Production method for eliminating martensite and bainite of 70Kg-grade welding steel wire rod

Abstract

The invention discloses a production method for eliminating martensite and bainite of a 70Kg-grade steel wire rod for welding, which comprises the working procedures of steel billet heating, controlled rolling, compensation heating and cooling and waste heat isothermal heat treatment, in the steel billet heating procedure, the heating time of a rectangular billet in a 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 finish rolling temperature is 900-960 DEG C, and the spinning temperature is 920-980 DEG C; in the compensation heating process, a coil runs on a Stelmor roller way for 14-18 minutes, the temperature is reduced to 650-700 DEG C, and the coil is collected; according to the waste heat isothermal heat treatment procedure, the coiled wire rod enters a 610-650 DEG C heat preservation gallery with temperature compensation, enters a slow cooling gallery after heat preservation is conducted for 2-3 h, is slowly cooled to 450-500 DEG C and is taken out of the slow cooling gallery to be naturally cooled to 200 DEG C or below, and packaging is conducted.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a production method for eliminating martensite and bainite of a 70kg-grade welding steel wire rod. Background Art

[0002] At present, the domestic 70Kg grade welding steel wire rod is the masterbatch for producing gas shielded solid welding wire. The welding wire is used in engineering machinery, nuclear power, pipelines, and occasionally in the coal machinery industry. The overall market demand is increasing year by year, and the market homogeneity competition is gradually intensifying. In order to improve the market competitiveness of this series of products, reducing the cost of the overall production process has become the key to seizing market share. However, the overall alloy content of 70Kg grade welding steel wire rod is relatively high, and the wire rod rolling adopts the Stelmor slow cooling process. It is inevitable that there are more martensite and bainite structures in the structure of the hot-rolled wire rod. Follow-up After the wire rod is mechanically descaled, it is directly made in one step in the high-speed continuous drawing and plating process at 30m / s. In the process of welding wire of different specifications, brittle fracture is prone to occur during drawing, which seriously affects the production efficiency of the welding wire factory.

[0003] When annealing is used to eliminate bainite and martensite in 70kg-grade welding steel produced by traditional technology, grain boundary oxidation often occurs on the surface of the wire rod, which reduces the bonding strength of the substrate surface and produces micro cracks on the surface during the subsequent drawing process. In the subsequent copper plating process, the copper plating layer falls off and the surface of the welding wire turns black. Therefore, the wire rod is not only annealed before drawing, but also needs to be pickled to remove the grain boundary oxidation layer on the surface.

[0004] At present, some manufacturers use the method of directly collecting the wire rods after coiling for online simulated annealing. However, due to the high spinning temperature of the wire rods, High temperature adhesion will occur in some parts of the wire rod, making it difficult to release the wire during the subsequent use by users, and it cannot be used; at the same time, high temperature direct coiling will cause local oxidized iron scale to burst and fall off, and subsequent secondary oxidation will form oxidized iron scale with a thickness of ≤3μm, which is difficult to remove during the user's processing; finally, high temperature direct coiling will cause a large temperature difference between the outside and inside of the coil, and the difference between the outside and inside of the coil during the online simulated annealing process is large, which cannot ensure the stability of the annealing structure and mechanical properties of the entire coil. Another part of the manufacturers, such as CN115245956A, a method for producing bainite high-strength welding wire steel with uniform structure, CN102513725A, an annealing-free welding wire steel wire rod and its production process, etc., only by adjusting the cooling water volume control during the rolling process and the slow cooling measures of the insulation cover, the 70kg-level welding steel wire rod structure is controlled to bainite, resulting in a significant increase in the tensile strength of the wire rod, increased wear during the subsequent user processing, and a significant increase in the tensile strength of the finished welding wire, affecting the final welding performance of the welding wire.

[0005] 70Kg grade welding steel contains relatively high levels of Si, Cr, Ni and other elements. During the cooling process after rolling, iron silicate, iron chromate and Ni-rich layers are formed, resulting in serious embedding of the iron oxide scale on the surface of the wire rod into the matrix. After the subsequent pickling to remove the iron oxide scale, many pits remain on the surface of the matrix, affecting the surface finish of the final welding wire. Conventional production using the Stelmor slow cooling process will increase the depth of the iron scale embedded in the matrix. The depth of the iron scale embedded in the matrix is ​​≥16μm, which seriously affects the surface quality of the final welding wire.

