Method for reducing anisotropy of mechanical property of pipeline steel, pipeline steel and application of pipeline steel

Abstract

The invention discloses a method for reducing mechanical property anisotropy of pipeline steel, the pipeline steel and application of the pipeline steel, and belongs to the technical field of pipeline steel production. According to the method for reducing the anisotropy of the mechanical property of the pipeline steel, {001} lt in the pipeline steel is reduced by controlling the production process of the pipeline steel; 110gt, 110gt; and the density of a {001} cleavage plane is reduced, so that the low-anisotropy pipeline steel is obtained. The steel grade of the pipeline steel is X80, the microscopic structure is acicular ferrite, and the texture is {112} lt; 110gt, 110gt; , {554} lt; 225gt, 225gt; , {332} lt; 113gt, 113gt; a texture and a {110} slip plane are dominated; the tensile strength is 650-710 MPa, the drop-weight shear area ratio at-20 DEG C is 90%-100%, the strength difference in all directions is not higher than 30 MPa, and the drop-weight shear area ratio difference in all directions is not higher than 10%. By adopting the method, the problem of performance anisotropy of the existing pipeline steel can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline steel production, relates to a production method of hot-rolled high-grade pipeline steel, and specifically relates to a method for reducing the anisotropy of mechanical properties of pipeline steel, pipeline steel and applications thereof. Background Art

[0002] Oil and gas pipelines have strict requirements on the safety and service performance of materials, among which the anisotropy of material properties has a significant impact. Generally speaking, pipeline steel has the highest strength in the transverse direction and the lowest strength between 30° and 45° in the rolling direction. In steel pipes, the longitudinal strength of spiral welded steel pipes is 30MPa to 50MPa higher than the transverse strength. Therefore, the anisotropy of the performance of the steel plate leads to the anisotropy of the performance of the steel pipe, which not only makes it difficult to choose welding wire, flux and welding process during girth welding, but also easily causes the performance fluctuation of the girth weld to increase, thereby reducing the safety performance of the steel pipe. Therefore, it is necessary to develop low anisotropy and high-grade pipeline steel coils to promote the promotion and application of high-grade steel for natural gas pipelines.

[0003] After searching, CN111926256B discloses an ultra-wide non-anisotropic steel plate with a width of ≥3500mm and a production method thereof, wherein the steel plate contains the following components in weight percentage: 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 are Fe and inevitable impurity elements; the ultra-wide non-anisotropic steel plate with a width ≥3500mm prepared by the method of the present invention has a yield strength of ≥420MPa at room temperature, a tensile strength of ≥540MPa, an elongation of ≥20%, and a transverse and longitudinal strength difference within 15MPa, and a transverse and longitudinal impact energy of ≥120J at -40°C. It has 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 IF isotropic steel for improving stamping forming and a manufacturing method thereof, wherein 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%, and the rest is Fe and unavoidable impurities; In the subsequent hot rolling, cold rolling, continuous annealing, leveling and drawing production process, the coiling temperature is controlled at 580-620°C, the cold rolling reduction rate is 85-95%, the annealing temperature is 708-742°C, the leveling elongation is 1.0-2.0% + the leveling elongation is 0.03-0.10%, and the surface roughness Ra is 0.36-0.56μm, the peak number Pc ≥ 126, the hardness is 95-110HV, the plastic strain ratio r90 value is ≥ 1.8, the work hardening index n90 value is ≥ 0.18, and the △r value is ≤ 0.20. The invention achieves the beneficial effect of deep drawing circular components without producing earing and hair pulling defects.

[0005] CN100473738C discloses a solid solution strengthened isotropic steel and a method for manufacturing the same, wherein the components by mass percentage are: 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, and the remainder is Fe and unavoidable impurities. The manufacturing method includes the following steps: 1) smelting, casting into steel billets; 2) hot rolling of steel billets, final rolling temperature: 830-930℃, coiling temperature: 520~620℃; 3) pickling, conventional pickling process; 4) cold rolling, reduction rate of 50~80%; 5) annealing, holding temperature: 630-720℃, holding time: 4-30h, cooling to below 200℃ and taking out of the furnace; 6) flattening to obtain cold-rolled products. The invention adopts the idea of ​​solid solution strengthening, uses 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, assisted by appropriate processes, to obtain ideal isotropic steel.

