409] In this process, the steel plate is subjected to 2-4 passes of temperature straightening after being discharged from the air-cooling self-tempering process.

[0410] In this process, the straightening speed is 0.1-0.5 m / s, and the straightening temperature is M s -(270-150)℃, the maximum reduction is ≤10 mm.

[0411] Thus, during the air-cooling self-tempering process, certain residual stress is still generated, which may cause buckling. Straightening the steel plate after air-cooling self-tempering can further release phase transformation stress and thermal stress, so as to finally reduce the residual stress of the pipeline steel plate product.

[0412] Preferably, in this process, the straightening temperature is M s -270℃, M s -260℃, M s -250℃, M s -240℃, M s -230℃, M s -220℃, M s -210℃, M s -200℃, M s -190℃, M s -180℃, M s -170℃, M s -160℃, M s -150℃.

[0413] <temperature-controlled cold straightening process>

[0414] In this process, the steel plate is subjected to 1-3 passes of cold straightening.

[0415] Wherein, the straightening speed is 0.1-0.5 m / s, and the straightening temperature is M s - (420-360) ℃, and the maximum reduction is ≤6 mm.

[0416] In this way, the phase transformation stress and the thermal stress are further released, so as to finally reduce the residual stress of the pipeline steel plate product.

[0417] Preferably, in the process, the straightening temperature is M s - 420 ℃, M s - 410 ℃, M s - 400 ℃, M s - 390 ℃, M s - 380 ℃, M s - 370 ℃, M s - 360 ℃.

[0418] Thirteenth embodiment

[0419] The embodiment provides a production method of a pipeline steel plate.

[0420] As a further optimization of any one of the preceding tenth to twelfth embodiments, the embodiment further adds the following processes: a surface treatment process, a tempering heat treatment process, and a post-tempering stacking process.

[0421] Hereinafter, only the three processes are described in detail. The other processes of the production method, such as the casting blank heating process, the hot rolling process, the controlled water cooling process, the air cooling and self-tempering process, the stacking process, the controlled temperature preheating and straightening process, the controlled temperature hot straightening process, the controlled temperature warm straightening process, and the controlled temperature cold straightening process, can be referred to the descriptions of the preceding tenth to twelfth embodiments, and will not be described in detail.

[0422] <surface treatment process>

[0423] In the embodiment, after the pipeline steel plate is cooled to room temperature, the surface treatment is performed on the steel plate by means of shot blasting or grit blasting.

[0424] Specifically, the surface treatment process is performed after the air cooling and self-tempering process, and when any one or several of the three processes of the controlled temperature warm straightening process, the stacking process, and the controlled temperature cold straightening process are selectively added after the air cooling and self-tempering process, the surface treatment process is performed at the end of the three processes that are selectively added (i.e., the surface treatment process is later than the air cooling and self-tempering process, the controlled temperature warm straightening process, the stacking process, and the controlled temperature cold straightening process).

[0425] In this way, by means of shot blasting or grit blasting on the pipeline steel plate cooled to room temperature, surface compressive stress can be achieved, and the residual tensile stress inside the pipeline steel plate can be offset by the surface compressive stress, so as to reduce the residual stress and improve the residual stress distribution.

[0426] Preferably, in one embodiment, for the pipeline steel plate with thickness d of 6-20 mm, the shot used for shot blasting or shot peening is a mixture of shot with diameter of 0.5 mm and shot with diameter of 0.7 mm in mass ratio of (7-8):5.

[0427] For the pipeline steel plate with thickness d of 20-50 mm, the shot used for shot blasting or shot peening is a mixture of shot with diameter of 0.7 mm and shot with diameter of 1.0 mm in mass ratio of (9-11):5.

[0428] For the pipeline steel plate with thickness d>50 mm, the shot used for shot blasting or shot peening is a mixture of shot with diameter of 1.0 mm and shot with diameter of 1.2 mm in mass ratio of (4-6):5.

