High-efficiency and high-quality production method for low-alloy high-speed steel wire rod based on continuous casting

Abstract

A high-efficiency and high-quality production method for a low-alloy high-speed steel wire rod based on continuous casting comprises the following steps: adding production ingredients into an electric furnace for smelting, then carrying out LF furnace refining and VD furnace refining, transferring to an arc-shaped square billet continuous casting machine for continuous casting, producing a square billet through a continuous casting machine, and carrying out segmented high-line rolling forming after returning, so as to obtain the high-quality low-alloy high-speed steel wire rod. And finally, high-quality formed disc steel bars are annealed through a bell-type furnace. According to the method, continuous casting and continuous rolling processes are combined, argon of a cover type annealing furnace is adopted for protective annealing, the overall production efficiency is improved, a surface decarburized layer is guaranteed, pollution to the environment is reduced, the overall quality of a product is improved, the production cost is reduced, and application of the low-alloy high-speed steel wire rod can be popularized easily; and support is provided for cost reduction, benefit increase and productivity expansion of required enterprises.

Description

Technical Field

[0001] The present invention relates to steel for tools and cutting tools and a manufacturing method thereof, and in particular to a production and manufacturing method of a low-alloy high-speed steel wire rod 4241B (W4Mo2Cr4V-B). Background Art

[0002] The development of production technology for low-alloy high-speed steel 4241B round bar began in the 1970s. Early processes involved die casting, forging, and hot rolling. However, slow cooling rates led to coarsening of carbides (>8μm) and yield rates of less than 70%. The introduction of continuous casting in the 1990s shortened production cycles and reduced cracking rates, but problems persisted with central porosity and carbide network precipitation in the ingot. The application of controlled rolling and controlled cooling in the 2000s refined carbides to 3-4μm and improved diameter tolerances to ±0.25mm. However, scale control relied on energy-intensive post-processing, resulting in a yield rate of only 85%. Since 2010, full-process integration has become mainstream. Through vacuum degassing, electromagnetic continuous casting, multi-pass warm rolling, and in-line annealing, carbide sizes of ≤2μm, yields exceeding 90%, and diameter tolerances of ±0.15mm have been achieved. However, achieving the stability and ultimate precision (±0.1mm) of ultrafine carbides still faces equipment and cost bottlenecks. As a cost-effective cutting tool substrate, the manufacturing significance of 4241B round steel bar lies in: significantly reducing dependence on scarce resources through low-alloy design (tungsten content is more than 60% lower than traditional high-speed steel), relying on process innovation to balance performance and cost, making it the preferred material for precision drills, taps and other tools, and promoting the transformation of the mechanical processing industry to high efficiency and energy saving; at the same time, the round shape is directly adapted to the cold drawing forming process, shortening the tool manufacturing chain, and helping small and medium-sized tool companies to reduce costs and increase efficiency.

[0003] At present, low-alloy high-speed steel 4241B is generally delivered in the form of annealed wire rod, with specifications mainly ranging from φ5.5 to 15 mm. Due to its high carbon content and tungsten, molybdenum and vanadium content, there are more carbides in the annealed structure. The conventional process: electric furnace, refining outside the furnace, die-cast steel ingot, blanking and rolling wire rod to wire rod annealing has low production efficiency. In addition, due to the slow cooling of the steel ingot, the primary carbide grows seriously, and there is a large network structure in the cast structure. The subsequent rolling deformation is difficult to eliminate, resulting in carbide aggregation, which seriously affects the subsequent drawing processing and subsequent quenching and tempering of the wire rod. Therefore, how to improve production efficiency, improve carbide size, and improve organizational uniformity is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] To solve the above problems, the present invention discloses a method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting, the specific steps of which are as follows:

[0005] (1) Electric furnace smelting: Scrap steel and high carbon ferrochrome and other alloy materials are added to the electric arc furnace to melt and smelt the alloy and then tap the steel;

