Boron-containing martensite heat-resistant steel forge piece and preparation method thereof

Abstract

The invention discloses a boron-containing martensite heat-resistant steel forge piece and a preparation method thereof, belongs to the technical field of preparation of heat-resistant steel, and solves the problems that in the preparation process of an existing boron-containing martensite heat-resistant steel forge piece, the performance cannot meet the use requirement due to the fact that grains are not uniform or too large or the limit sensitivity of an ultrasonic flaw detection center is too high. The preparation method comprises the following steps: 1, preparing a steel ingot; 2, the steel ingot is forged, and a forging stock is obtained; 3, the forging stock is subjected to step heat preservation austenitizing heat treatment and then quenched to the room temperature; and 4, tempering is conducted twice, and the boron-containing martensite heat-resistant steel forge piece is obtained. The method is simple, and the prepared forge piece can meet the technical requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of heat-resistant steel, and particularly relates to a boron-containing martensitic heat-resistant steel forging and a preparation method thereof. Background Art

[0002] Compared with traditional thermal power units, ultra-supercritical thermal power units with increased steam temperature and pressure can significantly improve power generation efficiency. However, at the same time, the safety of the unit structure materials also poses more stringent requirements on the mechanical properties of materials under high temperature and high pressure.

[0003] Boron-containing martensitic heat-resistant steel materials have excellent high-temperature creep properties at a service temperature of 620 - 625 °C and are widely used in important components of large-capacity, high-parameter coal-fired thermal power units. The heat treatment method is an important means to ensure the uniformity of the surface and core properties of large-section forgings of boron-containing martensitic heat-resistant steel. In the prior art, during the heat treatment process of boron-containing martensitic heat-resistant steel, there are often problems such as non-uniform grains, over-large grains, and excessive ultrasonic flaw detection center limit sensitivity, resulting in the tensile strength, creep properties, or high-temperature properties not meeting the service requirements. Summary of the Invention

[0004] In view of the above situation, the present invention aims to provide a boron-containing martensitic heat-resistant steel forging and a preparation method thereof, which can at least solve one of the following technical problems: during the preparation process of existing boron-containing martensitic heat-resistant steel forgings, there are problems such as non-uniform grains, over-large grains, or excessive flaw detection sensitivity, and the performance does not meet the service requirements.

[0005] The object of the present invention is mainly achieved through the following technical solutions:

[0006] The present invention provides a preparation method of a boron-containing martensitic heat-resistant steel forging, and the preparation method includes:

[0007] Step 1: Prepare an ingot;

[0008] Step 2: Forge the ingot to obtain a forging blank;

[0009] Step 3: Perform stepwise heat preservation austenitizing heat treatment on the forging blank, and then quench to room temperature;

[0010] Step 4: Perform two temperings to obtain a boron-containing martensitic heat-resistant steel forging.

[0011] Further, in step 3, the stepwise heat preservation austenitizing heat treatment includes the following steps:

[0012] S301: Keep the forging blank at 200 - 250 °C for heat preservation before processing;

[0013] S302: Heat up to 790 - 810 °C and keep it warm;

[0014] S303. Heat up to 1055 - 1065 °C and hold the temperature.

[0015] S304. Heat up to 1095 - 1105 °C, hold the temperature, and then quench to room temperature.

[0016] Furthermore, in S301, the holding time t1 and the cross-sectional diameter d of the forging blank satisfy the following relationship: t1 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t1 is h.

[0017] Furthermore, in S302, the holding time t2 and the cross-sectional diameter d of the forging blank satisfy the following relationship: t2 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t2 is h.

[0018] Furthermore, in S303, the holding time t3 and the cross-sectional diameter d of the forging blank satisfy the following relationship: t3 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t3 is h.

[0019] Furthermore, the heating rate v1 in S302, the heating rate v2 in S303, and the heating rate v3 in S304 satisfy the following relationship: v3 ≥ v2 > v1.

[0020] Furthermore, in step 4, the temperature of the first tempering is lower than the temperature of the second tempering.

