A production process for improving the performance of small-diameter spring steel wire rods

Abstract

This invention belongs to the field of steel rolling technology and relates to a production process for improving the performance of small-diameter spring steel wire rods. The process includes billet loading into the furnace, heating, roughing and intermediate rolling, pre-finishing rolling, finishing rolling, wire drawing, and controlled cooling. Based on a walking beam furnace, this invention improves gas convection heat transfer and billet heat absorption by altering the billet arrangement within the furnace, while reducing decarburization through short-duration low-temperature heating. It also reduces the impact of cooling water on the billet temperature at the contact points by alternating the contact positions between the billet and the moving and stationary beams of the walking beam. Furthermore, it controls the gas injection length by adjusting the opening of the gas and air booster pumps, thereby increasing the temperature in the middle of the billet and reducing the temperature difference with both ends, ensuring uniform temperature across the head, middle, and tail of the billet. By appropriately opening each group of water tanks, it ensures uniform core and surface temperatures of the rolled product. Finally, by setting the opening of the airflow distributor, it ensures uniform temperature across all positions within the same coil during cooling, thus solving the problem of large performance fluctuations in small-diameter spring steel wire rods.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling technology and relates to a production process for improving the performance of small-diameter spring steel wire rods. Specifically, it is a production method designed to reduce performance fluctuations of small-diameter spring steel wire rods. Background Technology

[0002] Before being used to produce oil-quenched steel wire, spring steel wire rod typically requires drawing with a reduction in surface area of ​​nearly 30%. Spring steel wire rod has high strength, and large fluctuations in its tensile properties can significantly complicate the drawing process and affect production stability. Therefore, it is necessary to reduce the performance fluctuations of spring steel wire rod and improve its overall performance.

[0003] On the other hand, spring steel, due to its high carbon content and numerous alloying elements, especially high Si content, has a strong tendency to decarburize. Decarburization of the spring steel surface negatively impacts its strength, surface hardness, and fatigue performance. Therefore, it is necessary to reduce decarburization in spring steel. This is typically controlled through two aspects: billet heating and wire rod cooling. Billet heating has a greater impact on decarburization, thus requiring shorter heating times and lower heating temperatures.

[0004] Compared to pusher-type furnaces, walking beam furnaces produce better billet surface quality during heating. Modern steel rolling mills primarily use walking beam furnaces for billet heating. The walking beam of a walking beam furnace consists of a moving beam and a stationary beam, with circulating cooling water inside. When spring steel is heated in a walking beam furnace, the two ends of the billet are closer to the furnace wall and gas burners, where radiative and convective heat transfer are favorable, resulting in higher temperatures than the middle of the billet. Because spring steel requires less decarburization, the heating time and temperature of the billet need to be shortened, leading to uneven billet temperature. The temperature is especially lower at the contact points between the billet and the walking beam due to the cooling water inside the beam. Typically, after high-pressure water descaling, the temperature difference between the two ends and the middle of the spring steel billet can exceed 100°C. The surface temperature in the middle of the billet after exiting the furnace can sometimes even be less than 850°C. This negatively impacts mill load, rolling tension control, billet shape and size control, and the welding of internal defects and deformations in the billet.

[0005] Existing heating processes mainly reduce the heating temperature difference of steel billets by increasing the heating temperature and extending the heating time. However, this method is not applicable to spring steel 55SiCrA, which is sensitive to decarburization.

