Design method of hot-rolled steel ingot heating process

Abstract

The invention relates to the technical field of metal material hot working, in particular to a design method of a hot-rolled steel ingot heating process, which comprises the following steps: A) combining a stress field and tensile strength to determine a first-stage heating temperature of a steel ingot, and the temperature after the first-stage heating does not exceed an austenitizing temperature; b) combining the stress field and the tensile strength to determine the second-stage heating rate of the steel ingot, and the temperature after the second-stage heating does not exceed the austenitizing temperature; c) determining the soaking time of the third stage by combining the temperature field, and controlling the internal and external temperature difference of the steel ingot to be less than 100 DEG C; d) combining the stress field and the tensile strength to determine the fourth-stage heating rate, and determining the cut-off temperature after heating according to the characteristics of the steel grade; and E) determining the soaking time of the fifth stage by combining the temperature field, and controlling the internal and external temperature difference of the steel ingot to be less than 20 DEG C. According to the method, the risk of thermal cracking is avoided, the heating time of each stage of the heating process can be shortened to the maximum extent, and an adaptive heating process is designed in a customized mode according to the characteristics of ingot types and steel types.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot working of metal materials, and particularly relates to a design method of a hot-rolling steel ingot heating process. BACKGROUND

[0002] In the field of hot rolling, steel ingot heating is an important link. In large steel plants, the cost proportion of hot rolling production is large, and energy consumption is the main source of hot rolling cost, so shortening the heating time is the most effective means to reduce energy consumption. The heating temperature, holding time and heating speed in the steel ingot heating process directly determine the length of the steel ingot heating time. At present, the steel ingot heating process of most domestic steel plants is determined by experience.

[0003] The experience method is a result obtained according to a large number of tests, which usually divides the heating temperature into three stages. The first stage is from room temperature to the core of the steel ingot reaching 500-550 DEG C. The plasticity of most steel grades is poor below 550 DEG C, so the heating speed needs to be slow;

[0004] The second stage is from the core of the steel ingot reaching 550 DEG C to the surface of the steel ingot reaching the highest heating temperature. The highest heating temperature is calculated according to the experience formula (1);

[0005] T max = solidus temperature - a formula (1);

[0006] In formula (1), the size of a has a relationship with the composition, and is usually taken as 150-200 DEG C;

[0007] The third stage is from the surface temperature of the steel ingot reaching the highest heating temperature to the core of the steel ingot burning through. The total heating time can be calculated according to the experience formula (2);

[0008] T 总 =t1+t2+t3 formula (2);

[0009] In formula (2), t1=9.2D 2 , t2=4.9D 2 , t3=5.4D 2 , and D is the average diameter of the cross section of the steel ingot.

[0010] However, the experience method is too rough, and there is a risk of hot cracking. SUMMARY

[0011] Therefore, the present application aims to provide a design method of a hot-rolled steel ingot heating process.

[0012] The present application provides a design method of a hot-rolled steel ingot heating process, comprising the following steps:

[0013] A) determining a first-stage heating temperature of the steel ingot in combination with a stress field and a tensile strength, and performing a soaking treatment at the first-stage heating temperature; the temperature after the first-stage heating is not higher than an austenitizing temperature;

[0014] B) determining a second-stage heating rate of the steel ingot in combination with the stress field and the tensile strength, and performing a second-stage heating; the temperature after the second-stage heating is not higher than the austenitizing temperature;

[0015] C) determining a third-stage soaking time in combination with a temperature field, and performing a third-stage soaking; in the third-stage soaking, an internal-external temperature difference of the steel ingot is less than 100℃;

[0016] D) determining a fourth-stage heating rate in combination with the stress field and the tensile strength, and performing a fourth-stage heating; a cut-off temperature after the fourth-stage heating is determined by a steel grade characteristic;

[0017] E) determining a fifth-stage soaking time in combination with the temperature field, and performing a fifth-stage soaking; in the fifth-stage soaking, the internal-external temperature difference of the steel ingot is less than 20℃.

[0018] Preferably, in step A),

[0019] the first-stage defined temperature range is normal temperature to the austenitizing temperature;

[0020] the stress field of the heart of the steel ingot at different temperatures in the first-stage defined temperature range is calculated to obtain a maximum tensile stress value of the heart of the steel ingot at different temperatures, the maximum tensile stress value is compared with a corresponding tensile strength at the test temperature, and a temperature at which the tensile stress peak value is closest to the tensile strength is selected as the first-stage heating temperature.

