RU2447163C1 - Method of metal structure alloy thermal treatment - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: first method comprises heating for austenite formation and subsequent cooling in conditions for formation of preset structural state. Note here that cooling is conducted in conditions providing austenite areas in alloy structure that feature chemical composition approximating to eutectoid composition followed by marinite formation while preset structural state is formed to produce perlite of various dispersity and/or hardening structures. Second method comprises heating for austenite formation and subsequent cooling in conditions for formation of preset structural state. Note here that heating is conducted in conditions providing marinite formation in alloy structure while preset structural state is formed to produce perlite of various dispersity and/or hardening structures. Note also that pulse cooling, plastic deformation and magnetic field effects are used to this end.

EFFECT: reduced production cycle, preset structural state.

41 cl, 19 ex, 10 dwg

Description

The group of inventions relates to metallurgy and, in particular, to heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight and is aimed at producing alloys with a given structural state and with the required properties.

A known method of heat treatment of steel products, in particular, long products, providing the formation in the bars of structural alloyed steels with a long period of pearlite transformation or not having its two-layer structure: ferrite-pearlite with low hardness in the surface layer and sorbitol with higher hardness in the central layer. This allows subsequent cold machining of the bars by cutting.

To obtain the specified result in the method of heat treatment of long products, which consists in accelerated cooling from the temperature of the end of deformation, isothermal holding at 600-700 ° C, lasting no more than 3 hours and subsequent cooling, accelerated cooling is carried out until the surface layer reaches a temperature below the point M _n at a depth of 5-10 mm (RU 2044779 [1]).

The disadvantage of this method is its low productivity, due to the large time spent on operations, allowing to ensure the formation of the required structural state.

As a result of accelerated cooling of the surface layer with a depth of 5-10 mm below the temperature M _n , a martensite structure forms on the surface of the bar. With subsequent heating and aging at 600-700 ° C, martensite decomposes much faster into a ferrite-pearlite mixture than the direct transformation of austenite throughout the entire volume of the rod. Thus, a two-layer structure is formed in the bar: the surface is ferritic-pearlitic with a low hardness and sorbitol in the central layer with a higher hardness. At the same time, a relatively large (up to 3 hours) isothermal exposure time remains.

A known method of heat treatment of products from an alloy based on iron, in particular hot-rolled running and railway rails with profile parts of various masses, including the stages of preliminary and final cooling after rolling heating of profile parts of various masses with the formation of the desired structure with increased strength in the profile parts of the rail, particularly in the rail head. Pre-cooling of the rail after rolling heating is carried out to a temperature of the rail head core of 750-850 ° C to prevent intermediate supercooling of the surface area of the rail head and local premature phase transformation, then the step of heating the surface zone of the rail head is carried out at least to the core temperature and final cooling of the rail is carried out with such a high heat flux that for the central zone of the rail head is achieved as short as possible The burden in the cooling zone of the phase change of 800 to 500 ° C. In this case, the final cooling of the rail head in the phase transformation zone is carried out so quickly that the desired thin plate pearlite structure is formed and the surface zone is cooled below the bainite formation temperature (RU 2272080 [2]). The disadvantage of this method is the length of the heat treatment process, which leads to the production of products from steel with a given final structural state, and the limited range of products (assortment) of the obtained steels with the required (specified) properties.

Closest to the claimed invention in technical essence and the achieved result is a known method of heat treatment of steel products to obtain a given final fine-plate pearlite or ferrite / pearlite structure (RU 2266966 [3]). The known method involves heating a workpiece, in particular a rolled steel profile in the form of a rail, to temperatures of about 850 ° C and its further cooling by individual pulses, providing a pearlite or ferrite / pearlite structure without the appearance of quenching structures (in particular, bainite). To do this, the workpiece or the finished product is passed through a cooling section, which consists of separate, independent cooling modules sequentially located along the length of the cooling section, which is essentially equivalent to pulse cooling with independently adjustable cooling parameters, and there are intermediate regions between the cooling modules to relieve structural stresses from means for determining the actual temperature of the product in these intermediate areas, and, depending on The actual temperature of the part in the intermediate region is controlled by the cooling parameters, especially the cooling rate, of at least the next cooling module to ensure the set temperature of the part during the entire passage of the cooling section, and the set temperature of the part is accordingly maintained above the critical temperature at which bainitic structural components. Moreover, in the pauses between the stages (pulses) of the cooling process, temporary phases of reheating and / or thermal exposure and / or temporary phases of slow cooling are used to relieve structural stresses.

The disadvantage of this method is the duration of the heat treatment process, leading to the production of steel with a given structural state, and the limited range of products (assortment) of the obtained steels with the desired (specified) properties.

The inventive methods are aimed at reducing the timing of technological processes that ensure the production of products from alloys based on iron with predetermined structural states, and therefore, with the physico-mechanical and qualitative characteristics required in each particular case.

This result is achieved by the fact that the first method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight includes heating, which ensures the formation of austenite and subsequent cooling according to the regimes that ensure the formation of a given structural state, while cooling is carried out according to the modes ensuring the presence of austenite regions with a chemical composition close to eutectoid, with the subsequent receipt of marinite in them, and a given structural state is formed to obtain in it perlite of varying degrees of dispersion and / or quenching structures.

The indicated result is also achieved by the fact that cooling is carried out according to the regimes ensuring the formation of a predetermined fraction of austenite regions with a chemical composition close to eutectoid, followed by obtaining a predetermined fraction of marinite in them.

The indicated result is also achieved by the fact that the regimes ensuring the formation of a given fraction of marinite from austenite regions with a chemical composition close to eutectoid are determined by calculation or experimentally.

The indicated result is also achieved by the fact that a predetermined structural state is formed with obtaining in it predetermined perlite fractions of varying degrees of dispersion and / or quenching structures.

The indicated result is also achieved by the fact that in the calculation determination of the regimes ensuring the production of marinite from areas of austenite with a chemical composition close to eutectoid, the temperature range for the implementation of marinite, satisfying the conditions

,

,

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода, определяемая методом квантово-механического расчета,Where

- the temperature of the local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum-mechanical calculation,

T _TEX - temperature selected taking into account technological limitations,

and choose a cooling rate at which the dependence of the cooling temperature on time T (t) satisfies the condition T (t) <Θ (t), where the dependence Θ (t) is determined by the lines of the beginning of the pearlite and bainitic transformations on the thermokinetic diagram.

The indicated result is also achieved by the fact that during the experimental determination of the regimes ensuring the production of marinite from austenite with a chemical composition close to eutectoid, the samples are quenched from fixed temperatures at different exposure times, and the fact of the existence of marinite is established by the presence of rutite in the quenched sample .

The indicated result is also achieved by the fact that the presence of rutite is established by diffraction methods.

The indicated result is also achieved by the fact that the determination of the cooling mode from the realized marinite, leading to the formation of a given amount of perlite in a given structural state, is carried out by quenching the experimental samples and the subsequent determination of their structural state.

The indicated result is also achieved by the fact that the determination of the cooling mode from the realized marinite, which leads to the formation of a given structural state, is carried out by measuring the temperature at selected points in the volume of the model alloy sample of simple form during cooling at the rates leading to the desired structural state in the alloy sample, by determining values of thermokinetic constants providing, at known heat fluxes on the sample surface, the temperature dependences о time obtained during model experiment and as a result of solving the system of equations consisting of a thermal conductivity equation

,

,

имеет размерность м^-1, r - радиус-вектор точки, в которой производятся вычисления, ρ - плотность, измеряемая в кг/м³, q_i - удельная энтальпия образования i-й фазы, измеряемая в Дж/кг, f_i(r, t, T) - безразмерная массовая доля фазы i в окрестности точки r в момент времени t при температуре Т,

- поток тепла, измеряемый в Дж/(м²·с), Н(r, t, T) - распределение энтальпии, измеряемой в Дж/м³, по объему образца,where is the operator

has the dimension m ^-1 , r is the radius vector of the point at which the calculations are made, ρ is the density measured in kg / m ³ , q _i is the specific enthalpy of formation of the i-th phase, measured in J / kg, f _i (r , t, T) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T,

is the heat flux measured in J / (m ² · s), N (r, t, T) is the distribution of the enthalpy measured in J / m ³ over the volume of the sample,

energy conservation equation

- удельная теплоемкость фазы i при постоянном давлении от температуры, измеряемая в Дж/(кг·К), и кинетическое уравнениеWhere

- the specific heat of phase i at constant pressure versus temperature, measured in J / (kg · K), and the kinetic equation

where M _ik (T, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation, and using the above equations and found thermokinetic constants for calculating the dependence of the heat flux on time over the surface of an alloy product, providing a trajectory of temperature change over time, leading to the formation of a given structural state.

The indicated result is also achieved by the fact that after the implementation of marinite, cooling is carried out according to the regimes leading to the formation of the specified fractions of the phases of ferrite and iron carbides in the given structural state without the formation of quenching structures or with the formation of them in fractions not exceeding the specified ones.

The specified result is also achieved by the fact that after the formation of a given fraction of perlite, the cooling of alloy products is carried out at speeds sufficient to suppress diffusion transformations.

The specified result is also achieved by the fact that the cooling is carried out impulse.

The indicated result is also achieved by the fact that cooling is carried out by pulses that alternate with pauses with durations selected sufficient for a given reduction of the difference between the maximum and minimum temperature values over the cross section of alloy products.

The indicated result is also achieved by the fact that the duration of each of the cooling pulses is chosen so that they do not lead to the formation of quenching structures in a given structural state.

The indicated result is also achieved by the fact that the cooling is carried out in a pulsed manner, while one of the cooling pulses is selected to provide the maximum decrease in the surface temperature of alloy products without the formation of quenching structures in a given structural state.

The indicated result is also achieved by the fact that after the formation of a given fraction of austenite in the alloy, sufficient to obtain in a given structural state the specified fractions of perlite of varying degrees of dispersion and / or quenching structures, the temperature reduction required for the implementation of marinite is carried out by cooling pulses.

The indicated result is also achieved by the fact that after reaching the fractions of the phases of ferrite and iron carbides, which subsequently provide a given structural state, impulse cooling is stopped and transitions to monotonic cooling and / or isothermal aging.

The indicated result is also achieved by the fact that after heating the alloy products to temperatures ensuring the formation of a predetermined austenite fraction in the alloy, the alloy products are subjected to plastic deformation.

The specified result is also achieved by the fact that plastic deformation of alloy products is carried out or completed at temperatures t _Kfer ± 50 ° C, where t _Kfer is the Curie temperature of ferrite, ° C.

The indicated result is also achieved by the fact that during the implementation of marinite, alloy products are exposed to a constant or pulsed magnetic field.

The specified result is also achieved by the fact that water or aqueous media are used for cooling.

This result is achieved by the fact that the second method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight involves heating and subsequent cooling according to the modes providing the formation of a given structural state, while heating is carried out according to the modes providing the formation of marinite and a predetermined structural state is formed to produce perlite in it of varying degrees of dispersion and / or quenching structures.

The specified result is also achieved by the fact that the heating is carried out according to modes that ensure the formation of a given fraction of marinite.

The specified result is also achieved by the fact that the modes that ensure the formation of a given fraction of marinite are determined by calculation or experimentally.

The indicated result is also achieved by the fact that a predetermined structural state is formed with obtaining in it predetermined perlite fractions of varying degrees of dispersion and / or quenching structures.

The specified result is also achieved by the fact that in the calculation determination of the modes that ensure the implementation of marinite, set the temperature range of the heating, satisfying

,

,

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода, определяемая методом квантово-механического расчета,Where

- the temperature of the local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum-mechanical calculation,

T _X is the eutectoid temperature for the alloy of the corresponding chemical composition,

and the exposure time t in seconds required to dissolve a given fraction of cementite f _C , determined from the equation

f _C = 1.05 f _C0 exp (-kt ⁿ ),

where f _C0 is the dimensionless fraction of cementite at the initial instant of time, 4>n> 3 is a power exponent, k is a parameter that determines the dissolution rate of cementite in an alloy of the corresponding chemical composition at a temperature T in s ^-n .

The indicated result is also achieved by the fact that during the experimental determination of the implementation conditions in the marinite alloy, the samples are quenched from fixed temperatures at various holding times, and the fact of the existence of marinite is established by the presence of rutite in the quenched sample.

The indicated result is also achieved by the fact that the presence of rutite is established by diffraction methods.

The indicated result is also achieved by the fact that the determination of the cooling mode from the realized marinite, leading to the formation of a given amount of perlite in a given structural state, is carried out by quenching the experimental samples and the subsequent determination of their structural state.

The indicated result is also achieved by the fact that the determination of the cooling mode from the realized marinite, which leads to the formation of a given structural state, is carried out by measuring the temperature at selected points in the volume of the model alloy sample of simple form during cooling at the rates leading to the desired structural state in the alloy sample, by determining values of thermokinetic constants providing, at known heat fluxes on the sample surface, the temperature dependences о time obtained during model experiment and as a result of solving the system of equations consisting of a thermal conductivity equation

имеет размерность м^-1, r - радиус-вектор точки, в которой производятся вычисления, ρ - плотность, измеряемая в кг/м³, q_i - удельная энтальпия образования i-й фазы, измеряемая в Дж/кг, f_i(r, t, T) - безразмерная массовая доля фазы i в окрестности точки r в момент времени t при температуре T,

- поток тепла, измеряемый в Дж/(м²·с), Н(r, t, T) - распределение энтальпии, измеряемой в Дж/м³, по объему образца,where is the operator

has the dimension m ^-1 , r is the radius vector of the point at which the calculations are made, ρ is the density measured in kg / m ³ , q _i is the specific enthalpy of formation of the i-th phase, measured in J / kg, f _i (r , t, T) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T,

is the heat flux measured in J / (m ² · s), N (r, t, T) is the distribution of the enthalpy measured in J / m ³ over the volume of the sample,

energy conservation equation

- удельная теплоемкость фазы i при постоянном давлении от температуры, измеряемая в Дж/(кг·К) и кинетическое уравнениеWhere

- the specific heat of phase i at constant pressure versus temperature, measured in J / (kg · K) and the kinetic equation

where M _ik (T, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation, and using the above equations and found thermokinetic constants for calculating the dependence of the heat flux on time over the surface of an alloy product, providing a trajectory of temperature change over time, leading to the formation of a given structural state.