[0006] Conventional high-speed wire rod production processes for hot-rolled wire rods rely solely on pyrometer temperature measurements for control, neglecting the impact of actual differences in core and surface temperature on the wire rod's microstructure and properties. Medium and large diameter wire rods (Φ8.0–14.0mm and Φ15.0–25.0mm) have relatively slow rolling speeds and larger billet sizes, storing more heat, thus the water cooling process has a relatively small impact on billet temperature. However, small diameter wire rods (Φ5.5mm and Φ6.5mm) can reach final rolling speeds of 120m / s. This extremely high coiling speed results in a high coil stacking density after coiling. The coils are tightly stacked at the overlap with the conveyor rollers, hindering airflow and making heat dissipation difficult. Consequently, the cooling rate varies significantly across different parts of the coil, resulting in large temperature differences and variations in microstructure and properties within the same coil. The cooling rate at the overlap between the coil and the roller conveyor is slower, resulting in larger spacing between ferrite grains and pearlite lamellars compared to the non-overlapping areas. Consequently, the strength, plasticity, and hardness of the coil at the overlap are lower than those at the non-overlapping areas. Furthermore, 55SiCrA spring steel, due to its higher content of Si, Mn, and Cr alloying elements, is more sensitive to temperature fluctuations in its microstructure and properties than carbon steel. For small-diameter 55SiCrA spring steel coils (Φ5.5mm and Φ6.5mm), using existing traditional temperature control processes, the tensile strength fluctuation within a single batch can reach 80–130 MPa, and the hardness (HBW) fluctuation can reach 20–35 HBW. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems by providing a production process for improving the performance of small-diameter (Φ5.5mm~Φ6.5mm) spring steel wire rods. Based on a walking beam furnace, this process reduces decarburization by using short-duration low-temperature heating, thereby increasing the temperature in the middle of the billet, narrowing the temperature difference with both ends, and improving the temperature uniformity of the entire billet, ensuring uniform temperature across the head, middle, and tail of the billet. This results in hot-rolled spring steel wire rods with minimal fluctuations in performance, solving the problems of large temperature differences within the same coil, significant performance fluctuations, and difficulty in simultaneously achieving low decarburization in small-diameter spring steel wire rods.

[0008] To achieve the above-mentioned technical objectives, this invention provides a production process for improving the performance of small-diameter spring steel wire rods. The production process is as follows: billet entering the furnace → heating → roughing and intermediate rolling → pre-finishing rolling → finish rolling → wire drawing → controlled cooling. The specific process steps are as follows:

[0009] (1) Steel billet loading: The steel billet is loaded into the furnace by rotating roller conveyor, using the empty step distance method;

[0010] (2) Heating: After the steel billet enters the three-stage walking beam regenerative furnace, it first enters the preheating section. The furnace temperature in the preheating section is controlled at 600-800℃ by adjusting the opening of the gas and air flow valves, and the air-fuel ratio is controlled at 0.4-0.6. The time for the steel billet to pass through the preheating section is 35-45 minutes. After the steel billet is heated in the preheating section, it enters the heating section through the periodic movement of the walking beam. The furnace temperature in the heating section is controlled at 850-950℃, and the air-fuel ratio is controlled at 0.4-0.6. The time for the steel billet to pass through the heating section is 25-35 minutes. Similarly, after the steel billet is heated in the heating section, it enters the soaking section through the periodic movement of the walking beam. The furnace temperature in the soaking section is controlled at 1000-1100℃, and the air-fuel ratio is controlled at 0.4-0.6. The time for the steel billet to pass through the soaking section is 25-35 minutes.

[0011] Furthermore, the empty step distance method of loading steel in step (1) is as follows: after one steel billet enters the furnace, the next one is not pushed onto the furnace roller table. After the step beam in step (2) has completed one cycle, the next one enters the furnace. That is, after each billet enters, there is a one-step gap, which is conducive to the heat transfer of gas around the billet and the middle part of the billet can absorb more heat.

[0012] Furthermore, the walking beam in step (2) consists of a moving beam and a stationary beam. There is circulating cooling water inside the walking beam. After the moving beam lifts the steel billet on the stationary beam into position by hydraulic power, it pauses briefly (5-10 seconds) before lowering down to put the steel billet on the stationary beam and then retreating to position. The pause of the moving beam can prolong the contact time between the steel billet and the moving beam and shorten the contact time with the stationary beam, so that the contact time between the steel billet and the walking beam is as even as possible, and reduce the influence of the cooling water in the beam on the local temperature of the steel billet.

