RU2675308C2 - Corrosion and wear resistant cold work tool steel - Google Patents

Abstract

FIELD: powder metallurgy.SUBSTANCE: invention relates to corrosion-resistant and wear-resistant cold work tool steel obtained by powder metallurgy. Said steel contains, wt. %: C 0.3–0.8, N 1.0–2.2, Si≤1.0, Mn 0.2–2.0, Cr 13–30, Mo 0.5–3.0, W≤1, V 2.0–5.0, Nb≤2.0, (Ti + Zr + Al)≤7.0, Ta≤0.5, Co≤10.0, Ni≤5.0, Cu≤3.0, Sn≤0.3, V≤0.01, Be≤0.2, Bi≤0.3, Se≤0.3, Te≤0.3, Mg≤0.01, P3M≤0.2, Ca≤0.05, S≤0.5, iron and impurities - the balance, provided the following conditions are met: (C + N) = 1.3–2.2, C/N = 0.17–0.50, (Mo + W/2) = 0.5–3.0, (V + Nb/2) = 2.0–5.0. Method of obtaining steel using powder metallurgy includes spraying a steel alloy having a chemical composition corresponding to the chemical composition of the claimed nitrogen-free alloy, treating the powder by nitriding in such a way as to adjust the nitrogen content in the alloy to the content specified in the claimed alloy, loading the powder into a capsule, hot isostatic pressing (HIP) of the capsule to form steel and quenching and tempering thereof.EFFECT: invention is intended to obtain steel with high wear resistance and corrosion resistance.14 cl, 3 ex, 3 tbl, 5 dwg

Description

State of the art

The invention relates to corrosion-resistant and wear-resistant tool steel for cold working and a method for manufacturing steel for cold working and the use of tool steel for cold working.

State of the art

Nitrogen-alloyed martensitic tool steels have recently appeared on the market and have attracted considerable interest because they combine high wear resistance and excellent corrosion resistance. These steels have a wide range of applications, including applications for forming aggressive plastics, for knives and other food processing components, and for reducing corrosion caused by fouling in the metallurgical industry.

These steels are usually produced using powder metallurgy. The basic composition of the steel is first finely ground and then nitrided to introduce the required amount of nitrogen into the powder. After that, the powder is loaded into the capsule and subjected to hot isostatic pressing (ISU) to obtain isotropic steel.

The amount of carbon is usually lowered to a very low level compared to conventional tool steels. By replacing most of the carbon with nitrogen, it is possible to replace chromium-rich carbides of the M ₇ C ₃ and M ₂₃ C _{6 type with} very stable MN nitride solid particles.

Achieve two important effects. First, the relatively soft and anisotropic phase of M ₇ C ₃ carbide (≈1700 TB (Vickers hardness unit)) is replaced by a very hard and stable phase of small and uniformly distributed particles of the solid phase of the MN type (≈ 2800 TB). By this, wear resistance is improved with the same volume fraction of solid phase. Secondly, the amount of Cr, Mo, and N in the solid solution at the quenching temperature increases significantly because less chromium binds in the solid phase and because carbides of the type M ₂₃ C ₆ and M ₇ C ₃ do not have any solubility for nitrogen. As a result, more chromium remains in the solid solution and hardens a thin chromium-rich passivating surface film, which leads to increased resistance to general corrosion and pitting.

Therefore, in order to obtain good corrosion resistance, the carbon content was limited to less than 0.3% C, preferably less than 0.1% C in DE 4231695 A1 and to a value less than or equal to 0.12% C in WO 2005/054531 A1.

Description of the invention

The general objective of the invention is the provision obtained by powder metallurgy (PM) of nitrogen-alloyed tool steel for cold working, having improved properties, in particular good corrosion resistance combined with high hardness.

A particular goal is to provide nitrogen-alloyed martensitic tool steels for cold working, with improved corrosion resistance at a fixed chromium content.

