CN114250414B

CN114250414B - Seamless steel pipe for pipeline and preparation method thereof

Info

Publication number: CN114250414B
Application number: CN202111471049.1A
Authority: CN
Inventors: 王建华; 谢凯意; 宋光鑫; 邹喜洋; 卓钊; 周正平; 昝启飞; 李端正; 郭胜; 夏文斌
Original assignee: Hengyang Valin Steel Tube Co Ltd
Current assignee: Hengyang Valin Steel Tube Co Ltd
Priority date: 2021-12-03
Filing date: 2021-12-03
Publication date: 2022-10-18
Anticipated expiration: 2041-12-03
Also published as: CN114250414A

Abstract

The invention discloses a seamless steel pipe for a pipeline and a preparation method thereof. Wherein, this seamless steel pipe for pipeline contains: c:0.06% -0.12%, si: 0.10-0.45%, mn: 1.35-1.65%, cr: 0.12-0.25%, mo:0.15% -0.25%, V: 0.01-0.05%, al: 0.025-0.060%, nb 0.01-0.04%, ni:0.15% -0.45%, N: 0.003-0.010% of P: less than or equal to 0.015 percent, less than or equal to 0.003 percent of S, 0.01 to 0.15 percent of Cu and the like. By applying the technical scheme of the invention, the size precision of the prepared seamless steel tube for the pipeline can be within the standard requirement by strictly controlling the component content, and the requirement of X65 steel grade of the marine riser can be met.

Description

Seamless steel pipe for pipeline and preparation method thereof

Technical Field

The invention relates to the technical field of steel pipe manufacturing, in particular to a seamless steel pipe for a pipeline and a preparation method thereof.

Background

With the gradual shrinkage of onshore oil and gas resources, the field of human petroleum exploitation is gradually transited to the sea, and from shallow sea to deep sea, the human marine industry is building petroleum exploration and production systems to deeper sea areas, which is a trend of the world marine oil and gas industry. With the increasing water depth, technical equipment developed in deep water is continuously facing new challenges. Offshore platforms and riser systems are constantly being developed, and oil and gas production and storage platforms have complex motion characteristics under the action of the ocean, thus placing strict requirements on risers connecting subsea pipelines and platforms.

The pipeline pipe refers to a seamless steel pipe for oil and gas transportation laid on land or suspended on the sea floor or suspended on an ocean platform, wherein a marine oil riser is suitable for deep sea oil and gas transportation, and the marine riser is shown in figure 1. In FIG. 1, the part of the pipeline 3 hanging from the platform is the marine riser, wherein in FIG. 1, 1 is the drilling platform, 2 is the horizontal plane, 4 is the submarine pipeline, and 5 is the sea depth (for example ≧ 1500 meters).

The seamless steel pipe for pipelines and the pipe for marine oil and gas, particularly the marine riser, have extremely severe use environment, are influenced by factors such as self gravity, surge, vortex-induced vibration, deep water pressure, ocean current environment and the like, and are also subjected to sea salt and seawater corrosion, and the suspension section and the line section thereof generate floating motion in the ocean and interact with the ocean floor along with the influence of the ocean current, and are extremely easy to generate fatigue damage. Therefore, the steel pipe requires not only higher strength, lower yield ratio, elongation of more than 25%, but also good low temperature toughness and higher CTOD value and fatigue failure resistance. In order to meet excellent welding performance, carbon equivalent Epcm is required, and P and S elements are particularly required, the overall design idea of the steel grade is low-carbon microalloy and excellent welding performance, but certain tensile property and low yield ratio are ensured to ensure the safety of long-term service.

The size precision of seamless steel pipes for pipelines, especially marine service risers, is an important factor affecting fatigue performance. Because the pipe is suspended under an ocean platform and is impacted by ocean waves, the centers of all pipe ends are ensured to be consistent as much as possible, fatigue cracks are reduced, and the service life of decades of years is ensured. In addition, when the marine riser is laid on the sea, the requirement on the size precision of the steel pipe is strict due to the limitation of a site, the technical index in the aspect of main size requires the wall thickness precision of the end of the steel pipe to be +/-1 mm, and the deviation of the inner diameter of the end of the steel pipe is controlled to be +/-0.25 mm. The traditional seamless steel tube production mode is difficult to meet the requirements of the marine riser. The hot rolled steel pipe and the internal boring external raking are adopted, the requirement on size precision can be met, but the marine vertical pipe is long, the length of the marine vertical pipe is larger than 12m, the boring rod naturally droops under the action of gravity during internal boring, the processing force of the middle part of the steel pipe is insufficient, so the processed size cannot meet the requirement, and in addition, the waste metal is overlarge and the cost is high due to the adoption of the internal boring external raking mode. In addition, the method of seamless steel pipe and cold rolling can only meet the size requirement of partial thin-wall small-caliber steel pipes, and the cold rolling of steel pipes with medium and large calibers and wall thicknesses of more than or equal to 20mm has the defects of large rolling resistance, extremely low production efficiency, higher cost and the like. By adopting the common seamless steel pipe, cold drawing method and heat treatment production process, although the wall thickness precision can meet the requirements, the inner diameter of the steel pipe cannot meet the requirements in the subsequent heat treatment and straightening processes. In addition, seamless steel pipes for pipelines, particularly marine risers, have requirements on weight, thick wall thickness and heavy weight, and inner holes have enough machining allowance, but the whole riser platform bears larger force, so that the service safety is influenced. The steel pipe wall is thin and light, the machining allowance of the inner hole of the subsequent pipe end is not enough, and the subsequent pipe end has poor size and cannot be made into a material. Therefore, the size of the vertical pipe needs to be designed comprehensively, so that the size and weight deviation can be met, the subsequent pipe end machining is not influenced, and a balance point needs to be found among the size, the weight and the machining allowance of the steel pipe.

Disclosure of Invention

The invention aims to provide a seamless steel pipe for a pipeline and a preparation method thereof, and provides a new steel grade of X65 steel for a new pipeline pipe.

In order to achieve the above object, according to one aspect of the present invention, there is provided a seamless steel pipe for a pipeline. The seamless steel pipe for the pipeline comprises the following chemical components in percentage by weight: c:0.06% -0.12%, si: 0.10-0.45%, mn: 1.35-1.65%, cr:0.12% -0.25%, mo:0.15% -0.25%, V: 0.01-0.05%, al: 0.025-0.060%, nb 0.01-0.04%, ni:0.15% -0.45%, N: 0.003-0.010% of P: less than or equal to 0.015 percent, less than or equal to 0.003 percent of S, 0.01 to 0.15 percent of Cu, less than or equal to 0.01 percent of Ti, and CE _pcm : less than or equal to 0.25 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements.

Further, C: 0.08-0.11%, si: 0.25-0.45%, mn:1.35 to 1.55 percent of Ni, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.10 percent of Cu, ni: 0.20-0.30%, cr:0.15 to 0.20%, mo:0.15% -0.25%, V:0.02% -0.03%, nb:0.01 to 0.02 percent of Ti: < 0.01, al:0.025% -0.045%, N: 0.003-0.008 percent, B is less than or equal to 0.0005 percent, ca: less than 0.005%, al/N > 2.0 _pcm Less than or equal to 0.22 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements.

According to another aspect of the invention, a method for preparing the seamless steel pipe for the pipeline is provided. The preparation method comprises the following steps: s1, preparing materials, smelting and casting into blanks according to chemical components of the seamless steel tube for the pipeline; s2, rolling the prepared blank into a seamless steel tube; s3, performing cold drawing treatment on the seamless steel pipe; s4, carrying out heat treatment on the seamless steel pipe obtained by cold drawing; and S5, processing the inner hole of the end of the seamless steel pipe to obtain the seamless steel pipe for the pipeline.

Further, S1 specifically includes: preparing materials, smelting in an electric furnace, refining outside the furnace, vacuum degassing and arc continuous casting to obtain a blank; preferably, the raw materials of the ingredients in S1 comprise various molten iron, pipe heads, pure materials, scrap steel, ferroalloy and aluminum, and the addition amount of the molten iron is more than or equal to 60 percent; wherein the molten iron is the molten iron with P less than or equal to 0.20 percent, S less than or equal to 0.050 percent, as less than or equal to 0.015 percent, sn less than or equal to 0.015 percent and Pb less than or equal to 0.003 percent; the pure material is the scrap steel bulk material without rust, oil stain and coating; as + Sn + Pb + Bi in the scrap steel is less than or equal to 0.020%; preferably, in the electric furnace smelting process, tapping conditions are as follows: the temperature of molten steel is more than or equal to 1620 ℃, P is less than or equal to 0.008 percent, and C is less than or equal to 0.05 percent; preferably, in the electric furnace smelting process, the ratio of the low-titanium low-boron high-aluminum slag to the lime is 1 to 3-1, the content of titanium in the low-titanium low-boron high-aluminum slag is less than 0.010 percent, the content of boron is less than 0.0005 percent, and the content of aluminum is 0.020-0.050 percent.

Further, in the process of external refining, a whole-process argon blowing refining process is adopted, calcium carbide, aluminum particles and carbon powder are uniformly added in batches for deoxidation, and the vacuum degassing process comprises the following steps: the air pressure under the ultimate vacuum condition is less than or equal to 67Pa, the holding time is more than or equal to 20min, and the pure calcium core-spun yarn is fed for calcium treatment at 0.7-2.0 m/t after vacuum degassing; the argon blowing time is more than or equal to 10min; preferably, in the process of arc continuous casting, the withdrawal speed is controlled to be 0.3-1.0 m/min, and the superheat degree is controlled to be 35-44 ℃.

