High-strength steel 31Si2MnCrMoVE for aviation and a strengthening and toughening heat treatment process thereof
Patent Information
- Application Number
- CN202611014888.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-09
- Publication Date
- 2026-09-11
AI Technical Summary
[0003]现有奥氏体化处理多采用普通保护气氛炉进行加热，加热过程中钢件表面仍会发生轻微的氧化脱碳现象，同时易出现局部成分偏析问题，导致基体组织均匀性较差，表面形成隐性的应力集中源，在交变载荷作用下极易萌生早期疲劳裂纹
该航空用高强钢31Si2MnCrMoVE强韧化热处理工艺，通过真空奥氏体化处理避免了钢件表面氧化脱碳与成分偏析，保证了基体组织的均匀性与表面完整性，消除了表面应力集中源，避免了早期疲劳裂纹的产生，同时通过盐浴分级预冷通过晶界弥散碳化物的析出实现晶界钉扎与强化，既抑制了奥氏体晶粒异常长大，又有效阻断了裂纹沿晶界的快速扩展路径，降低了高强钢在低温与冲击载荷下的脆性断裂风险，并且通过双温等温淬火构建的双尺度下贝氏体复合组织，实现了强度与韧性的最优协同匹配，粗尺度下贝氏体提供充足的静载承载能力，细尺度下贝氏体则有效吸收冲击能量，使钢件能够同时承受航空服役中的高静载荷、交变疲劳载荷与突发冲击载荷，提升了钢件的疲劳寿命与长期服役可靠性。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of steel heat treatment technology, specifically a heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications. Background Technology
[0002] 31Si2MnCrMoVE high-strength steel, due to its high strength and good processing properties, is widely used in critical load-bearing components in the aerospace field, such as landing gear and fuselage connectors. Its heat treatment process is a core factor determining the final mechanical properties and service reliability of the steel. Currently, the industry mostly uses conventional quenching and tempering processes or single-temperature isothermal quenching processes for the heat treatment of this steel, achieving strength and toughness enhancement by controlling the microstructure transformation to meet the basic usage requirements of aerospace equipment.
[0003] Current austenitizing treatments mostly employ conventional protective atmosphere furnaces for heating. During this process, slight oxidation and decarburization still occur on the surface of the steel, and localized component segregation is prone to occur, resulting in poor matrix uniformity and the formation of hidden stress concentration sources on the surface. Under alternating loads, these areas are highly susceptible to initiating early fatigue cracks. Existing staged precooling treatments have limited ability to control the precipitation behavior of grain boundary carbides, making it difficult to form uniformly dispersed fine carbide particles. This fails to effectively suppress abnormal austenite grain growth, resulting in low grain boundary strength and rapid crack propagation along grain boundaries. Consequently, the steel parts face a high risk of brittle fracture under low-temperature environments and impact loads.
[0004] Furthermore, the existing single-temperature isothermal quenching process can only form a single-scale lower bainite structure, which cannot achieve the optimal synergistic matching of strength and toughness. A single coarse-scale structure has insufficient toughness and is difficult to absorb impact energy, while a single fine-scale structure has limited static load bearing capacity and is difficult to withstand high static loads, alternating fatigue loads and sudden impact loads during aerospace service. It cannot meet the working requirements of steel heat treatment. Therefore, a strengthening and toughening heat treatment process for aerospace high-strength steel 31Si2MnCrMoVE is proposed. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications, thereby solving the aforementioned technical problems.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications, comprising the following steps: S1 Vacuum austenitizing heating and heat preservation treatment: First, the 31Si2MnCrMoVE steel part is placed in a vacuum heat treatment furnace, heated to the austenitizing temperature and held at that temperature to make the steel part completely austenitized. S2 salt bath staged precooling and grain boundary carbide regulation treatment: The austenitized steel parts in step S1 are transferred to a salt bath furnace at a temperature higher than the martensite transformation temperature for graded precooling treatment and heat preservation, so as to homogenize the austenite composition and precipitate fine carbide particles at the grain boundaries, while inhibiting the growth of austenite grains. S3 dual-temperature isothermal quenching and dual-scale bainite microstructure construction: After the steel parts are pre-cooled in stages, they are transferred to the first isothermal salt bath furnace and held at the first isothermal temperature to transform some of the austenite into acicular lower bainite. Then they are transferred to the second isothermal salt bath furnace and held at the second isothermal temperature, which is lower than the first isothermal temperature, to transform the remaining austenite into finer lower bainite, forming a dual-scale lower bainite composite structure. S4 multi-cycle short-time cryogenic tissue refinement treatment: After the steel part is quenched by dual temperature isothermal heat in laser step S3, it is taken out and air-cooled to room temperature. Then, a short-time deep cryogenic cycle is performed. The steel part is placed in a liquid nitrogen environment for short-time heat preservation, then taken out and naturally restored to room temperature. The cycle is repeated at least twice to eliminate residual austenite and refine martensite laths. S5 segmented gradient tempering toughening control treatment: After cryogenic treatment, the steel parts are placed in a tempering furnace for segmented tempering. First, they are held at a low temperature, then heated to a high temperature and held thereafter, and finally air-cooled to room temperature to complete the entire strengthening and toughening heat treatment process.