An additional objective is to provide a method of obtaining the specified material.

The aforementioned goals, as well as additional advantages, are achieved to a large extent by providing tool steel for cold working having the composition presented in the claims describing the alloy.

The invention is defined by the claims.

DETAILED DESCRIPTION OF THE INVENTION The importance of the individual elements and their interaction with each other, as well as the limitations on the chemical components of the claimed alloy, are briefly explained below. All percentages of the chemical composition of steel are given in mass. % throughout the description.

Carbon (0.3-0.8%)

must be present in a minimum content of 0.3%, preferably at least 0.35%. At high carbon contents, carbides of the type M ₂₃ C ₆ and M ₇ C ₃ are formed in the steel. The carbon content should therefore not exceed 0.8%. The upper limit for carbon can be set at 0.7% or 0.6%. Preferably, the carbon content is limited to 0.5%. Preferred ranges are 0.32-0.48%, 0.35-0.45%, 0.37-0.44% and 0.38-0.42%. In any case, the amount of carbon must be adjusted so that the amount of carbides of type M ₂₃ C ₆ and M ₇ Cz in steel is limited to 10 vol. %, preferably the steel does not contain these carbides.

Nitrogen (1.0-2.2%)

Unlike carbon, nitrogen cannot be included in M ₇ Cz. The nitrogen content should therefore be much higher than the carbon content in order to avoid the precipitation of M ₇ C3 carbides. In order to obtain the required type and the required amount of solid phases, the nitrogen content is balanced with the contents of strong carbide-forming elements, in particular vanadium. The nitrogen content is limited to 1.0-2.2%, preferably 1.1-1.8% or 1.3-1.7%.

(C + N) (1.3-2.2%)

The total amount of carbon and nitrogen is an essential feature of the present invention. The combined amount (C + N) should be in the range of 1.3-2.2%, preferably 1.7-2.1%, or 1.8-2.0%.

C / N (0.17-0.50)

The proper balance of carbon and nitrogen is an essential feature of the present invention. By controlling the carbon and nitrogen contents, the type and amount of solid phases can be controlled. In particular, the amount of hexagonal phase M ₂ X decreases after quenching. The C / N ratio should therefore be between 0.17 and 0.50. The lower limit of the ratio can be 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24 or 0.25. The upper limit may be 0.5, 0.48, 0.46, 0.45, 0.44, 0.42, 0.40, 0.38, 0.36 or 0.34. The upper limit can be freely combined with the lower limit. Preferred ranges are 0.20-0.46 and 0.22-0.45.

Chrome (13-30%)

When it is present in a dissolved amount of at least 11%, chromium leads to the formation of a passivating film on the surface of the steel. Chromium must be present in steel in an amount of 13 to 30% in order to give the steel a good ability to accept hardening and resistance to oxidation and corrosion. Preferably, chromium is present in an amount of more than 16% to ensure good pitting resistance. The lower limit is set in accordance with the intended use, and it can be 17%, 18%, 19%, 20%, 21% and 22%. However, chromium is a strong element forming ferrite and in order to avoid ferrite after quenching, its amount must be regulated. For practical reasons, the upper limit can be lowered to 26%, 24%, or even 22%. Preferred ranges include 16-26%, 18-24%, 19-21%, 20-22% and 21-23%.

Molybdenum (0.5-3.0%)

It is known that Mo has a very favorable effect on the ability to take quenching. It is also known to improve pitting resistance. The minimum content is 0.5% and can be set at 0.6%, 0.7%, 0.8% or 1.0%. Molybdenum is a strong carbide forming element as well as a strong ferrite forming element. The maximum molybdenum content is therefore 3.0%. Preferably, Mo is limited to 2.0%, 1.7% or even 1.5%.

Tungsten (≤1%)

In principle, molybdenum can be replaced with twice as much tungsten. However, tungsten is expensive and also difficult to process scrap metal. The maximum amount of tungsten is therefore limited to 1%, preferably 0.2%, and most preferably no additions are made.

