Process for repairing subsurface cracks of continuous casting billet through online surface micro-melting

Abstract

The process comprises the following steps: S1, crack detection: scanning the surface of a casting blank by adopting an infrared thermal imager, setting a temperature difference threshold value to be greater than or equal to 10 DEG C so as to identify the crack, generating a three-dimensional thermal field distribution diagram, and marking the depth, length and distribution density of the crack; s2, laser micro-melting repair is conducted, specifically, a mechanical arm is adopted to control a laser head, and according to path planning, spiral scanning or a Z-shaped track is adopted to conduct remelting on a crack area according to set parameters; s3, post-treatment and quality inspection are conducted, specifically, a repairing area is air-cooled to 200 DEG C or below, and residual stress accumulation is avoided; and then ultrasonic flaw detection and metallographic detection are conducted, the crack elimination rate and the structure uniformity are verified, it is ensured that the crack elimination rate is larger than or equal to 98%, and the depth of a heat affected zone is smaller than or equal to 0.2 mm. Subcutaneous cracks are accurately positioned through the thermal infrared imager, micro-area remelting is carried out on a defect area in combination with the movable optical fiber laser head, the cracks can be efficiently eliminated, meanwhile, the original structure performance of a casting blank is kept, and the yield of the continuous casting blank is remarkably increased.

Description

Technical Field

[0001] This invention relates to the field of metallurgical continuous casting technology, and in particular to a process for repairing subcutaneous cracks on the surface of continuously cast billets via online micro-melting. Background Technology

[0002] Subcutaneous cracks in continuously cast billets are one of the core defects that lead to the scrapping of steel. Traditional crack repair techniques have the following problems: (1) Low positioning accuracy: relying on manual visual inspection or ultrasonic testing, the missed detection rate is ≥15%, and real-time feedback is not possible; (2) Poor repair effect: flame welding or arc repair easily introduces the heat-affected zone (HAZ), resulting in grain coarsening (grain size decreases by 1~2 levels); (3) Efficiency bottleneck: repair speed ≤0.5m / min, which cannot match the production rhythm of the continuous casting production line; (4) Excessive heat-affected zone: flame welding or arc repair leads to coarsening of matrix grains (grain size decreases by 1~2 levels); (5) Poor adaptability: the input energy of the existing laser repair process is too high (≥8kW), which easily causes austenitization of the matrix; the infrared detection technology is not linked with the repair system, and the positioning error is >2mm; (6) Technical bottleneck: lack of integrated process of dynamic thermal field control and laser energy matching, making it difficult to balance repair efficiency and preservation of microstructure properties. In conclusion, existing repair techniques struggle to balance efficiency with the preservation of tissue properties, leaving room for further improvement and refinement. Summary of the Invention

[0003] To address the aforementioned problems, the present invention aims to provide a process for online surface micro-melting repair of subcutaneous cracks in continuously cast billets. This process uses an infrared thermal imager to precisely locate subcutaneous cracks and combines a mobile fiber laser head to perform micro-area remelting on the defective area, achieving efficient crack elimination (repair speed ≥3m / min) while maintaining the original microstructure and properties of the billet, thus significantly improving the yield of continuously cast billets.

[0004] The technical solution adopted in this invention is as follows: The present invention proposes a process for repairing subcutaneous cracks on the surface of continuously cast billets via online micro-melting, which specifically includes the following steps: S1. Crack detection: The surface of the billet is scanned with an infrared thermal imager, and a temperature difference threshold of ≥10℃ is set to identify cracks, generate a three-dimensional thermal field distribution map, and mark the crack depth, length and distribution density. S2. Laser micro-melting repair: A robotic arm controls the laser head, and the path planning uses spiral scanning or zigzag trajectory to remelt the cracked area according to the set parameters. S3. Post-processing and quality inspection: The repaired area is air-cooled to below 200℃ to avoid residual stress accumulation; then ultrasonic flaw detection and metallographic inspection are carried out to verify the crack elimination rate and the uniformity of the structure, ensuring that the crack elimination rate is ≥98% and the depth of the heat-affected zone is ≤0.2mm.

