Heat-resistant crmoniv cast steel material and preparation method therefor

Abstract

The present invention belongs to the technical field of casting materials, and the technical problem to be solved thereby is to provide a heat-resistant CrMoNiV cast steel material having higher strength. A heat-resistant CrMoNiV cast steel material and a preparation method therefor. The material is composed of the following components in percentages by weight: C: 0.21-0.26%; Si: 0.20-0.40%; Mn: 0.60-0.80%; Cr: 11.60-12.20%; Ni: 0.60-1.00%; Mo: 1.00-1.20%; V: 0.25-0.35%; Ti: 0.015-0.025%; Al: ≤0.025%; Cu: ≤0.30%; P≤0.020%; and S≤0.020%; with the balance being Fe and inevitable impurities. Upon a room temperature test, Rp0.2≥550 MPa, Rm: 750-880 MPa, A≥16%, Z≥40%, KV2≥38 J, and HBW: 230-270; and upon a 550ºC test, Rp0.2≥320 MPa, and Rm≥400 MPa. The casting material adopts a specific chemical component proportion, which can ensure higher specific mechanical properties, and can be used under high-temperature conditions; the preparation method therefor is simple and easy to operate; and the obtained product has good and stable mechanical properties, can avoid the occurrence of cracks on the casting, and has reliable quality, thereby providing a new pathway for the design and material selection of a large-scale gas turbine steel casting.

Description

Heat-resistant CrMoNiV cast steel material and preparation method thereof Technical Field

[0001] The invention relates to a heat-resistant CrMoNiV cast steel material and a preparation method thereof, belonging to the technical field of casting materials. Background Art

[0002] Gas turbines are key components of clean power generation and power systems, boasting a broad market application and earning them the nickname "the crown jewel of industry." With the large-scale development and utilization of my country's natural gas resources, the West-East Gas Pipeline, offshore natural gas development, the introduction of foreign liquefied natural gas resources, and the vigorous promotion of energy conservation and emission reduction, my country's gas turbine market is poised for significant growth, driving a rapid increase in demand for heat-resistant cast steel materials.

[0003] The Chinese invention patent application number 201710790113.X discloses a preparation method for heat-resistant CrMoV steel castings and heat-resistant CrMoV steel casting materials. The main chemical components and weight percentages of the steel castings are: C: 0.12-0.20, Si: 0.20-0.60, Mn: 0.5-0.9, P≤0.020, S≤0.012, Cr: 1.0-1.5, Mo: 0.9-1.2, Ni: 0.1-0.5, V: 0.20-0.35, and the rest are iron and residual elements. The steel castings with the above components are normalized and tempered. The castings produced by this preparation method can be used to produce castings working in high-temperature environments, such as gas turbine castings, and have high high-temperature long-lasting mechanical properties. At the same time, they can meet the mechanical property requirements of normal and high temperature conditions. The steel casting material is a bainite structure, and the highest strength grade at room temperature is R p0.2 ≥440MPa, R m :590~780MPa,A≥15%,KV≥27J,R at 550℃ p0.2 ≥260MPa, needs to be further improved.

[0004] Higher strength cast steel materials should usually be high-alloy martensitic structures. Cast steel parts are usually quenched and heat treated as blanks. Microscopic chemical composition segregation is prone to occur during the casting of large high-alloy materials. The stress is high when the martensitic material undergoes structural transformation. The combination of the above factors can easily cause high-alloy martensitic cast steel parts to be prone to cracks during quenching heat treatment. Therefore, a heat treatment method is needed that can both ensure the mechanical properties of the cast steel parts and avoid cracks to produce higher-grade heat-resistant cast steel materials.

[0005] Summary of the Invention

[0006] In view of the above defects, the technical problem solved by the present invention is to provide a CrMoNiV martensitic heat-resistant cast steel material with a higher strength grade.

[0007] The heat-resistant CrMoNiV cast steel material of the present invention comprises the following components in chemical composition by weight: C: 0.21-0.26%; Si: 0.20-0.40%; Mn: 0.60-0.80%; Cr: 11.60-12.20%; Ni: 0.60-1.00%; Mo: 1.00-1.20%; V: 0.25-0.35%; Ti: 0.015-0.025%; Al: ≤0.025%; Cu: ≤0.30%; P ≤0.020%; S ≤0.020%; the remainder being Fe and unavoidable impurities.

[0008] Its mechanical properties are: when tested at room temperature, Rp0.2≥550MPa, Rm: 750~880MPa, A≥16%, Z≥40%, KV2≥38J, HBW 230~270; when tested at 550℃, Rp0.2≥320MPa, Rm≥400MPa.

