RU2516213C1 - Method to produce metal product with specified structural condition - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: stock is made of steel containing wt %: C 0.05-0.18, Si 0.05-0.6, Mn 1.30-2.05, S not more than 0.015, P not more than 0.020, Cr 0.02-0.35, Ni 0.02-0.45, Cu 0.05-0.30, Ti not more than 0.050, Nb 0.010-0.100, V not more than 0.120, N not more than 0.012, Al not more than 0.050, Mo not more than 0.45, iron and unavoidable admixtures - balance. The stock is heated, and rough rolling is carried out under temperatures exceeding temperature of austenite recrystallisation, with a deformation-to-deformation pause, providing for required reduction of metal temperature, then finishing rolling is carried out, straightening and accelerated cooling of rolled metal, at the same time heating temperature for rolling T is set to ensure required solubility of carbides and nitrides of microalloying elements, and using the following dependence: t+280°C<T<t+310°C, where t=883-313.95C+37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu+110.18Ti+5.5Nb+76.74V-142.53N+71.45Al+23.67Mo, °C, and heat removal from the rolled metal surface in process of accelerated cooling is sent to ensure formation of the required volume share of bainite in the cross section of the metal product.

EFFECT: provision of required level of consumer properties of rolled metal.

3 cl, 4 ex

Description

The invention relates to the field of thermomechanical processing of metals and can be used for the manufacture of steel products with the required properties, due to their structural state.

A known method of manufacturing a thin high-strength hot-rolled sheet steel with a thickness of not more than 3.5 mm, which has high uniformity and good mechanical properties of steel sheets, as well as a method of hot rolling sheet steel (US 6364968 [1]). Steel contains C: 0.05-0.30 wt.%, Si: 0.03-1.0 wt.%, Mn: 1.5-3.5 wt.%, P: not more than 0.02 wt. %, S: not more than 0.005 wt.%, Al, not more than 0.150 wt.%, N: not more than 0.0200 wt.%, And one or two of Nb: 0.003-0.20 wt.% And Ti: 0.005 -0.20 wt.%. The workpiece is heated to a temperature not exceeding 1200 ° C. Hot rolling is carried out with a temperature of the end of the finishing stage not lower than 800 ° C. Finishing rolling is carried out at a temperature of 950-1050 ° C. The hot-rolled sheet is rapidly cooled for two seconds after the end of rolling, and then continuously cooled to a winding temperature with a cooling rate of 20-150 ° C / s. The hot-rolled sheet is wound at a temperature of 300-550 ° C, preferably above 400 ° C. The result is a sheet with a fine bainite structure, in which the average grain size is not more than 3.0 μm with a grain axis ratio of not more than 1.5, while the size of the major axis does not exceed 10 μm.

The disadvantage of this method is that it does not take into account the solubility of carbonitrides of alloying elements and does not give recommendations on the optimal heating regime of the workpieces.

A known method of producing cold-rolled and annealed steel sheet with a strength of more than 1200 MPa (RU 2437945 [2]). To implement the method, steel of the composition is melted, in wt.%: 0.10≤C≤0.25, 1≤Mn≤3, Al≥0.010, Si≤2,990, S≤0,015, P≥0,1, N≤0,008, wherein 1≤Si + Al≤3, if necessary, the composition contains: 0.05≤V≤0.15, B≤0.005, Mo≤0.25, Cr≤1.65, while Cr + (3 × Mo) ≥0.3, Ti≤0.040, while Ti / N≥4, iron and inevitable impurities obtained by smelting - the rest. The billet is cast from steel and heated to a temperature of more than 1150 ° C, hot rolled to produce a hot-rolled sheet, wound the sheet, clean the surface of the sheet, cold rolled the sheet with a compression ratio of 30 to 80%, the cold-rolled sheet is heated at a speed of V _c from 5 up to 15 ° C / s to a temperature T ₁ ranging from Ac ₃ to Ac ₃ + 20 ° C for a time t ₁ from 50 to 150 s, then this sheet is cooled with a speed V _R1 exceeding 40 ° C / s and at 100 ° C / s, to a temperature T ₂ which is in the range of M _s -30 ° C to M _s + 30 ° C, stand it at that temperature T ₂ for a time t ₂ 150 to 350 and cooling is carried out with V _R2 at less than 30 ° C / s to ambient temperature. The microstructure of the steel sheet contains from 15 to 90% bainite, and the rest is martensite and residual austenite.

