A method of plasma arc cutting of high manganese austenitic steel

Abstract

The application discloses a plasma arc cutting method of high-manganese austenitic steel, which comprises the following steps: S1, preheating a steel plate to 150-250 DEG C; S2, cutting by using a plasma arc with specific parameters, wherein a cutting current I and a plate thickness d satisfy I=kd, and a cutting speed v and the plate thickness d satisfy v=(12000 / d) * alpha; S3, during the cutting process, synchronously spraying mixed cooling gas of compressed air and carbon dioxide to the cutting area for rapid cooling; and S4, immediately after the cutting, embedding the workpiece into a heat preservation medium for slow cooling. The application has the advantages that the temperature difference stress is reduced by preheating, the grain growth is inhibited by synchronous cooling, and the hardened structure is eliminated by slow cooling after welding, and the three synergistically act, effectively inhibiting the generation of micro-cracks on the cutting surface, significantly improving the quality of the cutting surface, and being suitable for cutting processing of various high-manganese austenitic steel plates.

Description

Technical Field

[0001] This invention belongs to the field of metal material cutting and processing technology, and particularly relates to a plasma arc cutting method for high-manganese austenitic steel. Background Technology

[0002] High-manganese steel, due to its high Mn content (usually not less than 12%) and a single austenitic microstructure, possesses extremely high work hardening ability, good low-temperature toughness, and wear resistance. It is widely used in cryogenic storage tanks, railway frogs, excavator bucket teeth, bulletproof steel plates, and other applications subjected to strong impacts and severe wear. However, high-manganese austenitic steel has low thermal conductivity, a large coefficient of linear expansion, and its austenite grains tend to coarsen at high temperatures.

[0003] Currently, there are three main problems with cutting high-manganese austenitic steel: First, when using traditional oxygen cutting, the high content of alloying elements such as Mn and Cr in high-manganese steel results in oxides with high melting points and high viscosity, leading to uneven cutting surfaces, severe slag buildup, low cutting efficiency, and a tendency to crack at the cutting edges. Second, while laser cutting offers extremely high precision and a very small heat-affected zone, it requires significant equipment investment and has limited capacity for cutting thick plates. Third, plasma arc cutting, which offers a relatively balanced approach in terms of cost, efficiency, and precision, can lead to coarse austenitic grains in the heat-affected zone due to overheating if the heat energy and cooling conditions are not strictly controlled. Furthermore, excessive thermal stress during subsequent cooling can cause intergranular cracks, severely impacting subsequent processing and the service life of the components.

[0004] Chinese patent application CN202310175408.1 discloses a high-manganese steel cutting device and method, which includes a traveling trolley and an oxyacetylene torch and a plasma cutting torch connected to the trolley. The position and angle of the oxyacetylene torch and the plasma cutting torch can be adjusted via an adjusting rod to form a bevel at a specific angle when cutting high-manganese steel. However, this patent focuses more on cutting efficiency and is suitable for scenarios requiring welding preparation. It achieves preheating and bevel formation during the cutting process through a dual-torch combination, but it does not address the metallurgical quality of high-manganese steel cutting and lacks technical measures to solve the problems of cracking and microstructure deterioration through full-process thermal cycle control.

