Preparation of ultra-high strength multi-phase steel repair layer and method for regulating microstructure and performance thereof
By using laser deposition technology and online control of the material temperature field, an ultra-high strength multiphase steel repair layer was prepared, which solved the problems of shape and hydrogen embrittlement in the repair of surface damage of heavy-haul railway rails, and achieved a repair effect with high strength and toughness and low hydrogen embrittlement. This simplified the production process and reduced costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EAST CHINA JIAOTONG UNIVERSITY
- Filing Date
- 2023-12-27
- Publication Date
- 2026-05-12
AI Technical Summary
Repairing surface damage on heavy-haul railway rails presents challenges such as limited shape repair and high sensitivity to hydrogen embrittlement. Existing repair techniques are costly, wasteful of resources, and unable to effectively reduce the tendency for hydrogen embrittlement.
By employing laser deposition technology combined with online temperature field control and special composition design, an ultra-high strength multiphase steel repair layer was prepared. By controlling the microstructure through preheating, a multiphase structure dominated by bainite was obtained, avoiding subsequent heat treatment and reducing hydrogen embrittlement sensitivity.
The preparation of a high-strength and tough repair layer has been achieved. The microstructure is regulated to have both good mechanical properties and low hydrogen embrittlement sensitivity over a wide range, simplifying the production process and reducing costs. It is suitable for online repair of heavy-haul railway rails.
Smart Images
Figure CN117926246B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of online rail repair, and specifically relates to a method for preparing an ultra-high strength multiphase steel repair layer and controlling its microstructure and properties. Background Technology
[0002] Heavy-haul railway transportation is characterized by high axle loads, high train density, and large transport volumes, placing higher demands on the service performance of rail materials. Bainitic rails, with their superior strength, toughness, and resistance to contact fatigue, are gradually replacing pearlitic rails and becoming an important development direction for heavy-haul rail materials. In recent years, with the increasing speed and axle load of heavy-haul trains, despite the excellent mechanical properties of bainitic rails, damage is still inevitable, especially in vulnerable locations such as small-radius curves or rail joints. Due to continuous friction, compression, and impact from the wheels, surface damage such as spalling, crushing, wavy wear, and side wear on bainitic rails is increasingly aggravated, posing serious threats to railway transportation safety. Therefore, solving the problem of surface damage repair for bainitic rails is urgently needed.
[0003] Traditionally, rail repair primarily involved rail replacement. However, frequent rail replacements severely disrupt railway operations, leading to significant economic losses and resource waste. Therefore, online rail repair technology has gained increasing attention, mainly categorized into subtractive manufacturing repair (such as machining) and additive manufacturing repair (such as surface welding). Machining methods, like grinding and milling, remove material from the top of the rail to repair its shape, but their repair capabilities are limited, failing to address larger areas of damage such as spalling or chipping. Surface additive manufacturing repair methods, such as welding and laser cladding, are suitable for various types of damage, producing a strong bond between the repair layer and the substrate, resulting in a high-performance surface. However, the rapid heating and cooling of these processes can lead to the formation of martensite in the repair layer and heat-affected zone, often requiring complex subsequent heat treatments, which limits the application of these online rail repair technologies.
[0004] Furthermore, during actual service, rails inevitably come into contact with corrosive environments such as humid air, water, and acidic media. Hydrogen evolution reactions occur due to electrochemical corrosion, and the generated hydrogen diffuses into the rail. As the hydrogen content in the rail increases, it exhibits a greater tendency for hydrogen embrittlement, leading to brittle spalling, which has become one of the key factors affecting the service life of rails. Especially for ultra-high strength bainitic heavy-duty rails, which inherently have a higher hydrogen embrittlement sensitivity than traditional pearlitic rails, the deformation caused by the compression and impact of heavy-duty train wheels further exacerbates this tendency. Therefore, when performing surface repair on bainitic rails, the hydrogen embrittlement sensitivity of the repair layer must be taken into account to minimize its tendency to occur. Summary of the Invention
[0005] To address the problems existing in the surface repair of heavy-haul railway rails, the present invention aims to provide a method for preparing an ultra-high strength multiphase steel repair layer and controlling its microstructure and properties. By utilizing online control of the material temperature field during laser deposition and combining it with the design of special material composition, the laser-deposited multiphase steel repair layer can obtain a bainite-dominant microstructure under air-cooling conditions without subsequent heat treatment. At the same time, the mechanical properties and hydrogen embrittlement resistance of the material can be controlled within a wide range according to the service conditions required by the material. The repair layer has both high strength and toughness and low hydrogen embrittlement sensitivity.