The disadvantage of this method is the complexity of the implementation and high energy consumption to obtain a given structural state in the sheet, since it requires re-heating and multi-stage cooling.

Closest to the invention in its technical essence is a method for producing a thick-walled high-strength hot-rolled steel sheet, known from RU 2011107730 [3]. The method of obtaining a thick-walled high-strength hot-rolled steel sheet involves heating a steel material containing, based on wt.%:

0.02% -0.08% C,

0.01% -0.50% Si,

0.5% -1.8% Mn,

0.025% or less P,

0.005% or less than S,

0.005% -0.10% Al,

0.01% -0.10% Nb,

0.001% -0.05% Ti,

0.01% to 1.0% Cr

the rest is Fe and inevitable impurities, while the content of C, Ti, and Nb satisfies the ratio (Ti + Nb / 2)) / C <4.

Then hot rolling is carried out, including rough rolling and finishing rolling, accelerated cooling at an average cooling rate in the middle of the steel sheet in the thickness direction of 10 ° C / s or more until the cooling termination temperature corresponding in the middle of the steel sheet in the thickness direction to BFS or lower where BFS is determined by the expression: BFS (° C) = 770-300C-70Mn-70Cr-170Mo-40Cu-40Ni-1,5CR and coiling at a winding temperature equal to BFSO or lower in the middle of the steel sheet in the thickness direction, where bfso is determined by nation: BFSO (° C) = 770-300C-70Mn-70Cr-170Mo-40Cu-40Ni, where in the above expressions each of C, Mn, Cr, Mo, Cu and Ni represents their content fractions (wt.%), and CR represents the cooling rate (° C / s) in the middle of the steel sheet in the thickness direction. Accelerated cooling is performed at an average cooling rate of 1 mm from the surface of the steel sheet in the direction of the thickness of 100 ° C / s or more, and coiling is carried out at a winding temperature of in the middle of the steel sheet in the direction of the thickness of 300 ° C or higher .

The disadvantage of this method is the high energy consumption to obtain a given structural state in the sheet, due to not optimal heating mode.

The inventive method of obtaining metal products with a given structural state is aimed at achieving the required level of consumer properties of metal.

The specified result is achieved by the fact that the method of producing metal products with a given structural state of steel, having in its composition in wt.%:

C 0.05-0.18 Cu 0.05-0.30 Si 0.05-0.6 Ti no more than 0,050 Mn 1.30-2.05 Nb 0.010-0.100 S no more than 0.015 V no more than 0,120 P no more than 0,020 N no more than 0,012 Cr 0.02-0.35 Al no more than 0,050 Ni 0.02-0.45 Mo no more than 0.45 Fe and unavoidable impurities - the rest

includes heating for rolling, rough rolling at temperatures higher than the austenite recrystallization temperature, an inter-deformation pause, which provides the required decrease in metal temperature, finish rolling, straightening and accelerated cooling of the rolling, while the heating temperature for rolling T is set to provide the required solubility of carbide and nitride microalloying elements and determined from t + 280 ° C <T <t + 310 ° C,

where t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142.53N + 71.45Al + 23 , 67Mo, ° C,

where instead of the chemical designation of each element is substituted the content of this element, wt.%,

and the heat sink from the surface of the rolled metal in the process of its accelerated cooling is set to ensure the formation of the required volume fraction of bainite in the metal section.

The specified result is also achieved by the fact that the heat sink from the surface of the rental during its accelerated cooling is controlled by measuring the temperature of its surface.

The specified result is also achieved by the fact that the measurement of the surface temperature of the car is carried out before and at the end of accelerated cooling.

The given range of concentrations of elements in steel is due to the grades of steel, which primarily include grades for the production of large-diameter pipes, ship and structural steels.

The billet is heated to the dissolution temperatures of carbides and nitrides of microalloying elements such as Ti, Nb, V. This is necessary in order to ensure the required concentration of these elements in austenite in order to implement mechanisms of hardening by these elements during further processing.

