CN110648421B - A calculation method for the thickness of decarburized layer on the surface of decarburized spring steel - Google Patents

Abstract

The invention provides a method for calculating the thickness of the decarburized layer on the surface of decarburized spring steel, which belongs to the technical field of high-speed wire rolling. The method firstly calculates the theoretical equilibrium carbon concentration on the surface of the steel under different decarburization atmosphere conditions; then, calculates the carbon content in the decarburized layer and the carbon diffusion coefficient in ferrite under different heating temperature and heating time conditions ; Finally, according to the calculation formula of the decarburization model and combined with the Gaussian error function analysis, the thickness of the decarburized layer on the steel surface is calculated. Through the furnace atmosphere parameters, temperature parameters and time parameters in the real-time database of the hot rolling production line, the online prediction of the thickness of the decarburized layer during the hot continuous rolling process can be carried out in real time, and the hot rolling process parameters can be adjusted accordingly to reduce the thickness of the decarburized layer. , the purpose of improving the surface quality of spring steel.

Description

A calculation method for the thickness of decarburized layer on the surface of decarburized spring steel

technical field

The invention relates to the technical field of high-wire steel rolling, in particular to a method for calculating the thickness of a decarburized layer on the surface of decarburized spring steel.

Background technique

Spring steel is widely used in various machinery, instruments, meters, transportation, petrochemical and other fields. As the working conditions of spring steel become more and more severe, the requirements for the surface quality of spring steel are becoming more and more strict. In the hot continuous rolling process of spring steel bar and wire, the control of the thickness of the surface decarburization layer is one of the key technologies of surface quality control. Real-time monitoring of the thickness change of the surface decarburization layer is the basis for controlling the surface quality. Therefore, it is more and more important to explore the precise evolution law of the thickness of the decarburized layer in different atmospheres during the hot continuous rolling of spring steel.

At present, most of the research on the thickness of the decarburized layer of steel is focused on offline measurement, mainly using metallographic method. In addition, Chinese patent CN108195331A discloses a method for obtaining the thickness of the decarburized layer on the steel surface. The indenter is used to press into the steel to be tested, and the thickness of the decarburized layer is measured according to the change of the indentation speed. However, at present, there are few studies on the thickness of decarburized layer of steel during hot tandem rolling process from theoretical calculation to online soft measurement.

The invention realizes the real-time control of the thickness of the decarburized layer of the surface layer of the spring steel by using the online prediction calculation method in the hot continuous rolling process, which has an important influence on the development of reducing the production cost and producing the spring steel bar and wire rod with high surface quality.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a method for calculating the thickness of the decarburized layer on the surface of decarburized spring steel. Real-time prediction of the change in the thickness of the decarburized layer is realized, so as to adjust the process parameters to control the thickness of the decarburized layer, improve the surface quality of the spring steel bar and wire, and provide a new development direction for the high-quality surface processing technology of the bar and wire.

The method includes the following steps:

(1) Determine the equilibrium carbon concentration according to the furnace atmosphere:

The content of H ₂ O, CO ₂ , O ₂ , and H ₂ in the decarburization atmosphere of spring steel varies with the decarburization reaction, and the equilibrium carbon concentration C _s is set to be 0–0.01;

(2) Determine the carbon content in the decarburized layer and the diffusion coefficient of carbon in the ferrite:

The formula for calculating the carbon content C of the spring steel in the decarburized layer is as follows:

Among them, C is the carbon content in the decarburized layer, %; the original carbon content in the C ₀ steel, %; t is the holding time, s; D is the diffusion coefficient of carbon in the ferrite, m ² /s; d is the thickness of the decarburized layer, m;

The formula for calculating the diffusion coefficient D of carbon in ferrite is as follows:

Among them, D ₀ is the diffusion constant, m ² /s; Q is the activation energy of diffusion, J/mol; R is the gas constant, J/(mol·K); T is the absolute temperature, K;

(3) Establish a decarburization measurement model of spring steel under different holding temperatures and holding times, and determine the thickness of the decarburized layer on the surface:

Using the method described in step (1), calculate the theoretical equilibrium carbon concentration C _s on the surface of the steel under different partial pressure conditions of furnace gas components; using the method described in step (2), calculate the decarburization in the steel at different temperatures The carbon content in the layer, C, and the diffusion coefficient of carbon in the ferrite, D.

The calculation formula of the decarburization model of spring steel at different heating temperatures, different heating times and different furnace atmospheres is:

Among them, d is the thickness of the decarburized layer in the steel. According to the above formula and combined with the Gaussian error function, the evolution law of the thickness d of the decarburized layer in the steel can be obtained.