[0006] In summary, in the existing patents, the steel types involved in reducing the anisotropy of performance are mainly medium and thick plates, IF steel, etc. Medium and thick plates mainly achieve isotropy of performance by controlling the process of horizontal rolling width and longitudinal rolling length, and IF steel mainly achieves uniformity and isotropy of organizational performance through cold rolling annealing, reducing the risk of deep drawing ear defects in the material. There are no relevant reports on reducing the anisotropy of pipeline steel performance. Summary of the invention

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

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

[0009] In a first aspect, the present invention provides a method for reducing the anisotropy of mechanical properties of pipeline steel: by controlling the production process of pipeline steel, reducing the {001} <110> The texture content is increased, the density of the {001} cleavage plane is reduced, and low anisotropy pipeline steel is obtained.

[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°C to 1200°C, and the time in the furnace is 180min to 300min.

[0011] In the above method, the rough rolling number of pipeline steel is controlled to be 5 to 6 times, the rough rolling start temperature is 1050°C to 1100°C, and the rough rolling finish temperature is 980°C to 1000°C.

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

[0013] Control the deformation of the rough rolling mill stand to ≥30%;

[0014] Control the deformation of the last two rough rolling passes to be ≥20%, and the interval time between the last two rough rolling passes is 4s to 8s.

[0015] In the above method, the finishing rolling passes are controlled to be 6 to 7 passes, the finishing rolling start temperature is 910°C to 930°C, and the finishing rolling final temperature is 830°C to 880°C.

[0016] In the above method, the laminar cooling rate is controlled to be 15°C / s to 25°C / s, the midpoint temperature is 400°C to 460°C, and the coiling temperature is 360°C to 400°C.

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

[0018] The steel grade of the pipeline steel is X80, the microstructure is acicular ferrite, and the texture is {112} <110> , {554} <225> , {332} <113> Texture, and {110} slip plane are dominant.

[0019] The tensile strength of the above pipeline steel is 650MPa-710MPa, the -20°C drop weight shear area ratio is 90%-100%, the strength difference in each direction is not higher than 30MPa, and the drop weight shear area ratio difference in each direction is not higher than 10%.

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

[0021] The beneficial effects of the present invention are as follows: the present invention is the first to propose a targeted production process control method for the anisotropy of pipeline steel performance. The process method adopted by the present invention is optimized and designed on the basis of the existing hot rolling process, and has the advantages of strong process adaptability, easy implementation and easy operation. The production method described in the present invention is conducive to improving the performance isotropy of oil and gas pipelines and improving the safety performance of oil and gas pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the morphology of the steel drop weight specimen in Example 1 of the present invention;

[0023] Figure 2 The texture component of the steel of Example 1 of the present invention;

[0024] Figure 3 This is the drop weight specimen morphology of the steel of Comparative Example 1 of the present invention;

[0025] Figure 4 The texture components of the steel of Comparative Example 1 of the present invention;

[0026] Figure 5 It is the texture component of the steel of comparative example 2 of the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention can be specifically implemented in the following manner.

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

[0029] Pipeline Steel {112} <110> Texture is beneficial to the toughness of the material. It is generally obtained by rolling at the recrystallization temperature Tnr. It is relatively stable and beneficial to the longitudinal toughness of the material. <110> Texture is not conducive to the toughness of the material, especially at a 45° angle to the longitudinal direction of the material. Its presence makes the material prone to brittle fracture, causing delamination and cleavage fracture of the material, reducing the safe performance of the material. {554} <225> Texture and {332} <113> Texture is the most favorable texture for reducing the anisotropy of material toughness because {554} <225> and {332} <113> The texture components provide a uniform angle for the cleavage fracture of the material and make the {110} planes parallel to the cleavage planes evenly distributed in different directions. Therefore, from the perspective of improving the strength and toughness of the material, it is necessary to enhance the texture components that are beneficial to toughness and strength and reduce the texture components that are not beneficial to them. The present invention proposes to control the texture in the isotropic pipeline steel mainly to {112} <110> , {332} <113> and {554} <225> Texture, reduce {001} <110> Texture content.