[0021] Preferably, when the steel ingot is 95Cr18 steel, the first-stage defined temperature range is 550-800℃, the first-stage heating temperature is 580-620℃, and the first-stage soaking treatment time is 1.3-1.7h.

[0022] Preferably, in step B), the temperature after the second stage of heating is 20-30℃ below the austenitizing temperature.

[0023] In the second stage of heating, the maximum stress value is not more than the maximum stress value in the first stage of heating. In the heating rate that meets the conditions, the maximum value is selected as the heating rate of the second stage.

[0024] Preferably, in step B), when the ingot is 95Cr18 steel, the second stage of heating has a rate of not more than 100℃ / h, and the temperature after the second stage of heating is 20-30℃ below the austenitizing temperature.

[0025] Preferably, in step C), based on the end of the second stage of heating, the third stage of heating temperature field is calculated, the third stage of soaking temperature is the cut-off temperature of the second stage of heating, the change of the ingot internal temperature field during soaking is calculated, and the final soaking heating time of the third stage is determined based on the criterion that the ingot internal and external temperature difference is less than 100℃.

[0026] Preferably, in step C), when the ingot is 95Cr18 steel, the ingot internal and external temperature difference is less than 50℃ during the third stage of soaking; the temperature of the third stage of soaking is 780-820℃, and the time of the third stage of soaking is 3.5-5.5h.

[0027] Preferably, in step D), the stress field of the ingot inside at different heating rates in the fourth stage of temperature interval is calculated, the stress peak value of the ingot inside at different heating rates is obtained, and the corresponding tensile strength at the temperature is compared, so that the fastest heating rate is selected as the heating rate of the fourth stage based on the criterion that the stress peak value is not more than the tensile strength.

[0028] Preferably, in step D), when the ingot is 95Cr18 steel, the fourth stage of heating has a rate of 120-160℃ / h, and the cut-off temperature after the fourth stage of heating is 1170-1210℃.

[0029] Preferably, in step E), the temperature of the fifth stage of soaking is the cut-off temperature of the fourth stage of heating, the temperature field of the ingot inside at the soaking temperature is calculated, and the final holding time is determined based on the criterion that the ingot internal and external temperature difference is less than 20℃.

[0030] When the ingot is 95Cr18 steel, the temperature of the fifth stage of soaking is 1170-1210℃, and the time of the fifth stage of soaking is 3.5-5.5h.

[0031] The application provides a design method of a hot-rolled steel ingot heating process, comprising the following steps: A) determining a first stage heating temperature of the steel ingot in combination with a stress field and a tensile strength, and carrying out a soaking treatment at the first stage heating temperature; the temperature after the first stage heating is not higher than an austenitizing temperature; B) determining a second stage heating rate of the steel ingot in combination with the stress field and the tensile strength, and carrying out a second stage heating; the temperature after the second stage heating is not higher than the austenitizing temperature; C) determining a third stage soaking time in combination with a temperature field, and carrying out a third stage soaking; in the third stage soaking, an internal-external temperature difference of the steel ingot is less than 100 DEG C; D) determining a fourth stage heating rate in combination with the stress field and the tensile strength, and carrying out a fourth stage heating; a cut-off temperature after the fourth stage heating is determined by the steel type characteristics; E) determining a fifth stage soaking time in combination with the temperature field, and carrying out a fifth stage soaking; in the fifth stage soaking, the internal-external temperature difference of the steel ingot is less than 20 DEG C. The heating process design method in the application is completely different from the rough empirical method, the heating process designed by the application will not have a hot cracking risk, the heating process designed by the application can be fine to minutes, so that the heating time of each stage in the heating process is minimized, the shortest heating process is formulated, the heating capacity is avoided to be excessive, and the heating process suitable for the ingot type and the steel type characteristics can be customized and designed according to the heating process requirements of some special steel types. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a heating process diagram of the hot-rolled steel ingot in the application;

[0033] Figure 2 It is the elastic modulus, the thermal conductivity coefficient and the volume expansion coefficient of 95Cr18 steel;

