Heat treatment method for high-strength steel blind hole part

Abstract

The application discloses a heat treatment method of high-strength steel blind hole parts, which comprises the following steps: processing the blind hole parts by using a blank; taking a tensile sample, an impact sample, a standard sample and a simulation product front end solid part equivalent diameter furnace sample on the blank; fixing the blind hole parts by using a tool, and performing vacuum normalizing treatment on the blind hole parts, the tensile sample, the impact sample and the furnace sample, wherein the hole of the blind hole parts faces downward, and air or quenching oil can enter and exit from the hole; fixing the blind hole parts by using a tool, and performing vacuum quenching treatment and vacuum tempering treatment on the blind hole parts, the tensile sample, the impact sample and the furnace sample. The application adopts the tensile sample and the impact test to simulate the heat treatment performance of the thin wall position of the blind hole parts, and the furnace sample simulates the heat treatment performance of the end solid position, so that the austenitizing of the solid part is ensured to be fully completed, the hardenability during oil quenching is ensured, and the influence degree of the prolonging of the holding time on the performance of the thinnest position of the product is verified.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, and in particular, to a heat treatment method for high-strength steel blind hole parts. Background Technology

[0002] For half a century, ultra-high strength steel has been developed into a widely used material in important equipment, with extensive applications in engine casings, aircraft landing components, special equipment, pressure vessels, and conventional weapons, and its application scope continues to expand.

[0003] 32SiMnCrNi5MoVA (DT300) steel is a new high-strength and high-toughness steel independently developed in my country to meet engineering needs. This steel is a low-carbon, low-alloy, ultra-high-strength steel based on the SiMnCrNiMoV system, with a low-carbon martensitic matrix. Through strengthening measures such as solid solution strengthening, phase transformation strengthening, dispersion strengthening, and grain refinement, as well as toughening measures such as obtaining a certain amount of retained austenite between lath martensite, high material purity, inclusion improvement and modification, and microstructure refinement, it achieves high strength, high impact toughness, and good processing performance, making it widely applicable to high-strength and high-toughness load-bearing components. Its chemical composition is: C: 0.28%–0.35%, Si: 1.4%–1.9%, Mn: 0.6%–0.9%, Ni: 4.6%–6.0%, Cr: 0.9%–1.2%, Mo: 0.4%–0.7%, S: ≤0.01%, P: ≤0.01%, V: ≤0.35%, Cu: ≤0.2%, O: ≤0.002%, N: ≤0.004%, with the remainder being iron. The bars are smelted using an electric arc furnace + vacuum refining + vacuum arc remelting method. After heat treatment, the mechanical properties must meet the following requirements: tensile strength R... m ≥1730 MPa, yield strength R p0.2 ≥1350Mpa, elongation ≥8%, reduction of area 40%.

[0004] Parts made of DT300 material are typically blind hole parts with complex shapes, varied cross-sections, and significant thickness differences. The heat treatment process for such parts has the following drawbacks:

[0005] Heat treatment, as a special process in production (referring to processes where certain processing quality is difficult or cannot be fully verified through subsequent inspection or testing), requires representative furnace-mounted samples to be heat-treated along with the product parts. The mechanical properties of these samples are then examined to determine whether the product meets standard requirements after heat treatment. However, in current production, due to a mismatch between the furnace-mounted samples and the product, the mechanical properties of the samples after heat treatment are often lower than expected or fail to meet standard requirements, leading to the scrapping of some products and a low pass rate. Summary of the Invention

[0006] This invention provides a heat treatment method for high-strength steel blind hole parts to solve the technical problem of low product qualification rate caused by the mismatch between the existing furnace-fed sample setup and the product.