Vanadium (2.0-5.0%)

Vanadium forms uniformly distributed primary deposited nitrocarbides of type M (N, C) in the steel matrix. In real steels, M is mainly vanadium, however, significant amounts of Cr and Mo may be present. Vanadium must therefore be present in an amount of 2-5%. The upper limit can be set at 4.8%, 4.6%, 4.4%, 4.2% or 4.0%. The lower limit may be 2.2%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8% and 2.9%. The upper and lower limits can be freely combined within the limits presented in paragraph 1 of the claims. The preferred range is 2-4%.

Niobium (≤2.0%)

Niobium is similar to vanadium in that it forms nitrocarbides of type M (N, C), and in principle it can be used to replace vanadium, but this requires a double amount of niobium compared to vanadium. Therefore, the maximum addition of Nb is 2.0%. The combined amount (V + Nb / 2) should be 2.0-5.0%. However, Nb leads to a more angular shape of M (N, C). The preferred maximum amount is therefore 0.5%. Preferably no niobium is added.

Silicon (≤1.0%)

Silicon is used for deoxidation. Si is present in steel in dissolved form. Si is a strong ferrite-forming element and therefore should be limited to ≤1.0%.

Manganese (0.2-2.0%)

Manganese contributes to improving the ability of steel to take quenching and, together with sulfur, manganese contributes to improving the machining ability by forming manganese sulfides. Manganese must therefore be present in a minimum content of 0.2%, preferably at least 0.3%. At high sulfur contents, manganese prevents the brittleness of steel at a red heat. The steel should contain a maximum of 2.0%, preferably a maximum of 1.0% Mn. Preferred ranges are 0.2-0.5%, 0.2-0.4%, 0.3-0.5% and 0.3-0.4%.

Nickel (≤5.0%)

Nickel is a possible element and may be present in an amount of up to 5%. It gives steel a good ability to take hardening and ductility. Due to its high cost, the nickel content in steel should be limited as much as possible. Accordingly, the Ni content is limited to 1%, preferably 0.25%.

Copper (≤3.0%)

C is a possible element. It can contribute to an increase in the hardness and corrosion resistance of steel. If used, the preferred range is 0.02-2% and the most preferred range is 0.04-1.6%. However, it is not possible to extract copper from steel after it has been added. This makes scrap scrap much more difficult. For this reason, copper is usually not deliberately added.

Cobalt (≤10.0%)

Co is a possible element. It contributes to an increase in the hardness of martensite. The maximum amount is 10% and, if added, the effective amount is from about 4 to 6%. However, for practical reasons, such as the processing of scrap metal, do not intentionally add Co. The preferred maximum content is 0.2%.

Sulfur (≤0.5%)

S contributes to improving the machining ability of steel. At higher sulfur contents, there is a risk of steel brittleness at a red heat. In addition, a high sulfur content can adversely affect the fatigue properties of steel. Steel should therefore contain ≤0.5%, preferably ≤0.035% sulfur.

Be, Bi, Se, Mg and REM (rare earth metals)

These elements can be added to the steel in the declared amounts in order to further improve the machinability, hot workability and / or weldability.

Boron (≤0.01%)

Boron can be used to further increase the hardness of steel. Its amount is limited to 0.01%, preferably ≤0.004%.

Ti, Zr, Al and Ta

These elements are carbide-forming and may be present in the alloy at the stated intervals to change the composition of the solid phases. However, usually none of these elements are added.

