A cooling method for a p92 steel ingot

Abstract

The present application relates to a kind of P92 steel ingot cooling method, to P92 high alloy big steel ingot cooling process after demoulding, according to different process parameters, simulate analysis is carried out, the change rule of the internal temperature field of steel ingot is quantitatively studied, according to simulation result, air cooling, an economic, efficient cooling medium is used to implement the regulated air cooling of steel ingot after demoulding, so that steel ingot is cooled scientifically and efficiently, can guarantee product quality, effectively shorten the equalizing time of P92 big steel ingot in heat treatment furnace, effectively improve the cooling efficiency of P92 steel ingot in heat treatment furnace, so that the equalizing, heat preservation and cooling time of P92 steel ingot in heat treatment furnace is saved by more than 50h originally, i.e. heat treatment furnace usage time is shortened by about one third.

Description

Technical Field

[0001] This invention belongs to the field of metal heat treatment technology, specifically relating to a cooling method for P92 steel ingots, and more particularly to a cooling method for P92 refined steel ingots (20-50t). Background Technology

[0002] P92 high-alloy steel ingots, as one of the main raw materials for the manufacture of large-scale high-end equipment, are widely used in advanced supercritical and ultra-supercritical power generation equipment worldwide. In recent years, the size and tonnage of single refined steel ingots used in the manufacture of large-diameter, thick-walled seamless P92 steel pipes have increased accordingly. Due to the increased ingot specifications, the time required for heat treatment furnace soaking and cooling after demolding has increased exponentially. This extended soaking time not only consumes more energy but also affects the frequency of furnace use and reduces equipment efficiency, becoming one of the technical bottlenecks for further lean manufacturing in high-tech enterprises in the new era, especially for P92 steel ingots of 20 tons or more. For example, a 23-ton P92 steel ingot requires soaking and cooling in a heat treatment furnace for more than 150 hours, severely restricting the production efficiency and profitability of enterprises. However, if the temperature field inside the steel ingot is not analyzed in conjunction with the changes and distribution patterns of the heat treatment environment and time, and the heat treatment environment and time of the P92 high alloy steel ingot are simply and directly shortened, the risk of defects on the surface of the steel ingot will increase, or even serious quality problems such as longitudinal cracking of the steel ingot leading to scrapping will occur.

[0003] Therefore, after casting large steel ingots, under the premise of ensuring quality, how to shorten the homogenization and holding temperature and time of the large steel ingots in the heat treatment furnace is a technical challenge 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] This invention provides a cooling method for P92 steel ingots. The technical problem to be solved is to address the issues of long cooling time for large P92 high-alloy steel ingots, which leads to serious energy waste and low equipment utilization. It also solves the quality problems such as surface cracking and scrapping of steel ingots caused by simply shortening the furnace cooling time.

[0005] To solve the above technical problems, the present invention provides a cooling method for P92 steel ingots, characterized by comprising the following steps:

[0006] S1. After the molten steel poured into the ingot mold has completely solidified, the ingot should be demolded immediately and air-cooled for 0 to 3 hours to ensure that the lowest temperature range 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 overall temperature of the ingot at the equilibrium transformation point of this material, the air cooling should be stopped.

[0007] S2. After the steel ingot is air-cooled, it is loaded into a heat treatment furnace with a furnace temperature of 500±10℃ and kept at the same temperature for 0 to 6 hours.

[0008] S3. After the furnace temperature is 500±10℃ and the furnace holding is completed, the furnace 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℃, hold it for 18~24h to allow the internal structure of the steel ingot to complete the transformation to a balanced state.

[0010] S5. After homogenization and heat preservation in a heat treatment furnace at a furnace temperature of 750℃±10℃, the heat treatment furnace is cooled down to 150℃ at a rate of 25~35℃ / h.

[0011] S6. After the steel ingot is homogenized and held at a heat treatment furnace at a furnace temperature of 150℃ for 45-60 hours, it is air-cooled to room temperature.

[0012] Beneficial effects: This invention, through simulation analysis of the steel ingot cooling process and combined with the TTT curve of P92 material microstructure transformation, innovatively proposes a time-saving, energy-saving, economical, and efficient real-time controllable cooling method for P92 steel ingots (20-50t). After demolding, the P92 refined steel ingot is quantitatively air-cooled, allowing the ingot to release heat quickly and efficiently. Then, it is held at the microstructure equilibrium transformation temperature to quickly complete the microstructure transformation, shortening the furnace cooling and holding time by one-third compared to conventional processes.