[0006] The technical solution of this invention is:
[0007] A method for preparing an ultra-high strength multiphase steel repair layer and controlling its microstructure and properties is carried out according to the following steps:
[0008] (1) Composition design of multiphase steel repair layer: 30CrMnSiA powder and metal elemental powder are weighed and mixed in proportion, wherein the elemental powder Ni is 0.50~0.80wt%, Mo is 0.30~0.60wt%, and the balance is 30CrMnSiA powder;
[0009] (2) Powder ball milling treatment;
[0010] (3) Preheating the substrate: Using 30CrMnSiA plate as the substrate, the martensitic transformation start temperature of the metal powder to be deposited was determined to be 272.1~348.5℃ and the bainitic transformation temperature range was 272.1~461.4℃ using thermodynamic calculation software; based on the above calculation results of the metal solid phase transformation temperature range, the substrate was preheated to the specified temperature of 270~320℃.
[0011] (4) Laser deposition: The temperature of the substrate and the surface of the deposited metal is monitored online using a non-contact infrared thermometer. Laser deposition begins when the surface of the substrate reaches the set temperature. After each layer of metal is deposited, the deposition is paused for 2-3 minutes. When the surface temperature of the deposited metal reaches the set temperature again, the next layer of metal is deposited until the thickness of the metal deposition layer reaches 5-6 mm. Laser deposition is then stopped and the laser-deposited metal material is placed in the air to cool naturally, finally obtaining an ultra-high strength multiphase steel repair layer.
[0012] The preparation method of the ultra-high strength multiphase steel repair layer and its microstructure and properties control method, in step (1), the mass percentage of each element in the ultra-high strength multiphase steel repair layer is: C 0.20~0.30%, Si 1.50~2.30%, Mn 1.50~1.90%, Cr 0.80~1.05%, Ni 0.50~0.80%, Mo 0.30~0.60%, with the balance being Fe.
[0013] In the preparation of the ultra-high strength multiphase steel repair layer and its microstructure and performance control method, in step (2), after the mixed powder is put into the ball mill jar, agate balls are added. The ball-to-material mass ratio is 1:1. The powder is ball-milled and mixed using a horizontal planetary ball mill at a speed of 240-300 r / min and a time of 90-150 min. Then the ball-milled powder is placed in a constant temperature drying oven for drying.
[0014] The preparation of the ultra-high strength multiphase steel repair layer and its microstructure performance regulation method, in step (4), the laser deposition process is as follows: the laser power is 900-1200W, the laser spot is a circular spot with a spot diameter of 2mm, the scanning speed is 300-360mm / min, the powder feeding rate is 8-9g / min, the carrier gas flow rate is 8-10L / min, the powder feeding method is coaxial powder feeding, it is a multi-pass multi-layer deposition method, the powder particle size is between 45μm and 105μm, the overlap rate is 50%, the scanning path is zigzag, and the thickness of a single layer of deposited metal is 0.3-0.5mm.
[0015] In the preparation and microstructure property control method of the ultra-high strength multiphase steel repair layer, in step (4), the tensile strength of the ultra-high strength multiphase steel repair layer is 1380MPa~1530MPa and the elongation is 10.1%~15.4%.
