Heating process design method of hot-delivery and hot-charging steel ingot for rolling

Abstract

The invention provides a heating process design method for a hot-charging and hot-discharging steel ingot for rolling. The heating process design method comprises the following steps that the heating process comprises a first-stage constant-temperature heating process, a second-stage heating process and a third-stage constant-temperature heating process; firstly, a first-stage constant soaking temperature is determined by combining a stress field and tensile strength of a steel ingot; then determining the heating rate of two-stage heating by combining the stress field and the tensile strength of the steel ingot; and finally, determining the three-stage constant-temperature soaking time in combination with the temperature field of the steel ingot. According to the method, the reasonable hot-feeding and hot-charging steel ingot heating process is formulated in an experiment and theoretical calculation mode, the time of the steel ingot heating process can be shortened to the maximum extent from the process perspective, the production efficiency is improved, the energy consumption is reduced, steel types and purposes are not distinguished, and the method can be applied to all processes needing to heat steel ingots. According to the heating process design method provided by the invention, the optimal heating time of the hot-feeding and hot-charging steel ingots can be formulated, and the generation of red-feeding cracks can be avoided to the greatest extent.

Description

Technical Field

[0001] This invention relates to the field of hot-charged steel ingot preparation technology for rolling, and specifically to a heating process design method for hot-charged steel ingots for rolling. Background Technology

[0002] In the field of hot rolling, steel ingot heating is an important step. Hot delivery and hot charging refers to sending the steel ingot into the heating furnace for heating after the steel ingot is cast and before it has completely cooled down. In large steel plants, hot rolling production accounts for a large proportion of the cost, and energy consumption is the main source of the cost of hot rolling. Among the existing methods to reduce energy consumption, increasing the temperature of hot delivery and hot charging is the most effective and direct method.

[0003] The heating temperature, holding time, and heating rate are key factors in the hot charging process of steel ingots, directly determining the required heating time. Excessive heating time will reduce production efficiency and increase energy consumption, while insufficient heating time may result in uneven temperatures inside and outside the steel ingot. Furthermore, excessively rapid heating or an inappropriate selection of the heating temperature range may lead to the formation of hot charging cracks, causing the steel ingot to be scrapped.

[0004] Therefore, how to develop a more suitable heating process for hot-charged steel ingots used in rolling and improve production efficiency has become a focus of attention for many front-line researchers in the industry. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a heating process design method for hot-charged steel ingots for rolling. The present invention can minimize the heating time of steel ingots, improve production efficiency, and reduce energy consumption from a process perspective. Furthermore, this technology is not differentiated by steel type or application; it can be applied to any process that requires heating steel ingots. Moreover, the method is simple, the conditions are controllable, and the stability is good, making it more suitable for industrial promotion and application.

[0006] This invention provides a heating process design method for hot-charged steel ingots used in rolling, comprising the following steps:

[0007] The heating process includes a three-stage heating process: a first-stage constant temperature, a second-stage heating, and a third-stage constant temperature.

[0008] 1) Determine the homogenization temperature for the first stage of constant temperature by combining the stress field and tensile strength of the steel ingot;

[0009] 2) Determine the heating rate for the second stage of heating by combining the stress field and tensile strength of the steel ingot;

[0010] 3) Determine the homogenization time for the three-stage isothermal process by combining the temperature field of the steel ingot.

[0011] Preferably, the hot charging temperature of the steel ingot before heating is greater than or equal to 600°C.

[0012] Preferably, the steel ingots include one or more of the following: 95Cr18 mold steel, Cr12MoV mold steel, D2 mold steel, 40Cr13 stainless steel, and 42CrMo alloy steel.

[0013] Preferably, step 1) specifically comprises:

[0014] Based on the austenitizing temperature and the core overheating temperature of the steel ingot, the design range of the homogenization temperature for the first-stage isothermal process is determined. The lowest temperature in the homogenization temperature design range is higher than the austenitizing temperature of the steel ingot, and the highest temperature in the homogenization temperature design range is lower than the core overheating temperature of the steel ingot.

