Preparation method of 1200MPa-grade high-strength non-magnetic cup-shaped part

Abstract

The invention discloses a preparation method of a 1200MPa-grade high-strength non-magnetic cup-shaped part, which comprises the working procedures of smelting, temperature-controlled rolling, low-temperature destressing treatment and punch forming: 1) smelting working procedure: controlling the C content of molten steel to be 5,000-5,500 ppm; the content of N is controlled to be 5500 ppm to 6000 ppm; the content of C + N is controlled to be more than or equal to 10800ppm, and the content of S is less than or equal to The blank is heated to 1210 DEG C along with a furnace, and the heat preservation time is 4-5 h, the plate is subjected to hot rolling at the temperature of 420-430 DEG C and subjected to heat preservation for 90-100 min, and the die temperature is adjusted and controlled to guarantee that the corner temperature of a stamping outer die is stably controlled to 320-350 DEG C, the side wall is stably controlled to 260-290 DEG C, and the bottom is stably controlled to be smaller than or equal to 220 DEG C. The part obtained through the method is stable in structure performance.

Description

Technical Field

[0001] The invention belongs to the technical field of stamping processing, and specifically relates to a method for preparing a 1200MPa-level high-strength non-magnetic cup-shaped part. Background Art

[0002] Cup-shaped parts used in some special fields are required not to be affected by magnetic fields during the service process, and the parts must be non-magnetic under the conditions of use; because they need to withstand instantaneous high-intensity impact, the tensile strength of the parts must be ≥1200MPa; in order to ensure the comprehensive performance of the material, the overall uniformity of the parts needs to be controlled.

[0003] Due to the ultra-high strength of the material, conventional processing methods cannot meet the requirements. The common preparation process is to process the part through CNC turning on 90mm forged or rolled bars. The raw materials are seriously wasted and the processing cost is extremely high. Some stamping units also tried to process it through sheet metal stamping technology, but failed due to a series of problems such as stamping cracks, inconsistent strength, and uneven performance.

[0004] Based on the above problems, this field urgently needs to develop a low-cost preparation method for 1200MPa-level high-strength non-magnetic cup-type parts, so as to produce non-magnetic, high-strength and stable performance parts products while greatly reducing the manufacturing cost of parts.

[0005] Research has found that the main ways to increase material strength are: solid solution strengthening, phase transformation strengthening, precipitation strengthening, deformation strengthening, etc. In order to ensure the non-magnetic properties of the material, this part needs to maintain the austenite structure, which cannot be strengthened by phase transformation strengthening and precipitation strengthening. Therefore, solid solution strengthening and deformation strengthening are the main methods to increase the strength of parts. After research, it was found that carbon and nitrogen elements can be used as solid solution elements in the face-centered cubic austenite to increase the strength of the material by solid solution. For every 0.1% increase in nitrogen content, the strength increases by 60 to 100 MPa. Therefore, adding a certain amount of carbon and nitrogen can greatly improve the strength. However, if the carbon content is too high, it is easy to form a large amount of carbides that are enriched at the grain boundaries, reducing the plasticity of the material; as a gas element, nitrogen content is too high, exceeding the solubility of the material, and nitrogen bubbles are easily formed during the smelting and casting process, affecting the uniformity of the ingot structure, seriously causing the material to be scrapped. Combining theoretical analysis and multiple tests, it is determined that the C content is controlled at 5000ppm~5500ppm; the N content is controlled at 5500ppm~6000ppm; and the C+N content is controlled at ≥10800ppm. Within this range, the material has a stable structure after processing and the strength meets the requirements. To ensure the processability and serviceability of the material, the sulfur content must be ≤10ppm.

[0006] Single solid solution strength cannot meet the strength requirements, and deformation strengthening is required to further improve the strength. Experiments have found that the strength of the material and the grain size show a Hall-Page formula relationship. The smaller the grain, the higher the strength. Therefore, the present invention can stabilize the good processing plasticity of the material under the premise of ensuring the fine recrystallized grains of the material by hot rolling-low temperature stress relief-low temperature stamping. Summary of the invention

[0007] The present invention provides a low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method, which can stabilize the good processing plasticity of the material under the premise of ensuring fine recrystallized grains of the material.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a low-cost 1200MPa-level high-strength non-magnetic cup-shaped parts preparation method, the preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, and is specifically operated according to the following steps:

[0009] 1) Smelting process: high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control the C and N content of molten steel, C content is controlled at 5000ppm~5500ppm; N content is controlled at 5500ppm~6000ppm; C+N content is controlled at ≥10800ppm, to ensure material purity, S content ≤10ppm;

[0010] 2) Temperature-controlled rolling: strictly control the rolling passes and the rolling temperature and deformation of each pass, the original billet size is (200±5mm)*(90±5mm)*(300~400mm), the billet is heated to 1205~1215℃ with the furnace, and the holding time is 4~5h;

[0011] 3) Low temperature stress relief treatment: hot rolled plate at 420-430℃, heat preservation for 90-100min;

[0012] 4) Stamping: local temperature adjustment for highly uniform automatic stamping, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process through a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the temperature of the corners of the stamping outer mold is stably controlled at 320-350°C, the side wall is stably controlled at 260-290°C, and the bottom is stably controlled at ≤220°C.

