A method for producing an ml40cr hot-rolled wire rod

Abstract

This invention provides a method for producing ML40Cr hot-rolled wire rod, comprising the following steps: (a) heating the billet; (b) rough rolling, pre-finish rolling, and finish rolling the product from step (a) to form coils into wire; (c) controlling the temperature of the wire using a STEM air-cooled line and closing the insulation cover for heat preservation; (d) coiling the product from step (c) and passing it through an insulation corridor for further heat preservation, wherein the temperature of the coiled product entering the insulation corridor is controlled at 745–755°C, the temperature after passing through the insulation corridor is controlled at 200–300°C, and the time spent passing through the insulation corridor is controlled at 100–105 min; (e) finishing the ends of the product after passing through the insulation corridor and then packaging it. Reducing the pearlite clusters and grains in the product's metallographic structure helps improve its uniformity and thus enhances the product's performance.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and relates to a method for producing wire rod, specifically a method for producing ML40Cr hot-rolled wire rod. Background Technology

[0002] Wire rod (coiled steel) typically refers to small-diameter round steel coils, with diameters ranging from 5 to 19 mm (usually 6-9 mm). The lower limit of this value represents the minimum cross-sectional dimension of hot-rolled steel. ML40Cr is a cold-heading steel that can be heat-treated by quenching at 850℃, oil cooling, tempering at 520℃, and then water or oil cooling. Its main chemical components are: carbon 0.38-0.45%, silicon ≤0.30%, manganese 0.6-0.9%, sulfur ≤0.035%, phosphorus ≤0.035%, chromium 0.90-1.20%, nickel ≤0.020%, and copper ≤0.020%.

[0003] Chinese invention patent application number 202310759114.3 discloses a rolling method for reducing the Rockwell hardness of wire rod for fasteners of grade 8.8, comprising the following steps: (a) heating the steel billet, wherein the heating is performed using a regenerative gas-fired furnace and the billet is descaled by high-pressure water before being tapped, and the heating temperature of the regenerative gas-fired furnace is controlled at a certain temperature; (b) rolling: the steel from step (a) is subjected to rough rolling, intermediate rolling, pre-finish rolling and finish rolling in sequence to obtain wire rod; (c) coiling: the wire rod from step (b) is coiled into coils, wherein the coiling temperature is 800-850℃; (d) air cooling: the coiled wire rod from step (c) is cooled in a controlled manner using a Stellmore air-cooling line. It can be seen that in this application, the final coiled wire rod is air-cooled without any further treatment and is allowed to cool naturally. Similarly, Chinese invention patent application number 201810476278.4 discloses an alloy steel wire rod for standard parts, whose chemical composition by weight percentage is: C: 0.38~0.48%, Mn: 0.75~1.00%, Si: 0.15~0.35%, P: ≤0.035%, S: ≤0.040%, Cr: 0.80~1.10%, Mo: 0.15~0.25%, with the balance being Fe and unavoidable impurities; its preparation method includes the following steps: (a) heating: heating the steel billet to 1000~1060℃ in a regenerative blast furnace gas heater, and then tapping the steel at a temperature of 920~980℃; (b) rolling: rolling the steel billet using a multi-pass rolling mill with alternating horizontal and vertical arrangement, controlling the rolling temperature of the steel billet to ≤950℃; (c) cooling: cooling the rolled steel billet to form a coil at 820~860℃. This results in a metallographic structure primarily composed of ferrite and pearlite, giving the product excellent plasticity and reducing the softening annealing time for users. In this application, the final alloy steel wire rod is rapidly cooled to 680–720°C, then held at that temperature for 75–80 seconds at a rate of ≤1.5°C / s, followed by natural cooling.

[0004] The aforementioned patents all employ high airflow for rapid cooling, thereby controlling the precipitation of ferrite, increasing undercooling, and ultimately improving strength. However, the final product contains relatively large pearlite clusters and coarse grains, therefore the controlled cooling process after rolling requires further optimization. Summary of the Invention

[0005] To address the aforementioned deficiencies, this invention provides a method for producing ML40Cr hot-rolled wire rod.

[0006] To achieve the above technical objectives, the present invention provides a method for producing ML40Cr hot-rolled wire rod, comprising the following steps:

[0007] (a) Heating the billet, wherein the heating temperature is controlled as follows: the preheating section temperature is 770-870℃, the first stage of the heating furnace temperature is 890-970℃, the second stage of the heating furnace temperature is 1000-1080℃, the soaking section temperature is 1060-1120℃, and the tapping temperature is 970-1010℃.

