EA036004B1 - High chromium martensitic heat-resistant steel with combined high creep rupture strength and oxidation resistance - Google Patents

Abstract

Disclosed is a martensitic heat-resistant steel for boiler applications with a unique combination of enhanced creep strength and excellent oxidation resistance upon high temperature exposure in steam containing environments, having the following melt analysis, wt.%: C: 0.10 to 0.16%, Si: 0.20 to 0.60%, Mn: 0.30 to 0.80%, P0.020%, S0.010%, Al0.020%, Cr: 10.5 to 12.00%, Mo: 0.10 to 0.60%, V: 0.15 to 0.30%, Ni: 0.10 to 0.40%, B: 0.008 to 0.015%, N: 0.002 to 0.020%, Co: 1.50 to 3.00%, W: 1.50 to 2.50%, Nb: 0.02 to 0.07%, Ti: 0.001-0.020%. The balance of the steel consists of iron and unavoidable impurities. The steel is normalized for a period of about 10 to about 120 min in the temperature range between 1050 and 1170°C and cooled down in air or water to room temperature, and then tempered for at least 1 h in the temperature range between 750 and 820°C. It exhibits martensitic microstructure with average -ferrite content of less than 5 vol.%.

Description

The present invention relates to martensitic high-chromium high-temperature steels for components operating at elevated temperatures, for example, 550 to 750 ° C, and at high voltages. The steel of the present invention can be used in the power generation, chemical and petrochemical industries.

State of the art

Ferritic / martensitic high chromium steel materials are widely used in modern power plants as materials for reheater / superheater tubes and steam conduits. To further improve the overall efficiency of thermal power plants, it is necessary to increase the steam parameters, pressure and temperature. Consequently, more efficient power plant cycles will require stronger materials with improved steam oxidation resistance. Known attempts to create a new martensitic high-chromium steel that combines excellent long-term strength properties and excellent oxidation resistance have so far failed as a result of the formation of the so-called Z-phase. The Z-phase is a complex nitride that rapidly coarsens, thereby absorbing the surrounding hardening sediments MX, M is: Nb, V, and X is C, N.

The expression high chromium steel material usually refers to steel grades containing more than 9% chromium by weight. However, the increased chromium content, i.e. a chromium content of more than 9% by weight, which is necessary for proper resistance to oxidation in water vapor, accelerates the formation of the Z-phase and also increases the rate of coarsening of chromium carbide precipitates. Together with the loss of the stabilization effect of the microstructure of the MX and chromium carbide deposits, they result in a decrease in the long-term long-term strength of the martensitic high-chromium heat-resistant steel grades. Therefore, the main challenge for future steel development is to resolve the apparent tension between long term strength and oxidation resistance.

Currently for use in high temperature environments, i.e. use at operating temperatures above 550 ° С, grades 91 and 92 according to ASTM, containing 9% chromium by weight, with a long-term strength of more than 10 ⁵ hours at 600 ° С at 90 and 114 MPa, are widely used. The main difference between the two steel grades is that grade 92 contains W in the range of 1.8 wt% and less Mo in the range of 0.4 wt%, compared to 1% in the case of grade 91. In addition, grade 92 contains small amounts of B, less than 0.005 wt.%.

Both steel grades are characterized by insufficient resistance to oxidation in vapor atmospheres at temperatures above 600 ° C, which significantly limits the temperature range of use. Especially in the components of a heat transfer boiler, the scale acts as a thermal insulating material, thereby increasing the metal temperature and, as a result, reducing the service life of the corresponding components. In addition, scale chipping off during operation or entering the steam turbine onto the turbine blades and guide vanes will erode downstream steam transport components. Chipped scale can clog the pipe, especially in the bend area, obstructing steam flow, often resulting in localized overheating and catastrophic failure.