[0013] In the step 2) of the present invention, the temperature-controlled rolling process is performed, and the rolling passes and the temperature are matched as shown in the table below.

[0014]

[0015] In step 4) of the present invention, in the stamping process, the stamping stroke of the upper mold is 39-41 mm, and the stamping speed is adjusted in stages: the first 30 mm: V stamping = 0.4-0.6 mm / s; the last 10 mm: V stamping = 0.15-0.25 mm / s; after the stamping, the force of 49-51 KN is maintained for 4-6 seconds.

[0016] The tensile strength of the parts prepared by the method of the present invention is ≥1250MPa, the magnetic permeability is ≤1.02h / m, and the grain size of the material is stably controlled to be ≥8 levels.

[0017] The grain size difference of the corner, side wall and bottom of the part prepared by the method of the present invention is ≤1.5 levels.

[0018] The design principle of the present invention: Regarding chemical composition, both C and N have a solid solution strengthening effect. When the sum of the contents of these two elements is ≥10800ppm, the overall tensile strength of the material can be significantly improved. However, if the C content is too high, large carbide particles are easily formed, which deteriorates the plasticity of the material. Therefore, the C content should not exceed 5500ppm; if the N content is too high, it exceeds the material solubility, and nitrogen bubbles are easily formed during the smelting and casting process, which affects the uniformity of the ingot structure and seriously causes the material to be scrapped. The N content should not exceed 6000ppm.

[0019] Regarding the overall design, the present invention adds appropriate amounts of C and N elements, relies on solid solution strengthening to increase the tensile strength of the material, and deformation strengthening to make the tensile strength of the shell ≥1200MPa, relies on stable rolling and stamping processes to prepare high-strength, non-magnetic shell parts, and according to the stress conditions of different parts, each part of the stamping die is heated separately to make the strength of each part of the finished parts reach a uniform level.

[0020] The beneficial effects of adopting the above technical solution are: the strength of the parts prepared by the present invention is ≥1250MPa, the magnetic permeability is ≤1.02h / m; the material grain size is stably controlled to be ≥8 levels, and the grain size difference of the corners, side walls and bottom of the parts is ≤1.5 levels. DETAILED DESCRIPTION

[0021] The scheme of the present invention is further described in detail below in conjunction with specific embodiments.

[0022] Example 1

[0023] A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, which are specifically performed in the following steps:

[0024] 1) Smelting process: electric furnace smelting + continuous casting, preparation of 90mm thick plate, high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control C and N content, C content controlled at 5010ppm; N content controlled at 5910ppm; C+N content controlled at 10920ppm, to ensure material purity, S content 8ppm.

[0025] 2) Temperature-controlled rolling: Strictly control the rolling passes, rolling temperature and deformation of each pass. The original billet size is 201mm*90mm*340mm. The billet is heated to 1210℃ with the furnace and the insulation time is 4h. The rolling passes and temperatures are strictly matched as shown in the table below.

[0026] Rolling pass Doci-ichi Second pass Path 3 Path 4 Path 5 Path 6 Path 7 Rolling temperature / ℃ 1120 1101 1070 1030 960 950 890 Rolling size / mm 67 45 26 15 9.2 7.3 6.9

[0027] 3) Low temperature stress relief treatment: hot rolled plate at 425℃, keep warm for 100min.

[0028] 4) Stamping: local temperature adjustment for highly uniform automatic stamping and forming, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process through a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the temperature of the corners of the stamping outer mold is stably controlled at 320°C, the side walls are stably controlled at 283°C, and the bottom is stably controlled at 210°C; the stamping stroke of the upper mold is 41mm, and the stamping speed is regulated in stages: the first 30mm: Vstamping = 0.4mm / s; the last 10mm: Vstamping = 0.15mm / s; after stamping, the pressure is maintained at 49KN for 4s.

[0029] The specific properties of the 1200MPa high-strength non-magnetic cup-shaped parts obtained in this embodiment are shown in Table 1. The grain size difference of the corners, side walls and bottom of the parts is 1.5 levels.