[0013] The above steps (1) and (2) use the empty step distance method to load steel. The moving beam of the walking beam rises and lifts the steel billet on the stationary beam. After moving forward to the position, it stays for 5 to 10 seconds and then descends to put the steel billet on the stationary beam and then moves backward to the position. This optimizes convective heat transfer and contact heat transfer, and has an outstanding effect on improving the temperature uniformity of the steel billet in the heating furnace.

[0014] Furthermore, in step (2), the preferred temperature of the heating section is 900-950℃, and the preferred temperature of the heat spreader section is 1050-1100℃.

[0015] Furthermore, in step (2), the opening of the gas and air flow booster pumps in the heating furnace is controlled at 60-100% to ensure that the gas pressure reaches more than 15 kPa and the length of the sprayed flame is not less than 4 m. The temperature difference between the furnace wall and the furnace top is controlled within 20℃ to ensure that the temperature of the billet head, middle and tail is uniform, which is conducive to the uniform temperature of the billet in the subsequent rolling process, thereby ensuring that the temperature of the wire rod is uniform after the wire is coiled.

[0016] (3) After the billet is slowly heated to a uniform and stable temperature in the soaking section, the billet is lifted by the walking beam onto the exit roller conveyor. The roller conveyor rotates and transports the billet out of the furnace. After the billet is descaled by high-pressure water, the initial rolling temperature is 930-1030℃. Subsequently, the billet passes through the roughing and intermediate rolling mills at 900-980℃.

[0017] Furthermore, a pyrometer is installed after the high-pressure water descaling device in step (3) to measure the temperature of the entire steel billet after descaling.

[0018] Furthermore, the preferred rolling temperature in step (3) is 960-1000℃, and the preferred roughing and intermediate rolling temperature is 930-960℃.

[0019] Furthermore, in step (3), the pressure of the high-pressure water descaling is not less than 16MPa, and the temperature difference between the head, middle and tail of the billet is controlled within 20℃.

[0020] (4) The billet then passes through the pre-finishing mill at 880-940℃. After rolling, it is cooled by the Zone 1 water tank and then reaches the finishing mill after passing through the temperature-regulating guide groove to achieve uniform temperature.

[0021] Furthermore, the pre-finishing temperature in step (4) is preferably 900–920°C;

[0022] Furthermore, steps (3) and (4) of roughing, intermediate rolling, and pre-finishing rolling together need to complete more than 95% of the total deformation.

[0023] Further, in step (4), Zone 1 water tank refers to the first group of water tanks, including two: 1# and 2#. Only 1# water tank is turned on and 2# water tank is turned off. The temperature of the billet arriving at the finishing mill is controlled by adjusting the flow rate of 1# water tank. The temperature of the billet arriving at the finishing mill is controlled to be 830-870℃. Turning off 2# water tank is beneficial for the billet to recover its temperature after strong water penetration (the cooling rate can reach about 50℃ / s), thereby ensuring that the core and surface temperature of the billet are uniform.

[0024] (5) The billet is then rolled into finished product specifications at 830-870℃ by the finishing mill. It is cooled by water tanks in Zone 2 (the second group includes 3: 3#, 4#, 5#) and Zone 3 (the third group includes 2: 6#, 7#). After the temperature is uniformly circulated by the reheating guide groove, the wire reaches the spinning machine.

[0025] Furthermore, the finishing rolling temperature in step (5) is preferably 840–860°C;

[0026] Furthermore, in step (5), only the No. 3 water tank in Zone 2 is turned on and the No. 4 and No. 5 water tanks are turned off, while the No. 6 and No. 7 water tanks in Zone 3 are turned off. By adjusting the flow rate of the No. 3 water tank, the spinning temperature of the subsequent wire rod is controlled. Turning off the No. 4, No. 5, No. 6 and No. 7 water tanks is conducive to the recovery of the wire rod after strong water penetration, thereby ensuring that the core and surface temperatures are uniform.