Further, the process of external refining also comprises deep dephosphorization, desulfurization and reduction of the content of Pb, sn, as, sb and Bi; preferably, the desulfurization includes the addition of BaO and Li ₂ Desulfurization of O slag, baO and Li ₂ The O slag comprises: 40 to 60 percent of CaO and SiO ₂ 2％～10％，Al ₂ O ₃ 15％～30％，BaO 5％～15％，Li ₂ 0.1 to 2 percent of O and 3 to 10 percent of MgO; preferably, the arsenic content of the fed materials is controlled to be below 0.03 percent, the slag alkalinity R2 is controlled to be 1.10-1.25, the slag amount is 310-330kg/t, the temperature of molten iron is 1465-1490 ℃, and the top pressure of the blast furnace is 180-200 KPa.

Further, S2 includes: heating the blank in an annular furnace to 1220-1300 ℃ to obtain a hot blank, perforating the hot blank to obtain a tubular billet, rolling the tubular billet into a pierced billet by using a tube rolling mill set, and sizing the pierced billet to obtain the hot-rolled seamless steel tube.

Further, the tube rolling mill is a periodic tube rolling mill, the rolling ratio is more than or equal to 8, and the grain size of the pierced billet after hot rolling is more than or equal to 7 grade; preferably, the periodic roll pass of the periodic pipe rolling unit comprises a forging and rolling section, a finish rolling section and an idle rolling section; the side wall angle of the finish rolling section of the periodic roll pass is 20-22 degrees, and the roll gap value of the roll of the periodic tube rolling unit is 50-60 mm; preferably, the forging and rolling section is a reducing area of the roller, the curve of the forging and rolling section adopts an envelope curve, the central angle of the envelope curve is 80-90 degrees,

wherein Y is the depth of the pass, A = L-B/tan eta, ^b the method comprises the following steps of = a/tan eta-1, a = B/A, wherein eta is a cutting angle of a starting point of a forging section, B is the opening depth of the forging section, L is the length of the forging section, and X is the moving position of a deformation point of the forging section; A. a and b are calculation coefficients; preferably, the finish rolling section further performs uniform wall rolling on the tubular billet rolled by the forging and rolling section to ensure that the wall thickness of the tubular billet meets the size requirement, the radius of the bottom of a rolling groove of the finish rolling section is constant, the curve of the finish rolling section adopts a straight line, and the central angle of the finish rolling section is 65-80 degrees; preferably, the surface of the pierced billet is gradually separated from the roller in the final rolling section, and the central angle of the final rolling section is 15-20 degrees; preferably, the roller is not contacted with the steel pipe in the idle rolling section, and the curve of the idle rolling section is formed by one or a combination of a parabola, an envelope curve and an arc.

Further, in the cold drawing treatment in S3, external cooling water rings are arranged on two sides of the cold drawing external die, the steel pipe head-tail external diameter difference of the seamless steel pipe obtained by cold drawing is less than or equal to 0.1mm, the external diameter precision of the seamless steel pipe obtained by cold drawing is controlled within +/-0.5 mm, the external diameter ovality is less than or equal to 0.6mm, and the wall thickness eccentricity is less than or equal to 6 percent S, wherein S represents the actual wall thickness of the steel pipe.

Further, the heat treatment in S4 comprises quenching by adopting forced cooling in an internal spraying and external spraying mode at the temperature range of 880-1000 ℃, and after the steel plate is taken out of the quenching furnace, the cooling speed is as follows: 10 to 100 ℃/S, preferably 20 to 100 ℃/S, more preferably 30 to 100 ℃/S; forcibly cooling the seamless steel pipe to below 50 ℃, more preferably to below 35 ℃; and tempering the quenched seamless steel pipe at the temperature of 660-700 ℃ to obtain a tempered structure, wherein the bainite content of the seamless steel pipe exceeds 80%, and the grain size is more than or equal to grade 8.

Furthermore, the elongation of the tempered seamless steel pipe is more than or equal to 25 percent, and the ductile-brittle transition temperature is below minus 80 ℃, and the CTOD (crack tip opening displacement value) is more than 1.5mm at minus 30 ℃.

Further, after heat treatment, the straightness of the pipe end of the seamless steel pipe is less than or equal to 1.5mm/1.5m.

By applying the technical scheme of the invention, the size precision of the prepared seamless steel tube for the pipeline can be within the standard requirement by strictly controlling the component content, and the requirement of X65 steel grade of the marine riser can be met; and the yield strength, tensile strength, elongation, hardness, grain size and low-temperature toughness of the steel pipe are almost equivalent to or even higher than the requirements of X65 steel grade, and particularly the low-temperature ductile-brittle transition temperature and the CTOD value (crack tip opening displacement) are far superior to those of common pipeline pipes.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 shows a schematic diagram of a marine riser use;

fig. 2 is a schematic structural view illustrating cold drawing of inner and outer molds according to an embodiment of the present invention, wherein in fig. 2, 1 is an outer mold, 2 is an inner mold, 3 is cooling water, and 4 is a steel pipe;

FIG. 3 shows CCT curves (i.e., super cooled austenite continuous cooling transition curves) for selected steel grades of X65 steel grade;

FIG. 4 shows a schematic view of the internal bore machining of a tube end according to an embodiment of the present invention;

fig. 5 shows a schematic diagram of the 457.2 × 31.8 gauge cold-drawn inner die structure of example 1:

FIG. 6 is a schematic view showing the construction of a 457.2X 31.8 gauge cold-drawn outer mold in example 1;

FIG. 7 shows the CCT curve for the steel grade of example 1;

FIG. 8 shows a diagram of the tempered bainite structure of the steel produced in example 1;

FIG. 9 is a schematic diagram showing a structure of a standard specimen in example 1;

FIG. 10 shows the impact ductile to brittle transition curve of example 1;

FIG. 11 is a schematic drawing showing the pipe end dimensions after turning the inner bore of the seamless steel pipe of example 1;

FIG. 12 is a schematic view showing a structure of a 323.9X 27 gauge cold-drawn inner die in example 2;

FIG. 13 is a schematic view showing the structure of a 323.9X 27 gauge cold-drawn outer mold in example 2;

FIG. 14 shows the CCT curve for the steel grade of example 2;

FIG. 15 shows a diagram of the tempered bainite structure of the steel produced in example 2;

FIG. 16 shows the impact ductile to brittle transition curve of example 2; and

figure 17 shows a schematic drawing of the tube end dimensions after turning the inner bore of the seamless steel tube of example 2.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

Aiming at the defects in the prior art, the invention provides the following technical scheme.

According to one aspect of the present invention, there is provided a seamless steel pipe for a pipeline. The seamless steel pipe for the pipeline comprises the following chemical components in percentage by weight: c:0.06% -0.12%, si: 0.10-0.45%, mn: 1.35-1.65%, cr: 0.12-0.25%, mo:0.15% -0.25%, V: 0.01-0.05%, al: 0.025-0.060%, nb 0.01-0.04%, ni:0.15% -0.45%, N: 0.003-0.010%, P: less than or equal to 0.015 percent, less than or equal to 0.003 percent of S, 0.01 to 0.15 percent of Cu, less than or equal to 0.01 percent of Ti, and CE _pcm : less than or equal to 0.25 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements.

By applying the technical scheme of the invention, the size precision of the prepared seamless steel tube for the pipeline can be within the standard requirement by strictly controlling the component content, and the requirement of X65 steel grade of the marine riser can be met; and the yield strength, tensile strength, elongation, hardness, grain size and low-temperature toughness of the steel pipe are almost equal to or even higher than those of X65 steel grade, and especially the low-temperature ductile-brittle transition temperature and the CTOD value (crack tip opening displacement) of the steel pipe are far superior to those of common pipeline pipes.

Further, C: 0.08-0.11%, si: 0.25-0.45%, mn:1.35 to 1.55 percent of Ni, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.01 to 0.10 percent of Cu, ni: 0.20-0.30%, cr:0.15 to 0.20%, mo:0.15% -0.25%, V:0.02% -0.03%, nb:0.01 to 0.02 percent of Ti: < 0.01, al:0.025% -0.045%, N: 0.003-0.008%, B is less than or equal to 0.0005%, ca: less than 0.005%, al/N > 2.0 _pcm Less than or equal to 0.22 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements. The main design idea is low carbon and microalloy, reduces P, S and five harmful elements, adopts large rolling ratio, crushes and casts dendritic crystal, and obtains finer grain size. The hardenability of proper steel grade is designed to obtain a lower bainite metallographic structure with certain strength and high toughness, so that good mechanical properties and low carbon equivalent CE are obtained _pcm And the excellent welding performance of the steel pipe is ensured. Wherein P is less than or equal to 0.015 percent, S is less than or equal to 0.003 percent, the content of harmful elements in the steel is reduced, and the quality stability of the steel is ensured so as to ensure the toughness and CTOD performance of subsequent steel.

Wherein, CE _pcm ：＝C+Mn/6+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B。

Hereinafter, the reason why the chemical components of the seamless steel pipe for line pipe according to the present invention are defined as above will be described, wherein "%" indicating the content (concentration) of the chemical composition means "% by mass".

C：0.06％～0.12％

C is a carbide forming element, can effectively improve the strength and the hardenability of the steel, the strength of the steel is improved along with the increase of the carbon content, but the impact toughness and the elongation rate are obviously reduced, and the welding performance is not favorable, therefore, the content of C is controlled to be 0.06-0.12 percent, the strength and the toughness of the steel can be maintained, and the welding performance is not influenced.

Mn：1.35％～1.65％

Mn is an austenite forming element, can improve the strength of the steel pipe, can improve the hardenability of the steel pipe and reduce the quenching temperature, has the effects of deoxidation and desulfurization, and can weaken the adverse effect of sulfur, but when the content of Mn is too high, the Mn has the sensitivity of coarsening crystal grains and increasing the temper brittleness, and is not favorable for the toughness of the seamless steel pipe, particularly the low-temperature impact toughness and the CTOD value. Therefore, the upper limit of the Mn content is set to 1.65%, and the lower limit of the Mn content is preferably set to 1.35%, and the lower limit of the Mn content is preferably set to 1.45%, in order to ensure emphasis and increase quenching.

