Austempered steel friction stir welding apparatus and method

Abstract

The application discloses a kind of metastable austenitic steel friction stir welding device and method, setting: material conveying cavity, material conveying cavity is sequentially connected by top to bottom first-stage material conveying cavity and second-stage material conveying cavity, and spiral material conveying component is arranged in first-stage material conveying cavity from top; second-stage material conveying cavity lower end is connected with stir head, and the channel that is communicated with second-stage material conveying cavity 12 is embedded in the stir head;Second-stage material conveying cavity is installed with heating component outside it.The application mixes austenite stabilizing element or reinforcing particle into weld, utilizes heat diffusion effect and pipe dislocation diffusion effect, accelerates austenite stabilizing element to diffuse into austenite interior quickly, obtains welded joint containing austenite by quenching distribution heat treatment;Furthermore, intense plastic deformation can significantly refine grain, and austenite grain size refinement can also improve austenite stability;Simultaneously, fully heat welding area, so that a large number of annealing twin crystals are formed in weld interior;Based on the above method, high-quality welding of metastable high-strength steel is realized.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic processing, specifically relating to a device and method for metastable austenitic steel friction stir welding. Background Technology

[0002] The automotive industry has become a pillar industry of the national economy. To further reduce vehicle weight, lower energy consumption, and achieve green and low-carbon development, replacing traditional low-strength steel with advanced high-strength steel has become a development trend. As representatives of advanced high-strength steel, transformation-induced plasticity steel (TRIP steel), quenched and partitioned steel (QP steel), and twinned induced plasticity steel (TWIP steel) possess excellent strength and toughness, making them the most promising and potentially applicable lightweight materials. The main reason why TRIP steel, QP steel, and TWIP steel maintain excellent strength and plasticity lies in the presence of metastable austenite within them. During plastic deformation, the metastable austenite undergoes phase transformation or twinning, coordinating the plastic deformation and producing the TRIP or TWIP effect, enabling the material to maintain high work hardening performance and exhibit excellent strength and plasticity. However, in practical applications, metastable austenitic steel inevitably faces welding requirements.

[0003] Currently, the main welding methods for metastable austenitic steels include laser welding, resistance welding, and electron beam welding. However, these methods are prone to causing solidification defects such as porosity, inclusions, and cracks within the joint. Friction stir welding (FSW), as a solid-state welding method, has low heat input, is environmentally friendly, and can effectively avoid the defects of traditional fusion welding, thus improving weld quality. However, when welding metastable austenitic steels using conventional FSW, the intense plastic deformation and thermal cycling effects cause phase transformation of the metastable austenite in the joint. This leads to the formation of a large amount of brittle martensite in the weld area, inhibiting the TRIP or TWIP effect, resulting in low joint strength and ductility, which is difficult to meet the requirements of engineering applications. Summary of the Invention

[0004] In view of the defects and deficiencies of the above-mentioned technologies, the purpose of this invention is to provide a metastable austenitic steel friction stir welding device and method.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A metastable austenitic steel friction stir welding device is provided, comprising: a feeding chamber, wherein a primary feeding chamber and a secondary feeding chamber are sequentially connected from top to bottom; a spiral feeding assembly is installed extending from the top into the primary feeding chamber; a stirring head is connected to the lower end of the secondary feeding chamber, wherein a channel communicating with the secondary feeding chamber is embedded in the stirring head; and a heating assembly is installed outside the secondary feeding chamber.

[0007] Optionally, the spiral conveying assembly includes a conveying bin and a conveying rod arranged from top to bottom; the conveying rod is provided with spiral blades in the circumferential direction.

[0008] Optionally, the stirring head includes a shaft shoulder and a stirring needle connected by a shaft, with a main channel arranged axially inside the shaft shoulder and communicating with the main channel, and a branch channel arranged inside the stirring needle.

[0009] Optionally, there are multiple branch channels, and the branch channels are arranged in a centrifugal oblique direction.

[0010] Optionally, the outer diameter of the stirring head is 10-15 mm, the inner diameter of the main channel is 3-5 mm, and the inner diameter of the branch channel is 2-3 mm.

[0011] Optionally, the heating component is provided with a fixed outer shell, with an installation head at one end of the fixed outer shell, and an insulation layer, a heating tube and an array of heat dissipation holes are sequentially attached inside the fixed outer shell.