[0027] (6) The wire rod spinning temperature is controlled at 850-890℃;

[0028] Furthermore, the preferred spinning temperature in step (6) is 860–880°C.

[0029] (7) After the wire is spun into a coil, the wire rod is placed on the Stellmore roller conveyor. By setting the roller conveyor speed parameters, opening and closing the heat insulation cover, and turning on the Stellmore fan, the temperature of the wire rod entering the cover is controlled at 660-700℃ and the temperature of the wire rod exiting the cover is not higher than 630℃. By adjusting the air volume distributor, the temperature difference of the same coil before the wire rod enters the cover is controlled within 30℃.

[0030] Furthermore, the preferred temperature for the wire rod entering the cover in step (7) is 670–690°C;

[0031] Further, in step (7), the speed of the Steyrmo roller conveyor is set to 25-35 m / min, 2-4 heat insulation covers are turned on, and 2-4 motors with a power of 2×10 are turned on. 5 The Stellmore fan of W has an airflow opening of 10-40%, and the airflow distributor opening is 0-30%. Setting a faster Stellmore roller speed can reduce the stacking density between coils, and make it easier for the coil and roller overlap to dissipate heat. Several insulation covers near the spinning machine are opened and several fans are turned on, which helps the coil cool down quickly to the pearlite transformation range, allowing more time for the subsequent pearlite transformation in the insulation cover. The airflow distributor can control the airflow distribution at the overlap and non-overlap areas of the coil and roller, which can ensure uniform temperature of the entire coil, thereby reducing the fluctuation of the coil's performance.

[0032] The chemical composition of the spring steel wire rod obtained by this invention, by mass percentage, is as follows: C: 0.51-0.59%, Si: 1.20-1.60%, Mn: 0.50-0.80%, Cr: 0.50-0.80%, Ni≤0.35%, Cu≤0.25%, Al≤0.025%, P≤0.025%, S≤0.020%, with the remainder being iron and unavoidable impurities.

[0033] This invention employs a hollow-step loading method for steel, optimizing convective and contact heat transfer during heating to improve the temperature uniformity of the billet within the heating furnace. By controlling the opening of the gas and air booster pumps to regulate the gas injection length, the flame length is ensured, resulting in uniform furnace temperature and thus uniform temperature at the head, middle, and tail of the billet. This facilitates uniform billet temperature during subsequent rolling, ensuring uniform wire rod temperature after coiling. Furthermore, the optimal opening of water tanks and reheat guide channels ensures uniform core and surface temperature of the rolled product. Adjusting the airflow distributor opening ensures uniform temperature across all positions within the same coil during cooling. These measures effectively reduce performance fluctuations in spring steel wire rod, resulting in hot-rolled spring steel wire rods with minimal performance fluctuations, thus resolving the issues of large temperature differences and performance fluctuations within the same coil for small-diameter spring steel wire rods.

[0034] The beneficial effects of this invention are as follows: Through the above-described process, the spring steel billet is heated in a shorter time and at a lower temperature, thereby ensuring a shallower decarburization layer on the subsequently rolled wire rod, while simultaneously solving the problem of large performance fluctuations. The produced small-diameter spring steel wire rods can guarantee that the tensile strength fluctuation of the entire rod does not exceed 20 MPa, the hardness fluctuation does not exceed 5 HBW, and the total decarburization layer depth does not exceed 0.03 mm, achieving excellent decarburization of ≤0.5%D. This meets the drawing processing effect and performance requirements of downstream spring steel wire manufacturers, improving production stability and overall product performance. Detailed Implementation

[0035] The present invention will now be described in conjunction with the production implementation of small-diameter spring steel wire rods with a finished product specification of Φ5.5mm, produced from steel billets with the following chemical composition: C: 0.55%, Si: 1.45%, Mn: 0.69%, Cr: 0.74%, Ni: 0.08%, Cu: 0.06%, Al: 0.03%, P: 0.007%, S: 0.003%, on a small-diameter dedicated production line (total furnace length 26m, total step distance 100 steps).