Si：0.10％～0.45％

Si can remove oxygen in steel, so that the toughness of the steel pipe is improved, the development of temper brittleness is promoted by too high Si content, the plasticity is reduced, and the welding performance is influenced by too high Si content. Moreover, the heat-transmitting capacity of Si is poor, and the rolling defects such as inward folding, cracks and the like are easy to occur in the billet rolling process due to the addition of more Si. Therefore, as required for deoxidation, the minimum Si content is set to 0.1%, and the upper limit of the Si content is set to 0.45%.

Cr：0.12％～0.25％

Cr is a carbide forming element, so that the strength and the hardenability of the steel pipe can be improved, and meanwhile, complex carbide formed by Cr and Fe is fine and difficult to dissolve, so that grains can be refined, the tempering stability can be improved, but the brittleness transformation temperature of the steel is improved and the low-temperature impact toughness of the steel is reduced due to the overhigh Cr, and the welding performance is influenced.

Mo：0.15％～0.25％

Mo can improve the hardenability of steel, improve the strength of the steel by forming carbides which are dispersed and distributed on grain boundaries, refine crystal grains and improve the tempering stability of the steel, and can reduce or inhibit the tempering brittleness caused by other elements, so that the impact toughness and the CTOD value of the steel are obviously improved while the strength of the steel is improved. However, too high Mo content affects the weldability and toughness.

V：0.01％～0.05％

V is easy to form extremely stable carbide and nitride with C and N in steel, and vanadium carbide and vanadium nitride are usually present in the steel in a fine and dispersed form, so that the structure and crystal grains of the steel can be obviously refined, the coarsening temperature of the crystal grains is increased, the overheating sensitivity of the steel is reduced, the strength and the toughness of the steel are simultaneously improved, a secondary hardening phenomenon can be formed in the tempering process when the content is higher, and simultaneously the vanadium carbide and the vanadium nitride can be separated out from the interior of the crystal grains to reduce the toughness of the steel.

Ni：0.15％～0.45％

Ni is a main alloy element for forming and stabilizing austenite, can exist in steel in a form of being mutually soluble with Fe to improve the strength of the steel, and simultaneously improves the low-temperature toughness of the steel and reduces the low-temperature brittle transition temperature of the steel and improves the CTOD value by refining alpha-phase grains, which has an extremely important effect on the use of the riser in the marine low-temperature environment, but the Ni content is too high and is easy to saturate, and is unfavorable for the welding performance of the steel.

Al：0.025％～0.060％

Al is a good deoxidizer in steel, can be matched with Si to remove oxygen in raw materials, can generate highly-finely-divided and ultra-microscopic oxides, can effectively prevent the growth of crystal grains during steel heating, and can refine the crystal grains. Because the deoxidation effect of Al is saturated and inclusions are prevented from appearing in a lump form, but excessive Al added to Cr-containing steel can form a layer of more compact iron oxide scale on the surface of the steel pipe, which is not easy to remove under high pressure water, the upper limit of the Al content is 0.060%.

P: less than 0.015%

P segregates at grain boundaries and it is difficult to obtain a uniform structure, and since little P increases the susceptibility of the steel to temper embrittlement, P increases the brittleness, particularly low temperature brittleness, of the steel, so that the content of P should be minimized. The P content is set to 0.015%, more preferably 0.010%.

S: less than 0.003%

S forms sulfide inclusions, which seriously reduce the ductility and toughness, particularly impact toughness and CTOD value, of the steel, so that the S content should be minimized to 0.003% at maximum.

B:0.0005% or less

B has an effect of improving hardenability, but the content of B exceeding 0.0005% promotes the formation of coarse grain-boundary carbides, resulting in a decrease in toughness of the steel. Therefore, the B content is set to 0.0005% at the maximum.

Nb：0.010～0.040％

Nb is used as rare earth element, and can play a role in refining grains. It forms carbide and nitride with C and N in steel to inhibit austenite in steel from growing by heating, but it is easily saturated, so the Nb content is designed to be 0.010 to 0.040%.

Ca：0.001～0.005％

A small amount of Ca is added to fix the impurity element S to form a ball-shaped object, which is beneficial to the toughness and the CTOD value of the steel. However, ca in steel is easily saturated, and therefore, ca is designed to be: 0.001 to 0.005 percent.

CE _pcm ：≤0.22％。

CEpcm: = C + Mn/6+ (Mn + Cu + Cr)/20 + Ni/60+ Mo/15+ V/10+5B, when the carbon equivalent CEpcm is less than or equal to 0.22%, high strength can be obtained simultaneously, the toughness and brittleness performance and the CTOD value are excellent, and the welding performance is good. When CEpcm > 0.22% in carbon equivalent, the strength becomes high, the CTOD value becomes drastically poor, and the impact and weldability become poor.

In the pipeline steel pipe, ti, W, N, as, sn, pb, sb and Bi bring impurity elements or unnecessary added elements for smelting, and the impurity elements are removed or not added As much As possible, and the balance is Fe.

In order to solve the problem of high dimensional accuracy of the steel pipe, the conventional hot rolling, cold drawing or machining is difficult to solve independently, the invention provides a novel process route, and the method adopts the modes of hot rolling, cold drawing, heat treatment and pipe end machining to machine an inner hole, so that the problems of high required dimensional accuracy and weight limitation of the steel pipe are solved.

According to an exemplary embodiment of the present invention, there is provided a method of manufacturing the seamless steel pipe for a pipeline described above. The preparation method comprises the following steps: s1, preparing materials, smelting and casting into blanks according to chemical components of the seamless steel tube for the pipeline; s2, rolling the prepared blank into a seamless steel tube; s3, performing cold drawing treatment on the seamless steel pipe; s4, carrying out heat treatment on the seamless steel pipe obtained by cold drawing; and S5, processing the inner hole of the end of the seamless steel pipe to obtain the seamless steel pipe for the pipeline.

The invention relates to a smelting process of a seamless steel pipe for a pipeline, which specifically comprises the following steps: the method comprises the steps of material preparation, electric furnace smelting, external refining, vacuum degassing and arc continuous casting to obtain continuous casting blanks with circular sections.

According to a typical embodiment of the invention, the raw materials of the ingredients comprise high-quality molten iron, high-quality scrap steel, pure materials and ferroalloy, and the addition amount of the high-quality molten iron is more than or equal to 50%. The high-quality molten iron, high-quality scrap steel and pure materials mainly mean that compared with similar raw and auxiliary materials, the five-harmful elements and the impurity content are less. Wherein, in the high-quality molten iron, P is less than or equal to 0.20 percent, S is less than or equal to 0.050 percent, as is less than or equal to 0.015 percent, sn is less than or equal to 0.015 percent, and Pb is less than or equal to 0.003 percent. Pure material refers to pure scrap bulk material, such as steel billets, pipe heads, rails, wire rods, plates or various scrap materials, which is clean and free of rust, oil and coatings. The five harmful elements of the high-quality scrap steel and the pure material are required as follows: as + Sb + Sn + Pb + Bi is less than or equal to 0.020%.

In one embodiment of the invention, the electric furnace smelting adopts the foamed slag process operation, the low-temperature rapid dephosphorization is carried out in the early stage, and the decarburization, the degassing and the inclusion removal are carried out in the later stage. The tapping conditions of electric furnace smelting are as follows: the molten steel temperature is as follows: 1620-1650 ℃, less than or equal to 0.008 percent of P and less than or equal to 0.05 percent of C. The electric furnace smelting adopts the following steps that the ratio of low-titanium low-boron high-aluminum slag to lime is about 1 to 4.

In one embodiment of the invention, the external refining adopts a whole-process argon blowing refining process, calcium carbide and carbon powder are uniformly added in batches for deoxidation in the refining process, and the good refining reducing atmosphere is kept. Taking component samples at intervals of 10-15 min, adjusting the components of the molten steel according to the sampling result, and adding a proper amount of other alloys.

In one embodiment of the invention, VD is vacuum degassed to remove hydrogen and nitrogen from the molten steel so as not to affect the toughness of the steel. A vacuum degassing process: VD vacuum degree is less than or equal to 67Pa, and holding time is more than or equal to 15min. After VD (vacuum degassing), feeding pure calcium core-spun yarn 0.7-2.0 m/t for calcium treatment; the time for blowing protective argon is more than or equal to 10min.

In one embodiment of the invention, two groups of electromagnetic stirrers are used in the crystallizer during the arc-shaped continuous casting process to homogenize the composition of the molten steel and reduce composition segregation. The withdrawal speed is controlled to be 0.3-1.0 m/min, the superheat degree is controlled to be 19-25 ℃, and the withdrawal speed and the superheat degree are controlled in the ranges, so that the structural segregation degree of a seamless steel tube product is favorably improved, and the impact toughness is favorably improved. Arc continuous casting to obtain circular pipe blank with circular cross section.

According to an exemplary embodiment of the present invention, the external refining process further comprises deep dephosphorization, desulfurization and reduction of Pb, sn, as, sb and Bi contents, i.e., deep dephosphorization, desulfurization and five-harm reduction processes. The contents of P, S and five-harmful elements are low, thereby ensuring various physical and chemical properties and the service safety of the steel pipe.

Wherein, dephosphorization needs better thermodynamic and kinetic conditions, slag needs higher alkalinity and oxidability, slag fluidity is required to be good, and steel slag interface reaction is strong. Metallurgical theory and electric arc furnace steelmaking practice show that the P content in steel is related to the slag amount of electric furnace tapping. The larger the slag quantity is, the higher the P content in the slag is, and the stronger the reducibility of the ladle slag is, the larger the phosphorus return amount of the molten steel is, so that the control of the slag quantity of the electric furnace and the reduction of the P content in the electric furnace slag are the keys for reducing the phosphorus return amount of the molten steel. The electric furnace is operated by adopting oxygen melting and combining processes, the electric furnace operation steps are carried out according to the electric energy consumption, powder spraying is started when 70% -80% of the electric energy is melted, and the whole process of foaming slag process is carried out. The electric furnace adopts an intensified dephosphorization technology, the main task in the early stage of oxidation is dephosphorization, and a steel sample is taken out at 1600 ℃ in the final stage of oxidation. When steel making is carried out, the steel can be tapped only when P is less than or equal to 0.008 percent.

