A production method for eliminating the martensite and bainite of 70kg grade welding steel wire rod

Abstract

The application discloses a production method for eliminating martensite and bainite of 70Kg-grade welding steel wire rod, which comprises the following steps: a steel billet heating process, a controlled rolling process, a compensation heating and cooling process and a residual heat isothermal heat treatment process.In the steel billet heating process, the heating time of the rectangular billet in the heating furnace is greater than or equal to 5 hours, the heating temperature is 1120-1180 DEG C, and the soaking temperature is 1140-1200 DEG C.In the controlled rolling process, the final rolling temperature is 900-960 DEG C, and the wire feeding temperature is 920-980 DEG C.In the compensation heating process, the coiling is run on the Stelmor roller way for 14-18 minutes, the temperature is reduced to 650-700 DEG C, and the coiling is collected.In the residual heat isothermal heat treatment process, the wire rod is put into the temperature compensation holding corridor at 610-650 DEG C after the coiling, is put into the slow cooling corridor after 2-3 hours of holding, is slowly cooled to 450-500 DEG C, is naturally cooled to below 200 DEG C after leaving the slow cooling corridor, and is packed.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod. Background Technology

[0002] Currently, 70kg-grade welding steel wire rods in China are used as masterbatch for producing gas-shielded solid welding wires. These wires are applied in engineering machinery, nuclear power, and pipelines, and occasionally in the coal mining machinery industry. Overall market demand is increasing year by year, and competition due to product homogeneity is intensifying. Improving the market competitiveness of this product series and reducing overall production costs are key to capturing market share. However, 70kg-grade welding steel wire rods have a high overall alloy content, and the Stellmore slow-cooling process used in the rolling process inevitably results in a significant amount of martensite and bainite in the microstructure of the hot-rolled wire rods. Further developments are needed. After mechanical descaling, the wire rod is directly processed in one step using a high-speed continuous drawing and plating process at 30m / s. During the welding process, brittle fracture is prone to occur when welding wire is used, which seriously affects the production efficiency of welding wire manufacturers.

[0003] Traditional processes for producing 70kg-grade welding steel often result in grain boundary oxidation on the wire rod surface during annealing to remove bainite and martensite. This oxidation reduces the bonding strength between the wire rod and the substrate during subsequent drawing, leading to microcracks on the surface. Consequently, copper plating peels off, and the welding wire surface turns black. Therefore, in addition to annealing, the wire rod must undergo pickling to remove the grain boundary oxide layer before drawing.

[0004] Currently, some manufacturers use wire rod coiling followed by direct collection for online simulated annealing. However, due to the high wire rod extrusion temperature, direct coiling... High-temperature adhesion occurs in some parts of the wire rod, making it difficult for users to lay out the wire and rendering it unusable. Simultaneously, direct high-temperature coiling causes localized iron oxide scale to peel off, leading to secondary oxidation and the formation of iron oxide scale ≤3μm thick, which is difficult for users to remove during processing. Finally, direct high-temperature coiling creates a significant temperature difference between the outer and inner sides of the coil, resulting in a large difference in microstructure between the outer and inner sides during online simulated annealing, which cannot guarantee the stability of the annealed microstructure and mechanical properties of the entire coil. Other manufacturers, such as CN115245956A (a method for producing uniformly microstructured bainitic high-strength welding wire steel) and CN102513725A (an anneal-free welding wire steel wire rod and its production process), only control the cooling water volume during the rolling process and use a heat insulation cover for slow cooling to control the microstructure of 70kg-grade welding steel wire rod to bainitic. This results in a significant increase in the tensile strength of the wire rod, leading to increased wear during subsequent processing and a significant increase in the tensile strength of the finished welding wire, affecting the final welding performance.

[0005] 70kg grade welding steel contains high levels of elements such as Si, Cr, and Ni. During the cooling process after rolling, ferrosilicon, ferrochromate, and Ni-rich layers are formed, resulting in severe embedding of iron oxide scale into the substrate on the wire rod surface. After pickling to remove the iron oxide scale, numerous pits remain on the substrate surface, affecting the final surface finish of the welding wire. The conventional Stellmore slow cooling process further exacerbates the embedding depth of the iron oxide scale, reaching ≥16μm, severely impacting the surface quality of the final welding wire.