The indicated result is also achieved by the fact that after the implementation of marinite, cooling is carried out according to the regimes leading to the formation of the specified fractions of the phases of ferrite and iron carbides in the given structural state without the formation of quenching structures or with the formation of them in fractions not exceeding the specified ones.

The specified result is also achieved by the fact that after the formation of a given fraction of perlite, the cooling of alloy products is carried out at speeds sufficient to suppress diffusion transformations.

The specified result is also achieved by the fact that the cooling is carried out impulse.

The indicated result is also achieved by the fact that cooling is carried out by pulses that alternate with pauses with durations selected sufficient for a given reduction of the difference between the maximum and minimum temperature values over the cross section of alloy products.

The indicated result is also achieved by the fact that the duration of each of the cooling pulses is chosen so that they do not lead to the formation of quenching structures in a given structural state.

The indicated result is also achieved by the fact that the cooling is carried out in a pulsed manner, while one of the cooling pulses is selected to provide the maximum reduction in the surface temperature of the alloy product without the formation of quenching structures in a given structural state.

The indicated result is also achieved by the fact that after reaching the fractions of the phases of ferrite and iron carbides, which subsequently provide a given structural state, impulse cooling is stopped and transitions to monotonic cooling and / or isothermal aging.

The indicated result is also achieved by the fact that the alloy products are subjected to plastic deformation when heated to or during the implementation of marinite.

The specified result is also achieved by the fact that the alloy products after the implementation of marinite are subjected to plastic deformation.

The specified result is also achieved by the fact that plastic deformation of alloy products is carried out or completed at temperatures t _Kfer ± 50 ° C, where t _Kfer is the Curie temperature of ferrite, ° C.

The specified result is also achieved by the fact that water or aqueous media are used for cooling.

In the text of this application, the following terms are used.

Structural state - a set of structural elements formed as a result of thermal or thermomechanical processing, characterized by phase composition, morphology and size.

Phase - thermodynamically equilibrium state of a substance, which differs in its physical properties from other equilibrium states of the same substance.

Austenite is a solid solution of carbon in fcc iron.

Ferrite is a solid solution of carbon in bcc iron.

Cementite is iron carbide Fe ₃ C _x , where 0.75≤x≤1, with a rhombic unit cell.

Perlite is a structural component of iron-carbon alloys - steels and cast irons: it is a eutectoid mixture of two phases - ferrite and cementite.

Lamellar perlite - perlite, in which ferrite and cementite are predominantly lamellar in shape.

Granular perlite - perlite, in which cementite has a predominantly spherical shape.

Sorbitol is dispersed perlite.

Sorbitization time - the time interval from the moment the onset of sorbitol to the moment of completion of the formation of the sorbitol structure over the cross section of the workpiece (product).

Troostitis is a highly dispersed perlite.

Bainite (upper, lower) is a quenching structure that forms when austenite is supercooled into a temperature range limited by the temperatures of the onset of bainitic transformation and the beginning of martensitic transformation.

Martensite is a quenching structure formed by shear from austenite and is a solid solution of carbon in bct iron.

Ledeburite is a structural component resulting from a eutectic reaction in which the iron-carbon melt solidifies with the formation of austenite and cementite, and upon further cooling, austenite turns into perlite.

Marinite is the structural state of an alloy based on iron and carbon, characterized by the presence in the fcc matrix of iron of carbon-rich regions of quasistatic atomic displacements that translate the fcc into a fcc lattice with a short ferromagnetic order, and carbon-depleted regions.

Rutite is a structural state of an alloy based on iron and carbon, which is formed upon rapid cooling (quenching) of marinite.

Quasistatic displacements are correlated displacements of atoms from their equilibrium positions in the crystal lattice, which persist for a time significantly exceeding the period of thermal vibrations.

The Curie temperature of ferrite is the temperature of the transition from the ferromagnetic to paramagnetic state upon heating; at this temperature, ferrite loses spontaneous magnetization.

Quenching (rapid cooling) - cooling at a speed sufficient to suppress diffusion transformations.

Hardened Sample — A hardened sample.

Quenching structures - structures formed as a result of quenching.

Diffusion transformation - the transformation of one phase into another as a result of the movement of atoms by diffusion.

Shear transformation is the transformation of one phase into another by cooperative atomic displacement, accompanied by deformation of the crystal lattice.

A cooling pulse is a thermophysical process that develops as a result of a short-term exposure to a workpiece by a cooling medium.

Residual austenite - austenite preserved in the structure after cooling to room temperature.

The nearest magnetic order is the ordering in the mutual arrangement of magnetic moments, repeated at distances comparable with interatomic ones.

The short-range atomic arrangement is ordering in the mutual arrangement of atoms, repeated at distances commensurate with interatomic ones.

The inventive group of methods for heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight, which provides them with a given structural state, is based on the general principle of providing conditions for the formation of a structural state, called by the authors "MARINIT", characterized by the presence in matrix of fcc iron of carbon-enriched regions of quasistatic atomic displacements that convert fcc to a fcc lattice with a short ferromagnetic order and carbon-depleted regions by changing temperature (increase or decrease) and subsequent cooling to achieve a given structural state of the alloy.

The methods differ from each other by the conditions for the formation of marinite. In the first case, marinite is realized by cooling preformed austenite, in the second case, by heating a mixture of phases of ferrite and iron carbides.

The fact of the presence of such a special structural state is confirmed by a number of experimental data obtained by the authors.

To clarify the conditions for the formation of marinite, studies of structurally dependent physical properties were carried out.

One of these properties is the temperature dependence of the magnetic susceptibility χ (T), which was studied at the Institute of Metal Physics (Yekaterinburg) on a magnetometer with a high-temperature attachment. To ensure a sufficiently high sensitivity and low noise level, the measurements were carried out in a weak alternating magnetic field (intensity 10 Oe, frequency 80 Hz). The temperature changed at speeds of 6-12 degrees / min. The results for eutectoid steel are presented in figure 1. The magnetic susceptibility χ (T) shows a rapid drop upon heating, which begins at a temperature of ~ 740 ° C and ends when the Curie temperature α-Fe (T _C = 778 ° C) is reached. At the same time, a subsequent decrease in temperature from 850 ° C to a value of T ~ 700 ° C is accompanied by a slow increase in χ (T), which is replaced by a sharp rise at 700 ° C, when α-Fe appears in the structure. An increase in χ (Т) upon cooling to Т> 700 ° С indicates the presence of dispersed particles of the magnetic phase or regions of short-range magnetic order in it. Thus, the behavior of the magnetic susceptibility χ (Т) indicates the formation of a heterogeneous state in a certain temperature range below the Curie point of α-Fe, but above the temperature of the α-γ transformation A ₁ .

Also, at the Institute of Metal Physics (Yekaterinburg), we measured the temperature dependence of the coefficient of thermal expansion α (T) for eutectoid steel on a highly sensitive dilatometer in a wide temperature range during heating and cooling at a rate of 3 deg / min. An unusual feature of the obtained dependence α (T) is a decrease in the coefficient of thermal expansion during heating, starting from temperatures T> 500 ° C and a sharp drop in α (T) above the point of the α-γ transition in the temperature range 740-850 ° C (figure 2) . When cooling in the temperature range 800-690 ° C, there is a slight change in the coefficient of thermal expansion with temperature. At the γ-α transition point, the quantity α (Т) experiences a jump, and with a further decrease in temperature, the usual behavior of α (Т) is observed, at which dα / dT> 0.

As is known, the normal behavior of a homogeneous system is a slight increase in the coefficient of thermal expansion with temperature, dα / dT> 0 [4]. According to the ideas set forth in [5], a slight change in α (T) observed in the temperature range T = 690–800 ° C indicates the existence of a heterogeneous state, which is an ensemble of dispersed particles (or clusters) that have a specific volume smaller than matrix. As a result, thermal expansion is determined not only by lattice anharmonisms, but depends mainly on changes in the relative fraction of clusters. When heated, the anomaly in the dependence α (T) is much more pronounced (figure 2). This result indicates that kinetic factors play a significant role in the formation of this state. In particular, a rapid decrease in α (T) upon heating may be due to the continued dissolution of carbide particles, while a slight change in α (T) upon cooling can be due to the formation of carbon inhomogeneities with a characteristic size of 10-100 nm.

Thus, both the behavior of the magnetic susceptibility and the data on thermal expansion indicate the existence of a special structural state that is realized under conditions close to equilibrium in the temperature range A ₁ <T <T _C.

In order to find out how the steel structure changes during slow heating and cooling, when kinetic effects can be neglected, neutron diffraction studies were carried out at the IVV-2M stationary research nuclear reactor at the Beloyarsk NPP. Neutron diffraction patterns of the samples were obtained on a neutron diffractometer with a high angular resolution (Δd / d = 0.2%). The survey was carried out in the temperature range (20-800 ° C) after preliminary exposure for 1 hour at a given temperature to achieve an equilibrium state. The structural parameters were refined by the Rietveld full-profile analysis method [6], which, based on a comparison of theoretical and experimental diffraction patterns, allows one to establish atom coordinates, the general thermal factor, individual isotropic or anisotropic thermal factors, and position populations by atoms of different sorts.

As a result, it was found that the samples at temperatures below the γ-α transition contain α-Fe and cementite with an orthorhombic unit cell (17% by mass), and at temperatures above the γ-α transition, they contain γ-Fe, in which carbon atoms are located in octahedral internodes. When analyzing the population of cementite positions by Fe and C atoms, it turned out that its composition is not constant, but varies significantly depending on temperature (Fig. 3). Moreover, its fraction and orthorhombic lattice are preserved up to the temperature of the γ-α transition; at higher temperatures, cementite disappears. Thus, the composition of cementite in the general case can be represented by the formula Fe ₃ C _X , in which the value of X decreases with increasing temperature from X≈1 (at 20 ° C) to X≈0.75 (at temperatures close to the point of the γ-α transition ), therefore, depending on the heat treatment mode, the composition of cementite may vary.

In order to determine in detail what constitutes the studied structural state, fcc-Fe calculations were carried out using the methods of the theory of the electron density functional [7]. These calculations showed the presence of several equilibrium states that differ in the magnitude of the magnetic moment, type of magnetic structure, and specific volume. Among them, the most significant are the high-spin (HS) ferromagnetic (FM) state, with higher energy and higher volume per atom, and the low-spin (LS) antiferromagnetic (AFM) state, with lower energy and lower volume per atom. More consistent calculations, taking into account the possibility of the appearance of noncollinear magnetic structures modeled by spin helices, also lead to two equilibrium states: the HS-FM state (spin spiral vector q = 0) and the state, which is a set of LS-degenerate states with 0.2 <q≤ 0.5 (q in units of 2π / a, and a is the fcc lattice parameter of Fe, measured in nanometers, q = 0.5 corresponds to AFM). An essential feature established in these calculations is that the fcc lattice corresponds to the equilibrium state of γ-Fe, but the fcc lattice. The magnitude of the tetragonality c / a depends on the magnetic structure and ranges from 4 to 10%.

At present, there is no doubt that the decisive role in the phase stability of Fe and its alloys is played by magnetism (see [8] and [9]). The presence of several magnetic states creates the prerequisites for the emergence of heterogeneity in γ Fe and is the cause of the invariable behavior of alloys based on it [9].

The possibility of the formation of a short-range magnetic order at temperatures close to A ₁ (~ 1000 K) can be judged on the basis of our assessment of the exchange energy responsible for the formation of the ferromagnetic state. Figure 4 shows the results of calculations of the parameter J ₀ , measured in eV / atom and characterizing the gain in magnetic energy as a result of the formation of ferro (J ₀ <0) or antiferromagnetic (J ₀ > 0) order [10]. It can be seen that this gain reaches ~ 1000 K with a volume close to the experimental one (12.2 A ³ / atom) and a tetragonal strain of about -5% (s / a≈0.95, curve 3); in this case, the fcc lattice is distorted toward the bcc structure. Thus, due to a gain in magnetic energy, one should expect the appearance of tetragonally distorted regions with a ferromagnetic short-range order at temperatures close to A ₁ .

Our calculations [11] in the framework of the theory of the electron density functional for the partially ordered magnetic state of iron by the method of disordered magnetic moments (DLM) showed that with magnetization M ~ 0.5M _max (M _max is the maximum magnetization realized in the ferromagnetic state), the minimum energy is achieved for an MTC lattice with a tetragonality value c / a≈0.95. This result gives direct confirmation of the conclusions based on the assessment of the exchange energy J ₀ given above.

Thus, due to the strong coupling of the lattice and magnetic degrees of freedom in γ-Fe in a certain temperature range T> A ₃ , two stable states can coexist: paramagnetic fcc and tetragonally distorted (fcc) with short-range ferromagnetic order. This leads to the special nature of spin-lattice dynamics, the existence of which explains the observed “anti-invariant” behavior of γ-Fe [9] and plays a key role in the nucleation of a new phase during the γ-α transformation. The structure of spin-lattice excitations at a fixed time can be represented as consisting of alternating nanoscale regions of the fcc and fcc lattices.

