Heat-resistant CrMoNiV cast steel material and preparation method thereof

Abstract

The invention relates to a heat-resistant CrMoNiV cast steel material and a preparation method thereof, and belongs to the technical field of casting materials. The technical problem solved by the invention is to provide a heat-resistant CrMoNiV cast steel material with higher strength. The material is composed of the following components in weight percentage: 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 inevitable impurities. In room temperature test, Rp0.2≥550MPa, Rm: 750-880MPa, A≥16%, Z≥40%, KV2≥38J, HBW 230-270; in 550℃ test, Rp0.2≥320MPa, Rm≥400MPa. The casting material of the invention adopts a specific chemical composition ratio, can ensure higher specific mechanical properties, can be used under high temperature conditions, and its preparation method is simple and easy to operate. The obtained product has good and stable mechanical properties, can avoid cracks in the casting, and has reliable quality, which provides a new way for the design and material selection of large gas turbine steel castings.

Description

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 equipment for clean power generation and power systems. They have a wide range of applications and are known as the "crown jewel of industry". With the large-scale development and utilization of my country's natural gas resources, the west-to-east gas transmission, offshore natural gas development, and the introduction of foreign liquefied natural gas resources, as well as the vigorous promotion of energy conservation and emission reduction, my country's gas turbine market will have a large development, and the new demand for heat-resistant cast steel materials will also grow rapidly.

[0003] The Chinese invention patent with application number 201710790113.X discloses a preparation method of 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, while meeting the mechanical property requirements under 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] However, 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 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 cracks in high-alloy martensitic cast steel parts during quenching and heat treatment. Therefore, a heat treatment method is needed that can both ensure the mechanical properties of the cast steel parts and avoid cracks, so as to prepare higher-grade heat-resistant cast steel materials. Summary of the invention

[0005] 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.

[0006] The heat-resistant CrMoNiV cast steel material of the present invention comprises the following components in chemical composition by weight percentage: 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 inevitable impurities;

[0007] 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.

[0008] Preferably, the microstructure of the heat-resistant CrMoNiV cast steel material of the present invention is tempered martensite.

[0009] The present invention also provides a method for preparing the heat-resistant CrMoNiV cast steel material of the present invention.

[0010] The preparation method of the heat-resistant CrMoNiV cast steel material of the present invention comprises a casting and a heat treatment process, wherein the heat treatment process is:

[0011] a. Heating: Heat the casting obtained after casting to 1040℃~1070℃ for insulation;

[0012] 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:

[0013] The first stage of quenching: the casting is quenched in the coolant for 10 to 20 minutes after entering the coolant;

[0014] Second stage of static quenching: After the first stage of quenching, the casting is immersed in the coolant and quenched at rest;

[0015] 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.

[0016] 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.

[0017] In a specific embodiment of the present invention, in step a, the holding time is calculated as follows:

[0018] 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 oscillation time of the first stage of oscillation quenching is 15 minutes.

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

[0022] In a specific embodiment of the present invention, in step b, the time of the second static quenching is calculated as follows:

[0023] T2=[0.02×D+(2.1~2.6)] 2 -15;

[0024] 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.

[0025] In a specific embodiment of the present invention, in step c, the holding time of tempering is calculated as follows:

[0026] T3 = D / 100*(3-3.5)+3;

[0027] Wherein, T3 is the holding time of tempering, in hours, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The CrMoNiV casting material of the present invention adopts a specific chemical component ratio and can ensure higher specific mechanical properties. In a room temperature test, Rp0.2≥550MPa, Rm: 750-880MPa, A≥16%, Z≥40%, KV≥38J, HBW 230-270; in a 550°C test, Rp0.2≥320MPa, Rm≥400MPa. The casting material can be used under high temperature conditions, providing a new way for the design and material selection of large gas turbine steel castings.

[0030] The preparation method of the CrMoNiV casting material of the present invention adopts a specific heat treatment process, the method is simple, the operation is easy, the obtained product has good and stable mechanical properties, cracks in the casting can be avoided, the quality is reliable, and it is suitable for the production of large steel castings for gas turbines. DETAILED DESCRIPTION

[0031] The heat-resistant CrMoNiV cast steel material of the present invention comprises the following components in chemical composition by weight percentage: 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 inevitable impurities;

[0032] 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.