[0007] This invention provides a heat treatment method for high-strength steel blind hole parts, comprising the following steps:

[0008] (1) A blind hole part is machined from a blank, wherein the blind hole part includes a blind hole side and a non-blind hole side, the end of the blind hole side is a conical solid, the maximum diameter of the conical solid is D, wherein 80mm≤D≤170mm; the minimum wall thickness of the hole section of the non-blind hole side is d, wherein 20mm≤d≤50mm;

[0009] (2) Take tensile test specimens, impact test specimens, and furnace-fed test specimens from the billet. The tensile test specimen is a cylinder with a diameter of d; the impact test specimen is a cube with a square cross-section having a side length of d; the furnace-fed test specimen is a cylinder with a diameter of 2 / 3D; the tensile test specimen is processed according to the national standard GB / T228.1-2010 to meet the height requirements of the test specimen therein; the impact test specimen is processed according to the height requirements of the national standard GB229-2007-T to meet the height requirements of the test specimen therein; the height of the furnace-fed test specimen is greater than or equal to D and is greater than the height requirements of the test specimen in the national standard GB / T228.1-2010.

[0010] (3) Fix the blind hole part with tooling and perform vacuum normalizing treatment together with tensile test specimens, impact test specimens and furnace test specimens. The hole of the blind hole part is facing down, and air or quenching oil can enter and exit through the hole. The vacuum normalizing treatment includes preheating at 580-620℃ for 30-90 minutes, then heating to 900-920℃, holding for 90-120 minutes, and air cooling.

[0011] (4) Fix the blind hole part with tooling and vacuum quench it together with the tensile test specimen, impact test specimen and furnace test specimen. The vacuum quenching process includes preheating at 580-620℃ for 30-90 min, then heating to 880-900℃, holding for 180-210 min, and oil cooling.

[0012] (5) Fix the blind hole part with a tooling and perform vacuum tempering treatment together with the tensile test specimen, impact test specimen and furnace test specimen. The vacuum tempering treatment includes heating from room temperature to 240-260°C, holding for 270-330 minutes, and air cooling.

[0013] Furthermore, the blank used is a bar, and the sampling position for taking tensile test specimens on the bar is the section wall thickness of the non-blind hole side of the blind hole part when the bar is assumed to be machined into a blind hole part.

[0014] Furthermore, the billet used is a bar, and the equivalent diameter of the conical solid simulating the blind hole side end on the bar is taken as a furnace sample, with the sampling location being the core of the bar.

[0015] Furthermore, the vacuum degree of the vacuum normalizing treatment, vacuum quenching treatment and vacuum tempering treatment is 2.95 to 4.16 Pa.

[0016] Furthermore, during the vacuum normalizing, vacuum quenching, and vacuum tempering processes, the tensile test specimen and the impact test specimen are fixed to the non-blind hole end of the blind hole part; the furnace-fed test specimen is fixed to the blind hole end of the blind hole part.

[0017] Furthermore, the quenching transfer time in step (4) is no more than 45s.

[0018] Furthermore, in step (4), oil cooling includes circulating the oil inside and outside the oil tank and vigorous stirring, cooling the oil to below 60°C.

[0019] Furthermore, step (5) includes cleaning the quenching oil from the blind hole part and drying it.

[0020] Furthermore, step (5) includes mechanical property testing of the tensile and impact specimens.

[0021] Furthermore, after the mechanical properties have passed the test, the heat-treated blind hole parts are precision machined.

[0022] The present invention has the following beneficial effects:

[0023] The heat treatment method for high-strength steel blind hole parts provided by this invention involves heat treating tensile test specimens, furnace-fed specimens, and impact test specimens together with the blind hole parts. Tensile test specimens simulate the heat treatment performance of the thin-walled portion of the blind hole part, while furnace-fed specimens simulate the heat treatment performance of the solid end portion. The diameter of the furnace-fed specimen is equal to the effective diameter (2 / 3D) of the conical head of the workpiece. The performance of this portion is a critical property required by the product and must be fully hardened. In this application, the holding time for vacuum quenching is calculated based on the diameter of the furnace-fed specimen, and then appropriately adjusted according to the furnace loading and heating time to ensure full hardening. This method ensures that the solid portion is fully austenitized, guaranteeing hardenability during oil quenching, and also verifies the impact of extended holding time on the performance of the thinnest portion of the product (if the holding time is calculated based on the thickest portion of the blind hole part, the thinnest portion may have coarse grains, leading to a reduction in the overall mechanical properties of the thinnest portion). This method is suitable for verifying the heat treatment performance of blind hole parts with large differences in wall thickness or effective thickness.