[0005] The existing plasma arc cutting process lacks systematic control over the thermal cycle throughout the entire cutting process, from before to after cutting. It fails to effectively balance the contradiction between "preheating to reduce stress" and "cooling to refine the microstructure," making it difficult to meet the stringent requirements of high-end equipment for a cut surface free of microcracks and a small heat-affected zone. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of easy cracking, heat-affected zone microstructure deterioration, and poor cut surface quality when cutting high manganese steel. It provides a plasma arc cutting method for high manganese austenitic steel, which can effectively suppress micro-cracks on the cut surface and microstructure deterioration in the heat-affected zone, reduce production costs, improve production efficiency, and ensure cutting quality.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A plasma arc cutting method for high-manganese austenitic steel, comprising the following steps: S1. Pre-cutting treatment: Clean the surface of the high manganese austenitic steel plate to be cut to remove oil and oxide scale, and then preheat the plate as a whole. The preheating temperature is 150℃~250℃. The preheating time coefficient is calculated as 2min / mm according to the plate thickness. S2, Plasma arc cutting parameter settings: Use micro-beam plasma arc or high-power plasma arc cutting equipment, set the cutting current I and cutting speed v, and introduce a mixture of argon and nitrogen with a volume ratio of (70~80):(20~30) as ion gas, while controlling the line energy E according to the plate thickness. Among them, the cutting current I and the steel plate thickness d satisfy the relationship: I = kd, and the coefficient k ranges from 5 to 30. The cutting speed v and the steel plate thickness d satisfy the following relationship: v = (12000 / d)×α, where α is the heat input adjustment coefficient, and the value of α ranges from 0.8 to 3.0. S3, auxiliary cooling during cutting: An annular gas cooling nozzle is installed behind the plasma arc cutting torch, and a cooling gas mixture is sprayed onto the cut surface and heat-affected zone through the annular gas cooling nozzle while cutting is being performed. The cooling gas mixture is a mixture of compressed air and carbon dioxide gas with a volume ratio of (5~10):1, and the injection flow rate is 15~25L / min. S4. Post-cutting slow cooling treatment: After cutting, immediately transfer the cut workpiece to an asbestos powder or lime powder covering layer for slow cooling. The slow cooling time shall not be less than 2 hours. Take out the workpiece after it has cooled to room temperature.

[0008] Further, in step S1, the chemical composition of the high-manganese austenitic steel by weight percentage includes: C: 0.4~1.2%, Mn: 12~25.5%, Cr: 0~4%, Si: 0.3~1.0%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, in step S1, when the Mn content of the high-manganese austenitic steel exceeds 20%, the preheating temperature is preferably increased to 200~250℃.

[0010] Furthermore, in step S2, the line energy E is controlled in stages according to the plate thickness, specifically including: When the steel plate thickness d ≤ 20mm, E = 0.8~1.8 kJ / mm; When the steel plate thickness is 20mm < d ≤ 40mm, E = 1.5~3.8 kJ / mm; When the steel plate thickness d > 40 mm, E = 3.5~8.5 kJ / mm; The formula for calculating the cutting line energy E is E=(U×I) / v, where U is the arc voltage in V; I is the cutting current in A; and v is the cutting speed in mm / s.

[0011] Furthermore, in step S3, the horizontal distance between the annular gas cooling nozzle and the cutting gun nozzle is 30~50mm, and the spray direction forms an angle of 30~45° with the plane of the steel plate, facing the cutting seam.

[0012] Furthermore, in step S3, the cooling gas mixture undergoes pre-cooling treatment before injection, with a pre-cooling temperature of -5℃ to 5℃.

[0013] The technical solution of this invention adopts an integrated process of "preheating-cutting-controlled cooling". Preheating reduces temperature difference stress, synchronous cooling inhibits grain growth, and slow cooling after welding eliminates hardened structures. The three work together to effectively suppress the generation of microcracks on the cutting surface and significantly improve the quality of the cutting surface. It is suitable for cutting and processing various high-manganese austenitic steel plates. Attached Figure Description

[0014] Figure 1 This is a comparative analysis table of the cutting effects of Examples 1-5 and Comparative Examples 1-5 of the present invention. Detailed Implementation Example 1

[0015] To make the present invention clearer, the following description further illustrates a plasma arc cutting method for high-manganese austenitic steel. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0016] In this embodiment, a 10mm thick high-manganese austenitic steel plate is selected, and its chemical composition by weight percentage includes: C: 1.1%, Mn: 13%, Si: 0.5%, Cr: 2.0%, with the balance being Fe.

[0017] The above-mentioned high-manganese austenitic steel plate is cut according to the plasma arc cutting method of the present invention, specifically as follows: (1) Preheating: Preheat the steel plate to 180°C, and keep it at 2 min / mm for 20 min.

[0018] (2) Cutting: Fine plasma arc cutting equipment is used, the cutting current is set to I=170A, the cutting speed is v=1200mm / min, the ion gas is a mixture of argon and nitrogen with a volume ratio of 75:25, and the voltage is U=140V. The linear energy E is calculated as follows: Cutting speed conversion: v = 1200 mm / min ÷ 60 = 20 mm / s; Power P = UI = 140V × 170A = 23800W = 23.8kW; Linear energy E = P / v = 23.8 kW / 20 mm / s = 1.19 kJ / mm; This value falls within the linear energy range of 0.8~1.8 kJ / mm when the thickness of the plate is d≤20mm.

