RU2336316C2 - Round bar out of boron containing steel for cold die forging - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to production of bar. To facilitate rational conditions of cold die forging of complex profile high tensile mounting units a bar is produced out of steel containing wt %: C 0.06-0.35, Mn 0.60-1.40, Si 0.001-0.37, S 0.005-0.020, Cr 0.001-0.35, V 0.001-0.05, Nb 0.005-0.02, Ti 0.01-0.04, B 0.0005-0.0050, Al 0.02-0.06, N 0.005-0.015, As 0.0001-0.03, Sn 0.0001-0.02, Pb 0.0001-0.01, Zn 0.0001-0.005, iron and impurities, at ratios: (As+Sn+Pb+5Zn)≤0.07; [3000×(Ti/24-N/7)+2.2]≥0. As impurities steel contains: phosphorus not more, than 0.25, copper not more, than 0.15, oxygen not more, than 0.004, molybdenum not more, than 0.10, nickel not more, than 0.10. The bar has metallic inclusions of sulphides, oxides, silicates, and nitrides not more, than 3 points in each kind, it has a ferrite-pearlite structure, the dimension of the actual grain is 5-10 points, the diameter is from 10 to 25 mm, a decarbonised layer is not less, than 1.5% from the bar diameter, the value of cold yielding is not less, than 1/3 of the height, tensile strength is not more, than 580 N/mm², yield point is not more, than 540 N/mm², specific elongation is not less, than 18%, contraction ratio is not less, than 55%, the cutoff diameter at oil quenching is not less, than 15 mm.

EFFECT: production of round bar with upgraded level of consumer characteristics.

9 cl, 7 ex

Description

The invention relates to the field of metallurgy, in particular to the production of long products, round from boron-containing steel for cold forming for high-strength fasteners of particularly complex shape.

Known long products with a diameter of 10-25 mm from boron-containing steel for cold forming, having non-metallic inclusions for sulfides, oxides, silicates and nitrides not exceeding 3 points for each type of inclusions, the actual grain size is 5-10 points, decarburized layer is not more than 1 , 5% of the rolled diameter, cold draft not less than 1/3 of the height, temporary tensile strength not more than 580 N / mm ² , elongation not less than 18%, relative narrowing not less than 55% (RU 2249625 C1, C21D 8/06 April 10, 2005).

Known long products with a diameter of 10-25 mm from boron-containing steel for cold forming, having non-metallic inclusions for sulfides, oxides, silicates and nitrides not exceeding 3 points for each type of inclusions, the actual grain size is 5-10 points, decarburized layer is not more than 1 , 5% of rolled diameter, cold draft not less than 1/3 of the height, temporary tensile strength not more than 580 N / mm ² , elongation not less than 18%, relative narrowing not less than 55% (RU 2249626 C1, C21D 8/06 April 10, 2005).

The objective of the invention is to provide rational conditions for the cold forging of complex-profile high-strength fasteners while ensuring uniform mechanical properties along the rolled section and increased hardenability characteristics of steel.

The most important requirement for long products, round, made of boron-containing steel for cold forging of high-strength fasteners of particularly complex shape, is, on the one hand, high technological ductility and low coefficient of strain hardening in the delivery state and, on the other hand, the ability to provide the specified level of consumer properties after the final hardening.

The task is achieved in that long products with a diameter of 10-25 mm from medium-carbon boron-containing steel for cold forming are obtained from steel containing the following ratio of components, wt.%:

carbon 0.06-0.35 manganese 0.60-1.40 silicon 0.001-0.37 sulfur 0.005-0.020 chromium 0.001-0.35 vanadium 0.001-0.05 niobium 0.005-0.02 titanium 0.01-0.04 boron 0.0005-0.0050 aluminum 0.02-0.06 nitrogen 0.005-0.015 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities rest,

when the relations are satisfied: (As + Sn + Pb + 5 × Zn) ≤0.07;

rolled metal has a uniform ferrite-pearlite structure, the actual grain size is 5-10 points, the maximum score of non-metallic and inclusions for sulfides, oxides, silicates and nitrides does not exceed 3 points for each type of inclusions, decarburized layer is not more than 1.5% of the rolled diameter, the value of cold precipitation is not less than 1/3 of the height, mechanical properties: temporary tensile strength not more than 580 N / mm ² , yield strength not more than 540 N / mm ² , elongation not less than 18%, relative narrowing not less than 55%, critical diameter when hardening in oil not less than 15 mm.