[0036] Example 1

[0037] 1. Steel billet is fed into the furnace.

[0038] The billet positioning device is pre-adjusted via a screw to ensure accurate positioning of the billet on the furnace feed roller conveyor and inside the heating furnace. The overhead crane places the billet on the loading platform, and the pusher pushes the billet from the platform onto the furnace feed roller conveyor. The roller conveyor rotates and transports the billet into the furnace. After one billet enters the furnace, the next billet is not pushed onto the furnace feed roller conveyor. Instead, the next billet enters the furnace after one cycle of the walking beam, creating a blank step.

[0039] 2. Heating

[0040] After the steel billet enters the three-stage walking beam regenerative furnace, it first enters the preheating section. The furnace temperature in the preheating section is controlled at 600-800℃ and the air-fuel ratio is controlled at 0.4-0.6 by adjusting the opening of the gas and air flow valves. The steel billet spends 40 minutes in the preheating section. After the steel billet is heated in the preheating section, it slowly enters the heating section through the periodic movement of the walking beam. The furnace temperature in the heating section is controlled at 900-950℃ and the air-fuel ratio is controlled at 0.4-0.6. The steel billet spends 30 minutes in the heating section. Similarly, after the steel billet is rapidly heated in the heating section, it slowly enters the soaking section through the periodic movement of the walking beam. The furnace temperature in the soaking section is controlled at 1050-1100℃ and the air-fuel ratio is controlled at 0.4-0.6. The steel billet spends 30 minutes in the soaking section. During the operation of the walking beam system, which consists of a moving beam and a stationary beam with internal circulating cooling water, the moving beam, powered by hydraulic force, lifts the steel billet from the stationary beam and advances it to its designated position. After a 8-second pause, the moving beam descends to place the billet onto the stationary beam and then retreats to its final position. The gas and air flow booster pumps in the heating furnace are both operating at 80% capacity, with a gas pressure reaching 18 kPa, a jet flame length of 5 m, and the temperature difference between the furnace wall and the furnace roof controlled within 15°C.

[0041] 3. Roughing and intermediate rolling

[0042] After the billet is slowly heated to a uniform and stable temperature in the soaking section, it is lifted by the walking beam onto the exit roller conveyor. The roller conveyor rotates and transports the billet out of the furnace. After the billet exits the furnace, it is descaled by 18MPa high-pressure water and then rolled at a rolling temperature of 960-1000℃. The temperature difference between the head, middle and tail of the billet is controlled within 20℃. Subsequently, the billet passes through the roughing and intermediate rolling mills at 930-960℃.

[0043] 4. Pre-finish rolling

[0044] The billet then passes through the pre-finishing mill at 900-920℃. After rolling, it is cooled by the Zone 1 water tank and then passes through the reheat guide groove to even out the temperature. Only the No. 1 water tank in Zone 1 is opened and the No. 2 water tank is closed. The temperature of the billet reaching the finishing mill is controlled by adjusting the flow rate of the No. 1 water tank. The roughing, intermediate rolling and pre-finishing rolling together need to complete 97% of the total deformation.

[0045] 5. Finish rolling

[0046] The billet is then rolled into finished product specifications at 840-860℃ by the finishing mill. After being cooled by the Zone 2 and Zone 3 water tanks and uniformly heated by the reheat guide trough, the wire reaches the spinning machine. In Zone 2, only the No. 3 water tank is opened and the No. 4 and No. 5 water tanks are closed. In Zone 3, the No. 6 and No. 7 water tanks are completely closed.

[0047] 6. Spitting silk

[0048] The wire rod spinning temperature is controlled at 860-880℃.