The desulfurization process requires that S is less than or equal to 0.008 percent for general corrosion-resistant pipeline pipes. The lower the S content in the steel, the better, studies have shown that the CTOD (crack tip displacement cracking) value of the steel pipe is higher when S is less than or equal to 0.003%. Therefore, the marine riser is required to have a sulfur content of 0.003% or less as much as possible. Based on the traditional desulfurization slag system, the invention provides a desulfurization slag system containing BaO and Li ₂ The deep desulfurization slag system of O comprises the following components: caO 40-60%, siO ₂ 2％～10％，Al ₂ O ₃ 15％～30％，BaO 5％～15％，Li ₂ 0.1 to 2 percent of O and 3 to 10 percent of MgO. Theoretical studies show that: the optical basicity of BaO is 1.15 times of that of CaO, and theoretically, the desulfurization effect of BaO is better than that of CaO. According to the theoretical analysis of an ionic structure, the ionic radius of BaO in the slag liquid is larger than that of CaO, the ionic attraction is smaller, and the ionic percentage BaO is higher than that of CaO, so that BaO can release oxygen ions more easily, and the desulfurization capacity of BaO with the same mole number is larger than that of CaO; the melting point of BaO is 1918 ℃, the melting point value of the refining slag can be effectively reduced by replacing a high-melting-point material with a low-melting-point material, and the influence on the slag-steel interfacial tension is hardly generated. Li ₂ The optical basicity of O is 1.0, like CaO ₂ O can react with SiO in the slag ₂ Formation of phase 2Li of low melting point (900 ℃ C.) ₂ O·SiO ₂ And the melting point of the whole slag system is reduced. In addition, li ₂ O itself has strong alkalinity and low relative atomic mass, which also results in good desulfurization effect.

The As removing technology is used for controlling As to use 50% molten iron and 40% high-quality pure scrap steel ingredients, controlling As of the molten iron to be within 0.008%, controlling As of the pure scrap steel to be within 0.005%, and dynamically controlling superheat degree of the molten steel to be between 19 and 25 ℃ and proper superheat degree, so that As elements in the steel are oxidized and taken away from slag, five harmful elements in the steel can be controlled to be below 0.010%, and harm of the harmful elements to the steel is reduced.

The seamless steel pipe for the pipeline can be used for common land oil and gas pipelines and is more suitable for deep-sea risers. The invention designs corresponding chemical components, and obtains the lower bainite in a metallographic structure with the volume of more than 80 percent and the grain size of more than or equal to grade 8 through large rolling ratio rolling and precise heat treatment. The steel grade has good hardenability, and even a thick-wall steel pipe with the wall thickness of 30-50 mm can ensure the central quenching effect of the wall thickness of the steel pipe. The low-temperature impact-resistant and high-temperature-resistant composite material has excellent low-temperature impact property and high CTOD value, and can obtain proper tensile property and excellent welding property.

According to the periodic roll pass provided by the invention, a steel pipe with excellent wall thickness precision is rolled, and then a finished steel pipe is obtained through the technological routes of high-precision cold drawing, precise heat treatment and pipe end machining, so that the finished steel pipe is high in yield and excellent in dimensional precision.

According to an exemplary embodiment of the present invention, a tube rolling process includes billet preparation, piercing, rolling, and sizing operations. Cold saw cutting and blanking a round pipe blank obtained by arc continuous casting, heating the round pipe blank in an annular furnace to 1220-1300 ℃ to obtain a hot blank with good plasticity; perforating the hot blank to obtain a capillary; rolling the hollow billet into a pierced billet by using a tube rolling mill set; and sizing the pierced billet to obtain the hot-rolled seamless steel pipe.

In one embodiment of the present invention, a billet is prepared: the heating process of the blank sequentially comprises a preheating section heating, a heating section I heating, a heating section II heating, a heating section III heating, a heating section IV and a soaking section; wherein the heating time of the blank heated into the hot blank is determined according to the diameter of the continuous casting round blank. The preheating section heats the blank to the temperature of less than or equal to 940 ℃; heating the blank to 960-1040 ℃ in the heating I section, heating the blank to 1070-1150 ℃ in the heating II section, heating the blank to 1180-1240 ℃ in the heating III section, and heating the blank to 1230-1310 ℃ in the heating IV section. The temperature of the soaking section is kept between 1240 ℃ and 1280 ℃, and the heating time and the total heating time of each section are determined according to the diameter of the continuous casting round pipe billet. Through the sectional heating, the tube blank is gradually heated to the set temperature, the tube blank is fully heated, and the defect that the hot rolled steel tube is cracked due to too fast temperature rise is avoided.

And (4) perforating, namely heating the blank to a plastic optimal temperature area, and perforating to obtain the capillary.

In one embodiment of the invention, the tube rolling is performed by a periodic tube rolling mill, or by other tube rolling mills, and the pierced blank tube is rolled by the periodic tube rolling mill to obtain a pierced blank tube. The periodic rolling pipe is arranged in a roll pass, the rough rolling and the finish rolling are completed, the deformation is large, steel is in a three-way compressive stress state in the roll pass, several deformation modes of forging, rolling and extruding are integrated, the small defects of a casting blank can be welded, the cast dendritic crystal can be effectively crushed, and the fine structure of crystal grains can be obtained. The rolling ratio of the periodic tube rolling process adopted by the invention, namely the cross-sectional area ratio of the blank to the steel tube, is not less than 8, compared with the traditional continuous rolling process, the billet deformation is larger, the better effect of crushing dendritic crystals is brought, the small defects of the welded casting blank are overcome, and the texture grain size after hot rolling is not less than 7 grade.

According to the manufacturing method of the seamless steel tube, in the process of processing the seamless steel tube from the blank, the tubular billet is rolled by the periodic tube rolling unit to obtain the pierced billet. Because the weight of the steel pipe is limited, particularly the weight of the marine riser is heavier, the bearing capacity of a water surface platform is larger, the wall thickness of the marine riser cannot be rolled without limitation, and the rolling of the wall thickness of the steel pipe is thin or the wall thickness is single, so that the subsequent pipe end cannot be scrapped due to insufficient machining allowance, or the wall thickness of the steel pipe is still poor or single after the pipe end inner hole is machined, therefore, the wall thickness deviation and the straightness of the steel pipe are well controlled, and the marine riser is the basis for subsequent machining. Although there is a cold drawing process for correcting the outer diameter and wall thickness of a hot-rolled pipe, there is a limit to improvement in the correction, and it is still necessary to control the wall thickness variation of the steel pipe in the hot-rolling process.

According to an exemplary embodiment of the present invention, a periodic roll pass is provided having the effect of improving the wall thickness of a steel pipe. In order to improve the wall thickness deviation of the steel pipe, increase the length of the working section of the roller, reduce the side wall angle of the roller pass and design a reasonable roll gap value, the roller is more suitable for rolling the steel pipe between 15 and 50 mm. The periodic roll pass is divided into a forging section, a finish rolling section and an idle rolling section. The side wall angle of the finish rolling section of the roll pass is designed to be 20-22 degrees, and the roll gap value of the roll is designed to be 50-60 mm.

The roll forging section is a main reducing diameter and wall area of the roll, the curve adopts an envelope curve, the central angle of the envelope curve is 80-90 degrees,

wherein Y is the depth of the pass, A = L-B/tan eta, ^b the method comprises the following steps of = a/tan eta-1, a = B/A, wherein eta is a cutting angle of a starting point of a forging and rolling section, B is the opening depth of the forging and rolling section, L is the length of the forging and rolling section, and X is the moving position of a deformation point of the forging and rolling section; A. b and a are calculation coefficients.

The finish rolling section further rolls the rough pipe rolled by the forging and rolling section uniformly, so that the wall thickness of the rough pipe meets the size requirement, the radius of the bottom of a rolling groove of the finish rolling section is unchanged, the curve of the bottom of the rolling groove adopts a straight line, and the central angle of the finish rolling section is 65-80 degrees.

The function of the final rolling section is to gradually separate the surface of the pierced billet from the roller, and the central angle of the final rolling section is 15-20 degrees.

The roller is not contacted with the steel pipe in the idle rolling section, and the curve can be formed by one or a combination of a parabola, an envelope line and an arc.

In a typical embodiment of the present invention, a dedicated mandrel bar is further prepared in the tube rolling pass, and the difference in outer diameter between the head and the tail of the mandrel bar is controlled to be within 1mm, thereby preventing the longitudinal wall thickness from being uneven due to the difference in outer diameter of the mandrel bar.

The pierced billet after the peripheral rolling has fine grains, and can be directly sized to obtain the hot-rolled seamless steel pipe without on-line normalization. The steel pipe can also be normalized on line, the temperature of the steel pipe is cooled to be below 550 ℃ after the periodic rolling, and the steel pipe is reheated and sized, so that the grain size is better.

Cold drawing process

The cold-drawing die for improving the integral wall thickness of the steel pipe is designed, and the obtained steel pipe has the advantages of uniform wall thickness and small ovality of the outer diameter.

The steel pipe obtained by hot rolling is not satisfactory in dimensional variation and weight variation, and therefore, cold drawing is required. In a typical embodiment of the present invention, an inner die and an outer die are cold-drawn, and cooling water is added on both sides of the outer die, which is schematically shown in fig. 2, to reduce the outer diameter deviation of the steel pipe head and tail caused by the expansion of the outer die due to friction heating of the die during cold-drawing, which leads to the beginning of cold-drawing and the end of cold-drawing, and the difference of the average outer diameters of the steel pipe head and tail after cold-drawing is less than or equal to 0.1mm. And a process of cooling the cold-drawing outer die by cooling water is not adopted, the difference value of the average outer diameters of the head and the tail of the steel pipe after cold drawing is 0.2-0.4 mm, the influence on the common steel pipe is small, but the value of the difference value influences the wall thickness of the pipe end after machining, so that one end is thicker than the other end.

