CN108277438A

CN108277438A - Mo ultralow-carbon martensitic stainless steel seamless pipe and its manufacturing method

Info

Publication number: CN108277438A
Application number: CN201810269087.0A
Authority: CN
Inventors: 李阳; 徐芳泓; 方旭东; 赵建伟; 夏焱; 张威
Original assignee: Taiyuan Iron and Steel Group Co Ltd
Current assignee: Taiyuan Iron and Steel Group Co Ltd
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2018-07-13

Abstract

The invention discloses a kind of Mo ultralow-carbon martensitic stainless steel seamless pipes, are made of Mo ultralow-carbon martensitic stainless steel, and Mo ultralow-carbon martensitic stainless steel includes following compositions, is calculated in mass percent：It is 0.2~0.5%, P≤0.015% that C≤0.03%, Si, which are 0.1~0.5%, Mn, and it be 5.2~5.7%, Mo be 1.9~2.1%, Cu is 0.1~1.6% that S≤0.002%, Cr, which are 12.2~13.2%, Ni, and surplus is Fe and other impurity.Above-mentioned seamless pipe is applicable to oil gas field.The present invention also provides a kind of manufacturing methods of above-mentioned seamless pipe, including step：Smelting, pipe hot-working, steel pipe hot-working and heat treatment, wherein, the hot worked heating temperature of pipe is 1200~1280 DEG C, and the heating temperature of extrusion tubulation is 1150~1250 DEG C, the heating temperature of perforation cold-rolling practice tubulation is 1200~1280 DEG C, and heat treating regime is：900~1050 DEG C of quenchings and 550~680 DEG C of tempering.Seamless pipe produced by the present invention is in CO₂、ClCoexisting has excellent intensity and corrosion resistance under corrosive environment and high-temperature and high-pressure conditions.

Description

Ultra-low carbon martensitic stainless steel seamless pipe and manufacturing method thereof

Technical Field

The invention relates to the field of stainless steel, in particular to an ultra-low carbon martensitic stainless steel seamless pipe suitable for oil and gas fields and a manufacturing method thereof.

Background

With the development of global economy, the demand of countries in the world on oil and gas resources is continuously increased, so that developed oil and gas fields are more and more deep, and a plurality of ultra-deep and ultra-high well killing wells are developed. The difficulty of exploration and development of high-pressure high-temperature and ultrahigh-pressure high-temperature wells is suddenly increased, so that the problems of well drilling are increased, and the problems mainly relate to a series of problems of design, tools, processes, equipment, well control, reservoir transformation, safety, material selection and the like of an oil well, wherein the most critical problem is the material selection problem.

High pressure and ultra high pressure and high temperature wells typically contain CO₂、H₂S、Cl^－Ionic, etc., highest CO content₂Content of more than 10%, H₂S is more than 6 ten thousand ppm, Cl^－The ion content exceeds 10 ten thousand ppm, so that the corrosion becomes CO-containing₂、H₂S and Cl^－Is used in the environment of (a). At present, the catalyst is used for containing CO at home and abroad₂、H₂S and Cl^－The materials adopted in the oil well are Cr13 type martensitic stainless steel, duplex stainless steel and nickel-based alloy in sequence according to the environment severity. The Cr13 type martensitic stainless steel has the use temperature limit of 150 ℃, is difficult to meet the use requirements under the existing severe corrosion environment, and most of underground oil pipes are broken, and leakage accidents of gas collecting main lines occur, so that a plurality of oil and gas field wells are abandoned in advance when put into operation for less than one year, thereby not only causing huge economic loss, but also threatening the national energy strategic safety. To avoid corrosion of oil well pipes under such harsh conditions, it is necessary to choose a CO resistance₂、H₂S and Cl^－Duplex stainless steel and nickel base alloy with excellent corrosion and stress corrosion cracking performance, but the price is very expensive and mainly depends on import, so that the investment cost for constructing oil wells is too high.