[0049] 7. Cooling control

[0050] After being spun into coils, the wire rod is placed on the Steyrmo roller conveyor, with the roller speed set at 30 m / min. Three heat insulation covers are turned on, and three 2×10 power units are activated. 5 The W Stellmore fan has an air volume opening of 20% and an air volume distributor opening of 10%, which controls the temperature of the wire rod entering the shroud at 670-690℃ and the temperature exiting the shroud at no more than 630℃. The temperature difference between the same coil before entering the shroud is controlled within 20℃.

[0051] Example 2

[0052] Compared with Example 1, Example 2 involves the following steps: the billet is heated for 35 minutes in the preheating section, 25 minutes in the heating section, and 25 minutes in the soaking section of the heating furnace. The high-pressure water descaling pressure is 17 MPa. All other operations are the same as in Example 1.

[0053] Comparative Example 1

[0054] The main difference between Comparative Example 1 and Example 1 is that step 1 of Example 1, which involves intermittent feeding of steel billets into the furnace, is replaced with continuous feeding, i.e., no empty steps are generated. Other conditions are the same as in Example 1.

[0055] Comparative Example 2

[0056] Compared with Example 1, the main difference of Comparative Example 2 is that the brief pause after the moving beam lifts the steel billet on the stationary beam in step 2 of Example 1 is removed. That is, after the moving beam moves forward to the stationary beam, it immediately lowers and puts the steel billet on the stationary beam and then moves backward to the stationary beam. Other conditions are the same as in Example 1.

[0057] Comparative Example 3

[0058] Compared with Example 1, the main difference of Comparative Example 3 is that the state of water tank #2 after pre-rolling in step 4 of Example 1 is changed from closed to open, while other conditions are the same as in Example 1.

[0059] Comparative Example 4

[0060] Compared with Example 1, the main difference of Comparative Example 4 is that the status of water tanks 4#, 5#, 6# and 7# after fine rolling in step 4 of Example 1 is changed from closed to open, while other conditions are the same as in Example 1.

[0061] Comparative Example 5

[0062] Steps 1-6 are the same as in Example 1.

[0063] 7. Cooling Control: After the wire is coiled, it is placed on the Steyrmo roller conveyor. The roller conveyor speed is set to 30m / min. Three heat insulation covers are turned on, and three 2×1000 heat exchangers are turned on. 5W's Stellmore fan, with an air volume opening of 20%, an air volume distributor opening of 40%, a wire rod entry temperature controlled at 650-700℃, an exit temperature not exceeding 635℃, and a temperature difference of less than 50℃ between the same coil before the wire rod enters the shroud.

[0064] Comparative Example 6

[0065] Compared with Example 1, Comparative Example 6 replaces the intermittent feeding of steel billets in step 1 of Example 1 with continuous feeding, i.e., no empty steps occur; the brief pause after the moving beam lifts the steel billet on the stationary beam in step 2 of Example 1 is removed, i.e., the moving beam immediately lowers and places the steel billet on the stationary beam after moving to the stationary beam and then moves back to the stationary beam after moving to the stationary beam; the gas and air flow booster pumps in step 2 of Example 1 are turned off; the furnace temperature in the preheating section is 700-900℃, the furnace temperature in the heating section is 980-1050℃, and the furnace temperature in the soaking section is 1100-1160℃, and other operations are the same as in Example 1.

[0066] Increasing the heating temperature improves the temperature uniformity of the billet, but the stabilization effect is worse than in Example 1, and decarburization is exacerbated.

[0067] Comparative Example 7

[0068] Compared with Example 1, Comparative Example 7 replaces the intermittent feeding of steel billets in step 1 of Example 1 with continuous feeding, i.e., no empty steps are generated; the brief pause after the moving beam lifts the steel billet on the stationary beam in step 2 of Example 1 is removed, i.e., the moving beam immediately lowers and places the steel billet on the stationary beam after moving to the stationary beam and then moves back to the stationary beam after moving to the stationary beam; the gas and air flow booster pumps in step 2 of Example 1 are turned off; the heating time of the steel billet in the preheating section of the heating furnace is 50 minutes, the heating time in the heating section is 50 minutes, and the heating time in the soaking section is 50 minutes, and other operations are the same as in Example 1.