[0021] Furthermore, the components of the boron-containing martensitic heat-resistant steel forging, by mass percentage, include: C: 0.10% - 0.16%, Si ≤ 0.12%, Mn: 0.2% - 0.6%, Cr: 9.0% - 9.8%, Mo: 1.2% - 1.7%, Ni ≤ 0.3%, V: 0.1% - 0.3%, N: 0.01% - 0.03%, Nb: 0.03% - 0.07%, B: 70 - 120 ppm, and the balance is Fe and unavoidable impurities.

[0022] Furthermore, the cross-sectional diameter of the boron-containing martensitic heat-resistant steel forging is 900 - 1300 mm.

[0023] The present invention also provides a boron-containing martensitic heat-resistant steel forging prepared by the above preparation method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] a) In the preparation method of the boron-containing martensitic heat-resistant steel forging of the present invention, by precisely controlling process parameters such as the number of stages of stepped heat preservation, heating rate, heat preservation temperature, heat preservation time, and cooling rate, it is ensured that both the surface and the core of the forging reach excellent grain size, room temperature strength, and high-temperature creep properties.

[0026] b) In the preparation method of the present invention, by precisely controlling each process step and the control of key process parameters, the heat preservation time can be precisely controlled, thereby reducing the overlong heat preservation time, lowering the cost, and improving the production efficiency.

[0027] c) The grains in different parts of the boron-containing martensitic heat-resistant steel forgings of the present invention are uniform, the difference in grain size grade between different parts is below 0.5, and the central limit sensitivity of ultrasonic flaw detection is small. The boron-containing martensitic heat-resistant steel forgings of the present invention have excellent room temperature properties, uniform properties on the surface and in the core, and excellent high-temperature creep rupture properties. For example, the room temperature properties are as follows: Surface: Tensile strength is above 860 Mpa (for example, 863 - 880 Mpa), yield strength is above 710 Mpa (for example, 710 - 720 Mpa); Core: Tensile strength is above 850 Mpa (for example, 852 - 875 Mpa), yield strength is above 695 Mpa (for example, 695 - 710 Mpa). The high-temperature creep rupture time at 620 °C and 210 MPa reaches above 680 h, for example, the surface reaches 730 - 780 h, and the core reaches 682 - 730 h.

[0028] Other features and advantages of the present invention will be described in the following specification, and part of them will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the content specifically pointed out in the written specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of showing specific embodiments, and are not considered as limitations to the present invention. Throughout the drawings, the same reference signs represent the same components.

[0030] Figure 1 is a schematic process flow diagram of the preparation method of the present invention;

[0031] Figure 2 is a microstructural diagram of the boron-containing martensitic heat-resistant steel forgings of Example 1;

[0032] Figure 3 is a microstructural diagram of the boron-containing martensitic heat-resistant steel forgings of Comparative Example 1;

[0033] Figure 4 is a diagram of undissolved BN particles in the microstructure of the boron-containing martensitic heat-resistant steel forgings of Comparative Example 1;

[0034] Figure 5 is a microstructural diagram of the boron-containing martensitic heat-resistant steel forgings of Comparative Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings, where the drawings form a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention.

[0036] The present invention provides a method for preparing a boron-containing martensitic heat-resistant steel forging, as Figure 1 shown, including:

[0037] Step 1: Prepare an ingot;

[0038] Step 2: Forge the ingot to obtain a forging blank;

[0039] Step 3: Perform stepwise heat preservation austenitizing heat treatment on the forging blank, and then quench it to room temperature;

[0040] Step 4: Perform two temperings to obtain a boron-containing martensitic heat-resistant steel forging.

[0041] Specifically, the components of the above boron-containing martensitic heat-resistant steel forging include, by mass percentage: C: 0.10% - 0.16%, Si ≤ 0.12%, Mn: 0.2% - 0.6%, Cr: 9.0% - 9.8%, Mo: 1.2% - 1.7%, Ni ≤ 0.3%, V: 0.1% - 0.3%, N: 0.01% - 0.03%, Nb: 0.03% - 0.07%, B: 70 - 120 ppm, and the balance is Fe and unavoidable impurities.