[0012] Optionally, an air blowing assembly is provided in communication with the secondary material conveying chamber. The air blowing assembly includes an air pump and an air pipe.

[0013] A welding method for TRIP-effect metastable austenitic steel, characterized in that welding is performed using any of the metastable austenitic steel friction stir welding apparatuses described in this invention, specifically including:

[0014] This process involves adding austenite stabilizing elements to the welding surface of the workpiece to be welded, performing friction stirring welding on the welding surface with a stirring head, applying auxiliary heating during the welding process, and then performing quenching and partitioning heat treatment after welding to obtain a welded joint containing residual austenite.

[0015] The austenite stabilizing element is carbon or manganese, with a purity greater than 99.9%. The particle size of the carbon powder is 10–1000 nm, and the particle size of the manganese powder is 0.2–50 μm. The amount of austenite stabilizing element added is 0.5%–3.0%.

[0016] The auxiliary heating temperature is 200–800℃; the conveyor bar rotation speed is 1.0–100 r / min;

[0017] The gas pressure range in the secondary feeding chamber is 0.4 to 0.8 MPa; the rotation speed of the stirring head is 200 to 2000 rpm, and the forward speed is 10 to 600 mm / min.

[0018] Optionally, the quenching and partitioning heat treatment includes:

[0019] First, heat to 800℃ and hold for 300 seconds; then cool to 260℃ and hold for 60 seconds; finally, heat to 400℃, hold for 180 seconds, and then cool to room temperature.

[0020] A welding method for metastable austenitic steel exhibiting the TWIP effect, comprising welding using any of the metastable austenitic steel friction stir welding apparatuses described in this invention, specifically including:

[0021] Aluminum carbide reinforcing particles with a particle size of 1-2000nm are added to the feeding hopper beforehand. The stirring head performs friction stirring welding on the welding surface of the workpiece to be welded. During the welding process, the aluminum carbide reinforcing particles enter the welding area, and the heating component heats the center area of ​​the weld.

[0022] The heating temperature is 200–800℃; the rotation speed of the conveyor rod is 1.0–100 r / min;

[0023] The gas pressure range in the secondary conveying chamber is 0.4–0.8 MPa;

[0024] The stirring head rotates at a speed of 200–2000 rpm and advances at a speed of 10–600 mm / min.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] 1. The metastable austenitic steel friction stir welding device provided by the present invention can effectively realize the connection of metastable austenitic steel, avoid solidification defects such as porosity, inclusions, and cracks, while retaining residual austenite inside the weld joint, controlling microstructure characteristics (grain size, annealing twins), etc., and improving the welding quality and strength and plasticity of metastable austenitic steel. The technical effect is significant.

[0027] 2. The raw material method provided by this invention mainly solves the problem of easy agglomeration of nano-sized powders through physical processes such as extrusion transport, gas acceleration, and rotational dispersion, achieving uniform dispersion of nano-sized or micron-sized powders within the weld seam. This method is applicable to the addition of single or multiple powders of different particle size ranges. The method is simple, allowing for simultaneous powder addition and welding, reducing welding steps and lowering welding costs.

[0028] 3. The technical principle of this invention is novel. Targeting TRIP-effect metastable austenitic steel, it adds austenite-stabilizing elements to increase austenite stability. Typically, the intense plastic deformation during friction stir welding disrupts the original austenite element distribution characteristics, reducing austenite stability and making it difficult to retain at room temperature. This invention solves the problem of difficulty in retaining metastable austenite by adding austenite-stabilizing elements, which enrich the austenite within the austenite structure. The technical effect is significant.

[0029] 4. To address the welding problem of metastable austenitic steel due to the TWIP effect, reinforcing particles are added during the welding process. This strengthens the weld joint and hinders grain size coarsening. Simultaneously, heating the weld joint promotes annealing twin formation, ensuring excellent strength and ductility.

[0030] 5. The austenite stabilizing elements provided by this invention include carbon and manganese, among which carbon is the most economical and effective austenite stabilizing and solid solution strengthening element, achieving both austenite stabilization and strengthening. Manganese is a strong austenite stabilizing element, effectively improving the stability of austenite. Adding these austenite stabilizing elements has little impact on welding costs but provides better technical results.