Chinese patent document CN100368579C provides a martensitic stainless steel having improved strength and corrosion resistance by adding 2.8 to 5.0% of Mo to form a mixed structure of tempered martensite, carbides precipitated during tempering, and Laves phase or σ -like intermetallic compounds precipitated finely during tempering. However, the high Mo content of the inventive steel grade reduces the toughness and the Laves or σ phase deteriorates the structure during use and is too costly.

Chinese patent document CN100453685C provides a high Cr series stainless steel seamless oil well pipe and a production method thereof, wherein the content of C is 0.02-0.25%, the content of Cr is 12-14%, the content of Ni is 3.0-6.0%, and additionally, elements such as Mo, Cu, Nb, Cu, Al, Ti, V and the like are added to improve the strength. However, the C content of the invention is too high, in CO₂And Cl^－The corrosion resistance in the coexistence environment is not enough, the types of alloy elements are too many, the structure change rule in the heat treatment process is too complex, and the difficulty is brought to the quenching and tempering treatment.

In view of the above, there is a need in the art to develop a new economic corrosion-resistant material for use in deep well oil and gas fields to meet the requirements of the oil and gas industry which is being developed.

Disclosure of Invention

In order to overcome the defects of the prior martensitic stainless steel and the steel pipe thereof, the invention aims to provide a method for preparing a high-concentration CO stainless steel₂、H₂S and Cl^－The ultra-low carbon martensitic stainless steel seamless tube for the deep well under the coexistence of high temperature, high pressure and ultra-high temperature and ultra-high pressure in the corrosive environment has the cost lower than that of dual-phase stainless steel and nickel-based alloy, and the service life is prolonged by 2 to 3 times compared with the original Cr13 martensitic stainless steel. Moreover, the invention also provides the high-concentration CO₂、H₂S and Cl^－A method for manufacturing an ultra-low carbon martensitic stainless steel seamless tube for a deep well under high temperature, high pressure and ultra-high temperature and ultra-high pressure in a coexisting corrosive environment.

It is emphasized that, unless otherwise indicated, the terms used herein correspond to the ordinary meanings of the various technical and scientific terms in the art, and the meanings of the technical terms defined in the various technical dictionaries, textbooks, etc. For example, high temperature and high pressure wells are generally defined herein as having normal rubber seal properties, meaning wells having a bottom hole temperature above 150 ℃ and a pressure above 70 MPa. Ultrahigh temperature and ultrahigh pressure wells are generally defined herein as the operational limits of electronic components, meaning wells with a bottom hole temperature above 205 ℃ and a pressure above 140 MPa. In this context, deep wells generally refer to wells having well depths in excess of 4500m or 15000 ft. The ultra-low carbon martensitic stainless steel generally refers to stainless steel with a tempered martensitic base metal microstructure by reducing the carbon content (0.07 percent at most) and increasing the nickel content (3.5 to 6.5 percent) on the basis of the traditional martensitic stainless steel. The hot conveying generally means that the steel material is not cooled after being heated and is conveyed while the steel material is hot.

In order to achieve the above purpose, the present invention improves the composition of the martensitic stainless steel in the prior art, and the technical concept thereof is as follows: on the basis of the components of the common 13Cr stainless steel for the oil well, the content of C is greatly reduced so as to improve the general corrosion resistance and the toughness; adding a certain amount of Ni to increase the strength to compensate for the strength loss of C reduction and improve CO resistance₂、H₂S stress corrosion; mo is added to improve the pitting corrosion resistance; a small amount of Cu is added to further improve the corrosion resistance; in addition, a small amount of N element is added to increase the martensite phase stability. Finally, an alloy system is formed: 0.01C-13 Cr-5.5 Ni-2 Mo-0.1 Cu-0.04N.

Therefore, in one aspect, according to an embodiment of the present invention, there is provided an ultra-low carbon martensitic stainless steel seamless pipe, wherein the seamless pipe is made of an ultra-low carbon martensitic stainless steel, and the ultra-low carbon martensitic stainless steel comprises the following components by mass percent: less than or equal to 0.03 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 0.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 12.2 to 13.2 percent of Cr, 5.2 to 5.7 percent of Ni, 1.9 to 2.1 percent of Mo, 0.1 to 1.6 percent of Cu, and the balance of Fe and other impurities.