. Наличие тетрагональных искажений вблизи атомов углерода увеличивает взаимодействие между ними, содействуя формированию ближнего порядка в обогащенных углеродом областях. Кроме того, способность углерода вызывать локальную магнитную поляризацию γ-Fe приводит к преимущественному расположению его внутри магнитоупорядоченных областей в переохлажденном аустените γ-Fe-C. В результате углерод оказался тем химическим элементом, который способствует стабилизации (увеличению времени существования) ГЦТ флуктуаций с ближним ферромагнитным порядком и тем самым формированию структурного состояния с квазистатическими смещениями в системе Fe-C; при этом области ГЦТ Fe обогащены углеродом.In order to elucidate the role of carbon in the formation of the special structural state of the Fe – C system under study, we calculated the electronic structure, lattice, and magnetic properties of the diluted carbon solid solution in γ Fe using the density functional theory methods [12]. A strong effect of carbon on the magnetic structure of γ-Fe was found. The introduction of carbon into the interstitial position leads to local magnetic polarization of the γ-Fe lattice and is accompanied by significant tetragonal deformations that distort the fcc lattice towards the bcc. In this case, the change in the energy of the exchange interactions turned out to be quite large (the energy of the local spin flip J ~ 1100 K), so that the magnetic inhomogeneities near the carbon atoms should be preserved to sufficiently high temperatures

. The presence of tetragonal distortions near carbon atoms increases the interaction between them, contributing to the formation of short-range order in carbon-enriched regions. In addition, the ability of carbon to cause local magnetic polarization of γ-Fe leads to its predominant location inside magnetically ordered regions in supercooled austenite of γ-Fe-C. As a result, carbon turned out to be the chemical element that contributes to the stabilization (increase in the lifetime) of MTC fluctuations with a short ferromagnetic order and thereby the formation of a structural state with quasistatic displacements in the Fe – C system; in this case, the regions of MCP Fe are enriched in carbon.

Thus, on the basis of experimental facts, as well as the results of the calculations, it was established that, under certain conditions, a special structural state is realized in the Fe-C system, called MARINIT. This state is characterized by the presence in the fcc matrix of iron of carbon-enriched regions of quasistatic atomic displacements that translate the fcc into a fcc lattice with a short ferromagnetic order, and carbon-depleted regions, which may have a paramagnetic fcc or ferromagnetic bcc structure.

In order to obtain additional information about what constitutes marinitis, the corresponding experiments were carried out.

In particular, the sample was heated to a temperature of 745 ° C, held for 2 min 55 s, and a cylindrical sample with a diameter of 8 mm made of steel of the following chemical composition was cooled in water (hereinafter, wt%): 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities (mode 1).

During the aging process, a special structural state of marinite was realized.

An electron microscopic study of the structure of the samples after cooling was carried out at the Institute of Metal Physics (Yekaterinburg) using a JEM 200CX transmission electron microscope.

The microstructure of the steel after such processing is shown in Fig. 5 and is characterized by well-organized colonies of martensitic plates, each of which contains many parallel microtwins (Fig. 5a). At the same time, a characteristic spotted (so-called "tweed") contrast is present in the entire visible field (Fig. 5b), which can be interpreted as the result of electron scattering on dispersed precipitates 2-5 nm in size. Such precipitates may be carbon-rich clusters or small carbide precipitates.

X-ray diffraction studies of the same sample, carried out at the Institute of Metal Physics (Yekaterinburg) on a DRON-1UM X-ray diffractometer in Fe K _α radiation, revealed an unusual feature of the X-ray lines (Fig. 6), which manifests itself in a violation of the standard 1: 2 ratio of doublet peak intensities (110) prescribed by the geometry of the tetragonal lattice of martensite [13]. The fulfillment of this ratio is clearly seen from the decomposition of the X-ray line intensity into a superposition of Lorentzian peaks for the sample quenched from T = 1100 ° C (Fig. 6a). To explain the intensity ratio (close to 1: 1) observed in samples quenched from 745 ° C, it is necessary to admit the presence of regions of the cubic phase along with the tetragonal phase. The mechanism of the formation of the x-ray pattern in this case is illustrated in Fig.6b, from which it is seen that 40% of the volume fraction of the cubic phase leads to a peak ratio close to 1: 1.

Samples of steel composition were subjected to neutron diffraction studies: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, after treatment according to the regime that consisted of heating in a furnace to 1005 ° C, cooling in air to 700 ° C, torsion strain in a torsion-type plastometer (relative deformation of the surface layer ε = 0.12, strain rate ξ = 0.2 s ^-1 ), cooling in nitrate (443 ° С) for 3 s and subsequent cooling in water; and samples of the same chemical composition with a martensitic structure obtained by direct quenching from the austenitic region. The neutron diffraction experiment was carried out at the IVV-2M stationary research nuclear reactor at the Beloyarsk NPP using a high angular resolution neutron diffractometer. Determination of the phase composition and refinement of the structural parameters of the phases was carried out by the method of full-profile Rietveld analysis [6].

As a result, it was found that the degree of tetragonality of the lattice of the samples during which marinite was heat treated was ~ 0.5%, while the tetragonality of the martensite lattice of the same chemical composition was ~ 2%.

The data obtained confirm the conclusions made on the basis of the results of the X-ray experiment, and indicate an abnormally low degree of tetragonality of the lattice in the structure that forms when the marinite is rapidly cooled.

In another experiment, a sample of the same form and the same chemical composition was heated to a temperature of 1010 ° C, molten salts were cooled in a composition of 41% KCl, 37% NaCl, 22% BaCl to a temperature of 745 ° C and then cooled in water (mode 2) . During the indicated heat treatment during cooling in the molten salt, the structural state of marinite was realized.

An analysis of the phase composition of the samples heat treated according to regimes 1 and 2 was carried out by scanning electron microscopy (SEM) and electron diffraction methods at large angles of reflection from the surface (EBSD). Typical SEM images of the etched surface structure of these samples are shown in FIGS. 7 and 8, respectively. The images in Figs. 7 and 8 are morphologically similar and topologically unambiguously interpreted as the projection of a complex relief formed as a result of etching, consisting of elements of a developed surface with a predominantly axial orientation and etched voids. A comparison of the results of SEM and EBSD analysis for these samples allows us to conclude that the elements of the developed surface are iron carbide, presumably Fe ₄ C _0.63 , and the volumes of voids formed after etching were filled with bcc Fe. Since such a structure was obtained by quenching of marinite, it can be concluded that iron carbides are formed from carbon-enriched regions, while carbon-depleted regions, when quenched, go into bcc Fe with an anomalously low tetragonality.

Thus, when comparing the above results, it can be argued that a suitable choice of temperature changes allows the implementation of marinite, the cooling of which leads to the formation of a structure containing a bct region with anomalously low tetragonality, which we will call “hardened marinite” or “RUTITE” in the future.

In order to find out how the kinetics of pearlite transformation changes if it proceeds from the previously realized structural state of marinite, the following experiments were carried out.

Heated to a temperature of 1005 ° C, cooled in air to a temperature of 745 ° C, followed by cooling in a molten saltpeter with a temperature of 443 ° C for 10 s and subsequent cooling in water. In this mode, a sorbitol structure is formed in the sample from the structural state of marinite realized during cooling, the volume fraction of which is close to 100% (Fig. 9).

Also, experiments were carried out on heating the samples to a temperature of 745 ° C with a holding time of 3 min, further cooling in a molten saltpeter with a temperature of 443 ° C for 10 s, and subsequent cooling in water. In this mode, a sorbitol structure is also formed in the sample from the structural state of marinite realized by heating (Fig. 10).

Both in that and in another experiment, the time of sorbitization of the samples was about 10 s. The time of sorbitization of a wire rod of the same diameter in the currently used technologies is 20-60 s [14, 15]. Thus, the implementation of marinite accelerates the formation of a sorbitol structure.

Thus, there is a whole series of experimental evidence of the existence of a special structural state (marinite) in the Fe – C system [16]. The formation of marinite leads to observed features in the temperature dependence of thermal expansion and magnetic susceptibility, and quenching of samples from the marinite state leads to the formation of rutite.

The temperature dependence of the magnetic susceptibility and thermal expansion (Fig. 16 and 2) indicates that the γ-α transformation upon cooling is preceded by the formation of magnetically ordered nanoscale regions. During cooling, in the temperature range A ₁ <T <T _{C, the} volume fraction of such regions grows and at T ~ A ₁ these regions combine, leading ultimately to the formation of the α phase.

As the calculations showed, carbon contributes to the stabilization of fct fluctuations with short-range magnetic order and thereby the formation of a structural state with quasistatic displacements in the Fe – C system. The formation of short-range magnetic order leads to a noticeable decrease in the elastic modulus C 'and a decrease in the lattice stability with respect to the fcc-bcc transformation. Therefore, with significant overcooling of marinite, the transformation will develop by the shear mechanism by loss of stability by the skeleton of “soft” magnetically ordered regions. As a result, an unusual structure is formed (hardened marinite - rutite) containing α-Fe with abnormally low tetragonality and regions enriched in carbon, or dispersed precipitates of carbides. Compared with upper and lower bainite, as well as granular and lamellar perlite of the same chemical composition, the indicated structural state is characterized by higher strength and hardness, and compared with martensite - increased ductility.

If the cooling of marinite is carried out at a lower rate, the leading process will be the decomposition of austenite into carbon. As a result, the transformation will proceed according to the pearlite mechanism and, depending on the cooling mode, will lead to the formation of either lamellar or granular perlite.

Thus, the implementation of marinite allows one to further obtain, depending on the modes of its cooling, either a structural state called rutite by the authors, which differs from martensite and bainite by a combination of high performance characteristics (crack resistance, ductility, hardness, strength), or ferrite-cementite structures (for example perlite of varying degrees of dispersion) for technologically shorter times.

The process of implementing marinite can be carried out either by cooling austenite, or by heating a structure whose phase composition is represented by ferrite and iron carbides. This explains the application of two methods of heat treatment.

A common feature for the claimed methods of heat treatment of products from alloys with a carbon content of up to 4.3% by weight is to provide the conditions necessary for the formation of marinite, and its subsequent cooling.

The first method can be characterized as the heat treatment of an alloy product by obtaining marinite upon cooling from the austenitic region and the formation of the required structural state containing specified fractions of perlite of varying degrees of dispersion and / or quenching structures during subsequent cooling.

In this case, the alloy is heated to create conditions that ensure the formation of austenite for the subsequent realization of marinite and further phase transformations, as a result of which the required structural state of the alloy will be obtained, for which the appropriate temperature reduction modes are selected or calculated.

As follows from the experiments, the necessary condition for the formation of marinite from austenite is the presence of austenite regions with a chemical composition close to eutectoid. Moreover, the larger the volume fraction of these areas, the greater the proportion of marinite can be realized.

The implementation of marinite is necessary to ensure the conditions for the formation of a given structural state: perlite of varying degrees of dispersion (for short technological times) and / or quenching structures.

Since, as experimentally established, rutite has a unique combination of properties (hardness, strength, ductility, fracture toughness), the products obtained as a result of heat treatment will have a set of consumer properties that are difficult to reach with traditional methods.

Further after the implementation of marinite, the cooling of an iron-based alloy product with a carbon content of up to 4.3% by weight is carried out according to the regimes that ensure the formation of specified fractions of perlite, rutite and hardening structures.

The range of carbon concentration in the alloy up to 4.3% by weight is due to the fact that for the implementation of marinite it is necessary to ensure the presence of alloy volumes in which the carbon concentration is close to eutectoid. As in alloys with a carbon concentration less than eutectoid, so in alloys with a concentration higher than eutectoid, by varying the temperature, conditions can be realized under which a carbon concentration close to eutectoid is achieved in some microvolumes. An increase in carbon concentration to values exceeding 4.3% by mass is not practical, since in this case the eutectoid concentration is achieved in microvolumes located inside the ledeburite.

In addition to carbon, other chemical elements may be present in the alloy both in the form of dopants and in the form of uncontrolled impurities, while their concentrations should be within the limits that allow the formation of austenite volumes in it when heating an alloy product, such that under certain conditions cooling conditions of eutectoid decay are realized.

Often, in practice, a given structural state is formed with the achievement of a regulated ratio of volume fractions of given structural components (perlite, rutite, and quenching structures). Based on this, it is advisable to set the fraction of austenite regions with a chemical composition close to eutectoid, sufficient to realize the given fraction of marinite, necessary for the formation of the required structural state.

The regimes that ensure the formation of a given fraction of marinite from austenite regions with a chemical composition close to eutectoid can in some cases be impossible to determine based on published data; therefore, it is advisable to determine them by calculation or experimentally.

The modes of heating and cooling, which will ensure the production of marinite from austenite with a chemical composition close to eutectoid, can be determined by calculation. For example, using the equations given in paragraph 5 of the claims.

In practice, it is advisable to supplement the calculation methods for determining the regimes that ensure the production of marinite from austenite with a chemical composition close to eutectoid, experimental, for example, by hardening the samples from fixed temperatures at different exposure times with them. In this experiment, you can use both samples whose chemical composition is identical to the chemical composition of the product alloy, and samples in which alloying impurity elements are present in the same concentration and the carbon concentration is eutectoid.

The fact of the existence of marinite is established by the presence of rutite in the quenched sample.

At the same time, it is advisable to establish the presence of rutite using diffraction methods as the most reliable. For example, diffraction of backscattered electrons, small-angle neutron scattering, x-ray diffraction.

After the implementation of marinite, further cooling of the alloy product is necessary to obtain a given structural state containing specified fractions of perlite and / or rutite. For this, an appropriate selection of cooling modes is carried out. It is possible to determine the cooling regime leading to the formation of a given structural state experimentally or by calculation. In this case, the experimental method includes quenching of the samples and subsequent determination of the volume fraction of perlite.

In particular cases of implementing the method, the calculation method is used to determine the cooling mode using the mathematical model given in paragraph 9 of the claims, which, after determining the thermokinetic constants for the model sample, allows the calculation of the cooling modes of products of arbitrary shape in various cooling media.

In special cases of implementation, after the formation of the required fraction of marinite, the cooling is carried out according to the regimes that do not include quenching until the formation of the specified fractions of the phases of ferrite and iron carbides in a given structural state. Processing according to this scheme allows one to accelerate the formation of a sorbitol structure (for example, for a bar with a diameter of 8 mm made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), heated to a temperature of 1005 ° C and cooled in air to 745 ° C, formation time sorbitol structure upon further cooling in a saltpeter melt with a temperature of 443 ° C is 10 s).