[0031] 6. Compared with traditional fusion welding technology, this invention uses friction stir welding technology to achieve metastable austenitic steel welding. By adding austenite stabilizing elements, weld joints containing austenite stabilizing elements can be prepared, improving the performance of the weld joints. At the same time, this technology is a solid-state welding technology, which is green and environmentally friendly, highly automated, and can significantly reduce time and energy costs. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate this disclosure and form part of the specification. They are used in conjunction with the following detailed description and are disclosed in connection with the invention, but do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a structural diagram of the metastable austenitic steel friction stir welding device of the present invention;

[0034] Figure 2 for Figure 1 Diagram of the stirring head structure in the image;

[0035] Figure 3 for Figure 1 The structural diagram of the heating component in the diagram;

[0036] Figure 4 The image shows the distribution of austenite detected by electron backscatter diffraction in Example 1 (the black part in the image represents austenite);

[0037] Figure 5 The image shows the distribution of austenite detected by electron backscatter diffraction in Comparative Example 1 (the black part in the image represents austenite).

[0038] Figure 6 The image shows the distribution of austenite detected by electron backscatter diffraction in Comparative Example 3 (the black part in the image represents austenite).

[0039] Figure 7 The image shows the distribution of austenite detected by electron backscatter diffraction in Comparative Example 2 (the black part in the image represents austenite).

[0040] The labels in the diagram represent:

[0041] 1-Feeding chamber, 11-Primary feeding chamber, 12-Secondary feeding chamber; 2-Screw feeding assembly, 21-Feeding rod, 211-Screw blade, 22-Feeding bin; 3-Stirring head, 31-Shoulder, 311-Main channel, 32-Stirring needle, 321-Branch channel; 4-Heating assembly, 41-Mounting head, 42-Fixed outer shell, 421-Insulation layer, 422-Heating tube, 423-Arrayed heat dissipation holes; 5-Air blowing assembly, 51-Air pump, 52-Air pipe; 6-Motor. Detailed Implementation

[0042] The present invention will be further explained and described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] This invention targets two types of metastable austenitic steels: the first type is metastable high-strength steel with the TRIP effect (e.g., QP980, QP1180, TRIP800, etc.); the second type is metastable high-strength steel with the TWIP effect (e.g., Fe-Mn-C or Fe-Mn-Al-Si series TWIP steels).

[0044] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0045] Combination Figures 1-3 The present invention relates to a metastable austenitic steel friction stir welding device for welding. The welding device is configured with: a feeding chamber 1, which is connected from top to bottom to a primary feeding chamber 11 and a secondary feeding chamber 12. A spiral feeding assembly 2 is installed extending from the top into the primary feeding chamber 11. The spiral feeding assembly 2 includes a hopper and a feeding rod connected from top to bottom. Raw materials are added to the feeding hopper 22 and flow into the feeding rod 21 by their own gravity. The feeding rod 21 is provided with spiral blades 211 along its circumference. The rotating feeding rod 21 conveys the raw materials axially downward along the spiral blades 211. The above process is completed in the primary feeding chamber 11. After that, the raw materials are conveyed to the secondary feeding chamber 12.

[0046] Since the raw materials used in this invention are basically nano-sized powders, a high-pressure gas is introduced into the secondary conveying chamber 12 by connecting the air pump 51 through the air pipe 52. The high-pressure gas not only prevents the nano-sized raw materials from agglomerating, but also speeds up the passage of the raw materials through the secondary conveying chamber 12.

[0047] The lower end of the secondary feeding chamber 12 is connected to the stirring head 3. The stirring head 3 includes a shoulder 31 and a stirring needle 32. In order to achieve simultaneous addition of raw materials and stirring, channels are set in the original stirring head and stirring needle to achieve simultaneous addition and stirring without hindering the rotation of the stirring head. For example, a main stirring channel 311 is set along the axial direction in the stirring head 3, and a branch channel 321 is set in the stirring needle 32. The direction of the branch channel 321 can be oblique or axial, and the shape of the channel is not limited. It can be straight, wavy, etc., as long as it can facilitate the passage of raw materials. The inner diameter and number of the branch channels 321 in the stirring needle 32 can be adjusted according to different requirements such as the amount of material added. For example, as shown in the figure, there are two or more branch channels 321, and the two or more channels are obliquely set along the stirring centrifugal direction of the stirring needle 32. By rotating the centrifugal force, the passage of raw materials is further accelerated. The stirring head 3 is mainly driven by the motor 6 to achieve friction stir welding.