[0429] More preferably, the time t of shot blasting or shot peening and the thickness d of the pipeline steel plate can satisfy t=kxd+C.

[0430] Wherein, the unit of t is min, k is 0.1-0.2 min / mm, and C is 5-7 min.

[0431] Still more preferably, the shot blasting amount or shot peening amount P and the thickness d of the pipeline steel plate satisfy P=k1xd+C1.

[0432] Wherein, the unit of P is kg / min, k1 is 0.4-0.6 kg / (min·mm), and C1 is 160-200 kg / min.

[0433] Yet more preferably, the speed S of shot blasting or shot peening and the thickness d of the pipeline steel plate satisfy S=k2xd+C2.

[0434] Wherein, the unit of S is m / s, k2 is 0.1-0.3 m / (s·mm), and C2 is 65-75 m / s.

[0435] In this way, the time t, the shot blasting amount or shot peening amount P, and the speed S of the present embodiment are jointly controlled with the thickness d of the plate, respectively, so that a uniform compressive stress layer can be formed on the surface of the pipeline steel plate, and the formed compressive stress can greatly eliminate residual tensile stress, achieving the effect of reducing residual stress and improving residual stress distribution.

[0436] Optionally, the shot used is cast steel shot with hardness of 35-50 HRC. The specific material of the cast steel shot is not limited in the present application.

[0437] <tempering heat treatment process>

[0438] In one embodiment, after the surface treatment process, the steel plate can be further subjected to a tempering heat treatment.

[0439] In the process, the heating rate is 8-15℃ / min.

[0440] and the tempering temperature T is B s +(-105~55)℃, and the holding time t1 of the tempering is controlled according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, and the unit of t1 is min.

[0441] That is, not only the tempering temperature T is controlled within a certain range, but also the tempering temperature T and the holding time t1 of the tempering are cooperatively controlled according to the formula. In this way, not only the structure and performance, including the mechanical properties, plasticity and toughness, hardness, and plate shape, can be optimized, but also the residual stress can be greatly reduced, the distribution of the residual stress can be improved, and the deformation and cracking in subsequent pipe processing can be prevented.

[0442] Preferably, for the pipeline steel plate with a thickness d of 6-20mm, the tempering temperature T is B s +(-65~55)℃.

[0443] For the pipeline steel plate with a thickness d of 20-50mm, the tempering temperature T is B s +(-85~35)℃.

[0444] For the pipeline steel plate with a thickness d>50mm, the tempering temperature T is B s +(-105~15)℃.

[0445] In this way, while cooperatively controlling the tempering temperature T and the holding time t1 of the tempering, and according to different thicknesses, the tempering temperature T is precisely controlled. On the one hand, the residual stress can be effectively reduced, and the decline of the material performance, especially the strength and toughness, can be avoided. On the other hand, the problem of excessive energy consumption and production cost caused by the introduction of the tempering heat treatment can also be avoided.

[0446] Preferably, in the process, the tempering heat treatment can be performed in a tempering furnace, and a nitrogen atmosphere can be maintained in the tempering furnace.

[0447] In this way, under the nitrogen atmosphere, not only the oxidation or decarburization of the steel plate during the tempering heat treatment can be prevented, and the surface quality of the steel plate can be protected, but also the uniformity of the residual stress can be further optimized.

[0448] <Stacking process after tempering>

[0449] In the process, after the holding time t1 of the tempering is reached, the steel plate is directly taken out of the furnace (i.e., the tempering furnace) and stacked.

[0450] The stacking temperature B s -(210~110)℃, the cooling rate is 10-30℃ / h, and the unstacking temperature is ≤B s- 450°C.

[0451] In this way, by rapid line-off and stacking, and controlling the cooling rate, the residual stress distribution is homogenized.

[0452] Preferably, the stacking duration is 12-24 hours.

[0453] The technical spirit of the present application and the basic situation of each embodiment are introduced above. Several test examples are provided below to show the beneficial effects of the present application. Of course, these test examples are only a part of the numerous changed embodiments contained in the present application, not all.