[0013] This invention can be used for the cooling and heat treatment of P92 refined steel ingots weighing 20-50 tons. The cooling process of this invention is simple and energy-saving, saving more than 50 hours of cooling time in the heat treatment furnace for each batch. Therefore, the economic benefits of this invention are considerable. The application of this process reduces the cost of cooling large P92 steel ingots, improves workshop labor productivity, stabilizes product quality, and significantly enhances the company's market competitiveness. Attached Figure Description

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

[0015] Figure 2 Typical cooling process curve for P92 refined steel ingots;

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

[0017] Figure 4 P92 Geometric model of refined steel ingot;

[0018] Figure 5 P92 Refined Steel Ingot Quarter CAE Model;

[0019] Figure 6 Temperature variation curves of internal and external testing points of steel ingot over time after process optimization.

[0020] Figure 1 In the diagram: T1 - Low-temperature holding temperature, T2 - Equilibrium transformation temperature, T3 - Furnace exit temperature, 1 - Ingot demolding; 2 - Air cooling; 3 - Low-temperature holding; 4 - Heating up; 5 - Equilibrium transformation; 6 - Furnace cooling; 7 - Air cooling;

[0021] Figure 2 In the diagram: T1 - Equilibrium transition temperature, T2 - Slow cooling, T3 - Furnace temperature at the outlet; 1 - Demolding of steel ingot; 2 - Loading into the furnace as soon as possible; 3 - Equilibrium structure transformation; 4 - Slow cooling; 5 - Isostatic temperature; 6 - Cooling inside the furnace; 7 - Isostatic temperature. Detailed Implementation

[0022] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below.

[0023] The present invention proposes a cooling method for P92 steel ingots, which includes the following steps in sequence:

[0024] S1 high-alloy steel (P92 material) molten steel is poured into the ingot mold using a bottom-pouring method. The ingot is immediately demolded after complete solidification. After demolding, the large ingot is placed in the waiting area of ​​the heat treatment furnace and air-cooled for 0–3 hours. During air cooling, a handheld thermometer is used to check the surface temperature of the ingot every 5 minutes to ensure that the lowest temperature range of the ingot is not lower than 450℃. Air cooling is stopped when the internal heat energy of the ingot is slightly greater than the heat energy contained at the equilibrium transformation temperature of this material (750℃).

[0025] Specifically, this invention uses numerical simulation technology to quantitatively simulate and analyze the temperature field change over time during the air cooling process of the steel ingot, taking the temperature distribution of the steel ingot after demolding as the initial condition. The air cooling time is determined to be 0–3 hours. During this time, the temperature of the lowest temperature region at the tail of the steel ingot is controlled between 500 and 550°C. When the internal heat energy of the steel ingot is slightly greater than the heat energy contained at the overall temperature of the steel ingot, which is close to the equilibrium transformation point temperature (750°C) of this material (i.e., the heat energy contained at the equilibrium transformation point of P92 material (T2 = 750°C), air cooling is stopped.

[0026] S2. After the steel ingot is air-cooled, it is placed in a heat treatment furnace at a temperature of 500±10℃ and kept at that temperature for 0 to 6 hours.

[0027] S3. After the furnace temperature is 500±10℃ and the furnace holding is completed, the furnace 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 through thermal radiation and convection; on the other hand, the temperature of the inner and outer surfaces of the steel ingot tends to be uniform through both internal to external heat conduction and external heating.

[0029] S4. After the heat treatment furnace temperature reaches 750±10℃, it is held for 18~24h to allow the internal structure of the steel ingot to complete the transformation to a balanced state.

[0030] S5. After homogenization and heat preservation in a heat treatment furnace at a furnace temperature of 750℃±10℃, the heat treatment furnace is cooled down to 150℃ at a rate of 25~35℃ / h for 20 hours.

[0031] Preferably, the heat treatment furnace cools down to 150°C at a rate of 30°C / h for 20 hours.

[0032] S6. The steel ingots are homogenized and held at a temperature of 150℃ in a heat treatment furnace for 45-60 hours. Then, the furnace door is opened, the steel ingots are lifted out and placed in the steel ingot area, and air-cooled to room temperature. The surface quality of the large steel ingots is then checked, recorded, and put into the steel ingot warehouse.

[0033] Example 1: This invention is for the rapid cooling of a 23t P92 refined steel ingot.

[0034] The temperature field distribution inside the 23tP92 refined steel ingot was quantitatively studied using FORGE NxT3.2 numerical simulation software during the air cooling process after demolding. It was determined that air cooling for 2 hours, utilizing this energy-saving, efficient and time-saving method, scientifically and efficiently releases the energy contained inside the steel ingot. When the heat energy inside the steel ingot is slightly greater than the heat energy contained in the overall temperature of the steel ingot, which is close to the equilibrium transformation temperature of the material at 750℃, the lowest temperature region on the surface of the steel ingot is about 530℃.