[0019] (3) Synchronous cooling: Turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 8:1 at a flow rate of 20L / min. The nozzle is 40mm away from the cutting gun.

[0020] (4) Slow cooling: Immediately after cutting, bury the workpiece in lime powder for slow cooling for 2.5 hours.

[0021] The cut steel plate was inspected and found to have a surface roughness Ra of 10.5 μm, a heat-affected zone depth of less than 0.3 mm, and no microcracks were found in the metallographic examination.

[0022] The above parameters were verified as follows: The current coefficient k = I / d = 170 / 10 = 17, which is in the range of 5 to 30. The speed coefficient α = vd / 12000 = 12000 / 12000 = 1.0, which is in the range of 0.8 to 3.0. Example 2

[0023] In this embodiment, a high-manganese austenitic steel plate with a thickness of 20mm is selected. Its chemical composition by weight percentage includes: C: 0.9%, Mn: 18.5%, Si: 0.5%, Cr: 2.0%, and the balance is Fe.

[0024] The above-mentioned high-manganese austenitic steel plate is cut according to the plasma arc cutting method of the present invention, specifically as follows: (1) Preheating: Preheat the steel plate to 200℃, keep it at 2min / mm for 40min.

[0025] (2) Cutting: Plasma arc cutting equipment is used, the cutting current is set to I=200A, the cutting speed is v=1160mm / min, the ion gas is a mixture of argon and nitrogen with a volume ratio of 75:25, and the voltage is U=145V. The linear energy E is calculated as follows: Cutting speed conversion: v = 1160 mm / min ÷ 60 = 19.33 mm / s; Power P = UI = 145V × 200A = 29000W = 29.0kW; Linear energy E = P / v = 29.0 kW / 19.33 mm / s = 1.50 kJ / mm; This value falls within the linear energy range of 0.8~1.8 kJ / mm when the thickness of the plate is d≤20mm.

[0026] (3) Synchronous cooling: Turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 8:1 at a flow rate of 20L / min. The nozzle is 40mm away from the cutting gun.

[0027] (4) Slow cooling: Immediately after cutting, bury the workpiece in lime powder for slow cooling for 3 hours.

[0028] The cut steel plate was inspected and found to have a surface roughness Ra of 11.2 μm, a heat-affected zone depth of less than 0.5 mm, and no microcracks were found in the metallographic examination.

[0029] The above parameters were verified as follows: The current coefficient k = I / d = 200 / 20 = 10, which is in the range of 5 to 30. The speed coefficient α = vd / 12000 = 23200 / 12000 ≈ 1.933, which is in the range of 0.8-3.0. Example 3

[0030] In this embodiment, a high-manganese austenitic steel plate with a thickness of 30mm is selected. Its chemical composition by weight percentage is: C: 0.8%, Mn: 19.5%, Si: 0.5%, Cr: 2.2%, with the balance being Fe.

[0031] The above-mentioned high-manganese austenitic steel plate is cut according to the plasma arc cutting method of the present invention, specifically as follows: (1) Preheating: Preheat the steel plate to 220℃, keep it at 2min / mm for 60min.

[0032] (2) Cutting: Plasma arc cutting equipment is used, the cutting current is set to I=280A, the cutting speed is v=800mm / min, the ion gas is a mixture of argon and nitrogen with a volume ratio of 75:25, and the voltage is U=150V; The linear energy E is calculated as follows: Cutting speed conversion: v = 800 mm / min ÷ 60 = 13.33 mm / s; Power P = UI = 150V × 280A = 42000W = 42.0kW; Linear energy E = P / v = 42.0 kW / 13.33 mm / s = 3.15 kJ / mm; This value falls within the linear energy range of 1.5~3.8 kJ / mm for medium-thick plates with a thickness of 20 mm < d ≤ 40 mm.

[0033] (3) Synchronous cooling: Turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 8:1 at a flow rate of 22L / min. The nozzle is 35mm away from the cutting gun.

