In-situ observation method for unidirectional solidification of weld metal remelted molten pool and application thereof

Abstract

The present application relates to the technical field of steel welding pool solidification, in particular to a method for in-situ observation of one-way solidification of weld metal remelted pool and application thereof. The method for in-situ observation of one-way solidification of weld metal remelted pool comprises: a container, a round sheet-shaped weld sample and a C-shaped isolator arranged between the weld sample and the container and partially in contact with the weld sample, the isolator is used for isolating heat conduction, a non-contact area is formed between the weld sample and the isolator, a point heat source is used for heating the container, the heating position corresponds to the non-contact area, and the weld sample in the non-contact area is locally melted to form a pool; then the pool is cooled at a cooling rate of 0.05-50 ℃ / s, and the solid-liquid interface solidification process of the pool is photographed. The method simulates the weld pool solidification phenomenon in a two-dimensional plane perspective, provides a new window for one-way solidification observation of the "pool" model, and provides an effective experimental simulation approach.

Description

Technical Field

[0001] This invention relates to the field of steel weld pool solidification technology, and more specifically, to an in-situ observation method for unidirectional solidification of weld metal remelting pool and its application. Background Technology

[0002] For a long time, fusion welding has been a key technology for metallurgical reactive bonding between metals through a molten pool. The quality of the weld largely depends on the solidification structure and properties of the weld pool. However, due to the limitations of high temperature, instantaneous time, and opacity of the weld pool in low-carbon and low-alloy steel welding, research on the formation of solidification defects in weld samples (such as hot cracking and microsegregation) and the control of solidification structure has been slow.

[0003] Although existing technologies have conducted extensive analyses of post-weld weld specimens, made final-state analyses and assumptions about solidification structure and defects, and established relevant models, little is known about their in-situ formation process. This is particularly evident in low-carbon, low-alloy steel weld specimens, where, after the weld specimen undergoes the process of liquid → δ-iron → austenite (γ) → α-ferrite, the room-temperature ferrite structure covers the solidified structure, making it difficult to reveal the solidification morphology of the weld specimen.

[0004] Therefore, there is an urgent need for an in-situ observation method to solve the solidification problem in weld specimens.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide an in-situ observation method for the unidirectional solidification of the weld metal remelting pool. This method, by setting up a micro-melting pool, can simulate the solidification process of the weld pool, including epitaxial growth, transformation from planar crystal to cellular crystal, competitive growth of cellular / columnar dendrites, transformation from columnar crystal to equiaxed crystal, transformation of equiaxed crystal to spheroidal dendrites, and concurrent disturbance of the solidification interface promoted by liquid inclusions. The simulation effect is good and it is beneficial to solve a series of solidification problems in weld samples.

[0007] The second objective of this invention is to provide the application of the in-situ observation method for the unidirectional solidification of the remelted weld metal pool in the preparation of welding materials.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] This invention provides an in-situ observation method for the unidirectional solidification of the remelted weld pool, comprising the following steps:

[0010] The container includes a circular weld sample and a C-shaped spacer placed between the weld sample and the container, which is in partial contact with the weld sample. The spacer is used to isolate heat conduction. The portion of the weld sample that is not in contact with the spacer forms a non-contact area. The container is heated using a point heat source, with the heating position corresponding to the non-contact area, causing the weld sample in the non-contact area to partially melt and form a molten pool. Then, it is cooled at a cooling rate of 0.05℃ / s to 50℃ / s, and the solidification process of the solid-liquid interface of the molten pool is photographed.

[0011] The present invention also provides the application of the in-situ observation method for unidirectional solidification of the remelted weld pool in the preparation of welding materials, wherein the welding materials include at least one of welding wire, welding rod and flux.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] (1) The in-situ observation method for unidirectional solidification of weld metal remelting pool provided by the present invention can simulate the solidification process of the weld pool, such as epitaxial growth, transformation from planar crystal to cellular crystal, competitive growth of cellular / columnar dendrites, transformation from columnar crystal to equiaxed crystal, transformation of equiaxed crystal to spheroidal dendrites, and concurrent disturbance of solidification structure interface promoted by liquid inclusions, by setting up a micro-melting pool. The simulation effect is good and it is helpful to solve a series of solidification problems in weld samples.