The reasons for limiting the functions and the ranges of the respective alloying elements of the ultra-low carbon martensitic stainless steel of the present invention will be described below.

C promotes precipitation of matrix carbides, and when the C content of the martensitic stainless steel exceeds 0.03%, CO is contained₂、H₂The corrosion resistance of stainless steel is obviously deteriorated under the corrosive environment of S and the like, and the tempering sensitization degree caused by Ni is increased due to the increase of the content of C. Therefore, the C content is selected to be 0 to 0.03%.

Si is added as a deoxidizer during steel making, but if the amount of Si is too large, the hot workability and toughness of the alloy are reduced, and therefore the Si content is limited to 0.1 to 0.5%.

Mn is an austenite forming element, can play roles of deoxidation and desulfurization in the smelting process, and simultaneously improves the strength and the hot workability. If the Mn content is too small, the effect cannot be obtained, and if the Mn content is too large, the toughness of the stainless steel is affected, and the corrosion resistance at high temperature is also lowered. Therefore, the content range of Mn in the stainless steel of the present invention is selected to be 0.2 to 0.5%.

P is an impurity which reduces the corrosion of stainless steel in CO₂Corrosion resistance and stress corrosion resistance in the environment. Therefore, the P content is limited to 0.015% or less.

S is extremely disadvantageous in hot workability in the production of the pipe blank and the steel pipe, and therefore the content of the element S is limited to 0.002% or less.

Cr can form an oxide film on the surface and is ensured to contain CO₂、Cl^－、H₂S and the like, and the important elements necessary for corrosion resistance and stress corrosion cracking resistance in a severe corrosion environment achieve the effect of high-temperature corrosion resistance. The Cr content must be 12.2% or more, but when the Cr content exceeds 13.2%, the ferrite content increases, the hot workability deteriorates rapidly, and the strength decreases. Therefore, the Cr content is selected to be 12.2 to 13.2%.

Ni is a typical austenite forming element for improving the general corrosion resistance, and can improve the stability of the protective film and improve the stability in CO₂、Cl^－、H₂Corrosion resistance in S environmentThe corrosion resistance and the stress corrosion resistance can be achieved only when the addition amount is more than 5.2 percent, and when the content is too high, the content of residual austenite can be increased, the alloy strength is reduced, and the manufacturing cost is increased. Therefore, in the present invention, the content of Ni is selected to be 5.2% to 5.7%.

Mo is a ferrite forming element, and on the premise of containing enough Cr, the addition of a proper amount of Mo can improve the pitting corrosion resistance and the stress corrosion resistance of the martensitic stainless steel, and the effect cannot be achieved when the content is below 1.9%, but when the content of the Mo element exceeds 2.1%, the strength of the stainless steel is reduced and the cost is increased. Comprehensively, the content of Mo in the invention is selected to be 1.9-2.1%.

Cu can reduce martensite in stainless steel H₂S corrosion rate in the environment. However, too high a Cu content significantly reduces the hot workability of the alloy. Therefore, the Cu content in the present invention is selected to be 0.1 to 1.6%.

The ultra-low carbon martensitic stainless steel seamless pipe can be suitable for oil and gas fields.

The tube diameter of the above seamless tube may typically be phi 76mm to phi 220mm, and the length may be at least 6000 mm.

On the other hand, according to another embodiment of the present invention, there is also provided a method for manufacturing the ultra-low carbon martensitic stainless steel seamless pipe as described above, comprising the steps of, in order:

a) smelting, wherein molten iron is taken as a main raw material to be smelted into molten steel according with the components of the ultra-low carbon martensitic stainless steel, namely the components of the molten steel reach the following proportions in percentage by mass: less than or equal to 0.03 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 0.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 12.2 to 13.2 percent of Cr, 5.2 to 5.7 percent of Ni, 1.9 to 2.1 percent of Mo, 0.1 to 1.6 percent of Cu,

then casting the molten steel into a steel ingot;

b) hot processing the tube blank, wherein, firstly heating, blooming, forging, annealing and peeling the steel ingot, and then cutting the steel ingot into rod-shaped tube blanks;