X20CrMoV11-1 is a robust high chromium ferritic / martensitic steel for high temperature applications containing 0.20% C by weight, 10.5-12% Cr by weight, 1% Mo by weight and 0.2% V by weight ... This steel exhibits better oxidation properties than grades 91 and 92 according to ASTM due to the higher Cr content, but poorer creep rupture strength (creep strength over 105 hours at 600 ° C is approximately 59 MPa). In addition, hot workability and weldability deteriorate due to the high C content of 0.20% by weight. ASTM Grade 122 contains 10-12% Cr, 1.8% W, 1% Cu, and additions of V, Nb and N to induce precipitation of MX hardener particles. The long-term strength is significantly lower than that of grade 92 according to ASTM, which demonstrates the long-term strength of 98 MPa at more than 10 ⁵ hours at 600 ° C.

Hot workability is also controversial due to the increased Cu content.

There is another steel with a Cr content of 11-12% by weight. It is mainly used for thin-walled pipe and is called VM12-SHC steel, which combines proper vapor side oxidation resistance and ASTM 91 grade creep rupture strength. The concept of such a steel is known from patent application WO 02081766, which discloses a steel for use at high temperatures, containing by weight: from 0.06 to 0.20% C, from 0.10 to 1.00% Si, from 0, 10 to 1.00% Mn, not more than 0.010% S, from 10.00 to 13.00% Cr, not more than 1.00% Ni, from 1.00 to 1.80% W, Mo so that ( W / 2 + Mo) is no more than 1.50%, from 0.50 to 2.00% Co, from 0.15 to 0.35% V, from 0.040 to 0.150% Nb, from 0.030 to 0.12% N, from 0.0010 to 0.0100% B, and optionally up to 0.0100% Ca, the remainder of the chemical composition consists of iron and impurities or residues obtained from or required by preparatory processes or steel casting. The content of chemical components preferably confirms the relationship that the steel after normalization of heat treatment in the range from

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1050 to 1080 ° C and tempering has a tempered martensite structure with no or practically no delta ferrite. Compared with this steel, the creep rupture strength can still be improved while maintaining intact other properties such as corrosion resistance and mechanical properties.

The purpose of the present invention and the solution of the technical problem

Thus, it is an object of the present invention to provide a seamless martensitic refractory steel tubular product with substantially better long term strength than ASTM 92 steel for fittings and pipes, and with high temperature corrosion and water vapor oxidation characteristics comparable to or better than for steels X20CrMoV11-1 and VM12-SHC described in the prior art.

It is an additional object of the present invention to provide a steel exhibiting a martensitic microstructure while limiting the content of delta ferrite, also known as 8-ferrite, to 5% by volume on average.

Another object of the present invention is to provide a steel that is suitable for the manufacture of seamless tubular products of small or large diameter, such as seamless pipes or seamless pipes, and steel suitable for the manufacture of welded pipes and pipes, stampings and plates using known and reliable manufacturing processes. ...

Steel is suitable as a manufacturing material for a variety of high-temperature energized components such as seamless and welded pipes / tubes, stampings and plates in the power generation, chemical and petrochemical industries. In addition, the steel according to the present invention is resistant to tempering, after prolonged tempering up to 30 hours at 800 ° C, the yield strength is greater than or equal to 440 MPa, the tensile stress is greater than or equal to 620 MPa, and the toughness at 20 ° C is greater than or equal to 40 J when tested in the longitudinal direction and 27 J when tested in the transverse direction.

In accordance with the present invention, the object can be achieved by using a seamless tubular product for use under high temperature conditions made of steel having the following chemical composition, wt%: C 0.10 to 0.16%, Si 0.20 to 0 , 60%, Mn from 0.30 to 0.80%, P <0.020%, S <0.010%, Al <0.020%, Cr from 10.50 to 12.00%, Mo from 0.10 to 0.60 %, V from 0.15 to 0.30%, Ni from 0.10 to 0.40%, B from 0.008 to 0.015%, N from 0.002 to 0.020%, Co from 1.50 to 3.00%, W 1.50 to 2.50%, Nb 0.02 to 0.07%, Ti: 0.001 to 0.020%, the rest of this steel is iron and inevitable impurities.