[0454] First, the chemical composition of the pipeline steel plate of several test examples is shown in Table 1. In the table, "-" indicates that the corresponding element is not added.

[0455] Among them, the steel plates of test examples 1-7 are produced according to the production method of the tenth embodiment, and the cast blank is treated by the cast blank heating process, hot rolling process, controlled water cooling process, air cooling self tempering process in sequence to prepare the steel plate product.

[0456] The steel plates of test examples 8-14 are produced according to the production method of the eleventh embodiment, and the cast blank is treated by the cast blank heating process, hot rolling process, controlled water cooling process, air cooling self tempering process, stacking process in sequence to prepare the steel plate product.

[0457] The steel plates of test examples 15-21 are produced according to the production method of the twelfth embodiment, and the cast blank is treated by the cast blank heating process, hot rolling process, controlled water cooling process, air cooling self tempering process, stacking process in sequence, and at least one or several of the temperature-controlled preheating straightening process, temperature-controlled hot straightening process, temperature-controlled warm straightening process, and temperature-controlled cold straightening process to prepare the steel plate product.

[0458] The steel plates of test examples 22-28 are produced according to the production method of the thirteenth embodiment, and the cast blank is treated by the cast blank heating process, hot rolling process, controlled water cooling process, air cooling self tempering process, stacking process, surface treatment process, tempering heat treatment process, and post-tempering stacking process, and optionally zero, one or several of the temperature-controlled preheating straightening process, temperature-controlled hot straightening process, temperature-controlled warm straightening process, and temperature-controlled cold straightening process to prepare the steel plate product.

[0459] [Table 1]

[0460]

[0461] Some important parameters in the production process are shown in Table 2, Table 3 and Table 4. In which, the thickness of the casting blank used in Examples 1-7 and 22-28 is 220 mm, and the thickness of the casting blank used in Examples 8-21 is 320 mm; in the second stage rolling, the last pass is stopped for 8-10 s before rolling. In addition, in Table 2-4, " / " means that the corresponding process is not performed, and the numerical value and "√" mean that the corresponding process is performed.

[0462] [Table 2]

[0463]

[0464] [Table 3]

[0465]

[0466] [Table 4]

[0467]

[0468] The microstructure and performance of the pipeline steel plates of each test example are detected, and the microstructure diagrams of some examples are shown, and the detection results are also shown in Table 5 and Table 6. Figures 2 to 8

[0469] In addition, the steel plates of all test examples: 0 ℃ impact energy KV2≥250 J; -20 ℃ impact energy KV2≥230 J; -40 ℃ impact energy KV2≥200 J; -60 ℃ impact energy KV2≥180 J; ductile-brittle transition temperature T t50%US ≤-80 ℃; -10 ℃ DWTT drop hammer shear area fraction 100%; -20 ℃ DWTT drop hammer shear area fraction≥90%; -30 ℃ DWTT drop hammer shear area fraction≥85%; 0 ℃ CTOD crack tip opening displacement≥0.6 mm; -20 ℃ CTOD crack tip opening displacement≥0.4 mm; -40 ℃ CTOD crack tip opening displacement≥0.2 mm.

[0470] [Table 5]

[0471]

[0472] [Table 6]

[0473]

[0474] It can be seen that the pipeline steel plates of each test example have excellent mechanical properties, low temperature toughness, thickness and shape, and low and uniform distribution of residual stress. Moreover, the production method of the pipeline steel plate provided by the embodiment of the present application can effectively reduce and control the residual stress in the steel plate at low production cost and process cost on the basis of ensuring the performance of the steel plate, and the pipeline steel plate with low and uniform distribution of residual stress is made.​