[0009] Preferably, the microstructure of the heat-resistant CrMoNiV cast steel material of the present invention is tempered martensite.

[0010] The present invention also provides a method for preparing the heat-resistant CrMoNiV cast steel material of the present invention.

[0011] The preparation method of the heat-resistant CrMoNiV cast steel material of the present invention includes casting and heat treatment processes, wherein the heat treatment process is:

[0012] a. Heating: Heat the casting to 1040℃~1070℃ and keep it warm;

[0013] b. Quenching: After the insulation in step a, the casting is immersed in a coolant for quenching. The coolant is oil or a liquid with a cooling capacity equivalent to that of oil. The quenching is divided into three stages:

[0014] The first stage of quenching: after the casting enters the coolant, it oscillates in the coolant for 10 to 20 minutes;

[0015] Second stage static quenching: After the first stage quenching is completed, the casting is immersed in the coolant and remains stationary for further quenching;

[0016] The third stage of quenching: After the second stage of quenching, the casting is taken out of the coolant and air-cooled for 5 minutes, and then the temperature is measured. If the casting temperature is higher than 260°C, continue to immerse in the coolant and cool for 10 to 15 minutes, then air-cool for 5 minutes and measure the temperature. Repeat this cycle until the casting temperature is ≤ 260°C.

[0017] c. Tempering: The casting is air-cooled to a temperature of ≤200°C after exiting the coolant, and then put into the furnace for tempering at 740°C to 750°C.

[0018] In one embodiment of the present invention, in step a, the holding time is calculated as follows: T1 = D / 100*(3-3.5);

[0019] Wherein, T1 is the holding time in hours, D is the maximum hot pitch circle diameter of the casting in mm, and 3~3.5 represents any value between 3 and 3.5.

[0020] In a specific embodiment of the present invention, in step b, the vibration time of the first vibration quenching is 15 minutes.

[0021] The movement described in the present invention is preferably an up and down movement.

[0022] In one embodiment of the present invention, in step b, the time of the second static quenching is calculated as follows: T2 = [0.02 × D + (2.1 to 2.6)] 2 -15;

[0023] Wherein, T2 is the time of the second static quenching, in minutes, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0024] In one embodiment of the present invention, in step c, the holding time of tempering is calculated as follows: T3=D / 100*(3-3.5)+3;

[0025] Among them, T3 is the holding time of tempering, in hours, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The CrMoNiV casting material of the present invention adopts a specific chemical composition ratio and can ensure higher specific mechanical properties. In a room temperature test, Rp0.2 is ≥550MPa, Rm is 750-880MPa, A is ≥16%, Z is ≥40%, KV is ≥38J, and HBW is 230-270. In a 550°C test, Rp0.2 is ≥320MPa and Rm is ≥400MPa. The casting material can be used under high temperature conditions, providing a new approach for the design and material selection of large gas turbine steel castings.

[0028] The preparation method of the CrMoNiV casting material of the present invention adopts a specific heat treatment process, is simple and easy to operate, and the obtained product has good and stable mechanical properties, can avoid cracks in the casting, has reliable quality, and is suitable for the production of large steel castings for gas turbines. DETAILED DESCRIPTION

[0029] The heat-resistant CrMoNiV cast steel material of the present invention comprises the following components in chemical composition by weight: C: 0.21-0.26%; Si: 0.20-0.40%; Mn: 0.60-0.80%; Cr: 11.60-12.20%; Ni: 0.60-1.00%; Mo: 1.00-1.20%; V: 0.25-0.35%; Ti: 0.015-0.025%; Al: ≤0.025%; Cu: ≤0.30%; P ≤0.020%; S ≤0.020%; the remainder being Fe and unavoidable impurities.

[0030] Its mechanical properties are: when tested at room temperature, Rp0.2≥550MPa, Rm: 750~880MPa, A≥16%, Z≥40%, KV2≥38J, HBW 230~270; when tested at 550℃, Rp0.2≥320MPa, Rm≥400MPa.

[0031] Rp0.2, Rm, A, and Z are all terms from the national standard GB / T 228. Rp0.2 is the yield strength at a specified plastic elongation of 0.2%; Rm is the tensile strength; A is the elongation at break with an original gauge length of 50 mm; and Z is the reduction of area. Room temperature tests refer to GB / T 228.1-2021, "Metallic materials - Tensile tests - Part 1: Room temperature test methods," and 550°C tests refer to GB / T 228.2-2015, "Metallic materials - Tensile tests - Part 2: Elevated temperature test methods." KV2 is the impact energy absorption, a term from the national standard GB / T 229, and the test refers to GB / T 229-2020, "Metallic materials - Charpy pendulum impact test method." HBW is the Brinell hardness, a term from GB / T 231.1, and the test refers to GB / T 231.1-2018, "Metallic materials - Brinell hardness test - Part 1: Test method."