Preferably the ratio of boron to nitrogen is ^B / _N 13

To achieve hot workability. Preferably the following equation is satisfied (wt%)

1.00% <Mo + 0.5W <1.50%

In another preferred embodiment, the following equation is satisfied (.% By weight): In ~ "lO-CV ^ ²⁾⁾ - _^(14/48) '- °' ⁰⁰⁷ ·

In another preferred embodiment, the following equation is satisfied (wt%): 2.6 <4 (Ni + Co + 0.5 Mn) - 20 (C + N) <11.2.

In a preferred embodiment, the carbon content is 0.13 to 0.16%.

In another preferred embodiment, the Mo content is 0.20 to 0.60%. Preferably, the B content is 0.0095 to 0.013%.

In a preferred embodiment, the Ti content is 0.001 to 0.005%.

In another preferred embodiment, the microstructure contains on average at least 95% tempered martensite, the remainder being delta ferrite.

In an even more preferred embodiment, the microstructure contains, on average, at least 98% tempered martensite, the remainder being delta ferrite.

In a most preferred embodiment, the microstructure is martensitic and does not contain delta ferrite.

The present invention also relates to a production method comprising the following steps: casting a steel with a chemical composition according to the present invention, thermoforming said steel, heating said steel, and holding said steel for a period of 10 to 120 minutes in a temperature range of 1050 to 1170 ° C, cooling said steel to room temperature, reheating said steel to tempering temperature TT and holding said steel at this temperature, which is from 750 to 820 ° C, for at least one hour, cooling said steel to room temperature temperature.

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Preferably, the cooling step is carried out by air cooling or water cooling.

The cooling step after the reheating step can be carried out by water cooling.

The cooling step after the heating step can be carried out by water cooling.

The present invention may also relate to the manufacture of a welded pipe, branch pipe, or plate using the same steel as steel for a seamless tubular article according to the present invention or in a method according to the present invention.

The drawing shows a diagram of the weight gain due to oxidation plotted against the chromium content.

The essence of the present invention

In accordance with the present invention, a martensitic high-chromium heat-resistant steel is produced with the following chemical composition:

(1) C: 0.10 to 0.16%, it is necessary to add C to at least 0.10% to obtain sufficient carbide precipitation. In addition, C is also an austenitic stabilizing element. A C content below 0.10% implies more δ-ferrite in the microstructure. The upper limit for carbon is 0.16%, as the excessive addition of C limits the toughness and weldability properties.

(2) Si: 0.20 to 0.60%,

Si is used for deoxidation in the steelmaking process. In addition, it is one of the key elements that determines the oxidation characteristics of steels. To achieve the effect of improving the complete oxidation of Si additives, an amount of at least 0.20% is required. The upper level of Si should preferably be limited to 0.60%, since an excessive addition of Si accelerates precipitation coarsening and decreases toughness. Preferably, the lower limit is 0.25%.

(3) Mn: 0.30 to 0.80%,

Mn is an effective deoxidizing element. It binds sulfur and reduces the formation of δ-ferrite. You can add at least 0.30% Mn. The upper limit should be 0.8%, as excessive additives reduce the long-term strength of steels at elevated temperatures.

(4) P <0.020%,

P is an active grain boundary element that reduces the toughness properties of steels. The content should be limited to 0.020% to avoid negative influence of P on the toughness properties. P may be present in an amount equal to or greater than 0.00% since it may be an unavoidable impurity.

(5) S <0.010%,

S forms sulfides and reduces the toughness and hot workability of steels. Limiting the upper limit of the S content to 0.010 prevents the formation of defects during hot working and negatively affects the toughness. S may be present in an amount equal to or greater than 0.00% since it may be an unavoidable impurity.

(6) Al <0.020%,

Al is an effective deoxidizing element used in the steelmaking process. Excessive addition of Al above 0.02% can cause the formation of AlN, thereby reducing the amount of reinforcing nitride deposits MX (M is Nb, V, and X is C, N) in the steel and as a result of the creep properties. Al may be present in an amount equal to or greater than 0.00% since it may be an unavoidable impurity.