The cooling of the alloy product with speeds sufficient to suppress diffusion transformations after the formation of a given fraction of perlite, allows you to form the specified fraction of rutite and quenching structures.

In some cases, it is advisable to cool the alloy product with one or more pulses, for example, in the production of long products and wire. However, in this case there is a danger of the formation of quenching structures in the surface layer. Their formation can be avoided by alternating cooling pulses with pauses, during which the temperature of the surface layer will increase due to heat transfer from the inner layers of the alloy product to the external, as a result of which the quenching structures disappear in the surface layer or their formation is prevented.

In special cases, the cooling process is organized so that the pulses alternate with pauses, the duration of which is assigned sufficient for a given reduction in the temperature difference between the maximum and minimum values over the cross section of the alloy product in order to reduce internal thermal stresses.

In particular cases of implementing the method, the duration of each of the cooling pulses is assigned so that they do not lead to the formation of quenching structures in a given structural state. This condition must be observed, since with a decrease in temperature such cooling pulses can be formed that the heat of the central layers of the product may not be enough to eliminate the formed quenching structures in the surface layer.

In particular cases of implementation, it is advisable to perform cooling in such a way that one of the pulses provides the maximum decrease in the surface temperature of the alloy product without the formation of quenching structures. This is necessary in order to, as experiments have shown, accelerate the kinetics of perlite formation. For example, if after heating to a temperature of 1005 ° C and cooling in air to 745 ° C, further cooling in a molten saltpeter with a temperature of 443 ° C is preceded by water cooling with a single pulse of 0.2 s duration, the formation of a sorbitol structure occurs in less time for a bar with a diameter 8 mm steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0 , 0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), is 4 s.

In some cases, it is advisable after the formation in the alloy of a given fraction of austenite sufficient to obtain in a given structural state the specified fractions of perlite of varying degrees of dispersion and / or quenching structures, the temperature reduction required for the implementation of marinite should be carried out by cooling pulses.

In those cases where there is no technological need to continue pulsed cooling, after reaching the fractions of the phases of ferrite and iron carbides in the alloy, which subsequently provide their specified content in the final structural state, pulsed cooling is stopped, proceeding to monotonic cooling and / or isothermal aging.

The kinetics of the formation of marinite and the subsequent formation of perlite can be accelerated if, after heating the alloy to temperatures ensuring the formation of the required fraction of austenite in it, the alloy is subjected to plastic deformation. In this case, plastic deformation can be carried out in a wide temperature range, but a more effective result is achieved if the alloy is subjected to plastic deformation at a temperature t _Kfer ± 50 ° C, where t _Kfer is the temperature of the Curie point of ferrite, ° C (for example, as shown by experiments, if before cooling the melt of ammonium nitrate at a temperature 443 ° C to deform the sample a torsion type rheometer at a value of the relative deformation of the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of 745 ° C, while the formation of sorbitol with ruktury significantly reduced). For example, for a bar with a diameter of 8 mm made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0, 08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), the formation time of the sorbitol structure during processing according to this scheme is 3 s.

The greatest acceleration of the formation of marinite and the subsequent formation of perlite is achieved by combining the accelerating effects of pulsed cooling and plastic deformation in one technological scheme. For example, if, after heating to a temperature of 1005 ° C and cooling in air to 745 ° C, a sample of a cylindrical shape with a diameter of 8 mm is made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S ; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), in a torsion-type plastometer with a relative strain the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of deformation 745 ° C, further subjected to water cooling by a single sample pulse of duration 0.2 seconds and then placed be it in the nitrate melt with a temperature of 443 ° C, while the formation of sorbitol is 1 with the structure.

It has been experimentally established that exposure to the alloy with a constant or pulsed magnetic field during the disappearance of austenite and the implementation of marinite also reduces the heat treatment time of the alloy. Marinite is characterized by the presence of a developed short-range magnetic order. Therefore, the application of an external magnetic field will stimulate its formation.

In all methods, mainly water or aqueous media are used for cooling. In principle, cooling can be carried out by any of the known media used in metallurgical processes (water, oils, air, various emulsions, salt melts). However, since some operations require cooling at high speeds, it is advisable to use media with high heat capacity, which include water, solutions and emulsions based on it.

The second method can be characterized as the heat treatment of an alloy product by obtaining marinite during heating and the formation of the desired structural state containing predetermined perlite fractions of varying degrees of dispersion and / or quenching structures during subsequent cooling.

The method described in paragraph 22 of the claims, it is advisable to apply when there are no technological requirements to ensure high heating temperatures (heat drawing, forging, warm upsetting, warm pressing).

As experiments have shown, for the formation of marinite in the alloy when it is heated from room temperature, a necessary condition is the presence of volumes (regions) in which the carbon content, taking into account the presence of other chemical elements in these volumes, is close to eutectoid. Thus, depending on the structural state of the alloy, marinite will form either during the dissolution of cementite of pearlite colonies, or in volumes containing a sufficient number of carbides, or in volumes of quenching structures of the corresponding chemical composition.

The implementation of marinite is necessary to ensure the conditions for the formation in a given structural state of specified perlite fractions of varying degrees of dispersion (for short technological times) and / or quenching structures.

Since, as experimentally established, rutite has a unique combination of properties (hardness, strength, ductility, fracture toughness), the products obtained as a result of heat treatment will have a set of consumer properties that are difficult to reach with traditional methods.

Further after the implementation of marinite, the cooling of an iron-based alloy product with a carbon content of up to 4.3% by weight is carried out according to the regimes that ensure the formation of specified fractions of perlite, rutite and hardening structures.

The range of carbon concentration in the alloy up to 4.3% by weight is due to the fact that for the implementation of marinite it is necessary to ensure the presence of alloy volumes with a carbon content close to eutectoid. As in alloys with a carbon concentration less than eutectoid, in alloys with a concentration higher than eutectoid, by varying the temperature, conditions can be realized under which this condition is satisfied for some volumes of the alloy. An increase in carbon concentration to values exceeding 4.3% by mass is not practical, since in this case the eutectoid concentration is achieved in microvolumes located inside the ledeburite.

In addition to carbon, other chemical elements may be present in the alloy, both in the form of dopants and in the form of uncontrolled impurities, while their concentrations must be within the limits that allow under certain conditions the eutectoid decay in the alloy.

Often, in practice, a given structural state is formed with the achievement of a regulated ratio of volume fractions of given structural components (perlite, rutite, and quenching structures). Based on this, it is advisable to set the proportion of marinite sufficient to form the desired structural state.

Modes that ensure the formation of a given fraction of marinite, in some cases it is impossible to determine based on literature data, so it is advisable to determine them calculated or experimentally.

Modes of heating and cooling, which will provide conditions for the implementation of marinite, can be determined by calculation. For example, using the equations given in paragraph 26 of the claims.

In practice, it is advisable to supplement the calculation methods for determining the regimes that ensure the implementation of marinite, experimental, for example, by hardening the samples from fixed temperatures at different exposure times with them. In this experiment, you can use both samples whose chemical composition is identical to the chemical composition of the product alloy, and samples in which alloying impurity elements are present in the same concentration and the carbon concentration is eutectoid.

The fact of the existence of marinite is established by the presence of rutite in the quenched sample.

As in the first method of heat treatment of products from alloys, in this method, the presence of rutite is established using diffraction methods; determine the cooling regimes leading to the formation of a given amount of perlite in a given structural state experimentally according to clause 29 or calculated by clause 30.

In special cases of implementation, after the formation of the required fraction of marinite, the cooling is carried out according to regimes that do not include quenching until the formation of the specified fractions of the phases of ferrite and iron carbides in the final structural state. Processing according to this scheme allows one to accelerate the formation of a sorbitol structure (for example, for a bar with a diameter of 8 mm made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), heated to a temperature of 745 ° C and kept at this temperature for 3 min, time the formation of a sorbitol structure upon further cooling in a saltpeter melt with a temperature of 443 ° C is 10 s).

The cooling of the alloy product with speeds sufficient to suppress diffusion transformations after the formation of a given fraction of perlite, allows you to form the specified fraction of rutite and quenching structures.

In some cases, it is advisable to cool the alloy product with one or more pulses, for example, in the production of long products and wire. However, in this case there is a danger of the formation of quenching structures in the surface layer. Their formation can be avoided by alternating cooling pulses with pauses, during which the temperature of the surface layer will increase due to heat transfer from the inner layers of the alloy product to the external, as a result of which the quenching structures disappear in the surface layer or their formation is prevented.

In special cases, the cooling process is organized so that the cooling pulses alternate with pauses, the duration of which is assigned sufficient for a given reduction in the temperature difference between the maximum and minimum values over the alloy cross section in order to reduce internal thermal stresses.

As in the first method, in particular cases of the implementation of this method, the duration of each of the cooling pulses is prescribed so that they do not lead to the formation of quenching structures in a given structural state. This condition must be observed, since during cooling, such cooling pulses can be formed that the heat of the central layers of the product may not be enough to eliminate the formed quenching structures in the surface layer.

In particular cases of implementation, it is advisable to perform cooling in such a way that one of the pulses ensures the maximum decrease in the surface temperature of the product without the formation of quenching structures. This is necessary in order to, as experiments have shown, accelerate the kinetics of perlite formation. For example, if, after heating to a temperature of 745 ° C and holding at this temperature for 3 minutes, further cooling in a saltpeter melt with a temperature of 443 ° C is preceded by water cooling with a single pulse of 0.2 s duration, the formation of a sorbitol structure takes place in less time for the bar 8 mm in diameter made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), is 4 s.

In those cases where there is no technological need to continue pulsed cooling, after reaching the fractions of the phases of ferrite and iron carbides in the alloy, which subsequently provide their specified content in the final structural state, pulsed cooling is stopped, proceeding to monotonic cooling and / or isothermal aging.

The kinetics of perlite formation can be accelerated if, after the implementation of marinite, the alloy is subjected to plastic deformation. The kinetics of the formation of marinite and the subsequent formation of perlite can be accelerated if the alloy is subjected to plastic deformation when the alloy is heated before or during the implementation of marinite.

In this case, plastic deformation can be carried out in a wide temperature range, but a more effective result is achieved if the alloy is subjected to plastic deformation at a temperature t _Kfer ± 50 ° C, where t _Kfer is the temperature of the Curie point of ferrite, ° C (for example, as shown by experiments, if Before cooling in a molten saltpeter with a temperature of 443 ° C, deform the sample in a torsion-type plastometer with a relative strain of the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of 745 ° C, then the formation of sorbitol st structure is significantly reduced). For example, for a bar with a diameter of 8 mm made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0, 08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), the formation time of the sorbitol structure during processing according to this scheme is 3 s.

As with the first method, the greatest acceleration of perlite formation is achieved by combining the accelerating effects of impulse cooling and plastic deformation in one technological scheme.

For example, if after heating to a temperature of 745 ° C and holding at this temperature for 3 min, a sample of a cylindrical shape with a diameter of 8 mm is made of steel with a composition close to eutectoid (0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities), in a torsion-type plastometer with a relative deformation of the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of deformation 745 ° C, further subjected to water cooling by a single sample pulse of duration 0.2 and then place it in the ammonium nitrate melt with a temperature of 443 ° C, while the formation of sorbitol is 1 with the structure.

In all methods, mainly water or aqueous media are used for cooling. In principle, cooling can be carried out by any of the known media used in metallurgical processes (water, oils, air, various emulsions, salt melts). However, since some operations require cooling at high speeds, it is advisable to use media with high heat capacity, which include water, solutions and emulsions based on it.

The method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight is illustrated by examples of their implementation and graphic images. On figa presents the dependence of magnetic susceptibility on temperature, on figb - its fragment on an enlarged scale in the temperature range 740-800 ° C. Figure 2 shows the dependence of the coefficient of thermal expansion α (T) on temperature (arrows indicate the direction of temperature change). Figure 3 presents the change in the concentration of carbon in carbide Fe ₃ C _X depending on the temperature. Figure 4 shows the dependence of the exchange energy J ₀ on the tetragonal strain s / a for the volume per atom V = 11.00А ³ (curve 1), 11.44А ³ (curve 2), 12.00 А ³ (curve 3), where the negative values correspond to the preferences of ferromagnetic, and positive ones correspond to antiferromagnetic ordering of moments. On figa, 5b and 5c presents examples of the microstructure of a sample of eutectoid steel, formed after exposure at 745 ° C for about 3 minutes and subsequent quenching in water (magnification × 30000). On figa presents x-ray hardened from a temperature of 1100 ° C of the sample, and on figb - x-ray hardened from a temperature of 745 ° C after exposure at this temperature for about 3 minutes, where the dashed line shows the decomposition of the observed line profile {110} into components . On figa and 7b presents examples of the microstructure of a sample of eutectoid steel, heated to 745 ° C, aged at this temperature for 2 min 55 s and cooled in water. On figa and 8b presents examples of the microstructure of a sample of eutectoid steel, heated to 1010 ° C, cooled in chlorine salt with a temperature of 745 ° C to the temperature of the salt and then cooled in water. Figure 9 shows the microstructure of a sample of eutectoid steel heated to a temperature of 1005 ° C, cooled in air to a temperature of 745 ° C, cooled in a molten saltpeter with a temperature of 443 ° C for 10 s and then cooled in water. Figure 10 shows the microstructure of a sample of eutectoid steel heated to a temperature of 745 ° C, maintained at this temperature for 3 minutes, cooled in a molten saltpeter with a temperature of 443 ° C for 10 s and then cooled in water.

Example 1. In its most general form, the first method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight (claim 1 of the claims) was implemented as follows.

The product (billet) was heated to temperatures ensuring the formation of a given fraction of austenite sufficient to obtain, in a given structural state, specified fractions of perlite of varying degrees of dispersion and / or quenching structures. If the specified final structural state should not contain a fraction of the initial structure that was in the alloy product before the start of heat treatment, then the fraction of austenite in the heated product will be 100%, otherwise 100% minus the fraction of the initial structure.