[0024] The heat treatment method for high-strength steel blind hole parts provided by this invention involves fixing the blind hole parts with tooling during vacuum quenching, with the hole opening facing downwards, allowing air to enter and exit through the opening. This solves the problem of quenching oil not flowing within the blind hole parts, allowing the quenching oil to flow smoothly into the inner cavity during quenching. The quenching oil at the bottom can circulate and cool with the quenching oil in the oil bath, ensuring that the mechanical properties of the end material are also qualified.

[0025] The heat treatment method for high-strength steel blind hole parts provided by this invention involves fixing the blind hole parts with tooling during vacuum quenching, and placing the blind hole parts vertically with the hole opening facing downwards. This effectively reduces the amount of deformation during heat treatment, resulting in a bright surface after quenching, reducing the finishing allowance, and saving production cycle time.

[0026] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a schematic diagram of the structure of a blind hole component according to a preferred embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the tooling used to fix the blind hole part according to a preferred embodiment of the present invention.

[0030] Legend:

[0031] 100 - Blind hole part; 200 - Tooling; 1 - Blind hole side; 2 - Non-blind hole side; 10 - Tensile test specimen; 20 - Impact test specimen; 30 - Furnace test specimen. Detailed Implementation

[0032] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0033] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0034] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0035] Taking DT300 high-strength steel forgings as an example, they are generally air-cooled after forging. Due to varying forging temperatures and cooling rates, the resulting microstructure and hardness vary considerably, with larger diameter bars exhibiting poorer microstructure uniformity. To ensure uniform microstructure and reduce structural stress, a homogenization normalizing process is required. However, forging manufacturers often fail to perform sufficient normalizing, especially when the bar diameter is ≥200mm, resulting in even greater microstructure differences. Consequently, the mechanical properties of some samples after heat treatment do not meet standard requirements.

[0036] The factors affecting the austenitization of steel are heating temperature and holding time. If the quenching temperature is too high, the austenite grains coarsen, and the quenched martensite becomes coarse, leading to an "overheating" phenomenon. If the quenching temperature is too low, undissolved ferrite will be present, which is detrimental to the overall properties. Therefore, it is necessary to use a relatively low temperature for complete quenching within the single-phase austenite region.

[0037] Existing technologies mainly focus on quenching and tempering processes, with a particular emphasis on the effects of temperature on the microstructure and mechanical properties of DT300 high-strength steel. However, there is relatively little research on the effects of holding time on performance.

[0038] An embodiment of this application provides a heat treatment method for high-strength steel blind hole parts, comprising the following steps:

[0039] (1) A blind hole part 100 is machined from a blank, wherein the blind hole part 100 includes a blind hole side 1 and a non-blind hole side 2. The end of the blind hole side 1 is a tapered solid, and the maximum diameter of the tapered solid is D, wherein 80mm≤D≤170mm; the minimum wall thickness of the hole opening section of the non-blind hole side 2 is d, wherein 20mm≤d≤50mm;

[0040] (2) Take tensile specimens, impact specimens 20 and furnace-fed specimens 30 from the billet. The tensile specimen is a cylinder with a diameter of d; the impact specimen 20 is a cube with a square cross-section of side length d; the furnace-fed specimen is a cylinder with a diameter of 2 / 3D. The tensile specimen is processed according to the national standard GB / T228.1-2010 "Metallic materials, tensile testing - Part 1: Test at room temperature" and meets the height requirements of the test specimen therein. The impact specimen 20 is processed according to the national standard GB229-2007-T "Metallic materials, Charpy pendulum impact test method" and meets the height requirements of the test specimen therein. The height of the furnace-fed specimen 30 is greater than or equal to D and is greater than the height requirement of the test specimen in the national standard GB / T228.1-2010 "Metallic materials, tensile testing - Part 1: Test at room temperature".

[0041] (3) Fix the blind hole part 100 with tooling 200 and perform vacuum normalizing treatment together with tensile test specimen, impact test specimen 20 and furnace test specimen 30. The hole of the blind hole part 100 is facing downward, and air or quenching oil can enter and exit from the hole. The vacuum normalizing treatment includes preheating at 580-620°C for 30-90 minutes, then heating to 900-920°C, holding for 90-120 minutes, and air cooling.