As impurities, the steel additionally contains, in May%: phosphorus no more than 0.025; copper no more than 0.15; oxygen no more than 0.004; molybdenum not more than 0.10; nickel no more than 0.10.

When the carbon content in the steel is 0.06-0.10%; chromium 0.001-0.10%; Manganese 0.60-0.90% rolling has mechanical properties: temporary tensile strength not more than 420 N / mm ² , yield strength not more than 370 N / mm ² , elongation not less than 34%, relative narrowing not less than 68%, critical diameter when quenching in oil not less than 15 mm.

When the carbon content in the steel is 0.08-0.14%; chromium 0.05-0.20%; Manganese 0.90-1.30%, rolling has mechanical properties; temporary tensile strength not more than 470 N / mm ² , yield strength not more than 410 N / mm ² , elongation not less than 33%, relative narrowing not less than 66%, critical diameter when quenching in oil not less than 15 mm.

When the carbon content in the steel is 0.14-0.17%; chromium 0.05-0.20%; Manganese 0.90-1.30% rolling has mechanical properties: temporary tensile strength not more than 490 N / mm ² , yield strength not more than 440 N / mm ² , elongation not less than 32%, relative narrowing not less than 64%, critical diameter when quenching in oil not less than 18 mm.

When the carbon content in the steel is 0.17-0.23%, chromium 0.05-0.30%, manganese 0.90-1.30%, the rolled metal has mechanical properties: temporary tensile strength not more than 510 N / mm ² , limit yield strength not more than 480 N / mm ² , elongation not less than 30%, relative narrowing not less than 62%, critical diameter when quenching in oil not less than 23 mm.

With a carbon content of 0.20-0.25%, chromium 0.10-0.30%; Manganese 0.90-1.30% rolled has mechanical properties: temporary tensile strength not more than 540 N / mm ² , yield strength not more than 500 N / mm ² , elongation not less than 28%, relative narrowing not less than 60%. The critical diameter when quenching in oil is at least 27 mm.

When the carbon content of steel is 0.27-0.31%, chromium 0.10-0.30%, manganese 0.90-1.30%, rolled metal has mechanical properties: temporary tensile strength not more than 580 N / mm ² , limit yield no more than 540 N / mm ² , elongation of at least 20%, relative narrowing of at least 55%. The critical diameter when quenching in oil is at least 35 mm.

When the carbon content in the steel is 0.30-0.34%, chromium 0.10-0.30%, manganese 0.90-1.30%, rolled metal has mechanical properties: temporary tensile strength not more than 580 N / mm ² , limit yield no more than 540 N / mm ² , elongation not less than 18%, relative narrowing not less than 55%, critical diameter when quenching in oil not less than 45 mm.

The given combinations of alloying elements (item 1) make it possible to obtain a finely dispersed ferrite-pearlite structure, the optimal content and morphology of nonmetallic inclusions, a homogeneous macrostructure, and a favorable combination of strength, hardenability, and ductility characteristics.

Carbon and carbonitride-forming elements are introduced into the composition of this steel in order to provide a finely dispersed granular structure, which will increase both its strength level and provide a given level of ductility. In this case, niobium controls processes in the austenitic region (determines the tendency to growth of austenite grain, stabilizes the structure during thermomechanical processing, increases the recrystallization temperature and, as a result, affects the nature of the γ-α transformation), while the effect of vanadium is manifested at temperatures below And ₁ , since it is in this region that the interval of intense release of vanadium carbonitride is located. Vanadium also contributes to the hardening of steel during thermal improvement. The upper limit of carbon content (0.35%), vanadium (0.05%) and niobium (0.02%) is due to the need to ensure the required level of ductility of steel, and the lower (respectively 0.06%, 0.001% and 0.005%) - providing the required level of strength of this steel.