[0030] Example 2

[0031] A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, which are specifically performed in the following steps:

[0032] 1) Smelting process: electric furnace smelting + continuous casting, preparation of 85mm thick plate, high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control C and N content, C content controlled at 5100ppm; N content controlled at 5990ppm; C+N content controlled at 11100ppm, to ensure material purity, S content 9ppm.

[0033] 2) Temperature-controlled rolling: Strictly control the rolling passes, rolling temperature and deformation of each pass. The original billet size is 195mm*85mm*302mm. The billet is heated to 1205℃ with the furnace and the insulation time is 4.5h. The rolling passes and temperatures are strictly matched as shown in the table below.

[0034]

[0035]

[0036] 3) Low temperature stress relief treatment: hot rolled plate at 430℃, keep warm for 90min.

[0037] 4) Stamping: local temperature adjustment for highly uniform automatic stamping, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process by a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the corner temperature of the stamping outer mold is stably controlled at 350°C, the side wall is stably controlled at 290°C, and the bottom is stably controlled at 201°C; the stamping stroke of the upper mold is 40mm, and the stamping speed is regulated in stages: the first 30mm: Vstamping = 0.5mm / s; the last 10mm: Vstamping = 0.2mm / s; after stamping, the pressure is maintained at 50KN for 5s.

[0038] The specific properties of the 1200MPa high-strength non-magnetic cup-shaped parts obtained in this embodiment are shown in Table 1. The grain size difference of the corners, side walls and bottom of the parts is 1 level.

[0039] Example 3

[0040] A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, which are specifically performed in the following steps:

[0041] 1) Smelting process: electric furnace smelting + continuous casting, preparation of 95mm thick plate, high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control C and N content, C content controlled at 5400ppm; N content controlled at 5508ppm; C+N content controlled at 10908ppm, to ensure material purity, S content 8ppm.

[0042] 2) Temperature-controlled rolling: Strictly control the rolling passes, the rolling temperature and the deformation of each pass. The original billet size is 205mm*95mm*400mm. The billet is heated to 1215℃ with the furnace and the insulation time is 4.5h. The rolling passes and temperatures are strictly matched as shown in the table below.

[0043] Rolling pass Doci-ichi Second pass Path 3 Path 4 Path 5 Path 6 Path 7 Rolling temperature / ℃ 1140 1080 1060 1020 990 930 900 Rolling size / mm 70 48 30 18 10 7.5 7.0

[0044] 3) Low temperature stress relief treatment: hot rolled plate at 420℃, keep warm for 100min.

[0045] 4) Stamping: local temperature adjustment for highly uniform automatic stamping, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process by a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the corner temperature of the stamping outer mold is stably controlled at 320°C, the side wall is stably controlled at 260°C, and the bottom is stably controlled at 195°C; the stamping stroke of the upper mold is 39mm, and the stamping speed is regulated in stages: the first 30mm: Vstamping = 0.4mm / s; the last 10mm: Vstamping = 0.25mm / s; after stamping, the pressure is maintained at 51KN for 6s.

[0046] The specific properties of the 1200MPa high-strength non-magnetic cup-shaped parts obtained in this embodiment are shown in Table 1. The grain size difference of the corners, side walls and bottom of the parts is 1 level.

[0047] Example 4

[0048] A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, which are specifically performed in the following steps:

[0049] 1) Smelting process: electric furnace smelting + continuous casting, preparation of 92mm thick plate, high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control C and N content, C content controlled at 5500ppm; N content controlled at 5900ppm; C+N content controlled at 11400ppm, to ensure material purity, S content 10ppm.

[0050] 2) Temperature-controlled rolling: Strictly control the rolling passes, rolling temperature and deformation of each pass. The original billet size is 205mm*92mm*380mm. The billet is heated to 1213℃ with the furnace and the insulation time is 5h. The rolling passes and temperatures are strictly matched as shown in the table below.

[0051] Rolling pass Dociichi Second pass Third Path 4 Path 5 Path 6 Path 7 Rolling temperature / ℃ 1140 1090 1070 1008 984 945 893 Rolling size / mm 60 44 20 16 8 7.6 7.0

[0052] 3) Low temperature stress relief treatment: hot rolled plate at 422℃, heat preservation for 97min.

[0053] 4) Stamping: local temperature adjustment for highly uniform automatic stamping and forming, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process through a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the temperature of the corners of the stamping outer mold is stably controlled at 333°C, the side walls are stably controlled at 284°C, and the bottom is stably controlled at 195°C; the stamping stroke of the upper mold is 41mm, and the stamping speed is regulated in stages: the first 30mm: Vstamping = 0.5mm / s; the last 10mm: Vstamping = 0.23mm / s; after stamping, the pressure is maintained at 50KN for 4s.