The studies conducted by the authors showed that the temperature range of heating for rolling [t + 280 ° C; t + 310 ° C], where t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142, 53N + 71.45Al + 23.67Mo, ° C, is optimal for providing the dissolution of carbides and nitrides of these microalloying elements.

The heating temperature for rolling is lower (t + 280 ° C) will not ensure the transition of the required number of microalloying elements to the composition of the solid solution based on fcc iron. Subsequently, this will lead to insufficient hardening of the rolling stock according to the dispersion hardening mechanism and, accordingly, will not allow achieving the required level of mechanical properties. In addition, a lower heating temperature for rolling leads to an increase in the power parameters of the rolling process and an increase in the load on the rolling equipment.

It is impractical to heat the billet for rolling above temperature (t + 310 ° C), as this leads to excessive growth of austenite grain and excessive energy consumption.

Rough rolling must be carried out at temperatures higher than the austenite recrystallization temperature in order to ensure the flow of austenitic grains recrystallization in order to form a fine-grained structure before finishing rolling. An inter-deformation pause is carried out in order to provide cooling of the metal to the temperatures of the beginning of the finish rolling. Preliminary editing is necessary to ensure the necessary flatness of the rolled products before accelerated cooling.

Accelerated cooling of rolled products is necessary in order to ensure the formation in the process of phase transformations of the required volume fraction of bainite from austenite in the cross section of metal products.

In this case, the necessary heat removal from the metal surface depends on the thermophysical parameters of the steel itself, determined by its chemical composition, and the technical characteristics of the unit for accelerated cooling in the mill stream.

For large metal products, the formation of a structure homogeneous in volume of the metal is a complex engineering task. In this regard, it is advisable to operate with the concept of the required volume fraction of bainite in the cross section of metal products sufficient to ensure the specified consumer properties.

In practice, it is convenient to control the heat removal from the surface by the corresponding average rate of change of the surface temperature in the corresponding temperature range.

Moreover, in particular cases of implementation, it is advisable to measure the surface temperature of the rolled metal before and at the end of accelerated cooling.

The heat removal from the rolled surface during its accelerated cooling, which ensures the formation of the required volume fraction of bainite in the metal section, can be determined by conducting preliminary experiments.

For this, the samples of the steel under study were subjected to cooling from the austenitic region, realizing various conditions of heat removal from the metal surface in the temperature range of the bainitic transformation. In this case, the heat removal process was controlled by measuring the surface temperature of the sample.

Then, the samples were examined using an optical and electron microscope and a microhardness tester, and the volume fraction of bainite in the cross section of the metal product was established.

It is also possible to determine the required cooling regimes by the experimental calculation method described in RU 2413777 [4], according to which the corresponding parameters of the thermal effect in the cooling process are found by solving a system of equations that includes the heat equation in general

dQ = L · ∇T · dS · dt, where dQ is the heat flux through the surface dS in m ² during the time dt in seconds, measured in J, L is the thermal conductivity in J / K * m * s, ∇T is the temperature gradient in K / m;

, где H и H₀ - начальные энтальпии фаз в Дж, H′ и $$H_0^{\text{'}}$$

- начальные энтальпии фаз в Дж через время Δt в секундах, q - удельное энерговыделение при фазовом превращении в Дж/кг, Δm - изменение массы фаз в кг в течение заданного промежутка времени, Q - приток тепла из окружающей среды в Дж/с,energy conservation equation that takes into account energy release due to changes in the chemical and phase composition of the material of the processed metal $$H+H_0=H\text{'}\text{'}+H_0^{\text{'}\text{'}}-q\Delta m-Q\Delta t$$

, where H and H ₀ are the initial enthalpies of phases in J, H ′ and $$H_0^{\text{'}\text{'}}$$

- initial phase enthalpies in J after a time Δt in seconds, q - specific energy release during a phase transformation in J / kg, Δm - phase mass change in kg during a given period of time, Q - heat influx from the environment in J / s,

для случая, когда не произошло столкновения границ зерен растущей фазы или фронтов концентрационных возмущений и $$\frac{\text{dη}}{\text{dt}}={\text{k}}_{\text{3}}{\text{(1}-\text{η)}}^{\raisebox{1ex}{$\text{2}$}\!\left/ \!\raisebox{-1ex}{$\text{3}$}\right.}$$