[0014] (2) The in-situ observation method for unidirectional solidification of weld metal remelting pool provided by the present invention simulates the solidification phenomenon of weld pool from a two-dimensional plane perspective, providing a "new window" for observing unidirectional solidification of the "pool" model and an effective experimental simulation approach.

[0015] (3) The in-situ observation method for unidirectional solidification of weld metal remelting pool provided by the present invention can realize observation at the micrometer scale. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 An exploded view of the container, weld sample, and separator provided by the present invention;

[0018] Figure 2 A top view of the assembled container, weld specimen, and separator provided by the present invention;

[0019] Figure 3 A cross-sectional view of the welded joint provided by the present invention;

[0020] Figure 4 A top view of another container, weld specimen and separator assembled according to the present invention;

[0021] Figure 5 A top view of another container, weld specimen, and separator assembled according to the present invention;

[0022] Figure 6 A cross-sectional view of yet another welded joint provided by the present invention;

[0023] Figure 7 This is a photograph of the transformation result of cellular crystals to equiaxed crystals in the molten pool provided in Embodiment 1 of the present invention;

[0024] Figure 8 A cross-sectional view of another welded joint provided by the present invention;

[0025] Figure 9 This is a photograph of the results of molten pool epitaxial growth and planar crystal instability provided in Embodiment 2 of the present invention;

[0026] Figure 10 These are photographs of the transformation results from cellular to equiaxed crystals within the molten pool and the peritectic reaction results provided in Embodiment 3 of the present invention; wherein, Figure 10 (a) and Figure 10 (b) represents the transformation from cellular to isometric crystals. Figure 10 (c) shows the peritectic reaction result.

[0027] Figure label:

[0028] 1-Container; 2-Weld specimen; 3-Isolation component; 4-Non-contact area; 5-Observation area. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] In a first aspect, the present invention provides an in-situ observation method for unidirectional solidification of the remelted weld pool, comprising the following steps:

[0031] The container 1 includes a circular weld sample 2 (i.e., a weld metal sample) and a C-shaped spacer 3 disposed between the weld sample 2 and the container 1, and in partial contact with the weld sample 2. See also Figure 1 The diagram shown is an exploded view of container 1, weld specimen 2, and spacer 3. It can be understood that one plane of spacer 3 is in contact with one plane of weld specimen 2, and these two planes are parallel to each other. Because spacer 3 is C-shaped, i.e. has a notch, a portion of weld specimen 2 is in contact with spacer 3, while the other portion of weld specimen 2 is not in contact with spacer 3.

[0032] The insulating element 3 is used to isolate heat conduction. The portion of the weld sample 2 that does not contact the insulating element 3 forms a non-contact area 4. See also... Figure 2 The image shown is a top view of the assembled container 1, weld sample 2, and separator 3.

[0033] A point heat source is used to heat container 1, causing the weld sample 2 inside container 1 to partially melt, thus achieving unidirectional solidification. The heating location corresponds to the non-contact area 4, meaning the heating point is within the range corresponding to the non-contact area 4. Heating causes the weld sample 2 within the non-contact area 4 to partially melt, forming a molten pool (the separator 3 does not melt). The weld sample 2 is then cooled at a rate of 0.05℃ / s to 50℃ / s, and the solid / liquid interface is tracked during cooling, with the solidification process of the molten pool being photographed.

[0034] The metal that makes up the weld is called weld metal, or weld sample 2, which is a component of the metal welded joint.

[0035] The in-situ observation method for unidirectional solidification of weld metal remelting pool provided by this invention, by setting up a micro-melting pool, can simulate the solidification process of the weld pool, including epitaxial growth, transformation from planar crystal to cellular crystal, competitive growth of cellular / columnar dendrites, transformation from columnar crystal to equiaxed crystal, transformation of equiaxed crystal to spheroidal dendrites, and concurrent disturbance of the solidification interface promoted by liquid inclusions. The simulation effect is good, which can further supplement and develop the solidification theory and model proposed in the field of metal welding, and is conducive to solving a series of solidification problems in weld metal.

[0036] This method simulates the solidification phenomenon of weld pool from a two-dimensional plane perspective, providing a new window for observing unidirectional solidification of the "pool" model and an effective experimental simulation approach.