[0030] In addition, the distribution of slip planes and cleavage planes also has a significant effect on the toughness of the material. In BCC metals, cracks are most likely to cleave along the {001} cleavage plane. The smaller the angle between the long axis of the sample and the normal of the {001} cleavage plane, the easier the crystal is to break. In contrast, the {110} slip plane plays an important role in improving the low-temperature toughness of the material. The {110} plane that participates in the nucleation of micropores and the aggregation and expansion will increase the amount of plastic deformation. Therefore, in order to improve the low-temperature toughness of the material, it is necessary to increase the density of the {110} slip plane and reduce the density of the {001} cleavage plane.

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

[0032] First, in terms of slab heating process. It is necessary to ensure that the microalloying elements are fully dissolved so that various microalloying elements can play a role in the subsequent austenite recrystallization, growth, and phase transformation process. If the slab heating temperature is low or the heating time is short, the segregation elements may not be fully diffused, resulting in local unevenness of the finished steel structure and performance, thereby affecting the isotropy of the material performance. Therefore, the present invention requires that the slab heating temperature of the pipeline steel be 1180°C to 1200°C, and the furnace time be 180min to 300min.

[0033] Second, in terms of rough rolling process, with the decrease of recrystallization interval time, the decrease of deformation temperature in the recrystallization zone and the increase of deformation amount, the grain size and cleavage unit size of the structure are significantly refined. At the same time, when the final rolling temperature in the rough rolling stage is reduced to 980℃, more {110} slip planes can be obtained, which improves the toughness. As the deformation amount in the rough rolling stage increases, {112} <110> Therefore, the present invention requires that the rough rolling stage of the pipeline steel should reduce the deformation temperature as much as possible, increase the reduction, and shorten the interval between passes. The specific requirements are: the rough rolling start temperature is 1050℃~1100℃, the rough rolling final rolling temperature is 980℃~1000℃, the rough rolling final stand deformation is ≥30%, or the last two rough rolling deformations are ≥20%, and the interval between the last two rough rolling passes is 4s~8s.

[0034] Third, in the finishing rolling process, in the non-recrystallization zone rolling stage, with the decrease of deformation temperature and the increase of cumulative deformation, the effective grain size and cleavage unit size are significantly refined. At the same time, with the increase of deformation in the finishing rolling stage and the decrease of final rolling temperature, {112} <110> The texture enhancement is generally beneficial to toughness without producing {001} <110> texture. At the same time, {554} <225> and {332} <113> The strength of the texture components increases with the decrease of rolling temperature in the austenite non-recrystallization zone. Therefore, the present invention requires a lower deformation temperature for finishing rolling, specifically: the finishing rolling start temperature is 910℃~930℃, and the finishing rolling final temperature is 830℃~880℃.

[0035] Fourth, in terms of laminar cooling process, as the cooling rate increases, the phase change supercooling increases, and the number of nucleation points increases, which can refine the grain size and cleavage unit of the structure and improve the toughness of the material; furthermore, as the cooling rate increases, the microtexture type of the material remains unchanged, but the texture strength is slightly enhanced. Taking all factors into consideration, increasing the cooling rate is beneficial to improving the toughness of the material. The present invention defines the laminar cooling process as follows: the laminar cooling rate is 15℃ / s~25℃ / s, the midpoint temperature is 400℃~460℃, and the coiling temperature is 360℃~400℃

[0036] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0037] Example 1

[0038] The pipeline steel is prepared by the process of hot rolling-laminar cooling-coiling. The slab heating temperature is 1195℃, the furnace time is 238min, the rough rolling adopts 5 passes, the rough rolling start temperature is 1077℃, the rough rolling final temperature is 993℃, the rough rolling end stand deformation is 32%, the finishing rolling start temperature is 918℃, the finishing rolling final temperature is 855℃, the laminar cooling rate is 19℃ / s, the midpoint temperature is 442℃, and the coiling temperature is 388℃.

[0039] The strength of the samples of pipeline steel prepared by the above process at 0°, 30°, 45°, 60° and 90° to the rolling direction are 682MPa, 676MPa, 688MPa, 679MPa and 693MPa respectively, and the shear area of ​​the drop weight in the transverse and longitudinal directions at -20℃ is 100%, 100%, 100%, 100% and 95% respectively (see Appendix). Figure 1 ). The maximum difference in the strength of the steel in Example 1 is 17 MPa, and the maximum difference in the shear area of ​​the drop weight in each direction is 5%, and the anisotropy of the performance is small. The ODF diagram of the texture component of the steel in Example 1 is shown in Figure 2 It can be seen that the pipeline steel described in Example 1 contains a relatively strong {112} <110> texture, and a slightly weaker {554} <225> and {332} <113> Texture.

