Cooling method of P92 steel ingot

Abstract

The invention relates to a cooling method of a P92 steel ingot, which comprises the following steps of: performing simulation analysis on the cooling process of the demoulded P92 high-alloy large steel ingot according to different process parameters, quantitatively researching the change rule of an internal temperature field of the steel ingot, and formulating an economic and efficient cooling medium of air cooling according to a simulation result to implement regulation type air cooling on the demoulded steel ingot. The steel ingot is scientifically and efficiently cooled, the product quality can be guaranteed, the uniform heat preservation time of the P92 large steel ingot in the heat treatment furnace is effectively shortened, the cooling efficiency of the P92 steel ingot in the heat treatment furnace is effectively improved, and the uniform heat preservation and cooling time of the P92 steel ingot in the heat treatment furnace is shortened by more than 50 hours from the original time, namely the service time of the heat treatment furnace is shortened by about one third.

Description

Technical Field

[0001] The invention belongs to the technical field of metal hot processing, and specifically relates to a cooling method for a P92 steel ingot, in particular to a cooling method for a P92 refined steel ingot (20-50t). Background Art

[0002] As one of the main raw materials for the manufacture of large-scale high-end equipment, P92 high-alloy steel ingots are widely used in the world's advanced supercritical and super (super) critical power generation equipment. In recent years, the size and tonnage of single refined steel ingots used in the manufacture of P92 large-diameter thick-walled seamless steel pipes have increased accordingly. Due to the increase in the specifications of steel ingots, the time required for the steel ingots to be demolded and transferred to the heat treatment furnace for insulation and cooling has doubled. The longer insulation time not only consumes more energy, but also affects the frequency of use of the heat treatment furnace and reduces equipment efficiency. It has become one of the technical bottlenecks for further lean production and manufacturing of high-tech manufacturing enterprises in the new era, especially for P92 steel ingots above 20t. For example: 23t P92 steel ingots need to be insulated and cooled in the heat treatment furnace for more than 150 hours, which seriously restricts the production efficiency and benefits of the enterprise. However, if the changes and distribution patterns of the temperature field inside the steel ingot accompanied by the uniform insulation, cooling environment and time are not analyzed, and the insulation, cooling environment and time of the P92 high-alloy large steel ingot in the heat treatment furnace are simply and directly shortened, the risk of defects on the surface of the large steel ingot will increase, and even serious quality problems such as longitudinal cracks in the steel ingot, resulting in scrapping, will occur.

[0003] Therefore, after the large steel ingot is cast, how to shorten the even and holding temperature and time of the large steel ingot in the heat treatment furnace under the premise of ensuring qualified quality is a technical difficulty in this field. For example, if the air cooling time t1 is too long, the steel ingot is prone to cracking and scrapping; if the time is too short, the purpose of economical and efficient cooling cannot be achieved, resulting in a long cooling time. Summary of the invention

[0004] The present invention provides a cooling method for a P92 steel ingot, and the technical problems to be solved are: solving the problems of long cooling time of a large P92 high-alloy steel ingot, causing serious waste of energy, low equipment utilization rate, etc., and also solving the quality problems of simply shortening the cooling time in the furnace causing the steel ingot surface to crack and be scrapped.

[0005] In order to solve the above technical problems, the present invention provides a cooling method for a P92 steel ingot, characterized in that it comprises the following steps:

[0006] S1. After the molten steel poured into the ingot mold is completely solidified, the ingot is immediately demolded and air-cooled. The air-cooling time is 0 to 3 hours. Ensure that the lowest temperature area of ​​the ingot is not lower than 450°C. When the internal heat energy of the ingot is greater than the heat energy contained in the temperature point of the material equilibrium structure transition point at the overall temperature of the ingot, stop air-cooling.

[0007] S2. After the air cooling of the steel ingot is completed, it is loaded into a heat treatment furnace with a temperature of 500±10℃ for averaging and heat preservation for 0-6h;

[0008] S3. After the furnace temperature is 500±10℃ and the heat preservation in the furnace is completed, the temperature of the heat treatment furnace is increased from 500±10℃ to 750±10℃ at a rate of 60-100℃ / h, and the heating time is not more than 6h;

[0009] S4. After the heat treatment furnace temperature reaches 750±10℃, keep it warm for 18-24h to complete the transformation of the internal structure equilibrium of the steel ingot;

[0010] S5. After being evenly heated and kept warm in a heat treatment furnace at a temperature of 750°C ± 10°C, the heat treatment furnace is cooled to 150°C at a rate of 25-35°C / h;

[0011] S6. After the steel ingot is evenly heated and kept in a heat treatment furnace at 150°C for 45 to 60 hours, it is air-cooled to room temperature.