[0006] (2) LF furnace refining: Add lime and fluorite to the LF furnace, turn on the electricity to slag, control the slag in the range of R2.5-3.5 and adjust the alloy composition, and then heat up for refining. Use deoxidizers such as ferrosilicon for deoxidation, and use the amount to maintain white slag operation. Sampling and analysis are carried out. When the various alloy components meet the standard requirements, the white slag is tapped at a certain temperature;

[0007] (3) VD furnace refining: Before entering the VD furnace, slag removal and vacuuming are carried out. When the vacuum reaches 67Pa, maintain it for 14 to 18 minutes. After breaking the vacuum, measure the temperature, take samples for full analysis, add covering agent, maintain calmness and weak argon blowing for 12 to 14 minutes, and when the temperature reaches 1550℃, transfer to the continuous casting machine platform.

[0008] (4) Continuous casting of billets: Curved billets are cast using a continuous casting machine. A combination of a crystallizer and end-stage electromagnetic stirring is used during casting, and the billets are pulled out at a certain speed. The secondary cooling zone uses a three-stage water distribution method, with the specific water volume automatically adjusted to the pulling speed. The material temperature entering the straightening machine is 1000-1200°C. The billets are cut to length upon discharge, resulting in continuously cast billets with a certain cross-section specification.

[0009] (5) Annealing of continuous casting billets: After being cut, the continuous casting billets are immediately transferred to a chamber furnace for annealing. The annealing process is to keep the temperature at 850-860℃ for 6 hours, and then cool to 265-300℃ before being taken out of the furnace.

[0010] (6) High-speed wire rolling: Heating in a walking beam heating furnace, the heating temperature of the initial rolled square billet is controlled according to the following requirements: preheating section: 600-840℃, heating time 30min; heating section: 840-1060℃, heating time 50min; soaking section: 1060-1100℃, heating time 150min. Rolling is carried out at a certain temperature, the final rolling temperature is controlled at 980-1000℃, the finishing speed is controlled at 34m / s, the rolling specification is Φ5.5mm, the heat is collected and enters the intelligent slow cooling tunnel furnace, and the cooling is carried out in three stages with a gradient drop of 250℃. After slow cooling for ≥48 hours, it is transferred to the bell furnace for annealing. The out-of-roundness of the hot-rolled wire rod is controlled to ±0.15mm.

[0011] (7) Hood furnace annealing: Hot rolled wire rods need to be annealed within 8 hours. Hood annealing is used. Nitrogen is purged at room temperature before heating. Nitrogen is filled for protection during heating, insulation and cooling. The flow rate is set at 15m 3 / h, purging until the oxygen content in the furnace chamber is ≤200ppm. The heating system is as follows: heating with the furnace, ensuring a heating time of 8 hours from room temperature to 860℃, keeping at 860±10℃ for 10 hours, cooling with the furnace to below 500℃, and then taking it out of the furnace and air cooling.

[0012] The tapping temperature in step (1) is 1600° C. to 1620° C., and the temperature is controlled 18 minutes before tapping. P is 0.018% to 0.030%. Slag removal is required before tapping, and argon blowing is immediately performed on the bottom of the ladle to homogenize the composition.

[0013] Wherein, in step (2), the white slag is kept for 14 to 18 minutes, and the steel is tapped at a temperature of T=1610 to 1650°C;

[0014] The relationship between the target casting speed and the target temperature in step (4) satisfies the following requirements:

[0015]

[0016] Where V is the actual casting speed (m / min), T is the measured casting temperature (°C), a and b are the lower and upper limits of the target temperature (°C), c and d are the lower and upper limits of the target casting speed (m / min). K is the correction coefficient for electromagnetic stirring (0.8 to 1.2);

[0017] The relationship between the specific water volume and the speed in step (4) satisfies the following requirements:

[0018]

[0019] Where J is the specific water content (L / (m 2 ·min), V is the pulling speed (m / min), T t is the target temperature at the inlet of the tension and leveling machine (℃), T a is the measured surface temperature of the ingot (℃), k, n, and m are process coefficients, which need to be determined according to the material and size of the ingot.