[0042] (4) Fix the blind hole part 100 with tooling 200, and vacuum quench it together with tensile test specimen 10, impact test specimen 20 and furnace test specimen 30. The vacuum quenching process includes preheating at 580-620℃ for 30-90 min, then heating to 880-900℃, holding for 180-210 min, and oil cooling.

[0043] (5) Fix the blind hole part 100 with the tooling 200, and perform vacuum tempering treatment together with the tensile test specimen 10, the impact test specimen 20 and the furnace test specimen 30. The vacuum tempering treatment includes heating from room temperature to 240-260°C, holding for 270-330 minutes, and air cooling.

[0044] In the embodiments of this application, the purpose of vacuum normalizing is twofold: first, to homogenize the carbide structure, and second, to refine the grain size to ensure the grain size of the material during formal heat treatment.

[0045] In the embodiments of this application, the total holding time for vacuum quenching is calculated based on the diameter of the sample 30 carried in the furnace. The calculation method is T = T (soaking time) + T (holding time) = αKH (α is the soaking coefficient in mm / min, K is the furnace loading correction coefficient, and H is the effective thickness of the workpiece (i.e., the diameter of the sample 30 carried in the furnace, 2 / 3D) + 40~60min. In this case, α = 1 for alloy steel, and the furnace loading correction coefficient is set to 1 for the part placed flat and receiving better heating conditions.

[0046] Taking a cone-shaped solid with a maximum diameter of 180mm as an example, the effective diameter of the cone-shaped solid is calculated to be Φ120mm. The heat preservation time calculated according to the above formula is 160-180min. Since vacuum heating is a single radiation heat transfer, the actual heating time generally needs to be increased by 20-30min. Therefore, the selected actual heating time is 180-210min.

[0047] The holding time calculated using the above method can effectively ensure that the mechanical properties of the product across its entire thickness range meet the standard requirements during vacuum quenching.

[0048] The heat treatment method for high-strength steel blind hole parts 100 provided by this invention, during vacuum quenching, involves fixing the blind hole part 100 with a tooling 200, ensuring the hole faces downwards, allowing air or quenching oil to enter and exit through the hole. This solves the problem of incomplete air extraction or quenching oil flow into the blind hole cavity. During the vacuum quenching process of this application, quenching oil can smoothly flow into the inner cavity, and the quenching oil inside the cavity can circulate and cool with the quenching oil in the oil bath under gravity, ensuring that the mechanical properties of the end material are also qualified.

[0049] The heat treatment method for high-strength steel blind hole parts 100 provided by the present invention involves fixing the blind hole parts 100 with tooling 200 during vacuum quenching, and placing the blind hole parts 100 vertically with the hole facing downwards. This effectively reduces the amount of deformation during heat treatment, obtains a bright surface after quenching, reduces the finishing allowance, and saves the production cycle.

[0050] In the embodiments of this application, the structure of tooling 200 is not specifically limited, and can be as follows: Figure 2 The tooling shown ensures that blind hole parts are placed vertically with the hole facing downwards, allowing air to enter and exit through the hole.

[0051] In the embodiments of this application, the blank used is a bar. The sampling position of the tensile specimen 10 on the bar is at the wall thickness of the non-blind hole side 2 of the blind hole part 100 when the bar is assumed to be machined into a blind hole part 100. The sampling position of the tensile specimen 10 corresponds to the minimum wall thickness of the non-blind hole side 2 of the blind hole part 100. The mechanical properties of the tensile specimen 10 after heat treatment are used to simulate the performance of the non-blind hole side 2 of the blind hole part 100.

[0052] In the embodiments of this application, the billet used is a bar, and the sampling location for the furnace-fed sample 30 is the core of the bar. The above-mentioned sampling method for the furnace-fed sample 30 can be used to simulate the performance of the blind hole side 1 of the blind hole part 100.

[0053] In the embodiments of this application, the vacuum degree of the vacuum normalizing treatment, vacuum quenching treatment and vacuum tempering treatment is 2.95 to 4.16 Pa. Under the above vacuum degree, the oxygen concentration is low and the cost performance is the highest.