Then, the temperature of the product was reduced according to previously experimentally or computationally defined modes, ensuring the formation of a predetermined fraction of austenite regions with a chemical composition close to eutectoid, followed by obtaining a predetermined fraction of marinite in them and subsequent cooling according to the regimes providing the formation of a given structural state with perlite of varying degrees of dispersion and / or quenching structures.

When implementing the method using the experimental determination of the regimes ensuring the production of marinite from areas of austenite with a chemical composition close to eutectoid, the conditions for the existence of marinite were first determined for each alloy.

For this, the samples, representing round rods with a diameter of 6.5-8 mm and a length of 500-800 mm, were heated to a temperature of 1050 ° C, which was obviously higher than the temperature of existence of marinite and ensured the formation of austenite with a volume fraction of 100%. At this temperature, the samples were kept for about 15 minutes, and then cooled to temperatures from the interval 815-500 ° C in increments of 15 ° C, providing exposure at the indicated temperatures from 0 to 600 s, and quenched.

During these actions, a temperature-time curve was recorded from a thermocouple hammered into the sample to a depth of 1/2 of the radius of the rod. To record the cooling curves, a well-known technique was used, for example, an analog input module for connecting ADAM 6018 thermocouples. Hardened samples were studied by known methods, in particular, diffraction methods (X-ray and neutron diffraction). Based on the results of the study, a conclusion was drawn about the existence of marinite in the sample, while the presence of marinite in the sample was judged by the presence of rutite in the sample, quenched from fixed temperatures at various holding times.

Based on these experiments, the temperature-time conditions for the realization of marinite in the alloy were determined.

When calculating the determination of temperature reduction regimes ensuring the production of marinite from areas of austenite with a chemical composition close to eutectoid, the temperature range for the implementation of marinite was set, satisfying the conditions

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода, определяемая методом квантого-механического расчета, T_TEX - температура, выбираемая с учетом технологических ограничений, и выбирали скорость охлаждения, при которой зависимость температуры охлаждения от времени T(t) удовлетворяет условию T(t)<Θ(t), где зависимость Θ(t) определена линиями начала перлитного и бейнитного превращений на термокинетической диаграмме.Where

is the temperature of local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum-mechanical calculation, T _TEX is the temperature chosen taking into account technological limitations, and the cooling rate was chosen at which the dependence of the cooling temperature on time T (t) satisfies the condition T (t ) <Θ (t), where the dependence Θ (t) is determined by the lines of the beginning of pearlitic and bainitic transformations on the thermokinetic diagram.

The regimes of temperature reduction from the realized marinite, leading to the formation of a given amount of perlite of the required degree of dispersion in a given final structural state, were carried out either experimentally, by quenching the experimental samples and subsequent determination of their structural state, or by calculation.

In the experimental determination of the cooling regimes leading to the formation of a given amount of perlite of the required degree of dispersion in a given structural state, the experimental samples were quenched from temperatures of 745-440 ° C and their structural state was determined. For this, the experimental samples, which are cylinders with a diameter of 8 mm and a length of 500 mm, with thermocouples milled to a depth of 2 mm, were cooled from temperatures of 745-500 ° C in air or in a saltpeter melt with a temperature of 440 ° C and quenched from various temperatures (730 -440 ° C) as measured by thermocouple. The structural state of quenched samples was determined by metallographic and diffraction methods.

Experimentally obtained cooling curves were used to determine the thermokinetic constants, allowing calculations of the cooling regimes of products of arbitrary shape in various cooling media. The determination of thermokinetic constants was carried out, ensuring that the experimental temperature dependences of time coincide with the dependences obtained by solving a system of equations that includes the heat equation

имеет размерность м^-1, r - радиус-вектор точки, в которой производятся вычисления, ρ - плотность, измеряемая в кг/м³, q_i - удельная энтальпия образования i-й фазы, измеряемая в Дж/кг, f_i(r, t, T) - безразмерная массовая доля фазы i в окрестности точки r в момент времени t при температуре T,

- поток тепла, измеряемый в Дж/(м²·с), H(r, t, T) - распределение энтальпии, измеряемой в Дж/м³, по объему образца,where is the operator

has the dimension m ^-1 , r is the radius vector of the point at which the calculations are made, ρ is the density measured in kg / m ³ , q _i is the specific enthalpy of formation of the i-th phase, measured in J / kg, f _i (r , t, T) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T,

is the heat flux measured in J / (m ² · s), H (r, t, T) is the distribution of the enthalpy measured in J / m ³ over the volume of the sample,

energy conservation equation

- удельная теплоемкость фазы i при постоянном давлении от температуры, измеряемая в Дж/(кг·К),Where

- the specific heat of phase i at constant pressure versus temperature, measured in J / (kg · K),

and kinetic equation

where M _ik (T, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation, and using the above equations and found thermokinetic constants for calculating the dependence of the heat flux on time over the surface of the product, providing a trajectory of temperature change over time, leading to the formation of a given structural state.

Based on the data obtained, a method of heat treatment of products from iron-based alloys was implemented to obtain products with a given structural state. To do this, first, the workpiece was heated to temperatures ensuring the formation of austenite. After that, the preform was cooled according to the regimes ensuring the production of marinite from areas of austenite with a chemical composition close to eutectoid. Then, further cooling of the alloy product was carried out according to the regimes ensuring the formation of a given fraction of perlite of the required degree of dispersion and / or quenching structures.

Thus, as a result of experimental and / or computational selection of the conditions for the formation (realization) of marinite and the corresponding modes (trajectories) of subsequent cooling, it is possible to obtain products with a given structural state with a perlite content of the required degree of dispersion and / or quenching structures.

In special cases, the implementation of the method to ensure the production of products with a given structural state and the required mechanical properties and to reduce the technological times for producing a pearlite structure, it is advisable to apply a magnetic field to the workpiece or workpiece, subject it to plastic deformation and lower the temperature using pulse cooling with different pulse times and pauses between them.

Example 2. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following predetermined structural state: ~ 100% sorbitol, for short technological sorbitol times. For this, the preform was heated to an experimentally set temperature of 1005 ° C with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is ~ 100%.

In order to determine the modes that ensure the production of marinite from austenite with a chemical composition close to eutectoid, in accordance with paragraph 5 of the claims, the temperature range was determined in which it is possible to form marinite that satisfies the conditions

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода определялась методом квантово-механического расчета и составила ~1100 K или 817°С, а T_TEX выбрана равной 975 К или 702°C.Where

- the temperature of local ferromagnetic ordering in austenite near the carbon atom was determined by quantum mechanical calculation and amounted to ~ 1100 K or 817 ° C, and T _{TEX was} chosen equal to 975 K or 702 ° C.

To clarify the modes of formation of marinite determined by calculation, experimentally obtained cooling curves in air from the indicated heating temperatures (~ 1005 ° C). The experimental samples were round rods with a diameter of 6.5-8 mm and a length of 500-800 mm. Cooling curves were recorded from a thermocouple hammered into the sample to a depth of 1/2 of the radius of the rod. To record the cooling curves, we used an analog input module for connecting ASAM 6018 thermocouples. During cooling in air, the samples were quenched from various temperatures from the range of 700–820 ° С (in increments of 10 ° C). After which the samples were investigated by various known methods. In the samples quenched from 730 to 760 ° C, structural features characteristic of rutite were observed: bct regions with anomalously low tetragonality (about 0.5%) and hardness of ~ 750 HV. Consequently, in the studied temperature range, under the indicated cooling conditions, marinite was realized in samples of steel 85. As the experiment showed, in order to realize ~ 100% marinite, it is necessary to carry out cooling in air to temperatures of 740-750 ° C.

Knowing the conditions for the formation of marinite, we determined the kinetics of the formation of a given final structural state under the cooling mode selected for the model experiment.

For this, in a model sample, which is a cylinder with a diameter of 8 mm and a length of 500 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, according to the readings of a thermocouple chased to a depth of 2 mm, recorded a change in its temperature upon cooling in air from a temperature of 745 ° C.

Using the experimentally obtained time dependence of the sample temperature, the coefficients of the calculation model characterizing the material and heat transfer process (thermophysical and kinetic constants) were determined by calculation.

The calculation was carried out as follows. For the transition from marinite to perlite, the following functional dependence is valid, which determines the rate of change with time of the dimensionless mass fraction of perlite:

Here: k ₁ = c ₁ × ΔT ₀

k ₂ = c ₂ × ΔTΔT ₀ ^1/3

k ₃ = c ₂ × ΔTΔT ₀ ^1/3

ΔТ, measured in degrees Kelvin, is the deviation of the temperature from the temperature of phase equilibrium, ΔТ ₀ , K is the deviation of the temperature from the temperature of phase equilibrium at the beginning of the phase transformation, with ₁ (having dimension K ^-1 ) and c ₂ (measured in K ^{-4 / 3} ) - kinetic constants.

After the transition to the finite-difference form, the energy conservation equation for the cell of the difference grid will look like:

where c _m (J / kg · K) is the heat capacity of marinite, c _p (J / kg · K) is the heat capacity of perlite, m ₀ (kg) is the mass of the finite difference mesh, q (J / kg) is the thermal effect of the phase transformations, Q (J) is the influx of heat from the outside, the data without a stroke and with a stroke refer to the start and end times, respectively.

The heat equation determines the conductive heat influx, measured in J / m ² · s through the cell surface of the finite-difference grid:

where λ is the thermal conductivity coefficient in (J / m · s · K) (reference value), dT / dr is the temperature gradient along the radius of the sample.

When a model sample with a temperature of more than 600 ° C is cooled in air, the heat flux on the surface can be considered purely radiative, in which the boundary conditions on the surface of the sample are determined by the Stefan-Boltzmann law:

Q _s = ε · σ · T ⁴ ,

where ε equal to 0.8 is the dimensionless blackness coefficient of steel, σ is the Boltzmann constant, having a dimension of J / m ² · s · K ⁴ , T is the temperature of the surface of the sample.

The coefficients of the calculation model, determined from the condition that the experimental and calculated dependences of the temperature of the model sample on time are given in table 1.

Table 1 Parameter Exp. No. 1 Exp. Number 2 Critical temperature ° C 755 752 The thermal effect of the conversion, j / kg 8 · 10 ⁴ 7.7 · 10 ⁴ The incubation period of transformation, with 24 26 Kinetic constants: c ₁ 10 ^-7 10 ^-7 c ₂ 3.3 · 10 ^-4 3.5 · 10 ^-4 Specific heat of the model sample, J / kg * deg Before phase transition (at a temperature of 737 ° C) 630 630 After a phase transition (at a temperature of 617 ° C) 700 660

Then, using the obtained coefficients, the dependences of temperature on time were calculated during cooling of the sample from a temperature of 745 ° C in a saltpeter melt. The calculation was made for various temperatures of the molten saltpeter using reference values of the heat transfer coefficients. As a result, the melt temperature of 443 ° C was chosen as providing the most complete transformation (formation of a finely dispersed pearlite structure) during 10 s. Then carried out rapid cooling in water (quenching).

Thus, it was found that in the temperature range from 1005 to 745 ° C, it is necessary to carry out cooling in air, then to carry out cooling in the melt of nitrate with a temperature of 443 ° C for at least 10 seconds, and subsequent cooling to room temperature with a decrease rate surface temperature 90-110 deg / s, corresponding to cooling in water. After that, a blank of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C and its cooling was carried out along the indicated trajectories. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 10 s. Metallographic analysis and diffraction studies of a sample of the billet cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given final structural state. The required technical result is achieved.

Example 3. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following specified structural state: ~ 80% sorbitol for short technological sorbitol times and ~ 20% quenching structures (martensite). For this, the preform was heated to an experimentally set temperature of 1005 ° С with the formation of a volume fraction of austenite of ~ 100%.

To determine the modes of realization of a given fraction of marinite from areas of austenite with a chemical composition close to eutectoid, experimentally obtained cooling curves in air from the specified heating temperature. The samples were round rods with a diameter of 6.5-8 mm and a length of 500-800 mm. Cooling curves were recorded from a thermocouple hammered into the sample to a depth of 1/2 of the radius of the rod. To record the cooling curves, we used an analog input module for connecting ADAM 6018 thermocouples. During cooling in air, the samples were quenched from various temperatures from the range of 700–820 ° C (in increments of 10 ° C). After which the samples were investigated by various known methods. In the samples quenched from 730 to 760 ° C, structural features characteristic of rutite were observed: bct regions with anomalously low tetragonality (about 0.5%) and hardness of ~ 750 HV. Therefore, in the studied temperature range under the indicated cooling conditions, marinite was realized in steel 85. As the experiment showed, in order to realize ~ 80% of marinite, it is necessary to carry out cooling in air to a temperature of ~ 750 ° C.

Knowing the conditions for the formation of marinite, we carried out the experimental determination of the kinetics of the formation of a given final structural state. For this purpose, in the indicated samples, according to the readings of a thermocouple chased to a depth of 2 mm, a change in their temperature was recorded upon cooling in the molten saltpeter with a temperature of 440 ° C from a temperature of 750 ° C. Using the experimentally obtained time dependence of the temperature of the sample, the samples were quenched in water as a function of various temperatures from the moment of the onset of evidence of heat release on the cooling curve associated with the pearlite transformation (approx. 610-620 ° C) with subsequent determination of their structural state. As a result of the experiment, it was found that for the formation of ~ 80% perlite (sorbitol), it is necessary to ensure that the samples stay in the saltpeter melt for 7 s and subsequent quenching in water. In the sample volume that was not transformed into sorbitol (~ 20%), a quenching structure (martensite) was formed.