для случая, когда столкновение уже произошло, где η - безразмерное локальное относительное содержание растущей фазы, k_i=k_i(Т, ΔT) - кинетические коэффициенты в с^-1, T - локальная температура, a ΔT - отклонение локальной температуры от температуры фазового равновесия, измеряемые в градусах Кельвина, при этом период охлаждения разбивают на интервалы, тепловое воздействие на поверхность изделия на выбранном интервале определяют итерациями до совпадения результатов расчетного и заданного значения температуры. В результате определяется тепловой поток в момент фазового превращения, что дает возможность рассчитать целевое значение потока тепла с поверхности (теплоотвод) и среднюю скорость изменения температуры в соответствующем температурном диапазоне, обеспечивающую формирование требуемой объемной доли бейнита в сечении металлоизделия с учетом теплопроводности металла и тепловых эффектов фазовых превращений.and kinetic equations describing phase transformations in the volume of a product of the form $$\frac{\text{dη}}{\text{dt}}={\text{k}}_{\text{one}}+{\text{k}}_{\text{2}}{\text{η}}^{\raisebox{1ex}{$\text{2}$}\!\left/ \!\raisebox{-1ex}{$\text{3}$}\right.}$$

for the case when there was no collision of grain boundaries of the growing phase or fronts of concentration perturbations and $$\frac{\text{dη}}{\text{dt}}={\text{k}}_{\text{3}}{\text{(one}-\text{η)}}^{\raisebox{1ex}{$\text{2}$}\!\left/ \!\raisebox{-1ex}{$\text{3}$}\right.}$$

for the case when the collision has already occurred, where η is the dimensionless local relative content of the growing phase, k _i = k _i (Т, ΔT) are the kinetic coefficients in s ^-1 , T is the local temperature, and ΔT is the deviation of the local temperature from the phase temperature equilibrium, measured in degrees Kelvin, while the cooling period is divided into intervals, the thermal effect on the surface of the product in the selected interval is determined by iterations until the results of the calculated and specified temperature values coincide. As a result, the heat flux at the time of phase transformation is determined, which makes it possible to calculate the target value of the heat flux from the surface (heat sink) and the average rate of temperature change in the corresponding temperature range, which ensures the formation of the required volume fraction of bainite in the metal section taking into account the thermal conductivity of the metal and the thermal effects of phase transformations.

At the same time, both the heating temperature for rolling, and the necessary heat removal from the surface of the rental during its accelerated cooling are technological parameters, the observance of which is necessary to achieve the required properties of the products.

Optimum heating for rolling does not allow excessive grain growth of austenite and provides the possibility of implementing mechanisms of hardening by microalloying elements during further rolling and accelerated cooling. However, if the heat removal carried out during accelerated cooling is insufficient to form the required proportion of bainite in the cross section, then the desired properties will not be achieved.

If the heat removal from the surface necessary for the formation of the required volume fraction of bainite in the cross section of the metal product is realized, but a large austenite grain or the concentration of microalloying elements in austenite is lower than necessary is formed during heating, then the specified consumer properties will also not be provided.

The essence of the proposed method is illustrated by examples of implementation.

Example 1. In the most General case, the method of obtaining metal products with a given structural state is as follows.

Preliminarily, the necessary heat removal from the surface of the rolled metal is determined in the process of its accelerated cooling to ensure the formation of the required volume fraction of bainite in the metal section according to the methods described above. Additionally, the average rate of change of the surface temperature of the metal when determining the required heat sink in the corresponding temperature range is determined.

The workpiece (slab) is heated to a temperature that provides the required solubility of carbides and nitrides of microalloying elements. The value of the heating temperature is determined from the interval of values t + 280 ° C <T <t + 310 ° C, based on its chemical composition, where t = 883-313.95C + 37.88Si-9.58Mn-2.79 Cr-15, 99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142.53N + 71.45Al + 23.67Mo, ° C,

After heating, rough rolling is carried out at temperatures exceeding the recrystallization temperature, then an inter-deformation pause, which provides the required decrease in the metal temperature for finish rolling, finish rolling, straightening and accelerated cooling of the rolling, providing heat removal from the surface, required for the formation of a given volume fraction of bainite in the metal section.