[0020] Wherein, in step (6), the slow cooling tunnel furnace is equipped with an exhaust gas waste heat recovery system, and the exhaust gas above 600°C is used for bell furnace preheating, and the heat recovery efficiency is ≥62%;

[0021] Wherein, the rolling temperature in step (6) meets the following requirements:

[0022]

[0023] Where, T represents the rolling temperature (℃), σ t represents the target tensile strength (MPa), σ n Indicates the conventional tensile strength of the material under the formula (MPa);

[0024] Wherein, in step (7), the heating rate satisfies

[0025]

[0026] Where V is the heating rate (℃ / h), Tn is the room temperature (℃), Δσ is the deviation between the actual measured value of the wire rod yield strength and the required target value, σ s It is the actual measured yield strength (MPa).

[0027] After adopting the above technical solution, the beneficial effects of the present invention are:

[0028] 1. Through secondary cooling water weak cooling and electromagnetic stirring, the core segregation of the continuous casting billet is reduced, thereby alleviating the state of large carbide size and uneven carbide distribution caused by selective crystallization during casting, and effectively achieving fine and dispersed distribution of carbides;

[0029] 2. High-speed wire rod rolling is adopted, and the whole process of rolling and cooling is realized through 36 rolling mills, 4 water tanks, and induction heating furnace temperature supplementation, effectively avoiding overheating and overheating of the core;

[0030] 3. Using argon atmosphere annealing in a bell-type annealing furnace instead of traditional canning annealing can effectively reduce the surface decarburization layer. The decarburization layer + transition layer is controlled to ≤40um, avoiding the performance of the subsequent heat treatment failing to meet the requirements.

[0031] 4. This method combines continuous casting and continuous rolling processes, and then uses argon in a bell-type annealing furnace for protective annealing, which improves the overall production efficiency, ensures the surface decarburization layer, reduces pollution to the environment, improves the overall quality of the product and reduces production costs. It is conducive to promoting the application of low-alloy high-speed steel wire rods and provides support for enterprises to reduce costs, increase efficiency and expand productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 , Flowchart of the efficient and high-quality production method of low-alloy high-speed steel wire rod based on continuous casting;

[0033] Figure 2 , 4241BФ5.5 transverse metallography;

[0034] Figure 3 , 4241BФ5.5 eutectic carbide unevenness. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0036] Example 1:

[0037] like Figure 1 As shown in Table 1, the product specification is 4241B annealed wire rod with a diameter of 5.5 mm. Its chemical composition is shown in Table 1.

[0038] Table 1 Chemical composition of 4241B wire rod in Example 1

[0039] element C Si Mn P S Cr Mo V W content / % 0.98 0.92 0.35 0.030 0.003 4.45 0.95 0.35 1.08

[0040] Step 1: Add scrap steel and high-carbon ferrochrome and other alloy materials into the electric arc furnace for melting and primary refining of the alloy. The tapping temperature is 1680°C, P=0.028%, and slag removal is required before tapping.

[0041] Step 2: Add lime and fluorite to the LF furnace, electrify the slag, control the slag R3.0 to adjust the alloy composition, heat up and refine, use deoxidizers such as ferrosilicon for deoxidation, and use the amount to maintain white slag operation. Take samples for analysis. When the various alloy components meet the standard requirements, keep the white slag for 15 minutes. When T=1630℃, the steel is transferred to the VD station.

[0042] Step 3: Before entering the VD furnace, slag removal and vacuuming are carried out. The vacuum reaches 67Pa and is maintained for 15 minutes. After breaking the vacuum, temperature measurement, sampling and full analysis are carried out, and a covering agent is added. Maintain calmness and weak argon blowing for 12 minutes. When the temperature is measured at T = 1550℃, transfer to the continuous casting machine platform.

[0043] Step 4: Continuous casting of curved billets is carried out using a continuous casting machine. A combination of a mold and end-stage electromagnetic stirring is used for casting. The casting speed is controlled according to the table below. The casting speed is determined to be 1.15 m / min.