Wherein, in step (1), decarburization chemical reaction equation is:

ax+[C]=by+cz

Among them, a, b, c are the coefficients of the chemical equation, x is the gas involved in the reaction, and y and z are the production gas.

In step (1), the equilibrium carbon concentration is related to the carbon activity on the surface of the spring steel, and the calculation formula of the carbon activity on the surface of the spring steel is:

Among them, a _c is the activity of carbon in the austenitized steel; K _P is the equilibrium constant, and K _P is a constant when the temperature is constant; P _x , P _y , and P _z represent the partial pressure of each component of the furnace gas, respectively, %; C _sat is the austenite saturated carbon concentration, when the temperature is constant, C _sat is a constant, %; C _s is the carbon content when the steel surface is in equilibrium with the furnace gas, %, which determines the decarburization degree and speed of the steel surface.

It can be seen from the above formula that different partial pressures of furnace gas components determine the theoretical equilibrium carbon concentration C _s on the steel surface. If in the actual production process, the furnace gas is constantly flowing, and the decarburization reaction products are continuously taken away, so that the reaction is continuously shifted to the right, and the equilibrium carbon concentration C _s can be set as a simplified treatment value of 0–0.01.

Under the condition of variable temperature, the thickness of the decarburized layer in the steel can be decomposed into several tiny isothermal units to calculate the sum of its generation. At this time, the calculation model formula of the thickness of the decarburized layer in step (3) is:

Among them, C _i represents the carbon content in the decarburized layer at time i, %; C _si represents the carbon content in the equilibrium between the steel surface and the furnace gas at time _i , %; Di represents the diffusion coefficient of carbon in the ferrite at time i, cm ² /s; t _i represents the time step at time i, s; d _i represents the thickening of the thickness of the decarburized layer at time _i and constant temperature Ti, mm, where i=1, 2, 3,...N; T _i represents the decarburization temperature at time i, K; C ₀ represents the original content of carbon in the steel.

The beneficial effects of the above-mentioned technical solutions of the present invention are as follows:

In the above scheme, the thickness of the surface decarburization layer can be predicted in real time, which is simple and fast, and is of great significance to the actual production of the enterprise site.

Description of drawings

Fig. 1 is the schematic diagram of the calculation method of the decarburized layer thickness on the surface of the decarburized spring steel of the present invention controlling the thickness model of the decarburized layer on the surface of the steel part on-line at the production site of the enterprise;

Figure 2 shows the total thickness of the decarburized layer measured by hot continuous rolling of 55SiCr type spring steel in an on-site 1000°C air atmosphere in the embodiment of the present invention.

Detailed ways

In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

The invention provides a method for calculating the thickness of the decarburized layer on the surface of decarburized spring steel.

As shown in Figure 1, the method includes the following steps:

(1) Determine the equilibrium carbon concentration according to the furnace atmosphere:

The content of H ₂ O, CO ₂ , O ₂ , and H ₂ in the decarburization atmosphere of spring steel varies with the decarburization reaction, and the equilibrium carbon concentration C _s is set to be 0–0.01;

(2) Determine the carbon content in the decarburized layer and the diffusion coefficient of carbon in the ferrite:

The formula for calculating the carbon content C of the spring steel in the decarburized layer is as follows:

Among them, C is the carbon content in the decarburized layer, %; the original carbon content in the C ₀ steel, %; t is the holding time, s; D is the diffusion coefficient of carbon in the ferrite, m ² /s; d is the thickness of the decarburized layer, m;

The formula for calculating the diffusion coefficient D of carbon in ferrite is as follows:

Among them, D ₀ is the diffusion constant, m ² /s; Q is the activation energy of diffusion, J/mol; R is the gas constant, J/(mol·K); T is the absolute temperature, K;

(3) Establish a decarburization measurement model of spring steel under different holding temperatures and holding times, and determine the thickness of the decarburized layer on the surface:

The calculation formula of the decarburization model of spring steel at different heating temperatures, different heating times and different furnace atmospheres is:

Among them, d is the thickness of the decarburized layer in the steel.

The following description will be given in conjunction with specific embodiments.

Example 1

线材。In the embodiment of the present invention, 55SiCr type spring steel is used,

wire.

