Preparation method of P92 steel with excellent high-temperature creep performance

Abstract

This invention belongs to the field of metal material preparation technology, and particularly relates to a method for preparing columnar-like P92 steel with excellent high-temperature creep performance. The method is characterized by including pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering. By optimizing the rolling and heat treatment processes, the P92 steel forms a columnar-like crystal structure with grain boundaries parallel to the rolling direction. This ensures that the grain boundary direction is parallel to the stress direction, inhibiting the initiation and propagation of grain boundary cracks and improving the high-temperature creep performance of the steel. The columnar-like P92 steel prepared by this invention achieves a high-temperature creep life of 300-340 hours at 650℃ / 170MPa, with an elongation maintained at 9-10%. This effectively solves the key problem of the short high-temperature creep service life of existing P92 steel, which is insufficient to meet the long-term service requirements of ultra-supercritical thermal power units under high temperature, high pressure, and high stress. This effectively extends the service life of thermal power units and reduces power plant operation and maintenance costs and downtime losses.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, and in particular relates to a method for preparing columnar P92 steel with excellent high-temperature creep properties. Background Technology

[0002] P92 steel is an improvement upon P91. By reducing Mo and adding W, P92 improves high-temperature creep strength and resistance to creep. With its excellent high-temperature strength, good oxidation and corrosion resistance, and relatively low coefficient of thermal expansion, P92 steel is considered the preferred structural material for high-temperature components in ultra-supercritical thermal power units. It is widely used in key components such as main steam pipes, superheaters, and reheaters, which require long-term service under high temperature, high pressure, and high stress conditions. Both P92 and P91 steel pipes are ferritic-martensitic heat-resistant alloy steels, widely used in supercritical and ultra-supercritical power plant boilers and in high-temperature and high-pressure fields such as petrochemicals. Currently, P92 steel has a relatively low high-temperature creep service life, which greatly limits the service life of thermal power units. Therefore, improving the high-temperature creep life of P92 steel is crucial for ensuring the safe, stable, and long-term operation of ultra-supercritical thermal power units and reducing power plant operation and maintenance costs and downtime losses.

[0003] Patent document CN121472676A discloses a lightweight refractory multi-principal element alloy with excellent high-temperature creep properties, its preparation method and uses. By introducing high-melting-point refractory metals into the alloy matrix, the melting point of the alloy is greatly increased, thereby improving the high-temperature creep properties of the steel. However, the unit price of refractory metals is relatively high, which will significantly increase the cost of the material.

[0004] Patent document CN111074101A discloses a high-strength, low-specific-weight redirected solidification nickel-based superalloy, its preparation method, and its application. It describes the preparation of columnar crystals in a nickel-based superalloy through a directional solidification process, thereby improving the alloy's high-temperature mechanical properties. However, the directional solidification process is also costly and unsuitable for the industrial production of P92 steel. From the aforementioned existing technologies, it is clear that current technical approaches to improving the high-temperature creep performance of P92 steel all have significant limitations: while introducing refractory metals or employing directional solidification processes can improve high-temperature mechanical properties to some extent, they generally suffer from high costs and are difficult to adapt to the industrial production of P92 steel. Therefore, to overcome the cost bottleneck and high-temperature performance contradiction of existing technologies, effectively improve the high-temperature creep life of P92 steel, and meet its industrial production needs, it is urgent to develop a new technology that can overcome the limitations of existing technologies and balance the high-temperature creep performance and economy of P92 steel. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing columnar-like P92 steel with excellent high-temperature creep performance. To address the shortcomings of P92 steel in high-temperature creep performance, this method involves forming columnar-like grains within the steel during the rolling and heat treatment processes. This ensures that the grain boundaries are parallel to the direction of stress, suppressing the initiation and propagation of grain boundary cracks. Simultaneously, it significantly refines the size of subgrains and carbides in the steel, thereby improving the high-temperature creep performance of the steel.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing columnar-crystal P92 steel with excellent high-temperature creep properties includes pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering treatment. The specific operation steps are as follows: Step 1: Pre-rolling annealing. The P92 steel ingot is homogenized and annealed at 1100℃-1200℃ for 2-3 hours. Step 2, continuous rolling: the homogenized annealed steel ingot is subjected to multiple rolling processes. The initial rolling temperature is 1000-1100℃, the single reduction is 23-30%, and the final rolling temperature is 800-850℃. Step 3: Ultra-fast cooling treatment. After continuous rolling, the steel plate is cooled from the final rolling temperature to room temperature using an ultra-fast cooling process. The ultra-fast cooling process is a water cooling process, where the water temperature is room temperature and the water pressure is not less than 0.4 MPa. Step 4: Tempering treatment. After cooling, the steel plate is tempered at 700-730℃ for 15-30 minutes. After tempering, columnar P92 steel with excellent high-temperature creep properties is obtained.