[0015] The maximum surface stress value of the steel ingot is detected at different temperatures within the design range of the homogenization temperature. The temperature corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

[0016] Preferably, step 1) further includes:

[0017] The tensile strength of the steel ingot is tested at different temperatures within the design range of the homogenization temperature. The maximum surface stress value is compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress value does not exceed the tensile strength, the temperature 'a' corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

[0018] Preferably, step 1) further includes determining the homogenization time for a stage of constant temperature based on the temperature field of the steel ingot.

[0019] Preferably, the specific steps for determining the homogenization time of the first-stage isothermal process are as follows: the steel ingot is subjected to homogenization treatment at the homogenization temperature, the cross-sectional temperature field of the steel ingot is detected, and the minimum time for the overall temperature of the steel ingot to exceed the austenitization temperature is determined, which is taken as the minimum homogenization time of the first-stage isothermal process.

[0020] Preferably, step 2) specifically comprises:

[0021] The steel ingot was heated to the final heating temperature at different heating rates. The tensile strength and maximum surface stress of the steel ingot at different temperatures were measured. The maximum surface stress at the same temperature was compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress does not exceed the tensile strength at the same temperature, the fastest heating rate was selected as the heating rate for the second stage heating.

[0022] Preferably, the final heating temperature is less than or equal to the core overheating temperature of the steel ingot.

[0023] Preferably, step 3) specifically comprises:

[0024] The steel ingot was subjected to isothermal treatment under three stages of constant temperature, and the cross-sectional temperature field of the steel ingot was detected. The time when the temperature difference between the inside and outside of the steel ingot was less than or equal to 20°C was taken as the minimum isothermal treatment time under the three stages of constant temperature.

[0025] This invention provides a heating process design method for hot-charged steel ingots used in rolling, comprising the following steps: the heating process includes a three-stage heating process consisting of a first-stage isothermal heating, a second-stage heating, and a third-stage isothermal heating; firstly, the homogenization temperature for the first-stage isothermal heating is determined based on the stress field and tensile strength of the steel ingot; then, the heating rate for the second-stage heating is determined based on the stress field and tensile strength of the steel ingot; finally, the homogenization time for the third-stage isothermal heating is determined based on the temperature field of the steel ingot. Compared with existing technologies, most current literature on the design methods for heating processes of hot-charged steel ingots focuses on heating processes for a specific steel grade, and directly provides heating process ranges based on experience, without specifying a design method for the heating process itself. This invention suggests that the heating temperature, holding time, and heating rate are key factors in the hot-loading steel ingot heating process, directly determining the required heating time. Excessive heating time reduces production efficiency and increases energy consumption, while insufficient heating time may result in uneven temperatures inside and outside the steel ingot. Furthermore, excessively rapid heating or inappropriate selection of the heating temperature range may lead to the formation of hot-loading cracks, causing the steel ingot to be scrapped.

[0026] Based on this, the present invention creatively develops a heating process design method for hot-charged steel ingots used in rolling. This hot-charged steel ingot heating process, formulated through experiments and theoretical calculations, maximizes the reduction of ingot heating time, improves production efficiency, and reduces energy consumption from a process perspective. Furthermore, this technology is not differentiated by steel type or application; it can be applied to any process requiring ingot heating, aligning with the enduring themes of energy conservation, emission reduction, quality improvement, and efficiency enhancement in the steel industry.

[0027] The heating process design method for hot-charged steel ingots for rolling provided by this invention can determine the optimal heating time for hot-charged steel ingots and minimize the occurrence of hot-charge cracks.

[0028] Practical application results show that, when applied at Panzhihua Iron and Steel Group Jiangyou Great Wall Special Steel Co., Ltd., based on an annual self-smelting steel production capacity of 300,000 tons, the heating process designed in this invention can reduce the cost by about 50 yuan per ton of steel, resulting in an annual cost reduction of 15 million yuan. Attached Figure Description

[0029] Figure 1 Curves of each stage of the heating process in the heating process design method provided by the present invention;

[0030] Figure 2The elastic modulus, thermal conductivity, and volume expansion coefficient of 95Cr18 steel in Example 1 of this invention;

[0031] Figure 3 This refers to the surface stress of 95Cr18 steel during the entire heating process at different homogenization temperatures in one stage, as described in Example 1 of this invention.