[0008] (b) The product from step (a) is subjected to rough rolling, pre-finish rolling, and finish rolling to form coils and obtain wire.

[0009] (c) Temperature control is performed on the wire using a STEM air-cooled wire, and the insulation cover is closed for insulation.

[0010] Its characteristic is that it further includes the following steps:

[0011] (d) After the product from step (c) is rolled up, it is passed through the heat-insulating corridor for further heat preservation. The temperature of the rolled-up product when entering the heat-insulating corridor is controlled at 745-755°C, the temperature after passing through the heat-insulating corridor is controlled at 250-300°C, and the time for passing through the heat-insulating corridor is controlled at 100-105 min.

[0012] (e) After finishing the ends of the products that have passed through the insulated corridor, arrange for packaging.

[0013] Ideally, in step (d), the length of the insulated corridor is 75–80 m.

[0014] Further, in step (d), the insulated corridor is assembled from multiple insulated units (1) connected end to end, and the gap (2) between two adjacent insulated units (1) is filled with an aluminum silicate cotton blanket with a thickness of 5 to 10 mm.

[0015] Ideally, in step (c), the STEM air-cooling line has 4 to 6 continuous roller conveyors, and the speed of the inlet section roller conveyor of the STEM air-cooling line is 0.18 to 0.22 m / s.

[0016] Furthermore, in step (c), the first half of the STEM air-cooled line uses a cooling fan with a power of 150-180 kW, and the second half uses a cooling fan with a power of 240-260 kW.

[0017] Ideally, in step (e), the pressure during packaging is 25-35t.

[0018] Optimally, in step (a), the composition and weight percentage of the billet are: C: 0.39-0.41%, Si: 0.17-0.23%, Mn: 0.62-0.68%, P≤0.020%, S≤0.010%, Cr: 0.92-0.96%, Al: 0.020-0.040%, Ni≤0.20%, and Cu≤0.20%.

[0019] Further, in step (b), the inlet temperature of the finishing mill is 880-930℃, the outlet temperature is ≤1020℃, and the wire drawing temperature is 880-920℃.

[0020] Furthermore, in step (c), the length of the STEM air-cooling line is 35-45m, and the air-cooling time of the line is 150-180s.

[0021] Furthermore, in step (c), the inlet temperature of the STEM air-cooled line is 850–870°C and the outlet temperature is 755–765°C.

[0022] The present invention discloses a production method for ML40Cr hot-rolled wire rod. By adding an insulation corridor after the STEM air-cooling line for further insulation and by precisely controlling the process parameters of the insulation corridor, the cooling rate of the product can be slowed down, the pearlite clusters and grains in the product's metallographic structure can be reduced, and the uniformity of the product can be improved, thereby increasing the product's performance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the heat-insulating corridor structure used in the production of ML40Cr hot-rolled wire rod according to the present invention. Detailed Implementation

[0024] The present invention discloses a method for producing ML40Cr hot-rolled wire rod, comprising the following steps: (a) heating the billet, wherein the heating temperature is controlled as follows: preheating section temperature is 770-870℃, first stage of heating furnace temperature is 890-970℃, second stage of heating furnace temperature is 1000-1080℃, soaking section temperature is 1060-1120℃, and tapping temperature is 970-1010℃; (b) roughing, pre-finishing, and finishing rolling are performed on the product from step (a), and the wire is coiled to obtain wire rod; (c) the... The wire is temperature-controlled using a STEM air-cooled line, and the insulation cover is closed for heat preservation; (d) the product from step (c) is coiled and passed through an insulated corridor for further heat preservation. The temperature of the coiled product entering the insulated corridor is controlled at 745-755°C, and the temperature after passing through the insulated corridor is controlled at 250-300°C. The time spent passing through the insulated corridor is controlled at 100-105 minutes; (e) the product passing through the insulated corridor is finished at both ends and then packaged. By adding an insulated corridor after the STEM air-cooled line for further heat preservation, and by precisely controlling the process parameters of the insulated corridor, the cooling rate of the product can be slowed down, the pearlite clusters and grains in the product's metallographic structure can be reduced, which is beneficial to improving its uniformity and thus increasing the product's performance.