[0037] In a preferred embodiment, the point heat source includes an infrared point heat source.

[0038] In a preferred embodiment, the heating is performed using a high-temperature confocal microscope (also known as a high-temperature confocal infrared furnace).

[0039] In a preferred embodiment, the heating rate is 0.1℃ / s to 5℃ / s, including but not limited to a point value of any one of 0.5℃ / s, 1℃ / s, 2℃ / s, 3℃ / s, and 4℃ / s, or a range between any two.

[0040] In a preferred embodiment, the heating temperature is 1400℃~1540℃, including but not limited to any one of 1420℃, 1440℃, 1450℃, 1480℃, 1500℃, and 1520℃, or a range between any two.

[0041] In a preferred embodiment, the cooling rate is 0.1℃ / s to 30℃ / s, including but not limited to a point value or a range between any one of 0.5℃ / s, 1℃ / s, 2℃ / s, 3℃ / s, 5℃ / s, 10℃ / s, 15℃ / s, 20℃ / s, and 25℃ / s. If the cooling rate is too fast, the solidification process at the solid-liquid interface cannot be captured.

[0042] In a preferred embodiment, the cooling method includes air cooling.

[0043] In a preferred embodiment, see Figure 2 The weld sample 2 has a circular cross-section, and the spacer 3 has a fan-shaped cross-section. The central angle subtended by the fan-shaped ring is between 240° and 300°, including but not limited to a point value of any one of 250°, 260°, 270°, 280°, or 290°, or a range between any two. If the central angle subtended by the fan-shaped ring is too small, liquid surface collapse may occur, affecting observation.

[0044] In a preferred embodiment, the difference between the diameter of the circle and the outer diameter of the fan ring is ≤0.2mm, that is, the difference between the diameter of the cross-section of the weld sample 2 and the outer diameter of the fan ring is ≤0.2mm, including but not limited to any one of 0.18mm, 0.15mm, 0.10mm, 0.08mm, 0.06mm, 0.05mm, 0.03mm, 0.01mm, 0mm or any range between two of them.

[0045] It is understandable that the weld sample 2 is in the shape of a thin circular sheet, the spacer 3 is in the shape of a C, and the cross-sectional shape of the spacer 3 is a fan ring. A fan ring is the shape formed by cutting a part of a circular ring into a fan shape. The fan ring has an outer circle and an inner circle. The outer circle diameter mentioned above refers to the diameter of the outer circle of the fan ring (i.e., the larger diameter, which is also twice the distance from the outer circle to the center).

[0046] In a preferred embodiment, the thickness of the weld sample 2 is 1 mm to 2 mm, including but not limited to point values ​​or ranges between any two of 1.2 mm, 1.4 mm, 1.5 mm, 1.7 mm, and 1.9 mm. Weld samples 2 with the above thickness range are relatively thin, which can eliminate the influence of the longitudinal temperature gradient, ensuring that the weld sample 2 has a temperature difference only in the diametrical direction for solidification.

[0047] The thickness of the separator 3 is 0.5mm to 1.5mm, including but not limited to any one of 0.7mm, 0.9mm, 1.0mm, 1.2mm, and 1.4mm, or any range between two of them.

[0048] Using this thickness range helps to isolate the heat conduction at the bottom of the crucible, thereby achieving local melting of the weld sample 2 and forming a molten pool.

[0049] In a preferred embodiment, the diameter of the cross-section of the weld sample 2 is 5mm to 8mm, including but not limited to point values ​​of any one of 5.5mm, 6mm, 6.5mm, 7mm, and 7.5mm, or a range between any two.

[0050] In a preferred embodiment, the inner diameter of the crucible is 5mm to 8.5mm, including but not limited to any one of 5.5mm, 6mm, 7mm, and 8mm, or a range between any two. The height of the crucible is 3mm to 5.5mm, including but not limited to any one of 3.5mm, 4mm, 4.5mm, and 5mm, or a range between any two. The wall thickness of the crucible is 1.5mm to 2.5mm, including but not limited to any one of 1.7mm, 1.9mm, 2.0mm, 2.2mm, and 2.4mm, or a range between any two.