[0042] Specifically, the cross-sectional diameter of the above boron-containing martensitic heat-resistant steel forging is 900 - 1300 mm. Due to the large cross-sectional diameter of the boron-containing martensitic heat-resistant steel forging, problems such as uneven heating and resulting non-uniform microstructure and performance not meeting technical requirements are likely to occur during the preparation process. Uneven grain size and coarse grains will lead to a large central limit sensitivity of ultrasonic flaw detection, that is, the forging cannot be detected, and heat treatment repair is required to refine the grains. If the quenching temperature is low and the grain size is controlled to be relatively fine, the tensile strength and high-temperature creep performance requirements cannot be met. After in-depth research, the inventor adopted a stepwise heat preservation scheme to ensure a balance between "grain size, central limit sensitivity of ultrasonic flaw detection" and "tensile strength, high-temperature creep performance", both of which can meet the requirements.

[0043] Specifically, in the above step 3, the stepwise heat preservation austenitizing heat treatment includes the following steps:

[0044] S301: Keep the forging blank at 200 - 250 °C for heat preservation before processing;

[0045] S302: Raise the temperature to 790 - 810 °C and keep it warm;

[0046] S303: Raise the temperature to 1055 - 1065 °C and keep it warm;

[0047] S304. Heat up to 1095 - 1105 °C, hold for heat preservation, and then quench to room temperature.

[0048] Specifically, in the above S301, holding the forging blank at 200 - 250 °C for heat preservation can make the internal and external temperatures uniform to prevent the increase of thermal stress in the forging due to too fast heating rate.

[0049] Specifically, in the above S301, if the heat preservation time is too short, the effect of uniform consistency between the surface and the core of the forging cannot be achieved; if the heat preservation time is too long, it will cause waste of production resources. Therefore, control the heat preservation time t1 and the cross-sectional diameter d of the forging blank to meet the following relationship: t1 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t1 is h.

[0050] Specifically, in the above S302, the function of heat preservation at this stage is to reduce the temperature difference during the heating process of the large cross-section forging and provide a basis for the synchronization of austenitization. Considering that if the heat preservation temperature is too low and the heat preservation time is too short, the temperature difference between the surface and the core of the forging cannot be fully balanced; if the heat preservation temperature is too high and reaches or exceeds the Ac1 temperature of the forging, local austenite transformation will occur in the forging, resulting in non-simultaneity of austenite transformation. If the heat preservation time is too long, it will cause waste of production resources. Therefore, control the heat preservation at 790 - 810 °C at this stage. The heat preservation time t2 and the cross-sectional diameter d of the forging blank meet the following relationship: t2 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t2 is h.

[0051] Specifically, in the above S303, the function of heat preservation at this stage is to dissolve most of the carbides and clustered BN particles, and at the same time reduce the temperature difference between the surface and the core of the forging. Considering that if the heat preservation temperature is too low and the heat preservation time is too short, the alloy carbides and clustered BN particles cannot be fully dissolved; if the heat preservation temperature is too high and the heat preservation time is too long, the grains will rapidly coarsen. Therefore, control the heat preservation at 1055 - 1065 °C at this stage. The heat preservation time t3 and the cross-sectional diameter d of the forging blank meet the following relationship: t3 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t3 is h.

[0052] Specifically, in the above S304, the function of heat preservation at this stage is to further dissolve the clustered BN particles into the matrix and regulate the room temperature strength and high-temperature creep properties of the forging. Considering that if the heat preservation temperature is too low and the heat preservation time is too short, the carbides and BN particles cannot be fully dissolved, and the effect of improving the hardenability of the forging cannot be achieved; if the heat preservation temperature is too high and the heat preservation time is too long, the grains will coarsen severely, reducing the impact toughness. Therefore, control the heat preservation at 1095 - 1105 °C at this stage. The heat preservation time t4 and the cross-sectional diameter d of the forging blank meet the following relationship: t4 = (0.9 - 1.1)d / 100, where the unit of d is mm and the unit of t4 is h.