Example 2. The task was set of steel of the following composition, wt.%: 0.05% C; 0.28% Si; 1.37% Mn; 0.001% S; 0.007% P; 0.02% Cr; 0.38% Ni; 0.29% Cu; 0.038% Al; 0.006% N; 0.004% V; 0.015% Ti; 0.038% Nb; 0.15% Mo; the rest of Fe and uncontrolled impurities to get the roll size 40 × 2560 × 15000 mm with a volume fraction of bainite in the cross section of metal 20%.

For this, a workpiece weighing 11.96 tons with dimensions 300 × 2000 × 2640 mm made of steel of the specified chemical composition, obtained after casting on a continuous casting machine, was transferred to a hot-rolled plate mill.

Preliminarily, the necessary heat removal from the rolled surface during accelerated cooling was determined to ensure the formation of a 20% volume fraction of bainite in the metal section experimentally described above. It was found that the necessary heat removal from the surface is achieved at an average rate of change of surface temperature in the range of 730-530 ° C, comprising 16-20 ° C / s.

Based on the chemical composition of the steel, using the equation t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142, 53N + 71.45Al + 23.67Mo, ° C, we determined the value of the parameter t = 865 ° C of the heating temperature T from the range t + 280 ° C <T <t + 310 ° C equal to 1170 ° C, and the workpiece was heated to of this value.

After that, rough rolling was carried out in 6 passes in a reversing stand in the temperature range 1070-1010 ° C, which is higher than the austenite recrystallization temperature, with a total degree of deformation of 51% for 80 s.

Then, inter-deformation cooling of the roll in air (inter-deformation pause) was performed until the metal surface temperature reached 750 ° C.

Finishing rolling was carried out in 19 passes in a reversing stand in the temperature range of 750-730 ° C with a total degree of deformation of 73% for 170 s.

After finishing rolling, the resulting rolled products were subjected to accelerated cooling in a spray and laminar cooling unit using industrial water in the temperature range of 730–530 ° C with an average rate of change of the metal surface temperature of 17 ° C / s.

Structural studies of finished products showed that the volume fraction of bainite in the cross section of metal products was 20%. The required technical result is achieved.

Example 3. The task was set of steel of the following composition, wt.%: 0.10% C; 0.34% Si; 1.62% Mn; 0.002% S; 0.009% P; 0.03% Cr; 0.02% Ni; 0.05% Cu; 0.04% Al; 0.007% N; 0.047% V; 0.025% Ti; 0.042% No; 0.01% Mo; the rest of Fe and uncontrolled impurities to obtain a roll with dimensions of 16.8 × 4530 × 38500 mm with a volume fraction of bainite in the metal section of 15%.

For this, a workpiece weighing 23.24 tons with dimensions of 300 × 2600 × 3900 mm from steel of the specified chemical composition, obtained after casting on a continuous casting machine, was transferred to a hot-rolling plate mill.

Preliminarily, the necessary heat removal from the rolled surface during accelerated cooling was determined to ensure the formation of a 15% volume fraction of bainite in the metal section by the calculation method described above. It was found that the necessary heat removal from the surface is achieved at an average rate of change of surface temperature in the range of 715-620 ° C, comprising 12-26 ° C / s.

Based on the chemical composition of the steel, using the equation t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142, 53N + 71.45Al + 23.67Mo, ° C, determined the value of the parameter t = 855 ° C of the heating temperature T from the range t + 280 ° C <T <t + 310 ° C, equal to 1150 ° C, and the workpiece was heated to of this value.

After that, rough rolling was carried out in 12 passes in a reversing stand in the temperature range of 1090-1000 ° C, which is higher than the austenite recrystallization temperature, with a total degree of deformation of 73% for 130 s.

Then, inter-deformation cooling of the roll in air (inter-deformation pause) was carried out until the metal surface temperature reached 830 ° C.

Finishing rolling was carried out in 15 passes in a reversing stand in the temperature range of 830–740 ° C with a total degree of deformation of 79% for 140 s.