[0032] Preferably, the microstructure of the heat-resistant CrMoNiV cast steel material of the present invention is tempered martensite.

[0033] The present invention also provides a method for preparing the heat-resistant CrMoNiV cast steel material of the present invention.

[0034] The preparation method of the heat-resistant CrMoNiV cast steel material of the present invention includes casting and heat treatment processes, wherein the heat treatment process is:

[0035] a. Heating: Heat the casting to 1040℃~1070℃ and keep it warm;

[0036] b. Quenching: After the insulation in step a, the casting is immersed in a coolant for quenching. The coolant is oil or a liquid with a cooling capacity equivalent to that of oil. The quenching is divided into three stages:

[0037] The first stage of quenching: after the casting enters the coolant, it oscillates in the coolant for 10 to 20 minutes;

[0038] Second stage static quenching: After the first stage quenching is completed, the casting is immersed in the coolant and remains stationary for further quenching;

[0039] The third stage of quenching: After the second stage of quenching, the casting is taken out of the coolant and air-cooled for 5 minutes, and then the temperature is measured. If the casting temperature is higher than 260°C, continue to immerse in the coolant and cool for 10 to 15 minutes, then air-cool for 5 minutes and measure the temperature. Repeat this cycle until the casting temperature is ≤ 260°C.

[0040] c. Tempering: The casting is air-cooled to a temperature of ≤200°C after exiting the coolant, and then put into the furnace for tempering at 740°C to 750°C.

[0041] The preparation method of the CrMoNiV casting material of the present invention adopts a specific heat treatment process, is simple and easy to operate, and the obtained product has stable mechanical properties, can avoid cracks in the casting, has reliable quality, and is suitable for the production of large steel castings for gas turbines.

[0042] Step a is heating, which involves heating the casting to a certain temperature, keeping it warm, and then cooling it, which can improve the performance of the casting.

[0043] Research has found that if the heating temperature is too low, the casting performance stability is poor and the pass rate is low, while if the heating temperature is too high, not only will the cost be too high and the economy be poor, but the performance will also be reduced. Therefore, heating the casting to 1040℃~1070℃ is a more appropriate temperature. After heat treatment at this temperature, the casting performance is stable and can meet the mechanical performance requirements.

[0044] The holding time of the casting at the quenching temperature can be determined based on the maximum hot pitch diameter of the casting. The smaller the maximum hot pitch diameter of the casting, the shorter the holding time, while the larger the maximum hot pitch diameter of the casting, the longer the holding time. In one embodiment of the present invention, in step a, the holding time is calculated as follows: T1 = D / 100*(3 to 3.5);

[0045] Wherein, T1 is the holding time in hours, D is the maximum hot pitch circle diameter of the casting in mm, and 3~3.5 represents any value between 3 and 3.5.

[0046] In step b, quenching is performed using oil quenching or a liquid with a cooling capacity equivalent to that of oil quenching, such as a composite quenching liquid or a liquid-air alternating time-controlled quenching method. The oil used in the oil quenching is a quenching oil commonly used in the art, such as 20# engine oil, 30# engine oil, or 32# engine oil.

[0047] The present invention adopts a specific quenching step, especially in the late stage of quenching, the workpiece temperature is higher than 260°C, and the workpiece is further cooled in oil for 10 to 15 minutes, and then air-cooled for 5 minutes to measure the temperature. The oil cooling cycle is repeated until the casting is out of oil and air-cooled to a workpiece temperature of ≤200°C, and then the casting is promptly put into the furnace for tempering. This can effectively avoid quenching cracks in the casting while ensuring the mechanical properties of the casting.

[0048] The first and second quenching stages are controlled by time, and the third quenching stage is controlled by temperature. In a specific embodiment of the present invention, in step b, the quenching time of the first stage is 15 minutes.

[0049] The movement described in the present invention is preferably an up and down movement.

[0050] In one embodiment of the present invention, in step b, the time of the second static quenching is calculated as follows: T2 = [0.02 × D + (2.1 to 2.6)] 2 -15;

[0051] Wherein, T2 is the time of the second static quenching, in minutes, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0052] Step C is tempering. After quenching the casting, it is air-cooled to a temperature of ≤200°C and then placed in a furnace for tempering at 740°C to 750°C. The temperature referred to in this invention refers to the casting temperature. This oil quenching and tempering heat treatment improves the overall performance of the casting material.