[0016] In the preparation and microstructure property control method of the ultra-high strength multiphase steel repair layer, in step (4), the microstructure of the ultra-high strength multiphase steel repair layer is a multiphase structure composed of lath bainite / martensite and retained austenite, with a bainite volume fraction of 47.3-69.2%, a martensite volume fraction of 22.6-40.6%, and a retained austenite volume fraction of 8.2-12.1%; the hydrogen embrittlement sensitivity index is 54.6-80.9%.
[0017] This invention fully considers the characteristics of material temperature field evolution during additive manufacturing processes such as laser deposition. Compared with existing technologies, its design concept, advantages, and beneficial effects are as follows:
[0018] 1. In this invention, the laser deposition process only requires protection by purging inert gases such as argon near the molten metal pool, which can ensure the performance of the laser-deposited multiphase steel repair layer. It does not require atmosphere protection for the entire forming system, which is more conducive to the realization of industrial application scenarios such as bainitic rail and fork repair.
[0019] 2. This invention utilizes online temperature field control of materials during laser deposition, combined with special composition design, to obtain a multiphase steel repair layer with bainite as the main microstructure after laser deposition and air cooling. This eliminates the need for subsequent offline austenitization, isothermal quenching, and other heat treatment processes, thus avoiding deformation and cracking that may occur during quenching and avoiding the use of heating media such as metal compound salts. This significantly simplifies the manufacturing process, reduces production costs, and is safer, more environmentally friendly, and lower in carbon emissions.
[0020] 3. Compared with other ultra-high strength steels (tensile strength higher than 1000MPa) manufactured by laser additive manufacturing, such as 18Ni300 (Mo: 4.6-5.2wt%; Ni: 18-19wt%; Co: 8.5-9.5wt%), AerMet100 (Mo: 0.1-1.3wt%; Ni: 11-12wt%; Co: 13-14wt%), and 34CrNiMo6 (Cr: 1.4-1.6wt%; Ni: 1.4-1.6wt%; Mo: 0.3-0.4wt%), the multiphase steel repair layer of this invention has significantly lower content of alloying elements such as Mo (0.30-0.60wt%) and Ni (0.50-0.80wt%), and does not contain Co, which will greatly reduce the cost of the alloy.
[0021] 4. The multiphase steel repair layer prepared by this invention has good forming quality, with ultra-high tensile strength (1380MPa~1530MPa) and good plasticity (10.1%~15.4%). The strength-ductility product of the material (14.5~23.2GPa·%) exceeds that of most existing laser-deposited bainitic steels and other ultra-high-strength steels. By controlling the preheating temperature of the substrate during laser deposition, the relative content of bainite / martensite in the microstructure can be changed, thereby achieving control over the mechanical properties and hydrogen embrittlement resistance of the material within a wide range. Attached Figure Description
[0022] Figure 1 This is a macroscopic morphology image of the multiphase steel repair layer prepared by laser deposition.
[0023] Figure 2 This is the X-ray diffraction (XRD) pattern of the laser-deposited ultra-high strength multiphase steel repair layer. In the figure, the horizontal axis 2θ represents the diffraction angle (°), and the vertical axis Intensity represents the relative intensity (au).
[0024] Figure 3(a) shows the color metallographic microstructure of the laser-deposited ultra-high strength multiphase steel repair layer, representing the deposited (comparative example), preheated at 270℃ (Example 1), preheated at 295℃ (Example 2), and preheated at 320℃ (Example 3). In the figure, blue represents bainite, brownish-yellow represents martensite, and white represents retained austenite. Figure 3(b) shows the volume content of bainite and martensite phases in the laser-deposited ultra-high strength multiphase steel repair layer, representing the preheated phases at 270℃ (Example 1), 295℃ (Example 2), and 320℃ (Example 3). In the figure, the horizontal axis represents the preheating temperature (℃), and the vertical axis represents the volume fraction of phases (%). B V represents the volume fraction of the bainitic phase. M This represents the volume fraction of the martensitic phase.