[0048] Heating component 4 is connected to the secondary conveying chamber 12 and includes a power supply, heating element, infrared temperature measuring device, etc. Figure 3 The structure shown includes a fixed outer shell 42, with an installation head 41 at one end, such as a threaded shaft or rod, for easy installation and disassembly. The fixed outer shell 42 is shaped like a rectangular bent shell. Inside the shell, an insulation layer 421, a heating tube 422, and an array of heat dissipation holes 423 are sequentially attached to achieve precise heating of the welding surface below. During operation, the raw material feeding device pushes the raw material from the hopper into the feeding channel. The air pump 51 pressurizes the raw material and quickly enters the main channel 311 and branch channel 321 of the stirring head 3. As the stirring head 3 rotates at high speed, the raw material is added to the welding area. With the auxiliary heating of the heating component 4, the parts to be welded are connected simultaneously.

[0049] Its working principle is as follows: First, stable austenitic elements, such as carbon and manganese, are selected according to the elemental composition of the workpiece to be welded. The raw materials are added to the feeding bin 22 and flow into the feeding rod 21 by their own gravity. The spiral blades 211 drive the raw materials from the primary feeding chamber 11 into the secondary feeding chamber 12. The secondary feeding chamber 12 is an acceleration chamber. The raw materials can be accelerated by connecting the air pipe 52 and the air pump 51. The raw materials reach the cross-section of the workpiece to be welded through the main stirring channel 311 and the branch channel 321. Next, welding is carried out. During the high-speed rotation of the stirring head 3, the raw materials are mixed into the workpiece to be welded. After welding, quenching and distribution heat treatment is carried out to obtain stable austenite.

[0050] The metastable austenitic steel friction stir welding apparatus of the present invention, through the spiral feeding assembly 2, the feeding chamber 1, and the feeding channel connected to the feeding chamber, can achieve the purpose of integrated addition of austenitic stabilizing elements and welding, thereby improving welding production efficiency. The air blowing assembly 5 can accelerate the raw material, allowing it to quickly reach the workpiece to be welded; simultaneously, high-speed airflow can disperse nano-sized powder, solving the problem of easy agglomeration of nano-sized powder. This apparatus has strong applicability and can meet the addition of different types and sizes of austenitic stabilizing elements, thus expanding the application range of the metastable austenitic friction stir welding method and apparatus of the present invention. For example, the rotation speed of the feeding rod 21 is 1.0 r / min to 100 r / min; the air pump 51 mainly functions to accelerate the feeding of raw materials, break up the agglomeration of nano-powder, and ensure that the raw material is evenly distributed inside the weld. The gas pressure range is 0.4 to 0.8 MPa; the outer diameter of the stirring head 3 is 10 to 15 mm, and its internal shape is "tree-like," i.e., one channel at the top and two channels at the bottom. The main channel 311 has an inner diameter of 3–5 mm, and the branch channel 321 has an inner diameter of 2–3 mm. The stirring head 3 rotates at a speed of 200 rpm to 2000 rpm and advances at a speed of 10 mm / min to 600 mm / min. The stirring head material is a tungsten-based alloy. Metastable austenitic steel includes TRIP steel, QP steel, and TWIP steel, as well as high-strength steel with the TRIP / TWIP effect. The thickness of the metastable austenitic steel is 1–2 mm.

[0051] The method for friction stir welding of metastable austenitic steel includes the following steps:

[0052] Step 1: Determine the raw materials to be added based on the composition of the materials to be welded;

[0053] Step 2: Add the raw material to the raw material hopper. The extrusion rod squeezes the raw material vertically downwards and sends the material to be added into the acceleration hopper through the raw material channel. The air pump accelerates the raw material into the hollow stirring head through the acceleration gas. Then, insert the high-speed rotating stirring head into the middle of the workpiece to be welded. After rotating for a period of time, turn on the heating component to start welding. After welding is completed, turn off all components.