Thus, it was found that in the temperature range from 1005 to 750 ° C, it is necessary to carry out cooling in air, then to carry out cooling in the melt of nitrate with a temperature of 443 ° C for 7 seconds, and subsequent cooling to room temperature with a rate of decrease in surface temperature 90-110 deg / s, corresponding to cooling in water. After that, the billet made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C and its cooling was carried out along the indicated trajectories. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. Metallographic analysis and diffraction studies of the sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 80%, and the volume fraction of quenching structures (martensite) is ~ 20%, which corresponds to a given structural state. The required technical result is achieved.

Example 4. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following predetermined structural state: ~ 100% rutite. For this, the preform was heated to an experimentally set temperature of 1005 ° C with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is 400%.

The modes that ensure the specified fraction of marinite from austenite regions with a chemical composition close to eutectoid in the steel of the specified chemical composition were determined first by calculation, and then refined by the experimental method, as described in Example 2, for cooling salts with a composition of 41% in the melt KCl, 37% NaCl, 22% BaCl with a temperature of 740 ° C. As the experiment showed, in order to realize ~ 100% marinite, it is necessary to carry out cooling in the indicated medium to the melt temperature.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that in the temperature range from 1005 to 740 ° C it is necessary to carry out cooling in a melt of salts with a composition of 41% KCl, 37% NaCl, 22% BaCl with a temperature of 740 ° C to a temperature of the molten salt, and subsequent cooling to room temperature lead at a rate of surface temperature reduction of 90-110 deg / s, corresponding to cooling in water. After that, the billet made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C and its cooling was carried out along the indicated trajectories. Cooling was carried out using for this purpose a molten salt of the specified composition with a temperature of about 740 ° C and industrial water. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 5. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, the following specified structural state: ~ 100% sorbitol, for technological sorbitol times not exceeding 5 s. For this, the preform was heated to an experimentally set temperature of 1005 ° C with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is ~ 100%.

The temperature reduction regimes that ensure that the specified fraction of marinite from the austenite regions with a chemical composition close to eutectoid in the specified alloy is realized were determined first by calculation and then refined by the experimental method, as described in Example 2. As shown by the experiment, to realize ~ 100 % marinite, it is necessary to carry out cooling in air to temperatures of 740-750 ° C.

After the implementation of marinite, cooling was carried out by a pulse with a single water pulse of 0.2 s duration. An impulse of such a duration ensured a maximum decrease in surface temperature and did not lead to the formation of quenching structures in a given structural state. After that, pulsed cooling was stopped and switched to monotonous cooling in a molten saltpeter with a temperature of 443 ° C. The flow time of the pearlite transformation in the specified method was about 4 s. Then carried out rapid cooling in water (quenching).

Thus, it was found that in the temperature range from 1005 to 745 ° C, it is necessary to carry out cooling in air, then to perform cooling with a single water pulse of 0.2 s duration, followed by cooling in a molten saltpeter with a temperature of 443 ° C for at least 4 seconds, and further cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to cooling in water. After that, the billet made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C and its cooling was carried out along the indicated trajectories. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 4 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 6. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, the following specified structural state: ~ 100% sorbitol, for technological sorbitol times not exceeding 3 s. For this, the preform was heated to an experimentally set temperature of 1005 ° С with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is ~ 100%.

The temperature reduction regimes ensuring the implementation of the specified fraction of marinite in the specified alloy from austenite regions with a chemical composition close to eutectoid were determined by the experimental method specified in Example 3. As shown by the experiment, in order to realize ~ 100% marinite, it is necessary to cool in air to temperatures 740-750 ° C.

After the implementation of marinite, a steel sample of the specified chemical composition was subjected to plastic deformation at a relative deformation of the surface layer of 23% and a strain rate of 0.2 s ^-1 at deformation temperatures of t _Kfer ± 50 ° C, where t _Kfer , ° C is the temperature of the Curie point of ferrite, at a temperature of 745 ° C in this case. Further cooling was carried out in a saltpeter melt with a temperature of 443 ° C. The flow time of the pearlite transformation in the specified method was about 3 s. Then carried out rapid cooling in water (quenching).

Thus, it was found that in the temperature range from 1005 to 745 ° C, it is necessary to carry out cooling in air, then plastic deformation of the sample is carried out at a relative strain of the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of 745 ° C and subsequent cooling in the molten saltpeter with a temperature of 443 ° C for at least 3 seconds, and further cooling to room temperature with a rate of decrease in surface temperature of 90-110 deg / s, corresponding to cooling in water. After that, a bar made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C, subjected to cooling in air to a temperature of 745 ° C, its deformation was carried out at this temperature, and cooling along the indicated trajectories. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 3 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 7. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, the following specified structural state: ~ 100% sorbitol, for technological sorbitol times not exceeding 2 s. For this, the preform was heated to an experimentally set temperature of 1005 ° С with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is ~ 100%.

The modes that ensure the specified fraction of marinite from austenite regions with a chemical composition close to eutectoid in the steel of the indicated chemical composition were determined by the experimental method specified in Example 3. As shown by the experiment, in order to realize ~ 100% of marinite, it is necessary to cool in air to temperatures 740-750 ° C.

After the implementation of marinite, a steel sample of the indicated chemical composition was first subjected to plastic deformation at a relative deformation of the surface layer of 23% and a strain rate of 0.2 s ^-1 at deformation temperatures of t _Kfer ± 50 ° C, where t _Kfer , ° C is the temperature of the Curie point of ferrite , at a temperature of 745 ° C in this case, and then pulsed cooling was performed with a single water pulse of 0.2 s duration. An impulse of such a duration ensured a maximum decrease in surface temperature and did not lead to the formation of quenching structures in a given structural state. After that, pulsed cooling was stopped and switched to monotonous cooling in a molten saltpeter with a temperature of 443 ° C. The flow time of pearlite transformation in the specified method was 1 s. Then carried out rapid cooling in water (quenching).

Thus, it was found that in the temperature range from 1005 to 745 ° C, it is necessary to carry out cooling in air, then plastic deformation of the sample is carried out at a relative strain of the surface layer of 23% and a strain rate of 0.2 s ^-1 at a temperature of 745 ° C, then carry out cooling with a single water pulse of 0.2 s duration, followed by cooling in the molten saltpeter with a temperature of 443 ° C for 1 second, and further cooling to room temperature with a rate of temperature decrease s surface 90-110 deg / s, corresponding to cooling in water. After that, a bar made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C, subjected to cooling in air to a temperature of 745 ° C, its deformation was carried out at this temperature, and cooling along the indicated trajectories. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 1 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 8. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following predetermined structural state: ~ 100% rutite. For this, the preform was heated to an experimentally set temperature of 1005 ° C with the formation of a volume fraction of austenite of ~ 100%.

For the indicated chemical composition, the maximum achievable volume fraction of austenite regions with a chemical composition close to eutectoid is ~ 100%.

The modes that ensure the specified fraction of marinite from austenite regions with a chemical composition close to eutectoid in the steel of the specified chemical composition were determined first by calculation, and then refined by the experimental method, as described in example 2, but after heating the workpiece to temperatures ensuring the formation of the required fraction of austenite in it, the workpiece was exposed to a magnetic field.

For this, the preform heated to a temperature of 1005 ° C was placed in a solenoid inside which a constant magnetic field of 0.5 T was created and subjected to cooling in air. As a result of the magnetic field, the formation of marinitis was stimulated. Cooling to a temperature of 800 ° C was sufficient to realize ~ 100% marinite.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that during cooling in the temperature range from 1005 to 800 ° C, the workpiece must be exposed to a constant magnetic field, and then cooling to room temperature with a surface temperature reduction rate of 90-110 deg / s, corresponding to cooling in water . After that, a bar made of steel of grade 85 in the form of a rod was heated to a temperature above 1005 ° C, it was cooled in air under the application of a magnetic field of 0.5 T and subsequent rapid cooling (quenching). Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 9. In its most general form, the second method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight (claim 22 of the claims) was implemented as follows.

First, experimentally or by calculation, the modes of implementation of marinite were identified in the process of heating the alloy, then the product (billet) was heated to ensure the formation of marinite. After that, cooling was carried out according to the regimes ensuring the formation of a given structural state with a given fraction of perlite of varying degrees of dispersion and / or quenching structures.

When implementing the method using the experimental determination of the modes that ensure the production of marinite, first, for each alloy, the conditions for its formation were determined.

For this, the samples, which are round rods with a diameter of 6.5-8 mm and a length of 500-800 mm, were heated to temperatures from the interval 500-800 ° C in increments of 15 ° C, providing exposure at the indicated temperatures from 0 to 600 s, and hardened.

During these actions, a temperature-time curve was recorded from a thermocouple hammered into the sample to a depth of 1/2 of the radius of the rod. To record the cooling curves, a well-known technique was used, for example, an analog input module for connecting ADAM 6018 thermocouples. Hardened samples were studied by known methods, in particular, diffraction methods (X-ray and neutron diffraction). Based on the results of the study, a conclusion was drawn about the existence of marinite in the sample, while the presence of marinite in the sample was judged by the presence of rutite in the sample, quenched from fixed temperatures at various holding times.

Based on these experiments, the temperature-time conditions for the realization of marinite in the alloy were determined.

When calculating the determination of the modes that ensure the implementation of marinite, we set the temperature range of the heating, satisfying

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода, определяемая методом квантого-механического расчета, Т_х - эвтектоидная температура для сплава соответствующего химического состава, и задавали время выдержки t в секундах, необходимое для растворения заданной доли цементита f_c, определяемое из уравненияWhere

is the temperature of the local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum mechanical calculation, T _x is the eutectoid temperature for the alloy of the corresponding chemical composition, and the exposure time t in seconds required to dissolve a given fraction of cementite f _c determined from the equation

f _c = 1.05 f _C0 exp (-kt ⁿ ),

where f _C0 is the dimensionless fraction of cementite at the initial instant of time, 4>n> 3 is a power exponent, k is a parameter that determines the dissolution rate of cementite in an alloy of the corresponding chemical composition at a temperature T in s ^-n .

The regimes of temperature reduction from the realized marinite, leading to the formation of a given amount of perlite of the required degree of dispersion in a given final structural state, were carried out either experimentally, by quenching the experimental samples and subsequent determination of their structural state, or by calculation.

In the experimental determination of the cooling regimes leading to the formation of a given amount of perlite of the required degree of dispersion in a given structural state, the experimental samples were quenched from temperatures of 745–440 ° C and their structural state was determined. To do this, experimental samples, which are cylinders with a diameter of 8 mm and a length of 500 mm, with thermocouples milled to a depth of 2 mm, were cooled from temperatures of 745-500 ° С in air or in a saltpeter melt with a temperature of 440 ° С and quenched from various temperatures (730 -440 ° C) as measured by thermocouple. The structural state of quenched samples was determined by metallographic and diffraction methods.

Experimentally obtained cooling curves were used to determine the thermokinetic constants, allowing calculations of the cooling regimes of products of arbitrary shape in various cooling media. The determination of thermokinetic constants was carried out, ensuring that the experimental temperature dependences of time coincide with the dependences obtained by solving a system of equations that includes the heat equation

имеет размерность м^-1, r - радиус-вектор точки, в которой производятся вычисления, ρ - плотность, измеряемая в кг/м³, q_i - удельная энтальпия образования i-й фазы, измеряемая в Дж/кг, f_i(r, t, T) - безразмерная массовая доля фазы i в окрестности точки r в момент времени t при температуре Т,

- поток тепла, измеряемый в Дж/(м²·с), Н(r, t, T) - распределение энтальпии, измеряемой в Дж/м³, по объему образца,where is the operator

has the dimension m ^-1 , r is the radius vector of the point at which the calculations are made, ρ is the density measured in kg / m ³ , q _i is the specific enthalpy of formation of the i-th phase, measured in J / kg, f _i (r , t, T) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T,

is the heat flux measured in J / (m ² · s), N (r, t, T) is the distribution of the enthalpy measured in J / m ³ over the volume of the sample,

energy conservation equation

- удельная теплоемкость фазы i при постоянном давлении от температуры, измеряемая в Дж/(кг·К)Where

- specific heat of phase i at constant pressure versus temperature, measured in J / (kg · K)

and kinetic equation

where M _ik (T, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation, and using the above equations and found thermokinetic constants for calculating the dependence of the heat flux on time over the surface of an alloy product, providing a trajectory of temperature change over time, leading to the formation of a given structural state.

Based on the data obtained, a method of heat treatment of products from iron-based alloys was implemented to obtain products with a given structural state. To do this, first, the billet was heated to ensure the formation of the required fraction of marinite. Then, the alloy product was cooled according to the regimes ensuring the formation of a predetermined perlite fraction of the required degree of dispersion and / or quenching structures.

Thus, as a result of experimental and / or computational selection of the conditions for the formation (realization) of marinite and the corresponding modes (trajectories) of subsequent cooling, it is possible to obtain products with a given structural state with a perlite content of the required degree of dispersion and / or quenching structures.

In special cases, the implementation of the method to ensure the receipt of products with a given structural state and the required mechanical properties and to reduce technological times for producing a pearlite structure, it is advisable to subject the workpiece or preform to plastic deformation and lower the temperature using pulse cooling with different pulse times and pauses between them.

Example 10. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following predetermined structural state: ~ 100% sorbitol, for short technological sorbitol times.

For this, the preform was heated to a temperature determined in accordance with paragraph 26 of the claims and satisfying the conditions

- температура локального ферромагнитного упорядочения в аустените вблизи атома углерода определялась методом квантово-механического расчета и составила ~1100 K или 817°C, а температура Т_X для стали эвтектоидного состава равна 1010 K или 727°C. При температуре нагрева из указанного интервала производили выдержку заготовки в течение времени t, необходимого для растворения 100% цементита, определяемого из уравненияWhere

- the temperature of local ferromagnetic ordering in austenite near the carbon atom was determined by quantum mechanical calculation and amounted to ~ 1100 K or 817 ° C, and the temperature T _X for eutectoid steel was 1010 K or 727 ° C. At a heating temperature from the specified interval, the workpiece was aged for a time t necessary to dissolve 100% cementite, determined from the equation

1 = 1.05 exp (-6 * 10 ^-10 t ^3.5 ),

which for steel of the indicated chemical composition was ~ 3 min.

