High-carbon-equivalent medium-carbon quenched and tempered steel weld joint structure, welding method and application

Abstract

The invention provides a high-carbon-equivalent medium-carbon quenched and tempered steel weld joint structure, a welding method and application. The high-carbon-equivalent medium-carbon quenched and tempered steel weld joint structure sequentially comprises a base layer, a transition layer and a covering layer. The deposited metal of the base layer is austenitic stainless steel, the deposited metal of the transition layer is duplex stainless steel, the deposited metal of the capping layer is high-strength steel, and gradient transition weld metal is formed; the welding method adopts a non-preheating laser arc hybrid welding process. According to the high-carbon-equivalent medium-carbon quenched and tempered steel weld joint structure, the welding method and the application, based on the technical advantage of rapid heating of a laser-arc hybrid welding heat source, the technical scheme of gradient weld joint structure regulation and control of the priming layer, the transition layer and the capping layer under low heat input is provided, non-preheating crack-free welding of the high-carbon-equivalent medium-carbon quenched and tempered steel is achieved, and the welding quality is improved. And a new solution is provided for welding of medium-carbon quenched and tempered steel with similar components.

Description

Technical Field

[0001] This invention relates to the field of alloy steel welding technology, and more specifically, to a weld structure, welding method, and application of high carbon equivalent medium carbon quenched and tempered steel. Background Technology

[0002] Oil and gas drilling tools, represented by lead-edge grinding shoes, play an irreplaceable role in well completion and downhole accident handling (casing fragment grinding, broken drill pipe grinding, etc.). Due to the harsh and complex working conditions in deep-sea wells, current deep-sea drilling tools mostly use high-carbon equivalent medium-carbon quenched and tempered steel, such as 40CrMnMo quenched and tempered steel forgings, as the matrix material. They are then manufactured by beveling the matrix and preheating it to 350℃ before welding different shaped cutting edges.

[0003] The following problems exist in the welding and manufacturing of 40CrMnMo downhole drilling tools: According to the International Institute of Welding's definition of carbon equivalent, the carbon equivalent of 40CrMnMo steel is approximately 0.9%, which is classified as an extremely difficult steel to weld in welding standards and textbooks. Frequent post-weld cold cracking has become a major pain point in the welding, manufacturing, and application of this type of product. Specifically, during non-destructive testing after 48 hours of post-weld resting, cold cracks of varying lengths are frequently detected randomly at the cutting edge weld of the drilling tool. Repairing these cracks requires repeated preheating at 350℃ and post-weld heat treatment, resulting in a significant increase in production costs.

[0004] According to publicly available literature, Sun Xian et al. from Taiyuan University of Technology were among the first in China to conduct research on non-preheating welding technology for medium carbon alloy steel. They used shielded metal arc welding (SMAW) with high chromium-nickel austenitic stainless steel as the root pass weld and structural steel welding wire with a composition similar to that of medium carbon alloy steel as the filler and cover pass, to repair welds on coal mine fully mechanized mining supports.

[0005] The welding process described by Sun Xian et al. has the following problems: They used shielded metal arc welding (SMAW) for medium carbon alloy steel without preheating. The SMAW diameter was 4mm, which, compared to a 1.2mm diameter solid welding wire, resulted in an excessively wide arc heating zone. This led to a prolonged residence time of the heat-affected zone (HAZ) in the high-temperature region, consequently reducing the HAZ's toughness. Furthermore, the two-layer weld combination of stainless steel as the base layer and carbon steel as the cover layer also suffered from excessive compositional gradient and significant differences in linear expansion coefficients (the linear expansion coefficient of stainless steel is approximately 18 × 10⁻⁶). -6 / ℃, while the coefficient of linear expansion of carbon steel is approximately 12×10 -6 / ℃).

[0006] Patent CN102179602A proposes a welding process for non-preheating gradient microstructure matching of low-alloy high-strength steel with a yield strength of 800MPa. It adopts a gas shielded welding method, using Ni-Cr stainless steel welding wire as the root layer, structural steel welding wire with a tensile strength of 500MPa as the fill layer, and structural steel welding wire with a tensile strength of 800MPa as the cover layer, to achieve non-preheating welding of HQ785T1 low-alloy high-strength steel with a thickness of 28mm.