c) hot working the steel pipe, wherein after heating the pipe blank, the pipe blank is made into the steel pipe; and

d) a heat treatment in which the steel pipe subjected to the steel pipe hot working step is quenched and tempered to produce a finished pipe,

wherein,

in the smelting step, the pretreated molten iron is subjected to rough smelting, vacuum oxygen decarburization and ladle refining and then is tapped, wherein the vacuum degree is kept to be less than or equal to 106.4Pa during the vacuum oxygen decarburization, wherein other alloy components except C, such as Si, Mn, P, S, Cr, Ni, Mo and Cu, are adjusted to enter a control range during the ladle refining, and the ladle is cast into a steel ingot after the temperature is adjusted to 1540 +/-10 ℃ under the condition that the slag viscosity is ensured to be less than or equal to 0.3P (poise);

in the step of hot processing of the tube blank, in the heating process, the heating temperature is controlled according to 1200-1280 ℃, the finish rolling temperature and the finish forging temperature are greater than 900 ℃, the deformation of a rolling pass is controlled to be 20-40%, the deformation of a forging pass is controlled to be 30-40%, and the total forging ratio is greater than or equal to 3; and

in the heat treatment step, the quenching temperature is 900-1050 ℃, the temperature is kept for 10-30 min, the steel is cooled to room temperature at a cooling speed above air cooling, the tempering temperature is 550-680 ℃, the temperature is kept for 1-4 h, and the steel is cooled to room temperature at a speed above air cooling.

In one embodiment, in the step of hot working the steel pipe, after heating the pipe blank, the steel pipe is manufactured by an extrusion method, wherein the heating temperature of the pipe blank is 1150-1250 ℃, the extrusion rate is 100-120 mm/s, the initial deformation temperature is not less than 1050 ℃, and the final deformation temperature is not more than 1300 ℃.

In another embodiment, in the hot working step of the steel pipe, after heating the pipe blank, the steel pipe is manufactured by a piercing cold rolling method, wherein the heating temperature of the pipe blank is 1200 to 1280 ℃, the piercing deformation amount is 50 to 70%, and the cold rolling deformation amount is 40 to 60%.

In one embodiment, in the smelting step, the pretreated molten iron is roughly smelted in a top-bottom combined blown converter, decarburized in a vacuum oxygen decarburization furnace, and refined in a ladle refining furnace, and during the decarburization in the vacuum oxygen decarburization furnace, the over-blowing is avoided, and the end point carbon hit is ensured.

In one embodiment, in the smelting step, the degree of vacuum is maintained at 66.5Pa or less during the vacuum oxygen decarburization.

The four main steps, i.e., the smelting, the pipe blank hot working, the steel pipe hot working, and the heat treatment, which are sequentially performed, included in the manufacturing method of the ultra-low carbon martensitic stainless steel seamless pipe according to the present invention are explained in detail as follows.

Firstly, smelting step

After the pretreated molten iron is subjected to rough smelting in a top-bottom combined blown converter, decarburization in a vacuum oxygen decarburization furnace and refining in a ladle refining furnace, steel can be discharged when the component mass percentage of the molten steel meets the requirement, and then the molten steel is cast into steel ingots or continuous casting billets. The phrase "the mass percentages of the components of the molten steel meet the requirements" means that the components of the molten steel meet the following proportions in mass percentage; less than or equal to 0.03 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 0.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 12.2 to 13.2 percent of Cr, 5.2 to 5.7 percent of Ni, 1.9 to 2.1 percent of Mo, and 0.1 to 1.6 percent of Cu.

When the vacuum oxygen decarburization furnace is used for decarburization, the vacuum degree is kept to be less than or equal to 106.4Pa, preferably less than or equal to 66.5Pa, and over-blowing is avoided during decarburization in the vacuum oxygen decarburization furnace, so that end-point carbon hit is ensured. When refining in a ladle refining furnace, other alloy components except C, such as Si, Mn, P, S, Cr, Ni, Mo, Cu and the like are adjusted to enter a control range, so that Si is 0.1-0.5%, Mn is 0.2-0.5%, P is less than or equal to 0.015%, S is less than or equal to 0.002%, Cr is 12.2-13.2%, Ni is 5.2-5.7%, Mo is 1.9-2.1%, and Cu is 0.1-1.6%.