[0053] Specifically, the heating rate v1 in S302, the heating rate v2 in S303, and the heating rate v3 in S304 satisfy the following relationship: v3 ≥ v2 > v1.

[0054] Specifically, considering that if v1 is too small, the production cycle increases, and if v1 is too large, the temperature difference between the inside and outside of the forging increases, resulting in excessive thermal stress. Therefore, control the above v1 to be 15 - 30 °C / h, such as 15 °C / h, 20 °C / h, 25 °C / h, 30 °C / h.

[0055] Specifically, considering that if v2 is too small, the superheat degree during austenitization is small, and during the austenite transformation process, it is easy to nucleate and grow along the original coarse grain orientation in a needle shape, resulting in tissue heredity and coarse grains. If v2 is too large, the electric furnace power cannot be satisfied. Therefore, control the above v2 to be 60 - 80 °C / h, such as 60 °C / h, 70 °C / h, 80 °C / h.

[0056] Specifically, considering that if v3 is too small, the total holding time increases. If v3 is too large, the electric furnace power cannot reach the required value. Therefore, control the above v3 to be between 70 - 90 °C / h, such as 70 °C / h, 75 °C / h, 80 °C / h, 85 °C / h.

[0057] Specifically, in the above S304, considering that if the cooling rate during quenching is too small, it cannot meet the overall hardening requirements of large-section forgings, and if the cooling rate is too large, the forging is prone to cracking. Therefore, control the quenching to use oil cooling, and cool to 70 - 100 °C. During oil cooling, the cooling rate is fast in the high-temperature section and slow in the low-temperature section.

[0058] Specifically, in the above S304, control the content of untransformed retained austenite to be below 10% after oil cooling.

[0059] Specifically, in the above step 1, electroslag remelting can be used for smelting to obtain an ingot.

[0060] Specifically, in the above step 2, the ingot is subjected to high-temperature diffusion and then forged.

[0061] Specifically, in the above step 4, the temperature of the first tempering is lower than the temperature of the second tempering.

[0062] Specifically, in the above step 4, considering that if the holding temperature of the first tempering is too low, it cannot effectively promote the complete transformation of retained austenite, and if the holding temperature is too high, it causes waste of resources. Therefore, control the holding temperature of the first tempering to be 575 - 585 °C, such as 575 °C, 580 °C, 585 °C; preferably, the holding temperature of the first tempering is 580 °C.

[0063] Specifically, in the above step 4, considering that the heat preservation in the second tempering mainly controls the mechanical properties of the forging, if the temperature is too low, the yield strength is too high and the impact toughness decreases; if the heat preservation temperature is too high, the yield strength decreases. Therefore, the heat preservation temperature in the second tempering is controlled to be 680 - 690 °C, such as 680 °C, 685 °C, 690 °C; preferably, the heat preservation temperature in the second tempering is 685 °C.

[0064] The present invention also provides a boron-containing martensitic heat-resistant steel forging prepared by the above preparation method.

[0065] Specifically, the grains in different parts of the above boron-containing martensitic heat-resistant steel forging are uniform, and the difference in grain size grade between different parts is below 0.5.

[0066] Specifically, the grain size of the above boron-containing martensitic heat-resistant steel forging is 1.0 - 1.5 grades.

[0067] Specifically, the ultrasonic flaw detection center limit sensitivity of the above boron-containing martensitic heat-resistant steel forging is small, such as the ultrasonic flaw detection center limit sensitivity is below Ф1.5mm.

[0068] Specifically, the room temperature performance of the above boron-containing martensitic heat-resistant steel forging is excellent, and the performance of the surface and the core is uniform. For example, the room temperature performance is as follows: Surface: Tensile strength is above 860 Mpa (such as 863 - 880 Mpa), yield strength is above 710 Mpa (such as 710 - 720 Mpa); Core: Tensile strength is above 850 Mpa (such as 852 - 875 Mpa), yield strength is above 695 Mpa (such as 695 - 710 Mpa).