[0032] Figure 4 The surface stress of 95Cr18 steel during the entire heating process under different heating rates in two stages in Embodiment 1 of the present invention;

[0033] Figure 5 The temperature field of the steel ingot cross section after 3.5 hours of three-stage homogenization of 95Cr18 steel in Example 1 of the present invention;

[0034] Figure 6 This is the heating process curve for hot delivery and hot charging of 95Cr18 steel designed in Embodiment 1 of the present invention. Detailed Implementation

[0035] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0037] The purity of all raw materials used in this invention is not particularly limited, but the purity of industrial-grade pure or conventionally used in the preparation of hot-charged steel ingots is preferred.

[0038] This invention provides a heating process design method for hot-charged steel ingots used in rolling, comprising the following steps:

[0039] The heating process includes a three-stage heating process: a first-stage constant temperature, a second-stage heating, and a third-stage constant temperature.

[0040] 1) Determine the homogenization temperature for the first stage of constant temperature by combining the stress field and tensile strength of the steel ingot;

[0041] 2) Determine the heating rate for the second stage of heating by combining the stress field and tensile strength of the steel ingot;

[0042] 3) Determine the homogenization time for the three-stage isothermal process by combining the temperature field of the steel ingot.

[0043] In this invention, the hot charging temperature of the steel ingot before heating is preferably greater than or equal to 600°C.

[0044] In this invention, the type of steel ingot preferably includes one or more of 95Cr18 mold steel, Cr12MoV mold steel, D2 mold steel, 40Cr13 stainless steel and 42CrMo alloy steel, and more preferably 95Cr18 mold steel, Cr12MoV mold steel, D2 mold steel, 40Cr13 stainless steel or 42CrMo alloy steel.

[0045] This invention first determines the homogenization temperature for a one-stage constant temperature by combining the stress field and tensile strength of the steel ingot.

[0046] In this invention, step 1) is preferably:

[0047] Based on the austenitizing temperature and the core overheating temperature of the steel ingot, the design range of the homogenization temperature for the first-stage isothermal process is determined. The lowest temperature in the homogenization temperature design range is higher than the austenitizing temperature of the steel ingot, and the highest temperature in the homogenization temperature design range is lower than the core overheating temperature of the steel ingot.

[0048] The maximum surface stress value of the steel ingot is detected at different temperatures within the design range of the homogenization temperature. The temperature corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

[0049] In this invention, step 1) preferably further includes:

[0050] The tensile strength of the steel ingot is tested at different temperatures within the design range of the homogenization temperature. The maximum surface stress value is compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress value does not exceed the tensile strength, the temperature 'a' corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

[0051] In this invention, step 1) preferably also includes determining a stage of constant temperature homogenization time based on the temperature field of the steel ingot.

[0052] In this invention, the preferred step for determining the homogenization time of the first-stage isothermal process is to perform homogenization treatment on the steel ingot at the homogenization temperature, detect the cross-sectional temperature field of the steel ingot, and determine the minimum time for the overall temperature of the steel ingot to exceed the austenitizing temperature, which is then taken as the minimum homogenization time of the first-stage isothermal process.

[0053] This invention further combines the stress field and tensile strength of the steel ingot to determine the heating rate of the two-stage heating process.

[0054] In this invention, step 2) is preferably:

[0055] The steel ingot was heated to the final heating temperature at different heating rates. The tensile strength and maximum surface stress of the steel ingot at different temperatures were measured. The maximum surface stress at the same temperature was compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress does not exceed the tensile strength at the same temperature, the fastest heating rate was selected as the heating rate for the second stage heating.

[0056] In this invention, the final heating temperature is preferably less than or equal to the core overheating temperature of the steel ingot.