[0034] Figure 3 It is a stress field change curve of the heart with time under different temperatures;

[0035] Figure 4 It is a stress field change curve of the heart with time under different heating rates;

[0036] Figure 5 It is a cross section temperature field after the third stage 800 DEG C soaking for 4.5h;

[0037] Figure 6 It is a stress field change curve of the heart with time under different heating rates;

[0038] Figure 7 It is a cross section temperature field after the five stage 1190 DEG C soaking for 4.5h in the application;

[0039] Figure 8 It is a heating process diagram of 95Cr18 steel. DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0041] The present application provides a design method of hot-rolling steel ingot heating process, comprising the following steps:

[0042] A) determining the first stage heating temperature of the steel ingot in combination with the stress field and the tensile strength, and carrying out soaking treatment at the first stage heating temperature; the temperature after the first stage heating is not more than the austenitizing temperature;

[0043] B) determining the second stage heating rate of the steel ingot in combination with the stress field and the tensile strength, and carrying out second stage heating; the temperature after the second stage heating is not more than the austenitizing temperature;

[0044] C) determining the third stage soaking time in combination with the temperature field, and carrying out third stage soaking; in the third stage soaking, the temperature difference between the inside and outside of the steel ingot is less than 100℃;

[0045] D) determining the fourth stage heating rate in combination with the stress field and the tensile strength, and carrying out fourth stage heating; the cut-off temperature after the fourth stage heating is determined by the characteristics of the steel grade;

[0046] E) determining the fifth stage soaking time in combination with the temperature field, and carrying out fifth stage soaking; in the fifth stage soaking, the temperature difference between the inside and outside of the steel ingot is less than 20℃.

[0047] Regarding step A):

[0048] determining the first stage heating temperature of the steel ingot in combination with the stress field and the tensile strength, and carrying out soaking treatment at the first stage heating temperature; the temperature after the first stage heating is not more than the austenitizing temperature.

[0049] The heating process in the present application is not limited by the type of steel ingot, and is suitable for rolling ingots and forging ingots, and the main applicable steel grades are carbon alloy steel, stainless steel, plastic die steel, and part of hot work die steel, cold work die steel, etc. Specifically, the stainless steel can be 95Cr18 high-carbon martensitic stainless steel (abbreviated as 95Cr18 steel). The steel ingot is a steel ingot with a large head size of 660*660mm, a small head size of 510*510mm, and a length of 1800mm.

[0050] In the present application, the center of the ingot suffers the maximum tensile stress because the temperature of the center of the ingot is the lowest and the surface temperature of the ingot is the highest during the heating process of the ingot. Therefore, the stress value in the present application is the stress of the center of the ingot.

[0051] In the initial stage of the heating of the ingot, the first stage defines the temperature range from room temperature to the austenitizing temperature. Specifically, when the ingot is 95Cr18 steel, the first stage defines the temperature range of 550-800 ℃. Because the steel material will undergo phase change and produce structure transformation stress when heated to the austenitizing temperature, in order to prevent the superposition of thermal stress and structure transformation stress, the upper limit of the heating temperature in the first stage is the austenitizing temperature. The stress field of the center of the ingot at different temperatures in the temperature range is calculated to change with time, and the maximum tensile stress value of the center of the ingot at different temperatures is obtained. The maximum tensile stress value is compared with the corresponding tensile strength at the test temperature, and the temperature at which the tensile stress peak value is closest to the tensile strength is selected as the heating temperature in the first stage as the benchmark that does not exceed the tensile strength. Specifically, when the ingot is 95Cr18 steel, the heating temperature in the first stage is 580-620 ℃, and specifically can be 600 ℃.

[0052] After the heating temperature in the first stage is determined, the ingot is subjected to soaking treatment at the heating temperature in the first stage. During this process, the stress value will first gradually increase with time, reach a stress peak value, and then gradually decrease. The time required for the center of the ingot to reach the stress peak value is calculated, and the time required to reach the stress peak value is used as the time length of the soaking section in the first stage. Specifically, when the ingot is 95Cr18 steel, the time length of the soaking treatment in the first stage is 1.3-1.7 h, such as 1.5 h.

