Method for reducing mechanical property anisotropy of a pipeline steel, pipeline steel and use thereof

Abstract

The application discloses a method for reducing mechanical property anisotropy of pipeline steel, the pipeline steel and application thereof, and belongs to the technical field of pipeline steel production. The method for reducing mechanical property anisotropy of pipeline steel is to reduce the content of {001} <110> texture in the pipeline steel, reduce the density of {001} cleavage surface, and obtain the pipeline steel with low anisotropy by controlling the production process of the pipeline steel. The pipeline steel is of X80 grade, the microstructure is acicular ferrite, the texture is mainly {112} <110>, {554} <225>, {332} <113> texture and {110} slip surface; the tensile strength is 650-710 MPa, the -20 DEG C drop weight shear area ratio is 90%-100%, the difference between the anisotropy is not higher than 30 MPa, and the difference between the anisotropy of the drop weight shear area ratio is not higher than 10%. The method can effectively solve the problem of the performance anisotropy of the existing pipeline steel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipeline steel production, and relates to a production method of hot continuous rolling high-grade pipeline steel, in particular to a method for reducing the mechanical property anisotropy of pipeline steel, a pipeline steel and application thereof. BACKGROUND

[0002] The safety and service performance of materials for oil and gas pipelines are strictly required, and the anisotropy of material performance has a significant impact. Generally speaking, the strength of pipeline steel in the transverse direction is the highest, and the strength in the 30°-45° direction of the rolling direction is the lowest, which is manifested as that the longitudinal strength of the spiral welded steel pipe is 30MPa-50MPa higher than the transverse strength. Therefore, the performance anisotropy of the steel plate leads to the performance anisotropy of the steel pipe, which not only makes it difficult to select the welding wire, welding flux and welding process during girth welding, but also increases the performance fluctuation of the girth weld, thereby reducing the safety performance of the steel pipe. Therefore, it is necessary to develop low anisotropy high-grade pipeline steel coils to promote the popularization and application of high-grade steel for natural gas pipelines.

[0003] Through retrieval, CN111926256B discloses an ultra-wide anisotropy-free steel plate with a width of ≥3500mm and a production method thereof. The steel plate contains the following components with a weight percentage of C: 0.10-0.16%, Mn: 0.3-0.8%, Si: 0.15-0.50%, P≤0.020%, S≤0.003%, Nb: 0.010-0.025%, Als: 0.010-0.045%, Ti: 0.030-0.050%, Ca: ≥0.0005%, N: ≤0.0050%, and the rest is Fe and inevitable impurity elements. The ultra-wide anisotropy-free steel plate with a width of ≥3500mm produced by the method has a yield strength of ≥420MPa, a tensile strength of ≥540MPa, an elongation of ≥20% at room temperature, a difference between the transverse and longitudinal strength of within 15MPa, a transverse and longitudinal impact energy at-40℃ of ≥120J, high strength, high toughness, no anisotropy and no plate thickness effect, and can meet the performance requirements of structural steel for bridges and the like.

[0004] CN108728751B discloses an improved stamping forming IF isotropic steel and a manufacturing method thereof, the IF isotropic steel is composed of the following components in weight percentage: C: 0.0012-0.0026%, Si: ≤0.026%, Mn: 0.28-0.52%, P: ≤0.015%, S: ≤0.010%, Al: 0.042-0.082%, Ti: 0.046-0.066%, N: ≤0.0030%, the rest is Fe and inevitable impurities; the IF isotropic steel in the present application can obtain the IF isotropic steel with the surface roughness Ra of 0.36-0.56 μm, the peak number Pc≥126, the hardness of 95-110 HV, the plastic strain ratio r90 value≥1.8, the work hardening index n90 value≥0.18 and the △r value≤0.20 in the subsequent hot rolling, cold rolling, continuous annealing, skin pass and drawing production process, the coiling temperature is 580-620℃, the cold rolling reduction is 85-95%, the annealing temperature is 708-742℃, the skin pass elongation is 1.0-2.0%+the drawing and straightening elongation is 0.03-0.10%. The present application realizes the deep drawing of the circular member without the beneficial effects of ear and pilling defects.