[0057] Finally, this invention combines the temperature field of the steel ingot to determine the homogenization time for the three-stage isothermal process.

[0058] In this invention, step 3) is preferably:

[0059] The steel ingot was subjected to isothermal treatment under three stages of constant temperature, and the cross-sectional temperature field of the steel ingot was detected. The time when the temperature difference between the inside and outside of the steel ingot was less than or equal to 20°C was taken as the minimum isothermal treatment time under the three stages of constant temperature.

[0060] This invention aims to complete and refine the overall technical solution, better ensure the stability and repeatability of the heating process design method for hot-charged steel ingots used in rolling, and further improve the accuracy and efficiency of the heating process design method for hot-charged steel ingots used in rolling. Specifically, the heating process design method for hot-charged steel ingots used in rolling may include the following:

[0061] A design method for a hot-delivery and hot-charging steel ingot heating process, the design method comprising:

[0062] (1) Determine the first-stage heating temperature by combining the stress field and tensile strength;

[0063] (2) Determine the two-stage heating rate by combining the stress field and tensile strength;

[0064] (3) Combine the temperature field to determine the three-stage heating time, and the temperature difference between the inside and outside of the steel ingot is less than 20℃;

[0065] Specifically, the heating temperature, heating rate, and heat spread time are determined, as described below:

[0066] During the heating process of steel ingots, heat conduction takes time, creating a temperature difference between the inside and outside of the ingot. This leads to internal stress within the ingot. Since steel is a metallic material, cracking will occur when the internal stress exceeds the ingot's inherent limits. To ensure that the stress value does not exceed these limits during heating, it is necessary to calculate the magnitude of the internal stress and determine the ingot's maximum stress limit. The stress value can be calculated, while the maximum stress limit can be determined experimentally. By comparing the internal stress at different temperatures with the maximum stress limit, it is possible to ensure that the internal stress at each stage of the heating process does not exceed the maximum stress limit. Based on this, the optimal heating temperature, heating rate, and homogenization time can be selected to achieve the shortest possible heating process for the steel ingot.

[0067] Furthermore, steel ingot heating is a complex process. The most important aspect of designing the steel ingot heating process is to obtain a sufficiently realistic temperature field and stress field during the heating process. To this end, it is necessary to obtain some real thermal property parameters of the material through experiments.

[0068] 1. Stress-strain curve

[0069] The material is processed into standard high-temperature tensile specimens, and a uniaxial tensile test is performed using a tensile testing machine to determine the stress-strain curve of the material. Since the hot rolling of steel ingots is carried out at high temperatures, it is necessary to determine the stress-strain curve of the material at different temperatures within the rolling temperature range to obtain the elastic modulus and tensile strength of the material at different temperatures. Since the heating temperature range is large, it is not necessary to determine the stress-strain curve at every temperature. It is only necessary to perform a tensile test every 50°C or 100°C between the highest heating temperature and room temperature.

[0070] 2. Coefficient of thermal expansion: The volume of steel materials changes with temperature during the heating process. The phase transformation of steel materials during the heating process also leads to volume change. Due to the non-uniformity of temperature on the cross-section of the steel ingot during the heating process and the non-synchronous nature of the phase transformation, thermal stress and structural stress will be generated inside the steel ingot. Therefore, it is necessary to measure the volume change of the steel material itself within the heating temperature range. The linear expansion method or the volume expansion method can be used for measurement.

[0071] 3. Thermal conductivity: The rate of heat transfer during the heating process of steel materials determines the temperature difference between the inside and outside of the steel ingot. Different materials have very different thermal conductivity. Therefore, measuring the thermal conductivity is very important for calculating the temperature field during the heating process of steel ingot.

[0072] 4. Determine the phase transition temperature of the material: Steel materials undergo phase transitions with temperature changes. Phase transitions are inevitably accompanied by volume changes and generate structural stress. Different materials have different phase transition temperatures. Knowing the phase transition point of the material is crucial for designing the heating process.