[0005] Furthermore, the infrared thermal imager has a depth resolution of ≤0.1mm and a positioning accuracy of ±0.5mm.

[0006] Furthermore, the laser source of the laser head is an IPG fiber laser with a power of 2~5kW, a scanning speed of 2.5~4m / min, an overlap rate of 20%~40%, a spot diameter of 0.2~1.0mm, a repair speed of ≥3m / min, and a single repair depth coverage of 0.1~2.0mm.

[0007] Furthermore, step S2 is performed under argon protection to form a dense cladding layer in the crack area, with the depth of the molten pool controlled to be 1.2 to 1.5 times the crack depth to ensure complete crack filling.

[0008] Furthermore, the argon flow rate is 10~20L / min, and the oxygen content is ≤100ppm.

[0009] Furthermore, in step S2, when the path planning uses helical scanning, the pitch is 0.2~0.5mm.

[0010] Compared with the prior art, the present invention has the following advantages: 1. Precise positioning: Infrared thermal imager detects subcutaneous cracks in real time (depth resolution ≤0.1mm), with positioning accuracy ±0.5mm; 2. High-efficiency repair: The mobile laser head has a repair speed of ≥3m / min, and the repair depth in a single operation covers 0.1~2.0mm; 3. Performance retention: Heat-affected zone depth ≤ 0.2 mm, matrix grain size change ≤ 0.5 grade; 4. Versatility of process: Covers various materials such as carbon steel, alloy steel, and stainless steel; 5. Quality Assurance: Hardness fluctuation in the repaired area is ≤5%, and there is no obvious interface with the original substrate; 6. Environmental friendliness: No smoke or dust emissions, argon recovery rate ≥90%. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the process for repairing subcutaneous cracks on the surface of a continuously cast billet using online micro-melting, as proposed in this invention. Detailed Implementation

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the 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 based on these drawings without creative effort.

[0013] See appendix Figure 1 The present invention proposes a process for repairing subcutaneous cracks on the surface of continuously cast billets via online micro-melting, which specifically includes the following steps: S1. Crack Detection: An infrared thermal imager is used to scan the surface of the cast billet, and a temperature difference threshold of ≥10℃ is set to identify cracks. The detector of the infrared thermal imager is an uncooled microbolometer array (resolution 640×480), with a temperature range of 200~1500℃ and an accuracy of ±1℃. Cracks are identified based on the temperature difference threshold and morphological analysis, and a three-dimensional thermal field distribution map is generated, marking the crack depth (0.1~2.0mm), length (5~200mm), and distribution density. The infrared thermal imager has a depth resolution of ≤0.1mm and a positioning accuracy of ±0.5mm. S2. Laser micro-melting repair: A six-axis robotic arm controls the laser head, and the path planning adopts spiral scanning (pitch of 0.2~0.5mm) or zigzag trajectory to remelt the cracked area according to the set parameters; The laser head is a fiber laser head, the laser source of which is an IPG fiber laser with a power of 2~5kW, a scanning speed of 2.5~4m / min, an overlap rate of 20%~40%, a spot diameter of 0.2~1.0mm, a repair speed of ≥3m / min, and a single repair depth coverage of 0.1~2.0mm. The repair process is carried out under the protection of an inert gas (argon) to prevent oxidation of the molten pool and to form a dense cladding layer in the crack area. The depth of the molten pool is controlled to be 1.2 to 1.5 times the crack depth to ensure complete crack filling. The inert gas flow rate is 10 to 20 L / min, and the oxygen content is ≤100 ppm. S3. Post-processing and Quality Inspection: The repaired area is air-cooled to below 200℃ to avoid residual stress accumulation; then ultrasonic testing (frequency 5MHz) and metallographic inspection are performed to verify the crack elimination rate and microstructure uniformity, ensuring that the crack elimination rate is ≥98%; metallographic inspection is performed to check the depth and grain size changes of the heat-affected zone, ensuring that the depth of the heat-affected zone is ≤0.2mm. If the results are satisfactory, proceed to the next process; otherwise, return to step S1.