Adjusting the temperature to 1540 +/-10 ℃ under the condition that the viscosity of the slag in the ladle refining furnace is less than or equal to 0.3P (poise), and then casting the ladle into a steel ingot.

Second, hot working step of tube blank

During the hot processing of the pipe blank, the steel ingot is heated, initially rolled, forged, annealed and peeled, and then cut into rod-shaped pipe blanks.

1. Heating of

Soaking the steel ingot before cogging, wherein the heating temperature is as follows: 1200-1250 ℃; continuously heating the primary rolling blank before forging, wherein the heating temperature is as follows: 1220 to 1280 ℃. The total heating time of the two stages is not less than 12 hours.

2. Blooming and forging

And cogging and blooming the heated steel ingot by a blooming mill, controlling the deformation of rolling passes to be 20-40%, and controlling the final rolling temperature to be above 900 ℃, so that the rolled surface has no folding, cracks and serious scratch defects. And (3) continuously heating the primary rolling blank, forging the primary rolling blank to a steel bar, determining the forging deformation pass according to the specification of the tube blank, controlling the total forging ratio to be more than or equal to 3, controlling the pass deformation amount to be 30-40% and controlling the final forging temperature to be more than 900 ℃. The dimension D of the forged steel bar is (D +20) mm (D is the diameter of the pipe billet), and the surface of the forged steel bar cannot have folding, cracks and serious scratch defects.

3. Machining

And annealing the forged steel bar at 650-750 ℃, peeling the outer circle to the outer diameter d of the tube blank, and cutting the tube blank into a tube blank fixed size L. d and L are obtained by calculation according to the elongation coefficient and the yield according to the outer diameter, the wall thickness and the length of the finished steel pipe.

Thirdly, hot processing step of steel pipe

The steel pipe can be hot-processed into the steel pipe by adopting two process routes of an extrusion method and a piercing cold rolling method.

A: extrusion method

1) Blank preparation

A tube blank is processed into a central through hole by adopting a deep hole drilling machine, a flat end chamfer at one end surface is processed into a bell mouth, the angle of the bell mouth is 33.5 +/-5 degrees, and the surface of the machined tube blank has no cracks, pits, black skin and impurities.

2) Preheating in ring furnace

And sequentially discharging the tube blanks into an annular furnace for preheating, wherein the temperature of the heating furnace is 950 +/-20 ℃, the heating time is set to be 4-8 min/cm according to the wall thickness of the tube blanks, and the soaking time is set to be 1.0-1.5 min/cm according to the wall thickness of the tube blanks.

3) Primary induction heating

The tube blank is discharged from the annular furnace and then is heated in the induction furnace, the temperature of the tube blank is firstly heated by one-time induction at 1150-1200 ℃, the heating power of the heating section is 600-800 KW, the heat preservation power is 80-160 KW, and the tube blank is discharged after the temperature of the blank is uniform and stable.

4) Enlarging holes

And (3) carrying out reaming production on the tube blank subjected to primary induction heating by using a puncher, and reaming the inner hole of the tube blank to a size larger than the inner diameter of a finished tube at a reaming rate of 200-220 mm/s.

5) Secondary induction heating

And (3) conveying the reamed tube blank to an induction furnace for secondary induction heating, wherein the heating target temperature is 1180-1250 ℃, the heating section power is 200-300 KW, the heat preservation power is 60-100 KW, and discharging the tube blank after the temperature of the tube blank is uniform and stable.

6) Extrusion

And conveying the secondarily induction heated tube blank to a horizontal extruder to extrude the tube blank into a steel tube with a target size, controlling the extrusion speed to be 100-120 mm/s, lubricating the tube blank by adopting glass powder, and cooling the tube blank in water after extrusion.