[0005] CN100473738C discloses a solid solution strengthening isotropic steel and a manufacturing method thereof, the components are as follows in mass percentage: C: 0.03-0.07, Si: ≤0.03, Mn: 0.4-1.0, P: 0.02-0.08, S: ≤0.02, N: ≤0.005, B: 0.002-0.005, Al: 0.015-0.05, the rest is Fe and inevitable impurities. The manufacturing method comprises the following steps: 1) smelting, casting into a billet; 2) hot rolling of the billet, the final rolling temperature is 830-930℃, the coiling temperature is 520-620℃; 3) pickling, conventional pickling process; 4) cold rolling, the reduction is 50-80%; 5) annealing, the holding temperature is 630-720℃, the holding time is 4-30h, and the furnace is discharged after cooling to below 200℃; 6) skin pass, to obtain the cold rolling product. The present application adopts the solid solution strengthening idea, utilizes C and Mn to reduce the overall level of r value, and adjusts the relative difference of r value in three directions by adding P, and is assisted by appropriate process, to obtain the ideal isotropic steel.

[0006] In summary, in the existing patents, the steel types related to reducing performance anisotropy mainly include medium plate and IF steel. The medium plate mainly realizes the performance isotropy by controlling the process of close approach of transverse rolling expansion and longitudinal rolling expansion. The IF steel mainly realizes the uniformity and isotropy of organization and performance by cold rolling and annealing, to reduce the risk of deep drawing ear defect of the material. There is no related report about reducing the performance anisotropy of pipeline steel. SUMMARY

[0007] The technical problem solved by the present application is the performance anisotropy of the existing pipeline steel.

[0008] The technical solution adopted by the present application to solve the technical problem is:

[0009] In the first aspect, the present application provides a method for reducing the mechanical property anisotropy of pipeline steel: by controlling the production process of the pipeline steel, reducing the content of {001} <110> texture in the pipeline steel, and reducing the density of {001} cleavage plane, to obtain a pipeline steel with low anisotropy.

[0010] In the above method, the production process of the pipeline steel is slab heating, rough rolling, finish rolling, laminar cooling, and coiling; wherein the slab heating temperature of the pipeline steel is controlled to be 1180-1200℃, and the furnace time is 180-300min.

[0011] In the above method, the rough rolling passes of the pipeline steel are controlled to be 5-6 passes, the rough rolling opening temperature is controlled to be 1050-1100℃, and the rough rolling final rolling temperature is controlled to be 980-1000℃.

[0012] Further, the deformation amount at the rough rolling stage is controlled in any of the following ways:

[0013] The deformation amount at the last stand of rough rolling is controlled to be greater than or equal to 30%;

[0014] The deformation amount of the last two passes of rough rolling is controlled to be greater than or equal to 20%, and the interval time between the last two passes of rough rolling is controlled to be 4-8s.

[0015] In the above method, the finish rolling passes are controlled to be 6-7 passes, the finish rolling opening temperature is controlled to be 910-930℃, and the finish rolling final rolling temperature is controlled to be 830-880℃.

[0016] In the above method, the laminar cooling rate is controlled to be 15-25℃ / s, the intermediate point temperature is controlled to be 400-460℃, and the coiling temperature is controlled to be 360-400℃.

[0017] In the second aspect, the present application provides a pipeline steel produced by the above method for reducing the mechanical property anisotropy of pipeline steel.

[0018] The pipeline steel has a steel grade of X80, a microstructure of acicular ferrite, and a texture mainly composed of {112} <110>, {554} <225>, {332} <113> texture, and {110} slip plane.

[0019] The pipeline steel has a tensile strength of 650-710MPa, a -20℃ drop weight shear area ratio of 90-100%, a difference in anisotropic strength of not higher than 30MPa, and a difference in anisotropic drop weight shear area ratio of not higher than 10%.

[0020] In a third aspect, the present application provides the use of the pipeline steel in oil and gas pipelines.