[0007] The welding process described in patent CN102179602A has the following problems: Although this patent's welding technology for low-alloy high-strength steel without preheating employs a gradient weld transition structure with stainless steel welding wire for the root pass, low-strength carbon steel welding wire for the filler pass, and high-strength carbon steel welding wire for the cover pass, it still suffers from excessively large linear expansion coefficients in the root pass and filler passes, as well as excessively long dwell times in the high-temperature zone of the heat-affected zone. Furthermore, the base material HQ785T1 in this patent has a carbon equivalent of 0.53%, and the bevel type used in the embodiments is X-type, with a base material thickness of 28mm. Clearly, the technology involved in this patent cannot solve the problem of welding 40mm thick, 0.7% carbon equivalent medium-carbon quenched and tempered steel without preheating.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to address the problem of cold cracking in the welding and manufacturing of medium-carbon quenched and tempered steel, such as those used for deep-sea downhole drilling tools, in existing technologies. This invention provides a high-carbon equivalent medium-carbon quenched and tempered steel weld structure, welding method, and application. Based on the advantages of rapid heating from a laser-arc composite welding heat source, a technical solution is proposed to control the microstructure of gradient welds in the root pass, transition layer, and cap pass under low heat input. This achieves crack-free welding of high-carbon equivalent medium-carbon quenched and tempered steel without preheating and provides a new solution for welding medium-carbon quenched and tempered steel with similar compositions.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A weld structure of high carbon equivalent medium carbon quenched and tempered steel includes a root layer 6, a transition layer 7, and a cover layer 8. The weld metal of the root layer 6 is austenitic stainless steel, the weld metal of the transition layer 7 is duplex stainless steel, and the weld metal of the cover layer 8 is high-strength steel, forming a gradient transition weld metal.

[0011] Furthermore, the carbon equivalent of the high carbon equivalent tempered steel is not less than 0.70%; the base material of the high carbon equivalent tempered steel is at least one of 40CrMnMo, 35CrMo, and 35CrMnMo.

[0012] Furthermore, the thickness of the high carbon equivalent medium carbon quenched and tempered steel base material to be welded is not less than 40 mm, the thickness of the bottom layer 6 is 3~5 mm, the thickness of the transition layer 7 is 27~35 mm, and the thickness of the cover layer 8 is 4~6 mm.

[0013] Furthermore, the angle of the weld bevel is 55°~70°.

[0014] Furthermore, the root gap of the weld bevel is 0 mm, and the blunt edge is 2 mm.

[0015] A welding method for high-carbon equivalent medium-carbon quenched and tempered steel, used to prepare the above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel weld structure, includes the following steps: Step S1, Pre-treatment of base material surface: Grinding the base metal to be welded; Step S2, Root pass welding: Laser-arc hybrid welding method is used, with austenitic stainless steel welding wire as filler wire, to deposit the root pass weld. Step S3, Transition Layer Welding: The transition layer weld is deposited using a laser-arc hybrid welding method with duplex stainless steel welding wire as filler wire. Step S4, Cover Layer Welding: The laser-arc hybrid welding method is used, with high-strength steel welding wire as filler wire, to deposit the cover layer weld.

[0016] Furthermore, in step S1, mechanical grinding is used to grind the bevel of the base material to be welded and the metal on both sides.

[0017] Furthermore, preheating of the workpiece to be welded is not required before the actual welding.

[0018] Furthermore, tack welding is performed before the formal welding: the workpieces to be welded are tack welded together, using the same welding wire as the one used for the root pass of the formal welding.

[0019] Furthermore, in step S1, mechanical grinding is used to grind the bevel of the base material to be welded and the metal within a range of 30-50mm on both sides until the metal luster is exposed.

[0020] Furthermore, a single gas shielded welding method is used to tack weld the workpieces.

[0021] Furthermore, the tack weld length is 10~15mm.

[0022] Furthermore, in step S2, the bottom layer welding adopts a composite welding method with laser in front and arc behind. The distance h between the laser and the welding wire is 2~4mm, the angle between the welding gun axis and the horizontal plane is 45°~60°, the laser power is 1200~1600W, the welding current is 210~270A, the welding voltage is 25~30V, and the welding speed is 500~800mm / min.

[0023] Furthermore, in step S2, the austenitic stainless steel welding wire used for the root pass welding is at least one of ER309L or ER308L.

[0024] Furthermore, in step S2, the austenitic stainless steel welding wire with a diameter of 1.2 mm is used for the root pass welding.

[0025] Furthermore, in step S3, the transition layer welding adopts a composite welding method with laser in front and electric arc behind. The distance h between the laser and the welding wire is 2~4mm, the angle between the welding torch axis and the horizontal plane is 45°~60°, the laser power is 1200~1600W, the welding current is 210~270A, the welding voltage is 25~30V, and the welding speed is 500~800mm / min.