Manganese and chromium are used, on the one hand, as solid solution hardeners, and on the other hand, as elements that increase the stability of supercooled austenite in steel. The upper level of manganese 1.40%, chromium 0.35% is determined by the need to ensure the required level of steel viscosity, and the lower 0.60% and 0.001%, respectively, by the need to provide the required level of strength and hardenability and heat resistance of this steel.

Silicon refers to ferrite-forming elements. The lower silicon limit of 0.001% is due to the need to provide a given level of elasticity for steel. A silicon content above 0.37% will adversely affect the viscosity and ductility characteristics of steel.

Boron contributes to a sharp increase in the hardenability of steel. Moreover, the upper limit of the boron content is determined by considerations of ductility of steel, and the lower - the need to ensure the required level of hardenability.

Aluminum and titanium are used as deoxidizers and protect boron from binding to nitrides, which contributes to a sharp increase in the hardenability of steel. So, the lower level of the content of these elements (0.02 and 0.01, respectively for aluminum and titanium) is determined by the requirement to ensure hardenability of steel, and the upper level (0.06 and 0.04) is determined by the requirement to ensure a given level of ductility of steel.

Nitrogen promotes the formation of nitrides in steel. The upper limit of the nitrogen content of 0.010% is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit of 0.005% is due to issues of manufacturability.

Sulfur determines the level of ductility and machinability by cutting steel. The upper limit (0.020%) is due to the need to obtain a given level of ductility and toughness of steel, and the lower limit (0.005%) is due to issues of manufacturability.

Arsenic, tin, lead and zinc are colored impurities that determine the overall level of ductility of steel and its tendency to manifest reversible temper brittleness during subsequent heat treatment of finished products from the pipe billet under consideration. The lower limit for arsenic, tin, lead and zinc (0.0001% for each element, respectively) is due to the technology of steel production, and the upper limit (0.03%, 0.02%, 0.01% and 0.005%, respectively) determines an increased tendency steel to reversible temper brittleness.

To ensure complete binding of nitrogen to nitrides such as TiN and A1N as a result of reactions:

[Ti] + [N] = TiN

[Al] + [N] -AlN

,the following ratio of elements is required:

,

otherwise, boron is not protected from binding to nitrides and the hardenability characteristics of steel are sharply reduced.

The ratio (As + Sn + Pb + 5 × Zn) ≤0.07 determines the reduced tendency of steel to manifest reversible temper brittleness.

The analysis of patent and scientific and technical information did not reveal solutions having a similar set of features that would achieve a similar effect - providing an increased level of consumer properties, while ensuring a favorable ratio of strength, ductility and viscosity, a minimum level of anisotropy of mechanical properties, low content of non-metallic inclusions, homogeneous macro and microstructure rolled.

Examples of the invention, not excluding others in the scope of the claims. Smelting of the investigated steel with various chemical compositions, wt.%:

Example 1: carbon — 0.08, manganese — 0.65, silicon — 0.05, chromium — 0.09, niobium — 0.01; vanadium - 0.02; sulfur — 0.008, nitrogen — 0.007, titanium — 0.025, aluminum — 0.041, boron — 0.0031, arsenic — 0.007, tin — 0.009, lead — 0.006, zinc — 0.002;

Example 2: carbon — 0.12, manganese — 1.25, silicon — 0.10, chromium — 0.19, niobium — 0.01; vanadium - 0.01; sulfur — 0.009, nitrogen — 0.008, titanium — 0.029, aluminum — 0.045, boron — 0.0033, arsenic — 0.008, tin — 0.009, lead — 0.004, zinc — 0.001;

Example 3: carbon — 0.15, manganese — 1.21, silicon — 0.14, chromium — 0.21, niobium — 0.01; vanadium - 0.02; sulfur — 0.009, nitrogen — 0.007, titanium — 0.029, aluminum — 0.045, boron — 0.0031, arsenic — 0.007, tin — 0.007, lead — 0.004, zinc — 0.001;