[0051] In a preferred embodiment, the weld sample 2 comprises at least one of low-carbon low-alloy steel, titanium alloy, copper alloy, aluminum alloy, and nickel-based alloy.

[0052] In a preferred embodiment, the material of the separator 3 includes alumina. Alumina has good high-temperature resistance and low cost.

[0053] In a preferred embodiment, the container 1 includes a crucible.

[0054] In a preferred embodiment, the crucible includes at least one of a magnesium oxide crucible and an alumina crucible; both magnesium oxide and alumina crucibles have good high-temperature resistance.

[0055] In a preferred embodiment, the inner wall of the crucible is provided with a rare earth oxide coating.

[0056] When weld sample 2 is at least one of titanium alloy, copper alloy, aluminum alloy, and nickel-based alloy, there is a phenomenon where the alloy melts and extends upwards and climbs along the wall of container 1, which affects the observation. The present invention can effectively solve the above problem by coating a layer of rare earth oxide on the inner wall of container 1, and avoid the phenomenon where at least one of titanium alloy, copper alloy, aluminum alloy, and nickel-based alloy melts and extends upwards and climbs along the wall of container 1.

[0057] When weld sample 2 is made of low-carbon low-alloy steel, the above-mentioned problem does not exist, so the rare earth oxide coating does not need to be applied to the inner wall of the crucible.

[0058] In a preferred embodiment, the rare earth oxide coating includes at least one of a cerium oxide coating and a yttrium oxide coating.

[0059] In a preferred embodiment, the imaging is performed using a high-temperature confocal microscope.

[0060] Using the above-mentioned in-situ observation method and taking pictures with a high-temperature confocal microscope, observations at the micrometer scale can be achieved.

[0061] In a preferred embodiment, the shooting is performed at a rate of 5 to 15 frames per second, including but not limited to point values ​​of any one of 7, 9, 10, 12, or 14 frames per second, or a range between any two. Shooting at this rate can capture the solidification process at the solid-liquid interface.

[0062] In a preferred embodiment, the solid-liquid interface solidification process includes at least one of the following: solid / liquid interface epitaxial growth, cellular / columnar dendritic competitive growth, planar crystal to cellular crystal transformation, columnar crystal to equiaxed crystal transformation, equiaxed crystal spheroidal dendrite transformation, and interaction between liquid inclusions and solidified structure.

[0063] In a preferred embodiment, the weld specimen 2 is pre-processed to a preset size before use (observation). The preset size preferably matches the shape and size of the container 1.

[0064] like Figure 3 The diagram shows a cross-sectional view of the welded joint, which forms a columnar crystal region (i.e., the weld zone) and an equiaxed crystal region (i.e., the heat-affected zone). In a preferred embodiment, the sampling location of the weld sample 2 includes at least one of the columnar crystal region (i.e., the weld zone) and the equiaxed crystal region (i.e., the heat-affected zone), more preferably including both the columnar crystal region (i.e., the weld zone) and the equiaxed crystal region (i.e., the heat-affected zone). A suitable sampling location is beneficial for targeted observation and study of experimental phenomena, such as observing epitaxial growth at the solid / liquid interface, competitive growth of cellular / columnar dendrites, transformation from planar crystals to cellular crystals, transformation from columnar crystals to equiaxed crystals, and transformation of equiaxed crystals into spheroidal dendrites.

[0065] In a preferred embodiment, after being processed to a preset size, the weld sample 2 is further subjected to sanding, polishing, and cleaning in sequence. Sanding is performed using sandpaper, and cleaning is done using ethanol. During polishing, all surfaces of the weld sample 2 are polished to a mirror finish.

[0066] Through the above-mentioned sanding, polishing and cleaning processes, the interference of foreign impurities on the experimental phenomena can be eliminated as much as possible, ensuring the best experimental observation results.

[0067] In a preferred embodiment, the sanding, polishing, and cleaning process specifically includes: first, grinding the sides, top and bottom surfaces of the weld sample 2 sequentially with 800#, 1000#, 1200#, 1500#, 2000#, 3000#, and 5000# sandpaper; then, hot-mounting the weld sample 2 to a thickness equal to the sample thickness; then, fine polishing with 0.05μm diamond polishing spray and ethanol, ensuring no visible scratches or contaminants under 1000x metallographic microscopy; measuring the sample dimensions with a thickness gauge; and finally, ultrasonic cleaning with ethanol for at least 10 minutes.