Solid phases

The total solids content of MX, M ₂ X, M ₂₃ C ₆ and M ₇ C ₃ must not exceed 50 vol. %, where M is one or more of the above metals, in particular V, Mo and / or Cr, and X represents C, N and / or B, and where the content of these solid phases satisfies the following requirements (in vol.%) :

MX 3-25 preferably 5-20 M ₂ X ≤10 preferably ≤5 M ₂₃ C ₆ + M ₇ C ₃ ≤10 preferably ≤5

More preferably, the MX content is 5-15 vol.%, The content of M ₂ X is <3 vol. % and the content of M ₂₃ C ₆ + M ₇ C ₃ is ≤3 vol. % Most preferably, the steel does not contain component M ₇ C ₃ .

Estc

The pitting resistance equivalent (PSTC) is often used to quantify pitting resistance of stainless steels. A higher value indicates a higher resistance to pitting corrosion. For martensitic stainless steels with a high nitrogen content, the following expression can be used

и

являются вычисленными равновеснымисодержаниями растворенными в матрице при температуре аустенизации (Т_А), и где содержание растворенного в аустените хрома составляет по меньшей мере 13%. Растворенные содержания можно вычислить с помощью программного обеспечения Thermo-Calc для действительной температуры аустенизации (Т_А) и/или измерить в стали после быстрого охлаждения.Where

and

are the calculated equilibrium contents dissolved in the matrix at the austenitization temperature (T _A ), and where the content of chromium dissolved in austenite is at least 13%. Dissolved contents can be calculated using Thermo-Calc software for the actual austenitization temperature (T _A ) and / or measured in steel after rapid cooling.

The austenitization temperature (T _A ) is in the range of 950-1200 ° C, usually 1080-1150 ° C.

From the above reasoning it follows that the composition of austenite at austenitizing temperature can have a significant effect on the resistance of pitting to steel. The lowest limit for the calculated ESTC value may be 25, 26, 27, 28, 29, 30, 31, 32, or 33.

High nitrogen stainless steels are based on the replacement of carbon with nitrogen. By replacing most of the carbon with nitrogen, one can replace chromium-rich carbides of the M ₇ C ₃ and M ₂₃ C _{6 type with} very stable MN type nitride solid particles. The amount of Cr, Mo, and N in the solid solution at the quenching temperature therefore increases very much because less chromium binds in the solid phase and because carbides of the type M ₇ C ₃ and M ₂₃ C ₆ do not have any solubility for nitrogen. As a result, more chromium remains in the solid solution and hardens a thin chromium-rich passivating surface film, which leads to increased resistance to general corrosion and pitting. Accordingly, pitting resistance should be expected to decrease if carbon replaces part of the nitrogen. High-nitrogen stainless steels known in the art therefore have a low carbon content.

However, the inventors of the present invention unexpectedly discovered that corrosion resistance can be increased by increasing the carbon content to about 0.3%, as will be discussed in connection with the examples.

Steel production

Tool steel having the declared chemical composition can be obtained by conventional gas spraying, followed by nitriding of the powder before the ISU. The nitrogen content in steel after gas spraying is usually less than 0.2%. The remaining nitrogen is then added during nitriding of the powder. After hardening, steel can be used in the form that is implemented by the ISU, or to give the desired shape to the steel. Steel is usually hardened and tempered before use. Austenization can be performed by annealing at a temperature (T _A ) of austenization in the range of 950-1200 ° C, usually 1080-1150 ° C. A common treatment is annealing at 1080 ° C for 30 minutes. Steel can be hardened by rapid cooling in a vacuum oven by deep cooling in liquid nitrogen and then subjected to tempering at 200 ° C 2 times for 2 hours (2 × 2 hours).

Example 1

In this example, the steel of the invention is compared with steel having a lower carbon content and a different ratio of carbon to nitrogen. Both steels were obtained using powder metallurgy.

The basic compositions for steels were melted and gas sprayed. Then, the obtained powders were nitrided to introduce the required amount of nitrogen into the powders. The nitrogen content was increased from about 0.1% to the corresponding content.

After nitriding, the powders were transformed into isotropic solid steel bodies by conventional hot isostatic pressing (HIP) at 1100 ° C for 2 hours. The applied pressure was 100 MPa.