(7) Cr: 10.5 to 12.00%,

Cr forms carbides that form at the boundaries of the martensitic microstructure. Chromium carbides are important for stabilizing the martensitic microstructure during exposure to elevated temperatures. Cr improves the high temperature oxidation characteristics of steels. A content of at least 10.5% is required to reveal the enhancing effect of the complete oxidation of Cr additives. Cr contents above 12% lead to increased formation of δ-ferrite.

(8) Mo: 0.10 to 0.60%,

Mo is an essential element for improving long-term strength, which is also responsible for solid solution hardening. This element is also found in carbides and intermetallic phases. The Mo content can be 0.10%. Mo additions above 0.60% will degrade toughness and cause an increase in the δ-ferrite content. It should be noted that the content of M and W must satisfy the ratio (wt.%) 1 <Mo + 0.5xW <1.5 to ensure sufficient precipitation of carbides and intermetallic phases.

(9) V: from 0.15 to 0.30%,

V in combination with N forms coherent nitrides MX (M is: Nb, V, and X is C, N), which improves the properties of long-term creep. A content of 3 036004 below 0.15% is not sufficient to achieve this effect of improving the long-term creep strength property, while a content of 0.30% reduces toughness and increases the risk of δ-ferrite content above 5% on average.

(10) Ni: 0.10 to 0.40%,

Ni is an important element for improving toughness. Thus, a minimum content of 0.10% is required. However, it lowers the temperature A _c1 and tends to decrease creep rupture strength when added at more than 0.40%.

(11) B: 0.008 to 0.015%,

B is a decisive element responsible for stabilizing M ₂₃ C ₆ carbides and delaying the restoration of the martensitic microstructure. It strengthens the grain boundaries and improves the long-term stability of long-term strength. In addition, B is responsible for a significant improvement in long-term deformability. To achieve the maximum hardening effect, additives are required in an amount of at least 0.008%. Content above 0.015%, however, significantly reduces the maximum processing temperature of steels and is considered unprofitable. Additives B and N satisfy a B / N ratio of <1.5 to allow conversion by known hot working methods. Moreover, this B / N ratio allows small or large diameter seamless and welded pipes, tubes and slabs to be fabricated using the production method of the present invention. Preferably, the B content should be in the range of 0.0095 to 0.0130 (wt%).

(12) N: 0.002 to 0.020%.

Nitrogen is required for the formation of nitrides and carbonitrides MX (M is: Nb, V and X is C, N), which are responsible for achieving long-term strength. At least 0.002% can be added. However, excessive N additions, i.e. higher than 0.020%, lead to increased formation of BN, thereby reducing the strengthening effect of additives B.

Preferably, the content of B and N (wt%) satisfies the following ratio:

B - I ¹¹ / _1D 11 N - 10 - ^ / 2.45) (^ 8 + 6.81) _ [14 /]. _Ti ]> Q QQ7 I ⁷ 14 And I ⁷ 4о / / (13) Co: from 1.50 to 3.00%,

Co is a very effective austenite-forming element and is used to limit the formation of δ-ferrite. Moreover, it only weakly affects the temperature A _c1 . In addition, it is this element that improves the long-term strength properties by reducing the size of the initial precipitation after heat treatment. Therefore, a minimum amount of 1.50% should be added. Preferably, the minimum content is 1.75%. However, excessive addition of Co can cause embrittlement as a result of increased precipitation of intermetallic phases during operation at high temperatures. At the same time, Co is very expensive. Therefore, limiting additives to 3.00%, preferably to 2.50%, is necessary.

It is preferable that the content of Ni, Co, Mn, C and N (wt%) corresponds to the following equation: 2.6 <4x (Ni + Co + 0.5xMn) -20x (C + N) <11.2.