[0068] In a preferred embodiment, the heating location is at a distance of 1 / 2 radius from the center point of the cross-section of the weld sample 2.

[0069] More preferably, the non-contact area 4 is fan-shaped, and the heating position is the location of the geometric center point (or centroid) of this fan shape. See [link to relevant documentation]. Figure 4 As shown.

[0070] In a preferred embodiment, the melting process tracks the solid / liquid interface, and the boundary of the formed molten pool does not exceed 1 / 2 of the cross-sectional diameter of the weld sample 2. That is, the melting position of the weld sample 2 is controlled within a fan-shaped area with a radius of 1 / 2 of the cross-sectional diameter of the weld sample 2, so as to avoid the molten pool boundary exceeding 1 / 2, which would cause the solid-liquid interface to be unclear during the observation process due to the surface tension generated by the large-area melting. In other words, it ensures that the unmelted solid achieves greater heat conduction and supercooling during the cooling process, which is beneficial to the unidirectional solidification of the molten pool.

[0071] In a preferred embodiment, before heating, the center of the weld sample 2 is marked with a microhardness indentation to determine the melting boundary of the molten pool and mark the melting position. Heating is stopped after the solid / liquid interface melts and contacts the microindentation.

[0072] The portion of the weld sample 2 that does not contact the spacer 3 forms a non-contact zone 4, while the portion of the weld sample 2 that contacts the spacer 3 forms a contact zone. In a preferred embodiment, an observation zone 5 is provided for easy observation, and the solidification process of the solid-liquid interface of the molten pool is photographed within the observation zone 5. Figure 5As shown, the observation area 5 is located at the junction of the non-contact area 4 and the non-contact area 4, and the distance between the observation area 5 and the center point of the cross-section of the weld specimen 2 is 1 / 2 of the radius of the cross-section of the weld specimen 2.

[0073] Secondly, the present invention provides the application of the in-situ observation method for unidirectional solidification of the weld metal remelting pool in the preparation of welding materials, wherein the welding materials include at least one of welding wire, welding rod and flux.

[0074] By simulating and observing the solid-liquid interface solidification process experienced by the weld pool, including epitaxial growth, transformation from planar crystals to cellular crystals, competitive growth of cellular / columnar dendrites, transformation from columnar crystals to equiaxed crystals, transformation of equiaxed crystals to spheroidal dendrites, and liquid inclusions promoting solidification and concurrent disturbance of the solidification interface, a series of solidification problems in weld sample 2 can be solved, thereby obtaining welding materials with better performance.

[0075] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0076] Example 1

[0077] This embodiment provides an in-situ observation method for the unidirectional solidification of the remelted weld pool in low-carbon low-alloy steel welds, comprising the following steps:

[0078] Step (1): Process the sample to the preset size; take a circular sample with a diameter of 8.2 mm and a thickness of 2.2 mm from the cross-section of the weld metal of EH36 ship plate steel, at the boundary between the columnar region and the equiaxial region. See the sampling area for details. Figure 6 As shown, the following treatment was performed: The sides and top and bottom surfaces of weld sample 2 were successively polished with 800#, 1000#, 1200#, 1500#, 2000#, 3000# and 5000# sandpaper. Then, weld sample 2 was hot-mounted with an inlay thickness equal to the sample thickness. After that, it was finely polished with 0.05μm diamond polishing spray and ethanol. Under a metallographic microscope at 1000x magnification, there were no visible scratches or contaminants. A thickness gauge was used to ensure the sample size. The treated sample size was ensured to be 8mm in diameter and 2mm in thickness. Finally, it was ultrasonically cleaned twice for 10 minutes each time.