B: cold piercing rolling method

1) Blank preparation

And (3) punching centering holes at two ends of the tube blank, wherein the outer diameter of each centering hole is 40-80 mm, and the depth of each centering hole is 5-10 mm. The eccentricity of the centering hole is required to be less than or equal to 0.3mm, and the round angle is in smooth transition.

2) Heating in ring or inclined hearth furnaces

And (3) conveying the tube blank to an annular furnace or an inclined bottom furnace for heating, wherein the heating temperature is 1200-1280 ℃, the heating time is set to be 4-8 min/cm according to the wall thickness of the tube blank, and the soaking time is set to be 1.0-1.5 min/cm according to the wall thickness of the tube blank.

3) Thermal perforation

And (3) conveying the heated tube blank to a piercing mill to produce a tubular billet, wherein the roll gap is 70-120 mm, the forward extension of the plug is 50-70 mm, and the feed angle is 10-15 degrees. The specification of the tubular billet is comprehensively considered according to the specification of a finished product pipe and the deformation of the subsequent processing process, and is about 50-70%.

4) Stretch reducing diameter

And (3) hot-rolling the hollow billet to a stretch reducing mill set, and cooling the hollow billet to room temperature by water or air to manufacture a pierced billet.

5) Cold rolling

And (3) cold rolling the pierced billet to a target size through 1-2 passes, wherein the single-pass deformation is 40-60%.

Fourthly, a heat treatment step

Firstly, quenching the cold-rolled steel pipe: heating the steel pipe to 900-1050 ℃, preserving heat for 10-30 min, and cooling to room temperature at a cooling speed higher than air cooling. By the above treatment, fine martensite and a small amount of retained austenite structure can be obtained (see fig. 1). When the heating temperature is 900 ℃ or lower, the martensite formation is insufficient and the strength is low. If the heating temperature is higher than 1050 ℃, the martensite structure is too coarse, and the toughness is lowered.

Then, the quenched steel pipe is subjected to a tempering heat treatment: heating to 550-680 ℃, keeping the temperature for 1-4 hours, cooling to room temperature at a speed higher than air cooling, and forming a structure of tempered martensite and a small amount of residual austenite (see fig. 2), thereby forming a seamless pipe with high strength, high toughness and excellent corrosion resistance.

Advantageous effects

The main properties of the ultra low carbon martensitic stainless steel seamless pipe examples of the present invention are shown in table 1 in comparison with those of the conventional steel pipes.

Table 1: the main performance of the ultra-low carbon martensitic stainless steel seamless pipe of the invention is compared with that of the prior 13Cr

As can be seen from Table 1, the tensile strength and yield strength of the test steel are higher than those of the comparative steel containing CO, compared with 13Cr, which is a conventional martensitic stainless steel for oil fields₂And Cl^－The corrosion rate in the environment is far less than that of the comparative steel, the corrosion resistance is very excellent, and the method is suitable for high-concentration CO₂、H₂S and Cl^—Deep wells in corrosive environments coexist.

Drawings

The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, 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 is a gold phase diagram of a quenched structure of an ultra-low carbon martensitic stainless steel seamless tube according to an embodiment of the invention;

FIG. 2 is a drawing of a tempered microstructure gold phase of an ultra-low carbon martensitic stainless steel seamless tube according to an embodiment of the invention; and

fig. 3 is a flowchart of a method for manufacturing an ultra-low carbon martensitic stainless steel seamless tube according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

The following examples are provided to describe embodiments of the present invention, but the present invention is not limited to the following examples.

First, an example of an ultra-low carbon martensitic stainless steel seamless tube according to an embodiment of the present invention is shown.

Table 2 lists the chemical compositions of seven different examples of ultra-low carbon martensitic stainless steel seamless tubes according to embodiments of the invention.