[0026] Furthermore, the duplex stainless steel welding wire used in step S3 for transition layer welding is at least one of ER2205, ER2304, and ER2507.

[0027] Furthermore, the diameter of the duplex stainless steel welding wire used for the transition layer welding in step S3 is 1.2~1.6mm.

[0028] Furthermore, in step S4, the cover layer welding adopts a composite welding method with laser in front and arc behind. The distance h between the laser and the welding wire is adjusted to 2~4mm, the angle between the welding torch axis and the horizontal plane is 45°~60°, the laser power is 1200~1600W, the welding current is 210~270A, the welding voltage is 25~30V, and the welding speed is 500~800mm / min.

[0029] Furthermore, the high-strength steel welding wire used in step S4, the cover layer welding, is at least one of ER100S-G, ER110S-G, and ER120S-G.

[0030] Furthermore, the high-strength steel welding wire used for the cover layer welding in step S4 has a diameter of 1.2~1.6mm.

[0031] The above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel weld structure, or the above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel welding method, is applied in the welding and manufacturing of downhole drilling tools.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention relates to a weld structure for high carbon equivalent medium carbon quenched and tempered steel. By controlling the weld structure through gradient welding of the root pass, transition layer, and cover pass, it achieves crack-free welding of high carbon equivalent medium carbon quenched and tempered steel without preheating. This solves the contradiction between the inability to preheat high carbon equivalent medium carbon quenched and tempered steel and its susceptibility to cracking in specific scenarios, and provides a new solution for welding medium carbon quenched and tempered steel with similar compositions.

[0033] 2. In the high carbon equivalent medium carbon quenched and tempered steel weld structure of the present invention, the residual diffusible hydrogen in the weld has no effect on the performance of the austenitic root pass weld. However, when carbon steel welding wire is used as the root pass filler metal, if the preheating temperature or the rust removal on both sides of the bevel before welding does not meet the production specifications, the residual diffusible hydrogen in the weld, the hardened martensite structure, and the restraint of the root pass weld will work together to cause cracking in the root pass.

[0034] 3. The high-carbon equivalent medium-carbon quenched and tempered steel weld structure of this invention has a weld structure with a gradient distribution of linear expansion coefficient, which alleviates the internal stress of the weld. The filling strategy of using austenitic stainless steel welding wire for the bottom layer, duplex stainless steel welding wire for the transition layer, and high-strength steel welding wire for the top layer forms a weld structure with a gradient distribution of linear expansion coefficient that matches the restraints experienced by various parts of the weld, effectively alleviating the internal stress of the weld.

[0035] 4. The welding method for high carbon equivalent medium carbon quenched and tempered steel of the present invention adopts a laser-arc hybrid welding process with low heat input. Based on the technical advantages of rapid heating of the laser-arc hybrid welding heat source, and utilizing its high power density and fast welding speed, the microstructure of the heat-affected zone of the weld of high carbon equivalent medium carbon quenched and tempered steel is controlled to prevent cold cracking in the heat-affected zone.

[0036] 5. The welding method for high-carbon equivalent medium-carbon quenched and tempered steel of the present invention utilizes a laser-arc composite heat source, which reduces the residence time of the heat-affected zone at high temperatures. The laser-arc composite heat source has a high power density, several times that of single-arc welding. This high-power-density composite heat source causes rapid heating of the heat-affected zone, thereby increasing the austenitizing temperature of the base metal. After slow cooling post-weld, this reduces the formation of martensitic hardened structures. Attached Figure Description

[0037] 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.

[0038] Figure 1 This is a schematic diagram of the laser-arc hybrid welding method of the present invention; Figure 2 This is a schematic diagram showing the distribution of the root layer, transition layer, and capping layer in the weld structure of the present invention. Figure 3 Magnetic particle inspection photograph of the weld seam 48 hours after the invention, Example 1; Figure 4 Magnetic particle inspection photograph of the weld seam 48 hours after the invention, Example 2; Figure 5Cold crack photograph of the 40CrMnMo product in Comparative Example 1 of this invention; Figure 6 Metallographic images of the oblique Y-shaped bevel section in Experiment Example 1 of this invention; Figure 7 Image of the tensile specimen in Test Example 1 of this invention; Explanation of reference numerals in the attached drawings: 1-Workpiece; 2-Weld seam; 3-Laser beam; 4-Welding wire; 5-Arc welding gun; 6-Root pass; 7-Transition layer; 8-Cover layer. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to 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.