[0021] The present application has the advantages that: the present application firstly proposes a targeted production process control method for the performance anisotropy of the pipeline steel. The process method adopted by the present application is an optimized design based on the existing hot continuous rolling process, and has the advantages of strong process adaptability, easy implementation and easy operation. The production method described in the present application is beneficial to improve the performance isotropy of the oil and gas pipeline and improve the safety performance of the oil and gas pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The figure is the morphology of the drop hammer sample of the steel in Example 1 of the present application;

[0023] Figure 2 The figure is the texture component of the steel in Example 1 of the present application;

[0024] Figure 3 The figure is the morphology of the drop hammer sample of the steel in Comparative Example 1 of the present application;

[0025] Figure 4 The figure is the texture component of the steel in Comparative Example 1 of the present application;

[0026] Figure 5 The figure is the texture component of the steel in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0027] The technical scheme of the present application can be implemented in the following manner.

[0028] Firstly, the influence of the texture type on the performance anisotropy of the pipeline steel described in the present application is explained, and the texture control direction of the isotropic pipeline steel is proposed.

[0029] {112} <110> texture in pipeline steel is beneficial to material toughness, which is generally obtained by rolling at recrystallization temperature Tnr, is relatively stable and is beneficial to material longitudinal toughness. In contrast, {001} <110> texture is not beneficial to material toughness, especially at a direction of 45° to material longitudinal direction, brittle fracture of material is prone to occur, which causes material delamination and cleavage fracture and reduces material safe use performance. {554} <225> texture and {332} <113> texture are the most beneficial textures to reduce material toughness anisotropy, because {554} <225> and {332} <113> texture components provide uniform angle for material cleavage fracture and make {110} planes of parallel cleavage planes uniformly distributed in different directions. Therefore, from the perspective of improving material strength and toughness, it is necessary to enhance texture components beneficial to toughness and strength and reduce texture components not beneficial to toughness and strength. The present application proposes to mainly control textures in isotropic pipeline steel as {112} <110>, {332} <113> and {554} <225> textures and reduce {001} <110> texture content.

[0030] In addition, distribution of slip planes and cleavage planes also significantly affects material toughness. In BCC metal, crack is most prone to cleave along {001} cleavage plane, the smaller the angle between long axis of sample and normal line of {001} cleavage plane, the more brittle the crystal. In contrast, {110} slip plane plays an important role in improving material low-temperature toughness, {110} plane participating in micropore nucleation and gathering tension will increase the amount of plastic deformation. Therefore, in order to improve material low-temperature toughness, it is necessary to increase {110} slip plane density and reduce {001} cleavage plane density.

[0031] Secondly, reasons for production process limitation of the isotropic pipeline steel described in the present application are explained, and the control method of the above-mentioned textures is mainly described.

[0032] Firstly, in slab heating process. To ensure that micro-alloying elements are fully solid-solved so that various micro-alloying elements play a role in subsequent austenite recrystallization, growth and phase transformation, if slab heating temperature is too low or heating time is too short, the segregation elements may not be fully diffused, which causes local non-uniformity of product steel organization and performance, and further affects performance isotropy of material. Therefore, the present application requires that the slab heating temperature of the pipeline steel is 1180-1200℃ and the furnace time is 180-300 min.

[0033] Secondly, in the rough rolling process, with the decrease of recrystallization interval time, the decrease of recrystallization zone deformation temperature and the increase of deformation amount, the grain size and cleavage unit size are significantly refined. Meanwhile, when the rough rolling stage finishing temperature is decreased to 980℃, more {110} slip planes can be obtained, so that the toughness is improved. With the increase of deformation amount in the rough rolling stage, the {112}<110> texture is increased. Therefore, the present application requires that the rough rolling stage of the pipeline steel decreases the deformation temperature as much as possible, increases the reduction amount and shortens the interval time, and specifically requires that the rough rolling starting temperature is 1050℃-1100℃, the rough rolling finishing temperature is 980℃-1000℃, the deformation amount of the last stand in the rough rolling is ≥30%, or the deformation amount of the last two passes in the rough rolling is ≥20%, and the interval time of the last two passes in the rough rolling is 4s-8s.