[0012] Beneficial effect: The present invention simulates and analyzes the cooling process of the steel ingot, combines the TTT curve of the microstructure transformation of the P92 material, and innovatively proposes a time-saving, energy-saving, economical, and efficient real-time control type P92 steel ingot (20-50t) cooling method. The P92 refined steel ingot is quantitatively air-cooled after demoulding, so that the steel ingot releases heat quickly and efficiently, and then is kept warm at the microstructure equilibrium transformation temperature to quickly complete the microstructure transformation, shortening the cooling and insulation time in the furnace by one third compared with the conventional process.

[0013] The present invention can be used for cooling heat treatment of 20-50t P92 refined steel ingots. The cooling process of the present invention is simple and energy-saving, and each batch saves more than 50h of cooling time in the heat treatment furnace. It can be seen that the present invention has considerable economic benefits. The application of this process reduces the cost of cooling large P92 steel ingots, improves the labor production efficiency of the workshop, stabilizes product quality, and significantly improves the market competitiveness of enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The cooling process curve of the P92 refined steel ingot of the present invention;

[0015] Figure 2 Usually P92 refined steel ingot cooling process curve;

[0016] Figure 3 The location distribution diagram of the temperature detection points on the outer surface and inside of the refined steel ingot;

[0017] Figure 4 P92 refined steel ingot geometry model;

[0018] Figure 5 P92 refined steel ingot quarter CAE model;

[0019] Figure 6 The temperature variation curve of the detection points inside and outside the steel ingot over time after the optimization process.

[0020] Figure 1 In: T1- low temperature holding temperature, T2- equilibrium state transformation temperature, T3- furnace temperature, 1- ingot demoulding; 2- air cooling; 3- low temperature holding; 4- heating; 5- equilibrium state structure transformation; 6- furnace cooling; 7- air cooling;

[0021] Figure 2 In Chinese: T1-equilibrium transition temperature, T2-slow cooling, T3-furnace temperature; 1-ingot demoulding; 2-loading the furnace as soon as possible; 3-equilibrium structure transformation; 4-slow cooling; 5-uniform temperature; 6-cooling in the furnace; 7-uniform temperature. DETAILED DESCRIPTION

[0022] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0023] A cooling method for a P92 steel ingot proposed by the present invention comprises the following steps in sequence:

[0024] S1. High alloy steel (P92 material) molten steel is poured into the ingot mold by bottom pouring method. The molten steel is demolded immediately after it is completely solidified. After demolding, the large ingot is placed in the material waiting area of ​​the heat treatment furnace, and the ingot is air-cooled for 0 to 3 hours. During the air-cooling period, a handheld thermometer is used to detect the surface temperature of the ingot once every 5 minutes to ensure that the lowest temperature area of ​​the ingot is not lower than 450℃. When the internal heat energy of the ingot is slightly greater than the heat energy contained in the overall temperature of the ingot when the material is balanced and the structure is transformed at the temperature point (750℃), the air cooling is stopped.

[0025] Specifically, the present invention uses numerical simulation technology with the temperature distribution of the steel ingot after demoulding as the initial condition, quantitatively simulates and analyzes the temperature field of the steel ingot during air cooling over time, and determines the air cooling of the steel ingot, and the air cooling time is 0 to 3 hours. At this time, the temperature of the lowest temperature area at the tail of the steel ingot is controlled between 500 and 550°C, so that the internal heat energy of the steel ingot is slightly greater than the heat energy contained in the temperature point (750°C) when the overall temperature of the steel ingot is close to the material equilibrium structure transition point, that is, the heat energy contained in the P92 material equilibrium structure transition point (T2 = 750°C), and then stop air cooling;

[0026] S2. After the air cooling of the steel ingot is completed, it is loaded into a heat treatment furnace with a temperature of 500±10℃ for averaging and heat preservation for 0 to 6 hours.