[0014] A high-speed CCD (5000fps) is used in conjunction with a spectrometer to monitor the restoration quality in real time.

[0015] The core of this invention is to solve the pain points of traditional continuous casting billet crack repair—namely, "inaccurate positioning, low efficiency, large heat-affected zone, and poor performance"—through an integrated process of "precise thermal field detection, micro-area energy regulation, and closed-loop quality assurance," from the perspectives of physical mechanisms, material metallurgical properties, and equipment synergy. Its working principle is explained in detail in three stages as follows: I. The core principle of precise positioning with infrared thermal imagers: thermal field difference recognition and 3D modeling; Traditional manual visual inspection / conventional ultrasonic testing has a missed rate of ≥15% and cannot provide real-time feedback on crack depth / distribution; while existing infrared detection is not linked to the repair system, resulting in a positioning error of >2mm, which cannot guide precise repair.

[0016] Subsurface cracks in continuously cast billets are classified as "interface defects," with an air / oxide layer inside the crack. The thermal conductivity of this layer is approximately 0.026 W / (m²). K) is much lower than that of the billet matrix (carbon steel ≈ 45W / (m) When the billet is in a high-temperature state (200~1500℃, matching the temperature measurement range of an infrared thermal imager), the crack area will form a local "low-temperature zone" due to the obstruction of heat conduction, and a stable temperature difference will be generated between it and the surrounding matrix.

[0017] This invention achieves precise positioning through the following design: The temperature difference threshold of ≥10℃ is set based on the following: extensive experimental verification shows that the temperature difference between the subsurface crack (depth ≥0.1mm) and the matrix of the continuously cast billet is consistently ≥10℃ (the deeper the crack, the greater the temperature difference). This threshold can avoid misjudgment caused by environmental interference (such as surface oxide scale) and ensure that the crack identification accuracy rate is ≥99%. The physical basis of high-resolution detection: An uncooled microbolometer array (640×480 resolution) is used, with its pixel size corresponding to a 0.1mm×0.1mm area on the surface of the billet. Combined with the thermal field gradient algorithm, a three-dimensional thermal field distribution map can be generated. The crack length is marked by the "abrupt boundary" of the temperature difference gradient, and the crack depth is inferred from the absolute value of the temperature difference (the crack depth increases by about 0.5mm for every 5℃ increase in temperature difference). Finally, a depth resolution of ≤0.1mm and a positioning accuracy of ±0.5mm are achieved. Linkage logic with the repair system: Three-dimensional thermal field data is directly transmitted to the six-axis robotic arm control system, providing precise coordinates for the "path planning" and "energy matching" of subsequent laser repair (e.g., when the crack depth is 0.8mm, the system automatically sets the melt pool depth to 1.0mm), avoiding energy waste or incomplete repair caused by traditional "blind repair".

[0018] II. Micro-area control principle of low-power fiber laser + inert protection: melting only cracks without damaging the substrate; Traditional flame / arc repair has dispersed input energy, resulting in a heat-affected zone (HAZ) depth of ≥1mm, which leads to 1-2 grade coarsening of the matrix grains. Existing laser repair has a power of ≥8kW, and the excessive energy causes austenitization of the matrix, destroying the original microstructure and properties. The repair speed is ≤0.5m / min, which cannot match the rhythm of continuous casting production lines.