[0079] Step (2), Assembly of Weld Specimen 2 and Matching Crucible: Place the circular weld specimen 2 obtained in step (1) into an alumina crucible with an inner diameter of 8.1 mm, an outer diameter of 9.1 mm, a height of 4.5 mm, and a bottom wall thickness of 1.0 mm. Place a C-shaped alumina spacer 3 at the bottom of the crucible and at the lower end of the weld specimen 2 to insulate against heat conduction. The spacer 3 contacts a portion of the weld specimen 2 to form a contact area, and the portion of the weld specimen 2 that does not contact the spacer 3 forms a non-contact area 4. The cross-sectional shape of the weld specimen 2 is circular, and the cross-sectional shape of the spacer 3 is a fan ring. The central angle subtended by the fan ring is 240°, the outer diameter of the fan ring is 8 mm, the inner diameter is 6 mm, and the thickness is 1 mm.

[0080] Step (3): Place the assembled crucible-isolation component 3-weld sample 2 on the alumina support of the high-temperature confocal infrared furnace. Mark the center of the weld sample 2 with a microhardness indentation, and then heat it to 1500℃ at a heating rate of 3℃ / s. See Figure 4 The non-contact area 4 is fan-shaped, and the heating position is located at the geometric center of this fan. After heating, the weld sample 2 in the non-contact area 4 undergoes localized melting, forming a molten pool. Heating is stopped after the solid / liquid interface melts and contacts the micro-indentation, and cooling is performed at a rate of 0.3℃ / s (air cooling). Simultaneously, high-speed imaging using a high-temperature confocal microscope is used to capture snapshots at 10 frames / s of the solidification process from vesicular crystals to equiaxed crystals within the observation area 5. The observation area 5 is located at the boundary between the non-contact area 4 and the non-contact area 4, and the distance between the observation area 5 and the center point of the cross-section of the weld sample 2 is half the radius of the cross-section of the weld sample 2. The location of the observation area 5 can be found in [reference needed]. Figure 5 As shown.

[0081] See Figure 7 As shown, this represents the real-time solidification transformation from cellular to equiaxed grains in the remelted pool of the weld metal sample in this embodiment. Figure 7 It can be seen that as the temperature decreases, equiaxed crystals continuously nucleate and grow, completing the transformation from cellular crystals to equiaxed crystals.

[0082] Example 2

[0083] This embodiment provides an in-situ observation method for the unidirectional solidification of the remelted weld pool in low-carbon low-alloy steel welds, comprising the following steps:

[0084] Step (1): Process a sample of the preset size; take a circular sample with a diameter of 8.2 mm and a thickness of 2.2 mm from the fusion line area of ​​the weld metal cross-section of EH36 ship plate steel. See the sampling area for details. Figure 8As shown, the following treatment was performed: The sides and top and bottom surfaces of weld sample 2 were successively polished with 800#, 1000#, 1200#, 1500#, 2000#, 3000# and 5000# sandpaper. Then, weld sample 2 was hot-mounted with an inlay thickness equal to the sample thickness. After that, it was finely polished with 0.05μm diamond polishing spray and ethanol. Under a metallographic microscope at 1000x magnification, there were no visible scratches or contaminants. A thickness gauge was used to ensure the sample size. The treated sample size was ensured to be 8mm in diameter and 2mm in thickness. Finally, it was ultrasonically cleaned twice for 10 minutes each time.

[0085] Step (2), Assembly of Weld Specimen 2 and Matching Crucible: Place the circular weld specimen 2 obtained in step (1) into an alumina crucible with an inner diameter of 8.1 mm, an outer diameter of 9.1 mm, a height of 4.5 mm, and a bottom wall thickness of 1.0 mm. Place a C-shaped alumina spacer 3 at the bottom of the crucible and at the lower end of the weld specimen 2 to insulate against heat conduction. The spacer 3 contacts a portion of the weld specimen 2 to form a contact area, and the portion of the weld specimen 2 that does not contact the spacer 3 forms a non-contact area 4. The cross-sectional shape of the weld specimen 2 is circular, and the cross-sectional shape of the spacer 3 is a fan ring. The central angle subtended by the fan ring is 240°, the outer diameter of the fan ring is 8 mm, the inner diameter is 6 mm, and the thickness is 1 mm.