[0053] Regarding step B):

[0054] In combination with the stress field and the tensile strength, the second stage temperature rising rate of the ingot is determined, and the second stage temperature rising is performed. The temperature after the second stage temperature rising does not exceed the austenitizing temperature.

[0055] On the basis of the end of the first stage heating, the temperature is raised at different temperature rising rates. The temperature field and the corresponding stress field at different temperature rising rates are calculated. In order to prevent the superposition of thermal stress and structure transformation stress, the cut-off temperature of the temperature rising is 20-30 ℃ below the austenitizing temperature. The maximum stress value in the temperature rising process is used as the benchmark that does not exceed the maximum stress value in the whole heating process in the first stage. The maximum value is selected as the temperature rising rate in the second stage from the temperature rising rates that meet the conditions.

[0056] In some embodiments of the present application, when the ingot is 95Cr18 steel, the temperature rising rate in the second stage does not exceed 100 ℃ / h, and specifically is 70 ℃ / h.

[0057] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the temperature after the second stage of heating is 20-30 DEG C below the austenitizing temperature, and specifically can be 780-820 DEG C, such as 800 DEG C.

[0058] Regarding step C):

[0059] In combination with the temperature field, the third stage of soaking time is determined, and the third stage of soaking is performed; in the third stage of soaking, the temperature difference between the inside and outside of the steel ingot is less than 100 DEG C.

[0060] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the temperature difference between the inside and outside of the steel ingot is less than 50 DEG C.

[0061] On the basis of the end of the second stage of heating, the third stage of heating temperature field is calculated, the third stage of soaking temperature is the cut-off temperature of the second stage of heating, long time soaking is performed at the temperature, the change of the temperature field in the steel ingot during the soaking process is calculated, and the third stage of final constant temperature heating time is determined based on the criterion that the temperature difference between the inside and outside of the steel ingot is less than 100 DEG C. The temperature difference between the inside and outside of the steel ingot is limited to 100 DEG C here in order to reduce thermal stress and avoid excessive stress caused by superimposition of subsequent organizational transformation stress and thermal stress.

[0062] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the temperature of the third stage of soaking is 780-820 DEG C, such as 800 DEG C.

[0063] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the time of the third stage of soaking is 3.5-5.5 h, such as 4.5 h.

[0064] Regarding step D):

[0065] In combination with the stress field and the tensile strength, the fourth stage of heating rate is determined, and the fourth stage of heating is performed; the cut-off temperature after the fourth stage of heating is determined by the characteristics of the steel.

[0066] On the basis of the end of the third stage of soaking, the fourth stage of heating rate is calculated, the fourth stage of heating starting temperature is the third stage of constant temperature heating temperature, and the fourth stage of heating cut-off temperature needs to be determined according to the characteristics of the steel ingot itself. For example, for high carbon steel, if the heating temperature is too high, problems such as overburning and decarburization will occur, and if the heating temperature is too low, the rolling is prone to cracking, therefore, the fourth stage of heating cut-off temperature needs to be determined according to the characteristics of the steel, the stress field in the steel ingot under different heating rates in the fourth stage of temperature interval is calculated, the stress peak value in the steel ingot under different heating rates is obtained, and the corresponding tensile strength at the temperature is compared, so as to select the fastest heating rate as the fourth stage of heating rate as the criterion that the stress peak value does not exceed the tensile strength.

[0067] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the fourth stage heating rate is 120-160℃ / h, such as 140℃ / h.

[0068] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the fourth stage heating cut-off temperature is 1170-1210℃, such as 1190℃.

[0069] Regarding step E):

[0070] In combination with the temperature field, the fifth stage soaking time is determined, and the fifth stage soaking is performed; in the fifth stage soaking, the temperature difference between the inside and outside of the steel ingot is less than 20℃.

[0071] The fifth stage soaking temperature is the fourth stage heating cut-off temperature, the temperature field inside the steel ingot at the soaking temperature is calculated, and the final holding time is determined according to the criterion that the temperature difference between the inside and outside of the steel ingot is less than 20℃; the five stages of heating are combined together, which is the complete heating process.

[0072] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the fifth stage soaking temperature is 1170-1210℃, such as 1190℃.

[0073] In some embodiments of the present application, when the steel ingot is 95Cr18 steel, the fifth stage soaking time is 3.5-5.5h, such as 4.5h.