[0040] Example 2

[0041] The pipeline steel is prepared by the process of hot rolling-laminar cooling-coiling. The slab heating temperature is 1188℃, the furnace time is 255min, the rough rolling is carried out in 6 passes, the start rolling temperature of rough rolling is 1064℃, the final rolling temperature of rough rolling is 985℃, the frame deformation of the two passes after rough rolling is 25% and 26%, the pass interval is 6s, the start rolling temperature of finishing rolling is 925℃, the final rolling temperature of finishing rolling is 839℃, the laminar cooling rate is 22℃ / s, the midpoint temperature is 428℃, and the coiling temperature is 366℃.

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

[0043] Comparative Example 1

[0044] The pipeline steel is prepared by the process of hot rolling-laminar cooling-coiling. The slab heating temperature is 1192℃, the furnace time is 194min, the rough rolling adopts 5 passes, the rough rolling start temperature is 1083℃, the rough rolling final temperature is 986℃, the rough rolling end stand deformation is 31%, the finishing rolling start temperature is 937℃, the finishing rolling final temperature is 879℃, the laminar cooling rate is 25℃ / s, the midpoint temperature is 433℃, and the coiling temperature is 394℃.

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

[0046] Comparative Example 2

[0047] The pipeline steel is prepared by the process of hot rolling-laminar cooling-coiling. The slab heating temperature is 1200℃, the furnace time is 293min, the rough rolling is carried out in 6 passes, the start rolling temperature of rough rolling is 1113℃, the final rolling temperature of rough rolling is 997℃, the deformation of the last two stands of rough rolling is 19% and 18%, the pass interval is 8s, the start rolling temperature of finishing rolling is 924℃, the final rolling temperature of finishing rolling is 844℃, the laminar cooling rate is 21℃ / s, the midpoint temperature is 428℃, and the coiling temperature is 396℃.

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

Claims

1. A method for reducing the anisotropy of mechanical properties of pipeline steel, characterized by: By controlling the production process of pipeline steel, the {001} <110> The content of texture reduces the density of {001} cleavage planes and obtains pipeline steel with low anisotropy; 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°C to 1200°C, and the time in the furnace is 180min to 300min.

2. The method for reducing the anisotropy of mechanical properties of pipeline steel according to claim 1, characterized in that: The rough rolling passes of the pipeline steel are controlled to be 5 to 6 passes, the rough rolling start temperature is 1050°C to 1100°C, and the rough rolling finish temperature is 980°C to 1000°C.

3. The method for reducing the anisotropy of mechanical properties of pipeline steel according to claim 2, characterized in that: Control the deformation of the rough rolling mill stand to ≥30%.

4. The method for reducing the anisotropy of mechanical properties of pipeline steel according to claim 2, characterized in that: Control the deformation of the last two passes of rough rolling to be ≥20%, and the interval time between the last two passes of rough rolling is 4s to 8s.

5. The method for reducing the anisotropy of mechanical properties of pipeline steel according to claim 1, characterized in that: The number of finishing passes is controlled to be 6 to 7, the starting temperature of finishing rolling is 910°C to 930°C, and the final temperature of finishing rolling is 830°C to 880°C.

6. The method for reducing the anisotropy of mechanical properties of pipeline steel according to claim 1, characterized in that: The laminar cooling rate is controlled to be 15°C / s to 25°C / s, the midpoint temperature is 400°C to 460°C, and the coiling temperature is 360°C to 400°C.

7. Pipeline steel produced by the method according to any one of claims 1 to 6.

8. The pipeline steel according to claim 7, characterized in that: The steel grade is X80, the microstructure is acicular ferrite, and the texture is {112} <110> , {554} <225> , {332} <113> Texture, and {110} slip plane are dominant.

9. The pipeline steel according to claim 8, characterized in that: The tensile strength is 650MPa to 710MPa, the shear area ratio of the drop weight at -20°C is 90% to 100%, the strength difference in each direction is not higher than 30MPa, and the shear area ratio difference of the drop weight in each direction is not higher than 10%.

10. Use of the pipeline steel according to any one of claims 7 to 9 in oil and natural gas transportation pipelines.

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