Example 4: carbon — 0.19, manganese — 1.28, silicon — 0.19, chromium — 0.20, niobium — 0.01; vanadium - 0.03; sulfur — 0.008, nitrogen — 0.006, titanium — 0.021, aluminum — 0.040, boron — 0.0039, arsenic — 0.008, tin — 0.006, lead — 0.010, zinc — 0.002;

Example 5: carbon 0.24, manganese 1.26, silicon 0.17, chromium 0.25, niobium 0.01; vanadium - 0.02; sulfur — 0.008, nitrogen — 0.007, titanium — 0.029, aluminum — 0.046, boron — 0.0025, arsenic — 0.009, tin — 0.009, lead — 0.011, zinc — 0.002;

Example 6: carbon 0.29, manganese 1.22, silicon 0.19, chromium 0.25, niobium 0.01; vanadium - 0.02; sulfur — 0.009, nitrogen — 0.006, titanium — 0.024, aluminum — 0.034, boron — 0.0029, arsenic — 0.007, tin — 0.007, lead — 0.008, zinc — 0.001;

Example 7: carbon — 0.34, manganese — 1.28, silicon — 0.22, chromium — 0.20, niobium — 0.01; vanadium - 0.02; sulfur is 0.008, nitrogen is 0.007, titanium is 0.026, aluminum is 0.031, boron is 0.0033, arsenic is 0.008, tin is 0.007, lead is 0.009, zinc is 0.002;) for each of the compounds produced in 150-ton arc steelmaking furnaces (chipboard) using 100% metallized pellets in the charge, which ensures that the mass fraction of nitrogen before being released from the chipboard is not more than 0.003%, as well as a low content of color impurities. The preliminary alloying of the metal with manganese and silicon is carried out in the ladle upon discharge from the particleboard. After the release, the metal was purged with argon through the bottom purge unit, during which the steel was deoxidized by aluminum. After that, the metal enters the integrated steel processing unit (AKOS), where it is possible to heat the metal to the required temperature, purge it with argon through the bottom blowing unit, dosed the necessary ferroalloys and treat the steel with flux-cored wire with various fillers. At AKOS, refining slag is imposed with an additive of lime and fluorspar, slag is deoxidized with granulated aluminum, the metal is alloyed with aluminum to a content of 0.050%, the metal is refined according to the manganese content, and it is heated to a temperature that ensures further processing. After processing at AKOS, the metal is subjected to vacuum treatment at a batch vacuum. During evacuation, a final adjustment of the chemical composition is made. After evacuation, the metal is treated with silicocalcium and transferred to casting. The casting is carried out on radial four-strand UNRS in an ingot 300 × 360 mm in size with a drawing speed of 0.6 ÷ 0.7 m / min, with metal protection from oxidation by using cover slag mixtures in the intermediate ladle and mold, protective tubes, immersion glasses and argon feed. It also provides a low nitrogen and oxygen content and metal purity from non-metallic inclusions. After casting and cutting to a measured length, the continuously cast billets obtained were cooled in controlled cooling furnaces. Hot rolling of long products starts at a temperature of 900-950 ° C and ends at a temperature of 740-850 ° C, with a deformation in the last passes of at least 20%. Heat treatment: quenching in oil.

As a result, long products of ⌀16 mm were obtained from steels of various compositions and ratios:

Example 1: structure of ferrite and pseudospheridized perlite, real grain score - 7. Macrostructure: central porosity - 2 points, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 2 points, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 1.0 point, point oxides - 0.5 points, line oxides - 1.0 point, brittle silicates - 0.5 points, plastic silicates - 0.5 points, undeformed silicates - 1.0 point. The depth of the decarburized layer is a transition zone of 0.09 mm. The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 15 mm. Tensile strength 380 N / mm ² , yield strength 310 N / mm ² , elongation of 35%, relative narrowing of 72%;

As + Sn + Pb + 5 × Zn = 0.032;