[0054] Step 3: Determine whether to perform quenching and component separation treatment on the weld joint based on the composition of the workpiece to be welded.

[0055] Based on the above-mentioned device, this invention proposes a welding method for TRIP-effect metastable austenitic steel. The method includes adding austenite-stabilizing elements such as carbon and manganese to the welding surfaces of the workpieces to be welded. Then, a stirring head 3 is used to perform friction stir welding on the weld seam of the workpieces with deposited austenite-stabilizing elements. Auxiliary heating is applied during the welding process. After welding, a quenching and partitioning heat treatment is performed to obtain a welded joint containing residual austenite. Specifically, the raw materials are mainly austenite-stabilizing elements such as carbon powder and manganese powder, with a purity greater than 99.9%. The particle size of the carbon powder is 10–1000 nm, and the particle size of the manganese powder is 0.2–50 μm. The purpose of heating is to allow the austenite-stabilizing elements to rapidly diffuse into the austenite interior, achieving the goal of stabilizing the austenite. The purpose of the quenching and partitioning heat treatment is to further increase the austenite content of the welded joint, ensuring that the welded joint has excellent strength and ductility. The heating assembly 4 is equipped with 2–4 heating tubes 422, and the heating temperature is 200–800℃.

[0056] Based on the aforementioned device, this invention proposes a welding method for metastable austenitic steel with the TWIP effect. The method includes pre-adding aluminum carbide reinforcing particles to a raw material hopper, and using a stirring head with a shoulder and stirring pin to perform friction stir welding on the workpiece. During welding, the aluminum carbide reinforcing particles enter the welding area through a feed channel and an acceleration chamber. Simultaneously, a heating assembly heats the central region of the weld to achieve austenite stabilization and microstructure control. Specifically, the raw material also includes reinforcing particles such as aluminum carbide, with a particle size of 1–2000 nm. The purpose of adding aluminum carbide reinforcing particles is twofold: first, to strengthen the weld joint performance; second, to hinder grain migration during repeated heating, preventing abnormal grain growth. The purpose of heating is twofold: first, to accelerate the formation of metallurgical bonding between the particles and the material to be welded; second, to allow annealed twins to form inside the TWIP steel weld, strengthening the joint performance while maintaining sufficient plasticity. The heating assembly includes 2–4 heating tubes, with a heating temperature of 200–800°C.

[0057] Specifically, the principle of this invention is to utilize the intense plastic flow of materials during friction stir welding to incorporate austenite stabilizing elements or reinforcing particles into the weld. Simultaneously, thermal diffusion and dislocation diffusion accelerate the rapid diffusion of austenite stabilizing elements into the austenite interior. A welded joint containing austenite is obtained through quenching and partitioning heat treatment. Furthermore, the intense plastic deformation during friction stir welding can significantly refine the grain size, and this refinement of austenite grain size also improves austenite stability. Simultaneously, the heating element fully heats the welding area, resulting in the formation of numerous annealed twins within the weld. Based on the above methods, high-quality welding of metastable high-strength steel is achieved.

[0058] Example 1:

[0059] Friction stir welding was performed on QP1180 steel exhibiting the TRIP effect. Before welding, the mating surfaces of the workpieces were cleaned with acetone to remove oil stains. Carbon was added during the QP1180 steel welding process at a rate of 1.8% of the weld volume. The stirring head rotated at 800 rpm, the welding speed was 300 mm / min, the stirring pin diameter was 5 mm, and the shoulder was 12 mm. The heating temperature during welding was 200℃. After welding, a quenching and partitioning heat treatment was performed. The quenching and partitioning heat treatment process was as follows: first, heating to 800℃ and holding for 300 s; then cooling to 260℃ and holding for 60 s; finally, heating to 400℃ and holding for 180 s, and then cooling to room temperature. The mechanical property test results of the joint are as follows:

[0060] tensile strength elongation Residual austenite content 1206MPa 24％ 15％

[0061] The distribution of retained austenite was characterized using electron backscattering technology, such as... Figure 4 As shown, the residual austenite content in the joint increased to 15%, which is higher than that in Comparative Examples 1-4. Compared with Comparative Examples 1-4, the elongation of the joint in Example 1 was significantly improved, fully demonstrating the significant improvement effect of this solution.