(14) W: 1.50 to 2.50%,

W is known to be effective in increasing the concentration of a solution. At the same time, it is contained in carbides and forms the C14 Laves phase, which can also contribute to an increase in long-term strength. Therefore, a minimum content of 1.50% is required. However, this element is expensive, delaminates strongly during the steel making and casting process, and forms intermetallic phases that lead to significant embrittlement. Therefore, the upper limit for W additives can be set up to 2.50%. It should be noted that the Mo and W content (wt%) must satisfy the ratio 1.00 <Mo + 0.5W <1.50 in order to ensure sufficient precipitation of carbides and intermetallic phases.

(15) Nb: 0.02 to 0.07%.

Nb forms stable MX carbonitrides, important not only for creep rupture properties but also for austenite grain size control. A minimum amount of 0.02% can be added. Nb contents above 0.07% lead to the formation of coarse Nb carbides, which can reduce creep rupture properties. Therefore, the upper limit is set to 0.07%.

(16) Ti: 0.001-0.020%

Ti is a strong nitride-forming element. It promotes free-form protection of B through the formation of nitrides. For this purpose, a minimum content of 0.001% is required. However, an excessive Ti content above 0.020% can reduce the toughness properties as a result of the formation of large TiN blocking deposits.

The remainder of the steel contains iron and common residuals obtained from the steel making and casting process. Only the casting techniques used are known to the person skilled in the art. Impurities are elements such as tantalum, zirconium and any other elements that cannot be avoided. It should be noted that tantalum and zirconium are inadvertently added to steel, but may be present in amounts less than 50 ppm overall as unavoidable impurities.

In one embodiment of the steel, unavoidable impurities may include one or more of copper (Cu), arsenic (As), tin (Sn), antimony (Sb), and lead (Pb).

Cu may be present in an amount equal to or less than 0.20%.

The As element may be present in an amount equal to or less than 150 ppm; Sn may be present in an amount equal to or less than 150 ppm; Sb may be present in an amount equal to or less than 50 ppm; Pb may be present in an amount equal to or less than 50 ppm, and the total As + Sn + Sb + Pb content is equal to or less than 0.04 wt%.

The steel is normalized for a period of about 10 to about 120 minutes in the temperature range from 1050 to 1170 ° C and cooled in air or water to room temperature, and then tempered for at least one hour in the temperature range from 750 to 820 ° FROM.

The resulting steel was found to have significant and absolutely superior strength at elevated temperatures and excellent resistance to oxidation in water vapor. Moreover, it was found that when the ratio Cg _eq , / M _eq . less than 2.3 the average content of δ-ferrite can be limited to less than 5% by volume to avoid problems with toughness, while Cg _eq . and number _equivalents. defined as Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb + 8Ti and 40C + 30N + 2Mn + 4Ni + 2Co + Cu, respectively. Surprisingly, it has been found that a B / N ratio equal to or less than 1.5 needs to be maintained to provide hot working by known conversion methods.

The delta ferrite content should not exceed 5% by volume, since a content higher than 5% by volume will impair the toughness properties.

Hot forming methods mean hot rolling, pilgrim rolling, hot drawing, stamping, mandrel rolling, racking mill pushing, where a piercing rod pushes an elongated recess through several in-line working stands to obtain continuous hollow rolling; other methods are also known. rolling. The steel of the present invention can be formed into pipes and pipes. Numerous attempts have been made to produce steel grades showing satisfactory properties such as oxidation characteristics, creep rupture strength, but these steel grades have failed to create a satisfactory product by these hot forming methods. In particular, it was sometimes even impossible to obtain seamless pipes or pipes. The steel according to the present invention provides seamless tubular products with satisfactory properties and the ability to produce seamless tubular products or plates by hot forming processes, these products meeting dimensional requirements.