Thus obtained steel had the following compositions (in wt.%)

the rest was iron and impurities.

The steel was austenized at 1080 ° C for 30 minutes and quenched by rapid cooling using deep cooling in liquid nitrogen in a vacuum oven, after which it was tempered at 200 ° C 2 times for 2 hours (2 × 2 hours). The steel of the invention had a hardness of 60 HRC (Rockwell hardness on a scale of C) and comparative steel had a hardness of 58 HRC.

The microstructure of the alloy consisted of tempered martensite and solid phases. Two distinct solid phases were identified in the microstructure of both steels: MX and M ₂ X.

In comparative steel, the hexagonal M ₂ X was the main phase and the face-centered cubic MX phase was in the minority. However, in the steel of the invention, MX was the main phase and M ₂ X was a minority phase.

The susceptibility of pitting materials was experimentally investigated using an anodic polarization curve. An electrochemical cell with a saturated Ag / AgCl reference electrode and a carbon cellular counter electrode was used for cyclic polarization measurements. For a sample crushed to 500 mesh, the open-circuit potential (RPC) was first recorded with a 0.1 M NaCl solution to ensure that a stable potential was achieved. Then, cyclic polarization measurements were performed with a scanning speed of 10 mV / min. The initial potential was -0.2 V relative to the PRC and the final potential was set at the level of the PRC. By choosing the software setting, the potential scan upward was automatically reversed when the anode current density reached 0.1 mA / cm ² .

In FIG. 1, a schematic curve of the anodic polarization and information that can be obtained from this curve are described. Direct scanning provides information on the onset of pitting and reverse scanning provides information on the behavior of alloy passivation. Еb represents the value of the potential for pitting corrosion, above which new corrosion ulcers arise and existing corrosion ulcers spread. As the potential decreases during reverse scanning, there is a decrease in current density. The alloy is repassivated when the reverse scan crosses the forward scan. Ep is the potential for repassivation or protective potential, that is, the potential below which no pitting occurs. The difference between Еb and ЕР characterizes susceptibility to pitting and contact corrosion. The greater the difference, the greater the exposure.

Table 1 shows that the steel according to the invention with a higher carbon content is less prone to local corrosion, and also that the steel according to the invention is also more easily passivated than comparative steel. Accordingly, the steel of the invention is much less sensitive to pitting and contact corrosion.

These results were completely unexpected, because the steel according to the invention had lower Cr, Mo and N contents than comparative steel. The reasons for this are currently not well understood. However, the authors of the present invention suggest that these differences may be related to the type and amount of solid phases remaining in the steel after austenization and rapid cooling.

Example 2

The effect of the relative amounts of carbon and nitrogen on the formation of various solid phases in the steel was calculated in Thermo-Calc for steels having different contents of C and N and the following basic composition in mass. %: Cr 19.8, Mo 2.5, V 2.75, Si 0.3, Mn 0.3, the rest Fe.

Table 2. The results of example 2 at 1080 ° C.

и

обозначают вычисленные растворенные содержания данных элементов в матрице при 1080°С. ЭСТК вычисляют из растворенных содержаний компонентов.The concentration of elements in wt.%. Solid phases in vol. %

and

denote the calculated dissolved contents of these elements in the matrix at 1080 ° C. ESTC is calculated from the dissolved contents of the components.

In FIG. 2 shows the amount of solid phases as a function of the C / N ratio, and it can be seen that the amount of M ₂ X decreases rapidly with increasing C / N ratio. However, M ₂₃ C ₆ begins to form already at a C / N ratio of approximately 0.25.

In FIG. 3 shows the calculated values of ESTC depending on the C / N ratio, and it can be seen that the highest values are obtained for the steels according to the invention.

Example 3

The effect of the relative amounts of carbon and nitrogen on the formation of various solid phases in the steel was calculated in Thermo-Calc for steels having different contents of C and N and the following basic composition, in mass. %: Cr 18.2, Mo 1.04, V 3.47, Si 0.3, Mn 0.3, the rest Fe.