[0062] Example 2:

[0063] Friction stir welding was performed on QP1180 steel exhibiting the TRIP effect. Before welding, the mating surfaces of the workpieces were cleaned with acetone to remove oil stains. During welding, the stirring head rotated at 1400 rpm, and the welding speed was 40 mm / min. Carbon was added during welding at 1.5% of the weld volume, the gas pressure was 0.3 MPa, and the heating temperature was 200℃. After welding, a quenching and fractional heat treatment was performed. The heat treatment process was as follows: heating to 800℃, holding for 300 s, rapidly cooling to 260℃, holding for 60 s, heating to 400℃, holding for 180 s, and then cooling to room temperature. The mechanical property test results of the joint are as follows:

[0064] tensile strength elongation Residual austenite content 1180MPa 21％ 12％

[0065] The distribution of retained austenite was characterized using electron backscattering technology, such as... Figure 4 As shown, the residual austenite content in the joint increased to 12%. Compared to Examples 5-7, the joint elongation was significantly improved, fully demonstrating the significant improvement effect of this solution.

[0066] Compared to the first method of addition, the second method enables integrated welding. This involves adding carbon, an austenite-stabilizing element, into the QP1180 steel during the welding process, allowing residual austenite to be retained in the weld. This significantly reduces welding time and economic costs.

[0067] Example 3:

[0068] Friction stir welding (TWIP) was performed on Fe-Mn-C series TWIP steels exhibiting the TWIP effect. Before welding, the mating surfaces of the workpieces were cleaned with acetone to remove oil stains. During the TWIP steel welding process, aluminum carbide particles were added at a rate of 1.0% of the weld volume. The stirring head rotation speed was 400 rpm, the welding speed was 200 mm / min, the gas pressure was 0.3 MPa, and the heating temperature was 400℃. No quenching or preheating treatment was performed. The mechanical properties of the joint were tested as follows:

[0069] tensile strength elongation Annealing twin content 1380MPa 66％ 25％

[0070] Electron backscattering technology revealed that the content of annealed twins inside the joint was 25%. Annealed twins can refine the grains and significantly improve the joint strength without reducing the joint plasticity, which fully demonstrates the significant improvement effect of this solution.

[0071] Comparative Example 1:

[0072] Similar to Example 1, except that no austenitic stabilizing elements were added and no heat treatment was performed in Comparative Example 1. The results of the joint mechanical property test are as follows:

[0073] tensile strength elongation Residual austenite content 1195MPa 12％ 0.1％

[0074] The distribution of austenite was characterized using electron backscattering technology, such as... Figure 5 As shown, the residual austenite content in the joint increased to 0.1%.

[0075] Comparative Example 2:

[0076] Similar to Example 1, except that this comparative example adds austenitic stabilizing carbon but does not undergo heat treatment. The joint mechanical properties test results are as follows:

[0077] tensile strength elongation Residual austenite content 1392MPa 10％ 0.3％

[0078] The residual austenite content in the central region of the welded joint is 0.3%. Figure 7 The joint strength is 1392 MPa and the elongation is 13%.

[0079] Comparative Example 3:

[0080] Similar to Example 1, except that no austenitic stabilizing elements were added in Comparative Example 1, and quenching and partitioning heat treatment was performed. The results of the joint mechanical property test are as follows:

[0081] tensile strength elongation Residual austenite content 1286MPa 13％ 7％

[0082] The distribution diagram of retained austenite is as follows Figure 6 As shown.

[0083] Comparative Example 5:

[0084] Similar to Example 2, but unlike Example 2, this comparative example did not include any austenitic stabilizing elements and did not undergo quenching and partitioning heat treatment. The joint mechanical property test results are as follows:

[0085] tensile strength elongation Residual austenite content 850MPa 9％ 0.1％

[0086] Comparative Example 6:

[0087] Similar to Example 2, but with an increased carbon content of 2.5%. The mechanical properties of the joint were tested as follows:

[0088] tensile strength elongation Residual austenite content 980MPa 8％ 20％

[0089] Compared with Example 2, increasing the amount of carbon added can effectively increase the content of retained austenite, but the tensile strength and elongation of the joint are reduced. This is mainly because the retained austenite in the joint is too stable and it is difficult to undergo phase transformation during plastic deformation. At the same time, a large amount of cementite is formed inside the joint, which deteriorates the joint performance.