[0034] Thirdly, in the finish rolling process, in the non-recrystallization zone rolling stage, with the decrease of deformation temperature and the increase of cumulative deformation amount, the effective grain size and cleavage unit size are obviously refined, and meanwhile, with the increase of deformation amount in the finish rolling stage and the decrease of finishing temperature, the enhancement of {112}<110> texture is beneficial to the toughness as a whole, and no {001}<110> texture with higher crack sensitivity is produced. Meanwhile, the intensity of {554}<225> and {332}<113> texture components is enhanced with the decrease of rolling temperature in the austenite non-recrystallization zone. Therefore, the present application requires that the finish rolling adopts a lower deformation temperature, and specifically requires that the finish rolling starting temperature is 910℃-930℃ and the finish rolling finishing temperature is 830℃-880℃.

[0035] Fourthly, in the laminar cooling process, with the increase of cooling speed, the phase transformation undercooling degree is increased, the nucleation points are increased, the grain size and cleavage unit of the structure are refined, and the material toughness is improved; furthermore, with the increase of cooling speed, the microstructure type of the material is unchanged, but the texture intensity is slightly enhanced. In consideration of the above, the increase of cooling speed is beneficial to the improvement of material toughness. The present application limits the laminar cooling process as follows: the laminar cooling rate is 15℃ / s-25℃ / s, the intermediate point temperature is 400℃-460℃, and the coiling temperature is 360℃-400℃.

[0036] The specific implementation of the present application will be further described below in combination with the embodiments, and the present application is not limited in the scope of the embodiments.

[0037] Example 1

[0038] The pipeline steel prepared by the process of hot continuous rolling-laminar cooling-coiling has a slab heating temperature of 1195°C, a time in the furnace of 238 min, 5 passes of rough rolling, a rough rolling starting temperature of 1077°C, a rough rolling finishing temperature of 993°C, a deformation of 32% at the last stand of rough rolling, a rough rolling finishing temperature of 918°C, a finishing rolling starting temperature of 918°C, a finishing rolling finishing temperature of 855°C, a laminar cooling rate of 19°C / s, an intermediate point temperature of 442°C, and a coiling temperature of 388°C.

[0039] The strength of the pipeline steel prepared by the above process is 682 MPa, 676 MPa, 688 MPa, 679 MPa and 693 MPa in the directions of 0°, 30°, 45°, 60° and 90° to the rolling direction respectively, and the cross and longitudinal drop hammer shear areas at -20°C are 100%, 100%, 100%, 100% and 95% respectively (see the attached Figure 1 ) chart). The maximum difference of the strength of the steel of Example 1 in different directions is 17 MPa, and the maximum difference of the cross and longitudinal drop hammer shear areas is 5%, and the performance anisotropy is small. The ODF chart of the texture component of the steel of Example 1 is shown in Figure 2 It can be seen that the pipeline steel of Example 1 contains strong {112} <110> texture and slightly weak {554} <225> and {332} <113> texture.

[0040] Example 2

[0041] The pipeline steel prepared by the process of hot continuous rolling-laminar cooling-coiling has a slab heating temperature of 1188°C, a time in the furnace of 255 min, 6 passes of rough rolling, a rough rolling starting temperature of 1064°C, a rough rolling finishing temperature of 985°C, a deformation of 25% and 26% at the last two stands of rough rolling, a pass interval time of 6 s, a rough rolling finishing temperature of 925°C, a finishing rolling starting temperature of 925°C, a finishing rolling finishing temperature of 839°C, a laminar cooling rate of 22°C / s, an intermediate point temperature of 428°C, and a coiling temperature of 366°C.

[0042] The strength of the pipeline steel prepared by the above process is 689 MPa, 686 MPa, 692 MPa, 695 MPa and 706 MPa in the directions of 0°, 30°, 45°, 60° and 90° to the rolling direction respectively, and the cross and longitudinal drop hammer shear areas at -20°C are 100%, 98%, 99%, 96% and 94% respectively. The maximum difference of the strength of the steel of Example 2 in different directions is 20 MPa, and the maximum difference of the cross and longitudinal drop hammer shear areas is 6%, and the performance anisotropy is small. The texture component of the steel of Example 2 is mainly {112} <110>, {554} <225> and {332} <113> texture.