[0034] (4) Slow cooling: Immediately after cutting, bury the workpiece in lime powder for slow cooling for 3.5 hours.

[0035] The cut steel plate was inspected and found to have a surface roughness Ra of 11.8 μm, a heat-affected zone depth of less than 0.8 mm, and no microcracks were found in the metallographic examination.

[0036] The above parameters were verified as follows: The current coefficient k = I / d = 280 / 30 ≈ 9.33, which is in the range of 5 to 30. The speed coefficient α = vd / 12000 = 24000 / 12000 = 2.0, which is in the range of 0.8 to 3.0. Example 4

[0037] In this embodiment, a high-manganese austenitic steel plate with a thickness of 40mm is selected. Its chemical composition by weight percentage is: C: 0.7%, Mn: 20.5%, Si: 0.5%, Cr: 2.5%, with the balance being Fe.

[0038] The above-mentioned high-manganese austenitic steel plate is cut according to the plasma arc cutting method of the present invention, specifically as follows: (1) Preheating: Preheat the steel plate to 240℃, keep it at 2min / mm for 80min.

[0039] (2) Cutting: Plasma arc cutting equipment is used, the cutting current is set to I=240A, the cutting speed is v=800mm / min, the ion gas is a mixture of argon and nitrogen with a volume ratio of 72:28, and the voltage is U=155V; The linear energy E is calculated as follows: Cutting speed conversion: v = 800 mm / min ÷ 60 = 13.33 mm / s; Power P = UI = 155V × 240A = 37200W = 37.2kW; Linear energy E = P / v = 37.2 kW / 13.33 mm / s = 2.79 kJ / mm; This value falls within the linear energy range of 1.5~3.8 kJ / mm for medium-thick plates with a thickness of 20mm < d ≤ 40mm.

[0040] (3) Synchronous cooling: Turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 7:1 at a flow rate of 24L / min. The nozzle is 40mm away from the cutting gun.

[0041] (4) Slow cooling: Immediately after cutting, bury the workpiece in asbestos powder for slow cooling for 4 hours.

[0042] The cut steel plate was inspected and found to have a surface roughness Ra of 12.5 μm, a heat-affected zone depth of less than 1.0 mm, and no microcracks were found in the metallographic examination.

[0043] The above parameters were verified as follows: The current coefficient k = I / d = 240 / 40 = 6, which is in the range of 5 to 30. The speed coefficient α = vd / 12000 = 32000 / 12000 ≈ 2.667, which is in the range of 0.8 to 3.0. Example 5

[0044] In this embodiment, a 50mm thick high-manganese austenitic steel plate is selected, and its chemical composition by weight percentage is: C: 0.5%, Mn: 25.5%, Si: 0.4%, Cr: 3.5%, with the balance being Fe.

[0045] The above-mentioned high-manganese austenitic steel plate is cut according to the plasma arc cutting method of the present invention, specifically as follows: (1) Preheating: Preheat the steel plate to 250°C and keep it warm for 100 minutes. Here, it is calculated as 2 minutes / mm. The preheating temperature is increased because the Mn content is >20%.

[0046] (2) Cutting: A high-power plasma arc cutting device is used, with the cutting current I=500A, the cutting speed v=650mm / min, the ion gas being a mixture of argon and nitrogen with a volume ratio of 70:30), and the voltage U=160V; The linear energy E is calculated as follows: Cutting speed conversion: v = 650 mm / min ÷ 60 = 10.833 mm / s; Power P = UI = 160V × 500A = 80000W = 80.0kW; Linear energy E = P / v = 80.0 kW / 10.833 mm / s = 7.38 kJ / mm; This value falls within the linear energy range of 3.5~8.5 kJ / mm when the thickness of the plate is greater than 40 mm.

[0047] (3) Synchronous cooling: spray a mixture of cooling gas pre-cooled to 0°C, compressed air: CO2 = 6:1, flow rate 25L / min, nozzle distance 40mm from cutting gun.

[0048] (4) Slow cooling: Immediately after cutting, bury in asbestos powder for slow cooling for 4 hours.

[0049] The cut steel plate was inspected: the cut surface was flat, the dye penetrant test showed no surface cracks, and the depth of the heat-affected zone was less than 1.2 mm.