[0086] Step (3): Place the assembled crucible-isolation component 3-weld sample 2 on the alumina support of the high-temperature confocal infrared furnace. Mark the center of the weld sample 2 with a microhardness indentation, and then heat it to 1400℃ at a heating rate of 4℃ / s. See also Figure 4 The non-contact area 4 is fan-shaped, and the heating point is located at the geometric center of this fan. After heating, the weld sample 2 in the non-contact area 4 undergoes localized melting, forming a molten pool. Heating is stopped after the solid / liquid interface melts and contacts the micro-indentation, and cooling is performed at a rate of 3℃ / s (air cooling). Simultaneously, high-speed imaging using a high-temperature confocal microscope is employed in the observation area 5 to capture snapshots of the solidification process from vesicular crystals to equiaxed crystals at 10 frames / s. The observation area 5 is located at the boundary between the non-contact area 4 and the non-contact area 4, and the distance between the observation area 5 and the center point of the cross-section of the weld sample 2 is half the radius of the cross-section of the weld sample 2. The location of the observation area 5 can be found in [reference needed]. Figure 5 As shown.

[0087] See Figure 9 The image shows the epitaxial growth of the remelted pool and the instability of planar grains in the weld metal sample of this embodiment. The instability of planar grain growth at the grain boundary triangular points in the molten steel pool was observed. Figure 9 The results validated the Mullins-Sekerka interface instability model.

[0088] Example 3

[0089] The in-situ observation method for unidirectional solidification of the remelted weld pool of low-carbon low-alloy steel weld metal provided in this embodiment includes the following steps:

[0090] Step (1): Process the sample to the preset size; take a circular sample with a diameter of 8.2 mm and a thickness of 2.2 mm from the cross-section of the weld metal of EH36 ship plate steel, at the boundary between the columnar region and the equiaxial region. See the sampling area for details. Figure 6 As shown, the following treatment was performed: The sides and top and bottom surfaces of weld sample 2 were successively polished with 800#, 1000#, 1200#, 1500#, 2000#, 3000# and 5000# sandpaper. Then, weld sample 2 was hot-mounted with an inlay thickness equal to the sample thickness. After that, it was finely polished with 0.05μm diamond polishing spray and ethanol. Under a metallographic microscope at 1000x magnification, there were no visible scratches or contaminants. A thickness gauge was used to ensure the sample size. The treated sample size was ensured to be 8mm in diameter and 2mm in thickness. Finally, it was ultrasonically cleaned twice for 10 minutes each time.

[0091] Step (2), Assembly of Weld Specimen 2 and Matching Crucible: Place the circular weld specimen 2 obtained in step (1) into an alumina crucible with an inner diameter of 8.1 mm, an outer diameter of 9.1 mm, a height of 4.5 mm, and a bottom wall thickness of 1.0 mm. Place a C-shaped alumina spacer 3 at the bottom of the crucible and at the lower end of the weld specimen 2 to insulate against heat conduction. The spacer 3 contacts a portion of the weld specimen 2 to form a contact area, and the portion of the weld specimen 2 that does not contact the spacer 3 forms a non-contact area 4. The cross-sectional shape of the weld specimen 2 is circular, and the cross-sectional shape of the spacer 3 is a fan ring. The central angle subtended by the fan ring is 240°, the outer diameter of the fan ring is 8 mm, the inner diameter is 6 mm, and the thickness is 1 mm.

[0092] Step (3): Place the assembled crucible-isolation component 3-weld sample 2 on the alumina support of the high-temperature confocal infrared furnace. Mark the center of the weld sample 2 with a microhardness indentation, and then heat it to 1540℃ at a heating rate of 5℃ / s. See Figure 4 The non-contact area 4 is fan-shaped, and the heating position is located at the geometric center of this fan. After heating, the weld sample 2 in the non-contact area 4 undergoes localized melting, forming a molten pool. Heating is stopped after the solid / liquid interface melts and contacts the micro-indentation, and cooling is performed at a rate of 0.3℃ / s (air cooling). Simultaneously, high-speed imaging using a high-temperature confocal microscope is used to capture snapshots at 10 frames / s of the solidification process from vesicular crystals to equiaxed crystals within the observation area 5. The observation area 5 is located at the boundary between the non-contact area 4 and the non-contact area 4, and the distance between the observation area 5 and the center point of the cross-section of the weld sample 2 is half the radius of the cross-section of the weld sample 2. The location of the observation area 5 can be found in [reference needed]. Figure 5 As shown.