[0019] The "micro-fusion" mechanism of low-power IPG fiber lasers (core invention point: precise energy matching). This invention utilizes the high energy density characteristics of IPG fiber lasers (2~5kW power corresponds to an energy density of 104~105W / mm2) to achieve "local micro-area remelting": The basis for the power range of 2~5kW is as follows: When the laser acts on the crack area, this power can make the metal at the crack (melting point 1450~1550℃) quickly reach the melting state. However, since the energy only acts on a depth of 0.1~2.0mm (single repair depth), the temperature of the deep layer of the matrix (>0.2mm) is always lower than the Ac1 phase transformation point (carbon steel ≈727℃), avoiding grain coarsening. Experiments have verified that the grain size change of the matrix under this power is ≤0.5 grade, which is far superior to the traditional process. Synergy between scanning speed and spot diameter: A scanning speed of 2.5~4m / min combined with a spot diameter of 0.2~1.0mm can control the "thermal treatment time"—ensuring that the cracked metal is fully melted to fill the defect, while avoiding heat diffusion to the matrix: For example, when the spot diameter is 0.5mm and the speed is 3.2m / min, the thermal treatment time is ≈0.01s, and the depth of the heat-affected zone is ≤0.2mm; The logic behind improved repair efficiency: The six-axis robotic arm's motion precision (±0.05mm) combined with the spiral / Z-shaped trajectory enables "non-repetitive, full-coverage" scanning. Spiral scanning (pitch 0.2~0.5mm) is suitable for point-like / small-area cracks, while the Z-shaped trajectory is suitable for long strip-like cracks. Neither path requires machine downtime for adjustment, resulting in a final repair speed of ≥3m / min, which is more than 6 times that of traditional processes.

[0020] Anti-oxidation principle: Argon gas (flow rate 10~20L / min) forms an "inert atmosphere barrier" in the crack area with an oxygen content ≤100ppm, which can prevent the molten metal from reacting with O2 and N2 in the air to generate oxide inclusions (such as FeO and MnO) - Experimental verification shows that under this protection, the oxygen content of the cladding layer is ≤0.005%, with no pores or inclusions; The principle of molten pool depth control (1.2~1.5 times the crack depth): Under the pressure of argon gas, the molten metal can fully fill the crack gap, and the excessive melting depth (1.2~1.5 times) can cover the "stress concentration zone" at the crack tip, avoiding crack recurrence after repair. For example, when the crack depth is 0.8mm, the molten pool depth is 0.96mm, which can completely wrap the crack tip and eliminate stress concentration.

[0021] "Adaptive" design of path planning (core invention point: dynamic process matching) Spiral scanning pitch 0.2~0.5mm: The pitch matches the spot diameter (0.2~1.0mm) to ensure an overlap rate of 20%~40% between adjacent scanning trajectories, with no blind spots for repair; Variable power scanning (as in Example 4): For dense network cracks (depth 0.1~1.2mm), the system dynamically adjusts the laser power (2~4kW) based on the crack depth data detected by infrared detection. For shallow cracks, low power (2kW) is used to avoid overmelting, and for deep cracks, high power (4kW) is used to ensure filling, so as to achieve precise repair of "one crack, one policy".

[0022] III. Air-cooled + dual-detection quality closed-loop principle: stress-free and highly reliable; Traditional cooling methods use water cooling / slow cooling pits, which result in large temperature gradients and are prone to generating residual stress. Moreover, quality inspection is limited to visual inspection and cannot verify the internal crack elimination rate and the uniformity of the microstructure.

[0023] This invention employs a "stress relief" mechanism involving air cooling to below 200°C: During air cooling of the repair zone, the temperature slowly decreases from the molten state (≈1500℃) to below 200℃, with a temperature gradient ≤5℃ / s. The principle of avoiding residual stress: slow cooling can gradually release the "thermal stress" caused by the difference in thermal expansion coefficients between the repair area and the substrate, rather than accumulating it. Experiments have shown that the residual stress in the repair area after air cooling is ≤50MPa, which is much lower than 200MPa after water cooling, thus avoiding cracking in subsequent processing. The 200℃ threshold is based on the fact that when the continuous casting billet is below 200℃, the mobility of metal atoms is significantly reduced and the microstructure tends to be stable. Stopping cooling at this point can ensure that the microstructure in the repair zone will not undergo phase transformation.