[0025] Figure 4 The figure shows the engineering stress-strain curves for laser-deposited ultra-high strength multiphase steel. In the figure, the horizontal axis represents engineering strain (%), and the vertical axis represents engineering stress (MPa).
[0026] Figure 5 This is a hydrogen embrittlement sensitivity index (HEI) graph for the laser-deposited ultra-high strength multiphase steel of this invention. In the graph, the horizontal axis represents the preheating temperature (°C), and the vertical axis represents the hydrogen embrittlement sensitivity index (%).
[0027] Figure 6 This is a comparison chart of the strength-ductility product of laser-deposited ultra-high strength multiphase steel in this invention and the strength-ductility product of existing laser-deposited high strength steel. In the chart, the horizontal axis UTS represents tensile strength (MPa), and the vertical axis EI represents elongation (%). Detailed Implementation
[0028] In specific implementation, the mass percentage of each element in the ultra-high strength multiphase steel repair layer of this invention is as follows: C 0.20-0.31%, Si 1.50-2.30%, Mn 1.50-1.90%, Cr 0.80-1.05%, Ni 0.50-0.80%, Mo 0.30-0.60%, with the balance being Fe; its tensile strength is 1380MPa-1530MPa, and its elongation is 10.1%-15.4%.
[0029] In the aforementioned ultra-high strength multiphase steel repair layer, the total content of alloying elements such as Cr, Mn, Mo, and Ni is less than 4.0 wt%, far lower than that of laser additive manufacturing ultra-high strength steels (tensile strength higher than 1000 MPa) such as 18Ni300, AerMet100, and 34CrNiMo6. The microstructure of the aforementioned ultra-high strength multiphase steel repair layer is a multiphase structure composed of lath bainite / martensite and retained austenite, with a bainite volume fraction of 47.3–69.2%, a martensite volume fraction of 22.6–40.6%, and a retained austenite volume fraction of 8.2–12.1%; its hydrogen embrittlement sensitivity index is 53.7–80.9%.
[0030] The preparation method of the ultra-high strength multiphase steel repair layer of the present invention is carried out according to the following steps:
[0031] 1. Composition design of the multiphase steel repair layer: 30CrMnSiA powder and elemental metal powder are weighed and mixed in a certain proportion, wherein the elemental powder contains Ni 0.50-0.80wt%, Mo 0.30-0.60wt%, and the balance is 30CrMnSiA powder; 30CrMnSiA alloy steel powder is the main component of the deposition material, and is weighed and mixed with other metal / non-metal elements in a certain proportion. The mass percentage of each element in the mixed powder is: C 0.20-0.30%, Si 1.50-2.30%, Mn 1.50-1.90%, Cr 0.80-1.05%, Ni+Mo 0.80-1.30%, and the balance is Fe; the total mass percentage of the above elements is 100%.
[0032] 2. Powder ball milling treatment: After putting the mixed powder into the ball mill jar, add an appropriate amount of agate balls. The ball-to-powder mass ratio is 1:1. Use a horizontal planetary ball mill to ball mill and mix the powder at a speed of 270 r / min for 120 min. Then place the ball-milled powder in a constant temperature drying oven to dry.