[0069] Specifically, the high-temperature creep rupture performance of the above boron-containing martensitic heat-resistant steel forging is excellent. For example, the high-temperature creep rupture time at 620 °C and 210 MPa reaches above 680 h, such as the surface reaches 730 - 780 h and the core reaches 682 - 730 h.

[0070] Compared with the prior art, in the preparation method of the boron-containing martensitic heat-resistant steel forging of the present invention, by precisely controlling process parameters such as the number of stages of stepped heat preservation, heating rate, heat preservation temperature, heat preservation time, cooling rate, etc.; it ensures that both the surface and the core of the forging reach excellent grain size, room temperature strength and high-temperature creep rupture performance.

[0071] In the preparation method of the present invention, by precisely controlling each process step and the control of key process parameters, the heat preservation time can be precisely controlled, thereby reducing the overlong heat preservation time, reducing costs and improving production efficiency.

[0072] The grains in different parts of the boron-containing martensitic heat-resistant steel forging of the present invention are uniform, the difference in grain size levels between different parts is below 0.5, and the central limit sensitivity of ultrasonic flaw detection is small. The boron-containing martensitic heat-resistant steel forging of the present invention has excellent room temperature properties, uniform properties on the surface and in the core, and excellent high-temperature creep rupture properties.

[0073] The following specific examples and comparative examples are used to demonstrate the advantages of precise control of the process parameters of the present invention.

[0074] Example 1

[0075] This example provides a boron-containing martensitic heat-resistant steel forging and a preparation method thereof. The cross-sectional diameter of the boron-containing martensitic heat-resistant steel forging in this example is 900 mm; the components are by mass percentage: C: 0.14%, Si: 0.11%, Mn: 0.4%, Cr: 9.45%, Mo: 1.52%, Ni: 0.2%, V: 0.21%, N: 0.024%, Nb: 0.05%, B: 98 ppm, and the balance is Fe and unavoidable impurities. The forging is required to have a grain size ≥ 1.0 grade, and the central limit sensitivity of ultrasonic flaw detection is lower than Ф1.6 mm.

[0076] The preparation method of the boron-containing martensitic heat-resistant steel forging in this example includes the following steps:

[0077] Step 1: Smelt by electroslag remelting to obtain an ingot.

[0078] Step 2: Subject the ingot to high-temperature diffusion and then forge it to obtain a forging blank.

[0079] Step 3: Perform stepwise heat preservation austenitizing heat treatment on the forging blank, and then quench it to room temperature; the stepwise heat preservation austenitizing heat treatment includes the following steps:

[0080] S301: Keep the forging blank at 230 °C for heat preservation for 9 h.

[0081] S302: Heat up to 800 °C at a heating rate of 30 °C / h and keep it for heat preservation for 9 h.

[0082] S303: Heat up to 1060 °C at a heating rate of 80 °C / h and keep it for heat preservation for 9 h.

[0083] S304: Heat up to 1100 °C at a heating rate of 80 °C / h, keep it for heat preservation for 9 h, and then cool it in oil to 70 °C, controlling the content of untransformed retained austenite below 10%.

[0084] Step 4: Perform two temperings to obtain the boron-containing martensitic heat-resistant steel forging; the temperature of the first tempering is 580 °C, and the temperature of the second tempering is 685 °C.

[0085] The microstructure of the boron-containing martensitic heat-resistant steel forging in this embodiment is tempered martensite. As Figure 2 shown, the grain uniformity is good in different parts, and the grain size grade and performance results are shown in Table 1 below.

[0086] Example 2

[0087] This embodiment provides a boron-containing martensitic heat-resistant steel forging and a preparation method thereof. The cross-sectional diameter of the boron-containing martensitic heat-resistant steel forging in this embodiment is 1300 mm; the components are by mass percentage: C: 0.12%, Si: 0.11%, Mn: 0.5%, Cr: 9.5%, Mo: 1.45%, Ni: 0.1%, V: 0.25%, N: 0.022%, Nb: 0.055%, B: 105 ppm, and the balance is Fe and unavoidable impurities. The forging is required to have a grain size of ≥1.0 grade, and the central limit sensitivity of ultrasonic flaw detection is lower than Ф1.6 mm.