The calculation model for the thickness of the decarburized layer on the surface of the hot continuous rolled 55SiCr spring steel includes the following steps:

Taking the heating temperature of 1000 °C and heating for 60 minutes in an air atmosphere as an example, if the carbon concentration is reduced to 85% as the starting point of semi-decarburization, the depth of the decarburization layer of the 55SiCr spring steel is 85% of the carbon content in the steel. the distance from the tissue to the surface.

Step 1: Under the condition of air atmosphere, the main decarburization chemical reaction equation that occurs on the surface of 55SiCr spring steel is:

The theoretical equilibrium carbon concentration C _s on the surface of 55SiCr spring steel:

C _s =C _sat · _ac =1.55×0.24=0.37%

Step 2: The carbon content of the 55SiCr spring steel in the decarburized layer is:

C=C ₀ ×85%=0.0055×0.85=0.47%

At a heating temperature of 1000 °C, the diffusion coefficient of carbon in ferrite is:

Step 3: Establish a decarburization measurement model of 55SiCr spring steel under the conditions of holding temperature of 1000℃ and holding time of 3600s, and determine the thickness of the decarburized layer on the surface:

Using the method described in step 1, calculate the theoretical equilibrium carbon concentration C _s on the surface of the 55SiCr steel under the air atmosphere; using the method described in step 2, calculate the carbon content C in the decarburized layer in the 55SiCr steel at 1000°C , the diffusion coefficient D of carbon in ferrite.

The calculation formula of decarburization model of 55SiCr spring steel under the condition of holding temperature of 1000℃, holding time of 3600s and air atmosphere is:

From the Gaussian error function, we get:

d=0.372(mm)

The thickness of the total decarburized layer measured by hot continuous rolling of 55SiCr spring steel in an air atmosphere at 1000 °C is shown in Figure 2.

The above are the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (1)

1. A method for calculating the thickness of a decarburized layer on the surface of decarburized spring steel is characterized by comprising the following steps of: the method comprises the following steps:

(1) determining the equilibrium carbon concentration according to the furnace atmosphere:

spring steel in decarburization atmosphere H₂O、CO₂、O₂And H₂The content of (A) is varied with the decarburization reaction, and the equilibrium carbon concentration C is set_s0 to 0.01;

(2) determining the carbon content in the decarburization layer and the diffusion coefficient of carbon in ferrite:

the carbon content C of the spring steel in the decarburization layer is calculated according to the following formula:

wherein C is the carbon content in the decarburization layer,%; c₀Is the original carbon content in the steel,%; t is the holding time, s; d is the diffusion coefficient of carbon in ferrite, m²S; d is the thickness of the decarburized layer, m;

the diffusion coefficient D of carbon in ferrite is calculated as follows:

wherein D is₀Is a diffusion constant, m²S; q is the diffusion activation energy, J/mol; r is a gas constant, J/(mol. K); t is absolute temperature, K;

(3) establishing spring steel decarburization measurement models at different heat preservation temperatures and different heat preservation times, and determining the thickness of the surface decarburized layer:

the spring steel decarburization model calculation formula at different heating temperatures, different heating times and different furnace atmospheres is as follows:

wherein d is the thickness of the decarburized layer in the steel;

the equilibrium carbon concentration in the step (1) is related to the carbon activity of the surface of the spring steel, and the calculation formula of the carbon activity of the surface of the spring steel is as follows:

wherein, a_cIs the activity of carbon in austenitized steel; k_PAs an equilibrium constant, when the temperature is constant K_PIs a constant; p_x、P_y、P_zRespectively representing the partial pressure,%, of each component of the furnace gas; c_satA saturated carbon concentration of austenite, when the temperature is constant, C_satIs constant,%; c_sThe content of carbon in the steel surface and the furnace gas in balance determines the decarburization degree and speed of the steel surface layer;

under the condition of variable temperature, the calculation model formula of the thickness of the decarburized layer in the step (3) is as follows:

wherein, C_iRepresents the carbon content,%, in the decarburization layer at time i; c_siRepresents the content of carbon,%, at time i when the steel surface and the furnace gas are in equilibrium; d_iDenotes the diffusion coefficient of carbon in ferrite, cm at time i²/s；t_iRepresents the time step at time i, s; d_iShowing time i, constant temperature T_iA thickening of the decarburisation layer thickness, mm, wherein i ═ 1, 2, 3, … N; t is_iRepresents the decarburization temperature at time i, K; c₀Represents the original content of carbon in the steel;

the chemical reaction equation of decarburization in the step (1) is as follows:

ax+[C]＝by+cz

wherein a, b and c are coefficients of a chemical equation, x is a reaction participating gas, and y and z are production gases.

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