и

обозначают вычисленные растворенные содержания данных элементов в матрице при 108°С. ЭСТК вычисляют из растворенных содержаний компонентов.Table 3. The results of example 3 at 1080 ° C. The concentration of elements in the mass. % Solid phases in vol. %

and

denote the calculated dissolved contents of these elements in the matrix at 108 ° C. ESTC is calculated from the dissolved contents of the components.

In FIG. 4 shows the amount of solid phases depending on the C / N ratio, and it can be seen that the amount of M ₂ X decreases very rapidly with increasing C / N ratio. You can also see that M ₂₃ C ₆ begins to form already at a C / N ratio of approximately 0.3.

In FIG. 5 shows the calculated ESTC values as a function of the C / N ratio, and again it can be seen that the highest values are obtained for the steels of the invention.

These results confirm that an appropriate balance of carbon and nitrogen is an essential feature of the present invention. A carefully controlled increase in carbon can be achieved without problems with carbides of the type M ₂₃ C ₆ and M ₇ Cz in steel. These results also show that if the carbon and nitrogen contents are controlled as defined in the claims, then the amount of hexagonal phase M ₂ X decreases after quenching. This phase is mainly called Cr ₂ N, however, it may also include a significant amount of Mo. The decrease in the amount of M ₂ X is the result of dissolution during austenization. Although part of these elements under certain conditions can be found in the increased proportion of MX (Fig. 2), it should be clear that the dissolution of M ₂ X leads to an increased amount of Cr, Mo and N dissolved in the matrix with a corresponding increase in ECC to a certain limit. After that, the value of ECC decreases as a result of the formation of M ₂₃ C ₆ , because this phase is rich in Cr and Mo.

Another mechanism that can contribute to the improved corrosion resistance described in Table 1 and in FIG. 1 may consist in the fact that the boundary regions surrounding the solid phase M ₂ X may be depleted in Cr and Mo due to the formation of rich Cr and Mo M ₂ X.

Another possible mechanism that can influence corrosion resistance is that an increased carbon content in the MX solid phase can lead to lower solubility of Cr in this phase. This should result in a lower MX volume fraction and greater retention of chromium in the solid solution, which helps to improve corrosion resistance.

Accordingly, the present invention provides for the provision of powder metallurgy (PM) nitrogen-alloyed cold work tool steels having improved corrosion resistance combined with high hardness.

Industrial applicability

The cold working tool steel of the present invention is particularly suitable in applications requiring good wear resistance combined with high pitting resistance.

Claims (22)