[0069] Extending the heating time improves the temperature uniformity of the billet, but the stabilization effect is worse than in Example 1, and decarburization is exacerbated.

[0070] The tensile strength, hardness HBW fluctuation, and total decarburization layer depth of Φ5.5mm small-specification spring steel wire rods produced in Examples 1, 2, 1, 2, 3, 4, 5, 6, and 7 of this invention (each batch has 3 rolls, and 4 samples are taken in a "+" shape on one coil of each roll, for a total of 12 samples per batch) are compared in Table 1.

[0071] Table 1. Tensile strength, hardness (HBW) fluctuation, and total decarburization depth of Φ5.5mm small-diameter spring steel wire rod.

[0072]

[0073]

[0074] This invention improves gas convection heat transfer and billet heat absorption conditions by changing the arrangement of billets in the heating furnace. It reduces the impact of cooling water on the billet temperature at the contact points by alternating the contact positions of the billets with the moving and stationary beams of the walking beam, thereby increasing the temperature in the middle of the billet, reducing the temperature difference between the middle and ends, and improving the temperature uniformity of the entire billet. By controlling the opening of the gas and air booster pumps to control the gas injection length, the flame length is ensured to achieve uniform furnace temperature, thus ensuring uniform temperature at the head, middle, and tail of the billet. This facilitates uniform billet temperature during subsequent rolling, ensuring uniform wire rod temperature after coiling. The invention also ensures uniform core and surface temperature of the rolled product by appropriately opening each group of water tanks and reheat guide channels, and by setting the opening of the air volume distributor to ensure uniform temperature at all positions within the same coil during cooling. Therefore, the tensile strength fluctuation of the obtained Φ5.5mm small-diameter spring steel wire rod can be controlled within 20MPa, the hardness fluctuation can be controlled within 5HBW, and the total decarburization layer depth does not exceed 0.03mm, achieving excellent decarburization of ≤0.5%D. In contrast, the Φ5.5mm small-diameter spring steel wire rod obtained in the comparative example has large fluctuations in uniformity or a deep decarburization layer. Therefore, the Φ5.5mm small-diameter spring steel wire rod produced in this embodiment can better meet the drawing processing effect and performance requirements of downstream spring steel wire manufacturers, improving production stability and overall product performance.

[0075] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the art; the methods used in this invention, unless otherwise specified, are all conventional methods in the art. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications made to the above embodiments based on the technical essence of the present invention are included within the protection scope of the present invention.