[0040] A high-carbon equivalent medium-carbon quenched and tempered steel weld structure includes a root layer 6, a transition layer 7, and a cover layer 8. The weld metal of the root layer 6 is austenitic stainless steel, the weld metal of the transition layer 7 is duplex stainless steel, and the weld metal of the cover layer 8 is high-strength steel, forming a gradient transition weld metal.

[0041] Based on performance requirements, this invention divides the weld seam to be welded into a root pass, a transition pass, and a cap pass, and fills each pass with a different composition of deposited metal to form a weld metal with a performance gradient transition, thereby reducing the occurrence of cold cracks in the weld metal.

[0042] In this invention, the weld metal for the root pass is austenitic stainless steel. The residual diffusible hydrogen in the weld has no effect on the performance of the root pass weld with austenitic structure. However, when carbon steel welding wire is used as the filler metal for the root pass, if the preheating temperature or the cleaning of rust on both sides of the bevel before welding does not meet the production specifications, the residual diffusible hydrogen in the weld, the hardened martensite structure, and the restraint of the root pass weld will work together to cause cracking in the root pass.

[0043] The weld structure of this invention is a weld metal with a gradient transition. The weld structure with a gradient distribution of linear expansion coefficients alleviates the internal stress of the weld and forms a weld structure with a gradient distribution of linear expansion coefficients that matches the constraints on each part of the weld, effectively relieving the internal stress of the weld.

[0044] Preferably, the carbon equivalent of the high carbon equivalent tempered steel is not less than 0.70%, and the base material of the high carbon equivalent tempered steel is at least one of 40CrMnMo, 35CrMo, and 35CrMnMo; preferably 40CrMnMo.

[0045] Preferably, the thickness of the high carbon equivalent medium carbon quenched and tempered steel base material to be welded is not less than 40 mm, the thickness of the bottom layer 6 is 3~5 mm (including but not limited to 3 mm, 4 mm, 5 mm), the thickness of the transition layer 7 is 27~35 mm (including but not limited to 27 mm, 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm), and the thickness of the cover layer 8 is 4~6 mm (including but not limited to 4 mm, 5 mm, 6 mm).

[0046] Preferably, the angle of the weld bevel is 55°~70°, including but not limited to 55°, 60°, 65°, and 70°; 60° is preferred.

[0047] Preferably, the weld bevel root gap is 0 mm and the blunt edge is 2 mm.

[0048] This invention can solve the problem of cracking easily occurring during the welding and manufacturing of high carbon equivalent medium carbon quenched and tempered steel with a thickness greater than 40mm.

[0049] A welding method for high-carbon equivalent medium-carbon quenched and tempered steel, used to prepare the above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel weld structure, includes the following steps: Step S1, Pre-treatment of base material surface: Grinding the base metal to be welded; Step S2, Apply the bottom layer solder: such as Figure 1 As shown, a laser-arc hybrid welding method is used, with austenitic stainless steel welding wire as filler wire, to deposit the root weld. Step S3, Transition Layer Welding: The transition layer weld is deposited using a laser-arc hybrid welding method with duplex stainless steel welding wire as filler wire. Step S4, Cover Layer Welding: The laser-arc hybrid welding method is used, with high-strength steel welding wire as filler wire, to deposit the cover layer weld.

[0050] This invention employs a low-heat-input laser-arc hybrid welding process, utilizing its high power density and fast welding speed to regulate the microstructure of the heat-affected zone (HAZ) of medium-carbon quenched and tempered steel welds, preventing cold cracking in the HAZ. The laser-arc hybrid heat source reduces the residence time of the HAZ at high temperatures; its power density is several times that of single-arc welding. This high-power-density hybrid heat source causes rapid heating of the HAZ, thereby increasing the austenitizing temperature of the base metal. Post-weld slow cooling reduces the formation of martensitic hardened structures.

[0051] Preferably, in step S1, mechanical grinding is used to grind the metal within a 30-50mm (including but not limited to 30mm, 40mm, 50mm) range on both sides of the base material to be welded until the metal luster is exposed.

[0052] Preferably, preheating of the workpiece to be welded is not required before the actual welding.

[0053] Preferably, tack welding is performed before the formal welding: the workpieces to be welded are tack welded together, and the same welding wire is used as the root pass welding wire used in the formal welding.

[0054] Preferably, a single gas shielded welding method is used to tack weld the workpieces to be welded.