[0054] In the embodiments of this application, during the vacuum normalizing, vacuum quenching, and vacuum tempering processes, the tensile specimen 10 and the impact specimen 20 are fixed to the non-blind hole side 2 of the blind hole part 100; the furnace-fed specimen 30 is fixed to the blind hole side 1 of the blind hole part 100. This fixing method ensures that the tensile specimen 10 and the impact specimen 20 are heated under the same conditions as the non-blind hole side 2; and that the furnace-fed specimen 30 is heated under the same conditions as the blind hole side 1.

[0055] In the embodiments of this application, the quenching transfer time in step (4) is no more than 45s, which can avoid the workpiece temperature being too low when entering the oil and thus affecting the quenching effect.

[0056] In the embodiments of this application, the oil cooling in step (4) includes circulating the oil inside and outside the oil tank and stirring it vigorously, and cooling the oil to below 50°C.

[0057] In the embodiments of this application, step (5) is further performed by cleaning the quenching oil of the blind hole part and drying it.

[0058] In the embodiments of this application, step (5) is followed by mechanical property testing of the heat-treated tensile specimen 10, impact specimen 20 and furnace-fed specimen 30.

[0059] According to the embodiments of this application, tensile specimen 10 is prepared for tensile mechanical property testing, and impact specimen 20 is prepared for impact mechanical property testing; tensile specimen 10 and impact specimen 20 are obtained by wire cutting of furnace specimen 30 for mechanical property measurement.

[0060] In the embodiments of this application, after the mechanical properties have passed the test, the heat-treated blind hole part is precision machined.

[0061] Example

[0062] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0063] 1. Raw material testing:

[0064] Sampling and testing were conducted in accordance with the specifications in "Q / GYB795-2012 Technical Conditions for Vacuum Consumable Remelting 32SiMnCrNi5MoVA(DT300) Steel Bars".

[0065] (1) Hardness not greater than 340HBW or 36HRC;

[0066] (2) The low-magnification microstructure, non-metallic inclusions and grain size meet the standard requirements;

[0067] (3) Select the most representative location, i.e., half the radius of the bar, and cut a tensile and impact specimen 20 mm in diameter, ensuring an effective diameter of 20 mm. Perform heat treatment tests on this specimen according to the product's heat treatment process to verify its mechanical properties. If the mechanical properties are met, rough machining can begin; if the mechanical properties are not met, the heat treatment process needs to be adjusted according to the test results (mainly adjusting the tempering temperature and tempering time to optimize the strength-toughness match).

[0068] (4) Compile formal product heat treatment process specifications.

[0069] 2. Roughly machined parts blanks and furnace-made sample blanks:

[0070] (1) Rough machining of part blanks: Machining of blind hole parts 100, with an 80mm chuck reserved at one end of the blind hole side for easy clamping and positioning of turning and boring and milling. A machining allowance of 1mm is reserved on the inner and outer cavity surfaces, and the grooves and edges are rounded to avoid cracks at the sharp corners due to excessive cooling during heat treatment.

[0071] (2) Design and processing of sampling method for in-furnace test billets: based on Figure 1 Taking the blind hole part 100 as an example, the minimum wall thickness of the elliptical cross-section of the two holes on the non-blind hole side is 20mm. At a position approximately equal to the elliptical diameter of the forging blank, Φ20×130 tensile test specimen 30 and 22×22×130 impact test specimen 20 are taken to simulate the heat treatment performance of the material on the non-end side. The cross-sectional thickness gradually increases from the two holes on the non-blind hole side to the end of the blind hole. The end of the blind hole side is a conical solid with a maximum diameter of 180mm. Relevant standards stipulate that the effective diameter of this part is calculated based on 2 / 3 of the cone's height diameter. Therefore, the effective diameter of the conical solid is approximately Φ120mm. Thus, for this part, a Φ120×130 concentric cylindrical specimen is directly taken from the center of the forging blank as the furnace-fed specimen 30 for the conical solid at the end.

[0072] 3. Vacuum quenching (normalizing):

[0073] A vacuum vertical gas quenching furnace is selected for normalizing. The workpiece and fixture are vertically assembled with the blind hole facing downwards (e.g., Figure 2As shown, this method effectively controls deformation during the heating process. Φ20×130 tensile test specimens 30 and 22×22×130 impact test specimens 20 are evenly distributed and tied to the tail of the workpiece, while Φ120×130 rods are tied to the head of the workpiece. The furnace is heated to 600℃, preheated isothermally to 600℃ for 60 minutes, and then slowly heated to 910℃±10℃ for 150 minutes. The equipment is under vacuum of 2.95~4.16pa and cooled by air at 2 atmospheres.