[0007] Preferably, in step S1, before placing the steel parts in the vacuum heat treatment furnace, the steel parts are arranged neatly and then placed on the material rack of the vacuum heat treatment furnace, with uniform gaps between the steel parts. Then, the furnace is evacuated. After the vacuum degree in the furnace reaches the preset requirement, the heating begins. During the heating process, a segmented heating method is adopted, maintaining different heating rates in different temperature ranges. Through the arrangement and heating method, it can be ensured that all parts of the steel parts are heated evenly, effectively avoiding excessive thermal stress caused by a sudden temperature rise, preventing deformation or cracking of the steel parts, and laying a good foundation for subsequent microstructure transformation.
[0008] Preferably, in step S2, the salt bath medium used is a proportioned neutral mixed salt. During the transfer of the steel parts to the salt bath furnace, a transfer device with a protective gas hood is used to prevent the steel parts from oxidizing and decarburizing due to contact with air during the transfer process. In addition, the salt bath is continuously stirred at low speed during the heat preservation process to promote the uniform precipitation of carbides at the grain boundaries. By using neutral mixed salt, corrosion of the steel parts surface can be avoided. The protective gas hood can prevent oxidation and decarburization. Low-speed stirring can make the salt bath temperature distribution uniform and promote the uniform precipitation of fine carbides at the grain boundaries.
[0009] Preferably, in the first isothermal salt bath treatment in step S3, the first isothermal salt bath furnace is placed in a suspended manner, so that all surfaces of the steel parts are in contact with the salt bath medium. During the heat preservation process, the composition and temperature of the salt bath are tested regularly. The suspended placement can ensure that all surfaces of the steel parts are in full contact with the salt bath, avoiding inconsistent microstructure transformation caused by poor local contact. Regular testing can ensure that the performance of the salt bath always meets the process requirements.
[0010] Preferably, in step S3, a special device with a protective gas hood is also used during the process of transferring the steel part from the first isothermal salt bath furnace to the second isothermal salt bath furnace. After the heat preservation is completed, the steel part is first transferred to the transition cavity for short-term pre-cooling, and then taken out for air cooling. The protective gas hood can prevent oxidation of the steel part during the transfer process, and the pre-cooling of the transition cavity can avoid excessive internal stress in the steel part due to the sudden drop in temperature, ensuring that the remaining austenite is fully transformed into fine lower bainite.
[0011] Preferably, in step S4, the steel part is pre-cooled in a dry, low-temperature environment before cryogenic treatment. After the surface temperature of the steel part drops to room temperature, it is placed in a liquid nitrogen environment. The liquid nitrogen container adopts a sealed structure. After each cryogenic insulation, the steel part is taken out and placed in a ventilated and dry environment to naturally rise to room temperature. After rising to room temperature, it is kept still to allow the microstructure transformation to be fully completed before the next cycle. Pre-cooling can prevent frost corrosion on the surface of the steel part, the sealed container can ensure the stability of the cryogenic environment, and the stillness can allow the microstructure transformation to be fully completed, ensuring that the residual austenite is completely eliminated.
[0012] Preferably, in step S5, after the first low-temperature heat preservation, the steel part is first cooled to an intermediate temperature in the furnace, and then heated for a second heat preservation. The cooling process between the two tempering processes adopts a progressive cooling method, while the heating process adopts a uniform heating method. Progressive cooling can avoid tempering stress concentration, and uniform heating can ensure that the temperature in the furnace rises evenly, so that the internal structure of the steel part undergoes uniform tempering transformation, further improving the strength and toughness matching of the steel part.