[0073] 5. Temperature field and stress field calculations

[0074] Based on the above experimental data, a calculation model was established to calculate the temperature field inside the steel ingot and the stress field corresponding to the temperature field. For hot-delivered and hot-charged steel ingots, the core temperature of the steel ingot is the highest and the surface temperature is the lowest. Since the core temperature is usually higher than the austenitizing temperature, the plasticity is good and the core is not easy to crack. Due to the high initial furnace temperature when hot-delivered and hot-charged steel ingots enter the furnace, the surface is prone to thermal shock reaction, which can lead to cracks on the surface. Therefore, it is also necessary to calculate the stress field changes on the surface of the steel ingot.

[0075] Hot-charged steel ingots have strict requirements for ingot temperature, usually requiring an ingot temperature of no less than 600℃. Ingots with a temperature below 600℃ are treated as cold ingots. The selection of the first-stage heating temperature is based on the change in the surface stress field. Since the temperature of the steel ingot itself is high enough, and the internal temperature of the steel ingot is generally higher than the austenitizing temperature, the first-stage heating temperature range is usually taken between the austenitizing temperature and the final heating temperature (the overheating temperature of the steel ingot core). The tensile stress value of the steel ingot at different temperatures within the austenitizing temperature and the final heating temperature range is calculated to obtain the maximum tensile stress value of the steel ingot surface during the heating process at different temperatures. The maximum tensile stress value is compared with the tensile strength at the corresponding temperature. Based on the premise that it does not exceed the tensile strength, the heating temperature with the minimum stress is selected as the first-stage homogenization temperature.

[0076] After determining the first-stage homogenization temperature, the steel ingot is homogenized at this temperature. During this process, the stress value will first increase with time, reach the stress peak, and then gradually decrease. The overall temperature field of the steel ingot during the homogenization process is calculated. The time required for the overall temperature of the steel ingot to exceed the austenitizing temperature is taken as the first-stage homogenization time. This is to prevent the thermal stress and microstructure transformation stress from superimposing during the subsequent heating process.

[0077] After the first stage of heating is completed, it is necessary to determine the heating rate of the second stage. The temperature and stress fields under different heating rates are calculated to reach the final heating temperature. Based on the premise that the maximum stress value does not exceed the ultimate tensile strength at the corresponding temperature, the fastest heating rate in the range is selected as the heating rate of the second stage. Since only thermal stress exists in this process and the steel ingot itself has high temperature and good plasticity, for most steel grades, the heating rate of this stage can be carried out according to the maximum heating rate of the heating furnace.

[0078] Based on the second stage, the temperature field inside the steel ingot is calculated under the uniform heating temperature of the third stage. The final holding time is determined with the temperature difference between the inside and outside of the steel ingot being less than 20℃ as the criterion. Combining the three stages of steel ingot heating together results in a complete hot delivery and hot charging heating process.

[0079] See Figure 1 , Figure 1 The heating process design method provided by this invention includes curves for each stage of the heating process.

[0080] The present invention provides a heating process design method for hot-charged steel ingots used in rolling. This hot-charged steel ingot heating process, developed through experiments and theoretical calculations, maximizes the reduction of ingot heating time, improves production efficiency, and reduces energy consumption from a process perspective. Furthermore, this technology is not differentiated by steel type or application; it can be applied to any process requiring ingot heating, aligning with the enduring themes of energy conservation, emission reduction, quality improvement, and efficiency enhancement in the steel industry.

[0081] The heating process design method for hot-charged steel ingots for rolling provided by this invention can determine the optimal heating time for hot-charged steel ingots and minimize the occurrence of hot-charge cracks.

[0082] Practical application results show that, when applied at Panzhihua Iron and Steel Group Jiangyou Great Wall Special Steel Co., Ltd., based on an annual self-smelting steel production capacity of 300,000 tons, the heating process designed in this invention can reduce the cost by about 50 yuan per ton of steel, resulting in an annual cost reduction of 15 million yuan.