[0055] Preferably, the length of the tack weld is 10-15mm (including but not limited to 10mm, 11mm, 12mm, 13mm, 14mm, 15mm).

[0056] Preferably, step S2, the root pass welding, employs a hybrid welding method with laser preceding arc welding. The distance h between the laser and the welding wire is 2-4 mm (including but not limited to 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm), the angle between the welding torch axis and the horizontal plane is 45°-60° (including but not limited to 45°, 50°, 55°, 60°), and the laser power is 1200-1600W (including but not limited to 1200W, 1300W, 1400W, 1500W, 16...). 00W), welding current 210~270A (including but not limited to 210A, 220A, 230A, 240A, 250A, 260A, 270A), welding voltage 25~30V (including but not limited to 25V, 26V, 27V, 28V, 29V, 30V), welding speed 500~800mm / min (including but not limited to 500mm / min, 600mm / min, 700mm / min, 800mm / min).

[0057] Preferably, the austenitic stainless steel welding wire used in step S2 for the root pass welding is at least one of ER309L and ER308L; ER309L is preferred.

[0058] Preferably, the austenitic stainless steel welding wire used in step S2 for the root pass welding has a diameter of 1.2 mm.

[0059] Preferably, step S3, the transition layer welding, employs a composite welding method with laser in front and arc behind. The distance h between the laser and the welding wire is 2-4 mm (including but not limited to 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm), the angle between the welding torch axis and the horizontal plane is 45°-60° (including but not limited to 45°, 50°, 55°, 60°), and the laser power is 1200-1600W (including but not limited to 1200W, 1300W, 1400W, 1500W, 1600W). 00W), welding current 210~270A (including but not limited to 210A, 220A, 230A, 240A, 250A, 260A, 270A), welding voltage 25~30V (including but not limited to 25V, 26V, 27V, 28V, 29V, 30V), welding speed 500~800mm / min (including but not limited to 500mm / min, 600mm / min, 700mm / min, 800mm / min).

[0060] Preferably, the duplex stainless steel welding wire used in step S3 for transition layer welding is at least one of ER2205, ER2304, and ER2507; ER2205 is preferred.

[0061] Preferably, the diameter of the duplex stainless steel welding wire used for the transition layer welding in step S3 is 1.2mm to 1.6mm, including but not limited to 1.2mm, 1.3mm, 1.4mm, 1.5mm, and 1.6mm.

[0062] Preferably, step S4, the cover layer welding, employs a composite welding method with laser in front and arc behind. The distance h between the laser and the welding wire is adjusted to 2~4mm (including but not limited to 2mm, 2.5mm, 3mm, 3.5mm, 4mm), the angle between the welding torch axis and the horizontal plane is 45°~60° (including but not limited to 45°, 50°, 55°, 60°), and the laser power is 1200~1600W (including but not limited to 1200W, 1300W, 1400W, 1500W, 1...). 600W), welding current 210~270A (including but not limited to 210A, 220A, 230A, 240A, 250A, 260A, 270A), welding voltage 25~30V (including but not limited to 25V, 26V, 27V, 28V, 29V, 30V), welding speed 500~800mm / min (including but not limited to 500mm / min, 600mm / min, 700mm / min, 800mm / min).

[0063] Preferably, the high-strength steel welding wire used in step S4, the cover layer welding, is at least one of ER100S-G, ER110S-G, and ER120S-G; ER110S-G is preferred.

[0064] Preferably, the high-strength steel welding wire used for the cover layer welding in step S4 has a diameter of 1.2~1.6mm, including but not limited to 1.2mm, 1.3mm, 1.4mm, 1.5mm, and 1.6mm.

[0065] Preferably, non-destructive testing is performed after welding: a schematic diagram of the weld after the three layers of deposited metal are completed is shown below. Figures 2-3 As shown, the weld was subjected to non-destructive testing 48 hours after welding.

[0066] The above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel weld structure, or the above-mentioned high-carbon equivalent medium-carbon quenched and tempered steel welding method, is applied in the welding and manufacturing of downhole drilling tools.