1. Steel made by powder metallurgy, consisting of, wt.%: FROM 0.3-0.8 N 1.0-2.2 Si ≤1.0 Mn 0.2-2.0 Cr 13-30 Mo 0.5-3.0 W ≤1 V 2.0-5.0 Nb ≤2.0 (Ti + Zr + Al) ≤7.0 That ≤0.5 With ≤10.0 Ni ≤5.0 Cu ≤3.0 Sn ≤0.3 AT ≤0.01 Be ≤0.2 Bi ≤0.3 Se ≤0.3 Those ≤0.3 Mg ≤0.01 P3M ≤0.2 Ca ≤0.05 S ≤0.5 iron and impurities rest, under the following conditions: (C + N) 1.3-2.2; C / N 0.17-0.50; (Mo + W / 2) - 0.5-3.0; (V + Nb / 2) - 2.0-5.0. 2. Steel according to claim 1, in which the upper limit of the V content is limited to 4.8%, 4.6%, 4.4%, 4.2% or 4.0%. 3. Steel according to claim 1, in which for the content of the components at least one of the following conditions is met, wt.%: FROM 0.3-0.6 N 1.1-1.8 (C + N) 1.7-2.1 C / n 0.20-0.46 Cr 15-30 Mo 0.7-2.5 V 2.5-4.5 Nb ≤0.5. 4. Steel according to claim 1, in which at least one of the following conditions is met for the content of components, wt.%: FROM 0.35-0.45 N 1.3-1.7 (C + N) 1.8-2.0 C / n 0.22-0.45 Cr 16-28 Mo 0.8-2.0 V 2.5-3.8 With 4.0-6.0 Nb ≤0.1 Cu 0.02-2.0. 5. Steel according to claim 1, in which for the content of the components at least one of the following conditions is met, wt.%: Cr 18-26 Mo 0.8-1.5 Se <0.05 Cu 0.05-1.5 With ≤0.2 W ≤0.2 Ti ≤0.1 Nb ≤0.05 P3M ≤0.05 AT ≤0.004. 6. Steel according to claim 1, in which the microstructure consists of tempered martensite and solid phases comprising one or more phases selected from MX, M ₂ X, M ₂₃ C ₆ and M ₇ C ₃ , wherein the steel has a hardness of 58- 64 HRC, preferably 60-62 HRC. 7. Steel according to claim 6, in which the solid phases MX, M ₂ X, M ₂₃ C ₆ and M ₇ C ₃ are contained in the following amount, vol.%: MX 5-25, preferably 5-20, more preferably 5-15 M ₂ X ≤10, preferably ≤5, more preferably ≤1 M ₂₃ C ₆ + M ₇ C ₃ ≤10, preferably ≤5, more preferably ≤1, where M represents one or more elements of V, Mo and Cr, and X represents one or more elements of C, N or B. 8. Steel according to claim 1, which at an austenitizing temperature, T _{A of} 1080 ° C, has a calculated ECC ≥18, where ECC = Cr + 3.3Mo + 30N, while Cr, Mo and N are the calculated equilibrium contents of the elements dissolved in the matrix at T _a, a content of dissolved chromium in the austenite is at least 13%. 9. The steel according to claim 1, which at an austenitization temperature, T _{A of} 1080 ° C, has a calculated ECC ≥20, where ECC = Cr + 3.3Mo + 30N, while Cr, Mo and N are the calculated equilibrium contents of the elements dissolved in the matrix at T _A , and the content of chromium dissolved in austenite is at least 16%. 10. The steel according to claim 1, which at an austenitization temperature, T _{A of} 1080 ° C, has a calculated ECC ≥22, where ECC = Cr + 3.3Mo + 30N, while Cr, Mo and N are the calculated equilibrium contents of the elements dissolved in the matrix at T _a. 11. Steel according to any one of paragraphs. 1-10, which at an austenitization temperature, T _{A of} 1080 ° C, has a calculated ECC ≥25, where ECC = Cr + 3.3Mo + 30N, while Cr, Mo and N are the calculated equilibrium contents of the elements dissolved in the matrix with TA. 12. A method of producing steel by powder metallurgy, including spraying a steel alloy having a chemical composition corresponding to the chemical composition of the alloy according to any one of paragraphs. 1-11, with the exception of nitrogen, which is introduced by treating the powder with nitriding to a content corresponding to the nitrogen content in the indicated chemical composition of the alloy, loading the treated powder into a capsule, conducting the ISU capsule with the formation of steel and performing its quenching and tempering. 13. The method of producing steel according to claim 12, in which hardening is carried out at 950-1200 ° C, preferably at 1080-1150 ° C for 30 minutes with deep cooling in liquid nitrogen, and tempering is carried out twice at 180-250 ° C, preferably at 200 ± 10 ° C for 2 hours. 14. The method of producing steel according to claim 12, in which hardening is carried out at 950-1200 ° C, preferably at 1080-1150 ° C for 30 minutes with deep cooling in liquid nitrogen, and tempering is carried out twice at 450-550 ° C, preferably at 500 ± 10 ° C for 2 hours.

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