[0006] In summary, the traditional process structure and the presence of iron oxide scale cannot meet the user's processing requirements. Additional pickling and annealing processes are necessary, with pickling costs exceeding 200 RMB per ton of steel and annealing costs exceeding 350 RMB per ton of steel. Furthermore, the long production cycle severely restricts the market competitiveness of this product series. Simultaneously, the 70kg welding steel produced using the current traditional process suffers from embedded iron oxide scale, resulting in pits with a depth ≥24μm after pickling, which also significantly affects the final surface quality of the welding wire. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod.

[0008] To achieve the above objectives, this invention designs a production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod, including billet heating, controlled rolling, compensated heating and cooling, and residual heat isothermal heat treatment. In the billet heating process, the rectangular billet is heated in the heating furnace for ≥5 hours, the heating temperature is 1120-1180℃, and the soaking temperature is 1140-1200℃. This heating method can achieve an original austenite grain size of ≤7.0 grade in the billet, laying the foundation for subsequent reduction in wire rod strength.

[0009] The controlled rolling process has a final rolling temperature of 900-960℃ and a wire drawing temperature of 920-980℃. High-temperature rolling at 900-960℃ avoids low-temperature rolling and prevents grain refinement. High-temperature wire drawing at 920-980℃ enables rapid generation of iron oxide scale after rolling, increases the thickness of iron oxide scale, and relatively reduces the depth of iron oxide scale embedded in the matrix.

[0010] In the compensation heating process, the coiled wire runs on the Steyrmo roller conveyor for 14-18 minutes, and the temperature drops to 650-700℃ before being coiled. In the residual heat isothermal heat treatment process, after coiling, the wire enters a temperature-compensated insulated corridor at 610-650℃. After 2-3 hours of heat preservation, it enters a slow cooling corridor, where it is slowly cooled to 450-500℃. After exiting the slow cooling corridor, it is naturally cooled to below 200℃ before being packaged.

[0011] Preferably, the rectangular blank is a 180mm*240mm short fixed length 6.3m rectangular blank, which is heated in the heating furnace using a double-row material distribution method.

[0012] Preferably, in the heating compensation process, the wire rod runs at a speed of 0.20-0.40 m / s on the Steyrmo roller conveyor. At the same time, thermocouple devices are added at the middle positions of the insulation cover and the Steyrmo roller conveyor to compensate the temperature of the wire rod coiled in the middle of the roller conveyor, so that the temperature of the overlapping point and the middle position of the wire rod on the roller conveyor remains consistent, with the temperature difference controlled ≤5℃. Subsequently, during the winding process, a single annular sealed insulation box is provided to prevent further surface oxidation, and the wire rod enters the insulation corridor.

[0013] Preferably, in the waste heat isothermal heat treatment process, the wire rod runs in the slow cooling corridor at a speed of ≤0.03℃ / s.

[0014] The present invention has the following beneficial effects:

[0015] The production method of the present invention can eliminate bainite and martensite structures in wire rods, control the through-ring structure to be F+ dispersed cementite, ensure the tensile strength of wire rods is 600-650MPa, achieve anneal-free drawing, and at the same time, the grain boundary oxidation depth is ≤3μm, and the depth of iron oxide scale embedded in the matrix is ​​controlled to be ≤5μm. Attached Figure Description

[0016] Figure 1 A schematic diagram (horizontal -500X) of the microstructure for producing 70kg of welding steel wire rod using the process of Example 1.

[0017] Figure 2 A schematic diagram (horizontal 1000X) of the process for producing 70kg of welding steel wire rod iron oxide scale in Example 1.

[0018] Figure 3 A schematic diagram (horizontal 1000X) of the grain boundary oxidation of 70kg welding steel wire rod produced by the process of Example 1.

[0019] Figure 4 This is a schematic diagram illustrating the tensile strength of a 70kg weldable steel wire rod produced using the process described in Example 1.

[0020] Figure 5 A schematic diagram (horizontal -500X) of the microstructure for producing 70kg of welding steel wire rod using the process in Example 2.

[0021] Figure 6 A schematic diagram (horizontal 1000X) of the process for producing 70kg of welding steel wire rod iron oxide scale in Example 2.

[0022] Figure 7A schematic diagram (horizontal 1000X) of the grain boundary oxidation of 70kg welding steel wire rod produced by the process of Example 2.

[0023] Figure 8 This is a schematic diagram illustrating the tensile strength of a 70kg weldable steel wire rod produced using the process in Example 2.