[0033] Among them, Rp0.2, Rm, A, and Z are all terms in the national standard GB / T 228. Rp0.2 is the yield strength when the specified plastic elongation is 0.2%; Rm is the tensile strength; A is the elongation after fracture when the original gauge length is 50mm; and Z is the cross-sectional shrinkage. Among them, the room temperature test refers to the standard GB / T 228.1-2021 "Metallic Materials Tensile Test Part 1 Room Temperature Test Method", and the 550℃ test refers to the standard GB / T 228.2-2015 "Metallic Materials Tensile Test Part 2: High Temperature Test Method". KV2 is the impact absorption energy, which is a term in the national standard GB / T 229. The test refers to the standard GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method". HBW is the Brinell hardness, which is a term in GB / T 231.1. The test refers to the standard GB / T 231.1-2018 "Metallic Materials Brinell Hardness Test Part 1: Test Method".

[0034] Preferably, the microstructure of the heat-resistant CrMoNiV cast steel material of the present invention is tempered martensite.

[0035] The present invention also provides a method for preparing the heat-resistant CrMoNiV cast steel material of the present invention.

[0036] The preparation method of the heat-resistant CrMoNiV cast steel material of the present invention comprises a casting and a heat treatment process, wherein the heat treatment process is:

[0037] a. Heating: Heat the casting obtained after casting to 1040℃~1070℃ for insulation;

[0038] 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:

[0039] The first stage of quenching: the casting is quenched in the coolant for 10 to 20 minutes after entering the coolant;

[0040] Second stage of static quenching: After the first stage of quenching, the casting is immersed in the coolant and quenched at rest;

[0041] 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.

[0042] 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.

[0043] The preparation method of the CrMoNiV casting material of the present invention adopts a specific heat treatment process, the method is simple, the operation is easy, the obtained product has stable mechanical properties, cracks in the casting can be avoided, the quality is reliable, and it is suitable for the production of large steel castings for gas turbines.

[0044] 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.

[0045] 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 is 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.

[0046] The holding time of the casting at the quenching temperature can be determined according to the maximum hot pitch circle diameter of the casting. The smaller the maximum hot pitch circle diameter of the casting, the shorter the holding time, while the larger the maximum hot pitch circle diameter of the casting, the longer the holding time. In a specific embodiment of the present invention, in step a, the holding time is calculated as follows:

[0047] T1 = D / 100*(3-3.5);

[0048] 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.

[0049] In step b, oil quenching or liquid with cooling capacity equivalent to oil quenching is used for quenching, such as composite quenching liquid, liquid-air alternating time-controlled quenching method, etc. The oil used for the oil quenching is quenching oil commonly used in the art, such as 20# engine oil, 30# engine oil, 32# engine oil, etc.

[0050] The present invention adopts a specific quenching step, especially in the later stage of quenching, the temperature of the workpiece is higher than 260°C, and the casting is 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 cooled in oil and air-cooled to a temperature of ≤200°C, and then the casting is tempered in the furnace in time, so that quenching cracks can be effectively avoided on the premise of ensuring the mechanical properties of the casting.

[0051] 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.

[0052] The movement described in the present invention is preferably an up and down movement.

[0053] In a specific embodiment of the present invention, in step b, the time of the second static quenching is calculated as follows:

[0054] T2=[0.02×D+(2.1~2.6)] 2 -15;

[0055] 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.

[0056] Step c is tempering. After the casting is quenched and oiled, it is air-cooled to a temperature of ≤200°C and then put into a furnace for tempering at 740°C to 750°C. The temperature of the casting in the present invention refers to the casting temperature. The comprehensive properties of the casting material can be improved through oil quenching + tempering heat treatment.

[0057] In a specific embodiment of the present invention, in step c, the holding time of tempering is calculated as follows:

[0058] T3 = D / 100*(3-3.5)+3;

[0059] Wherein, T3 is the holding time of tempering, in hours, and D is the maximum hot pitch circle diameter of the casting, in mm.