Example 2: structure of ferrite and pseudospheridized perlite, real grain score - 8. Macrostructure: central porosity - 1.5 points, point heterogeneity - 1.5 points, segregation square - 1 point, shrink segregation - 1.5 points, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 0.0 points, point oxides - 0.5 points, line oxides - 0.5 points, brittle silicates - 1.0 points, plastic silicates - 0.5 points, undeformed silicates - 1.0 points. The depth of the decarburized layer is a transition zone of 0.07 mm. The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 16 mm. Tensile strength 411 N / mm ² , yield strength 350 N / mm ² , elongation 34.5%, relative narrowing 70%;

As + Sn + Pb + 5 × Zn = 0.026;

Example 3: structure of ferrite and pseudospheridized perlite, real grain score - 7. Macrostructure: central porosity - 1.0 points, point heterogeneity - 1.0 points, segregation square - 1.5 points, shrink segregation - 1.0 points, segregation strips - 1.0 points. Non-metallic inclusions: point sulfides - 1.5 points, point oxides - 0.5 points, line oxides - 0.5 points, brittle silicates - 1.5 points, plastic silicates - 0.5 points, undeformed silicates - 1.5 points. The depth of the decarburized layer is the transition zone of 0.08 mm The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 23 mm. Tensile strength 464 N / mm ² , yield strength 392 N / mm ² , elongation 34%, relative narrowing 68%;

As + Sn + Pb + 5 × Zn = 0.025;

Example 4: the structure of ferrite and pseudospheridized perlite, the actual grain score is 8. Macrostructure: central porosity - 0.5 points, point heterogeneity - 2 points, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 0.5 points. Non-metallic inclusions: point sulfides - 2 points, point oxides - 1 point, line oxides - 1 point, brittle silicates - 1 point, plastic silicates - 0.5 points, non-deforming silicates - 1 point. The depth of the decarburized layer is a transition zone of 0.03 mm. The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 26 mm. Tensile strength 507 N / mm ² , yield strength 443 N / mm ² , elongation 31%, relative narrowing 67%;

As + Sn + Pb + 5 × Zn-0.034;

Example 5: structure of ferrite and pseudospheridized perlite, real grain score - 7. Macrostructure: central porosity - 0.5 points, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 2 points, point oxides - 1 point, line oxides - 1 point, brittle silicates - 2 points, plastic silicates - 2 points, non-deforming silicates - 1 point. The depth of the decarburized layer is the transition zone of 0.08 mm The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 33 mm. Tensile strength 533 N / mm ² , yield strength 484 N / mm ² , elongation 27%, relative narrowing 64%;

As + Sn + Pb + 5 × Zn-0.039;

Example 6: structure of ferrite and pseudospheridized perlite, real grain score - 7. Macrostructure: central porosity - 1 point, point heterogeneity - 1 point, segregation square - 2 points, shrink segregation - 2 points, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 1 point, point oxides - 1 point, line oxides - 1 point, brittle silicates - 1 point, plastic silicates - 1 point, non-deforming silicates - 1 point. The depth of the decarburized layer is a transition zone of 0.05 mm. The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 37 mm. Tensile strength 565 N / mm ² , yield strength 511 N / mm ² , elongation of 23%, relative narrowing of 63%;

As + Sn + Pb + 5 × Zn = 0.027;

Example 7: structure of ferrite and lamellar perlite, real grain score - 7. Macrostructure: central porosity - 0.5 points, point heterogeneity - 1 point, segregation square - 1 point, shrink segregation - 1 point, segregation strips - 1 point. Non-metallic inclusions: point sulfides - 2 points, point oxides - 1 point, line oxides - 1 point, brittle silicates - 2 points, plastic silicates - 2 points, non-deforming silicates - 1 point. The depth of the decarburized layer is a transition zone of 0.09 mm. The amount of cold precipitation is 1/4 of the height. The critical diameter when quenching in oil is 42 mm. Tensile strength 575 N / mm ² , yield strength 534 N / mm ² , elongation of 19%, relative narrowing of 60%;

As + Sn + Pb + 5 × Zn = 0.037;

The introduction of the proposed product - long products, round, from high-hardenability boron-containing steel provides directly in the stream of the mill (without additional spheroidizing annealing) the structure of long products, guaranteeing rational conditions for cold forging of complex profile high-strength fasteners.