[0006] In summary, the traditional process organization and the situation of iron oxide scale cannot meet the processing and use requirements of users. It is necessary to add additional pickling and annealing processes. The pickling cost per ton of steel is more than 200 yuan, and the annealing cost is more than 350 yuan. In addition, the production cycle is long, which seriously restricts the market competitiveness of this series of products. At the same time, the 70kg-grade welding steel currently produced by traditional processes has pits with a depth of ≥24μm after pickling due to the embedding of surface iron oxide scale in the matrix, which also seriously affects the final surface quality of the welding wire. Summary of the invention

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

[0008] In order to achieve the above-mentioned purpose, the present invention designs a production method for eliminating martensite and bainite of 70Kg-grade welding steel wire rod, including billet heating, controlled rolling, compensatory heating and cooling, and waste heat isothermal heat treatment processes. In the billet heating process, the rectangular billet is heated in a heating furnace for ≥5h, the heating temperature is 1120-1180°C, and the soaking temperature is 1140-1200°C. The heating method can achieve the original austenite grain size of the cast billet ≤7.0, laying a foundation for the subsequent reduction of the strength of the wire rod;

[0009] The controlled rolling process has a final rolling temperature of 900-960°C and a wire laying temperature of 920-980°C. High-temperature rolling at 900-960°C is adopted to avoid low-temperature rolling and prevent grain refinement. High-temperature wire laying at 920-980°C can achieve rapid generation of iron oxide scale after rolling, increase the thickness of the iron oxide scale, and relatively reduce the depth of the iron oxide scale embedded in the matrix.

[0010] In the compensation heating process, the coil runs on the Stelmor roller for 14-18 minutes, and the temperature is reduced to 650-700℃ for coiling; in the waste heat isothermal heat treatment process, the wire rods enter the insulation corridor with temperature compensation at 610-650℃ after coiling, and after 2-3h insulation, enter the slow cooling corridor, slowly cool down to 450-500℃, and naturally cool down to below 200℃ after leaving the slow cooling corridor for packaging.

[0011] Preferably, the rectangular blank is a short rectangular blank of 180mm*240mm and fixed length of 6.3m, and is heated in a heating furnace by a double-row feeding method.

[0012] Preferably, in the heating compensation process, the wire rod runs on the Stelmor roller at a speed of 0.20-0.40m / s. At the same time, a thermocouple device is added in the middle position of the insulation cover and the middle position of the Stelmor roller to perform temperature compensation on the wire rod coiled in the middle part of the roller, so that the temperature of the overlapping point and the middle position of the wire rod on the roller is always consistent, and the temperature difference is controlled to be ≤5°C. In the subsequent coiling process, a single annular sealed insulation box is equipped to avoid further surface oxidation and enter the insulation corridor.

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

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

[0015] The production method of the present invention can eliminate bainite and martensite structures in the wire rod, control the ring structure to F+ dispersed cementite, ensure the tensile strength of the wire rod to 600-650MPa, realize annealing-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. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the organization of 70kg welding steel wire rod produced by the process of Example 1 (horizontal - 500X).

[0017] Figure 2 Schematic diagram of producing 70kg of oxidized iron scale on steel wire rod for welding by the process of Example 1 (horizontally 1000X).

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

[0019] Figure 4 This is a schematic diagram of the tensile strength of a 70kg welding steel wire rod produced by the process of Example 1.

[0020] Figure 5 Schematic diagram of the structure of 70kg welding steel wire rod produced by the process of Example 2 (horizontal - 500X).

[0021] Figure 6 Schematic diagram of producing 70kg of oxidized iron scale on steel wire rod for welding by the process of Example 2 (horizontally 1000X).

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

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

[0024] Fig. 9 Schematic diagram of the structure of 70kg welding steel wire rod produced by the process of Example 3 (horizontal - 500X).

[0025] Fig.10 Schematic diagram of producing 70kg of oxidized iron scale on steel wire rod for welding by the process of Example 3 (horizontally 1000X).

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

[0027] Fig.12 This is a schematic diagram of the tensile strength of a 70kg welding steel wire rod produced by the process of Example 3.

[0028] Fig.13 Schematic diagram of the organization of 70kg welding steel wire rod produced by the process of Comparative Example 1 (horizontal - 500X).

[0029] Fig.14 Schematic diagram of producing 70kg of oxidized iron scale on steel wire rod for welding by the process of Comparative Example 1 (horizontally 1000X).

[0030] Fig.15 Schematic diagram of the grain boundary oxidation of 70kg welding steel wire rod produced by the process of Comparative Example 1 (horizontally 1000X).