[0074] Figure 1 The figure of each stage of the heating process of the hot-rolled steel ingot of the present application.

[0075] In order to further illustrate the present application, the design method of the heating process of the hot-rolled steel ingot provided by the present application is described in detail below in combination with examples, but it should not be understood as limiting the protection scope of the present application.

[0076] Example 1

[0077] 95Cr18 high-carbon martensitic stainless steel is used as the test steel grade, and a steel ingot with a large head size of 660×660mm, a small head size of 510×510mm, and a length of 1800mm is used as the test ingot for heating process design.

[0078] In the temperature range of 550-1200℃, uniaxial tensile test of 95Cr18 steel is performed every 50℃ on a Gleeble thermal tensile testing machine, and stress-strain curves at different temperatures are obtained, and the tensile strength at different temperatures is measured, and the results are shown in Table 1.

[0079] Table 1: Hot tensile strength of 95Cr18 steel

[0080]

[0081] The elastic modulus, thermal conductivity, and volume expansion coefficient of 95Cr18 steel were measured as follows: Figure 2 As shown, Figure 2 The elastic modulus, thermal conductivity, and coefficient of volume expansion of 95Cr18 steel were determined. The austenitizing temperature of 95Cr18 steel was measured to be 830℃. The initial furnace inlet temperature was determined: the furnace temperature was set to 400℃, 500℃, 600℃, and 700℃ respectively. The change in internal stress of the steel ingot over time was calculated when heating at different furnace temperatures. The calculation results are as follows: Figure 3 As shown. Figure 3 The curves show the stress field in the core at different temperatures as a function of time. Figure 3 (a) shows the stress in the core of a steel ingot at room temperature as a function of time during constant heating at 400℃; (b) shows the stress in the core of a steel ingot at room temperature as a function of time during constant heating at 500℃; (c) shows the stress in the core of a steel ingot at room temperature as a function of time during constant heating at 600℃; and (d) shows the stress in the core of a steel ingot at room temperature as a function of time during constant heating at 700℃.

[0082] from Figure 3It can be seen from (a) in the figure that the stress gradually increases with the extension of time, reaches the peak stress 175 MPa at 7000 s, and then gradually decreases, and the tensile strength decreases with the increase of temperature. The tensile strength at 500℃ in Table 1 is 776 MPa, and the tensile strength at 400℃ is only greater than 776 MPa, therefore, the stress peak 175 MPa at the furnace temperature of 400℃ is much smaller than the tensile strength at this temperature, therefore, taking 400℃ as the starting heating temperature of the furnace, the ingot has no risk of cracking; similarly, heating at the starting furnace temperature of 500℃, the stress in the center of the ingot reaches the peak value 285 MPa at 6000 s, the peak stress 285 MPa is less than the tensile strength 776 MPa at 500℃, therefore, heating the ingot at the starting furnace temperature of 500℃ will not crack; heating at the starting furnace temperature of 600℃, the stress in the center of the ingot reaches the peak value 415 MPa at 5000 s, the peak stress 415 MPa is less than the tensile strength 701 MPa at 600℃, therefore, heating the ingot at the starting furnace temperature of 600℃ will not crack; heating at the starting furnace temperature of 700℃, the stress in the center of the ingot reaches the peak value 510 MPa at 3800 s, although the peak stress 510 MPa at 700℃ is less than the tensile strength 544 MPa. According to the calculation results, the starting heating temperatures of 400℃, 500℃, 600℃ and 700℃ can be used, but the heating time required at 400℃ and 500℃ is longer, although 700℃ also meets the conditions, but the stress value is too close to the tensile strength, the heating process needs to have a certain safety redundancy, therefore, the starting heating temperature is set to 600℃, and the heating time needs to be more than 5000 s required to reach the stress peak, therefore, the holding time at 600℃ in the first stage is 1.5 h.

[0083] After determining the first stage heating temperature, the second stage heating section uses the same method to heat to 800℃ at the heating speed of 50℃, 60℃, 70℃ and 80℃. The reason for heating to 800℃ is that the austenitizing temperature of 95Cr18 steel is 830℃, in order to prevent the superposition of thermal stress and organizational stress, therefore, the soaking treatment needs to be carried out below 20-30℃ of the phase transition temperature, therefore, the temperature is raised to 800℃.