In an exemplary embodiment of the invention, cold drawing includes preparation before cold drawing and cold drawing processes, and the preparation before cold drawing includes acid washing, phosphating and saponification.

Acid pickling

And (3) placing the seamless steel pipe obtained by hot rolling into a pickling tank containing hydrochloric acid solution for pickling to remove the iron scale of the hot rolled pipe. Wherein, the mass concentration of the hydrochloric acid solution is controlled between 10 percent and 20 percent, and the pickling time is controlled between 60min and 100min, so as to obtain the pickled steel pipe.

Phosphating

And (2) carrying out outer surface phosphating treatment on the acid-washed pierced billet by using a zinc phosphate solution to generate a chemical coating of zinc phosphate, wherein the mass concentration of the zinc phosphate solution is controlled to be between 30 and 35 percent, the temperature of the zinc phosphate solution is controlled to be between 50 and 80 ℃, and the phosphating time of the acid-washed pierced billet is controlled to be between 30 and 60 minutes to obtain the phosphated steel pipe.

Saponification

And (2) saponifying the phosphated pierced billet by saponification liquid to form a metal soap lubricating coating on the surface of the pierced billet, wherein the temperature in the saponification process is controlled to be 60-80 ℃, the saponification time is controlled to be 20-35 min, and the pH value of the saponification liquid is controlled to be 8.5-9.5 to obtain the saponified steel pipe.

Cold drawing

And (3) carrying out a cold drawing process on the saponified steel pipe by a drawing machine, wherein the drawing force of the drawing machine is 300-1250 tons, and the cold drawing speed of the drawing machine is 0.85-1.25 m/min. Cold drawing belongs to non-austenite zone deformation, and compared with hot rolling, the external diameter precision and the wall thickness of the cold drawing are obviously improved. The size of the cold-drawn steel pipe is mainly determined by a cold-drawing die, after cold drawing, the precision of the outer diameter of the pipeline steel pipe is within +/-0.5 mm, the out-of-roundness of the outer diameter is less than or equal to 0.5mm, and the wall thickness eccentricity is less than or equal to 6 percent S.

Heat treatment of

After cold drawing, the obtained seamless steel pipe is subjected to thermal refining. CCT (super cooled austenite continuous cooling) curve of X65 grade mark obtained by simulation is shown in fig. 3. As can be seen from FIG. 3, the bainite structure was obtained after the cooling rate was 10 to 100 ℃/S. The cooling speed is 1-10 ℃/S, the structure is converted into ferrite in the cooling process, and the mechanical property can not meet the requirement of X65 steel grade. According to the principle of metallurgy, eutectoid steel obtains upper bainite at 550-350 ℃ and lower bainite at 240-350 ℃. In the lower bainite structure, carbide is dispersed in the ferrite matrix to play a role in dispersion strengthening, so that the strength and toughness of the steel can be obviously improved, and the ductile-brittle transition temperature is lower. This is the tissue that needs to be obtained in the present invention.

Heating and heat preservation are carried out on the steel pipe with the original fine grain structure (the grain size is more than or equal to 7 grade) obtained by cold drawing in the temperature range of 880-1000 ℃, and the heat preservation time is determined according to the wall thickness of the steel pipe. After the quenching furnace is taken out, the quenching furnace is internally sprayed and externally sprayed for forced cooling, and the average cooling speed is as follows: 10 to 100 ℃/S, preferably not less than 20 to 100 ℃/S, more preferably 30 to 100 ℃/S, and the steel pipe is forcibly cooled to 50 ℃ or less, more preferably 30 ℃ or less. The steel structure is transformed as much as possible, namely, the austenite is transformed into the bainite; tempering the cooled steel pipe at 660-700 ℃, and properly determining the heat preservation time according to the wall thickness of the steel pipe to obtain tempered bainite, which mainly comprises granular, needle-shaped and island-shaped bainite, the proportion of the tempered bainite is more than or equal to 80 percent, and a small amount of ferrite and carbide are dispersed and distributed. The grain size of the quenched and tempered steel pipe is more than or equal to 8 grades, and the fine grain strengthening effect is good. The tempered structure has excellent toughness and CTOD value, and the ductile-brittle transition temperature is below minus 80 ℃ at the lowest.

Since the subsequent machining of the end of the steel pipe is required, how to avoid bending of the steel pipe is also a problem that must be dealt with in the heat treatment. The bending deformation defect of the steel pipe is one of the common defects of heat treatment, most of the pipe bending can be straightened by a six-roller straightener, but the six-roller straightener has a straightening blind area. The bending of the pipe end cannot be straightened, and the subsequent processing quality and the processing efficiency of the steel pipe are adversely affected. The bending deformation of the heat treatment is mainly caused by uneven cooling and heating of all parts of the steel pipe after heating under the action of thermal stress and structural stress, and the deformation of the steel pipe can be reduced by improving the heating uniformity, the water quenching uniformity and the like of the steel pipe, so that the processing failure of the steel pipe caused by pipe end bending in the subsequent processing of the steel pipe is reduced.

After heat treatment, the resulting pipeline steel pipe has excellent properties, especially impact toughness and CTOD test (crack tip opening displacement) values. Under different heat treatment process conditions, the lowest impact transformation temperature of the pipeline steel pipe can reach-80 ℃, and the CTOD value is more than or equal to 1.5mm under the condition of-30 ℃. The straightness of the pipe end is less than or equal to 1.5mm/1.5m.

And machining the inner hole of the pipe end.

After the pipeline steel pipe obtained through heat treatment is subjected to conventional water pressure and flaw detection, the outer circle of the steel pipe is used as a reference circle to be calibrated by adopting a mechanical caliper so as to ensure that the machining circle center of the inner hole is concentric with the outer circle as much as possible. After the processing and calibration, a mode of rough turning and then finish turning is adopted. During roughing, a common cutter is adopted to feed at a feed rate of 0.5mm per minute, and the rotating speed of the lathe is 80-100 r/min; during finish machining, an R10 semicircular cutter is adopted to feed at the feed rate of 0.1-0.35 mm/min per minute, the rotating speed of the lathe is controlled at 40-60R/min, and the turning speed is reduced to prevent the steel pipe from shaking to form raised grains on the machined surface. The main processing parameters are shown in the figure, after the inner hole cylindrical section is turned, the conical surface is transited to an unmachined surface according to the ratio of 1. The schematic drawing of the machining of the inner hole of the pipe end is shown in figure 4 (in figure 4, A is an enlarged view of a transition region, L is the length of a parallel section of a turned inner hole, t is the wall thickness after turning, D is the inner diameter after turning, D is the outer diameter, and alpha is a chamfer angle of the transition region).

In one embodiment of the invention, after turning is finished, the wall thickness precision of the machining end of the pipeline is controlled to be +/-1 mm, the precision of an inner hole is controlled to be +/-0.25 mm, the inner diameter and the wall thickness are measured by adopting a mechanical code table and an ultrasonic thickness gauge respectively, the ovality of the inner diameter is less than or equal to 0.15mm, and the wall thickness is within the range of +/-1 mm of the target wall thickness. After the processing is finished, a finished product pipeline steel pipe is obtained, and the pipeline steel pipe is suitable for land ocean oil gas exploitation and is particularly suitable for being used as a deep sea riser.

The seamless steel pipe for the pipeline can be used for ocean oil and gas development, and is particularly suitable for an ocean riser.

The invention provides a seamless steel pipe for manufacturing pipelines and a manufacturing method thereof, which are particularly suitable for being used as a deep sea riser. Compared with the common seamless steel tube production process, the invention provides the process route of hot rolling, cold drawing, heat treatment and tube end machining, and has the characteristics of high dimensional precision, high production efficiency and low metal consumption.

The seamless steel pipe for the pipeline has high dimensional accuracy, high strength and high toughness of strength above X65 steel grade specified by API specification, ductile-brittle transition temperature below-80 ℃, elongation of more than 25 percent, grain size of more than or equal to 8 grades, high CTOD value and excellent welding performance. The device is not only suitable for land oil gas transportation, but also suitable for the field of submarine oil gas exploitation, in particular to a deep sea oil gas outlet pipeline or a riser.

The following examples are provided to further illustrate the advantageous effects of the present invention.

Example 1

By making

The specification X65 steel grade pipeline steel pipe illustrates the invention.

The chemical components are proportioned according to the design of the invention, and the raw materials are smelted by an electric furnace, refined outside the furnace, degassed in vacuum and subjected to arc continuous casting to obtain a blank.

The smelting process of the blank comprises the following steps: material preparation, electric furnace smelting, external refining, vacuum degassing and arc continuous casting.

The raw materials of the ingredients comprise high-quality molten iron, pipe heads, pure materials, high-quality scrap steel, ferroalloy and the like. The adding amount of the high-quality molten iron is more than or equal to 50 percent, wherein the high-quality molten iron, the pipe head, the pure material and the high-quality scrap steel mainly refer to that compared with similar raw and auxiliary materials, the contents of harmful elements and impurities are less. Wherein, P is less than or equal to 0.20 percent, S is less than or equal to 0.050 percent, as is less than or equal to 0.015 percent, sn is less than or equal to 0.0015 percent, and Pb is less than or equal to 0.003 percent in the high-quality molten iron. Pipe head, pure material (pure material refers to pure scrap steel bulk material, for example, pipe blank, pipe head, steel rail, wire rod, steel plate or various leftover bits, which is clean and has no rust, oil stain and coating), high-quality scrap steel, and the requirements of harmful elements are as follows: as + Sn + Pb + Bi is less than or equal to 0.020%.

In the electric furnace smelting process, tapping conditions are as follows: the temperature of molten steel is more than or equal to 1620 ℃, P is less than or equal to 0.008 percent, and C is less than or equal to 0.05 percent. The electric furnace smelting adopts the following steps that the ratio of low-titanium low-boron high-aluminum slag to lime is about 1 to 4. In the steel-making process, the five-harmful technology of deep dephosphorization, desulfurization and control is adopted.