Claims (9)

1. High-quality round steel with a diameter of 10-25 mm from boron-containing steel for cold forming, obtained from steel containing the following ratio of components, wt.%: carbon 0.06-0.35 manganese 0.60-1.40 silicon 0.001-0.37 sulfur 0.005-0.020 chromium 0.001-0.35 vanadium 0.001-0.05 niobium 0.005-0.02 titanium 0.01-0.04 boron 0.0005-0.0050 aluminum 0.02-0.06 nitrogen 0.005-0.015 arsenic 0.0001-0.03 tin 0.0001-0.02 lead 0.0001-0.01 zinc 0.0001-0.005 iron and inevitable impurities rest, when fulfilling the relations: (As + Sn + Pb + 5 × Zn) ≤0.07;

Moreover, it has a homogeneous ferrite-pearlite structure, the actual grain size is 5-10 points, the maximum score of non-metallic inclusions for sulfides, oxides, silicates and nitrides does not exceed 3 points for each type, the decarburized layer is not more than 1.5% of the rolled diameter, the value of cold precipitation is not less than 1/3 of its height, temporary tensile strength not more than 580 N / mm ² , yield strength not more than 540 N / mm ² , elongation not less than 18%, relative narrowing not less than 55%, critical diameter during hardening in oil not less than 15 mm. 2. Long products according to claim 1, characterized in that the steel contains inevitable impurities, wt.%: Phosphorus not more than 0.025, copper not more than 0.15, oxygen not more than 0.004, molybdenum not more than 0.10, nickel not more than 0.10. 3. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.06-0.10, chromium 0.001-0.10, manganese 0.60-0.90, he has a temporary tensile strength of not more than 420 N / mm ² , yield strength not more than 370 N / mm ² , elongation not less than 34%, relative narrowing not less than 68%, critical diameter when quenching in oil not less than 15 mm. 4. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.08-0.14, chromium 0.05-0.20, manganese 0.90-1.30 It has a temporary tensile strength of not more than 470 N / mm ² , a yield strength of not more than 410 N / mm ² , an elongation of at least 33%, a relative narrowing of at least 66%, and a critical diameter of at least 15 mm when quenched in oil. 5. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.14-0.17, chromium 0.05-0.20, manganese 0.90-1.30 It has a temporary tensile strength of not more than 490 N / mm ² , a yield strength of not more than 440 N / mm ² , an elongation of at least 32%, a relative narrowing of at least 64%, and a critical diameter of at least 18 mm when quenched in oil. 6. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.17-0.23, chromium 0.05-0.30, manganese 0.90-1.30 It has a temporary tensile strength of not more than 510 N / mm ² , a yield strength of not more than 480 N / mm ² , an elongation of at least 30%, a relative narrowing of at least 62%, and a critical diameter of at least 23 mm when quenched in oil. 7. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.20-0.25, chromium 0.10-0.30, manganese 0.90-1.30 It has a temporary tensile strength of not more than 540 N / mm ² , a yield strength of not more than 500 N / mm ² , an elongation of at least 28%, a relative narrowing of at least 60%, and a critical diameter of at least 27 mm when quenched in oil. 8. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.27-0.31, chromium 0.10-0.30, manganese 0.90-1.30 , it has a temporary tensile strength of not more than 580 N / mm ² , yield strength of not more than 540 N / mm ² , elongation of not less than 20%, relative narrowing of not less than 55%, critical diameter when quenching in oil of not less than 35 mm. 9. Long products according to claim 1 or 2, characterized in that when the content in steel, wt.%: Carbon 0.30-0.34, chromium 0.10-0.30, manganese 0.90-1.30 , it has a temporary tensile strength of not more than 580 N / mm ² , yield strength of not more than 540 N / mm ² , elongation of not less than 18%, relative narrowing of not less than 55%, critical diameter when quenching in oil of not less than 45 mm.