[0024] Figure 9 A schematic diagram (horizontal -500X) of the microstructure for producing 70kg of welding steel wire rod using the process of Example 3.

[0025] Figure 10 A schematic diagram (horizontal 1000X) of the process for producing 70kg of welding steel wire rod iron oxide scale in Example 3.

[0026] Figure 11 A schematic diagram (horizontal 1000X) of the grain boundary oxidation of 70kg welding steel wire rod produced by the process of Example 3.

[0027] Figure 12 This is a schematic diagram illustrating the tensile strength of a 70kg weldable steel wire rod produced using the process in Example 3.

[0028] Figure 13 A schematic diagram of the microstructure of 70kg welding steel wire rod produced by process 1 (horizontal -500X).

[0029] Figure 14 A schematic diagram (horizontal 1000X) of the process for producing 70kg of welding steel wire rod iron oxide scale for Comparative Example 1.

[0030] Figure 15 A schematic diagram (horizontal 1000X) of the grain boundary oxidation of 70kg welding steel wire rod produced by process 1 for comparative example.

[0031] Figure 16 A schematic diagram showing the depth of the corrosion pits after pickling 70kg of welding steel wire rod produced by process 1 (for comparison). Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0033] Example 1:

[0034] Reference Figure 1-4 This embodiment provides a production method for eliminating martensite and bainite in 70kg grade welding steel wire rod. The chemical composition of the welding steel wire rod is shown in Table 1, and the specifications are as follows: The rolling cooling process includes billet heating, controlled rolling, compensated heating and cooling, and residual heat isothermal heat treatment.

[0035] (1) Steel billet heating: 180mm*240mm rectangular billet with a short fixed length of 6.3mm, heated by double-row material distribution, heating time 5.5h, heating temperature 1160℃, heat spread temperature 1180℃, high pressure water descaling pressure 19MPa.

[0036] (2) Control the rolling process, with a final rolling temperature of 920℃ and a wire drawing temperature of 940℃.

[0037] (3) In the compensation heating process, the main speed of the roller conveyor is 0.25 m / s. The coil runs on the compensation heating roller conveyor for 15 minutes. Using thermocouple devices added in the middle of the insulation cover and the middle of the compensation heating roller conveyor, intelligent temperature compensation is performed on the coiled part in the middle of the roller conveyor. This ensures that the temperature of the coil at the overlap point and the middle position on the roller conveyor remains consistent, with a temperature difference set to ≤5℃. The coil is then cooled to 640℃ and assembled. After assembly, it is kept warm in an annular sealed insulation box and then enters the insulation corridor.

[0038] (4) Waste heat isothermal heat treatment process: the ring-shaped sealed heat preservation box containing the coil is put into the heat preservation corridor with heating compensator to ensure that the coil runs in the heat preservation corridor with temperature compensation at 630℃ for 2.5 hours. Then it enters the slow cooling corridor and is slowly cooled to 470℃ at a cooling rate of 0.02℃ / s. After exiting the slow cooling corridor, it is naturally cooled to 200℃ and packaged.

[0039] The microstructure of the finished wire rod obtained in this embodiment is ferrite + dispersed cementite (e.g. Figure 1 The overall iron oxide scale thickness is approximately 14 μm (e.g., Figure 2 ), for cases where the oxide depth at the grain boundary is ≤5μm (e.g. Figure 3 The iron oxide scale is embedded in the matrix to a depth ≤5μm, and the tensile strength of the through ring is 603-645MPa (e.g. Figure 4 ).

[0040] Example 2

[0041] Reference Figure 5-8 This embodiment provides a production method for eliminating martensite and bainite in 70kg grade welding steel wire rod. The chemical composition of the welding steel wire rod is shown in Table 1, and the specifications are as follows: The rolling cooling process includes billet heating, controlled rolling, compensated heating and cooling, and residual heat isothermal treatment.

[0042] (1) Steel billet heating: 180mm*240mm rectangular billet with a short fixed length of 6.3mm, heated by double-row material distribution, heating time 5.7h, heating temperature 1180℃, heat absorption temperature 1200℃, high-pressure water descaling pressure 18MPa.

[0043] (2) Control the rolling process, with a final rolling temperature of 960℃ and a wire drawing temperature of 980℃.