[0050] The above parameters were verified as follows: The current coefficient k = I / d = 500 / 50 = 10, which is in the range of 5 to 30. The speed coefficient α = vd / 12000 = 32500 / 12000 ≈ 2.71, which is in the range of 0.8 to 3.0.

[0051] To further verify the technical effects of the present invention, five comparative examples are provided, as follows: (a) Comparative Example 1 uses a 20mm thick high-manganese austenitic steel plate with the same material and specifications as Example 2, and the chemical composition is the same as Example 2.

[0052] A comparative experiment was conducted using conventional plasma arc cutting technology: Pre-cutting treatment: No preheating treatment was performed; the steel plate was at room temperature (25°C).

[0053] Cutting parameters: Plasma arc cutting equipment is used, with cutting current set to I=180A, cutting speed v=500mm / min, ion gas is ordinary compressed air, and voltage U=145V.

[0054] Line energy calculation: Cutting speed conversion: v = 500 mm / min ÷ 60 = 8.33 mm / s; Power P = UI = 145V × 180A = 26100W = 26.1kW; Linear energy E = P / v = 26.1 kW / 8.33 mm / s = 3.13 kJ / mm; This value exceeds the upper limit of the thin plate linear energy range of 0.8~1.8 kJ / mm for a 20mm plate.

[0055] Cooling method: Natural air cooling after cutting, without the use of synchronous cooling and slow cooling measures.

[0056] Post-cutting inspection results: (1) A slight cracking sound can be heard during the cutting process; (2) After cutting, obvious grinding burn marks are visible on the surface, with some areas turning bluish; (3) Dyeing flaw detection showed that there were a large number of network microcracks at the cutting edge; (4) Metallographic observation showed that there were obvious intergranular cracks in the heat-affected zone, with a depth of about 1.2 mm; (5) The surface roughness Ra of the cut surface reaches 25.6 μm, and the slag is serious.

[0057] Conclusion: Due to the lack of preheating, the excessive heat input during cutting, coupled with the absence of simultaneous cooling and slow cooling measures, resulted in thermal stress concentration, causing severe grinding cracks and substandard cutting quality.

[0058] (ii) Comparative Example 2 uses a 30mm thick high-manganese austenitic steel plate with the same material and specifications as Example 3, and the chemical composition is the same as Example 3.

[0059] A comparative experiment was conducted using the traditional oxyacetylene flame cutting process: Pre-cutting treatment: No preheating treatment was performed.

[0060] Cutting parameters: Oxyacetylene flame cutting gun is used, oxygen pressure is 0.7MPa, acetylene pressure is 0.05MPa, and cutting speed is v=120mm / min.

[0061] Since the heat input of flame cutting is difficult to calculate precisely, it is estimated from experience that for 30mm thick high manganese steel, the heat input of flame cutting is usually in the range of 10~15 kJ / mm, which is much higher than that of plasma cutting.

[0062] Cooling method: Natural air cooling after cutting.

[0063] Post-cutting inspection results: (1) Severe slag buildup during cutting, resulting in an uneven cutting surface; (2) There are obvious signs of overheating and melting at the cut edges; (3) The surface roughness of the cut surface is poor and cannot meet the requirements of subsequent processing; (4) Due to the high melting point and high viscosity of the oxides formed by Mn and Cr elements in high manganese steel, the cutting process is frequently interrupted to clean the slag, resulting in low cutting efficiency. (5) Metallographic observation shows that the heat-affected zone has coarse grains with a depth of more than 2.5 mm.

[0064] Conclusion: When flame cutting high-manganese austenitic steel, the high-melting-point oxides formed by alloying elements result in poor cut surface quality, severe slag buildup, and low efficiency, making it unsuitable for cutting scenarios requiring high quality.

[0065] (iii) Comparative Example 3 uses a 20mm thick high-manganese austenitic steel plate with the same material and specifications as Example 2.

[0066] Preheating: Preheat the entire steel plate to 200°C and hold for 4 minutes, using the same preheating conditions as in Example 2.

[0067] Cutting parameters: The same cutting parameters as in Example 2 were used: I=200A, v=1160mm / min, U=145V, E=1.5kJ / mm.