[0090] Comparative Example 7:

[0091] Similar to Example 2, but differing in that this example employs a quenching heat treatment. The heat treatment process is as follows: heating to 800℃, holding for 300 seconds, and then rapidly cooling to room temperature. The joint's mechanical properties are tested as follows:

[0092] tensile strength elongation Residual austenite content 1210MPa 11％ 1.0％

[0093] Comparative Example 8:

[0094] Similar to Example 3, except that no reinforcing particles were added and no heating was performed in the comparative example. The mechanical property test results of the joint are as follows:

[0095] tensile strength elongation Annealing twin content 1190MPa 70％ 9％

[0096] The preferred embodiments described above in conjunction with the accompanying drawings are preferred but not intended to limit the invention. The various specific technical features described above can be combined in any suitable form without contradiction, and this invention will not elaborate on them one by one. Any simple modifications or alterations made by those skilled in the art, such as arbitrary combinations or equivalent substitutions, to the technical solutions without departing from the scope of the technical solutions do not affect the essence of the technical solutions and still fall within the protection scope of the technical solutions represented by the embodiments of this invention.

Claims

1. A welding method of a TRIP effect metastable austenitic steel, characterized in that, The device is used for welding the metastable austenitic steel by friction stir welding, and specifically comprises the following steps: The device is used for welding the metastable austenitic steel by friction stir welding, and specifically comprises the following steps: The austenite stabilizing element is carbon or manganese, and the purity is greater than 99.9%. The particle size of the carbon powder is 10-1000 nm, and the particle size of the manganese powder is 0.2-50 µm. The addition amount of the austenite stabilizing element is 0.5%-3.0%. The heating temperature of the auxiliary heating is 200-800℃, and the rotation speed of the feeding rod (21) is 1.0-100 r / min. The gas pressure in the secondary feeding cavity (12) is 0.4-0.8 MPa, the rotation speed of the stirring head (3) is 200-2000 rpm, and the advancing speed is 10-600 mm / min. The device is used for welding the metastable austenitic steel by friction stir welding, and specifically comprises the following steps:

2. The welding method of TRIP effect metastable austenitic steel according to claim 1, characterized in that, The spiral feeding assembly (2) comprises a feeding bin (22) and a feeding rod (21) which are sequentially arranged from top to bottom.

3. The welding method of TRIP effect metastable austenitic steel according to claim 1 or 2, characterized in that, The stirring head (3) comprises a shaft shoulder (31) and a stirring needle (32) which are connected by a shaft, a main channel (311) is arranged in the shaft shoulder (31) in the axial direction, and a branch channel (321) is arranged in the stirring needle (32).

4. The welding method of TRIP effect metastable austenitic steel according to claim 3, characterized in that, The branch channel (321) has a plurality of branch channels which are arranged in a centrifugal inclined direction.

5. The welding method of the TRIP effect metastable austenitic steel according to claim 3, characterized in that, The outer diameter of the stirring head (3) is 10-15 mm, the inner diameter of the main channel (311) is 3-5 mm, and the inner diameter of the branch channel (321) is 2-3 mm.

6. The welding method of TRIP effect metastable austenitic steel according to claim 1 or 2, characterized in that, The heating assembly (4) is provided with a fixed shell (42), one end of the fixed shell (42) is provided with a mounting head (41), and the fixed shell (42) is sequentially attached with a heat preservation layer (421), a heating pipe (422) and an array type heat dissipation hole (423).

7. The welding method of TRIP effect metastable austenitic steel according to claim 1 or 2, characterized in that, A gas blowing assembly (5) is arranged in communication with the secondary feeding cavity (12), and the gas blowing assembly (5) comprises a gas pump (51) and a gas pipe (52).

8. The welding method of the TRIP effect metastable austenitic steel according to claim 1 or 2, characterized by, The quenching and partitioning heat treatment comprises the following steps: First, heat to 800℃ and keep for 300s; then cool to 260℃ and keep for 60s; finally, heat to 400℃ and keep for 180s, and then cool to room temperature.

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