Table 2: chemical composition of examples (% by mass)

	C	Si	Mn	P	S	Cr	Ni	Mo	Cu
										Example 1	0.005	0.12	0.5	0.008	0.001	12.2	5.7	1.91	1.6
Example 2	0.011	0.15	0.45	0.010	0.001	12.4	5.6	1.94	1.4
										Example 3	0.012	0.13	0.42	0.007	0.001	12.6	5.5	1.95	1.1
Examples4	0.015	0.16	0.4	0.007	0.001	12.7	5.5	2.01	0.9
										Example 5	0.022	0.29	0.35	0.006	0.001	12.8	5.4	2.03	0.5
Example 6	0.025	0.43	0.3	0.009	0.001	13.0	5.3	2.08	0.3
										Example 7	0.030	0.50	0.2	0.008	0.001	13.2	5.2	2.1	0.1

Next, examples of a method for manufacturing an ultra-low carbon martensitic stainless steel seamless pipe according to an embodiment of the present invention will be described.

The method for manufacturing an ultra-low carbon martensitic stainless steel seamless tube according to the embodiment of the present invention will be described below by taking two specifications of examples, one of which uses an extrusion method in the step of hot working the steel tube, and the other of which uses a piercing cold rolling method in the step of hot working the steel tube.

The method for manufacturing the ultra-low carbon martensitic stainless steel seamless pipe comprises the following steps of:

1. smelting

After the pretreated molten iron is subjected to rough smelting in a top-bottom combined blown converter, decarburization in a vacuum oxygen decarburization furnace and refining in a ladle refining furnace, the molten steel is tapped when the component mass percentage of the molten steel reaches the target requirement, and then the molten steel is cast into steel ingots or continuous casting billets. The phrase "the mass percentages of the components of the molten steel meet the target requirements" means that the components of the molten steel meet the following proportions in mass percentage; less than or equal to 0.03 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 0.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 12.2 to 13.2 percent of Cr, 5.2 to 5.7 percent of Ni, 1.9 to 2.1 percent of Mo, and 0.1 to 1.6 percent of Cu.

When the slag viscosity is 0.1P, tapping is carried out in a ladle refining furnace, the temperature is adjusted to 1543 ℃, then the ladle is hoisted to a die-casting process for casting, tapping is carried out, and the molten steel is die-cast into 5.8 tons of steel ingots. The specification of the steel ingot is 500 multiplied by 650 multiplied by 2300 mm.

2. Hot working of pipe blanks

The steel ingot is heated in a soaking furnace for 12 hours at the temperature of 1220 ℃, so that the steel ingot is uniformly burnt. Cogging into a primary rolling billet with the diameter of 400 x 400mm by a primary rolling mill with the diameter of 1000 mm. The finishing temperature in the cogging process is 1032 ℃, and no surface defect exists after rolling. The dimensions of the processed bloom are 400mm multiplied by 3600 mm.

And (3) heating the primary rolling blank, and sending the primary rolling blank into a natural gas heating furnace for heating, wherein the heating temperature is controlled to be 1250 ℃, and the total heating time is 6 hours and 30 minutes. After heating, the bar materials with phi 239mm and 230mm are respectively forged on a 1800t diameter forging machine for 5 passes, the first pass forging deformation is 30%, the final forging temperature is 1025 ℃, and no obvious defects exist on the surface of the bar materials after forging. After forging to form a rod, the skin is sawed into tube blanks with dimensions phi 219mm x 800mm and phi 130mm x 1200 mm.

3. Hot working of steel pipes

A: examples of extrusion methods

According to the dimension specification phi 73.02 × 5.51mm of a finished product, a phi 219mm × 800mm tube blank is processed into a phi 40mm central through hole by a deep hole drilling machine, a flat head chamfer is arranged on one end face of the tube blank to process a bell mouth, the angle of the bell mouth is 33.5 degrees, and cracks, pits, black skin and impurities cannot be formed on the surface of the machined tube blank. Heating the tube blank in a ring furnace for 3 hours to 950 ℃ for 80 min; soaking time is 20 min. Directly sending the hot gas to an induction heating furnace after the gas is discharged from the furnace. Heating to 1180 ℃ through primary induction heating, wherein the heating power of the heating section is 700KW, and the heat preservation power is 120 KW. And after the integral heating is uniform, expanding the inner hole to phi 60mm, wherein the expanding rate is 200 mm/s. Heating to 1230 ℃ through secondary induction, wherein the power of the heating section is 380KW, and the heat preservation power is 85 KW; extruded into a steel pipe of phi 73.02 × 5.51mm at an extrusion rate of 107mm/s, immediately cooled to room temperature with water.