[0035] The steel ingot is transferred to a heat treatment furnace at 500±10℃ and held at that temperature for 5 hours. During this stage, since the highest temperature zone inside the ingot is still no lower than 1300℃, the high-temperature zone at the core of the ingot conducts heat from the outside through its own heat conduction, causing the internal temperature to decrease and the surface temperature to increase. The temperature at the core of the ingot cools down from above 1300℃ to approximately 1010℃, while the lower-temperature zone at the tail end of the ingot first heats up from around 530℃ when it was introduced into the heat treatment furnace to approximately 610℃, and then drops back to approximately 590℃. Then, the heat treatment furnace heats the ingot from 500℃ to 750±10℃ (T2) over 4 hours. As the furnace temperature rises, the ingot is heated through heat radiation and convection. Through both internal-to-external heat conduction and external heating, the ingot as a whole approaches the temperature required for the microstructure equilibrium transformation in a shorter time.

[0036] Based on the time required for the equilibrium transformation of the P92 material microstructure, 23 tons of steel ingots were held at 750±10℃ in a heat treatment furnace for 20 hours to complete the equilibrium microstructure transformation within the ingots. Then, the furnace temperature was reduced to 150℃ at a rate of 30℃ / h over 20 hours and held for 47 hours. After homogenization and holding at 150℃, the ingots were removed from the heat treatment furnace, placed in the ingot area, and air-cooled to room temperature, completing the rapid cooling production of the 23 tons of steel ingots. On-site inspection showed that the surface quality of the ingots was intact. The total heat treatment time for the above 23 tons of P92 refined steel ingots in the heat treatment furnace was 96 hours, reducing the furnace's operating time by 54 hours.

[0037] Example 2: This invention is for the rapid cooling of a 50t P92 refined steel ingot.

[0038] The temperature field distribution inside a 50t P92 refined steel ingot during the air cooling process after demolding was quantitatively studied using FORGE NxT3.2 numerical simulation software. It was determined that after 3 hours of air cooling, the energy contained inside the steel ingot was released scientifically and efficiently using this energy-saving, efficient and time-saving method. When the heat energy inside the steel ingot is slightly greater than the heat energy contained in the overall temperature of the steel ingot, which is close to the equilibrium transformation temperature of the material at 750℃, the lowest temperature region on the surface of the steel ingot is about 535℃.

[0039] The steel ingot is transferred to a heat treatment furnace at 500±10℃ and held at that temperature for 6 hours. During this stage, since the highest temperature zone inside the ingot is still no lower than 1300℃, the high-temperature zone at the core of the ingot conducts heat from the outside through its own heat conduction, causing the internal temperature to decrease and the surface temperature to increase. The temperature at the core of the ingot cools down from above 1300℃ to approximately 1000℃, while the lower-temperature zone at the tail end of the ingot first heats up from approximately 535℃ when it was introduced into the heat treatment furnace to approximately 620℃, and then drops back to approximately 605℃. Then, the heating furnace heats the ingot from 500℃ to 750±10℃ over 6 hours. As the furnace temperature rises, the ingot is heated through heat radiation and convection. Through both internal-to-external heat conduction and external heating, the overall temperature of the ingot approaches the temperature required for the microstructure equilibrium transformation in the shortest possible time.

[0040] Based on the time required for the equilibrium transformation of the P92 material microstructure, 23 tons of steel ingots were held at a heating furnace at 750±10℃ for 24 hours to allow the internal microstructure to complete the equilibrium transformation. Then, the furnace temperature was reduced to 150℃ at a rate of 30℃ / h over 20 hours and held for 60 hours. After homogenization and holding at 150℃, the steel ingots were removed from the furnace, placed in the ingot area, and air-cooled to room temperature, completing the rapid cooling of 50 tons of steel ingots. On-site inspection showed that the surface quality of the steel ingots was intact. The total time spent in the heating furnace for the above 50 tons of P92 refined steel ingots was 119 hours, reducing the furnace usage time by 70 hours.

[0041] Example 3: This invention is for the rapid cooling of a 20t P92 refined steel ingot.

[0042] The temperature field distribution inside a 20t P92 refined steel ingot during the air cooling process after demolding was quantitatively studied using FORGE NxT3.2 numerical simulation software. It was determined that air cooling for 2 hours, utilizing this energy-saving, efficient and time-saving method, scientifically and efficiently releases the energy contained inside the steel ingot. When the internal heat energy of the steel ingot is slightly greater than the heat energy contained in the overall temperature of the steel ingot, which is close to the equilibrium transformation temperature of the material at 750℃, the lowest temperature region on the surface of the steel ingot is about 528℃.