[0007] Furthermore, the continuous rolling process rolls the steel billet from 60-67mm to 10-16mm through five passes.

[0008] Furthermore, in step 3, the steel plate is cooled from the final rolling temperature to room temperature at an ultra-fast temperature in 0.5-1 minute.

[0009] Furthermore, in step 4, a low-temperature short-time tempering process is adopted, and the tempering process uses salt bath heating.

[0010] Furthermore, the grain boundaries in the columnar P92 steel are columnar-like crystal structures parallel to the rolling direction, wherein the grain length is between 400-480 μm and the width is between 13-20 μm.

[0011] Furthermore, the subgrains and carbides in the columnar P92 steel are significantly refined, with the subgrain size between 250nm and 300nm and the carbide size between 35nm and 60nm.

[0012] Furthermore, the columnar crystal P92 steel has a high-temperature creep life of 300-340h and an elongation of 9-10% under conditions of 650℃ / 170MPa.

[0013] Furthermore, the homogenization annealing process in step 1 is carried out in a box-type resistance furnace.

[0014] Furthermore, in the ultra-fast cooling process of step 3, the water consumption per unit width is 150-200m. 3 / (h·m).

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention optimizes the rolling and heat treatment processes to form a columnar crystal structure in P92 steel with grain boundaries parallel to the rolling direction, making the grain boundary direction parallel to the stress direction, thus inhibiting the initiation and propagation of grain boundary cracks and improving the high-temperature creep performance of the steel. 2) The columnar P92 steel prepared by this invention has a high-temperature creep life of 300-340 hours under 650℃ / 170MPa conditions, with an elongation rate maintained at 9-10%. This represents a significant improvement in the high-temperature creep life compared to traditional equiaxed P92 steel, effectively solving the key problem of short high-temperature creep service life of existing P92 steel and its inability to meet the long-term service requirements of ultra-supercritical thermal power units under high temperature, high pressure, and high stress. This effectively extends the service life of thermal power units and reduces power plant operation and maintenance costs and downtime losses. 3) The preparation process of this invention is simple and controllable, requiring no complex special production equipment. The raw material is conventional ferritic heat-resistant steel P92, which does not contain refractory precious metal elements. The raw material and preparation costs are significantly reduced compared to existing technologies that use refractory metals or directional solidification processes. At the same time, this preparation method can also be applied to P91 steel, with a wider range of applications and easier industrial-scale production. Compared with existing technologies, it is more practical and economical. Attached Figure Description

[0016] Figure 1 This is a grain morphology diagram of the columnar P92 steel in Embodiment 1 of the present invention; Figure 2 The images show the subgrain and carbide morphology of the columnar P92 steel in Example 1 of this invention. Figure 3 This is a comparison of the creep performance curves of columnar P92 steel and traditional equiaxed P92 steel in Embodiment 1 of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in many different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. In the following embodiments, the conventional equiaxed P92 steel is based on ASME standards (such as ASTM A335). The standard chemical composition range of P92 steel is shown in Table 1.

[0019] Table 1 Standard Chemical Composition Range of P92 Steel Example 1 of this invention discloses a method for preparing columnar P92 steel with excellent high-temperature creep properties, comprising pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering treatment. The specific operation steps are as follows: Step 1: Pre-rolling annealing. The P92 steel ingot is homogenized and annealed at 1100℃ for 2 hours. Step 2, continuous rolling: the homogenized annealed steel ingot is subjected to multiple rolling processes. The initial rolling temperature is 1100℃, and the billet is rolled from 65mm to 16mm through five rolling processes. The single reduction is 24.5%, and the final rolling temperature is 850℃. Step 3: Ultra-rapid cooling treatment. After continuous rolling, the steel plate is cooled to room temperature ultra-rapidly. The ultra-rapid cooling process is a water cooling process, where the water temperature is room temperature, the water pressure is 0.4 MPa, and the water flow rate per unit width is 150 mm. 3 / (h·m); The steel plate cools from the final rolling temperature to room temperature in 1 minute; Step 4: Tempering treatment. After cooling, the steel plate is tempered at 725℃ for 30 minutes. Salt bath heating is used during the tempering process to ensure that the sample is heated to the target temperature quickly, so that the internal temperature of the plate is uniform and recrystallization does not occur. After tempering, columnar P92 steel with excellent high-temperature creep properties is obtained.