[0013] Preferably, in step S1, before performing vacuum austenitizing heating and heat preservation treatment, the 31Si2MnCrMoVE steel part is first subjected to surface pretreatment. The oil, oxide scale and impurities on the surface of the steel part are removed by mechanical grinding combined with chemical cleaning. Then, the steel part is placed in a preheating furnace for preheating treatment. During the preheating process, a slow heating method is adopted to make the overall temperature of the steel part rise uniformly. Surface pretreatment can thoroughly remove impurities on the surface of the steel part and eliminate surface defects. Slow preheating can reduce the thermal stress during the heating process of the steel part and effectively improve the uniformity of austenitization.
[0014] Preferably, in step S5, after the segmented gradient tempering and toughening control treatment is completed, the steel part is subjected to surface shot peening strengthening treatment. Spherical shot is used as the shot peening medium. During the shot peening process, the shot spraying angle and spraying speed are controlled in real time so that the surface of the steel part is uniformly impacted by the shot, forming a residual compressive stress layer on the surface of the steel part. Surface shot peening can form a uniform residual compressive stress layer on the surface of the steel part, effectively offsetting the tensile stress during service, and significantly improving the fatigue strength and impact resistance of the steel part.
[0015] Preferably, the heating furnaces used for the salt bath graded precooling treatment, the dual-temperature isothermal quenching treatment, and the segmented gradient tempering treatment are all equipped with a multi-point temperature detection system. That is, temperature sensors are evenly arranged at different positions in the furnace to monitor the temperature changes in each area of the furnace in real time. The multi-point temperature detection system can monitor the temperature changes in each area of the furnace in real time, accurately control the furnace temperature fluctuation, and avoid the problems of microstructure transformation and unstable mechanical properties caused by uneven temperature.
[0016] Compared with the prior art, the present invention provides a heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications, which has the following beneficial effects: The heat treatment process for strengthening and toughening 31Si2MnCrMoVE high-strength steel for aerospace applications avoids surface oxidation, decarburization, and compositional segregation through vacuum austenitization, ensuring the uniformity and surface integrity of the matrix structure, eliminating surface stress concentration sources, and preventing early fatigue cracks. Simultaneously, salt bath staged precooling promotes grain boundary pinning and strengthening through the precipitation of dispersed carbides, inhibiting abnormal austenite grain growth and effectively blocking the rapid crack propagation path along grain boundaries. This reduces the risk of brittle fracture of high-strength steel under low temperature and impact loads. Furthermore, the dual-scale bainitic composite structure constructed through dual-temperature isothermal quenching achieves optimal synergistic matching of strength and toughness. Coarse-scale bainite provides sufficient static load-bearing capacity, while fine-scale bainite effectively absorbs impact energy, enabling the steel to simultaneously withstand high static loads, alternating fatigue loads, and sudden impact loads during aerospace service, thus improving the fatigue life and long-term service reliability of the steel. Attached Figure Description
[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] Please see Figure 1 This invention provides a technical solution: a heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications, comprising the following steps: S1 Vacuum austenitizing heating and heat preservation treatment: First, the 31Si2MnCrMoVE steel part is placed in a vacuum heat treatment furnace, heated to the austenitizing temperature and held at that temperature to make the steel part completely austenitized. Before placing the steel parts into the vacuum heat treatment furnace, the steel parts are arranged neatly and then placed into the material rack of the vacuum heat treatment furnace, with uniform gaps between the steel parts. Then, the furnace is evacuated. After the vacuum degree in the furnace reaches the preset requirements, the temperature is raised. During the heating process, a segmented heating method is adopted, and different heating rates are maintained in different temperature ranges. Before vacuum austenitizing heating and heat preservation treatment, the surface of the 31Si2MnCrMoVE steel parts is pretreated by mechanical grinding combined with chemical cleaning to remove oil, oxide scale and impurities from the surface of the steel parts. Then the steel parts are placed in a preheating furnace for preheating treatment. During the preheating process, a slow heating method is used to make the overall temperature of the steel parts rise evenly. S2 salt bath staged precooling and grain boundary carbide regulation treatment: The austenitized steel parts in step S1 are transferred to a salt bath furnace at a temperature higher than the martensite transformation temperature for graded precooling treatment and heat preservation, so as to homogenize the austenite composition and precipitate fine carbide particles at the grain boundaries, while inhibiting the growth of austenite grains. The