To clarify the modes of formation of marinite determined by calculation, the following experiment was carried out. Samples, representing round rods with a diameter of 6.5-8 mm and a length of 500-800 mm, were heated to various temperatures in the range from 720 to 820 ° C (in increments of 10 ° C), kept at these temperatures for 1 to 10 min in increments of 10 s and quenched in water. After which the samples were investigated by various known methods. In the samples quenched from a heating temperature of 730–760 ° C and holding time for 2 min 30 s – 3 min, structural features characteristic of rutite were observed: bct regions with anomalously low tetragonality (about 0.5%) and hardness of ~ 750 HV . Therefore, in the studied temperature range, when the corresponding thermokinetic conditions were fulfilled, marinite was realized in samples of steel 85. As the experiment showed, in order to realize ~ 100% marinite, it is necessary at a temperature of ~ 745 ° C to provide a holding time of ~ 3 min.

Knowing the conditions for the formation of marinite, we carried out the determination of the kinetics of the formation of a given structural state, as indicated in example 2.

Thus, it was found that it was necessary to heat a steel sample of the specified chemical composition to a temperature of 745 ° C and ensure exposure at this temperature for ~ 3 min, and then to cool in a molten saltpeter with a temperature of 443 ° C for at least 10 seconds and subsequent cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to cooling in water. After that, the billet made of steel of grade 85 in the form of a rod was heated to the indicated temperature, held at this temperature, and it was cooled along the indicated paths. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 10 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 11. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following specified final structural state: ~ 50% sorbitol, for short technological sorbitol times, ~ 50% quenching structures (rutite).

To determine the implementation modes of marinite for steel of the specified chemical composition experimentally, the samples were heated to various temperatures in the range from 700 to 800 ° C (in increments of 10 ° C), kept at these temperatures for 1 to 10 minutes in increments of 10 s, and subjected quenching in water. After which the samples were investigated by various known methods. In the samples quenched from the heating temperature of 720–740 ° C and the exposure time therewith 2 min 30 s – 3 min, structural features characteristic of rutite were observed: bct regions with anomalously low tetragonality (about 0.5%) and hardness of ~ 750 HV . Therefore, in the studied temperature range, when the corresponding thermokinetic conditions were met, marinite was realized in steel 85. As the experiment showed, in order to realize ~ 100% marinite, it is necessary at a temperature of ~ 730 ° C to provide a shutter speed of ~ 2 min 50 s.

Knowing the conditions for the formation of marinite, we carried out an experimental determination of the kinetics of the formation of a given final structural state according to the method described in Example 3. As a result of the experiment, it was found that for the formation of ~ 50% perlite (sorbitol) it is necessary to ensure that the samples stay in the nitrate melt for 6 s and subsequent quenching in water. In the sample volume that was not transformed into sorbitol (~ 50%), the structural features characteristic of rutite were observed: bct regions with abnormally low tetragonality (about 0.5%) and hardness of ~ 750 HV.

Thus, it was found that it was necessary to heat a steel sample of the specified chemical composition to a temperature of 730 ° C and provide holding at this temperature for ~ 2 min 50 s, then to cool in a molten nitrate with a temperature of 443 ° C for 6 seconds, and subsequent cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to quenching in water. After that, the billet made of steel of grade 85 in the form of a rod was heated to the indicated temperature, held at this temperature, and it was cooled along the indicated paths. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. Metallographic analysis and diffraction studies of the sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 50%, and the volume fraction of quenching structures (rutite) is ~ 50%, which corresponds to a given structural state. The required technical result is achieved.

Example 12. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest is Fe and uncontrolled impurities, the following predetermined structural state: ~ 100% rutite.

The modes that ensure the implementation of marinite in steel of the specified chemical composition were determined first by calculation, and then refined by an experimental method, as described in example 10.

Knowing the conditions for the implementation of marinite, the sample was quenched from a heating temperature of 745–750 ° C and held at this temperature for 2 min 45 s, ensuring the formation of rutite.

Thus, it was found that it was necessary to heat a steel sample of the specified chemical composition to a temperature of 745-750 ° C and provide exposure at this temperature for 2 minutes 45 s, and then cool it to room temperature with a rate of decrease in surface temperature of 90-110 deg / s, corresponding to cooling in water. After that, a billet made of steel of grade 85 in the form of a rod was heated to the indicated temperature, held at this temperature, and it was quickly cooled (quenched). Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 13. The task was set to obtain for a bar with a diameter of 8 mm from steel grade 85, having the composition: 0.84% C; 0.59% Mn; 0.025% S; 0.24% Si; 0.012% P; 0.07% Cr; 0.08% Ni; 0.0075% Al; 0.05% Cu; the rest of Fe and uncontrolled impurities, the following specified structural state: ~ 100% sorbitol; for technological sorbitization times not exceeding 2 s.

The conditions that ensure the realization of marinite in steel of the indicated chemical composition were determined by the experimental method described in Example 11. As the experiment showed, to realize ~ 100% marinite, it is necessary to provide a holding time of ~ 3 min at a temperature of ~ 745 ° C.

After the implementation of marinite, a steel sample of the indicated chemical composition was first subjected to plastic deformation at a relative deformation of the surface layer of 23% and a strain rate of 0.2 s ^-1 at deformation temperatures of t _Kfer ± 50 ° C, where t _Kfer , ° C is the temperature of the Curie point of ferrite , at a temperature of 745 ° C in this case, and then pulsed cooling was performed with a single water pulse of 0.2 s duration. An impulse of such a duration ensured a maximum decrease in surface temperature and did not lead to the formation of quenching structures in a given structural state. After that, pulsed cooling was stopped and switched to monotonous cooling in a saltpeter melt with a temperature of 443 ° С. The flow time of pearlite transformation in the specified method was 1 s. Then carried out rapid cooling in water (quenching).

Thus, it was found that it is necessary to heat a steel sample of the specified chemical composition to a temperature of 745 ° C and ensure exposure at this temperature for ~ 3 min, during or after which plastic deformation of the sample is carried out at a relative strain of the surface layer of 23% and the strain rate of 0.2 s ^-1 at a temperature of 745 ° C, then carry out cooling with a single water pulse of 0.2 s duration followed by cooling in the molten saltpeter with a temperature of 443 ° C for 1 second dy, and further cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to cooling in water. After that, a billet of steel of grade 85 in the form of a rod was heated to the indicated temperature, held at this temperature, its deformation and cooling were carried out along the indicated paths. Cooling was carried out using a saltpeter melt with a temperature of 443 ° C and industrial water for this purpose. The sorbitization time in the technological cycle as a result of this was 1 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 14. The task was set to obtain for a plate measuring 8 × 30 × 150 mm from an alloy of iron with carbon, having the composition: 3.62% C; 0.01% Si; 0.01% Mn; 0.002% S; 0.004% P; 0.01% Cr; 0.05% Ni; 0.005% Cu; 0.024% Al; 0.039% Ti; 0.0015% Mo, the rest Fe and uncontrolled impurities, the following specified structural state: ~ 15% rutite, ~ 85% ledeburite and cementite. For this purpose, the preform was heated to an experimentally set temperature of 810 ° C and a holding time of ~ 3 min was ensured when ~ 15% of austenite formed.

The temperature reduction regimes ensuring the implementation in the specified alloy of a given fraction of marinite from austenite regions with a chemical composition close to eutectoid were determined by the experimental method specified in Example 3. As the experiment showed, in order to realize ~ 15% of marinite, it is necessary to carry out cooling in air to a temperature of 720 ° C.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that in the temperature range from 810 to 720 ° C it is necessary to carry out cooling in air, and further cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to cooling in water. After that, a billet of an alloy of the indicated chemical composition in the form of a plate was heated to a temperature of 810 ° C and held for ~ 3 min, subjected to cooling in air to a temperature of 720 ° C, and its rapid cooling (quenching) was performed. Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 15%, and the volume fraction of ledeburite and cementite is ~ 85%, which corresponds to a given structural state. The required technical result is achieved.

Example 15. The task was set to obtain for a plate measuring 8 × 30 × 150 mm from an alloy of iron with carbon, having the composition: 2.47% C; 0.02% Si; 0.023% Mn; 0.003% S; 0.001% P; 0.005% Cr; 0.02% Ni; 0.002% Cu; 0.035% Al, the rest Fe and uncontrolled impurities, the following specified final structural state: ~ 55% rutite, ~ 45% ledeburite and cementite.

Modes that ensure the implementation of marinite in the alloy of the indicated chemical composition were determined by the experimental procedure specified in Example 11. As the experiment showed, in order to realize ~ 50% of marinite, it is necessary at a temperature of ~ 750 ° С to provide a holding time of ~ 4 min.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that it is necessary to heat a sample of an alloy of the specified chemical composition to a temperature of ~ 750 ° C and ensure exposure at this temperature for ~ 4 min, and then cool it to room temperature with a rate of surface temperature decrease of 90-110 deg / c, corresponding to quenching in water. After that, a billet made of an alloy of the indicated chemical composition in the form of a plate was heated to the indicated temperature, held at this temperature, and it was quickly cooled (quenched). Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 55%, and the volume fraction of ledeburite and cementite is ~ 45%, which corresponds to a given structural state. The required technical result is achieved.

Example 16. The task was set of an ingot of cylindrical shape with a diameter of 50 mm and a height of 20 mm to obtain a plate with dimensions of 8 × 30 × 150 mm from steel having the composition: 1.76% C; 0.035% Si; 0.01% Mn; 0.009% S; 0.013% P; 0.01% Cr; 0.04% Ni; 0.09% Cu; 0.004% Al; 0.015% V, the rest Fe and uncontrolled impurities, the following specified final structural state: ~ 85% rutite, ~ 15% cementite.

The modes that ensure the implementation of marinite in steel of the specified chemical composition were determined first by calculation, and then refined by the experimental method specified in Example 10. As the experiment showed, in order to realize ~ 70% marinite in an ingot, it is necessary to provide a holding time of ~ 3 min at a surface temperature of ~ 770 ° C.

Then, the alloy ingot of the indicated chemical composition was subjected to plastic deformation. In this case, it was forged in the temperature range of 770-750 ° C, providing the workpiece with the shape of a plate of the specified size.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that it is necessary to heat an ingot of steel of the specified chemical composition to a surface temperature of ~ 770 ° C and provide exposure at this temperature for ~ 3 min, then plastic deformation of the ingot in the temperature range of 770-750 ° C before imparting it forms a plate with dimensions of 8 × 30 × 150 mm, and subsequent cooling to room temperature is carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to water quenching. After that, an alloy billet of the indicated chemical composition in the form of an ingot of cylindrical shape with a diameter of 50 mm and a height of 20 mm was heated to the indicated temperature, held at this temperature, deformation was carried out in the indicated temperature range, and rapid cooling (quenching) was performed. Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 85% and the volume fraction of cementite is ~ 15%, which corresponds to a given structural state. The required technical result is achieved.

Example 17. The task was set to obtain for a plate measuring 0.6 × 20 × 60 mm from steel grade 65G, having the composition: 0.64% C; 0.26% Si; 0.96% Mn; 0.006% S; 0.018% P; 0.03% Cr; 0.03% Ni; 0.05% Cu; 0.01% As; 0.05 N; 0.047% Al; 0.001% Nb; 0.015% V; 0.005% Ti; 0.002% Mo, the rest Fe and uncontrolled impurities, the following specified structural state: ~ 90% rutite; ~ 10% martensite. For this, the preform was heated to an experimentally set temperature of 980 ° C, when ferrite and cementite disappeared and ~ 100% austenite formed.

Modes that ensure the realization of marinite in steel of the indicated chemical composition were determined experimentally. For this, experiments were carried out to cool plate samples of the indicated sizes with compressed air flows at a temperature of 23 ° C, produced by a nozzle with an outlet diameter of 6 mm under various pressures in the line to room temperature. The pressure change step was 0.3 atm from the range of 2.5-8 atm. In this case, the average cooling rate was recorded in the temperature range of 900-600 ° C. After which the samples were investigated by various known methods. In the samples cooled in the temperature range 900-600 ° C with an average speed of 50-70 deg / s and quenched from 600 ° C in water, the structural features characteristic of rutite were observed: bct regions with an abnormally low tetragonality (about 0.5%) and hardness ~ 750 HV. Therefore, under the indicated cooling conditions, marinite was realized in 65G steel samples. The experiments showed that if cooling from 600 ° C is continued, using the same blowing parameters and unit settings (line pressure, nozzle diameter, flow rate, air temperature), as in the range 900-600 ° C, the average cooling rate in which was 50-70 deg / s, this will ensure the formation of ~ 90% of rutite in the final structural state.

Thus, it was found that in the temperature range from 980 ° C to room temperature, it is necessary to carry out cooling by streams of compressed air having a temperature of 23 ° C, discharged under constant pressure in the 4 atm line, providing an average plate cooling rate of 50-70 deg / s in the temperature range 900-600 ° C and further cooling using the same airflow parameters. After that, the workpiece made of 65G steel in the form of a plate was heated to a temperature of 980 ° C and it was cooled with compressed air with the indicated blowing parameters. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 90% and the volume fraction of martensite is ~ 10%, which corresponds to a given structural state. The required technical result is achieved.

Example 18. The task was set to obtain for a wire with a diameter of 1.0 mm from steel grade 80, having the composition: 0.82% C; 0.50% Mn; 0.002% S; 0.16% Si; 0.005% P; 0.02% Cr; 0.01% Ni; 0.002% Al; 0.01% Cu; the rest of Fe and uncontrolled impurities, the following specified final structural state: ~ 100% sorbitol, for technological sorbitol times not exceeding 5 s.

Modes that ensure the implementation of marinite in steel of the specified chemical composition were determined according to the experimental procedure specified in Example 11. As the experiment showed, in order to realize ~ 100% of marinite, it is necessary to heat the workpiece to a temperature of ~ 740 ° C and ensure exposure at it for 45 s.