[0044] Target temperature Target pulling speed 1470～1490℃ 1.0~1.2m / min

[0045] Cooling control: The secondary cooling zone adopts a three-stage zoned water distribution method. The water volume is automatically matched with the drawing speed. The material temperature entering the drawing and straightening machine is 1100℃. The billet is cut to a fixed length when it is discharged, and the continuous casting billet with a cross-section of 150×150mm and a length of 3000mm is obtained.

[0046] Step 5: Annealing of continuous casting billets. After being cut, the continuous casting billets are immediately transferred to a chamber furnace for annealing. The annealing process is to keep the temperature at 856℃ for 6 hours, and then cool to 285℃ before being taken out of the furnace.

[0047] Step 6: Heating in a walking beam furnace. The heating temperature of the billet is controlled as follows: preheating section: 600-840°C, heating time: 30 minutes; heating section: 840-1060°C, heating time: 50 minutes; soaking section: 1060-1100°C, heating time: 150 minutes. Rolling is carried out at a certain temperature, with the final rolling temperature controlled at 980-1000°C, the finishing speed controlled at 34m / s, and the rolling specification of Φ5.5mm. The heat is collected and sent to an intelligent slow cooling tunnel furnace. Cooling is carried out in three stages with a gradient drop of 250°C. After slow cooling for 50 hours, the billet is transferred to a bell-type furnace for annealing. The out-of-roundness of the hot-rolled wire rod is controlled to ±0.15mm.

[0048] Step 7: Annealing. The hot-rolled wire rod needs to be annealed within 8 hours. Annealing adopts hood annealing. Nitrogen is purged at room temperature before heating. Nitrogen is filled for protection during heating, insulation and cooling. The flow rate is set at 15m 3 / h, the heating system is: heating with the furnace, ensuring that the heating time from room temperature to 860℃ is 8 hours, keeping at 865℃ for 10 hours, cooling with the furnace to below 500℃, and then taking it out of the furnace for air cooling.

[0049] Laboratory test 4241B carbide distribution, as attached Figure 2 , Attachment Figure 3 Random sampling analysis was performed on two points in the figure, and the analysis results are shown in Table 1. The results show that the lateral size of the carbides and the eutectic carbide unevenness of level 2 meet the requirements of most industrial applications.

[0050] Table 1 Random sampling analysis

[0051] Serial number Carbide size (lateral) / um Eutectic carbide unevenness / grade 1# 11.5 2.0 2# 10.7 2.0

[0052] The laboratory selected two samples to simulate the customer's post-process pull-out test for tensile properties. The mechanical performance indicators are shown in Table 2. These performance indicators meet the needs of most customers, and the overall performance is relatively stable after multiple subsequent tests.

[0053] Table 2 Mechanical properties test indicators

[0054]