[0043] The steel ingot is transferred to a heat treatment furnace at 500±10℃ and held at that temperature for 5 hours. During this stage, since the highest temperature zone inside the ingot is still no lower than 1300℃, the high-temperature zone at the core of the ingot conducts heat from the outside through its own heat conduction, causing the internal temperature to decrease and the surface temperature to increase. The temperature at the core of the ingot cools down from above 1300℃ to approximately 1000℃, while the lower-temperature zone at the tail end of the ingot first rises from approximately 525℃ when it was introduced into the heat treatment furnace to approximately 617℃, and then falls back to approximately 595℃. Then, the heat treatment furnace heats the ingot from 500℃ to 750±10℃ (T2) over 4 hours. As the furnace temperature rises, the ingot is heated through heat radiation and convection. Through both internal-to-external heat conduction and external heating, the overall temperature of the ingot approaches the temperature required for the microstructure equilibrium transformation in the shortest possible time.

[0044] Based on the time required for the equilibrium transformation of the P92 material microstructure, 23 tons of steel ingots were held at 750±10℃ in a heat treatment furnace for 20 hours to complete the equilibrium transformation of the internal microstructure. Then, the furnace temperature was reduced to 150℃ at a rate of 30℃ / h over 20 hours and held for 46 hours. After homogenization and holding at 150℃, the steel ingots were removed from the heat treatment furnace, placed in the ingot area, and air-cooled to room temperature, completing the rapid cooling production of 20 tons of steel ingots. On-site inspection showed that the surface quality of the steel ingots was intact. The total heat treatment time for the above 20 tons of P92 refined steel ingots in the heat treatment furnace was 95 hours, reducing the heat treatment and furnace usage time by 55 hours.

[0045] This invention employs FORGE NxT3.2 numerical simulation technology to simulate the cooling process of P92 high-alloy steel ingots after demolding. Simulation analysis is conducted according to different process parameters to quantitatively study the variation law of the internal temperature field of the steel ingot. Specifically... Figure 1The process parameters t1, t2, t3, t4, t5, t6, T1, T2, and T3 are used. Numerical simulation technology is employed to extract data on the temperature field of the steel ingot during the heat treatment process and its changes over time. Based on the simulation results, a controlled air cooling method is developed to utilize air cooling, an economical and efficient cooling medium, on the steel ingot after demolding. This allows for scientific and efficient heat dissipation and cooling of the steel ingot, ensuring product quality and effectively shortening the heat treatment furnace holding time for P92 large steel ingots. This significantly improves the cooling efficiency of P92 steel ingots (20-50t) in the heat treatment furnace, reducing the heat treatment furnace usage time by more than 50 hours, which is approximately one-third shorter than the original time.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cooling method for P92 steel ingots, characterized in that, Includes the following steps: S1. After the molten steel poured into the ingot mold has completely solidified, the ingot is immediately demolded and air-cooled for 0 to 3 hours to ensure that the lowest temperature range of the ingot is controlled between 500 and 550°C. This ensures that the internal heat energy of the ingot is slightly greater than the heat energy contained at the temperature of the material's equilibrium microstructure transformation point. Then, stop the air cooling. S2. After the steel ingot is air-cooled, it is loaded into a heat treatment furnace with a furnace temperature of 500±10℃ and kept at the same temperature for 0 to 6 hours. S3. After the furnace temperature is 500±10℃ and the furnace holding is completed, the furnace 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℃, hold it for 18~24h to allow the internal structure of the steel ingot to complete the transformation to a balanced state. S5. After homogenization and heat preservation in a heat treatment furnace at a furnace temperature of 750℃±10℃, the heat treatment furnace is cooled down to 150℃ at a rate of 25~35℃ / h. S6. After the steel ingot is homogenized and held at a heat treatment furnace at a furnace temperature of 150℃ for 45-60 hours, it is air-cooled to room temperature.

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

3. The cooling method for P92 steel ingot according to claim 1, characterized in that: After the steel ingots are demolded, they are placed in the waiting area of ​​the heat treatment furnace.

4. The cooling method for P92 steel ingot according to claim 1, characterized in that: In S1, during air cooling, a handheld thermometer is used to check the surface temperature of the steel ingot once every 5 minutes.

5. The cooling method for P92 steel ingot according to claim 1, characterized in that: When the internal heat energy of the steel ingot is slightly greater than the heat energy contained in the overall temperature of the steel ingot (750℃, the equilibrium transformation point temperature of P92 material), air cooling is stopped.

6. The cooling method for 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 temperature of the inner and outer surfaces of the steel ingot tends to be uniform through both internal and external heat conduction and external heating.

7. The cooling method for P92 steel ingot according to claim 1, characterized in that: In S5, it takes 20 hours to cool down to 150℃.

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

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

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