[0083] To further illustrate the present invention, the following describes in detail the heating process design method for hot-charged steel ingots for rolling provided by the present invention with reference to embodiments. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, and are not intended to limit the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0084] Example 1

[0085] Using 95Cr18 high-carbon martensitic stainless steel as the test steel, and a steel ingot with a large end size of 660x660mm, a small end size of 510x510mm, and a length of 1800mm as the test ingot shape, the heating process was designed.

[0086] Within the temperature range of 550-1200℃, uniaxial tensile tests were performed on 95Cr18 steel at 50℃ intervals on a Gleeble hot tensile testing machine to obtain stress-strain curves at different temperatures. At the same time, the tensile strength at different temperatures was measured. The results are shown in Table 1, which shows the hot tensile strength of 95Cr18 in Example 1 of this invention.

[0087] Table 1

[0088]

[0089] The elastic modulus, thermal conductivity, and volume expansion coefficient of 95Cr18 steel were measured as follows: Figure 2 As shown, Figure 2 The figures show the elastic modulus, thermal conductivity, and coefficient of volume expansion of 95Cr18 steel in Example 1 of this invention. The top figure shows the elastic modulus of 95Cr18 steel, the middle figure shows the thermal conductivity, and the bottom figure shows the coefficient of volume expansion. Finally, the austenitizing temperature of 95Cr18 steel was measured to be 830℃.

[0090] The first-stage homogenization temperature is determined as follows: the austenitizing temperature of 95Cr18 steel is 830℃, and the final heating temperature is 1190℃ (core overheating temperature). Therefore, the first-stage heating temperature range is 840-1190℃. The changes in the surface stress field of the steel ingot at different temperatures within this temperature range are calculated, such as... Figure 3 As shown, Figure 3 This refers to the surface stress of 95Cr18 steel during the entire heating process at different homogenization temperatures in one stage, as described in Embodiment 1 of the present invention. Except for the different homogenization temperatures in the first stage, the homogenization time in the first stage, the heating rate in the second stage, and the homogenization time in the third stage are all kept consistent.

[0091] The figure only calculates the stress changes at 840, 900, and 1000℃. According to the selection principle, the surface stress at 900℃ is the smallest, only 35MPa. Therefore, among the three temperatures of 840, 900, and 1000℃, 900℃ should be selected as the homogenization temperature. After determining the homogenization temperature, the temperature field of the steel ingot cross section is calculated. When the homogenization time is 45 minutes, the overall temperature of the steel ingot reaches above 830℃. Therefore, the homogenization time in the first stage should not be less than 45 minutes.

[0092] Determining the two-stage heating rate: The maximum heating rate of the furnace is 150℃ / h. Therefore, the stress values ​​of the steel ingot section are calculated at heating rates of 60, 100, and 150℃ / h. The results are as follows. Figure 4 As shown, Figure 4This refers to the surface stress of 95Cr18 steel during the entire heating process at different heating rates in two stages, as described in Embodiment 1 of the present invention. Except for the different heating rates in the two stages, the homogenization temperature and time in the first stage and the homogenization time in the third stage remain consistent.

[0093] It can be seen that the stress peak of 95Cr18 steel is the smallest at a heating rate of 60℃ / h. The stress peaks at 100℃ / h and 150℃ / h are about the same, at 48MPa. This indicates that after the heating rate reaches 100℃, the stress no longer changes significantly with the increase of the heating rate, and neither exceeds the ultimate tensile strength at the corresponding temperature. Therefore, the maximum heating rate of the heating furnace, 150℃ / h, is directly used for heating. Thus, the second-stage heating rate is selected as 150℃ / h.

[0094] The three-stage soaking time was determined, and the temperature field of the steel ingot cross-section was calculated as a function of time. The results are as follows: Figure 5 As shown, Figure 5 This is the temperature field of the steel ingot cross section after 3.5 hours of three-stage homogenization heating of 95Cr18 steel in Example 1 of the present invention.

[0095] When the steel ingot is kept at a constant temperature for 3.5 hours, the temperature difference between the inside and outside of the steel ingot reaches the standard of less than 20°C. Therefore, the heating time of the three-stage heating stage should not be less than 3.5 hours.