[0054] The specific properties of the 1200MPa high-strength non-magnetic cup-shaped parts obtained in this embodiment are shown in Table 1. The grain size difference of the corners, side walls and bottom of the parts is 1 level.

[0055] Example 5

[0056] A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, which are specifically performed in the following steps:

[0057] 1) Smelting process: electric furnace smelting + continuous casting, preparation of 88mm thick plate, high purity, precise target element control smelting, to ensure sufficient solid solution strengthening element content, strictly control C and N content, C content controlled at 5300ppm; N content controlled at 6000ppm; C+N content controlled at 11300ppm, to ensure material purity, S content 8ppm.

[0058] 2) Temperature-controlled rolling: Strictly control the rolling passes, rolling temperature and deformation of each pass. The original billet size is 198mm*95mm*330mm. The billet is heated to 1208℃ with the furnace and the insulation time is 5h. The rolling passes and temperatures are strictly matched as shown in the table below.

[0059] Rolling pass Dociichi Second pass Path 3 Path 4 Path 5 Path 6 Path 7 Rolling temperature / ℃ 1130 1100 1045 1000 964 923 898 Rolling size / mm 68 50 28 12 8.5 7.2 7.1

[0060] 3) Low temperature stress relief treatment: hot rolled plate at 428℃, heat preservation for 93min.

[0061] 4) Stamping: local temperature adjustment for highly uniform automatic stamping and forming, temperature compensation at the corners of the stamping outer mold, real-time monitoring of the mold temperature during the stamping process through a high-precision laser temperature sensor, and adjustment and control of the mold temperature to ensure that the temperature of the corners of the stamping outer mold is stably controlled at 326°C, the side walls are stably controlled at 266°C, and the bottom is stably controlled at 220°C; the stamping stroke of the upper mold is 40mm, and the stamping speed is regulated in stages: the first 30mm: Vstamping = 0.6mm / s; the last 10mm: Vstamping = 0.17mm / s; after stamping, the pressure is maintained at 51KN for 6s.

[0062] The specific properties of the 1200MPa high-strength non-magnetic cup-shaped parts obtained in this embodiment are shown in Table 1. The grain size difference of the corners, side walls and bottom of the parts is 1 level.

[0063] Table 1 Performance test results of 1200MPa high-strength non-magnetic cup-shaped parts in various embodiments

[0064]

[0065] For ordinary technicians in this field, various equivalent modifications or substitutions can be made to the embodiments of the present invention without departing from the spirit and scope of the present invention, and these modifications or substitutions should all be within the scope of the present invention. Changes or substitutions that can be easily conceived should all be covered within the protection scope of the present invention.

Claims

1. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method, characterized in that: The preparation method includes smelting, temperature-controlled rolling, low-temperature stress relief treatment, and stamping forming processes, and is specifically performed in the following steps: 1) Smelting process: strictly control the C and N contents of molten steel, C content is controlled at 5000ppm~5500ppm; N content is controlled at 5500ppm~6000ppm; C+N content is controlled at ≥10800ppm, S content is ≤10ppm; 2) Temperature-controlled rolling: the original billet size is (200±5mm)*(90±5mm)*(300~400mm), the billet is heated to 1205~1215℃ with the furnace, and the holding time is 4~5h; 3) Low temperature stress relief treatment: hot rolled plate at 420-430℃, heat preservation for 90-100min; 4) Stamping: Adjust and control the mold temperature to ensure that the temperature of the corner of the stamping outer mold is stably controlled at 320-350℃, the side wall is stably controlled at 260-290℃, and the bottom is stably controlled at ≤220℃.

2. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to claim 1, characterized in that: In the step 2), the temperature-controlled rolling process is performed, and the rolling passes and the temperature are matched as shown in the table below.

3. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to claim 1, characterized in that: In the step 4), in the stamping process, the stamping stroke of the upper die is 39-41 mm, and the stamping speed is adjusted in stages: the first 30 mm: V stamping = 0.4-0.6 mm / s; the last 10 mm: V stamping = 0.15-0.25 mm / s; after the stamping, the pressure is maintained at 49-51 KN for 4-6 seconds.

4. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to any one of claims 1 to 3, characterized in that: The tensile strength of the parts prepared by the method is ≥1250MPa.

5. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to any one of claims 1 to 3, characterized in that: The magnetic permeability of the parts prepared by the method is ≤1.02h / m.

6. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to any one of claims 1 to 3, characterized in that: The grain size of the part material prepared by the method is stably controlled to be ≥ level 8.

7. A low-cost 1200MPa-level high-strength non-magnetic cup-shaped part preparation method according to any one of claims 1 to 3, characterized in that: The grain size difference of the corner, side wall and bottom of the part prepared by the method is ≤1.5 levels.

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