In the external refining process, a whole-process argon blowing refining process is adopted, and calcium carbide, aluminum particles and carbon powder are uniformly added in batches for deoxidation.

Vacuum Degassing (VD) process: under the condition of ultimate vacuum, the air pressure is less than or equal to 67Mpa, the holding time is more than or equal to 20min, after VD, pure calcium cored wires are fed for calcium treatment at the speed of 0.7-2.0 m/t, and the argon blowing time is more than or equal to 10min.

In the process of arc continuous casting, the withdrawal speed is controlled to be 0.3-1.0 m/min, and the superheat degree is controlled to be 35-44 ℃.

By the above process, the outer diameter is obtained

Continuously casting the round pipe blank, and optionally selecting a furnace, wherein the components of the round pipe blank are as shown in the following table 1:

TABLE 1

The hot rolled seamless steel pipe is obtained through the processes of perforation and pipe rolling. And in the process of feeding the prepared blank into a tube rolling machine, rolling the perforated hollow billet by adopting a periodic tube rolling machine set to obtain a pierced billet, and sizing the pierced billet to obtain the hot-rolled seamless steel tube. The periodic tube rolling process also adopts a special core rod, and the outer diameter difference of the head and the tail of the core rod is controlled within 1mm, so that the uneven longitudinal wall thickness caused by the different outer diameters of the core rod is prevented.

Before rolling, a special periodic rolling rod 490 caliber is designed, the design idea is to increase the working section length of the roller, reduce the side wall angle of part of the roller caliber, and design a reasonable roll gap value, so that the roller is more suitable for rolling high-precision steel pipes. In the rolling process, the feeding amount of the hollow billet is controlled to be 40 mm-50 mm/time, the rotating speed of the roller is controlled to be 40-45 rpm/min, and the air pressure of the feeder is set to be 5.5-7 bar. And (4) sizing the seamless steel tube obtained by periodically rolling to obtain a semi-finished seamless steel tube.

Pilger mill roll 490 passes. The periodic roller with the roller diameter of 1400mm is adopted, the roller completes the processes of forging, finish rolling and idle rolling turnover in a single pass, the deformation is large, and a rolled piece is always subjected to three-way pressure stress in a pass, which is similar to the forging process of a hammer head. The designed heavy rolling coefficient is more than or equal to 3; the roll finishing section side wall angle was set to 20 °.

The roll gap value of the roll is set to be 60mm; the initial entrance guide angle of the forging and rolling section is set as follows: 23 °;

the corresponding central angle of the forging and rolling section is set as follows: 80 degrees; the corresponding central angle of the finish rolling section is set as: 85 degrees;

the corresponding central angle of the final rolling section is set as follows: 20 degrees; the corresponding central angle of the idle rolling section is set as follows: 175 °;

the opening depth of the forging and rolling section is set as follows: 88mm; the maximum opening depth of the idle rolling section is set as follows: 102mm

The curve equation of the forging and rolling section is as follows:

the curve equation of the finish rolling section is as follows; y =215, (80 ° < X ≦ 165 °);

the curve equation of the final rolling section is as follows: y =215+ (X-155)/20, (165 ° < X ≦ 185 °)

The rough rolling and the finish rolling of the pierced billet after the peripheral rolling are completed in a roll pass, the deformation is large, the steel is in a three-way compressive stress state in the roll pass, several deformation modes of forging, rolling and extruding are integrated, the small defects of a casting blank can be welded, the cast dendrite can be effectively crushed, and the fine structure of grains can be obtained. The rolling ratio of the periodically rolled pipe pass adopted in the embodiment, namely the cross-sectional area ratio of the blank to the steel pipe, is not less than 8, compared with the traditional continuous rolling process, the rolling ratio is larger, the billet deformation is larger, the better effect of crushing dendritic crystals is brought, the small defects of the welded casting blank are overcome, and the grain size after hot rolling is not less than 7. The hot-rolled seamless steel pipe may be obtained by sizing without on-line normalization. The steel pipe can also be normalized on line, the temperature of the steel pipe is cooled to be below 550 ℃ after the periodic rolling, and the steel pipe is reheated and sized, so that the grain size is better.

The hot rolling step controlled the wall thickness variation of the steel pipe within. + -.5% of the actual wall thickness and the outer diameter variation within. + -.1 mm, thereby obtaining a hot-rolled seamless steel pipe.

The steel pipe obtained by hot rolling is not satisfactory in dimensional variation and weight variation, and therefore needs to be cold drawn. And (3) designing a special cold-drawing inner die and a special cold-drawing outer die (see figure 3), and adding cooling water at two sides of the cold-drawing outer die to reduce the outer diameter deviation of the head and the tail of the steel pipe caused by external die expansion caused by friction heating in the cold-drawing process and the cold-drawing end.

Cold drawing process

The cold drawing comprises preparation before cold drawing and cold drawing processes, wherein the preparation before cold drawing comprises acid washing, phosphating and saponification.

Acid pickling

And (3) placing the seamless steel pipe obtained by hot rolling into an acid washing tank containing hydrochloric acid solution for acid washing to remove the iron scale of the hot rolled pipe. Wherein, the mass concentration of the hydrochloric acid solution is controlled between 10 percent and 20 percent, and the pickling time is controlled between 60min and 100min, so as to obtain the pickled steel pipe.

Phosphating

And carrying out outer surface phosphating treatment on the acid-washed pierced billet by using a zinc phosphate solution to generate a zinc phosphate chemical coating, wherein the mass concentration of the zinc phosphate solution is controlled to be between 30 and 35 percent, the temperature of the zinc phosphate solution is controlled to be between 50 and 80 ℃, and the phosphating time of the acid-washed pierced billet is controlled to be between 30 and 60 minutes to obtain the phosphated steel pipe.

Saponification

And (2) saponifying the phosphorized pierced billet by saponification liquid to form a metal soap lubricating coating on the surface of the pierced billet, wherein the temperature in the saponification process is controlled to be 60-80 ℃, the saponification time is controlled to be 20-35 min, and the pH value of the saponification liquid is controlled to be 8.5-9.5, so that the saponified steel pipe is obtained.

Cold drawing

And (3) carrying out a cold drawing process on the saponified steel pipe through a drawing machine, wherein the drawing force of the drawing machine is 300-1250 tons, and the cold drawing speed of the drawing machine is 0.85-1.25 m/min. Cold drawing belongs to non-austenite zone deformation, and compared with hot rolling, the external diameter precision and the wall thickness of the cold drawing are obviously improved. The size of the cold-drawn steel pipe is mainly determined by the cold-drawing die, after cold-drawing, the precision of the outer diameter of the pipeline steel pipe is within +/-0.5 mm, the out-of-roundness of the outer diameter is less than or equal to 0.5mm, and the wall thickness eccentricity is less than or equal to 6 percent S.

The 457.2X 31.8 gauge cold drawn inner die is shown in FIG. 5.

A 457.2 x 31.8 gauge cold drawn outer die is shown in fig. 6.

In the cold drawing process, the inner die and the outer die are matched and used to limit the outer diameter and the inner diameter of the steel pipe, so that the steel pipe with high dimensional accuracy is obtained, the accuracy of the outer diameter is +/-0.7 mm, the ovality of the outer diameter is less than or equal to 0.7mm, and the wall thickness accuracy is +/-3 percent S. Higher dimensional accuracy is very critical to follow-up steel pipe turning hole, and dimensional accuracy is relatively poor, and steel pipe local probably can not be turned, and the steel pipe is probably scrapped, and the lumber recovery is low.

Heat treatment of

After cold drawing, the obtained seamless steel pipe is subjected to thermal refining. The CCT (super cooled austenite continuous cooling) curve of the grade corresponding to the X65 steel grade is obtained through simulation. As can be seen from FIG. 7 (CCT curve of 457.2X 31.8 standard), the bainite structure can be obtained at a cooling rate of 10 to 100 ℃ C/S. The cooling speed is 1-10 ℃/S, the structure is transformed into ferrite in the cooling process, and the mechanical property can not meet the requirement of X65 steel grade. Further increase in cooling rate is required. According to the principle of metallurgy, eutectoid steel obtains upper bainite at 550-350 ℃ and lower bainite at 240-350 ℃. In the lower bainite structure, carbide is dispersed in the ferrite matrix to play a role in dispersion strengthening, so that the strength and toughness of the steel can be obviously improved, and the ductile-brittle transition temperature is lower. This is the tissue that needs to be obtained in the present invention.

Heating and preserving heat before quenching the steel pipe with the original fine grain structure (the grain size is more than or equal to grade 7) obtained by hot rolling at the temperature of 880-1000 ℃, wherein the heat preservation time is determined according to the specification of the steel pipe. After the quenching furnace is taken out, the quenching furnace is internally sprayed and externally sprayed for forced cooling, and the average cooling speed is as follows: the steel pipe is forcibly cooled to 50 ℃ or lower, more preferably 35 ℃ or lower at 35 to 50 ℃/S. The steel structure is transformed as much as possible, and the austenite is transformed into bainite; tempering the cooled steel pipe at 660-700 ℃, wherein the heat preservation time is determined according to the wall thickness of the steel pipe, and tempered bainite is obtained, wherein the crystal grain of the tempered bainite is more than or equal to 8 grade, the tempered bainite mainly comprises granular, needle-shaped and island-shaped bainite, the proportion of the granular, needle-shaped and island-shaped bainite is more than or equal to 80 percent, and a small amount of ferrite and carbide are dispersed. The grain size of the quenched and tempered steel pipe is more than or equal to 8.5 grade, and the fine grain strengthening effect is good. The tempered metallographic phase has excellent toughness and CTOD value, and the ductile-brittle transition temperature is at least 80 ℃ below zero. The tempered bainite structure is shown in FIG. 8 (500. Times. Metallographic structure).