[0096] Combining the process times of the above three stages yields the final heating process, such as... Figure 6 As shown, Figure 6 This is the heating process curve for hot delivery and hot charging of 95Cr18 steel designed in Embodiment 1 of the present invention.

[0097] The above provides a detailed description of the heating process design method for hot-charged steel ingots for rolling, as provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of this invention, including the best mode, and also to enable any person skilled in the art to practice this invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those skilled in the art, several improvements and modifications can be made to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention. The scope of patent protection of this invention is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the wording of the claims, or if they include equivalent structural elements that are not substantially different from the wording of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A heating process design method for hot-charged steel ingots used in rolling, characterized in that, Includes the following steps: The heating process includes a three-stage heating process: a first-stage constant temperature, a second-stage heating, and a third-stage constant temperature. 1) Determine the homogenization temperature for the first stage of constant temperature by combining the stress field and tensile strength of the steel ingot; 2) Determine the heating rate for the second stage of heating by combining the stress field and tensile strength of the steel ingot; 3) Determine the homogenization time for the three-stage isothermal process by combining the temperature field of the steel ingot.

2. The heating process design method according to claim 1, characterized in that, The hot charging temperature of the steel ingot before heating is greater than or equal to 600℃.

3. The heating process design method according to claim 1, characterized in that, The steel ingots include one or more of the following: 95Cr18 mold steel, Cr12MoV mold steel, D2 mold steel, 40Cr13 stainless steel, and 42CrMo alloy steel.

4. The heating process design method according to claim 1, characterized in that, Step 1) specifically refers to: Based on the austenitizing temperature and the core overheating temperature of the steel ingot, the design range of the homogenization temperature for the first-stage isothermal process is determined. The lowest temperature in the homogenization temperature design range is higher than the austenitizing temperature of the steel ingot, and the highest temperature in the homogenization temperature design range is lower than the core overheating temperature of the steel ingot. The maximum surface stress value of the steel ingot is detected at different temperatures within the design range of the homogenization temperature. The temperature corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

5. The heating process design method according to claim 4, characterized in that, Step 1) further includes: The tensile strength of the steel ingot is tested at different temperatures within the design range of the homogenization temperature. The maximum surface stress value is compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress value does not exceed the tensile strength, the temperature 'a' corresponding to the minimum maximum surface stress value is selected as the homogenization temperature for the first stage of the isothermal process.

6. The heating process design method according to claim 1, characterized in that, Step 1) also includes determining the homogenization time for a stage of constant temperature based on the temperature field of the steel ingot.

7. The heating process design method according to claim 6, characterized in that, The specific steps for determining the homogenization time of the first-stage isothermal process are as follows: the steel ingot is subjected to homogenization treatment at the homogenization temperature, the cross-sectional temperature field of the steel ingot is detected, and the minimum time for the overall temperature of the steel ingot to exceed the austenitization temperature is determined, which is taken as the minimum homogenization time of the first-stage isothermal process.

8. The heating process design method according to claim 1, characterized in that, Step 2) specifically refers to: The steel ingot was heated to the final heating temperature at different heating rates. The tensile strength and maximum surface stress of the steel ingot at different temperatures were measured. The maximum surface stress at the same temperature was compared with the tensile strength at the corresponding temperature. Based on the premise that the maximum surface stress does not exceed the tensile strength at the same temperature, the fastest heating rate was selected as the heating rate for the second stage heating.

9. The heating process design method according to claim 8, characterized in that, The final heating temperature is less than or equal to the core overheating temperature of the steel ingot.

10. The heating process design method according to claim 1, characterized in that, Step 3) specifically refers to: The steel ingot was subjected to isothermal treatment under three stages of constant temperature, and the cross-sectional temperature field of the steel ingot was detected. The time when the temperature difference between the inside and outside of the steel ingot was less than or equal to 20°C was taken as the minimum isothermal treatment time under the three stages of constant temperature.

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