Examples of

The advantages of the steel of the present invention will be explained in more detail based on the following examples. Steels in accordance with the present invention (steel 1, steel 2, steel 3) and also comparative illustrative steels (steel 4, steel 5) having the chemical composition indicated in table. 1 was cast in 100 kg molds by means of a vacuum induction melting furnace, then hot rolled to obtain plates (13-25 mm thick) and then normalized and tempered. Normalizing heat treatment was carried out in the temperature range from 1060 to 1100 ° C for 30 min, followed by air cooling to room temperature. The tempering was carried out at 780 ° C for 120 min again, followed by cooling with air.

Comparative illustrative steels 4 and 5 have a B content below 0.008 and thus do not correspond to the present invention.

In the case of steel 4, the additions of Ni, Co, Mn, C and N do not satisfy the equation (wt%).

2.6 <4 (Ai + Co + 0.5 Mn) - 20 (C + N) <11.2

Steel 5 does not satisfy the following formula:

B ~ ^{(11/14) (; V} "10-α / ^{2 ^) · ^ Β - ^)} - ( _^14/48) Ti)> 0,007 (in% by weight) as well.

Table 1

Element Steel 1 (% by weight € Steel 2 y) (% by ve < Steel 3 y) (% by weight Steel 4 *: y) (% by weight Steel 5 * y) (% by weight) FROM 0.15 0.148 0.148 0.158 0.152 Si 0.39 0.52 0.29 0.49 0.39 Mp oh h 0.67 0.65 0.42 0.35 R 0.001 0.015 0.015 0.005 0.001

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S 0.002 0.001 0.002 0.001 0.002 Al 0.007 <0.002 0.007 0.007 0.006 Cr 11.19 11.4 11.3 11.36 10.85 Moe 0.49 0.46 0.25 0.31 0.49 V 0.27 0.21 0.2 0.25 0.25 Ni oh h 0.25 oh h 0.23 0.31 AT 0.0145 0.011 0.0100 0.0040 0.0052 N 0.011 0.0088 0.0103 0.042 0.015 Co 1.77 1.9 1.9 0.88 1.72 W 1.91 1.6 1.8 1.46 1.95 Nb 0.048 0.038 0.033 0.038 0.043 Ti 0.001 0.003 0.001 0.001 0.001

*) Comparative steel grades

For two illustrative steels (steel 1, steel 2, steel 3), the results are presented in table. 2 were obtained at room temperature for tensile strength, yield stress, tensile strength, surface reduction, and fracture energy of a Charpy V-notch specimen.

table 2

Steel 1 Steel 2 Steel 3 R92

Rpo 2 (MPa) 653 683 682 540 R _m (MPa) 840 855.5 859.5 710 A ₅ (%) 20.5 22 21 23 Z (%) 64 64 60 65 A _viso (J) -RT 72 52 56 140

Creep rupture tests carried out in accordance with ISO DIN EN 204 on samples of two illustrative steels additionally showed a significant improvement in creep rupture strength. This is reflected in the fracture time, which is at least almost double the time for prior art steels such as P91, P91, VM12-SHC, P122 and X20CrMoV11-1 in a long-term creep test at 130 MPa and 100 MPa. The results are shown in table. 3. Also, comparative illustrative steels did not achieve the creep rupture strength of steels according to the present invention.

Table 3

steel grade Destruction time in hours at 650 ° C under voltage 130 MPa 100 MPa Steel 1 6470 23844 Steel 2 1824 13867 Steel 3 2194 7552 Steel 4 have not experienced 5900 Steel 5 526 3354 VM12-SHC 517 2828 P91 * 44 498 P92 * 686 4682 P122 (single phase) ** 533 4572 X20CrMoVll-l * 55 210

*) Average values calculated on the basis of strength values are indicated on the ECCC data sheet **) K. Kimura et al. ASME PVP Conference Procedure (PVP2012), 2012, Toronto, Canada

The drawing shows a diagram of the weight gain due to oxidation in an atmosphere of water vapor at elevated temperatures, plotted against the content of chromium. The basis for the construction of the scheme is the oxidation test in an atmosphere of water vapor, carried out according to ISO 21608: 2012.

In the drawing, three areas representing different oxidation characteristics in water vapor are defined as follows:

(I) Performance in the absence of protection for a mass gain of more than 10 mg / cm ² at more than 5000 h.