[0020] The columnar grain morphology of the columnar P92 steel in Example 1 is as follows: Figure 1 As shown, the average length and width of the columnar crystals are 400 μm and 20 μm, respectively; the subgrain and carbide morphologies of the steel are as follows. Figure 2 As shown, the subgrain and carbide sizes are approximately 300 nm and 60 nm, respectively; the creep life, steady-state creep rate, and elongation of the steel at 650℃ / 170MPa are 303 h, 2.8 × 10⁻⁶, and 2.8 × 10⁻⁶, respectively. -8And 10%, compared with the comparative figure as follows Figure 3 As shown in Table 2, the creep life of the steel at 650℃ / 170MPa is about 130% higher than that of the conventional equiaxed P92 steel in the comparative example, the steady-state creep rate is reduced by about 65%, and the elongation is comparable. The specific grain parameters and creep properties of the steel under 650℃ / 170MPa conditions are shown in Table 2.

[0021] Example 2 of this invention discloses a method for preparing columnar-crystal P92 steel with excellent high-temperature creep properties, comprising pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering treatment. The specific operation steps are as follows: Step 1: Pre-rolling annealing. The P92 steel ingot is homogenized and annealed at 1150℃ for 2.5 hours. Step 2, continuous rolling: the steel ingot after homogenization and annealing is subjected to multiple rolling processes. The initial rolling temperature is 1050℃, and the billet is rolled from 67mm to 16mm through five rolling processes. The single reduction is 25%, and the final rolling temperature is 835℃. Step 3: Ultra-rapid cooling treatment. After continuous rolling, the steel plate is cooled to room temperature ultra-rapidly. The ultra-rapid cooling process is a water cooling process, in which the water temperature is room temperature, the water pressure is 0.42MPa, and the water flow rate per unit width is 175m. 3 / (h·m); The steel plate cooled from the final rolling temperature to room temperature in 0.8 minutes; Step 4: Tempering treatment. After cooling, the steel plate is tempered at 730℃ for 15 minutes. Salt bath heating is used during the tempering process to ensure that the sample is heated to the target temperature quickly, so that the internal temperature of the plate is uniform and recrystallization does not occur. After tempering, columnar P92 steel with excellent high-temperature creep properties is obtained.

[0022] The columnar-like P92 steel obtained in Example 2 has an average columnar crystal length and width of 450 μm and 15 μm, respectively; subgrain and carbide sizes are approximately 270 nm and 50 nm, respectively; the creep life, steady-state creep rate, and elongation of the steel at 650 °C / 170 MPa are 325 h, 2.6 × 10⁻⁶, and 15 μm, respectively. -8 And 9.5%. The creep life of the steel at 650℃ / 170MPa is about 150% higher than that of the conventional equiaxed P92 steel in the comparative example, the steady-state creep rate is reduced by about 68%, and the elongation is not significantly reduced. The specific grain parameters of the steel and the creep properties under 650℃ / 170MPa conditions are shown in Table 2.

[0023] Example 3 of this invention discloses a method for preparing columnar-crystal P92 steel with excellent high-temperature creep properties, comprising pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering treatment. The specific operation steps are as follows: Step 1: Pre-rolling annealing. The P92 steel ingot is homogenized and annealed at 1200℃ for 3 hours. Step 2, continuous rolling: the steel ingot after homogenization and annealing is subjected to multiple rolling processes. The initial rolling temperature is 1030℃, and the billet is rolled from 60mm to 10mm through five rolling processes. The single reduction is 30%, and the final rolling temperature is 820℃. Step 3: Ultra-rapid cooling treatment. After continuous rolling, the steel plate is cooled to room temperature ultra-rapidly. The ultra-rapid cooling process is a water cooling process, where the water temperature is room temperature, the water pressure is 0.45 MPa, and the water flow rate per unit width is 200 mm. 3 / (h·m); The steel plate cools from the final rolling temperature to room temperature in 0.5 minutes; Step 4: Tempering treatment. After cooling, the steel plate is tempered at 700℃ for 25 minutes. Salt bath heating is used during the tempering process to ensure that the sample is heated to the target temperature quickly, so that the internal temperature of the plate is uniform and recrystallization does not occur. After tempering, columnar P92 steel with excellent high-temperature creep properties is obtained.