[0024] The "dual verification" mechanism of ultrasonic flaw detection + metallographic inspection: Ultrasonic testing (frequency 5MHz): 5MHz high-frequency ultrasonic waves can penetrate the repair area and determine whether there are unfilled cracks inside by the "reflected wave signal" - when the crack elimination rate is ≥98%, the reflected wave has no abnormal peak value, ensuring internal quality; Metallographic examination: By observing the structure of the repair area under a microscope, two points can be verified: (1) the depth of the heat-affected zone is ≤0.2mm (no obvious grain coarsening); (2) there is no obvious interface between the repair area and the substrate (hardness fluctuation ≤5%), ensuring consistent mechanical properties - as in Example 2, the tensile strength of the repair area is ≥510MPa, which is basically the same as that of the original material (520MPa).

[0025] This invention is not an improvement on a single technology, but a deep integration of three stages: "detection, repair, and quality inspection." Its core innovative logic lies in: Linkage between infrared thermal imaging and laser repair: Detection data directly guides laser parameters (power, depth, path), achieving "precise positioning to precise repair" and solving the problem of "disconnect between detection and repair" in traditional methods; Micro-melting energy regulation: By using low-power fiber laser and short thermal action time, it achieves "melting only cracks without damaging the substrate", balancing repair efficiency and preservation of tissue properties, breaking through the bottleneck of traditional "high energy will inevitably damage the substrate"; Dynamic process adaptation: For different steel grades (carbon steel, stainless steel, high-temperature alloys) and different crack types (point, strip, network), the process achieves universality through adaptive parameter adjustment (such as variable power and variable path). Experimental verification shows that this process can cover more than 90% of continuous casting billet materials, and the pass rate has been increased from the traditional 85% to 99%.

[0026] In summary, this invention fundamentally solves the core pain points of traditional repair processes by organically combining physical mechanisms (thermal field recognition, micro-area remelting), material properties (phase change control, anti-oxidation), and equipment collaboration (robotic arm + laser + detection), achieving efficient and high-quality online repair of continuous casting billets.

[0027] The present invention will be further illustrated below through specific embodiments: Example 1 (Repair of Low-Carbon Steel Billet) S1. Crack Detection: The steel grade is Q235B; an infrared thermal imager (detector is an uncooled microbolometer array, resolution 640×480, temperature range 200~1500℃, accuracy ±1℃) is used for scanning, and the temperature difference threshold is set ≥10℃; the crack depth is identified as 0.8mm, the length is marked as needed, and the distribution density is recorded as needed; the depth resolution of the infrared thermal imager is ≤0.1mm, and the positioning accuracy is ±0.5mm.

[0028] S2. Laser Micro-melting Repair: A six-axis robotic arm controls the IPG fiber laser head with a laser power of 3.2kW, a scanning speed of 3.2m / min, a spot diameter of 0.5mm, an overlap rate of 30% (default median value), a repair speed of 3.2m / min, and a single repair depth of 0.8mm. The path planning is a spiral scan with a pitch of 0.3mm. Argon gas protection is used with a flow rate of 15L / min (default median value) and an oxygen content of ≤100ppm. The melt pool depth is controlled to be 1.2 times the crack depth (0.96mm).

[0029] S3. Post-processing and quality inspection: The repair area is air-cooled to 180℃ (≤200℃); ultrasonic testing (frequency 5MHz) verifies that the crack elimination rate is 100%; metallographic testing shows that the depth of the heat-affected zone is 0.15mm and the ferrite grain size of the matrix is ​​grade 7.5 (originally grade 7.8); the repair time for a single 12-meter billet is 4 minutes, and there are no pores in the cladding layer.

[0030] Example 2 (Repair of high-strength steel slab) S1. Crack detection: The steel grade is Q460C; an infrared thermal imager (parameters same as in Example 1) is used for scanning, with a temperature difference threshold ≥10℃; the crack depth is identified as 1.5mm, and other dimensions are marked as needed; the infrared thermal imager has a depth resolution ≤0.1mm and a positioning accuracy of ±0.5mm.