[0055] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above-mentioned embodiment, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A high-efficiency and high-quality production method for low-alloy high-speed steel wire rod based on continuous casting, characterized by: The specific steps are as follows: Step (1) electric furnace smelting: adding scrap steel and high carbon ferrochrome and other alloy materials into an electric arc furnace, melting and preliminarily smelting the alloy, and tapping the steel; Step (2) LF furnace refining: adding lime and fluorite to the LF furnace, electrifying the slag, controlling the slag in the range of R2.5 to 3.5 and adjusting the alloy composition, and heating and refining; using ferrosilicon and other deoxidizers for deoxidation, with the amount used being based on maintaining white slag operation, sampling and analysis, and when each alloy composition meets the standard requirements, tapping the white slag at a certain temperature; Step (3) VD furnace refining: before entering the VD furnace, slag removal and vacuuming are performed; the vacuum degree reaches 67 Pa and is maintained for 14 to 18 minutes; after breaking the vacuum, temperature measurement, sampling and full analysis are performed, and a covering agent is added. The furnace is kept calm and weakly blown with argon for 12 to 14 minutes. When the temperature reaches 1550°C, the furnace is transferred to the continuous casting machine platform; Step (4) continuous casting of billets: arc-shaped billets are continuously cast using a continuous casting machine, and a combination of a crystallizer and an end electromagnetic stirring method is used during casting, and the billets are pulled out at a certain speed; the secondary cooling zone adopts a three-stage zoned water distribution method, and the specific water volume is automatically matched with the pulling speed, and the material temperature entering the pulling and straightening machine is 1000-1200°C; the billets are cut to a fixed length when they are discharged, and the cross-section of the billets is obtained to a certain specification; Step (5) annealing of the continuous casting billet: immediately after the continuous casting billet is cut, it is transferred to a chamber furnace for annealing. The annealing process is to keep the temperature at 850-860°C for 6 hours, and then cool it to 265-300°C before being taken out of the furnace. Step (6) high-speed wire rolling: heating in a walking beam heating furnace, the heating temperature of the initial rolled square billet is controlled according to the following requirements: preheating section: 600-840°C, heating time 30min; heating section: 840-1060°C, heating time 50min; soaking section: 1060-1100°C, heating time 150min; rolling is carried out at a certain temperature, the final rolling wire drawing temperature is controlled at 980-1000°C, the finishing rolling speed is controlled at 34m / s, the rolling specification is Φ5.5mm, the heat is collected and enters the intelligent slow cooling tunnel furnace, and is cooled in three stages with a gradient drop of 250°C. The slow cooling is ≥48 hours and then transferred to a bell-type furnace for annealing. The out-of-roundness of the hot-rolled wire rod is controlled to ±0.15mm; Step (7) bell-type furnace annealing: The hot-rolled wire rod needs to be annealed within 8 hours. The annealing adopts bell-type annealing. Nitrogen is purged at room temperature before heating. Nitrogen is filled for protection during heating, insulation and cooling. The flow rate is set at 15m 3 / h, purge until the oxygen content in the furnace chamber is ≤200ppm; the heating system is: heat up with the furnace, and ensure that the heating time from room temperature to 860℃ is 8 hours, keep warm at 860±10℃ for 10 hours, cool with the furnace to below 500℃, and then take out of the furnace and air cool.

2. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The tapping temperature in step (1) is 1600°C to 1620°C, and the temperature is controlled 18 minutes before tapping. P is 0.018% to 0.030%. Slag removal is required before tapping, and argon blowing is performed on the bottom of the ladle immediately after slag removal to homogenize the composition.

3. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The white slag in step (1) is kept for 14 to 18 minutes, and the steel is tapped at a temperature of T=1610 to 1650°C.

4. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The relationship between the target casting speed and the target temperature in step (1) meets the following requirements: Where V is the actual pulling speed (m / min), T is the measured billet temperature (°C), a and b are the lower and upper limits of the target temperature (°C), c and d are the lower and upper limits of the target pulling speed (m / min); K is the correction coefficient of electromagnetic stirring (0.8~1.2).

5. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The relationship between the specific water volume and the speed in step (4) meets the following requirements: Where J is the specific water content (L / (m 2 ·min), V is the pulling speed (m / min), T t is the target temperature at the inlet of the tension and leveling machine (℃), T a is the measured surface temperature of the ingot (℃), k, n, and m are process coefficients, which need to be determined according to the material and size of the ingot.

6. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: In step (6), the slow cooling tunnel furnace is equipped with an exhaust gas waste heat recovery system, and the exhaust gas above 600°C is used for preheating the bell furnace, with a heat recovery efficiency of ≥62%.

7. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The rolling temperature in step (6) meets the following requirements: Where, T represents the rolling temperature (℃), σ t Indicates the target tensile strength (MPa), σ n Indicates the normal tensile strength (MPa) of the material itself under the formulation.

8. The method for producing low-alloy high-speed steel wire rod with high efficiency and high quality based on continuous casting according to claim 1, characterized in that: The heating rate in step (7) satisfies: Where V is the heating rate (℃ / h), Tn is the room temperature (℃), Δσ is the deviation between the actual measured value of the wire rod yield strength and the required target value, σ s It is the actual measured yield strength (MPa).

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