[0033] 3. Preheating the substrate and laser deposition: Using 30CrMnSiA plate as the substrate, the martensitic transformation start temperature (272.1~348.5℃) and bainitic transformation temperature range (272.1~461.4℃) of the metal powder to be deposited were determined using thermodynamic calculation software. Based on the calculation results of the above metal solid-state phase transformation temperature range, the substrate was preheated to the specified temperature (270~320℃). The surface temperature of the substrate and the deposited metal was monitored online using a non-contact infrared thermometer. Laser deposition began when the substrate surface reached the set temperature. After each layer of metal was deposited, the deposition was paused for 2~3 minutes. When the surface temperature of the deposited metal reached the set temperature again, the next layer of metal was deposited until the thickness of the metal deposition layer reached 5~6mm. Laser deposition was then stopped, and the laser-deposited metal material was placed in the air to cool naturally, finally obtaining an ultra-high strength laser-deposited multiphase steel repair layer. The laser deposition process is as follows: laser power is 900-1200W, the laser spot is circular with a diameter of 2mm, the scanning speed is 300-360mm / min, the powder feed rate is 8-9g / min, the carrier gas flow rate is 8-10L / min, the powder feed method is coaxial, it is a multi-pass, multi-layer deposition method, the powder particle size is between 45μm and 105μm, the overlap rate is 50%, the scanning path is zigzag, and the thickness of a single layer of deposited metal is 0.3-0.5mm.
[0034] 4. Microstructure Control of Laser-Deposited Multiphase Steel Repair Layer: By changing the preheating temperature, the microstructure of the laser-deposited multiphase steel repair layer can be controlled to obtain different contents of bainite, martensite, and retained austenite, thereby regulating the material's properties. The purpose of preheating is to induce bainitic transformation in the steel during laser deposition. After laser deposition, some of the supercooled austenite transforms into bainite under air cooling conditions, while the remaining portion undergoes martensitic transformation to form a mixed microstructure of martensite and retained austenite. The time required for bainitic phase transformation varies at different preheating temperatures, but the time required for laser deposition to prepare the multiphase steel repair layer is consistent. Therefore, by controlling the preheating temperature, the relative proportions of bainite and martensite in the microstructure can be controlled, thereby regulating the material's strength, plasticity, and hydrogen embrittlement sensitivity.
[0035] The technical solution of the present invention will be further described in detail below with reference to specific comparative examples, embodiments, and accompanying drawings. The following embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make equivalent changes to the disclosed technical content to create equivalent embodiments. Any simple modifications or equivalent changes made to the following embodiments based on the technical essence of the present invention without departing from the scope of the present invention fall within the protection scope of the present invention.
[0036] Comparative Example
[0037] In this comparative example, the repair layer was prepared using a direct laser deposition process, specifically following these steps:
[0038] Step 1: 30CrMnSiA alloy steel powder is the main component of the deposition material. It is weighed and mixed with Ni and Mo metal elements in a certain proportion. The mass percentage of each element in the mixed powder is: C 0.31%, Si 2.10%, Mn 1.80%, Cr 0.95%, Ni 0.65%, Mo 0.58%, and the balance is Fe.
[0039] Step 2: The above-mentioned mixed powder is ball-milled. After the powder is placed in the ball mill jar, an appropriate amount of agate balls are added. The ball-to-powder mass ratio is 1:1. The powder is ball-milled and mixed using a horizontal planetary ball mill at a speed of 270 r / min for 120 min. Then the ball-milled powder is placed in a constant temperature drying oven to dry.
[0040] Step 3: First, use wire EDM to cut the 30CrMnSiA steel plate into 100×70×10mm pieces. 3 The oxide scale on the steel plate was removed using sandpaper, followed by ultrasonic cleaning with anhydrous ethanol for 15 minutes and sandblasting. Then, powder deposition was performed directly on the 30CrMnSiA steel plate until the metal deposition layer thickness reached 5mm. The laser deposition process was as follows: laser power of 900W, laser scanning rate of 360mm / min, powder feed rate of 8g / min, carrier gas of argon flow rate of 9L / min, coaxial powder feeding method, multi-pass, multi-layer deposition, powder particle size between 45μm and 105μm, zigzag scanning path, and a single-layer metal deposition thickness of 0.5mm was measured. After deposition, the plate was allowed to cool naturally in air, ultimately obtaining a repair coating under ultra-high intensity laser deposition.