Claims

1. A method for producing pipeline steel plates, characterized in that, The production method includes sequential steps. Billet heating process: soaking temperature is T NbC +(50~125)℃, soaking time ≥25min; Hot rolling process: includes first-stage rolling, intermediate billet cooling, and second-stage rolling; during the first-stage rolling, the initial rolling temperature T... nr +(10~100)℃, final rolling temperature T nr +(5~50)℃; During intermediate billet cooling, the intermediate billet thickness is 2.5~3.5 times the target thickness of the pipeline steel plate, and the final cooling temperature is A. r3 +(0~90)℃, cooling time ≥50s; during the second stage of rolling, the initial rolling temperature A r3 +(-10~80)℃, the rolling temperature A of the final pass r3 The thickness d of the resulting pipeline steel plate shall not be less than 6mm after the temperature is +(-50~40)℃ and the plate is held for 8~10s before rolling. Controlling the water cooling process: Inlet water temperature A r3 +(-80~10)℃, outlet water temperature B s +(-220~100)℃, cooling rate 10~25℃ / s; Air-cooled self-tempering process: The steel plate is air-cooled on a cooling bed; Among them, T NbC T nr A r3 B s The following formulas are used to calculate the values ​​of each element, and the element symbols in each formula represent the mass percentage of the corresponding element in the billet. 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。 2. The method for producing pipeline steel plates according to claim 1, characterized in that, The billet heating process includes heat recovery, preheating, primary heating, secondary heating and homogenization. The heat recovery temperature is ≤800℃, the preheating temperature is ≤900℃, the primary heating temperature is 970~1030℃, the secondary heating temperature is 1070~1130℃, and the total heating time is 0.019~0.023h / mm billet thickness.

3. The method for producing pipeline steel plates according to claim 1, characterized in that, In the billet heating process, the billet's furnace entry temperature is ≥ M. S -350℃, M S The following formula is used for calculation, with the unit being ℃. The element symbols in the formula represent the mass percentage of the corresponding element in the billet. M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo。 4. The method for producing pipeline steel plates according to claim 1, characterized in that, In the air-cooled self-tempering process: the temperature B of the upper cooling bed s +(-270~50)℃, lower cooling bed temperature M s -(260~150)℃.

5. The method for producing pipeline steel plates according to claim 4, characterized in that, The production method further includes a stacking process after the air-cooled self-tempering process: stacking is carried out in a manner where n groups of steel plates are stacked sequentially from bottom to top, with the top layer covered by an auxiliary steel plate. Each group of steel plates consists of a lower auxiliary steel plate and an upper pipeline steel plate, where n is a positive integer; the stacking temperature of the auxiliary steel plates is M. s +(-110~50)℃, the unstacking temperature of pipeline steel plates shall not exceed M. s -(410~250)℃.

6. The method for producing pipeline steel plates according to claim 5, characterized in that, The production method further includes a temperature-controlled cold straightening process after the stacking process: performing 1-3 passes of cold straightening at a straightening speed of 0.1-0.5 m / s, a straightening temperature of Ms-(420-360)℃, and a maximum reduction of ≤6 mm; S The following formula is used for calculation, with the unit being ℃. The element symbols in the formula represent the mass percentage of the corresponding element in the billet. M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo。 7. The method for producing pipeline steel plates according to claim 1, characterized in that, The production method further includes a temperature-controlled straightening process after the air-cooled self-tempering process: performing 2-4 passes of secondary temperature straightening at a straightening speed of 0.1-0.5 m / s and a straightening temperature M. s -(270~150)℃, maximum reduction ≤10mm; M S The following formula is used for calculation, with the unit being ℃. The element symbols in the formula represent the mass percentage of the corresponding element in the billet. M S =539-423C-11Si-30.4Mn-12.1Cr-17.7Ni-7.5Mo。 8. The method for producing pipeline steel plates according to claim 1, characterized in that, The production method further includes a temperature-controlled preheating and straightening process between the hot rolling process and the controlled water cooling process: performing at least one preheating and straightening pass, with a straightening speed of 0.1~1.5 m / s and a straightening temperature A. r3 +(-65~25)℃, maximum reduction ≤4mm.