Claims

1. A production process for improving the performance of small-diameter spring steel wire rods, characterized in that: The production process is as follows: billet enters the furnace → heating → roughing and intermediate rolling → pre-finishing rolling → finish rolling → wire drawing → controlled cooling. The specific process steps are as follows: (1) The billet is fed into the furnace in an empty step-gap manner. It enters the three-section walking beam regenerative heating furnace. First, it enters the preheating section. The temperature of the preheating section is controlled at 600~800℃, the air-fuel ratio is controlled at 0.4~0.6, and the preheating time is 35~45min. Then, it enters the heating section through the walking beam cycle. The temperature of the heating section is controlled at 850~950℃, the air-fuel ratio is controlled at 0.4~0.6, and the billet takes 25~35min to pass through the heating section. After the billet is heated in the heating section, it enters the soaking section through the walking beam cycle. The temperature of the soaking section is controlled at 1000~1100℃, the air-fuel ratio is controlled at 0.4~0.6, and the billet takes 25~35min to pass through the soaking section. The temperature difference between the furnace wall and the furnace top is controlled within 20℃. The empty step-gap method for loading steel into the furnace is as follows: after each billet is fed, there is a one-step gap. (2) After the billet is slowly heated to a uniform and stable temperature in the soaking section, it is lifted by the walking beam onto the exit roller conveyor. The roller conveyor rotates and transports the billet out of the furnace. After the billet is descaled by high-pressure water, the initial rolling temperature is 930~1030℃. Subsequently, the billet passes through the roughing and intermediate rolling mills at 900~980℃. The temperature difference between the head, middle and tail of the billet is controlled within 20℃. (3) Subsequently, the billet passes through the pre-finishing mill at 880~940℃, and after rolling, it is cooled by water tank and then uniformly heated by the temperature guide groove before reaching the finishing mill. It is rolled into finished product specifications by the finishing mill at 830~870℃, cooled by water tank, and then uniformly heated by the temperature guide groove before reaching the wire rod. The wire rod's wire rod temperature is controlled at 850~890℃. The pre-finishing temperature in step (3) is 900~920℃. In Zone 1, only water tank #1 is opened and water tank #2 is closed. The total deformation amount needs to be completed by the pre-finishing and finishing rolling together, which is more than 95% of the total deformation amount; the finishing rolling temperature in step (3) is 840~860℃, only the No. 3 water tank in Zone 2 is opened and the No. 4 and No. 5 water tanks are closed, and the No. 6 and No. 7 water tanks in Zone 3 are all closed; among them, the Zone 1 water tank refers to the first group of water tanks, which includes two: No. 1 and No. 2; the Zone 2 water tank refers to the second group of water tanks, which includes three: No. 3, No. 4 and No. 5; the Zone 3 water tank refers to the third group, which includes two: No. 6 and No. 7; (4) After the wire is spun into coils, the wire rod is placed on the Steyrmore roller conveyor. By setting the roller conveyor speed parameters, opening and closing the heat insulation cover, and turning on the Steyrmore fan, the temperature of the wire rod entering the cover is controlled at 660~700℃, and the temperature of the wire rod exiting the cover is not higher than 630℃. By adjusting the air volume distributor, the temperature difference of the same coil before entering the cover is controlled within 30℃. In step (4), the wire spun temperature is 860~880℃; the wire rod entering the cover temperature is 670~690℃, the Steyrmore roller conveyor speed is set to 25~35m / min, 2~4 heat insulation covers are turned on, and 2~4 fans with a power of 2×10 are turned on. 5 W's Steyrmo fans have an airflow opening of 10-40% and an airflow distributor opening of 0-30%. The chemical composition of the wire rod, by mass percentage, is as follows: C: 0.51~0.59%, Si: 1.20~1.60%, Mn: 0.50~0.80%, Cr: 0.50~0.80%, Ni≤0.35%, Cu≤0.25%, Al≤0.025%, P≤0.025%, S≤0.020%, with the remainder being iron and unavoidable impurities.

2. The production process for improving the performance of small-diameter spring steel wire rods according to claim 1, characterized in that: Step (1) The cycle action of the walking beam refers to the moving beam of the walking beam lifting the steel billet on the stationary beam by hydraulic power and moving forward to the position, then pausing briefly, and then the moving beam lowers down to put the steel billet on the stationary beam and then moves back to the position; there is circulating cooling water inside the walking beam.

3. The production process for improving the performance of small-diameter spring steel wire rods according to claim 1, characterized in that: Step (1) The temperature of the heating section is 900~950℃ and the temperature of the soaking section is 1050~1100℃.

4. The production process for improving the performance of small-diameter spring steel wire rods according to claim 1, characterized in that: Step (2) The pressure of high-pressure water descaling shall not be less than 16 MPa.

5. The production process for improving the performance of small-diameter spring steel wire rods according to claim 1, characterized in that: Step (2) The initial rolling temperature is 960~1000℃, and the roughing and intermediate rolling temperature is 930~960℃.

6. The small-diameter spring steel wire rod obtained by the process according to any one of claims 1 to 5, characterized in that: The spring steel wire rod has a tensile strength fluctuation of no more than 20 MPa, a hardness fluctuation of no more than 5 HBW, and a total decarburization layer depth of no more than 0.03 mm, achieving excellent decarburization of ≤0.5%D.

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