/ _2 (II) Intermediate characteristic for weight gain in the range of 5-10 mg / cm ² (III) Characteristics with protection for weight gain values less than 5 mg / cm ² .

Accordingly, the classification of various high-chromium martensitic heat-resistant steels with respect to oxidation characteristics is made in table. 4 below. Regions I, II and III correspond to the weight gain values as shown in FIG. 1. Two illustrative steels clearly outperform P91, P92, P122 and X20CrMoV11-1 in terms of resistance to oxidation in water vapor. The steel according to the present invention exhibits characteristics comparable to those of VM12-SHC.

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Table 4

Mass gain

Temperature at (mg / cm ² )

VM12-SHC IIIIII

P92 II

X20CrMoVll-l IIII

P122 (one phase) IIIII

Steel according to the present invention ___________________

According to the present invention, it is possible to provide a high-chromium martensitic creep-resistant steel with improved creep rupture strength and water vapor oxidation resistance, which can be used to make pipes, stampings, pipes and plates for high temperature service in the power generation, chemical and petrochemical industries.

Claims (15)

CLAIM 1. Seamless tubular product for use in high temperature conditions, made of steel with the following chemical composition, wt.%: C from 0.10 to 0.16%, Si from 0.20 to 0.60%, Mn from 0, 30 to 0.80%, P <0.020%, S <0.010%, Al <0.020%, Cr from 10.50 to 12.00%, Mo from 0.10 to 0.60%, V from 0.15 to 0.30%, Ni from 0.10 to 0.40%, B from 0.008 to 0.015%, N from 0.002 to 0.020%, Co from 1.50 to 3.00%, W from 1.50 to 2.50 %, Nb from 0.02 to 0.07%, Ti from 0.001 to 0.020%, with the rest of this steel being iron and unavoidable impurities. 2. Seamless tubular product according to claim 1, where ^Β / ν G5 3. Seamless tubular article according to claim 1 or 2, where wt%: 1.00% <Mo + 0.5W <1.50% 4. Seamless tubular product according to any one of claims 1 to 3, where wt%: B - ( ^I / 1 ₄ ) (N - _ ( _14/48 ).> 0.007. 5. Seamless tubular article according to any one of claims 1 to 4, where wt%: 2.6 <4 (Ni + Co + 0.5 Mn) - 20 (C + N) <11.2. 6. Seamless tubular article according to any one of claims 1 to 5, wherein the carbon content is 0.13 to 0.16%. 7. Seamless tubular article according to any one of claims 1 to 6, wherein the Mo content is 0.30 to 0.60%. 8. Seamless tubular article according to any one of claims 1 to 7, wherein the B content is from 0.0095% to 0.013%. 9. Seamless tubular article according to any one of claims 1 to 8, wherein the Ti content is 0.001 to 0.005%. 10. Seamless tubular article according to any one of claims 1 to 9, wherein the microstructure contains at least 95% tempered martensite, with the remainder being delta ferrite. 11. Seamless tubular article according to any one of claims 1-10, wherein the microstructure contains at least 98% of tempered martensite, with the remainder being delta ferrite. 12. Seamless tubular article according to any one of claims 1 to 11, wherein the microstructure is martensitic and does not contain delta ferrite. 13. Seamless tubular product according to any one of claims 1-12, said product being a seamless pipe. 14. A method for producing a seamless tubular product according to any one of claims 1-12, comprising the following steps: casting steel with a chemical composition specified in any of claims 1 to 12, hot forming said steel, heating said steel and holding said steel for a period of 10 to 120 minutes in a temperature range of 1050 to 1170 ° C, cooling said steel to room temperature, reheating said steel to tempering temperature TT and holding said steel at this temperature, which is from 750 to 820 ° C., for at least one hour, cooling said steel to room temperature. 15. The method for producing a seamless tubular steel product according to claim 14, wherein the cooling steps are performed by air cooling or water cooling.