[0093] See Figure 10 The image shows the results of the real-time solidification transformation from cellular to equiaxed grains in the remelted pool of the weld metal sample in this embodiment, as well as the peritectic reaction results. The results of the transformation from cellular to equiaxed grains are shown in [reference needed]. Figure 10 (a) and Figure 10 (b) shows the peritectic reaction results. Figure 10 As shown in (c).

[0094] As can be seen from the above embodiments 1, 2 and 3, the in-situ test method for unidirectional solidification of weld metal remelting pool provided by the present invention realizes in-situ observation of solidification phenomenon, with significant effect and easy implementation.

[0095] Comparative Example 1

[0096] The in-situ observation method for the unidirectional solidification of the remelted weld pool of low-carbon low-alloy steel weld metal provided in this comparative example is basically the same as that in Example 1, except that no isolation element is set.

[0097] In this comparative example, the crystal growth during the solidification process could not be observed because the cooling rate was too fast, and the crystal growth was completed before it could be photographed.

[0098] Comparative Example 2

[0099] The in-situ observation method for the unidirectional solidification of the remelted weld pool of low-carbon low-alloy steel weld metal provided in this comparative example is basically the same as that in Example 1, except that the shape of the isolation element is a closed ring.

[0100] Crystal growth during solidification could not be observed in this comparative example because the molten pool was too large, making it difficult to locate the solid-liquid interface.

[0101] Comparative Example 3

[0102] The in-situ observation method for the unidirectional solidification of the remelted weld pool of low-carbon low-alloy steel weld metal provided in this comparative example is basically the same as that in Example 1, except that the cooling rate is replaced with 60°C / s.

[0103] In this comparative example, crystal growth during the solidification process could not be observed because no gasket was placed for heat insulation, causing the entire sample to melt.

[0104] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. An in-situ observation method for unidirectional solidification of the weld metal remelting pool, characterized in that, Includes the following steps: The container includes a circular weld sample and a C-shaped spacer positioned between the weld sample and the container, partially in contact with the weld sample. The weld sample's inner diameter and shape match the container's opening. The C-shaped spacer is placed below the weld sample within the container to insulate against heat conduction. The portion of the weld sample in contact with the spacer forms a contact area, while the portion not in contact with the spacer forms a non-contact area. The container is heated using a point heat source, with the heating position corresponding to the non-contact area, causing localized melting of the weld sample within the non-contact area to form a molten pool. The container is then cooled at a rate of 0.05℃ / s to 50℃ / s, and the solidification process of the molten pool's solid-liquid interface is photographed. The weld sample has a circular cross-section, and the spacer has a fan-shaped cross-section. The difference between the diameter of the weld sample's cross-section and the outer diameter of the fan-shaped cross-section is ≤0.2mm.

2. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The point heat source includes an infrared point heat source; And / or, the heating temperature is 1400℃~1540℃.

3. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The cooling rate is 0.1℃ / s to 30℃ / s.

4. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The central angle subtended by the fan ring is 240°~300°. And / or, the thickness of the weld sample is 1mm to 2mm, and the thickness of the separator is 0.5mm to 1.5mm.

5. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The weld samples include at least one of low-carbon low-alloy steel, titanium alloy, copper alloy, aluminum alloy and nickel-based alloy; And / or, the material of the separator includes aluminum oxide.

6. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The container includes a crucible.

7. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 6, characterized in that, The crucible includes a magnesium oxide crucible or an aluminum oxide crucible; And / or, the inner wall of the crucible is provided with a rare earth oxide coating.

8. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The imaging was performed using a high-temperature confocal microscope. And / or, the shooting is performed at a rate of 5 frames / s to 15 frames / s.

9. The in-situ observation method for unidirectional solidification of the weld metal remelting pool according to claim 1, characterized in that, The solid-liquid interface solidification process includes at least one of the following: solid / liquid interface epitaxial growth, cellular / columnar dendritic competitive growth, planar crystal to cellular crystal transformation, columnar crystal to equiaxed crystal transformation, equiaxed crystal spheroidal dendrite transformation, and interaction between liquid inclusions and solidified structures.

10. The application of the in-situ observation method for unidirectional solidification of the weld metal remelting pool as described in any one of claims 1 to 9 in the preparation of welding materials, characterized in that, The welding materials include at least one of welding wire, welding rod, and flux.

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