[0067] Example 1 A welding method for high-carbon equivalent medium-carbon quenched and tempered steel, employing a non-preheating laser-arc hybrid welding process, includes the following specific steps: 1) Surface pretreatment of the base material: The metal within a 30-50mm range on both sides of the 40CrMnMo bevel to be welded is ground by mechanical grinding until the metal luster is exposed; 2) Tack welding assembly: The 40CrMnMo workpiece to be welded is tack welded and assembled using a single gas shielded welding method. The length of the tack weld is 10~15mm. The welding wire used is the same as the wire used for the root pass of the formal weld, which is ER309L solid stainless steel welding wire. After tack welding, the assembly quality of the product is inspected to ensure that the process requirements for bevel root gap, blunt edge, and bevel angle are met. 3) Applying the root pass welding: such as Figure 1 As shown, a composite welding method with laser in front and electric arc behind is adopted. ER309L (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1600W, the welding current to 260A, the welding voltage to 25V, and the welding speed to 800mm / min to deposit the root pass weld. The height of the root pass weld metal is controlled to be 3mm. 4) Transition layer welding: A composite welding method with laser in front and arc behind is adopted. ER2205 (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1200W, the welding current to 270A, the welding voltage to 30V, and the welding speed to 800mm / min to deposit the transition layer weld. The height of the weld metal in the transition layer is controlled to be 35mm. 5) Cover layer welding: A composite welding method with laser in front and arc behind is adopted. ER110S-G (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1200W, the welding current to 270A, the welding voltage to 30V, and the welding speed to 800mm / min to deposit the cover layer weld. The height of the deposited metal in the cover layer is controlled to be 4mm.

[0068] Non-destructive testing: A schematic diagram of the weld after the three layers of deposited metal have been completed is shown below. Figure 3 As shown, magnetic particle testing of the weld was performed 48 hours after welding.

[0069] Example 2 A welding method for high-carbon equivalent medium-carbon quenched and tempered steel, employing a non-preheating laser-arc hybrid welding process, includes the following specific steps: 1) Surface pretreatment of the base material: The metal within a 30-50mm range on both sides of the 40CrMnMo bevel to be welded is ground by mechanical grinding until the metal luster is exposed; 2) Tack welding assembly: The 40CrMnMo workpiece to be welded is tack welded and assembled using a single gas shielded welding method. The length of the tack weld is 10~15mm. The welding wire used is the same as the wire used for the root pass of the formal weld, which is ER309L solid stainless steel welding wire. After tack welding, the assembly quality of the product is inspected to ensure that the process requirements for bevel root gap, blunt edge, and bevel angle are met. 3) Applying the root pass welding: such as Figure 1 As shown, a composite welding method with laser in front and electric arc behind is adopted. ER309L (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1600W, the welding current to 210A, the welding voltage to 25V, and the welding speed to 500mm / min to deposit the root layer weld. The height of the root layer weld metal is controlled to be 5mm. 4) Transition layer welding: A composite welding method with laser in front and arc behind is adopted. ER2205 (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1500W, the welding current to 230A, the welding voltage to 28V, and the welding speed to 500mm / min to deposit the transition layer weld. The height of the deposited metal in the transition layer is controlled at 27mm. 5) Cover layer welding: A composite welding method with laser in front and arc behind is adopted. ER110S-G (commercially available welding wire) with a diameter of 1.2mm is used as filler wire. The distance h between the laser and the welding wire is adjusted to 2mm. The angle between the welding torch axis and the horizontal plane is 45°. The laser power is set to 1500W, the welding current to 230A, the welding voltage to 28V, and the welding speed to 500mm / min to deposit the cover layer weld. The height of the deposited metal in the cover layer is controlled to be 6mm.

[0070] A schematic diagram of the weld after the three layers of deposited metal have been completed is shown below. Figure 4 As shown, magnetic particle testing of the weld was performed 48 hours after welding.

[0071] Comparative Example 1 A welding method for high-carbon equivalent medium-carbon quenched and tempered steel, employing the existing gas shielded welding preheating process, includes the following specific steps: 1) Surface pretreatment of the base material: The metal within a 30-50mm range on both sides of the 40CrMnMo bevel to be welded is ground by mechanical grinding until the metal luster is exposed; 2) Tack welding assembly: The 40CrMnMo workpieces to be welded are tack welded and assembled using gas shielded welding. The length of the tack weld is 10~15mm. The welding wire used is the same as the wire used for the root pass of the main weld, which is ER110S-G solid high-strength steel welding wire. After tack welding, the assembly quality of the product is inspected, and the root gap of the bevel is controlled to be 2~3mm, the blunt edge to be 2mm, and the bevel angle to be 60°. 3) Overall preheating: The assembled 40CrMnMo workpieces are preheated using an electric heating blast furnace. The preheating temperature is set to 350℃, and the temperature is held for 120 minutes after reaching the set temperature. The heating rate is controlled to be below 30℃. 4) Root pass welding: Use ER110S-G (commercially available welding wire) with a diameter of 1.2mm as filler wire, set the welding current to 240A, welding voltage to 26V, and welding speed to 240mm / min, and deposit the root pass weld, controlling the height of the root pass weld metal to 5mm. 5) Transition layer welding: Use ER110S-G (commercially available welding wire) with a diameter of 1.2mm as filler wire, set the welding current to 260A, welding voltage to 28V, and welding speed to 360mm / min, and deposit the transition layer weld, controlling the height of the deposited metal in the transition layer to 27mm. 6) Cover layer welding: Use ER110S-G (commercially available welding wire) with a diameter of 1.2mm as filler wire, set the welding current to 280A, welding voltage to 30V, and welding speed to 240mm / min, deposit the bottom layer weld, and control the height of the cover layer weld metal to 6mm.