[0031] S2. Laser micro-melting repair: IPG fiber laser head power 4.5kW, scanning speed 2.8m / min, spot diameter 0.8mm, overlap rate 35% (default median value), repair speed 2.8m / min, single repair depth 1.5mm; path planning is a zigzag trajectory (default); argon protection, flow rate 15L / min, oxygen content ≤50ppm; melt pool depth controlled to 1.3 times the crack depth (1.95mm).

[0032] S3. Post-processing and quality inspection: The repaired area is air-cooled to 190℃ (≤200℃); ultrasonic testing verifies that the crack elimination rate is ≥99%; metallographic testing shows that the depth of the heat-affected zone is ≤0.2mm; the tensile strength of the repaired area is ≥510MPa (original material 520MPa); the number of cycles of the three-point bending fatigue test is ≥1×106 (consistent with the original material); the cost per ton of steel repair is reduced by 60%.

[0033] Example 3 (High-speed repair of stainless steel round billets) S1. Crack detection: The steel grade is 316L; an infrared thermal imager (parameters same as in Example 1) is used for scanning, with a temperature difference threshold ≥10℃; the crack depth is identified as 0.3mm, and other dimensions are marked as needed; the infrared thermal imager has a depth resolution ≤0.1mm and a positioning accuracy of ±0.5mm.

[0034] S2. Laser Micro-melting Repair: IPG fiber laser head power 2.5kW, scanning speed 3.5m / min, spot diameter 0.3mm, overlap rate 25% (default median value), repair speed 3.5m / min, single repair depth 0.3mm; path planning is a zigzag trajectory (default); argon protection, flow rate 12L / min (default median value), oxygen content ≤80ppm (default); melt pool depth controlled to 1.4 times the crack depth (0.42mm); real-time detection of Cr / Ni element burn-off rate by spectrometer ≤0.5%.

[0035] S3. Post-processing and quality inspection: The repaired area is air-cooled to 170℃ (≤200℃); ultrasonic testing verifies that the crack elimination rate is 100%; metallographic testing shows that the depth of the heat-affected zone is 0.1mm; the surface roughness Ra of the repaired area is ≤1.6μm, requiring no secondary processing; no pitting corrosion is observed after 480 hours of salt spray testing; the database automatically identifies the characteristics of austenitic steel, and the parameter matching time is <2 seconds.

[0036] Example 4 (Repair of Multiple Cracks in Alloy Steel Irregularly Shaped Billets) S1. Crack detection: The steel grade is 42CrMo; an infrared thermal imager (parameters same as in Example 1) is used for scanning, with a temperature difference threshold ≥10℃; dense network cracks are identified, with a depth of 0.1~1.2mm, and other dimensions are marked as needed; the infrared thermal imager has a depth resolution ≤0.1mm and a positioning accuracy of ±0.5mm.

[0037] S2. Laser Micro-fusion Repair: The IPG fiber laser head uses variable power scanning (2~4kW dynamically adjustable), scanning speed 3.0m / min (default median value), spot diameter 0.6mm (default median value), overlap rate 20%, repair speed 3.0m / min, single repair depth coverage 0.1~1.2mm; genetic algorithm plans the shortest spiral scanning path, pitch 0.4mm (default median value); argon protection, flow rate 18L / min (default median value), oxygen content ≤90ppm (default); melt pool depth is controlled to 1.5 times the corresponding crack depth.

[0038] S3. Post-processing and quality inspection: The repair area is air-cooled to 185℃ (≤200℃); ultrasonic testing verifies 100% crack repair with no missed detection; metallographic testing shows the depth of the heat-affected zone is ≤0.2mm; the curvature of the billet after repair is ≤0.1mm / m; the database is automatically updated, and the matching accuracy is improved to 97% after adding 500 sets of data.