[0041] The microstructure obtained in this comparative example is almost complete martensite, with a tensile strength of 1077 MPa, a yield strength of 783 MPa, an elongation after fracture of 13.4%, a retained austenite volume fraction of 5.7%, and severe plasticity loss after hydrogen charging, with a hydrogen embrittlement sensitivity index of 86.8%.
[0042] Example 1
[0043] In this embodiment, an ultra-high strength multiphase steel repair layer is prepared using a preheating + laser deposition process, specifically following these steps:
[0044] Step 1: 30CrMnSiA alloy steel powder is the main component of the deposition material. It is weighed and mixed with Ni and Mo metal elements in a certain proportion. The mass percentage of each element in the mixed powder is: C 0.31%, Si 2.10%, Mn 1.80%, Cr 0.95%, Ni 0.65%, Mo 0.58%, and the balance is Fe.
[0045] Step 2: The above-mentioned mixed powder is ball-milled. After the powder is placed in the ball mill jar, an appropriate amount of agate balls are added. The ball-to-powder mass ratio is 1:1. The powder is ball-milled and mixed using a horizontal planetary ball mill at a speed of 270 r / min for 120 min. Then the ball-milled powder is placed in a constant temperature drying oven to dry.
[0046] Step 3: Use wire EDM to cut the 30CrMnSiA steel plate into 100×70×10mm pieces. 3 The oxide scale on the steel plate was removed using sandpaper, followed by ultrasonic cleaning with anhydrous ethanol for 15 minutes and sandblasting. The 100×70×10mm steel plate was then processed on a constant-temperature platform of model X1520T. 3 The 30CrMnSiA steel plate was preheated to 270℃. The surface temperature of the substrate and the deposited metal was monitored online using a non-contact infrared thermometer. Laser deposition began when the substrate surface reached the set temperature. After each layer of metal was deposited, the deposition was paused for 2 minutes. When the surface temperature of the deposited layer returned to the set temperature of 270℃, the next layer of metal was deposited until the metal deposition layer thickness reached 5mm. The laser deposition process was as follows: laser power of 900W, laser scanning rate of 360mm / min, powder feeding rate of 8g / min, carrier gas of argon with a flow rate of 9L / min, coaxial powder feeding, multi-pass and multi-layer deposition, powder particle size between 45μm and 105μm, zigzag scanning path, and single-layer deposited metal thickness of 0.5mm. After deposition, the laser deposition was stopped and the laser-deposited metal material was placed in the air to cool naturally, finally obtaining an ultra-high strength laser-deposited air-cooled multiphase steel repair layer.
[0047] In this embodiment, the obtained microstructure is a bainitic / martensitic multiphase microstructure with a tensile strength of 1388 MPa, a yield strength of 784 MPa, and an elongation after fracture of 15.4%; the volume fraction of bainite is 47.3%, the volume fraction of martensite is 40.6%, the volume fraction of retained austenite is 12.1%, and the hydrogen embrittlement sensitivity index is 80.9%.
[0048] Example 2
[0049] The difference from Example 1 is that in step 3: the 30CrMnSiA steel plate is first cut into 100×70×10mm pieces using wire cutting. 3 The oxide scale on the steel plate was removed using sandpaper, followed by ultrasonic cleaning with anhydrous ethanol for 15 minutes and sandblasting. The 100×70×10mm steel plate was then processed on a constant-temperature platform of model X1520T. 3The 30CrMnSiA steel plate was preheated at a temperature of 295℃. The high-strength multiphase steel repair layer in this embodiment was prepared using the same method as in Example 1. The resulting microstructure was a bainitic / martensitic multiphase structure with a tensile strength of 1528 MPa, a yield strength of 1178 MPa, and an elongation after fracture of 15.2%. The volume fraction of bainite was 57.5%, the volume fraction of martensite was 33.3%, the volume fraction of retained austenite was 9.2%, and the hydrogen embrittlement sensitivity index was 57.3%.