[0072] Non-destructive testing: A schematic diagram of the weld after filling is shown below. Figure 5 As shown, visual inspection and magnetic particle testing of the weld were performed 48 hours after welding. Figure 5 Photo of the product crack.

[0073] Detection Example 1 To compare the performance of the welds in Examples 1-2 and Comparative Example 1, full penetration butt welds were used on flat plates, and the performance of the welds in Examples 1-2 and Comparative Example 1 was tested according to the NB / T47014-2023 standard (welding parameters correspond to those of the examples and comparative examples, respectively). The results are shown in Table 1 below: Table 1. Results of weld performance testing in Examples 1-2 and Comparative Example 1

[0074] According to the test results, no cracks were detected in either of the two samples from Example 1 or the two samples from Example 2 during magnetic particle testing 48 hours after welding. Some sample photographs are shown below. Figure 3 and Figure 4 As shown, this indicates that the welding method of the present invention possesses significant process stability and has the potential for widespread application in actual production. Tensile test results show that all four tensile specimens from Examples 1-2 fractured at the base material, while the tensile specimen from Comparative Example 1 fractured at the weld. This comparison demonstrates that the weld toughness obtained using the filler material and filling process employed in this invention is superior to the weld toughness obtained in the comparative example. Lateral bending tests show that both the examples and the comparative example exhibit satisfactory bending performance.

[0075] In summary, the laser-arc hybrid welding process with low heat input of the present invention, which is matched with the layered filling cladding metal process scheme, has performance that is comparable to or even slightly better than the existing process scheme (preheating welding, filling with other base materials or other welding wires), and can effectively prevent the generation of cold cracks after welding in high carbon equivalent medium carbon quenched and tempered steel.

[0076] Experimental Example 1 As a new process, Experiment 1 used a slanted Y-groove test to evaluate the root pass and filler performance of ER309L austenitic stainless steel welding wire; and the same process flow and process parameters as in Example 1 were used for test plate welding. After welding, magnetic particle inspection was performed and samples were taken for tensile strength testing.

[0077] The results of the inclined Y-shaped bevel test are as follows Figure 6 As shown, the crack rate of the root pass weld of austenitic stainless steel is 0, proving that this type of welding wire can be used for the root pass weld filling of 40CrMnMo medium carbon quenched and tempered steel.

[0078] After 48 hours of post-weld resting, magnetic particle testing detected no cracks; the tensile strength test results are shown in Table 2 below. Except for one specimen that broke at the base material, all other specimens fractured at the weld. Figure 7 As shown.

[0079] Table 2 Test Results of Y-shaped Bevel in Experiment Example 1

[0080] While the embodiments disclosed in this invention are as described above, their content is merely for the purpose of facilitating understanding of the technical solutions of this invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the core technical solutions disclosed in this invention; however, the scope of protection defined by this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A high carbon equivalent medium carbon quenched and tempered steel weld structure, characterized in that, Sequentially include the base layer (6), the transition layer (7) and the cover layer (8);The deposited metal of the base layer (6) is austenitic stainless steel, the deposited metal of the transition layer (7) is duplex stainless steel, and the deposited metal of the cover layer (8) is high-strength steel, forming a gradient transition of weld metal.

2. The high carbon equivalent medium carbon quenched and tempered steel weld structure according to claim 1, characterized in that, The high-carbon equivalent medium-carbon quenched and tempered steel has a carbon equivalent not less than 0.70%; the high-carbon equivalent medium-carbon quenched and tempered steel base material is at least one of 40CrMnMo, 35CrMo and 35CrMnMo.