[0027] S3. After the furnace temperature is 500±10℃ and the heat preservation in the furnace is completed, the temperature of the heat treatment furnace is increased from 500±10℃ to 750±10℃ at a rate of 60-100℃ / h, and the heating time is not more than 6h;

[0028] As the heat treatment furnace heats up, on the one hand, the surface of the steel ingot is heated by thermal radiation, convection and the like; on the other hand, the temperatures of the inner and outer surfaces of the steel ingot tend to be uniform through heat conduction from the inside to the outside and external heating.

[0029] S4. After the heat treatment furnace temperature reaches 750±10℃, keep it warm for 18 to 24 hours to complete the transformation of the internal structure equilibrium state of the steel ingot.

[0030] S5. After being evenly heated and kept warm in a heat treatment furnace at a temperature of 750°C±10°C, the temperature in the heat treatment furnace is lowered to 150°C at a rate of 25-35°C / h within 20 hours.

[0031] Preferably, the heat treatment furnace is cooled to 150° C. at a rate of 30° C. / h within 20 hours.

[0032] S6. The steel ingot is evenly heated and kept warm in the heat treatment furnace at a temperature of 150°C for 45 to 60 hours. Subsequently, the furnace door is opened, the steel ingot is lifted out and placed in the steel ingot area, air-cooled to room temperature, and then the surface quality of the large steel ingot is checked, recorded, and stored in the steel ingot warehouse.

[0033] Example 1: The present invention is directed to the rapid cooling of a refined steel ingot weighing 23 t and made of P92.

[0034] FORGE NxT3.2 numerical simulation software was used to quantitatively study the temperature field distribution inside the 23tP92 refined steel ingot during the air cooling process after demolding. The air cooling time was determined to be 2h. The energy contained in the steel ingot was released scientifically and efficiently by using this energy-saving, efficient and time-saving method of air cooling. The internal heat energy of the steel ingot was slightly greater than the heat energy contained in the overall temperature of the steel ingot, which was close to the material equilibrium structure transformation temperature point of 750℃. At this time, the lowest temperature area on the surface of the steel ingot was about 530℃.

[0035] The ingot is transferred to a heat treatment furnace at 500±10℃ for material treatment and kept warm for 5h. At this stage, since the temperature of the highest temperature area inside the ingot is still not lower than 1300℃, the high temperature area in the core of the ingot conducts heat from the outside of the ingot through its own heat conduction, so that the internal temperature of the ingot is reduced and the surface temperature is increased. The temperature of the core of the ingot is cooled from a high temperature of more than 1300℃ to about 1010℃, and the tail end of the ingot with a lower temperature is heated from about 530℃ when it is introduced into the heat treatment furnace to about 610℃, and then falls back to about 590℃. Then, the heat treatment furnace takes 4h to heat up from 500℃ to 750±10℃ (T2). As the furnace temperature of the heat treatment increases, the ingot is heated by thermal radiation, convection and other means. The ingot is heated from the inside to the outside and external heating, so that the ingot as a whole approaches the temperature required for the equilibrium transformation of the organization in a shorter time.

[0036] According to the time required for the balanced transformation of the P92 material structure, the 23-ton steel ingots were kept in a heat treatment furnace at 750±10℃ for 20 hours to complete the balanced transformation of the structure inside the steel ingot. Then, the temperature of the heat treatment furnace was cooled to 150℃ at a rate of 30℃ / h in 20 hours and kept for 47 hours. After being evenly and warmly maintained in the 150℃ heat treatment furnace, the steel ingots were lifted out of the heat treatment, placed in the ingot area, and air-cooled to room temperature, completing the rapid cooling production of the 23-ton steel ingots. After on-site inspection, the surface quality of the steel ingots was intact. The above 23tP92 refined steel ingots were heat treated in the heat treatment furnace for a total of 96 hours, and the use time of the heat treatment furnace was shortened by 54 hours.

[0037] Example 2: The present invention is directed to the rapid cooling of a refined steel ingot weighing 50 tons and made of P92.

[0038] FORGE NxT3.2 numerical simulation software was used to quantitatively study the temperature field distribution inside the 50tP92 refined steel ingot during the air cooling process after demolding. The air cooling was determined to be 3h. The energy contained in the steel ingot was released scientifically and efficiently by using air cooling, an energy-saving, efficient and time-saving method. When the internal heat energy of the steel ingot was slightly greater than the heat energy contained in the overall temperature of the steel ingot and approached the equilibrium structure transformation temperature point of this material at 750℃, the lowest temperature area on the surface of the steel ingot was about 535℃.