[0088] The preparation method of the boron-containing martensitic heat-resistant steel forging in this embodiment includes the following steps:

[0089] Step 1: Smelt by electroslag remelting to obtain an ingot;

[0090] Step 2: Subject the ingot to high-temperature diffusion and then forge it to obtain a forging blank;

[0091] Step 3: Perform stepped heat preservation austenitizing heat treatment on the forging blank and then quench it to room temperature; the stepped heat preservation austenitizing heat treatment includes the following steps:

[0092] S301: Keep the forging blank at 230 °C for standby heat preservation for 13 h;

[0093] S302: Heat up to 805 °C at a heating rate of 25 °C / h and keep it for 13 h;

[0094] S303: Heat up to 1055 °C at a heating rate of 60 °C / h and keep it for 13 h;

[0095] S304: Heat up to 1100 °C at a heating rate of 70 °C / h, keep it for 13 h, and then cool it in oil to 100 °C; control the content of untransformed retained austenite to be below 10%;

[0096] Step 4: Perform two temperings to obtain the boron-containing martensitic heat-resistant steel forging; the temperature of the first tempering is 580 °C, and the temperature of the second tempering is 685 °C.

[0097] The microstructure of the boron-containing martensitic heat-resistant steel forging in this embodiment is tempered martensite structure. The grain uniformity is good in different parts, and the grain size grade and performance results are shown in Table 1 below.

[0098] During the research process, the inventors conducted a large amount of research, and now some solutions with poor performance are used as comparative examples.

[0099] Comparative Example 1

[0100] This comparative example provides a boron-containing martensitic heat-resistant steel forging and its preparation method. The components and dimensions of the boron-containing martensitic heat-resistant steel forging in this comparative example are the same as those in Example 1 and will not be elaborated here.

[0101] The preparation method of this comparative example is generally the same as that of Example 1, with the difference being:

[0102] S303, keep warm for 7 hours;

[0103] S304, keep warm for 7 hours.

[0104] Due to the short holding time, the grains of the boron-containing martensitic heat-resistant steel forging in this comparative example are controlled to be fine and uniform, as Figure 3 shown, but the structure is martensite + some undissolved BN particles, as Figure 4 shown, resulting in low yield strength and poor high-temperature creep properties, unable to meet the requirements for the use of forgings.

[0105] Comparative Example 2

[0106] This comparative example provides a boron-containing martensitic heat-resistant steel forging and its preparation method. The components and dimensions of the boron-containing martensitic heat-resistant steel forging in this comparative example are the same as those in Example 1 and will not be elaborated here.

[0107] The preparation method of this comparative example is generally the same as that of Example 1, with the difference being:

[0108] S303, keep warm for 11 hours;

[0109] S304, keep warm for 11 hours.

[0110] Due to the long holding time, the grains of the boron-containing martensitic heat-resistant steel forging in this comparative example are coarse, obtaining Figure 5 grade 0 grains as shown, resulting in a large central limit sensitivity of ultrasonic flaw detection and poor flaw detection penetration, unable to meet the standard requirements, and requiring heat treatment to refine the grains for repair, leading to an increase in the production cycle and production cost.

[0111] Comparative Example 3

[0112] This comparative example provides a boron-containing martensitic heat-resistant steel forging and its preparation method. The components and dimensions of the boron-containing martensitic heat-resistant steel forging in this comparative example are the same as those in Example 2 and will not be elaborated here.

[0113] The preparation method of this comparative example is generally the same as that of Example 2, with the difference being:

[0114] S303, keep warm for 10 hours;

[0115] S304. Insulate for 10 h.

[0116] Due to the short insulation time, the boron-containing martensitic heat-resistant steel forgings of this comparative example have a structure of martensite and contain some undissolved cluster-shaped BN particles, with low room-temperature strength and poor high-temperature creep properties.