[0053] In one embodiment of the present invention, in step c, the holding time of tempering is calculated as follows: T3=D / 100*(3-3.5)+3;

[0054] Among them, T3 is the holding time of tempering, in hours, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0055] The specific embodiments of the present invention are further described below in conjunction with examples, but the present invention is not limited to the scope of the examples.

[0056] Example 1

[0057] Steel is smelted according to the composition in Table 1. The specific composition test values ​​are shown in Table 1. Then it is cast. The sand castings after casting are heat treated. The heat treatment process is as follows: after the casting is heated to 1050℃, the holding time is calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours. Within 5 minutes after being taken out of the furnace, it is immersed in oil and quenched in three stages: the first stage is oscillation quenching, after the casting is put into oil, it is oscillated up and down in the oil pool for 15 minutes; the second stage is static quenching, after the first stage of quenching is completed, the casting is immersed in oil and continues to quench; the third stage is cycle quenching, after the second stage of quenching is completed, the casting is taken out of oil and air-cooled for 5 minutes and then the temperature is measured. If the casting temperature is higher than 260℃, it is continued to be cooled in oil for 12 minutes and then air-cooled for 5 minutes and the temperature is measured. This cycle of oil cooling is repeated until the casting temperature is ≤260℃ and then oil cooling is stopped. After the casting is taken out of oil and air-cooled to a temperature of ≤200℃, it is promptly put into the furnace for tempering at 745±10℃. The second stage quenching time (minutes) is calculated as T = [0.02 × the original diameter of the largest hot spot of the casting (mm) + (2.1 to 2.6)] 2 -15 is calculated as 42 minutes. The tempering holding time is calculated as 11 hours, calculated as the maximum hot pitch circle diameter (mm) / 100 * (3 to 3.5) + 3, followed by controlled cooling. The steel obtained by quenching and tempering was subjected to mechanical property testing, and the results are shown in Table 2. The test specimens for mechanical properties testing were 70 mm thick and were cast with the castings, poured in the same furnace, and heat-treated in the same furnace. Four parallel tests were performed in each group, and the average was taken.

[0058] Example 2

[0059] Steel is smelted according to the composition in Table 1. The specific composition test values ​​are shown in Table 1. Then it is cast. The sand castings after casting are heat treated. The heat treatment process is as follows: after the casting is heated to 1050℃, the holding time is calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours. Within 5 minutes after being taken out of the furnace, it is immersed in oil and quenched in three stages: the first stage is oscillation quenching, after the casting is put into oil, it is oscillated up and down in the oil pool for 15 minutes; the second stage is static quenching, after the first stage of quenching is completed, the casting is immersed in oil and continues to quench; the third stage is cycle quenching, after the second stage of quenching is completed, the casting is taken out of oil and air-cooled for 5 minutes and then the temperature is measured. If the casting temperature is higher than 260℃, it is continued to be cooled in oil for 15 minutes and then air-cooled for 5 minutes and the temperature is measured. This cycle of oil cooling is repeated until the casting temperature is ≤260℃ and then oil cooling is stopped. After the casting is taken out of oil and air-cooled to a temperature of ≤200℃, it is promptly put into the furnace for tempering at 745±10℃. The second stage quenching time (minutes) is calculated as T = [0.02 × the original diameter of the largest hot spot of the casting (mm) + (2.1 to 2.6)] 2-15 is calculated to take 43 minutes. The tempering hold time is calculated as 11 hours, calculated as the maximum hot pitch circle diameter (mm) / 100 * (3 to 3.5) + 3, followed by controlled cooling. The steel obtained by quenching and tempering was subjected to mechanical property testing, and the results are shown in Table 2. The test specimens for mechanical properties testing were 70 mm thick and were cast with the castings, poured in the same furnace, and heat treated in the same furnace. Four parallel tests were performed in each group, and the average was taken.