[0039] The ingot is transferred to a heat treatment furnace at 500±10℃ for averaging and heat preservation for 6h. At this stage, since the temperature of the highest temperature area inside the ingot is still not less than 1300℃, the high temperature area in the core of the ingot conducts heat from the outside of the ingot through its own heat conduction, so that the internal temperature of the ingot is reduced and the surface temperature is increased. The temperature of the core of the ingot is cooled from a high temperature of more than 1300℃ to about 1000℃, and the tail end of the ingot with a lower temperature is heated from about 535℃ when it is introduced into the heat treatment furnace to about 620℃, and then falls back to about 605℃. Then, the heating furnace takes 6h to heat up from 500℃ to 750±10℃. As the temperature of the heating furnace increases, the ingot is heated by heat radiation, convection and other means. The ingot is heated from the inside to the outside and external heating in two ways, so that the overall temperature of the ingot is closer to the temperature required for the equilibrium transformation of the organization in the shortest time.

[0040] According to the time required for the balanced transformation of the P92 material structure, the 23-ton steel ingots were kept in a heating furnace at 750±10℃ for 24 hours to complete the balanced transformation of the internal structure of the steel ingots. Then, the temperature of the heating furnace was cooled to 150℃ at a rate of 30℃ / h in 20 hours and kept for 60 hours. After being evenly heated and kept in the 150℃ heating furnace, the steel ingots were taken out of the heating furnace, placed in the steel ingot area, and air-cooled to room temperature to complete the rapid cooling of the 50t steel ingots. After on-site inspection, the surface quality of the steel ingots was intact. The above 50 tons of P92 refined steel ingots were in the heating furnace for a total of 119 hours, and the use time of the heating furnace was shortened by 70 hours.

[0041] Example 3: The present invention is directed to the rapid cooling of a refined steel ingot weighing 20 tons and made of P92.

[0042] FORGE NxT3.2 numerical simulation software was used to quantitatively study the temperature field distribution inside the 20tP92 refined steel ingot during the air cooling process after demolding. The air cooling time was determined to be 2h. The energy contained in the steel ingot was released scientifically and efficiently by using air cooling, an energy-saving, efficient and time-saving method. When the internal heat energy of the steel ingot was slightly greater than the heat energy contained in the overall temperature of the steel ingot and approached the equilibrium structure transformation temperature point of this material at 750℃, the lowest temperature area on the surface of the steel ingot was about 528℃.

[0043] The ingot is transferred to a heat treatment furnace at 500±10℃ for material treatment and kept warm for 5h. At this stage, since the temperature of the highest temperature area inside the ingot is still not less than 1300℃, the high temperature area in the core of the ingot conducts heat from the outside of the ingot through its own heat conduction, so that the internal temperature of the ingot is reduced and the surface temperature is increased. The temperature of the core of the ingot is cooled from a high temperature of more than 1300℃ to about 1000℃, and the tail end of the ingot with a lower temperature is heated from about 525℃ when it is introduced into the heat treatment furnace to about 617℃, and then falls back to about 595℃. Then, the heat treatment furnace takes 4h to heat up from 500℃ to 750±10℃ (T2). As the furnace temperature of the heat treatment increases, the ingot is heated by thermal radiation, convection and other means. The ingot is heated from the inside to the outside and external heating in two ways, so that the overall temperature of the ingot is closer to the temperature required for the equilibrium transformation of the organization in the shortest time.

[0044] According to the time required for the balanced transformation of the P92 material structure, the 23-ton steel ingot is kept in a heat treatment furnace at 750±10℃ for 20 hours to complete the balanced transformation of the structure inside the steel ingot. Then, the temperature of the heat treatment furnace is cooled to 150℃ at a rate of 30℃ / h in 20 hours and kept for 46 hours. After being evenly and warmly maintained in the 150℃ heat treatment furnace, the steel ingot is lifted out of the heat treatment, placed in the steel ingot area, and air-cooled to room temperature to complete the rapid cooling production of the 20t steel ingot. After on-site inspection, the surface quality of the steel ingot is intact. The above 20t P92 refined steel ingot is heat treated in the heat treatment furnace for a total of 95 hours, and the heat treatment and heat treatment furnace use time are shortened by 55 hours.