[0068] Cooling method: Natural air cooling after cutting, without the use of synchronous cooling and slow cooling measures.

[0069] Post-cutting inspection results: (1) The macroscopic morphology of the cut surface is good, with no visible cracks; (2) However, metallographic observation showed that there were a few microcracks in the heat-affected zone; (3) The depth of the heat-affected zone reaches 0.9 mm, which is greater than 0.5 mm in Example 2; (4) The hardness of the work-hardened layer is about 25% higher than that of the substrate.

[0070] Conclusion: Preheating alone, without simultaneous cooling and slow cooling, reduced macroscopic cracks, but microscopic cracks still existed, and the heat-affected zone control was not ideal. This indicates that simultaneous cooling and slow cooling steps are indispensable.

[0071] (iv) Comparative Example 4 uses a 20mm thick high-manganese austenitic steel plate with the same material and specifications as Example 2.

[0072] Preheating: Preheat the entire steel plate to 200℃ and hold for 40 minutes.

[0073] Cutting parameters: The same cutting parameters as in Example 2 were used: I=200A, v=1160mm / min, U=145V, E=1.5kJ / mm.

[0074] Synchronous cooling: Same as in Example 2, turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 8:1 at a flow rate of 20L / min.

[0075] Slow cooling: After cutting, the material was allowed to air cool naturally without being buried for slow cooling.

[0076] Post-cutting inspection results: (1) The cut surface has a good macroscopic morphology and no visible cracks; (2) Metallographic observation showed no microcracks in the heat-affected zone; (3) However, residual stress exists in the heat-affected zone. X-ray stress testing shows that the residual tensile stress on the surface is about 180 MPa. (4) After 24 hours, delayed cracks appeared on the edges of some samples.

[0077] Conclusion: Preheating and simultaneous cooling without slow cooling resulted in no initial cracks, but residual stress remained, posing a risk of delayed cracking. This indicates that slow cooling is crucial for eliminating residual stress.

[0078] (v) Comparative Example 5 uses a 20mm thick high-manganese austenitic steel plate with the same material and specifications as Example 2.

[0079] Preheating: Preheat the entire steel plate to 80°C, which is 150°C lower than the lower limit of this invention, and keep it at that temperature for 40 minutes.

[0080] Cutting parameters: The same cutting parameters as in Example 2 were used: I=200A, v=1160mm / min, U=145V, E=1.5kJ / mm.

[0081] Synchronous cooling: Same as in Example 2, turn on the annular cooling nozzle and spray a mixture of compressed air and carbon dioxide with a volume ratio of 8:1 at a flow rate of 20L / min.

[0082] Slow cooling: Immediately after cutting, bury in lime powder for slow cooling for 3 hours.

[0083] Post-cutting inspection results: (1) A slight cracking sound was heard during the cutting process; (2) Fine cracks are visible on the surface after cutting; (3) Dyeing flaw detection showed that there were discontinuous microcracks at the cutting edge; (4) Metallographic observation showed that there were intergranular cracks in the heat-affected zone with a depth of about 0.6 mm.

[0084] Conclusion: The preheating temperature was insufficient, only 80℃, which failed to effectively reduce the temperature gradient. Even with simultaneous cooling and slow cooling, cracks could not be completely suppressed. This indicates that the preheating temperature must reach at least 150℃ as specified in this invention.

[0085] See Figure 1 As shown, in comparison with Examples 1 and 2: Example 2, which uses the complete process of the present invention, has no cracks on the cut surface, a small heat-affected zone, and excellent surface quality; while Example 1, although using plasma cutting, lacks preheating and controlled cooling, resulting in severe cracks; Example 2 uses flame cutting, which has poor cut surface quality and low efficiency.

[0086] Comparing Example 2 with Comparative Examples 3 and 4: Comparative Example 3 only involved preheating without simultaneous cooling and slow cooling, which reduced macroscopic cracks but still resulted in microscopic cracks; Comparative Example 4 included preheating and simultaneous cooling but lacked slow cooling, resulting in no immediate cracks but residual stress and a risk of delayed cracking. This demonstrates that the three steps of preheating + simultaneous cooling + slow cooling in this invention are indispensable and have a synergistic effect.