[0044] (3) In the compensation heating process, the main speed of the roller conveyor is 0.20 m / s. The coil runs on the compensation heating roller conveyor for 18 minutes. Thermocouple devices are added at the middle positions of the insulation cover and the compensation heating roller conveyor to intelligently compensate the temperature of the coil in the middle of the roller conveyor, so that the temperature of the coil at the overlap point and the middle position on the roller conveyor is always consistent. The temperature difference is set to ≤5℃. The coil is cooled to 700℃ and then coiled. After coiling, it is kept warm in an annular sealed insulation box and then enters the insulation corridor.

[0045] (4) Waste heat isothermal heat treatment process: the ring-shaped sealed heat preservation box containing the coil is put into the heat preservation corridor with heating compensator to ensure that the coil runs in the heat preservation corridor with temperature compensation at 650℃ for 3 hours. Then it enters the slow cooling corridor and is slowly cooled to 500℃ at a cooling rate of 0.015℃ / s. After exiting the slow cooling corridor, it is naturally cooled to 200℃ and packaged.

[0046] The microstructure of the finished wire rod obtained in this embodiment is ferrite + dispersed cementite (e.g. Figure 5 The overall iron oxide scale thickness is approximately 6 μm (e.g., Figure 6 ), grain boundary oxidation depth ≤3μm (e.g. Figure 7 The iron oxide scale is embedded in the matrix to a depth ≤3μm, and the tensile strength of the through ring is 599-633MPa (e.g. Figure 8 ).

[0047] Example 3

[0048] Reference Figure 9-12 This embodiment provides a production method for eliminating martensite and bainite in 70kg grade welding steel wire rod. The chemical composition of the welding steel wire rod is shown in Table 1, and the specifications are as follows: The rolling cooling process includes billet heating, controlled rolling, compensated heating and cooling, and residual heat isothermal treatment.

[0049] (1) Steel billet heating: 180mm*240mm rectangular billet with a short fixed length of 6.3mm, heated by double-row material distribution, heating time of 5h, heating temperature of 1120℃, heat absorption temperature of 1140℃, and high-pressure water descaling pressure of 17MPa.

[0050] (2) Control the rolling process, with a final rolling temperature of 960℃ and a wire drawing temperature of 980℃.

[0051] (3) In the compensation heating process, the main speed of the roller conveyor is 0.20 m / s. The coil runs on the compensation heating roller conveyor for 18 minutes. Thermocouple devices are added at the middle positions of the insulation cover and the Stellmore roller conveyor to intelligently compensate the temperature of the coil in the middle of the roller conveyor, so that the temperature of the coil at the overlap point and the middle position on the roller conveyor is always consistent, with a temperature difference set at ≤5℃. The coil is then cooled to 700℃ and then wound up. After winding up, it is kept warm in an annular sealed insulation box and then enters the insulation corridor.

[0052] (4) Waste heat isothermal heat treatment process: the ring-shaped sealed heat preservation box containing the coil is put into the heat preservation corridor with heating compensator to ensure that the coil runs in the heat preservation corridor with temperature compensation at 650℃ for 3 hours. Then it enters the slow cooling corridor and is slowly cooled to 500℃ at a cooling rate of 0.015℃ / s. After exiting the slow cooling corridor, it is naturally cooled to 200℃ and packaged.

[0053] The microstructure of the finished wire rod obtained in this embodiment is ferrite + dispersed cementite (e.g. Figure 9 The overall iron oxide scale thickness is approximately 7 μm (e.g., Figure 10 ), grain boundary oxidation depth ≤ 4 μm (e.g. Figure 11 The iron oxide scale is embedded in the matrix to a depth ≤5μm, and the tensile strength of the through ring is 607-643MPa (e.g. Figure 12 ).

[0054] Comparative Example 1

[0055] Reference Figure 13-16 The chemical composition of the steel wire rod in this embodiment is shown in Table 1, and the specification is φ5.5mm. The rolling and cooling process includes billet heating, controlled rolling, Stellmore slow cooling, annealing, and pickling. The specific control process is as follows:

[0056] (1) Steel billet heating process: The steel billet is heated in a heating furnace at a heating temperature of 1120℃, a soaking temperature of 1140℃, and a high-pressure water descaling pressure of 20MPa.

[0057] (2) The billet controlled rolling process has a final rolling temperature of 900℃ and a wire drawing temperature of 880℃.