[0045] The present invention adopts FORGE NxT3.2 numerical simulation technology to simulate and analyze the cooling process of P92 high-alloy large steel ingot after demoulding according to different process parameters, and quantitatively studies the change law of the temperature field inside the steel ingot. Figure 1In the process parameters such as t1, t2, t3, t4, t5, t6, T1, T2, and T3, numerical simulation technology is used to mine the data of the temperature field of the steel ingot during the heat treatment process and its change with time. According to the simulation results, a method is formulated to use air cooling, an economical and efficient cooling medium, to implement regulated air cooling on the steel ingot after demolding, so that the steel ingot can dissipate heat and cool scientifically and efficiently, which can ensure product quality, effectively shorten the average holding time of P92 large ingots in the heat treatment furnace, effectively improve the cooling efficiency of P92 ingots (20-50t) in the heat treatment furnace, and save more than 50h of the original average, holding and cooling time of P92 ingots in the heat treatment furnace, that is, the use time of the heat treatment furnace is shortened by about one third.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cooling method for a P92 steel ingot, characterized in that: The following steps are involved: S1. After the molten steel poured into the ingot mold is completely solidified, the ingot is immediately demolded and air-cooled. The air-cooling time is 0 to 3 hours. Ensure that the lowest temperature area of ​​the ingot is not lower than 450°C. When the internal heat energy of the ingot is greater than the heat energy contained in the temperature point of the material equilibrium structure transition point at the overall temperature of the ingot, stop air-cooling. S2. After the air cooling of the steel ingot is completed, it is loaded into a heat treatment furnace with a temperature of 500±10℃ for averaging and heat preservation for 0-6h; S3. After the furnace temperature is 500±10℃ and the heat preservation in the furnace is completed, the temperature of the heat treatment furnace is increased from 500±10℃ to 750±10℃ at a rate of 60-100℃ / h, and the heating time is not more than 6h; S4. After the heat treatment furnace temperature reaches 750±10℃, keep it warm for 18-24h to complete the transformation of the internal structure equilibrium of the steel ingot; S5. After being evenly heated and kept warm in a heat treatment furnace at a temperature of 750°C ± 10°C, the heat treatment furnace is cooled to 150°C at a rate of 25-35°C / h; S6. After the steel ingot is evenly heated and kept in a heat treatment furnace at 150°C for 45 to 60 hours, it is air-cooled to room temperature.

2. The cooling method of a P92 steel ingot according to claim 1, characterized in that: In S1, the temperature distribution of the steel ingot after demoulding is used as the initial condition, and the numerical simulation technology is used to quantitatively simulate and analyze the change of the temperature field of the steel ingot during air cooling with time to determine the air cooling time of the steel ingot.

3. The cooling method of a P92 steel ingot according to claim 1, characterized in that: After the steel ingot is demoulded, it is placed in the waiting area of ​​the heat treatment furnace.

4. The cooling method of a P92 steel ingot according to claim 1, characterized in that: In S1, during air cooling, a handheld thermometer is used to detect the surface temperature of the steel ingot every 5 minutes to ensure that the temperature of the lowest temperature area at the tail of the steel ingot is controlled between 500 and 550°C.

5. The cooling method of a P92 steel ingot according to claim 1, characterized in that: When the internal heat energy of the steel ingot is greater than the heat energy contained in the temperature T2 of the equilibrium structure transition point of the steel ingot with the overall temperature of P92, stop air cooling.

6. The cooling method of a P92 steel ingot according to claim 1, characterized in that: In S3, as the heat treatment furnace heats up, on the one hand, the surface of the steel ingot is heated by thermal radiation and convection; on the other hand, the temperatures of the inner and outer surfaces of the steel ingot are made uniform by heat conduction from the inside to the outside and external heating.

7. The cooling method of a P92 steel ingot according to claim 1, characterized in that: In S5, the temperature is lowered to 150° C. in 20 hours.

8. The cooling method of a P92 steel ingot according to claim 1, characterized in that: In S5, the heat treatment furnace is cooled at a rate of 30°C / h.

9. The cooling method of a P92 steel ingot according to claim 1, characterized in that: The weight of P92 steel ingot is 20~50t.

10. The cooling method of a P92 steel ingot according to claim 5, characterized in that: T2＝750℃。

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