[0074] 4. Vacuum vertical oil quenching (hardening)

[0075] The installation method of parts and tooling 200, the position of the sample parts in the furnace, and the installation method after entering the furnace are consistent with those of normalizing. The whole is quenched in a vacuum vertical oil quenching furnace. After the workpiece enters the furnace, the vacuum degree of the equipment is set to 2.95~4.16pa. The furnace temperature is raised to 600℃, preheated to 600℃ at room temperature for 60min, and then slowly heated to 890℃±10℃ and held for 180min. The quenching transfer time is ≤45s. During cooling, the oil bath is circulated inside and outside and vigorously stirred. The workpiece is cooled in the oil to below 50℃ before being taken out of the furnace.

[0076] 5. Cleaning and drying: Use a special cleaning machine to clean the quenching oil in the inner and outer cavities and then dry them.

[0077] 6. Vacuum Tempering: The installation method of parts and tooling 200, the position of the sample in the furnace, and the installation method after entering the furnace are the same as the previous heat treatment process. The workpiece is tempered in a vacuum tempering furnace. The vacuum degree of the equipment is set to 2.95~4.16pa. The furnace temperature is raised to 250±3℃, heated from room temperature to 250℃ for 20 minutes, isothermal preheating at 250℃ for 300 minutes, and then air-cooled.

[0078] 7. Finishing:

[0079] (1) The blank size of the part is processed to the final machining drawing.

[0080] (2) The Φ120×130 furnace-fed tensile specimen 30 was processed into a tensile specimen 10 with an effective diameter of Φ10 according to GB / T228.1-2021 Metallic materials, tensile testing—Part 1: Test at room temperature. The 22×22×130 impact specimen 20 was processed into a 10×10×55 impact specimen 20 according to GB / T229-2020 Metallic materials, Charpy pendulum impact test. The notches were all opened on the surface away from the center of the blank. The Φ120×130 furnace-fed specimen 30 was cut by wire cutting at half the radius of the main body, and then processed to meet the standard dimensions and surface roughness.

[0081] 8. Mechanical property processing and testing:

[0082] Mechanical properties were tested on tensile specimen 10 and impact specimen 20 in section 4.6 respectively. All specimens were qualified if they met the following conditions: tensile strength Rm≥1730MPa, yield strength Rp0.2≥1350MPa, elongation≥8%, and reduction of area 40%.

[0083] The mechanical properties obtained using the above heat treatment process are shown in the table below:

[0084] Table 1 Mechanical properties of heat treatment process in Example 1

[0085]

[0086] Example 2

[0087] The heat treatment process in this embodiment includes the following steps:

[0088] Normalizing: Heat the furnace to 600℃, heat to 600℃ from room temperature for 60 minutes, preheat at 600℃ isothermally for 60 minutes, then slowly heat to 910℃±10℃ for 120 minutes and hold for 150 minutes, then air cool.

[0089] Quenching: Heat the furnace to 600℃, heat to 600℃ at room temperature for 60 minutes, preheat at 600℃ isothermally for 60 minutes, then slowly heat to 890℃±10℃ for 120 minutes and hold for 180 minutes, then oil cool to below 50℃.

[0090] Tempering: Heat the furnace to 250±3℃, heat from room temperature to 250℃ for 20 minutes, preheat at 250℃ isothermally for 300 minutes, and then air cool.