[0087] Comparing Example 2 with Comparative Example 5: The preheating temperature of Comparative Example 5 was insufficient, only 80°C. Even with subsequent synchronous cooling and slow cooling, it was still unable to completely suppress cracks, indicating that the preheating temperature must reach 150°C or higher as specified in this invention.

[0088] Examples 1-5 cover the commonly used thickness range of 10mm to 50mm, and all of them achieved crack-free cutting with the heat-affected zone controlled within 5% of the plate thickness, proving that the process of the present invention has good universality and stability.

[0089] This invention achieves crack-free, high-quality cutting of high-manganese austenitic steel through the synergistic effect of three steps: preheating, synchronous cooling, and slow cooling, as well as precise linear energy control. It represents a significant technological advancement and unexpected technical benefits.

[0090] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A plasma arc cutting method for high-manganese austenitic steel, characterized in that: S1. Pre-cutting treatment: Clean the surface of the high manganese austenitic steel plate to be cut to remove oil and oxide scale, and then preheat the plate as a whole. The preheating temperature is 150℃~250℃. The preheating time coefficient is calculated as 2min / mm according to the plate thickness. S2, Plasma arc cutting parameter settings: Use micro-beam plasma arc or high-power plasma arc cutting equipment, set the cutting current I and cutting speed v, and introduce a mixture of argon and nitrogen with a volume ratio of (70~80):(20~30) as ion gas, while controlling the line energy E according to the plate thickness. Among them, the cutting current I and the steel plate thickness d satisfy the relationship: I = kd, and the coefficient k ranges from 5 to 30. The cutting speed v and the steel plate thickness d satisfy the following relationship: v = (12000 / d)×α, where α is the heat input adjustment coefficient, and the value of α ranges from 0.8 to 3.

0. S3, auxiliary cooling during cutting: An annular gas cooling nozzle is installed behind the plasma arc cutting gun, and a cooling gas mixture is sprayed onto the cut surface and heat-affected zone through the annular gas cooling nozzle during cutting. The cooling gas mixture is a mixture of compressed air and carbon dioxide gas with a volume ratio of (5~10):1, and the injection flow rate is 15~25L / min. S4. Post-cutting slow cooling treatment: After cutting, immediately transfer the cut workpiece to an asbestos powder or lime powder covering layer for slow cooling. The slow cooling time shall not be less than 2 hours. Take out the workpiece after it has cooled to room temperature.

2. The plasma arc cutting method for high-manganese austenitic steel according to claim 1, characterized in that: In step S1, the chemical composition of the high-manganese austenitic steel by weight percentage includes: C: 0.4~1.2%, Mn: 12~25.5%, Cr: 0~4%, Si: 0.3~1.0%, with the balance being Fe and unavoidable impurities.

3. The plasma arc cutting method for high-manganese austenitic steel according to claim 2, characterized in that: Furthermore, in step S1, when the Mn content of the high-manganese austenitic steel exceeds 20%, the preheating temperature is preferably increased to 200~250℃.

4. The plasma arc cutting method for high-manganese austenitic steel according to any one of claims 1 to 3, characterized in that: In step S2, the line energy E is controlled in stages according to the plate thickness, specifically including: When the steel plate thickness d ≤ 20mm, E = 0.8~1.8 kJ / mm; When the steel plate thickness is 20mm < d ≤ 40mm, E = 1.5~3.8 kJ / mm; When the steel plate thickness d > 40 mm, E = 3.5~8.5 kJ / mm; The formula for calculating the cutting line energy E is E=(U×I) / v, where U is the arc voltage in V; I is the cutting current in A; and v is the cutting speed in mm / s.

5. The plasma arc cutting method for high-manganese austenitic steel according to any one of claims 1 to 3, characterized in that: In step S3, the horizontal distance between the annular gas cooling nozzle and the cutting gun nozzle is 30-50mm, and the spray direction is at an angle of 30-45° to the plane of the steel plate, facing the cutting seam.

6. The plasma arc cutting method for high-manganese austenitic steel according to any one of claims 1 to 3, characterized in that: In step S3, the cooling gas mixture is pre-cooled before injection, with a pre-cooling temperature of -5℃ to 5℃.

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