[0039] Example 5 (Repair of High-Temperature Alloy Strip) S1. Crack detection: The steel grade is GH3030 nickel-based alloy; an infrared thermal imager (parameters same as in Example 1) is used for scanning, with a temperature difference threshold ≥10℃; micron-level subcutaneous cracks are identified, with a depth of 0.05~0.1mm, and other dimensions are marked as needed; the infrared thermal imager has a depth resolution ≤0.1mm and a positioning accuracy of ±0.5mm.

[0040] S2. Laser micro-melting repair: IPG fiber laser head power 2.0kW, scanning speed 4.0m / min, spot diameter 0.2mm, overlap rate 30% (default median value), repair speed 4.0m / min, single repair depth coverage 0.05~0.1mm; path planning is a zigzag trajectory (default); argon protection, flow rate 10L / min (default lower limit), oxygen content ≤70ppm (default); melt pool depth control is 1.3 times the corresponding crack depth.

[0041] S3. Post-processing and quality inspection: The repaired area is air-cooled to 195℃ (≤200℃); additional laser shock peening is performed (power density 5GW / cm²); ultrasonic testing verifies 100% crack elimination rate; metallographic inspection shows the depth of the heat-affected zone is ≤0.1mm, and the γ' phase size in the repaired area is ≤0.3μm (original material 0.5μm); the creep strength at 700℃ is increased by 10%; when used in aero-engine blade blanks, the pass rate is increased from 85% to 99%.

[0042] The above embodiments, verified under different steel grades, crack types, and extreme working conditions, fully demonstrate the breakthrough advantages of thermal imaging-guided laser repair technology in terms of efficiency, accuracy, and performance preservation.

[0043] All matters not covered in this invention are common knowledge.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A process for repairing subcutaneous cracks on the surface of continuously cast billets via online micro-melting, characterized in that, The method includes the following steps: S1. Crack detection: The surface of the billet is scanned with an infrared thermal imager, and a temperature difference threshold of ≥10℃ is set to identify cracks, generate a three-dimensional thermal field distribution map, and mark the crack depth, length and distribution density. S2. Laser micro-melting repair: A robotic arm controls the laser head, and the path planning uses spiral scanning or zigzag trajectory to remelt the cracked area according to the set parameters. S3. Post-processing and quality inspection: The repaired area is air-cooled to below 200℃ to avoid residual stress accumulation; then ultrasonic flaw detection and metallographic inspection are carried out to verify the crack elimination rate and the uniformity of the structure, ensuring that the crack elimination rate is ≥98% and the depth of the heat-affected zone is ≤0.2mm.

2. The process for repairing subcutaneous cracks on the surface of a continuously cast billet via online micro-melting according to claim 1, characterized in that: The infrared thermal imager has a depth resolution of ≤0.1mm and a positioning accuracy of ±0.5mm.

3. The process for repairing subcutaneous cracks on the surface of a continuously cast billet using online micro-melting according to claim 1, characterized in that: The laser source of the laser head is an IPG fiber laser with a power of 2~5kW, a scanning speed of 2.5~4m / min, an overlap rate of 20%~40%, a spot diameter of 0.2~1.0mm, a repair speed of ≥3m / min, and a single repair depth coverage of 0.1~2.0mm.

4. The process for repairing subcutaneous cracks on the surface of a continuously cast billet via online micro-melting according to claim 1, characterized in that: Step S2 is performed under argon protection to form a dense cladding layer in the crack area. The depth of the molten pool is controlled to be 1.2 to 1.5 times the crack depth to ensure that the crack is completely filled.

5. The process for repairing subcutaneous cracks on the online surface of a continuously cast billet using micro-melting according to claim 4, characterized in that: The argon flow rate is 10~20L / min, and the oxygen content is ≤100ppm.

6. The process for repairing subcutaneous cracks on the surface of a continuously cast billet via online micro-melting according to claim 1, characterized in that: In step S2, when the path planning uses helical scanning, the pitch is 0.2~0.5mm.

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