[0043] Comparative Example 1

[0044] The pipeline steel prepared by the process of hot continuous rolling-laminar cooling-coiling has the slab heating temperature of 1192°C, the time in the furnace of 194 min, 5 passes for rough rolling, the rough rolling starting temperature of 1083°C, the rough rolling finishing temperature of 986°C, the deformation of 31% at the last stand of rough rolling, the precise rolling starting temperature of 937°C, the precise rolling finishing temperature of 879°C, the laminar cooling rate of 25°C / s, the intermediate point temperature of 433°C and the coiling temperature of 394°C.

[0045] The strength of the pipeline steel prepared by the above process is 687 MPa, 662 MPa, 690 MPa, 665 MPa and 699 MPa respectively in the direction of 0°, 30°, 45°, 60° and 90° to the rolling direction, and the cross and longitudinal drop hammer shearing area at -20°C is 98%, 85%, 100%, 85% and 92% respectively (see the attached Figure 3 ) The maximum difference of the strength in each direction of the steel of Comparative Example 1 is 37 MPa, and the maximum difference of the cross and longitudinal drop hammer shearing area is 13%, and the performance anisotropy is obvious. This is mainly because the deformation temperature in the non-recrystallization zone of the steel of Comparative Example 1 is too high, and the {112}<110>, {554}<225> and {332}<113> textures which can reduce the anisotropy are not significant (see the attached Figure 4

[0046] Comparative Example 2

[0047] The pipeline steel prepared by the process of hot continuous rolling-laminar cooling-coiling has the slab heating temperature of 1200°C, the time in the furnace of 293 min, 6 passes for rough rolling, the rough rolling starting temperature of 1113°C, the rough rolling finishing temperature of 997°C, the deformation of 19% and 18% at the last two stands of rough rolling, the pass interval time of 8 s, the precise rolling starting temperature of 924°C, the precise rolling finishing temperature of 844°C, the laminar cooling rate of 21°C / s, the intermediate point temperature of 428°C and the coiling temperature of 396°C.

[0048] The strength of the pipeline steel prepared by the above process is 677 MPa, 666 MPa, 673 MPa, 651 MPa and 684 MPa respectively in the direction of 0°, 30°, 45°, 60° and 90° to the rolling direction, and the cross and longitudinal drop hammer shearing area at -20°C is 95%, 85%, 92%, 80% and 89% respectively. The maximum difference of the strength in each direction of the steel of Comparative Example 2 is 33 MPa, and the maximum difference of the cross and longitudinal drop hammer shearing area is 15%, and the performance anisotropy is obvious. This is mainly because the deformation amount of the steel of Comparative Example 2 in the rough rolling pass is small, and the deformation temperature is high, and the proportion of the recrystallization texture {001}<110> in the texture component is high (3.96, see the attached Figure 5 ), which is not conducive to the toughness of the material and reduces the isotropy of the material.​

Claims

1. Pipeline steel with low anisotropy, characterized in that: The steel grade is X80, the microstructure is acicular ferrite, and the texture is {112}. <110> {554} <225> {332} <113> The texture, and the {110} slip surface are the main features; The production process of the pipeline steel is as follows: slab heating, rough rolling, finish rolling, laminar flow cooling, and coiling. The slab heating temperature for the pipeline steel is 1180~1200℃, and the furnace time is 180~300min. The roughing rolling of pipeline steel shall be performed in 5 to 6 passes, with an initial rolling temperature of 1050 to 1100℃ and a final rolling temperature of 980 to 1000℃; the deformation of the last stand of the roughing rolling mill shall be ≥30%, or the deformation of the last two passes shall be ≥20%, with an interval of 4 to 8 seconds. The finishing rolling passes are controlled to be 6 to 7, the initial rolling temperature is 910 to 930℃, and the final rolling temperature is 830 to 880℃. The laminar cooling rate is controlled at 15~25℃ / s, the midpoint temperature is 400~460℃, and the winding temperature is 360~400℃.

2. The pipeline steel according to claim 1, characterized in that: The tensile strength is 650MPa~710MPa, the drop shear area ratio at -20℃ is 90%~100%, the difference in strength in each direction is no higher than 30MPa, and the difference in drop shear area ratio in each direction is no higher than 10%.

3. The application of the pipeline steel according to claim 1 or 2 in oil and gas transmission pipelines.

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