[0025] In step (d), the length of the insulated corridor is 75-80m. This insulated corridor is assembled from multiple insulated units 1 connected end-to-end. The gaps 2 between adjacent insulated units 1 are filled with a 5-10mm thick aluminum silicate cotton blanket to ensure the airtightness and heat insulation of the corridor, thereby improving the insulation effect. In step (e), the pressure during packaging is 25-35t. The composition and weight percentage of the billet are: C: 0.39-0.41%, Si: 0.17-0.23%, Mn: 0.62-0.68%, P≤0.020%, S≤0.010%, Cr: 0.92-0.96%, Al: 0.020-0.040%, Ni≤0.20%, and Cu≤0.20%. The inlet temperature of the finishing mill is 880-930℃, the outlet temperature is ≤1020℃, and the wire drawing temperature is 880-920℃. In step (c), the STEM air-cooling line has 4-6 continuous roller conveyors. The inlet section roller speed of the STEM air-cooling line is 0.18-0.22m / s, the length of the STEM air-cooling line is 35-45m, and the air-cooling time of the wire is 150-180s. The first half of the STEM air-cooling line uses a cooling fan with a power of 150-180kW, and the second half uses a cooling fan with a power of 240-260kW. This slow cooling followed by strong cooling further improves the product performance. The preferred inlet temperature of the STEM air-cooling line is 850-870℃ and the outlet temperature is 755-765℃.

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in this industry.

[0027] Example 1

[0028] This invention provides a method for producing ML40Cr hot-rolled wire rod, comprising the following steps:

[0029] (a) The billet (with a cross-sectional size of 150mm×150mm, using commercially available Longteng Special Steel ML40Cr, whose composition and weight percentage are usually C: 0.39-0.41%, Si: 0.17-0.23%, Mn: 0.62-0.68%, P≤0.020%, S≤0.010%, Cr: 0.92-0.96%, Al: 0.020-0.040%, Ni≤0.20% and Cu≤0.20%) is heated, specifically: the billet is heated in a regenerative gas-fired heating furnace: the preheating section temperature is 770℃, the first stage of the heating furnace temperature is 890℃, the second stage of the heating furnace temperature is 1000℃, the soaking section temperature is 1060℃, and the tapping temperature is 970℃;

[0030] (b) Rough rolling of the product from step (a) (rolled piece dimensions are...) The rolling temperature is 860℃), pre-finishing rolling (the dimensions of the rolled piece are...) The circular rolled piece (rolling temperature is 960℃) and the finishing mill (10-stand top-intersection 45° no-twist mill, rolled into 10mm wire rod finished product; the entry temperature of the finishing mill is 900℃ and the exit temperature is 1020℃), and the wire is coiled (the coiling temperature is 880℃) to obtain the wire rod.

[0031] (c) Temperature control is performed on the STEM air-cooled line for wire (in this embodiment, the length of the STEM air-cooled line is 40m, and the air-cooling time of the wire is 160s) (inlet temperature is 860℃, outlet temperature is 760℃), and the insulation cover is closed for insulation; the STEM air-cooled line has 4 to 6 continuous roller conveyors (6 in this embodiment), the speed of the inlet section of the STEM air-cooled line is 0.18 to 0.22m / s (0.20m / s in this embodiment), the first half of the STEM air-cooled line (corresponding to the first three roller conveyors) uses a cooling fan with a power of 150 to 180kw (160kw in this embodiment), and the second half (corresponding to the last three roller conveyors) uses a cooling fan with a power of 240 to 260kw (250kw in this embodiment);

[0032] (d) After the product from step (c) is rolled up, it is passed through an insulated corridor (the length of the insulated corridor is 80m) for further insulation. The temperature of the rolled-up product is controlled at 750℃ when entering the insulated corridor and at 275℃ after passing through the insulated corridor. The time spent passing through the insulated corridor is controlled at 105min (in this embodiment, if...). Figure 1 As shown, the insulated corridor is assembled from 20 insulated units 1 connected end to end. The gaps 2 between two adjacent insulated units 1 are filled with aluminum silicate cotton blankets with a thickness of 5 to 10 mm.

[0033] (e) After finishing the product at both ends through the insulated corridor, arrange for packaging (pressure of 25-35t).

[0034] Example 2

[0035] This embodiment provides a production method for ML40Cr hot-rolled wire rod, which is basically the same as that in Embodiment 1, except that: in step (c), a 160kw cooling fan is used in the STEM air-cooling line.

[0036] Example 3

[0037] This embodiment provides a production method for ML40Cr hot-rolled wire rod, which is basically the same as that in Embodiment 1, except that: in step (c), a 250kw cooling fan is used in the STEM air-cooling line.