The resulting steel pipe was heat-treated, and sampled for impact and CTOD tests (crack tip opening displacement).

According to BS7748: part I: 1991. the CTOD test was carried out on the steel pipes obtained by the heat treatment according to BS7748: part2:1997, ISO12315 and ASTM E1290. It is divided into three parts: preparing a sample, prefabricating fatigue cracks and testing.

The samples were prepared using the one-sided notch bend test specimens defined in ISO 12135. The base material sample was XY and notched in the thickness direction, and a standard sample of 300mm (length) 24. + -. 0.1mm. + -.24.1 mm was prepared in FIG. 9 (the left drawing is a schematic drawing of sampling the steel pipe, and the right drawing is a schematic drawing of preparing a CTOD sample).

And (4) prefabricating fatigue cracks. All specimens were prepared for fatigue cracking. According to the requirement of BS7448-2, the prefabricated fatigue crack is divided into two steps, wherein in the first step, the stress ratio R =0.1 is adopted until the length of the prefabricated fatigue crack is 1mm; and a second step of prefabricating to a predetermined length using a stress ratio R = 0.7.

The test is carried out in an environment box at the temperature of-30 ℃, and the temperature is controlled and recorded to be accurate to +/-2 ℃ according to the requirement of specification BS 7748-1. After the ambient temperature stabilized at-30 ℃, the sample was frozen in an ambient oven for no less than 30 minutes. The loading speed ensures that the change rate of the stress intensity factor (K) is 0.5 MPa.m ^0.5 S ^-1 To 3.0 MPa.m ^0.5 S ^-1 Within the range.

Through the steps, the temperature is-30 DEG C

The results of the CTOD tests are shown in table 2, where 10 furnace numbers are randomly selected, and one sample block is taken from each furnace number to make 3 CTOD standard samples.

TABLE 2

As can be seen from the table above, the excellent CTOD performance of the steel obtained by the embodiment has the advantages that the single value and the average value are larger than 1.5mm, and the CTOD performance is excellent, which shows that the material has better fracture resistance at the temperature of-30 ℃ and has excellent performance when being used as a welding joint.

A transverse impact sample is taken from the steel pipe after heat treatment, 3 samples in each group are obtained, the specification of the sample is 10 multiplied by 10mm, a V8 notch is processed according to the ASTM A370 standard, impact tests are respectively carried out at the temperatures of 20 ℃, 0 ℃, 10 ℃, 30 ℃, 50 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃, 110 ℃ and 120 ℃, and an impact ductile-brittle transition curve is drawn according to the test result, and is shown in figure 10.

As can be seen from fig. 10, by a suitable heat treatment process, which heat treatment is followed,

specifications other mechanical properties are shown in table 3 below.

TABLE 3

Mechanical Properties	Results
		Average yield strength/Mpa	508
Minimum yield strength-maximum yield strength/Mpa	484-519
		Average tensile strength/MPa	597
Minimum tensile strength to maximum tensile strength/Mpa	570-632
		Average elongation A _f	30.0％
Maximum hardness/HV 10	214
		-30 ℃ minimum transverse impact value (J)	209
Transverse average impact value (J) at-30 DEG C	365
		Minimum grain size/grade	8.5

And (3) carrying out heat treatment on the obtained seamless steel pipe, then carrying out straightening, flaw detection and water pressure processes, and finally processing the inner hole at the pipe end of the steel pipe on a horizontal heavy-duty lathe to obtain a finished product pipe, so that the inner hole at the pipe end can reach high inner diameter and wall thickness precision, and the welding requirement of the deep sea vertical pipe is met. The size of the pipe end after turning the inner hole is shown in figure 11.

After turning, the basic dimensions of the 5-furnace steel pipe are randomly counted as the following table 4:

TABLE 4

As can be seen from the above table 4, the material has moderate tensile property, good impact property at-30 ℃, excellent CTOD property, high dimensional precision, and excellent combination of weight deviation, wall thickness deviation and machining allowance of the steel pipe, and can be used as a deep sea submarine pipeline and a deep sea riser.

Example 2

By making

This example is essentially the same as example 1, except that:

by the above process, the outer diameter is obtained

Continuously casting a round pipe blank, and randomly selecting a furnace, wherein the components of the furnace are as follows in the following table 5:

TABLE 5

Before tube rolling, a special periodic roller 340 hole pattern is prepared. In the rolling process, the feeding amount of the hollow billet is controlled to be 35 mm-45 mm/time, the rotating speed of the roller is controlled to be 50-55 rpm/min, and the air pressure of the feeder is set to be 5.5-7 bar.

And designing a pilger mill roller 340 pass. A periodic roll having a roll diameter of 1100mm was used.

The roll gap value of the roll is set to be 50mm; the initial entrance guide angle of the forging and rolling section is set as follows: 23 °;

the corresponding central angle of the forging and rolling section is set as follows: 80 degrees; the corresponding central angle of the finish rolling section is set as: 90 degrees;

the corresponding central angle of the final rolling section is set as follows: 20 degrees; the corresponding central angle of the idle rolling section is set as: 170 degrees;

the opening depth of the forging and rolling section is set as follows: 90mm; the maximum opening depth of the idle rolling section is set as follows: 105mm

The curve equation of the forging and rolling section is as follows:

the curve equation of the finish rolling section is as follows; y =145, (80 ° < X ≦ 170 °);

the curve equation of the final rolling section is as follows: y =145+ (X-155)/20, (170 ° < X ≦ 190 °)

Controlling the wall thickness deviation of the steel pipe within the range of + -5% S of the actual wall thickness and the outer diameter deviation within the range of + -1.5 mm by the hot rolling process, thereby obtaining a hot-rolled seamless steel pipe.

Cold drawing

The size of the cold-drawn steel pipe is mainly determined by a cold-drawing die, after cold drawing, the precision of the outer diameter of the pipeline steel pipe is within +/-0.6 mm, the out-of-roundness of the outer diameter is less than or equal to 0.5mm, and the wall thickness eccentricity is less than or equal to 6 percent S.

The 323.9 × 27 gauge cold drawn inner die is shown in fig. 12.

The 323.9 × 27 gauge cold-drawn external mold is shown in fig. 13.

In the cold drawing process, C12MoV forgings are adopted by the inner and outer cold drawing dies, the inner and outer dies are matched and used, the outer diameter and the inner diameter of the steel pipe are limited, the steel pipe with high dimensional accuracy is obtained, the accuracy of the outer diameter is +/-0.7 mm, the ovality of the outer diameter is less than or equal to 0.7mm, and the wall thickness accuracy is +/-3 percent S.

Thermal treatment

After cold drawing, the obtained seamless steel pipe is subjected to thermal refining. The CCT (super cooled austenite continuous cooling) curve of the grade X65 steel obtained by simulation is shown in figure 14 (the CCT curve of the 323.9 multiplied by 27 specification), and the bainite structure can be obtained after the cooling speed is 10-100 ℃/S. The cooling speed is 1-10 ℃/S, and a massive ferrite structure is generated in the cooling process, which is not favorable for the toughness and CTOD test. According to the principle of metallurgy, eutectoid steel obtains upper bainite at 550-350 ℃ and lower bainite at 240-350 ℃. In the lower bainite structure, carbide is dispersed in the ferrite matrix to play a role in dispersion strengthening, so that the strength and toughness of the steel can be obviously improved, and the ductile-brittle transition temperature is lower. This is the tissue that is desired to be obtained by the present invention.

Heating and heat preservation are carried out on the steel pipe with the original fine grain structure (the grain size is more than or equal to 7 grade) obtained by hot rolling at the temperature of 850-1000 ℃, and the heat preservation time is determined according to the wall thickness of the steel pipe. After the quenching furnace is taken out, the quenching furnace is internally sprayed and externally sprayed for forced cooling, and the average cooling speed is as follows: the steel pipe is cooled at a rate of 35 to 100 ℃/S and forcibly cooled to 50 ℃ or lower, more preferably 30 ℃ or lower. The steel structure is transformed as much as possible, and the austenite is transformed into bainite; tempering the steel pipe after quenching and cooling at the temperature of 660-700 ℃, wherein the heat preservation time is properly determined according to the wall thickness of the steel pipe, and tempered bainite is obtained, wherein the crystal grain of the tempered bainite is more than or equal to 8 grade, mainly comprises granular, needle-shaped and island-shaped bainite, the proportion of the granular, needle-shaped and island-shaped bainite is more than or equal to 80 percent, and a small amount of cementite is dispersed and distributed. The grain size of the quenched and tempered steel pipe is more than or equal to 8 grades, and the fine grain strengthening effect is good. The tempered metallographic phase has excellent toughness and CTOD value, and the ductile-brittle transition temperature is at least 80 ℃. The tempered bainite structure is shown in FIG. 15 (500. Times. Metallographic structure).

According to the same procedure as in example 1, the test was carried out at-30 ℃

The CTOD test results of the specifications are shown in table 6 below, and 5 furnace numbers are randomly selected, and one sample block is taken from each furnace number to prepare 3 CTOD standard samples.

TABLE 6

As can be seen from the table above, the excellent CTOD performance of the steel obtained by the embodiment has the single value and the average value larger than 1.5mm, and the excellent CTOD performance shows that the material has better fracture resistance and excellent performance when being used as a welding joint under the condition of-30 ℃.

As can be seen from FIG. 16, the ductile-brittle transition temperature is below-80 ℃ by a suitable heat treatment process.

After the heat treatment, the mixture is heated,

other mechanical properties are shown in Table 7 below.

TABLE 7

Mechanical Properties	As a result, the
		Average yield strength/Mpa	508
Minimum to maximum yield strength/Mpa	485-531
		Average tensile strength/Mpa	587
Minimum tensile strength to maximum tensile strength/Mpa	571-606
		Average elongation A _f	28.9％
Maximum hardness/HV 10	203
		Transverse average impact value (J) at-30 DEG C	392
-30 ℃ minimum transverse impact value (J)	293
		Minimum grain size/grade	Stage	8

As can be seen from the above table 7, the material has moderate tensile property and better impact property at-30 ℃, and can be used as a deep sea submarine pipeline and a deep sea riser.