[0060] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0061] Example 1

[0062] Steel is smelted according to the composition in Table 1, and the specific composition test values ​​are shown in Table 1. Then, the casting is performed, and the sand casting after casting is heat treated. The heat treatment process is that after the casting is heated to 1050°C, the holding time is calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours, and it is immersed in oil within 5 minutes after being taken out of the furnace. The quenching treatment is divided into three stages: the first stage is swaying quenching, and the casting is moved up and down in the oil pool for 15 minutes after entering the oil; the second stage is static quenching, after the first stage of quenching is completed, the casting is immersed in the oil and remains stationary for quenching; the third stage is cycle quenching, after the second stage of quenching is completed, the casting is air-cooled for 5 minutes after being taken out of the oil, and the temperature is measured. If the casting temperature is higher than 260°C, it is continued to be cooled in oil for 12 minutes and then air-cooled for 5 minutes to measure the temperature. According to this cycle of oil cooling, oil cooling is stopped until the piece temperature is ≤260°C. After the casting is air-cooled to a piece temperature of ≤200°C, it is promptly put into the furnace for tempering at 745±10°C. The second stage quenching time (minutes) is calculated as T = [0.02 × original diameter of the largest hot spot of the casting (mm) + (2.1 ~ 2.6)] 2 -15 is calculated to be 42 minutes. The tempering holding time is calculated as 11 hours according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5)+3, and then the temperature is controlled to drop. The steel obtained by quenching + tempering is tested for mechanical properties, and the results are shown in Table 2. The thickness of the test sample for mechanical properties test is 70mm, and it is cast with the casting, poured in the same furnace, and heat treated in the same furnace. Four parallel tests are performed in each group, and the average is taken.

[0063] Example 2

[0064] Steel is smelted according to the composition in Table 1, and the specific composition test values ​​are shown in Table 1. Then, the casting is performed. The sand casting after casting is heat treated. The heat treatment process is that after the casting is heated to 1050°C, the holding time is calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours, and it is immersed in oil within 5 minutes after being taken out of the furnace. The quenching treatment is divided into three stages: the first stage is swaying quenching, and the casting is moved up and down in the oil pool for 15 minutes after entering the oil; the second stage is static quenching, after the first stage of quenching is completed, the casting is immersed in the oil and continues to quench; the third stage is cycle quenching, after the second stage of quenching is completed, the casting is air-cooled for 5 minutes after the oil is removed, and the temperature is measured. If the casting temperature is higher than 260°C, it is continued to be cooled in oil for 15 minutes and then air-cooled for 5 minutes. According to this cycle of oil cooling, oil cooling is stopped until the temperature of the casting is ≤260°C. After the casting is air-cooled to the temperature of the casting ≤200°C, it is promptly put into the furnace for tempering at 745±10°C. The second stage quenching time (minutes) is calculated as T = [0.02 × original diameter of the largest hot spot of the casting (mm) + (2.1 ~ 2.6)] 2-15 is calculated to be 43 minutes. The tempering holding time is calculated as 11 hours according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5)+3, and then the temperature is controlled to drop. The steel obtained by quenching + tempering is tested for mechanical properties, and the results are shown in Table 2. The thickness of the test sample for mechanical properties test is 70mm, and it is cast with the casting, poured in the same furnace, and heat treated in the same furnace. Four parallel tests are performed in each group, and the average is taken.

[0065] Example 3

[0066] Steel is smelted according to the following composition, and the specific composition test values ​​are shown in Table 1. Then it is cast, and the sand castings after casting are heat treated. The heat treatment process is that after the casting is heated to 1050°C, the holding time is calculated according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5) for 8 hours, and it is immersed in oil within 5 minutes after being taken out of the furnace. The quenching treatment is divided into three stages: the first stage is swaying quenching, the casting is moved up and down in the oil pool for 15 minutes after entering the oil; the second stage is static quenching, after the first stage of quenching is completed, the casting is immersed in the oil and remains stationary for quenching; the third stage is cycle quenching, after the second stage of quenching is completed, the casting is air-cooled for 5 minutes after being taken out of the oil, and the temperature is measured. If the casting temperature is higher than 260°C, it is continued to be cooled in oil for 10 minutes and then air-cooled for 5 minutes to measure the temperature. According to this cycle of oil cooling, oil cooling is stopped until the temperature of the casting is ≤260°C. After the casting is air-cooled to the temperature of the casting ≤200°C, it is promptly put into the furnace for tempering at 745±10°C. The second stage quenching time (minutes) is calculated as T = [0.02 × original diameter of the largest hot spot of the casting (mm) + (2.1 ~ 2.6)] 2 -15 is calculated to be 41 minutes. The tempering holding time is calculated as 11 hours according to the maximum hot pitch circle diameter (mm) / 100*(3~3.5)+3, and then the temperature is controlled to drop. The steel obtained by quenching + tempering is tested for mechanical properties, and the results are shown in Table 2. The thickness of the test sample for mechanical properties test is 70mm, and it is cast with the casting, poured in the same furnace, and heat treated in the same furnace. Four parallel tests are performed in each group, and the average is taken.

[0067] Table 1

[0068]

[0069] Table 2

[0070]

[0071] As can be seen from the above implementation examples, the CrMoNiV casting material obtained by the method of the present invention has stable mechanical properties and good heat resistance. Currently, the material has been successfully applied to 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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