[0050] Example 3
[0051] The difference from Example 1 is that in this example, step 3: first, the 30CrMnSiA steel plate is cut into 100×70×10mm pieces using wire cutting. 3 The oxide scale on the steel plate was removed using sandpaper, followed by ultrasonic cleaning with anhydrous ethanol for 15 minutes and sandblasting. The 100×70×10mm steel plate was then processed on a constant-temperature platform of model X1520T. 3 The 30CrMnSiA steel plate was preheated at a temperature of 320℃. The high-strength multiphase steel repair layer in this embodiment was prepared using the same method as in Example 1. The resulting microstructure was a bainitic / martensitic multiphase structure with a tensile strength of 1434 MPa, a yield strength of 1157 MPa, and an elongation after fracture of 10.1%. The volume fraction of bainite was 69.2%, the volume fraction of martensite was 22.6%, the volume fraction of retained austenite was 8.2%, and the hydrogen embrittlement sensitivity index was 53.7%.
[0052] like Figure 1 The image shows the macroscopic morphology of the multiphase steel repair layer prepared by laser deposition. Figure 1 It can be seen that the prepared steel material coating has good forming quality and no macroscopic cracks.
[0053] like Figure 2 The image shows the X-ray diffraction (XRD) pattern of the laser-deposited ultra-high strength multiphase steel repair layer; (The image is from...) Figure 2 It can be seen that the main phases of the sample are α phase and γ phase, and the volume fraction of retained austenite (γ phase) is between 9.86% and 14.20%.
[0054] like Figures 3(a)-3(b) Figure 3 shows a color metallographic microstructure of the laser-deposited ultra-high strength multiphase steel repair layer, as well as volumetric content diagrams of bainite and martensite phases in the examples. As shown in Figure 3, for the laser-deposited ultra-high strength multiphase steel repair layer without preheating, the microstructure is primarily martensite with a small amount of retained austenite. After preheating, the microstructure of the laser-deposited repair layer transforms into a multiphase structure composed of bainite, martensite, and retained austenite. Furthermore, as the preheating temperature increases, the bainite volume content rises from 47.3% to 69.2%.
[0055] like Figure 4 As shown, the engineering stress-strain curves of laser-deposited ultra-high strength multiphase steel are presented; from Figure 4 It can be seen that the tensile strength of the laser-deposited sample is relatively low, reaching only 1077 MPa, and the elongation after fracture is 13.4%. Preheating the substrate greatly improves the mechanical properties of the sample. In particular, when the preheating temperature is 295℃, the tensile strength is significantly increased to 1528 MPa (an increase of 41.9%) without losing plasticity, and the strength-plasticity product can reach 23.2 GPa, showing an extremely excellent strength-plasticity match.
[0056] like Figure 5 As shown, the hydrogen embrittlement sensitivity index of laser-deposited ultra-high strength multiphase steel according to the present invention is illustrated; by Figure 5 It can be seen that as the preheating temperature increases, the martensite content decreases and the bainite content increases significantly. The hydrogen embrittlement sensitivity index of laser-deposited ultra-high strength multiphase steel decreases significantly from 86.8% (without preheating) to 53.7% (preheated at 320℃).
[0057] like Figure 6 As shown, the strength-ductility product of laser-deposited ultra-high strength multiphase steel in this invention is compared with the strength-ductility product of existing laser-deposited high strength steel. (From...) Figure 6 It can be seen that the strength-ductility product of the laser-deposited ultra-high strength multiphase steel in this invention is higher than that of most existing laser-deposited high strength steels, especially the ultra-high strength multiphase steels prepared in Example 1 (preheated at 270°C) and Example 2 (preheated at 295°C), whose strength-ductility product both exceed 20 GPa.
[0058] The results show that the present invention can realize the preparation and microstructure control of ultra-high strength multiphase steel repair layer under laser deposition process, and is expected to realize rapid online repair of surface damage of ultra-high strength bainitic steel rails of damaged heavy-haul railways, and significantly shorten the production and manufacturing process. It provides strong support for the repair and manufacturing of high-strength bainitic steel components, and enables the widespread application of laser additive manufacturing technology for repairing ultra-high strength bainitic steel components.