[0060] Example 3

[0061] Steel was smelted according to the following composition. The specific composition test values ​​are shown in Table 1. Then it was cast. The sand castings were heat treated after casting. The heat treatment process was as follows: after the casting was heated to 1050℃, the holding time was calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours. Within 5 minutes after being taken out of the furnace, it was immersed in oil and quenched in three stages: the first stage was oscillation quenching, in which the casting was moved up and down in the oil pool for 15 minutes after being put into the oil; the second stage was static quenching, in which the casting was immersed in the oil and continued to quench at rest after the first stage of quenching; the third stage was cyclic quenching, in which the casting was taken out of the oil and air-cooled for 5 minutes after the second stage of quenching was completed. The temperature was measured after the temperature of the casting was higher than 260℃, and the casting was continued to be cooled in oil for 10 minutes and then air-cooled for 5 minutes. The oil cooling cycle was repeated until the casting temperature was ≤260℃ and then the oil cooling was stopped. The casting was taken out of the oil and air-cooled to a temperature of ≤200℃ and then promptly put into the furnace for tempering at 745±10℃. The second stage quenching time (minutes) is calculated as T = [0.02 × the original diameter of the largest hot spot of the casting (mm) + (2.1 to 2.6)] 2 -15 is calculated to take 41 minutes. The tempering holding time is calculated as 11 hours, calculated as the maximum hot pitch circle diameter (mm) / 100 * (3 to 3.5) + 3, followed by controlled cooling. The steel obtained by quenching and tempering was subjected to mechanical property testing, and the results are shown in Table 2. The test specimens for mechanical properties testing were 70 mm thick and were cast with the castings, poured in the same furnace, and heat-treated in the same furnace. Four replicates were tested in each group, and the average was calculated.

[0062] Table 1

[0063] Table 2

[0064] As can be seen from the above examples, the CrMoNiV casting material obtained by the method of the present invention has stable mechanical properties and good heat resistance. Currently, this material has been successfully used in large heat-resistant steel castings for gas turbines.

Claims

1. Heat-resistant CrMoNiV cast steel material, characterized in that: Its chemical composition consists of the following components in weight percentage Composition: C: 0.21~0.26%; Si: 0.20~0.40%; Mn: 0.60~0.80%; Cr: 11.60~12.20%; Ni: 0.60~1.00%; Mo: 1.00~1.20%; V: 0.25~0.35%; Ti: 0.015~0.025%; Al: ≤0.025%; Cu: ≤0.30%; P≤0.020%; S≤0.020%; the rest is Fe and unavoidable impurities; Its mechanical properties are: when tested at room temperature, Rp0.2≥550MPa, Rm: 750~880MPa, A≥16%, Z≥40%, KV2≥38J, HBW 230~270; when tested at 550℃, Rp0.2≥320MPa, Rm≥400MPa.

2. The heat-resistant CrMoNiV cast steel material according to claim 1, characterized in that: The microstructure of the heat-resistant CrMoNiV cast steel material is tempered martensite.

3. The method for preparing the heat-resistant CrMoNiV cast steel material according to claim 1 or 2, comprising a casting and a heat treatment process, characterized in that: The heat treatment process is: a. Heating: Heat the casting obtained after casting to 1040℃~1070℃ for insulation; b. Quenching: After the insulation in step a, the casting is immersed in a coolant for quenching. The coolant is oil or a liquid with a cooling capacity equivalent to that of oil. The quenching is divided into three stages: The first stage of quenching: the casting is quenched in the coolant for 10 to 20 minutes after entering the coolant; Second stage of static quenching: After the first stage of quenching, the casting is immersed in the coolant and quenched at rest; The third stage of quenching: After the second stage of quenching, the casting is cooled in the coolant for 5 minutes and then the temperature is measured. If the casting temperature is higher than 260°C, continue to immerse in the coolant for 10-15 minutes and then air cool for 5 minutes and measure the temperature. Repeat this cycle until the casting temperature is ≤260°C. c. Tempering: The casting is air-cooled to a temperature of ≤200°C and then put into the furnace for tempering at 740°C to 750°C.

4. The method for preparing the heat-resistant CrMoNiV cast steel material according to claim 3, characterized in that: In step a, the holding time is calculated as follows: T1 = D / 100*(3-3.5); Wherein, T1 is the holding time in hours, and D is the maximum hot pitch circle diameter of the casting in mm.

5. The method for preparing the heat-resistant CrMoNiV cast steel material according to claim 3, characterized in that: In step b, the quenching time of the first stage of quenching is 15 minutes.

6. The method for preparing the heat-resistant CrMoNiV cast steel material according to claim 3, characterized in that: In step b, the time of the second static quenching is calculated as follows: T2 = [0.02 × D + (2.1 ~ 2.6)] 2 -15; Wherein, T2 is the time of the second static quenching, in minutes, and D is the maximum hot pitch circle diameter of the casting, in mm.

7. The method for preparing the heat-resistant CrMoNiV cast steel material according to claim 3, characterized in that: In step c, the holding time of tempering is calculated as follows: T3 = D / 100*(3-3.5)+3; Wherein, T3 is the holding time of tempering, in hours, and D is the maximum hot pitch circle diameter of the casting, in mm.

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