salt bath medium used above is a proportioned neutral mixed salt. At the same time, during the process of transferring the steel parts to the salt bath furnace, a transfer device with a protective gas cover is used to prevent the steel parts from oxidizing and decarburizing when they come into contact with air during the transfer process. In addition, the salt bath is continuously stirred at low speed during the heat preservation process to promote the uniform precipitation of carbides at the grain boundaries. S3 dual-temperature isothermal quenching and dual-scale bainite microstructure construction: After the steel parts are pre-cooled in stages, they are transferred to the first isothermal salt bath furnace and held at the first isothermal temperature to transform some of the austenite into acicular lower bainite. Then they are transferred to the second isothermal salt bath furnace and held at the second isothermal temperature, which is lower than the first isothermal temperature, to transform the remaining austenite into finer lower bainite, forming a dual-scale lower bainite composite structure. During the first isothermal salt bath treatment, the first isothermal salt bath furnace is placed in a suspended manner so that all surfaces of the steel parts are in contact with the salt bath medium. During the heat preservation process, the composition and temperature of the salt bath are monitored regularly. The steel parts are transferred from the first isothermal salt bath furnace to the second isothermal salt bath furnace using a special device with a protective air cover. After the heat preservation is completed, the steel parts are first transferred to the transition chamber for brief pre-cooling, and then taken out for air cooling. S4 multi-cycle short-time cryogenic tissue refinement treatment: After the steel part is quenched by dual temperature isothermal heat in laser step S3, it is taken out and air-cooled to room temperature. Then, a short-time deep cryogenic cycle is performed. The steel part is placed in a liquid nitrogen environment for short-time heat preservation, then taken out and naturally restored to room temperature. The cycle is repeated at least twice to eliminate residual austenite and refine martensite laths. Before cryogenic treatment, the steel parts are first placed in a dry, low-temperature environment for pre-cooling. After the surface temperature of the steel parts drops to room temperature, they are placed in a liquid nitrogen environment. The liquid nitrogen container adopts a sealed structure. After each cryogenic insulation, the steel parts are taken out and placed in a ventilated and dry environment to naturally rise to room temperature. After rising to room temperature, they are kept still to allow the microstructure transformation to be fully completed before the next cycle is carried out. S5 segmented gradient tempering toughening control treatment: After cryogenic treatment, the steel parts are placed in a tempering furnace for segmented tempering. First, they are held at a low temperature, then heated to a high temperature and held, and finally air-cooled to room temperature to complete the entire strengthening and toughening heat treatment process. After the first low temperature holding, the steel parts are cooled to an intermediate temperature in the furnace, and then heated for the second holding. The cooling process between the two temperings adopts a progressive cooling method, while the heating process adopts a uniform heating method. After the segmented gradient tempering toughening and control treatment is completed, the steel parts are subjected to surface shot peening strengthening treatment. Spherical shot is used as the shot peening medium. During the shot peening process, the shot spraying angle and spraying speed are controlled in real time so that the steel parts are uniformly impacted by the shot and a residual compressive stress layer is formed on the steel parts surface. The heating furnaces used for salt bath graded precooling treatment, dual-temperature isothermal quenching treatment and segmented gradient tempering treatment are all equipped with multi-point temperature detection systems, that is, temperature sensors are evenly arranged in different positions in the furnace to monitor the temperature changes in each area of the furnace in real time.
[0020] This solution avoids surface oxidation, decarburization, and compositional segregation in steel parts through vacuum austenitization treatment, ensuring the uniformity and surface integrity of the matrix structure, eliminating surface stress concentration sources, and preventing the generation of early fatigue cracks. At the same time, the salt bath staged precooling achieves grain boundary pinning and strengthening through the precipitation of dispersed carbides at grain boundaries, which not only inhibits abnormal growth of austenite grains but also effectively blocks the rapid crack propagation path along grain boundaries, reducing the risk of brittle fracture of high-strength steel under low temperature and impact loads. Furthermore, the dual-scale bainitic composite structure constructed through dual-temperature isothermal quenching achieves the optimal synergistic matching of strength and toughness. The coarse-scale bainite provides sufficient static load bearing capacity, while the fine-scale bainite effectively absorbs impact energy, enabling the steel parts to withstand high static loads, alternating fatigue loads, and sudden impact loads in aerospace service, thereby improving the fatigue life and long-term service reliability of the steel parts.