[0038] Example 4

[0039] This embodiment provides a production method for ML40Cr hot-rolled wire rod, which is basically the same as that in Embodiment 1. The difference is that in step (d), the temperature of the coiled product entering the insulation corridor is controlled at 745°C, the temperature after passing through the insulation corridor is controlled at 250°C, and the time for passing through the insulation corridor is controlled at 102 min.

[0040] Example 5

[0041] This embodiment provides a production method for ML40Cr hot-rolled wire rod, which is basically the same as that in Embodiment 1. The difference is that in step (d), the temperature of the coiled product entering the insulation corridor is controlled at 755°C, the temperature after passing through the insulation corridor is controlled at 300°C, and the time for passing through the insulation corridor is controlled at 100 min.

[0042] Comparative Example 1

[0043] This embodiment provides a method for producing ML40Cr hot-rolled wire rod, which is basically the same as that in Embodiment 1, except that step (d) is not performed.

[0044] The performance of ML40Cr hot-rolled wire rods from Examples 1-5 and Comparative Examples 1-2 was tested, and the results are listed in Table 1.

[0045] Table 1. Performance of ML40Cr hot-rolled wire rods in Examples 1-5 and Comparative Examples 1-2

[0046] Grain size Yield strength (MPa) Tensile strength (MPa) Example 1 8.6 588 769 Example 2 8.4 563 749 Example 3 8.5 571 750 Example 4 8.5 582 759 Example 5 8.4 583 761 Comparative Example 1 8.3 521 719

[0047] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for producing ML40Cr hot-rolled wire rod, comprising the following steps: (a) Heating the billet, wherein the heating temperature is controlled as follows: the preheating section temperature is 770~870℃, the first stage of the heating furnace temperature is 890-970℃, the second stage of the heating furnace temperature is 1000-1080℃, the soaking section temperature is 1060-1120℃, and the tapping temperature is 970-1010℃. (b) The product from step (a) is subjected to rough rolling, pre-finish rolling, and finish rolling to form coils and obtain wire. (c) The temperature of the wire is controlled using a STEM air-cooled wire, and the insulation cover is closed for insulation. Its characteristic is that it further includes the following steps: (d) After the product from step (c) is rolled up, it is passed through the heat-insulating corridor for further heat preservation. The temperature of the rolled-up product when entering the heat-insulating corridor is controlled at 745~755℃, the temperature after passing through the heat-insulating corridor is controlled at 250~300℃, and the time when passing through the heat-insulating corridor is controlled at 100~105min. (e) After finishing the ends of the products that have passed through the insulated corridor, arrange for packaging; The composition and weight percentage of the billet are as follows: C: 0.39-0.41%, Si: 0.17-0.23%, Mn: 0.62-0.68%, P≤0.020%, S≤0.010%, Cr: 0.92-0.96%, Al: 0.020-0.040%, Ni≤0.20%, and Cu≤0.20%.

2. The method for producing ML40Cr hot-rolled wire rod according to claim 1, characterized in that: In step (d), the length of the insulated corridor is 75~80m.

3. The method for producing ML40Cr hot-rolled wire rod according to claim 2, characterized in that: In step (d), the insulated corridor is assembled from multiple insulated units (1) connected end to end, and the gap (2) between two adjacent insulated units (1) is filled with aluminum silicate cotton blanket with a thickness of 5~10mm.

4. The process for production of ML40Cr hot rolled wire rod as claimed in claim 1 wherein: In step (c), the STEM air-cooling line has 4 to 6 continuous roller conveyors, and the speed of the inlet section roller conveyor of the STEM air-cooling line is 0.18 to 0.22 m / s.

5. The process for production of ML40Cr hot rolled wire rod as claimed in claim 4 wherein: In step (c), the first half of the STEM air-cooled line uses a cooling fan with a power of 150~180kw, and the second half uses a cooling fan with a power of 240~260kw.

6. The process for production of ML40Cr hot rolled wire rod as claimed in claim 1 wherein: In step (e), the pressure during packaging is 25~35t.

7. The process for production of ML40Cr hot rolled wire rod as claimed in claim 1 wherein: In step (b), the inlet temperature of the finishing mill is 880-930℃, the outlet temperature is ≤1020℃, and the wire drawing temperature is 880-920℃.

8. The process for producing the ML40Cr hot-rolled wire rod according to claim 4 or 5, characterized by: In step (c), the length of the STEM air-cooling line is 35~45m, and the air-cooling time of the line is 150~180s.

9. The process for production of ML40Cr hot rolled wire rod as claimed in claim 8 wherein: In step (c), the inlet temperature of the STEM air-cooled line is 850~870℃ and the outlet temperature is 755~765℃.

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