[0031] Fig.16 This is a schematic diagram of the depth of erosion pits after pickling of 70kg welding steel wire rod produced by the process of comparative example 1. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Embodiment 1:

[0034] Reference Figure 1-4 This embodiment provides a production method for eliminating martensite and bainite of 70Kg grade welding steel wire rod. The chemical composition of welding steel wire rod is shown in Table 1. The specification is The rolling cooling process includes billet heating, controlled rolling, compensatory heating and cooling, and waste heat isothermal heat treatment procedures.

[0035] (1) Billet heating: 180mm*240mm rectangular billet short length 6.3mm, double-row heating, heating time 5.5h, heating temperature 1160℃, soaking temperature 1180℃, high-pressure water descaling pressure 19MPa.

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

[0037] (3) In the compensation heating process, the roller main speed is 0.25m / s, and the coil runs on the compensation heating roller for 15 minutes. The thermocouple device added in the middle of the insulation cover and the middle of the compensation heating roller is used to perform intelligent temperature compensation on the wire rod in the middle of the roller, so that the temperature of the overlap point and the middle position of the wire rod on the roller is always consistent, and the temperature difference is set to ≤5℃. The temperature is reduced to 640℃ for coiling. After coiling, it is kept warm in a ring-shaped sealed insulation box and enters the insulation corridor.

[0038] (4) In the residual heat isothermal heat treatment process, the annular sealed insulation box wrapped with the coil enters the insulation corridor with a heating compensator to ensure that the wire rod runs in the insulation corridor with temperature compensation at 630℃ for 2.5 hours, and then enters the slow cooling corridor and slowly cools to 470℃ at a cooling rate of 0.02℃ / s. After leaving the slow cooling corridor, it is naturally cooled to 200℃ and packaged.

[0039] The finished wire rod structure obtained in this embodiment is ferrite + dispersed cementite (such as Figure 1 ), the overall oxide scale thickness is about 14μm (such as Figure 2 ), when the edge grain boundary oxidation depth is ≤5μm (such as Figure 3 ), the depth of iron oxide embedded in the matrix is ​​≤5μm, and the through-ring tensile strength is 603-645MPa (such as Figure 4 ).

[0040] Example 2

[0041] Reference Figure 5-8 This embodiment provides a production method for eliminating martensite and bainite of 70Kg grade welding steel wire rod. The chemical composition of welding steel wire rod is shown in Table 1. The specification is The rolling cooling process includes billet heating, controlled rolling, compensatory heating and cooling, and waste heat isothermal treatment.

[0042] (1) Billet heating: 180mm*240mm rectangular billet short length 6.3mm, double-row heating, heating time 5.7h, heating temperature 1180℃, soaking temperature 1200℃, high-pressure water descaling pressure 18MPa.

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

[0044] (3) In the compensation heating process, the roller main speed is 0.20m / s, and the coil runs on the compensation heating roller for 18 minutes. The thermocouple device installed in the middle of the insulation cover and the middle of the compensation heating roller is used to perform intelligent temperature compensation on the wire rod in the middle of the roller, so that the temperature of the overlap point and the middle position of the wire rod on the roller is always consistent, and the temperature difference is set to ≤5℃. The temperature is reduced to 700℃ for coiling. After coiling, it is kept warm in a ring-shaped sealed insulation box and enters the insulation corridor.

[0045] (4) In the residual heat isothermal heat treatment process, the annular sealed insulation box wrapped with the coil enters the insulation corridor with a heating compensator to ensure that the wire rod runs in the insulation corridor with temperature compensation at 650°C for 3 hours, and then enters the slow cooling corridor and slowly cools to 500°C at a cooling rate of 0.015°C / s. After leaving the slow cooling corridor, it is naturally cooled to 200°C and packaged.

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

[0047] Example 3

[0048] Reference Figure 9-12 This embodiment provides a production method for eliminating martensite and bainite of 70Kg grade welding steel wire rod. The chemical composition of welding steel wire rod is shown in Table 1. The specification is The rolling cooling process includes billet heating, controlled rolling, compensatory heating and cooling, and waste heat isothermal treatment.

[0049] (1) Billet heating: 180mm*240mm rectangular billet short length 6.3mm, double-row heating, heating time 5h, heating temperature 1120℃, soaking temperature 1140℃, high-pressure water descaling pressure 17MPa.