[0021] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0022] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications, characterized in that, Includes the following steps: S1 Vacuum austenitizing heating and heat preservation treatment: First, the 31Si2MnCrMoVE steel part is placed in a vacuum heat treatment furnace, heated to the austenitizing temperature and held at that temperature to make the steel part completely austenitized. S2 salt bath staged precooling and grain boundary carbide regulation treatment: The austenitized steel parts in step S1 are transferred to a salt bath furnace at a temperature higher than the martensite transformation temperature for graded precooling treatment and heat preservation, so as to homogenize the austenite composition and precipitate fine carbide particles at the grain boundaries, while inhibiting the growth of austenite grains. S3 dual-temperature isothermal quenching and dual-scale bainite microstructure construction: After the steel parts are pre-cooled in stages, they are transferred to the first isothermal salt bath furnace and held at the first isothermal temperature to transform some of the austenite into acicular lower bainite. Then they are transferred to the second isothermal salt bath furnace and held at the second isothermal temperature, which is lower than the first isothermal temperature, to transform the remaining austenite into finer lower bainite, forming a dual-scale lower bainite composite structure. S4 multi-cycle short-time cryogenic tissue refinement treatment: After the steel part is quenched by dual temperature isothermal heat in laser step S3, it is taken out and air-cooled to room temperature. Then, a short-time deep cryogenic cycle is performed. The steel part is placed in a liquid nitrogen environment for short-time heat preservation, then taken out and naturally restored to room temperature. The cycle is repeated at least twice to eliminate residual austenite and refine martensite laths. S5 segmented gradient tempering toughening control treatment: After cryogenic treatment, the steel parts are placed in a tempering furnace for segmented tempering. First, they are held at a low temperature, then heated to a high temperature and held thereafter, and finally air-cooled to room temperature to complete the entire strengthening and toughening heat treatment process.
2. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S1, before placing the steel parts in the vacuum heat treatment furnace, the steel parts are arranged neatly and then loaded onto the material rack of the vacuum heat treatment furnace, with uniform gaps between the steel parts. Then, the furnace is evacuated. After the vacuum degree in the furnace reaches the preset requirement, the temperature is raised. During the heating process, a segmented heating method is adopted, and different heating rates are maintained in different temperature ranges.
3. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S2, the salt bath medium used is a proportioned neutral mixed salt. At the same time, during the process of transferring the steel parts to the salt bath furnace, a transfer device with a protective gas hood is used to prevent the steel parts from oxidizing and decarburizing due to contact with air during the transfer process. In addition, the salt bath is continuously stirred at low speed during the heat preservation process to promote the uniform precipitation of carbides at the grain boundaries.
4. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In the first isothermal salt bath treatment in step S3, the first isothermal salt bath furnace is placed in a suspended manner so that all surfaces of the steel parts are in contact with the salt bath medium, and the composition and temperature of the salt bath are detected periodically during the heat preservation process.
5. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S3, a special device with a protective gas hood is also used when the steel part is transferred from the first isothermal salt bath furnace to the second isothermal salt bath furnace. After the heat preservation is completed, the steel part is first transferred to the transition chamber for brief pre-cooling, and then taken out for air cooling.
6. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S4, the steel parts are pre-cooled in a dry, low-temperature environment before cryogenic treatment. After the surface temperature of the steel parts drops to room temperature, they are placed in a liquid nitrogen environment. The liquid nitrogen container adopts a sealed structure. After each cryogenic insulation is completed, the steel parts are taken out and placed in a ventilated and dry environment to naturally rise to room temperature. After rising to room temperature, they are kept still to allow the microstructure transformation to be fully completed before the next cycle is carried out.
7. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S5, after the first low-temperature heat preservation, the steel part is first cooled to the intermediate temperature in the furnace, and then heated up for the second heat preservation. The cooling process between the two temperings adopts a progressive cooling method, while the heating process adopts a uniform heating method.
8. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S1, before the vacuum austenitizing heating and heat preservation treatment, the surface of the 31Si2MnCrMoVE steel part is pretreated by mechanical grinding combined with chemical cleaning to remove oil, oxide scale and impurities from the surface of the steel part. Then the steel part is placed in a preheating furnace for preheating treatment. During the preheating process, a slow heating method is adopted to make the overall temperature of the steel part rise evenly.
9. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: In step S5, after the segmented gradient tempering and toughening control treatment is completed, the steel part is subjected to surface shot peening strengthening treatment. Spherical shot is used as the shot peening medium. During the shot peening process, the shot spraying angle and spraying speed are controlled in real time so that the surface of the steel part is uniformly impacted by the shot, forming a residual compressive stress layer on the surface of the steel part.
10. The heat treatment process for strengthening and toughening high-strength steel 31Si2MnCrMoVE for aerospace applications according to claim 1, characterized in that: The heating furnaces used for the salt bath graded precooling treatment, dual-temperature isothermal quenching treatment, and segmented gradient tempering treatment are all equipped with a multi-point temperature detection system, that is, temperature sensors are evenly arranged at different positions in the furnace to monitor the temperature changes in each area of the furnace in real time.