9. The method for producing pipeline steel plates according to claim 1, characterized in that, The production method further includes a temperature-controlled hot straightening process following the water-cooling process: performing 1 to 3 passes of hot straightening at a straightening speed of 0.1 to 1.5 m / s and a straightening temperature B. s +(-230~90)℃, maximum reduction ≤4mm.

10. The method for producing pipeline steel plates according to claim 1, characterized in that, The production method also includes a surface treatment process: after the pipeline steel plate is cooled to room temperature, the steel plate is surface treated by shot blasting or shot peening.

11. The method for producing pipeline steel plates according to claim 10, characterized in that, The thickness d of the pipeline steel plate is 6~20mm. The shot used for shot blasting or shot peening is a mixture of shot with a diameter of 0.5mm and shot with a diameter of 0.7mm in a mass ratio of (7~8):

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

5. Alternatively, if the thickness d of the pipeline steel plate is greater than 50 mm, the shot used for shot blasting or shot peening is a mixture of shot with a diameter of 1.0 mm and shot with a diameter of 1.2 mm in a mass ratio of (4~6):

5.

12. The method for producing pipeline steel plates according to claim 10, characterized in that, The shot blasting or shot peening time t and the thickness d of the pipeline steel plate satisfy t=k×d+C, where the unit of t is min, k is 0.1~0.2min / mm, and C is 5~7min; And / or, the shot blasting amount or shot peening amount P and the thickness d of the pipeline steel plate satisfy P=k1×d+C1, where the unit of P is kg / min, k1 is 0.4~0.6kg / (min·mm), and C1 is 160~200kg / min; And / or, the shot blasting or shot peening velocity S and the thickness d of the pipeline steel plate satisfy S=k2×d+C2, where the unit of S is m / s, k2 is 0.1~0.3m / (s·mm), and C2 is 65~75m / s.

13. The method for producing pipeline steel plates according to any one of claims 1 to 12, characterized in that, The production method further includes a tempering heat treatment step: the heating rate is 8~15℃ / min, and the tempering temperature T is B. s +(-105~55)℃, and control the tempering holding time t1 according to the formula (T+273.15)×(20+lg(t1 / 60)) / 1000≥13.7, where t1 is in min.

14. The method for producing pipeline steel plates according to claim 13, characterized in that, The thickness d of the pipeline steel plate is 6~20mm, and the tempering temperature T is B. s +(-65~55)℃; Alternatively, the thickness d of the pipeline steel plate is 20~50mm, and the tempering temperature T is B. s +(-85~35)℃; Alternatively, the thickness d of the pipeline steel plate is greater than 50mm, and the tempering temperature T is B. s +(-105~15)℃.

15. The method for producing pipeline steel plates according to claim 13, characterized in that, The production method further includes a post-tempering stacking process following the tempering heat treatment process: after reaching the tempering holding time t1, the material is directly taken off the production line and stacked at a stacking temperature B. s -(210~110)℃, cooling rate 10~30℃ / h, destacking temperature ≤B s -450℃.

16. The method for producing pipeline steel plates according to claim 1, characterized in that, The chemical composition of the pipeline steel plate, by mass percentage, includes: C 0.03~0.15%, Si 0.09~0.26%, Mn 1.16~1.69%, Cr 0~0.29%, Ni 0~0.29%, Mo 0~0.18%, Cu 0~0.29%, Nb 0.009~0.066%, 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%, with the remainder being iron and unavoidable impurities.

17. The method for producing pipeline steel plates according to claim 16, characterized in that, The chemical composition of the pipeline steel plate, by mass percentage, also satisfies: CEV = C + Mn / 6 + (Cr + Mo) / 5 + (Cu + Ni) / 15 is 0.223~0.571; And / or, Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15 is 0.091~0.294; In the formula, the element symbols represent the mass percentage of the corresponding element.

Images