The size of the pipe end after the inner hole is turned is shown in figure 17.

After turning, the basic dimensions of the 5-furnace steel pipe are randomly counted as the following table 8:

TABLE 8

As can be seen from the above table 8, the material has moderate tensile property, good impact property at-30 ℃, excellent CTOD (carbon monoxide OD) property, high dimensional precision and excellent combination of weight deviation, wall thickness deviation and machining allowance of the steel pipe, and is suitable for being used as a deep sea submarine pipeline and a deep sea riser.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The seamless steel pipe for the pipeline is characterized by comprising the following chemical components in percentage by weight: c:0.06% -0.12%, si:0.10% -0.45%, mn: 1.35-1.65%, cr:0.12% -0.25%, mo:0.15% -0.25%, V:0.01% -0.05%, al: 0.025-0.060%, nb 0.01-0.04%, ni:0.15% -0.45%, N:0.003% -0.010%, P: less than or equal to 0.015 percent, less than or equal to 0.003 percent of S, 0.01 to 0.15 percent of Cu, less than or equal to 0.01 percent of Ti, and CE _pcm : less than or equal to 0.25 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements; the seamless steel pipe for the pipeline is prepared by the following preparation method:

the method comprises the following steps:

s1, preparing materials, smelting and casting into blanks according to chemical components of the seamless steel pipe for the pipeline;

s2, rolling the prepared blank into a seamless steel tube;

s3, performing cold drawing treatment on the seamless steel pipe;

s4, carrying out heat treatment on the seamless steel pipe obtained by cold drawing;

s5, processing an inner hole at the end of the seamless steel pipe to obtain the seamless steel pipe for the pipeline;

the S1 specifically comprises: preparing materials, smelting in an electric furnace, refining outside the furnace, vacuum degassing and arc continuous casting to obtain a blank;

in the external refining process, a whole argon blowing refining process is adopted, calcium carbide, aluminum particles and carbon powder are uniformly added in batches for deoxidation, and the vacuum degassing process comprises the following steps: the air pressure is less than or equal to 67Pa under the ultimate vacuum condition, the holding time is more than or equal to 20min, and the pure calcium cored wires are fed for calcium treatment at the speed of 0.7 to 2.0m/t after vacuum degassing; the argon blowing time is more than or equal to 10min;

the process of the external refining also comprises deep dephosphorization, desulfurization and reduction of the content of Pb, sn, as, sb and Bi;

the desulfurization includes the addition of BaO and Li ₂ Desulfurizing the O slag, wherein the BaO and the Li are ₂ The O slag comprises: 40-60% of CaO and SiO ₂ 2%~10%，Al ₂ O ₃ 15%~30%，BaO 5%~15%， Li ₂ 0.1-2% of O and 3-10% of MgO.

2. The seamless steel pipe for pipelines according to claim 1, wherein C:0.08% -0.11%, si:0.25% -0.45%, mn: 1.35-1.55%, P is less than or equal to 0.015%, S is less than or equal to 0.003%, cu is 0.01-0.10%, ni: 0.20-0.30%, cr:0.15 to 0.20%, mo:0.15% -0.25%, V:0.02% -0.03%, nb:0.01% -0.02%, ti: < 0.01, al:0.025% -0.045%, N: 0.003-0.008% of the total weight of the components, B is less than or equal to 0.0005%, ca: less than 0.005%, al/N > 2.0 _pcm Less than or equal to 0.22 percent, less than or equal to 0.010 percent of Sn, less than or equal to 0.010 percent of As, less than or equal to 0.005 percent of Pb, less than or equal to 0.005 percent of Sb, less than or equal to 0.005 percent of Bi, and the balance of Fe and inevitable impurity elements.

3. A method for producing a seamless steel pipe for pipelines according to claim 1 or 2, comprising the steps of:

s1, preparing materials according to the chemical components of the seamless steel tube for the pipeline, smelting and casting to form a blank;

s2, rolling the prepared blank into a seamless steel tube;

s3, performing cold drawing treatment on the seamless steel pipe;

the process of the secondary refining also comprises deep dephosphorization, desulfurization and reduction of the content of Pb, sn, as, sb and Bi.

4. The preparation method according to claim 3, wherein the raw materials of the ingredients in S1 comprise a plurality of molten iron, pipe heads, pure materials, scrap steel, ferroalloy and aluminum, and the addition amount of the molten iron is more than or equal to 60%; wherein the molten iron is the molten iron with P less than or equal to 0.20 percent, S less than or equal to 0.050 percent, as less than or equal to 0.015 percent, sn less than or equal to 0.015 percent and Pb less than or equal to 0.003 percent; the pure material is stainless, oil-free and coating-free scrap steel bulk material; as + Sn + Pb + Bi in the scrap steel is less than or equal to 0.020%.

5. The preparation method according to claim 4, wherein tapping conditions during electric furnace smelting are as follows: the temperature of the molten steel is more than or equal to 1620 ℃, P is less than or equal to 0.008 percent, and C is less than or equal to 0.05 percent.

6. The preparation method according to claim 4, wherein in the electric furnace smelting process, the ratio of the low-titanium low-boron high-aluminum slag to lime is 1 to 3 to 1, the content of titanium in the low-titanium low-boron high-aluminum slag is less than 0.010 percent, the content of boron in the low-titanium low-boron high-aluminum slag is less than 0.0005 percent, and the content of aluminum in the low-titanium low-boron high-aluminum slag is 0.020 to 0.050 percent.

7. The production method according to any one of claims 4 to 6, wherein a billet drawing speed is controlled to be 0.3 to 1.0m/min and a superheat degree is controlled to be 35 to 44 ℃ during the arc continuous casting.

8. The preparation method according to claim 3 or 7, characterized in that the content of arsenic in the fed material is controlled to be less than 0.03%, the basicity R2 of the slag is controlled to be 1.10-1.25, the slag amount is 310-330kg/t, the temperature of molten iron is 1465-1490 ℃, and the top pressure of a blast furnace is 180-200KPa.

9. The method according to claim 3, wherein the S2 includes: heating the blank in an annular furnace to 1220-1300 ℃ to obtain a hot blank, perforating the hot blank to obtain a hollow billet, rolling the hollow billet into a hollow billet by using a pipe rolling mill, and sizing the hollow billet to obtain a hot-rolled seamless steel pipe.

10. The preparation method according to claim 9, wherein the tube rolling mill is a periodical tube rolling mill, the rolling ratio is not less than 8, and the grain size of the pierced billet after hot rolling is not less than 7 grade.

11. The method of claim 10, wherein the periodic roll pass of the periodic tube rolling mill train includes a forging section, a finishing section, and a blank section; the side wall angle of the finish rolling section of the periodic roll pass is 20 to 22 degrees, and the roll gap value of a roll of the periodic tube rolling unit is 50 to 60mm.

12. The manufacturing method according to claim 11, wherein the forged section is a reduced-diameter wall area of a roller, a curve of the forged section adopts an envelope curve, a corresponding central angle of the envelope curve is 80 to 90 degrees,

wherein, Y is the depth of the hole pattern,

，

the cutting angle is the cutting angle of the starting point of the forging and rolling section, B is the opening depth of the forging and rolling section, L is the length of the forging and rolling section, and X is the moving position of a deformation point of the forging and rolling section; A. and a and b are calculation coefficients.

13. The production method according to claim 11, wherein the finish rolling section further performs wall-equalizing rolling of the hollow billet rolled by the forging section so that the wall thickness of the hollow billet meets the size requirement, the radius of the bottom of the groove of the finish rolling section is constant, the curve of the finish rolling section adopts a straight line, and the central angle of the finish rolling section is 65 to 80 °.

14. The production method according to claim 11, wherein the surface of the pierced billet is gradually separated from a roller by the final rolling section, and the central angle of the final rolling section is 15 to 20 °.

15. The manufacturing method of claim 11, wherein the roller does not contact the steel pipe in the idle rolling section, and the curve of the idle rolling section is formed by one or a combination of a parabola, an envelope curve and an arc.

16. The production method according to claim 3, wherein in the cold drawing treatment in S3, outer cooling water rings are installed on both sides of the cold drawing outer die, the steel tube head-to-tail outer diameter difference of the seamless steel tube obtained by cold drawing is less than or equal to 0.1mm, the outer diameter precision of the seamless steel tube obtained by cold drawing is controlled within +/-0.5 mm, the outer diameter ovality is less than or equal to 0.6mm, and the wall thickness eccentricity is less than or equal to 6% S, wherein S represents the actual wall thickness of the steel tube.

17. The preparation method of claim 3, wherein the heat treatment in S4 comprises quenching by forced cooling in an internal-spraying and external-spraying manner at a temperature range of 880-1000 ℃, and after the quenching furnace is taken out, the cooling speed is as follows: 10 to 100 ℃/S; forcibly cooling the seamless steel pipe to below 50 ℃; and tempering the quenched seamless steel pipe at the temperature of 660-700 ℃ to obtain a tempered structure, wherein the bainite content of the seamless steel pipe exceeds 80%, and the grain size is more than or equal to 8 grades.

18. The production method according to claim 17, wherein in S4, the cooling rate: 20-100 ℃/S.

19. The production method according to claim 18, wherein in S4, the cooling rate: 30 to 100 ℃/S.

20. The production method according to claim 17, wherein in S4, the seamless steel pipe is forcibly cooled to 35 ℃ or less.

21. The production method according to any one of claims 17 to 20, wherein the seamless steel pipe after tempering has an elongation of 25% or more and a ductile-brittle transition temperature of-80 ℃ or less and a crack tip opening displacement value of more than 1.5mm at-30 ℃.

22. The production method according to any one of claims 17 to 20, wherein the pipe end straightness after the heat treatment is 1.5mm/1.5m or less.