3. High carbon equivalent medium carbon quenched and tempered steel welded structure according to claim 1 or 2, characterized in that, The method comprises the following at least one technical feature: (1) the thickness of the high-carbon equivalent medium-carbon quenched and tempered steel base material to be welded is not less than 40 mm, the thickness of the base layer (6) is 3-5 mm, the thickness of the transition layer (7) is 27-35 mm, and the thickness of the cover layer (8) is 4-6 mm; (2) the angle of the weld groove is 55°-70°; (3) the root gap of the weld groove is 0, and the chamfer is 2 mm.

4. A welding method of a high carbon equivalent medium carbon quenched and tempered steel for manufacturing a high carbon equivalent medium carbon quenched and tempered steel welded structure as claimed in any one of claims 1 to 3, characterized in that, The method comprises the following steps: Step S1, surface pretreatment of the base material: polishing the metal of the base material to be welded; Step S2, base layer welding: using laser-arc composite welding method, using austenitic stainless steel welding wire as filler welding wire, and depositing the base layer weld; Step S3, transition layer welding: using laser-arc composite welding method, using duplex stainless steel welding wire as filler welding wire, and depositing the transition layer weld; Step S4, cover layer welding: using laser-arc composite welding method, using high-strength steel welding wire as filler welding wire, and depositing the cover layer weld.

5. The high carbon equivalent medium carbon quenched and tempered steel welding method according to claim 4, characterized in that, The method comprises the following at least one technical feature: (1) in step S1, the bevel and the metal on both sides of the base material to be welded are polished by mechanical polishing; (2) no preheating of the workpiece to be welded is required before formal welding; (3) point solid group matching before formal welding: the workpiece to be welded is subjected to point solid group matching, and the welding wire used is the same as the base layer welding wire used in formal welding.

6. The high carbon equivalent medium carbon quenched and tempered steel welding method according to claim 5, characterized by, The method comprises the following at least one technical feature: (1) in step S1, the bevel and the metal on both sides of the base material to be welded are polished by mechanical polishing, and the metal is polished until it is shiny; (2) the workpiece to be welded is subjected to point solid group matching by using single-gas shielded welding method; (3) the length of the positioning weld in point solid group matching is 10-15 mm.

7. The high carbon equivalent medium carbon quenched and tempered steel welding method according to claim 4, characterized by, The method comprises the following at least one technical feature: (1) in step S2, the base layer welding is performed by using laser-arc composite welding method, the distance h between laser and welding wire is 2-4 mm, the angle between the welding gun axis and the horizontal plane is 45°-60°, the laser power is 1200-1600 W, the welding current is 210-270 A, the welding voltage is 25-30 V, and the welding speed is 500-800 mm / min; (2) the austenitic stainless steel welding wire used in step S2 base layer welding is at least one of ER309L and ER308L; (3) the austenitic stainless steel welding wire used in step S2 base layer welding has a diameter of 1.2 mm.

8. The high carbon equivalent medium carbon quenched and tempered steel welding method according to claim 4, characterized by, The method comprises the following at least one technical feature: (1) the step S3 transition layer welding adopts a composite welding method with laser in front and electric arc in back, the distance h between laser and welding wire is 2-4mm, the angle between the axis of welding torch and horizontal plane is 45-60°, the laser power is 1200-1600W, the welding current is 210-270A, the welding voltage is 25-30V, and the welding speed is 500-800mm / min; (2) the step S3 transition layer welding adopts at least one of the following duplex stainless steel welding wire grades: ER2205, ER2304 and ER2507; (3) the step S3 transition layer welding adopts a duplex stainless steel welding wire with a diameter of 1.2-1.6mm.

9. The high carbon equivalent medium carbon quenched and tempered steel welding method according to claim 4, characterized by, including at least one of the following technical features: (1) the step S4 cover layer welding adopts a composite welding method with laser in front and electric arc in back, the distance h between laser and welding wire is 2-4mm, the angle between the axis of welding torch and horizontal plane is 45-60°, the laser power is 1200-1600W, the welding current is 210-270A, the welding voltage is 25-30V, and the welding speed is 500-800mm / min; (2) the step S4 cover layer welding adopts at least one of the following high-strength steel welding wire grades: ER100S-G, ER110S-G and ER120S-G; (3) the step S4 cover layer welding adopts a high-strength steel welding wire with a diameter of 1.2-1.6mm.

10. Application of the high-carbon-equivalent medium-carbon quenched and tempered steel weld structure according to any one of claims 1-3 or the high-carbon-equivalent medium-carbon quenched and tempered steel welding method according to any one of claims 4-9 in the welding manufacturing of downhole drilling tools.

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