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

[0051] (3) In the compensation heating process, the roller main speed is 0.20m / s, and the coil runs on the compensation heating roller for 18 minutes. The thermocouple device is added in the middle of the insulation cover and the middle of the Stelmo roller to perform intelligent temperature compensation on the wire rod in the middle of the roller, so that the temperature of the overlap point and the middle position of the wire rod on the roller is always consistent, and the temperature difference is set to ≤5℃. The temperature is reduced to 700℃ for coiling. After coiling, it is kept warm in a ring-shaped sealed insulation box and enters the insulation corridor.

[0052] (4) In the residual heat isothermal heat treatment process, the annular sealed insulation box wrapped with the coil enters the insulation corridor with a heating compensator to ensure that the wire rod runs in the insulation corridor with temperature compensation at 650°C for 3 hours, and then enters the slow cooling corridor and slowly cools to 500°C at a cooling rate of 0.015°C / s. After leaving the slow cooling corridor, it is naturally cooled to 200°C and packaged.

[0053] The finished wire rod structure obtained in this embodiment is ferrite + dispersed cementite (such as Fig. 9 ), the overall oxide scale thickness is about 7μm (such as Fig.10 ), grain boundary oxidation depth ≤ 4 μm (such as Fig.11 ), the depth of iron oxide embedded in the matrix is ​​≤5μm, and the through-ring tensile strength is 607-643MPa (such as Fig.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, Stelmor slow cooling, annealing, and pickling. The specific control process is as follows:

[0056] (1) Billet heating process: the billet is heated in a heating furnace at a heating temperature of 1120°C, a soaking temperature of 1140°C, and a high-pressure water descaling pressure of 20 MPa;

[0057] (2) The billet rolling process is controlled, with the final rolling temperature at 900°C and the wire drawing temperature at 880°C.

[0058] (3) Control the cooling process. After spinning, use Stelmor slow cooling, set the roller main speed to 0.12 m / s, run on the roller for 18 minutes, the wire rod entering the insulation cover temperature is 780-855 ° C, and the wire rod exiting the insulation cover temperature is 520-670 ° C.

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

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

[0061] The finished wire rod structure obtained in this comparative example is ferrite + cementite in the dispersed part (see Fig.13 ), the thickness of the iron oxide scale after wire rod annealing is 12μm, and the depth of grain boundary oxidation after wire rod annealing is about 15μm (see Fig.14 ), the iron oxide scale is embedded in the matrix to a depth of 16 μm (see Fig.15 Therefore, the iron oxide scale on the surface of the wire rod is difficult to remove by mechanical dephosphorization, and the problem of grain boundary oxidation caused by it can only be treated by pickling. However, after pickling, many corrosion pits will be formed on the surface, and the depth of the corrosion pits is 24μm (see Fig.16 ), resulting in a rough surface of 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 welding steel wire rods of Examples 1-3 and Comparative Example 1.

[0063] Table 1 Chemical composition and 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] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A production method for eliminating martensite and bainite of 70Kg grade welding steel wire rod, characterized in that: It includes billet heating, controlled rolling, compensated heating and cooling, and waste heat isothermal heat treatment processes. In the billet heating process, the rectangular billet is heated in the heating furnace for ≥5h, the heating temperature is 1120-1180℃, and the equalizing temperature is 1140-1200℃; in the controlled rolling process, the final rolling temperature is 900-960℃, and the spinning temperature is 920-980℃; in the compensated heating process, the coil runs on the Stelmor roller for 14-18 minutes, and the temperature is reduced to 650-700℃ for coiling; in the waste heat isothermal heat treatment process, after coiling, the wire rod enters a 610-650℃ insulation corridor with temperature compensation, and after 2-3h insulation, enters a slow cooling corridor, slowly cools to 450-500℃, and naturally cools to below 200℃ after leaving the slow cooling corridor for packaging.

2. The method for eliminating martensite and bainite of 70Kg grade welding steel wire rod according to claim 1, characterized in that: The rectangular blank is a short rectangular blank of 180mm*240mm with a fixed length of 6.3m, and is heated in a heating furnace by a double-row feeding method.

3. The method for eliminating martensite and bainite of 70Kg grade welding steel wire rod according to claim 1, characterized in that: In the heating compensation process, the wire rod runs on the Stelmor roller at a speed of 0.20-0.40m / s. At the same time, a thermocouple device is added in the middle position of the insulation cover and the middle position of the Stelmor roller to perform temperature compensation on the wire rod coiled in the middle part of the roller, so that the temperature of the overlap point and the middle position of the wire rod on the roller is always consistent, and the temperature difference is controlled to be ≤5°C. In the subsequent coiling process, a single annular sealed insulation box is equipped to avoid further surface oxidation and enter the insulation corridor.

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

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