B: examples of cold piercing rolling method

The tube blank with the diameter of 130mm multiplied by 1200mm is sent to a circular furnace to be heated, the heating temperature is 1230 ℃, the heating time is 25min, and the soaking time is 100 min. And (3) conveying the heated tube blank to a perforating machine to produce a tubular billet with phi 135 x 8.9mm, wherein the roll spacing is 80mm, the forward extension of the top is 60mm, and the feed angle is 10 degrees. And (3) the crude pipe is hot-fed to a stretch reducing mill to be processed into a crude pipe with phi 114 x 8.9mm, and the crude pipe is subjected to one-step cold rolling to obtain a finished pipe phi 89 x 7 mm.

4. Heat treatment Process

Quenching and tempering the steel pipe after hot working: heating at 1020 ℃ and preserving heat for 30min, then cooling by water, heating at 630 ℃ and preserving heat for 4h, and cooling by air to obtain the finished product pipe.

It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. An ultra-low carbon martensitic stainless steel seamless tube, characterized in that the seamless tube is made of ultra-low carbon martensitic stainless steel, and the ultra-low carbon martensitic stainless steel comprises the following components by mass percent: less than or equal to 0.03 percent of C, 0.1 to 0.5 percent of Si, 0.2 to 0.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 12.2 to 13.2 percent of Cr, 5.2 to 5.7 percent of Ni, 1.9 to 2.1 percent of Mo, 0.1 to 1.6 percent of Cu, and the balance of Fe and other impurities.

2. The ultra-low carbon martensitic stainless steel seamless tube according to claim 1, which is suitable for oil and gas fields.

3. The ultra-low carbon martensitic stainless steel seamless tube as claimed in claim 1, wherein the seamless tube has a tube diameter of phi 76mm to phi 220mm and a length of at least 6000 mm.

4. A method of manufacturing the ultra-low carbon martensitic stainless steel seamless tube according to any one of claims 1 to 3, comprising the steps of, in order:

then casting the molten steel into a steel ingot;

it is characterized in that the preparation method is characterized in that,

in the smelting step, the pretreated molten iron is subjected to rough smelting, vacuum oxygen decarburization and ladle refining and then is tapped, wherein the vacuum degree is kept to be less than or equal to 106.4Pa during the vacuum oxygen decarburization, wherein other alloy components except C, such as Si, Mn, P, S, Cr, Ni, Mo and Cu, are adjusted to enter a control range during the ladle refining, and the ladle is cast into a steel ingot after the temperature is adjusted to 1540 +/-10 ℃ under the condition that the slag viscosity is ensured to be less than or equal to 0.3P;

5. A method of manufacturing a seamless pipe according to claim 4, wherein in the hot working step of the steel pipe, the steel pipe is manufactured by an extrusion method after a pipe blank is heated, wherein the pipe blank is heated at 1150 to 1250 ℃, the extrusion rate is 100 to 120mm/s, the initial deformation temperature is not less than 1050 ℃, and the final deformation temperature is not more than 1300 ℃.

6. A method of manufacturing a seamless pipe according to claim 4, wherein in the hot working step of the steel pipe, the steel pipe is manufactured by a piercing cold rolling method after heating a shell, wherein the shell heating temperature is 1200 to 1280 ℃, the piercing deformation amount is 50 to 70%, and the cold rolling deformation amount is 40 to 60%.

7. The method of manufacturing a seamless tube according to claim 4, wherein in the smelting step, the pretreated molten iron is subjected to rough smelting in a top-bottom combined blown converter, decarburization in a vacuum oxygen decarburization furnace, and refining in a ladle refining furnace, and during decarburization in the vacuum oxygen decarburization furnace, over-blowing is avoided, and end point carbon hit is ensured.

8. A method according to claim 4, wherein the vacuum degree of the vacuum decarburization is maintained at 66.5Pa or less in the smelting step.