After finishing rolling, the resulting rolled products were subjected to accelerated cooling in a laminar cooling unit using industrial water in the temperature range of 715–620 ° C with an average rate of change of the metal surface temperature of 15 ° C / s.

Structural studies of finished products showed that the volume fraction of bainite in the cross section of metal products was 15%. The required technical result is achieved.

Example 4. The task was set of steel of the following composition, wt.%: 0.15% C; 0.4% Si; 1.70% Mn; 0.003% S; 0.012% P; 0.35% Cr; 0.25% Ni; 0.22% Cu; 0.035% Al; 0.008% N; 0.08% V; 0.025% Ti; 0.045% Nb; 0.02% Mo; the rest of Fe and uncontrolled impurities to obtain the roll size 30 × 2550 × 29200 mm with a volume fraction of bainite 30% in the cross section of metal products.

For this, a workpiece weighing 17.05 tons with dimensions of 300 × 2400 × 3100 mm from steel of the specified chemical composition, obtained after casting on a continuous casting machine, was transferred to a hot-rolling plate.

Preliminarily, the necessary heat removal from the surface of the rolled metal was determined in the process of its accelerated cooling to ensure the formation of a 30% volume fraction of bainite in the metal section experimentally described above. It was found that the necessary heat removal from the surface is achieved at an average rate of change of surface temperature in the range of 770-650 ° C, component 23-28 ° C / s.

Based on the chemical composition of the steel, using the equation t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142, 53N + 71.45Al + 23.67Mo, ° C, we determined the value of the parameter t = 840 ° C of the heating temperature T from the range t + 280 ° C <T <t + 310 ° C, equal to 1150 ° C, and the workpiece was heated to of this value.

After that, rough rolling was carried out in 10 passes in a reversing stand in the temperature range of 1080-990 ° C, which is higher than the austenite recrystallization temperature, with a total degree of deformation of 70% for 105 s.

Then, inter-deformation cooling of the roll in air (inter-deformation pause) was carried out until the metal surface temperature reached 840 ° C.

Finishing rolling was carried out in 15 passes in a reversing stand in the temperature range of 840–790 ° C with a total degree of deformation of 63% for 160 s.

After finishing rolling, the resulting rolled products were subjected to accelerated cooling in a sprayer and laminar cooling unit using industrial water in the temperature range of 770-650 ° C with an average rate of change of the metal surface temperature of 27 ° C / s.

Structural studies of finished products showed that the volume fraction of bainite in the cross section of metal products was 30%. The required technical result is achieved.

Literature

1. US 6364968.

2. RU 2437945.

3. RU 2011107730.

4. RU 2413777.

Claims (3)

1. The method of obtaining metal with a given structural state, including obtaining a billet of steel containing, wt.%:
C 0.05-0.18 Si 0.05-0.6 Mn 1.30-2.05 S no more than 0.015 R no more than 0,020 Cr 0.02-0.35 Ni 0.02-0.45 Cu 0.05-0.30 Ti no more than 0,050 Nb 0.010-0.100 V no more than 0,120 N no more than 0,012 Al no more than 0,050 Mo no more than 0.45 Fe and inevitable impurities rest
heating the billet, rough rolling at temperatures higher than the austenite recrystallization temperature, an inter-deformation pause providing the required decrease in the metal temperature, finish rolling, straightening and accelerated cooling of the rolling, while the heating temperature for rolling T is set from the condition of ensuring the required solubility of carbide and nitride microalloying elements and determined by the dependence:
t + 280 ° C <T <t + 310 ° C,
where t = 883-313.95C + 37.88Si-9.58Mn-2.79Cr-15.99Ni-2.55Cu + 110.18Ti + 5.5Nb + 76.74V-142.53N + 71.45Al + 23 , 67Mo, ° C,
where - C, Si, Mn, Cr, Ni, Cu, Ti, Nb, V, N, Al, Mo - the content of elements, wt.%, and heat removal from the surface of the rental during its accelerated cooling is carried out to ensure the formation of the required volume fraction bainite in the cross section of metal. 2. The method according to claim 1, characterized in that the heat sink from the surface of the rental during its accelerated cooling is controlled by measuring the surface temperature. 3. The method according to claim 2, characterized in that the measurement of the surface temperature of the rental is carried out before and at the end of accelerated cooling.