[0024] Example 3 yielded a columnar-crystal P92 steel with an average columnar crystal length and width of 480 μm and 13 μm, respectively; subgrain and carbide sizes were approximately 250 nm and 35 nm, respectively; the steel's creep life, steady-state creep rate, and elongation at 650 °C / 170 MPa were 340 h, 2.5 × 10⁻⁶, and 2.5 × 10⁻⁶, respectively. -8 And 9%. The creep life of the steel at 650℃ / 170MPa is about 160% higher than that of the conventional equiaxed P92 steel in the comparative example, the steady-state creep rate is reduced by about 69%, and the elongation is not significantly reduced. The specific grain parameters and creep properties of the steel at 650℃ / 170MPa are shown in Table 2.

[0025] The present invention provides a comparative example of conventional rolling and heat treatment of P92 steel ingots, the steps of which are as follows: Step 1: Homogenize and anneal the P92 steel ingot at 1200℃-1250℃ for 2 hours; Step 2: The homogenized annealed steel ingot is subjected to continuous rolling. The initial rolling temperature is 1200℃, and the steel is rolled from 60mm to 10mm in five passes with a single reduction of 30%. The final rolling temperature is 1080℃. Step 3: After continuous rolling, the steel plate is air-cooled to room temperature; Step 4: The rolled steel is solution-treated at 1050℃ for 30 minutes, water-cooled to room temperature, and then tempered at 760℃ for 30 minutes to obtain equiaxed P92 steel with an equiaxed grain diameter of approximately 15 μm; the subgrain and carbide sizes are approximately 400 nm and 110 nm, respectively; the creep life, steady-state creep rate, and elongation of the steel at 650℃ / 170 MPa are 130 h, 8 × 10⁻⁶, and 10⁻⁶, respectively. -8 And 12%. The specific grain parameters of the steel and its creep properties at 650℃ / 170MPa are shown in Table 2.

[0026] Table 2 Comparison of grain parameters and creep properties between Examples 1-3 and the comparative examples 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 method for preparing columnar-crystal P92 steel with excellent high-temperature creep properties, characterized in that, The process includes pre-rolling annealing, continuous rolling, ultra-rapid cooling, and tempering. The specific operating steps are as follows: Step 1: Pre-rolling annealing. The P92 steel ingot is homogenized and annealed at 1100℃-1200℃ for 2-3 hours. Step 2, continuous rolling: the homogenized annealed steel ingot is subjected to multiple rolling processes. The initial rolling temperature is 1000-1100℃, the single reduction is 23-30%, and the final rolling temperature is 800-850℃. Step 3: Ultra-fast cooling treatment. After continuous rolling, the steel plate is cooled from the final rolling temperature to room temperature using an ultra-fast cooling process. The ultra-fast cooling process is a water cooling process, where the water temperature is room temperature and the water pressure is not less than 0.4 MPa. Step 4: Tempering treatment. After cooling, the steel plate is tempered at 700-730℃ for 15-30 minutes. After tempering, columnar P92 steel with excellent high-temperature creep properties is obtained. In step 3, the steel plate is cooled from the final rolling temperature to room temperature at an ultra-rapid temperature in 0.5-1 minute. In step 4, a low-temperature short-time tempering process is used, and the tempering process is carried out by salt bath heating. The grain boundaries in the columnar P92 steel are columnar-like structures parallel to the rolling direction, with grain lengths between 400-480 μm and widths between 13-20 μm. The subgrains and carbides in the columnar P92 steel are significantly refined, with the subgrain size between 250nm and 300nm and the carbide size between 35nm and 60nm. The columnar P92 steel has a high-temperature creep life of 300-340h and an elongation of 9-10% under conditions of 650℃ / 170MPa.

2. The method for preparing columnar-like P92 steel with excellent high-temperature creep properties according to claim 1, characterized in that, The continuous rolling process involves five passes to roll the steel billet from 60-67mm to 10-16mm.

3. The method for preparing columnar-like P92 steel with excellent high-temperature creep properties according to claim 1, characterized in that, The homogenization annealing process in step 1 is carried out in a box-type resistance furnace.

4. The method for preparing columnar-like P92 steel with excellent high-temperature creep properties according to claim 1, characterized in that, In the ultra-fast cooling process of step 3, the water consumption per unit width is 150-200m. 3 / (h·m).

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