[0091] Everything else is the same as in Example 1. The mechanical properties obtained by the above heat treatment process are shown in the table below:

[0092] Table 2 Mechanical properties of heat treatment process in Example 2

[0093]

[0094] Comparative Example 1

[0095] This comparative example lacks the normalizing step, but everything else is the same as in Example 2. The mechanical properties obtained according to this heat treatment process are shown in the table below:

[0096] Table 3 Comparative Example 1 Mechanical Properties of Heat Treatment Process

[0097]

[0098] Comparative Example 2

[0099] The vacuum quenching time in this comparative example was 150 min, and all other parameters were the same as in Example 2. The mechanical properties obtained according to this heat treatment process are shown in the table below:

[0100] Table 4 Comparative Example 2 Mechanical Properties of Heat Treatment Process

[0101]

[0102] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A heat treatment method for high-strength steel blind hole parts, characterized in that, Includes the following steps: (1) A blind hole part (100) is machined from a blank, wherein the blind hole part (100) includes a blind hole side (1) and a non-blind hole side (2), wherein the end of the blind hole side (1) is a conical solid, and the maximum diameter of the conical solid is D, wherein 80mm≤D≤170mm; the minimum wall thickness of the hole section of the non-blind hole side (2) is d, wherein 20mm≤d≤50mm; (2) Take tensile test specimens (10), impact test specimens (20) and furnace test specimens (30) from the billet. The tensile test specimen (10) is a cylinder with a diameter of d; the impact test specimen (20) is a cube with a square cross-section with a side length of d; the furnace test specimen (30) is a cylinder with a diameter of 2D / 3; the tensile test specimen (10) is processed according to the national standard GB / T228.1-2010 to meet the height requirements of the test specimen therein; the impact test specimen (20) is processed according to the national standard GB229-2007-T to meet the height requirements of the test specimen therein; the height of the furnace test specimen (30) is greater than or equal to D and is greater than the height requirements of the test specimen in the national standard GB / T228.1-2010. (3) Fix the blind hole part (100) with tooling (200) and perform vacuum normalizing treatment together with tensile test specimen (10), impact test specimen (20) and furnace test specimen (30). The hole of the blind hole part (100) faces downward, and air or quenching oil can enter and exit from the hole. The vacuum normalizing treatment includes preheating at 580~620℃ for 30~90min, then heating to 900~920℃, holding for 90~120min, and air cooling. (4) Fix the blind hole part (100) with tooling (200) and vacuum quench it together with the tensile test specimen (10), impact test specimen (20) and furnace test specimen (30). The vacuum quenching process includes preheating at 580~620℃ for 30~90min, then heating to 880~900℃, holding for 180~210min, and oil cooling. (5) Fix the blind hole part (100) with tooling (200) and perform vacuum tempering treatment together with tensile test specimen (10), impact test specimen (20) and furnace test specimen (30). The vacuum tempering treatment includes heating from room temperature to 240~260℃, holding for 270~330min, and air cooling. The blank used is a bar. The sampling positions of the tensile test specimen (10) and impact test specimen (20) on the bar are assumed to be the non-blind hole side (2) of the hole section wall thickness when the bar is processed into a blind hole part (100). The billet used is a bar. The equivalent diameter of the conical solid at the end of the blind hole side (1) on the bar is taken from the furnace sample (30). The sampling position is the core of the bar. During the vacuum normalizing, vacuum quenching and vacuum tempering processes, the tensile test specimen (10) and the impact test specimen (20) are fixed to the non-blind hole end of the blind hole part (100); the furnace-fed test specimen (30) is fixed to the blind hole end of the blind hole part (100).

2. The heat treatment method for high-strength steel blind hole parts according to claim 1, characterized in that, The vacuum degree of the vacuum normalizing treatment, vacuum quenching treatment and vacuum tempering treatment is 2.95 to 4.16 Pa.

3. The heat treatment method for high-strength steel blind hole parts according to claim 1, characterized in that, The quenching transfer time in step (4) shall not exceed 45s.

4. The heat treatment method for high-strength steel blind hole parts according to claim 1, characterized in that, In step (4), oil cooling includes circulating the oil inside and outside the oil tank and vigorously stirring it to cool the oil to below 60°C.

5. The heat treatment method for high-strength steel blind hole parts according to claim 1, characterized in that, Step (5) also includes cleaning the quenching oil from the blind hole part and drying it.

6. The heat treatment method for high-strength steel blind hole parts according to claim 1, characterized in that, Step (5) is followed by mechanical property testing of the heat-treated tensile specimen (10), impact specimen (20) and furnace-fed specimen (30).

7. The heat treatment method for high-strength steel blind hole parts according to claim 6, characterized in that, After the mechanical properties pass the test, the heat-treated blind hole parts are precision machined.

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