[0117] Comparative Example 4

[0118] This comparative example provides a boron-containing martensitic heat-resistant steel forging and its preparation method. The components and dimensions of the boron-containing martensitic heat-resistant steel forgings of this comparative example are the same as those in Example 2, and will not be elaborated here.

[0119] The preparation method of this comparative example is generally the same as that of Example 1, except that:

[0120] S303. Insulate for 16 h;

[0121] S304. Insulate for 16 h.

[0122] Due to the long insulation time, the boron-containing martensitic heat-resistant steel forgings of this comparative example have coarse grains, a large central limit sensitivity in ultrasonic flaw detection, and poor flaw detection penetration, unable to meet the standard requirements, and need to be heat-treated to refine the grains for repair, resulting in an increase in the production cycle and production cost.

[0123] Comparative Example 5

[0124] This comparative example provides a boron-containing martensitic heat-resistant steel forging and its preparation method. The components and dimensions of the boron-containing martensitic heat-resistant steel forgings of this comparative example are the same as those in Example 1, and will not be elaborated here.

[0125] In the preparation method of this comparative example, in step S304, the forging is directly water-cooled, and cracks appear in the forging blank.

[0126] Table 1 Test Results

[0127]

[0128]

[0129] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a boron-containing martensitic heat-resistant steel forging, characterized in that: The preparation method comprises: Step 1: preparing steel ingot; Step 2: Forging the steel ingot to obtain a forging blank; Step 3: subjecting the forging blank to austenitizing heat treatment by step-by-step heat preservation, and then quenching to room temperature; Step 4: Perform tempering twice to obtain boron-containing martensitic heat-resistant steel forgings.

2. The preparation method according to claim 1, characterized in that: In step 3, the step-by-step heat-insulating austenitizing heat treatment comprises the following steps: S301, keeping the forging blank at 200-250°C; S302, heating to 790-810°C, keeping warm; S303, heating to 1055-1065°C, keeping warm; S304, heat to 1095 ~ 1105 ℃, keep warm, and then quench to room temperature.

3. The preparation method according to claim 2, characterized in that: In the above S301, the holding time t1 and the cross-sectional diameter d of the forging blank are controlled to meet the following relationship: t1=(0.9-1.1)d / 100, where the unit of d is mm and the unit of t1 is h.

4. The preparation method according to claim 2, characterized in that: In the above S302, the holding time t2 and the cross-sectional diameter d of the forging blank meet the following relationship: t2=(0.9-1.1)d / 100, where the unit of d is mm and the unit of t2 is h.

5. The preparation method according to claim 2, characterized in that: In the above S303, the holding time t3 and the cross-sectional diameter d of the forging billet meet the following relationship: t3=(0.9-1.1)d / 100, where the unit of d is mm and the unit of t3 is h.

6. The preparation method according to claim 1, characterized in that: The heating rate v1 in S302, the heating rate v2 in S303, and the heating rate v3 in S304 satisfy the following relationship: v3≥v2>v1.

7. The preparation method according to claim 1, characterized in that: In step 4, the temperature of the first tempering is lower than the temperature of the second tempering.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The components of the boron-containing martensitic heat-resistant steel forging include, by mass percentage, C: 0.10% to 0.16%, Si≤0.12%, Mn: 0.2% to 0.6%, Cr: 9.0% to 9.8%, Mo: 1.2% to 1.7%, Ni≤0.3%, V: 0.1% to 0.3%, N: 0.01% to 0.03%, Nb: 0.03% to 0.07%, B: 70 to 120 ppm, and the remainder is Fe and unavoidable impurities.

9. The preparation method according to any one of claims 1 to 7, characterized in that: The cross-sectional diameter of the boron-containing martensitic heat-resistant steel forging is 900-1300 mm.

10. A boron-containing martensitic heat-resistant steel forging, characterized in that: The boron-containing martensitic heat-resistant steel forging is prepared by the preparation method according to any one of claims 1 to 9.

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