Claims
1. A method for preparing an ultra-high strength multiphase steel repair layer and controlling its microstructure and properties, characterized in that, Follow these steps: (1) Composition design of multiphase steel repair layer: 30CrMnSiA powder and metal elemental powder are weighed and mixed in proportion, wherein the elemental powder Ni is 0.50~0.80 wt%, Mo is 0.30~0.60 wt%, and the balance is 30CrMnSiA powder; In step (1), the mass percentage of each element in the ultra-high strength multiphase steel repair layer is as follows: C 0.20~0.30%, Si 1.50~2.30%, Mn 1.50~1.90%, Cr 0.80~1.05%, Ni 0.50~0.80%, Mo 0.30~0.60%, with the balance being Fe; (2) Powder ball milling treatment; (3) Preheating the substrate: Using 30CrMnSiA plate as the substrate, the martensitic transformation start temperature of the metal powder to be deposited was determined to be 272.1~348.5℃ and the bainitic transformation temperature range was 272.1~461.4℃ using thermodynamic calculation software; based on the above calculation results of the metal solid phase transformation temperature range, the substrate was preheated to the specified temperature of 270~320 °C. (4) Laser deposition: The temperature of the substrate and the surface of the deposited metal is monitored online using a non-contact infrared thermometer. Laser deposition begins when the surface of the substrate reaches the set temperature. After each layer of metal is deposited, the deposition is paused for 2 to 3 minutes. When the surface temperature of the deposited metal reaches the set temperature again, the next layer of metal is deposited until the thickness of the metal deposition layer reaches 5 to 6 mm. Laser deposition is then stopped and the laser-deposited metal material is placed in the air to cool naturally, finally obtaining an ultra-high strength multiphase steel repair layer.
2. The method for preparing and controlling the microstructure and properties of the ultra-high strength multiphase steel repair layer according to claim 1, characterized in that, In step (2), after the mixed powder is placed in the ball mill jar, agate balls are added. The mass ratio of balls to powder is 1:
1. The powder is ball-milled and mixed using a horizontal planetary ball mill at a speed of 240-300 r / min and a time of 90-150 min. Then the ball-milled powder is placed in a constant temperature drying oven for drying.
3. The method for preparing and controlling the microstructure and properties of the ultra-high strength multiphase steel repair layer according to claim 1, characterized in that, In step (4), the laser deposition process is as follows: the laser power is 900-1200 W, the laser spot is a circular spot with a diameter of 2 mm, the scanning speed is 300-360 mm / min, the powder feeding rate is 8-9 g / min, the carrier gas flow rate is 8-10 L / min, the powder feeding method is coaxial powder feeding, it is a multi-pass, multi-layer deposition method, the powder particle size is between 45 μm and 105 μm, the overlap rate is 50%, the scanning path is zigzag, and the thickness of a single layer of deposited metal is 0.3-0.5 mm.
4. The method for preparing and controlling the microstructure and properties of the ultra-high strength multiphase steel repair layer according to claim 1, characterized in that, In step (4), the tensile strength of the ultra-high strength multiphase steel repair layer is 1380 MPa to 1530 MPa, and the elongation is 10.1% to 15.4%.
5. The method for preparing and controlling the microstructure and properties of the ultra-high strength multiphase steel repair layer according to claim 1, characterized in that, In step (4), the microstructure of the ultra-high strength multiphase steel repair layer is a multiphase structure composed of lath bainite / martensite and retained austenite, with a bainite volume fraction of 47.3-69.2%, a martensite volume fraction of 22.6-40.6%, and a retained austenite volume fraction of 8.2-12.1%; the hydrogen embrittlement sensitivity index is 54.6-80.9%.