[0058] (3) Control the cooling process. After spinning, use Stellmore slow cooling. Set the main speed of the roller conveyor to 0.12m / s and run on the roller conveyor for 18 minutes. The temperature of the wire entering the insulation cover is 780-855℃ and the temperature of the wire exiting the insulation cover is 520-670℃.

[0059] (4) After the wire rod is coiled, it is annealed as a whole. A bell-type annealing furnace is used, and nitrogen is used for protection. The furnace is heated from room temperature to 680°C in 3.5 hours, held for 5 hours, cooled in the furnace for 4 hours to 500°C, and then cooled with a cooling hood for 1 hour to 150°C before being taken out of the furnace.

[0060] (5) The coil is pickled in loose coil for 45 minutes to remove the surface grain boundary oxide layer.

[0061] The microstructure of the finished wire rod obtained in this comparative example is ferrite with dispersed cementite (see...). Figure 13 The thickness of the iron oxide scale after annealing of the wire rod is 12 μm, and the depth of the grain boundary oxidation after annealing is about 15 μm (see...). Figure 14 The iron oxide scale is embedded in the matrix to a depth of 16 μm (see...). Figure 15 Therefore, the iron oxide scale on the surface of the wire rod is difficult to remove by mechanical descaling, and the resulting grain boundary oxidation problem means that the wire rod can only be treated by pickling. However, pickling will form many etch pits on the surface, with a depth of 24 μm (see...). Figure 16 This results in a rough surface on the welding wire after drawing, and an uneven copper plating layer after copper plating.

[0062] Table 1 shows the chemical composition and mass percentage (%) of the steel wire rods used for welding in Examples 1-3 and Comparative Example 1.

[0063] Table 1. Chemical composition and its mass percentage (%)

[0064] Serial Number C Si Mn P S Ni Cr Mo Ti Example 1 0.07 0.56 1.62 0.009 0.012 0.65 0.15 0.35 0.13 Example 2 0.08 0.61 1.63 0.01 0.011 0.64 0.14 0.36 0.12 Example 3 0.09 0.65 1.64 0.008 0.013 0.66 0.16 0.38 0.14 Comparative Example 1 0.07 0.58 1.61 0.008 0.01 0.66 0.2 0.34 0.14

[0065] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A production method for eliminating martensite and bainite in 70kg grade welding steel wire rod, characterized in that: The process includes billet heating, controlled rolling, compensated heating and cooling, and residual heat treatment. In the billet heating process, the rectangular billet is heated in the furnace for ≥5 hours at a temperature of 1120-1180℃, with a soaking temperature of 1140-1200℃. In the controlled rolling process, the final rolling temperature is 900-960℃, and the wire drawing temperature is 920-980℃. In the compensated heating and cooling process, the billet is coiled and run on the Steyrmo roller conveyor for 14-18 minutes, while simultaneously being heated in the middle of the insulation cover and at the Steyrmo roller conveyor. A thermocouple device is added in the middle of the roller conveyor to compensate for the temperature of the coiled wire in the middle of the roller conveyor, so that the temperature of the coiled wire at the overlap point and the middle position on the roller conveyor is always consistent, and the temperature is reduced to 650-700℃ for coiling. In the residual heat isothermal heat treatment process, after coiling, the coiled wire enters the heat-insulated corridor with temperature compensation at 610-650℃. After 2-3 hours of heat preservation, it enters the slow cooling corridor and is slowly cooled to 450-500℃. After exiting the slow cooling corridor, it is naturally cooled to below 200℃ for packaging.

2. The production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod according to claim 1, characterized in that: The rectangular blank is a 180mm×240mm short fixed length 6.3m rectangular blank, which is heated in the heating furnace using a double-row material distribution method.

3. The production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod according to claim 1, characterized in that: In the compensation heating and cooling process, the wire rod runs at a speed of 0.20-0.40 m / s on the Stellmore roller conveyor. The temperature difference between the overlap point and the middle position of the wire rod on the roller conveyor is controlled to be ≤5℃. Subsequently, during the winding process, a single annular sealed heat preservation box is provided to prevent further surface oxidation, and the wire rod enters the heat preservation corridor.

4. The production method for eliminating martensite and bainite in 70Kg grade welding steel wire rod according to claim 1, characterized in that: In the waste heat isothermal heat treatment process, the wire rods run in the slow cooling corridor at a speed of ≤0.03℃ / s.

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