[0084] Figure 4 The stress field in the center of the ingot changes with time at different heating rates. From Figure 4As can be seen, during the heating process at a heating rate of 50℃ / h, the stress value did not exceed the first-stage stress peak of 415MPa, and the stress value continuously decreased over time. Therefore, the steel ingot will not crack when heated at a heating rate of 50℃ / h. Similarly, during the heating processes at heating rates of 60℃ / h and 70℃ / h, the stress value did not exceed the first-stage stress peak of 415MPa, and the stress value continuously decreased over time. However, during the heating process at a heating rate of 80℃ / h, the stress value exceeded the first-stage stress peak of 415MPa, and the stress value first increased and then decreased. In summary, the heating rate of the second stage should not exceed 80℃ / h, while heating rates of 50℃ / h, 60℃ / h, and 70℃ / h are all acceptable. Among them, the heating rate of 70℃ / h has the shortest time and the highest efficiency. Therefore, the heating rate of the second stage is set at 70℃ / h.

[0085] Building upon the second stage, the third stage of design is carried out. The purpose of the third stage, the soaking heat section, is to prevent the superposition of structural stress and thermal stress. Therefore, the thermal stress needs to be reduced sufficiently. For this purpose, the temperature difference between the inside and outside of the steel ingot must be sufficiently small. Here, the soaking heat time is designed based on a temperature difference of less than 50°C. Figure 5 As shown. Figure 5 The temperature field of the cross section after 4.5 hours of homogenization at 800℃ in the third stage.

[0086] from Figure 5 It can be seen that after 4.5 hours of uniform heating at 800℃, the temperature difference between the inside and outside reaches the standard of less than 50℃. Therefore, the uniform heating time for the third stage is set at 4.5 hours.

[0087] Based on the third stage, the fourth stage of the heating process is designed, which is the same as the design method of the second stage heating stage. The temperature is raised to 1180℃ at heating rates of 100℃ / h, 140℃ / h, and 180℃ / h. The reason for raising the temperature to 1180℃ is that if the heating temperature of 95Cr18 steel exceeds 1200℃, hard and brittle δ-ferrite will be rapidly precipitated, which will reduce the plasticity of the steel ingot. Therefore, the heating temperature should not be too high. Figure 6 The curves show the stress field in the core changing with time at different heating rates.

[0088] from Figure 6It can be seen that the ingot is heated at a heating rate of 100℃ / h to reach a stress peak of 180MPa at about 40000s, at which time the core temperature is about 850℃, corresponding to a tensile strength of 244MPa, and the stress peak does not exceed the tensile strength; the ingot is heated at a heating rate of 140℃ / h to reach a stress peak of 195MPa at about 39000s, at which time the core temperature is about 850℃, corresponding to a tensile strength of 244MPa, and the stress peak does not exceed the tensile strength; the ingot is heated at a heating rate of 180℃ / h to reach a stress peak of 230MPa at about 38000s, at which time the core temperature is about 850℃, corresponding to a tensile strength of 244MPa, and the stress peak does not exceed the tensile strength; it is not difficult to see from the comparison that the ingot has no cracking risk at the heating rates of 100℃ / h and 140℃ / h, and the heating time is shorter at the heating rate of 140℃ / h, and the efficiency is higher; at the heating rate of 180℃ / h, the stress peak is close to the tensile strength, and a certain safety redundancy is required, therefore, the heating rate in the fourth stage is reasonably set to 140℃ / h.

[0089] On the basis of the fourth stage, a fifth stage of the heating process is designed, and the main purpose of the fifth stage is to make the temperature of the ingot inside and outside uniform, therefore, the ingot is heat treated at a temperature of 1190℃, and the heat soaking time is determined according to the criterion that the temperature difference between the inside and outside of the ingot is less than 20℃, as shown in Figure 7 . Figure 7 The cross-sectional temperature field of the ingot after the five-stage 1190℃ heat soaking for 4.5h.

[0090] It can be seen from Figure 7 that the heat soaking time is 4.5h, and the temperature difference between the inside and outside of the ingot reaches the requirement of less than 20℃, therefore, the heat soaking time of the fifth stage is set to 4.5h.