Knowing the conditions for the formation of marinite, we carried out the determination of the kinetics of the formation of a given final structural state according to the experimental procedure indicated in Example 3. As a result of the experiment, it was found that for the formation of ~ 100% perlite (sorbitol), it is necessary to provide cooling of a wire with a diameter of 1.0 mm in air. The sorbitization time was about 4 s.

Thus, it was found that it is necessary to heat a steel sample of the specified chemical composition to a temperature of 740-750 ° C and provide exposure at this temperature for 45 s, then perform cooling in air. After that, a wire with a diameter of 1.0 mm from grade 80 steel was heated to the indicated temperature, held at this temperature, and it was cooled in air for at least 4 s. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of sorbitol is ~ 100%, which corresponds to a given structural state. The required technical result is achieved.

Example 19. The task was posed from a workpiece with dimensions of 14.2 × 200 × 1320 mm to obtain a strip with dimensions of 12.5 × 200 × 1500 mm from steel having the composition: 0.21% C; 0.01% Si; 0.39% Mn; 0.032% S; 0.016% P; 0.08% Cr; 0.07% Ni; 0.06% Cu; 0.005% Al, the rest Fe and uncontrolled impurities, the following specified final structural state: ~ 15% rutite, ~ 85% ferrite. For this, the preform was heated to an experimentally set temperature of 950 ° C, when ferrite and cementite disappeared and ~ 100% austenite formed.

The temperature reduction regimes ensuring the implementation in the specified alloy of a given fraction of marinite from austenite regions with a chemical composition close to eutectoid were determined by the experimental method specified in Example 3. As the experiment showed, in order to realize ~ 15% of marinite, it is necessary to cool a steel sample of the specified chemical composition in air to a temperature of 740 ° C, subject it to a plastic strain pulse at a relative strain of 6.34% at deformation temperatures of 740-760 ° C; holding at these temperatures for 60 s and a repeated pulse of the deforming effect at a relative strain of 6%.

Knowing the conditions for the formation of marinite, the sample was quenched from the temperatures determined above, ensuring the formation of rutite.

Thus, it was found that in the temperature range from 950 to 740 ° C, it is necessary to carry out cooling in air, then to carry out an impulse of plastic deformation at a relative strain of 6.34% at deformation temperatures of 740-760 ° C; holding at these temperatures for 60 s and a repeated pulse of the deforming effect at a relative strain of 6.34%, and further cooling to room temperature should be carried out at a rate of surface temperature decrease of 90-110 deg / s, corresponding to cooling in water. After that, a steel billet of the specified chemical composition in the form of a strip measuring 14.2 × 200 × 1320 mm was heated to a temperature of 950 ° C, subjected to cooling in air to a temperature of 740 ° C, rolled in a laboratory rolling mill in the indicated temperature range with absolute compression 0 , 9 mm, providing an impulse of plastic deformation of the required degree, was held at these temperatures for 60 s, another pass was carried out with an absolute compression of 0.8 mm (repeated impulse of deformation), ensuring the achievement of the required floor size wasps and rapid cooling (hardening). Cooling was carried out using industrial water for this purpose. Metallographic analysis and diffraction studies of a sample of the workpiece cooled to room temperature showed that the volume fraction of rutite is ~ 15%, and the volume fraction of ferrite is ~ 85%, which corresponds to a given structural state. The required technical result is achieved.

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Claims (41)

1. The method of heat treatment of products from alloys based on iron with a carbon content of up to 4.3% by weight, including heating, which ensures the formation of austenite and subsequent cooling according to the modes, providing the formation of a given structural state, characterized in that the cooling is carried out according to the modes, providing the formation in the structure of the alloy of austenite regions with a chemical composition close to eutectoid, followed by the formation of marinite in them, and a predetermined structural state is formed with obtaining in m perlite different fineness and / or quenching structures. 2. The method according to claim 1, characterized in that the cooling is carried out according to modes that ensure the formation in the structure of the alloy of a predetermined fraction of austenite regions with a chemical composition close to eutectoid, with the subsequent formation of a predetermined proportion of marinite in them. 3. The method according to claim 2, characterized in that the modes that ensure the formation in the alloy structure of a given fraction of marinite from areas of austenite with a chemical composition close to eutectoid are determined by calculation or experimentally. 4. The method according to claim 1, characterized in that the predetermined structural state of the alloy is formed to obtain specified proportions of perlite in it of varying degrees of dispersion and / or quenching structures. 5. The method according to claim 3, characterized in that in the calculated determination of the modes that ensure the formation of marinite from areas of austenite with a chemical composition close to eutectoid, set the temperature range for the formation of marinite, satisfying the conditions:

,
Where

- the temperature of local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum mechanical calculation;
T _TEX - temperature selected taking into account technological limitations,
in this case, the cooling rate is selected at which the dependence of the cooling temperature on time T (t) satisfies the condition T (t) <Θ (t), where the dependence Θ (t) is determined by the start lines of the pearlite and bainitic transformations on the thermokinetic diagram. 6. The method according to claim 3, characterized in that when determining the modes experimentally, ensuring the formation of marinite from areas of austenite with a chemical composition close to eutectoid, the samples are quenched from fixed temperatures at different exposure times, and the fact of obtaining marinite is established by the presence of in a hardened rutite sample. 7. The method according to claim 6, characterized in that the presence of rutite is established by diffraction methods. 8. The method according to claim 4, characterized in that the cooling mode, leading to the formation of a given amount of perlite in a given structural state, is determined by quenching the experimental samples with subsequent determination of their structural state. 9. The method according to claim 1, or 2, or 4, characterized in that the cooling mode leading to the formation of a given structural state is determined by measuring the temperature at selected points in the volume of the model sample of an alloy of simple form during cooling at speeds leading to the desired structural state in the alloy sample, and determination of the values of thermokinetic constants, which ensure, at known heat fluxes on the surface of the sample, the temperature dependences on time obtained during the model ksperimenta and by solving the system of equations, which includes:
heat equation:

,
where is the operator

has a dimension of m ^-1 ;
r is the radius vector of the point at which the calculations are made;
ρ is the density, kg / m ³ ;
q _i is the specific enthalpy of formation of the i-th phase, J / kg;
f _i (r, t, Т) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T;

- heat flux, J / (m ² · s);
N (r, t, T) is the distribution of enthalpy over the volume of the sample, J / m ³ ,
energy conservation equation:

,
Where

- specific heat of phase i at constant pressure on temperature, J / (kg · K),
kinetic equation:

,
where M _ik (Т, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation,
and using the above equations and the found thermokinetic constants to calculate the dependence of the heat flux on time over the surface of the alloy product, providing a trajectory of temperature change over time, leading to the formation of a given structural state. 10. The method according to claim 4, characterized in that after the formation of marinite, cooling is carried out according to the modes leading to the formation of the specified fractions of the phases of ferrite and iron carbides in a given structural state without the formation of quenching structures or with the formation of them in fractions not exceeding the specified ones. 11. The method according to claim 4, characterized in that after the formation of a given fraction of perlite, the cooling of alloy products is carried out at speeds sufficient to suppress diffusion transformations. 12. The method according to claim 1, or 10, or 11, characterized in that carry out pulse cooling. 13. The method according to p. 12, characterized in that the cooling is carried out with pulses that alternate with pauses, the duration of which is selected sufficient for a given reduction of the difference between the maximum and minimum temperature values over the cross section of alloy products. 14. The method according to p. 12, characterized in that the duration of each of the cooling pulses is chosen so that they do not lead to the formation of quenching structures in a given structural state. 15. The method according to p. 12, characterized in that the cooling is carried out with pulses, while one of the cooling pulses is selected to provide the maximum reduction in surface temperature of alloy products without the formation of quenching structures in a given structural state. 16. The method according to claim 4, characterized in that after the formation of a predetermined austenite fraction in the alloy structure, sufficient to obtain specified perlite fractions of varying degrees of dispersion and / or quenching structures in a given structural state, the temperature reduction required for the formation of marinite is carried out by a pulse cooling. 17. The method according to p. 12, characterized in that after reaching the fractions of the phases of ferrite and iron carbides, which further provide a given structural state, impulse cooling is stopped and transitions to monotonic cooling and / or isothermal aging. 18. The method according to claim 1, characterized in that after heating the alloy products to temperatures ensuring the formation of a predetermined austenite fraction in the alloy structure, the alloy products are subjected to plastic deformation. 19. The method according to p. 18, characterized in that the plastic deformation of the alloy products is carried out or completed at temperatures t _Kfer ± 50 ° C, where t _Kfer is the Curie temperature of ferrite, ° C. 20. The method according to claim 1, characterized in that in the process of the formation of marinite, alloy products are exposed to a constant or pulsed magnetic field. 21. The method according to claim 1, characterized in that for cooling use water or aqueous media. 22. The method of heat treatment of products from iron-based alloys with a carbon content of up to 4.3% by weight, including heating and subsequent cooling according to the modes that provide the formation of a given structural state, characterized in that the heating is carried out according to modes that ensure the formation in the alloy structure marinite, and a given structural state is formed to produce perlite in it of varying degrees of dispersion and / or quenching structures. 23. The method according to p. 22, characterized in that the heating is carried out according to modes that ensure the formation in the structure of the alloy of a given fraction of marinite. 24. The method according to item 23, wherein the modes that ensure the formation in the structure of the alloy of a given fraction of marinite, determined by calculation or experimentally. 25. The method according to p. 22, characterized in that a predetermined structural state is formed with obtaining specified fractions of perlite in it of varying degrees of dispersion and / or quenching structures. 26. The method according to paragraph 24, characterized in that when determining by calculation the modes that ensure the formation of marinite, set the temperature range of the heating, satisfying the conditions:

,
Where

- the temperature of local ferromagnetic ordering in austenite near the carbon atom, determined by the method of quantum mechanical calculation;
T _x - eutectoid temperature for the alloy of the corresponding chemical composition,
and the exposure time t in seconds required to dissolve a given fraction of cementite f _c , determined from the equation:
f _c = 1.05 f _C0 exp (-kt ⁿ ),
where f _C0 is the dimensionless fraction of cementite at the initial instant of time,
4>n> 3 is a power exponent;
k is a parameter that determines the rate of dissolution of cementite in an alloy of the corresponding chemical composition at a temperature T, s ^-n . 27. The method according to p. 24, characterized in that when experimentally determining the modes that ensure the formation of marinite in the alloy structure, the samples are quenched from fixed temperatures at different exposure times, and the fact of obtaining marinite is established by the presence of rutite in the quenched sample. 28. The method according to item 27, wherein the presence of rutite is established by diffraction methods. 29. The method according A.25, characterized in that the cooling mode, leading to the formation of a given amount of perlite in a given structural state, is determined by quenching the experimental samples with subsequent determination of their structural state. 30. The method according to p. 22, or 23, or 25, characterized in that the cooling mode leading to the formation of a given structural state is determined by measuring the temperature at selected points in the volume of the model alloy sample of simple form during cooling at speeds leading to the desired the structural state in the alloy sample, and determining the values of thermokinetic constants, which ensure, at known heat fluxes on the surface of the sample, the temperature dependences of the time obtained during the simulation about the experiment and by solving the system of equations, which includes:
heat equation:

,
where is the operator

has a dimension of m ^-1 ;
r is the radius vector of the point at which the calculations are made;
ρ is the density, kg / m ³ ;
q _i is the specific enthalpy of formation of the i-th phase, J / kg;
f _i (r, t, Т) is the dimensionless mass fraction of phase i in the vicinity of point r at time t at temperature T;

- heat flux, J / (m ² · s);
N (r, t, T) is the distribution of enthalpy over the volume of the sample, J / m ³ ,
energy conservation equation:

,
Where

- specific heat of phase i at constant pressure on temperature, J / (kg · K),
kinetic equation:

,
where M _ik (T, f _k (τ), (t-τ)) is a functional dependence that determines the rate of change with time t of the mass fraction f _{i of} phase i, determined for each phase transformation,
and using the above equations and the found thermokinetic constants to calculate the dependence of the heat flux on time over the surface of the alloy product, providing a trajectory of temperature change over time, leading to the formation of a given structural state. 31. The method according A.25, characterized in that after the formation of marinite, cooling is carried out according to the regimes leading to the formation of specified fractions of the phases of ferrite and iron carbides in a given structural state without the formation of quenching structures or with the formation of them in fractions not exceeding specified. 32. The method according A.25, characterized in that after the formation of a given fraction of perlite, the cooling of alloy products is carried out at speeds sufficient to suppress diffusion transformations. 33. The method according to item 22, or 31, or 32, characterized in that the pulse cooling is carried out. 34. The method according to p. 33, characterized in that the cooling is carried out with pulses that alternate with pauses, the duration of which is selected sufficient for a given reduction of the difference between the maximum and minimum values of temperature over the cross section of alloy products. 35. The method according to p. 33, characterized in that the duration of each of the cooling pulses is chosen so that they do not lead to the formation of quenching structures in a given structural state. 36. The method according to p. 33, characterized in that the cooling is carried out with pulses, while one of the cooling pulses is selected to provide the maximum reduction in the surface temperature of the alloy product without the formation of quenching structures in a given structural state. 37. The method according to p. 33, characterized in that after reaching the fractions of the phases of ferrite and iron carbides, which further provide a given structural state, impulse cooling is stopped and transferred to monotonic cooling and / or isothermal aging. 38. The method according to item 22, wherein the alloy products are subjected to plastic deformation when heated to or during the formation of marinite. 39. The method according to item 22, wherein the alloy products after the formation of marinite are subjected to plastic deformation. 40. The method according to § 38 or 39, characterized in that the plastic deformation of the alloy products is carried out or completed at temperatures t _Kfer ± 50 ° C, where t _Kfer is the Curie temperature of ferrite, ° C. 41. The method according to item 22, wherein the use of water or aqueous media for cooling.

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