[0091] In this regard, the final heating process of the 95Cr18 steel is obtained by comprehensively considering the above five stages, as shown in Figure 8 . Figure 8 The diagram of each stage of the heating process of the 95Cr18 steel.

[0092] The above examples are only used to help understand the method of the present application and its core idea. Various modifications of these examples will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these examples shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for designing a hot-rolling steel ingot heating process, comprising the following steps: A) determining a first stage heating temperature of the steel ingot in combination with a stress field and a tensile strength, and performing a soaking treatment at the first stage heating temperature; the temperature after the first stage heating does not exceed an austenitizing temperature; B) determining a second stage heating rate of the steel ingot in combination with the stress field and the tensile strength, and performing a second stage heating; the temperature after the second stage heating does not exceed the austenitizing temperature; C) determining a third stage soaking time in combination with a temperature field, and performing a third stage soaking; in the third stage soaking, an internal-external temperature difference of the steel ingot is less than 100℃; D) determining a fourth stage heating rate in combination with the stress field and the tensile strength, and performing a fourth stage heating; a cut-off temperature after the fourth stage heating is determined by a steel grade characteristic; E) determining a fifth stage soaking time in combination with the temperature field, and performing a fifth stage soaking; in the fifth stage soaking, the internal-external temperature difference of the steel ingot is less than 20℃.

2. The design method of claim 1, wherein In step A), the first stage defines a temperature interval from room temperature to the austenitizing temperature; a stress field of a heart of the steel ingot at different temperatures in the first stage defined temperature interval is calculated to change with time, a maximum tensile stress value of the heart of the steel ingot at different temperatures is obtained, the maximum tensile stress value is compared with a corresponding tensile strength at a test temperature, and a temperature at which the tensile stress peak value is closest to the tensile strength is selected as the first stage heating temperature based on the tensile strength not being exceeded.

3. The method of designing according to claim 2, wherein, When the steel ingot is 95Cr18 steel, the first stage defined temperature interval is 550-800℃, the first stage heating temperature is 580-620℃, and the first stage soaking treatment duration is 1.3-1.7h.

4. The method of claim 1, wherein In step B, the temperature after the second stage heating is 20-30℃ below the austenitizing temperature; a maximum stress value in the second stage heating process is taken as a reference based on the maximum stress value in the first stage entire heating process not being exceeded, and a maximum value is selected as the second stage heating rate in the heating rate meeting the condition.

5. The method of claim 1, wherein, In step B, when the steel ingot is 95Cr18 steel, the second stage heating rate does not exceed 100℃ / h, and the temperature after the second stage heating is 20-30℃ below the austenitizing temperature.

6. The method of claim 1, wherein, In step C, a third stage heating temperature field is calculated on the basis of the second stage heating ending, a third stage soaking temperature is the heating cut-off temperature of the second stage, a change of an internal temperature field of the steel ingot in the soaking process is calculated, and a final constant temperature heating time of the third stage is determined based on the internal-external temperature difference of the steel ingot being less than 100℃.

7. The method of claim 1, wherein In step C, when the steel ingot is 95Cr18 steel, the internal-external temperature difference of the steel ingot is less than 50℃ in the third stage soaking, the temperature of the third stage soaking is 780-820℃, and the time of the third stage soaking is 3.5-5.5h.

8. The design method of claim 1, wherein, In step D, a stress field of the steel ingot is calculated at different heating rates in a fourth stage temperature interval, a stress peak value of the steel ingot is obtained at different heating rates, a corresponding tensile strength at the relevant temperature is compared, the stress peak value is taken as a criterion, and a fastest heating rate is selected as the fourth stage heating rate.

9. The method of claim 1, wherein, In step D), when the steel ingot is 95Cr18 steel, the fourth stage heating rate is 120-160℃ / h, and the cut-off temperature after the fourth stage heating is 1170-1210℃.

10. The method of claim 1, wherein, In step E), the fifth stage soaking temperature is the cut-off temperature of the fourth stage, and the temperature field in the steel ingot is calculated at the soaking temperature, and the final holding time is determined according to the criterion that the temperature difference between the inside and outside of the steel ingot is less than 20℃. When the steel ingot is 95Cr18 steel, the fifth stage soaking temperature is 1170-1210℃, and the fifth stage soaking time is 3.5-5.5h.

Images