Method for improving same-circle mechanical property uniformity of low-carbon cold heading steel wire rod

Abstract

The invention relates to a method for improving the same-circle mechanical property uniformity of a low-carbon cold heading steel wire rod, which comprises the following steps of: firstly, carrying out sectional heating on a steel billet at the temperature of a preheating section of 715-785 DEG C, the heating temperature of a first section of 810-850 DEG C, the heating temperature of a second section of 920-960 DEG C and the temperature of a soaking section of 1000-1040 DEG C; then the prepared steel billet is rolled into a wire rod, the initial rolling temperature ranges from 910 DEG C to 950 DEG C, the finish rolling inlet temperature ranges from 865 DEG C to 885 DEG C, the finish rolling outlet temperature is smaller than or equal to 1020 DEG C, and the finish rolling temperature ranges from 890 DEG C to 910 DEG C; the prepared wire is subjected to water cooling to 840-860 DEG C for spinning, and then the wire is rolled into a wire rod at 780-850 DEG C; and finally, the prepared wire rod is placed on a stelmor slow cooling line for heat preservation and slow cooling, the stelmor slow cooling speed is 0.2-1 DEG C / s, the temperature of entering a heat preservation vestibule is 740-770 DEG C, the heat preservation time of the heat preservation vestibule is 75-150 min, and the temperature of leaving the heat preservation vestibule is smaller than or equal to 400 DEG C. By means of the method, the same-circle mechanical property tensile strength fluctuation of the steel wire rod is smaller than or equal to 10 Mpa, the percentage reduction of area fluctuation is smaller than or equal to 2%, the percentage elongation after fracture fluctuation is smaller than or equal to 2%, the yield strength fluctuation is smaller than or equal to 8 Mpa, metallographic structures are evenly distributed, and no abnormal structure exists.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling production, in particular to a method for improving the uniformity of mechanical properties of a low-carbon cold heading steel wire rod in the same circle. Background Art

[0002] The uniformity of steel is an important parameter to measure the quality of steel. Poor uniformity of steel can easily lead to uneven force on steel products during service, affecting the safety of steel products. Cold heading steel wire rods are mainly used for the production of 8.8-grade fasteners, welded parts and other structural parts. Among them, 8.8-grade fasteners are usually used in some occasions that need to bear large loads or important links, such as bridges, assembly of large mechanical equipment, etc. Therefore, there are strict requirements for the quality of these steel wire rods used as fasteners, especially the uniformity of the mechanical properties of the same circle of steel wire rods. The poor uniformity of the mechanical properties of the same circle of wire rods is mainly manifested in the large difference in the tensile strength of the same circle of wire rods, the large difference in the area reduction rate of the same circle of wire rods, and the large difference in the elongation after fracture of the same circle of wire rods. If the mechanical properties of the same circle of steel wire rods differ greatly, it will affect the service life of the product and the safety factor during use. Therefore, it is very important to improve the mechanical properties of the wire rods and the uniformity of the mechanical properties of the same circle, which requires all-round scientific design and fine control of the whole process. Summary of the invention

[0003] The purpose of the present invention is to provide a method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rods in the same circle, so that the mechanical properties of the prepared low-carbon cold heading steel wire rods in the same circle are uniform and excellent.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides a method for improving the uniformity of mechanical properties of a low-carbon cold heading steel wire rod in the same coil, which is characterized by comprising the following steps: S1: Heating, heating the steel billet in sections, wherein the preheating section temperature is 715-785°C, the first section heating temperature is 810-850°C, the second section heating temperature is 920-960°C, and the soaking section temperature is 1000-1040°C; S2: temperature-controlled rolling, rolling the steel billet obtained in step S1 into wire rod, wherein the starting rolling temperature is 910-950° C., the finishing rolling inlet temperature is 865-885° C., the finishing rolling outlet temperature is ≤1020° C., and the final rolling temperature is 890-910° C.; S3: spinning and coiling, cooling the wire obtained in step S2 to 840-860° C., spinning, and then coiling into wire rods at 780-850° C.; S4: Slow cooling and heat preservation, placing the wire rod prepared in step S3 on a Stelmor slow cooling line for heat preservation and slow cooling, the Stelmor slow cooling rate is 0.2~1℃ / s, the temperature entering the heat preservation corridor is 740~770℃, the heat preservation time in the heat preservation corridor is 75~150min, and the temperature out of the heat preservation corridor is ≤400℃.

[0005] Furthermore, the chemical elements of the applicable low carbon steel wire rod are, in mass percentage, C: 0.18~0.23%, Si≤0.10%, Mn: 0.70~1.00%, P≤0.03%, S≤0.035%, Al: 0.03~0.05%, Cr: 0.15~0.25%, Ti: 0.025~0.055%, B: 0.0018~0.0030%, Ni, Cu≤0.20%, As, Sn≤0.20%, Pb≤0.005%, and the rest are iron and unavoidable impurities.

[0006] Furthermore, in step S1, during heating, the temperature difference between the head, middle and tail of the billet is controlled to be less than 30°C, and the temperature of the tail is 15-30°C higher than that of the head.

[0007] Furthermore, in the step S2, the rolling process includes pre-finishing rolling and finishing rolling, a side looper is provided between the pre-finishing rolling and the finishing rolling, and a starting height of the side looper is set according to the specification of the wire rod.

[0008] Furthermore, when the wire specification is 5.5mm≤φ≤10mm, the side looper starting height between the pre-finishing rolling and the finishing rolling is 26%~30% of the adjustable maximum height; when the wire specification is 10mm<φ≤24mm, the side looper starting height between the pre-finishing rolling and the finishing rolling is 30%~35% of the adjustable maximum height.

[0009] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: The present invention obtains a wire rod with good organization by controlling the spinning temperature and slow cooling speed of the wire rod and adding a heat preservation corridor for further slow cooling, which solves the problem of large organizational differences and unevenness due to different cooling speeds at the overlap point and non-overlap point of the wire rod caused by the traditional slow cooling method. At the same time, by strictly controlling the cooling speed and the slow cooling environment when the wire rod undergoes phase change, the slow cooling speed of all parts in the heat preservation corridor before and after the phase change is the same, thereby obtaining good uniformity. At the same time, the slow cooling process of the present invention has wide applicability, good practicality, and flexible control method. DETAILED DESCRIPTION

[0010] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0011] The present invention provides a method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rods in the same coil, characterized in that it includes a heating process, a temperature-controlled rolling process, a wire laying and coiling process, and a slow cooling and heat preservation process. The chemical elements of the low-carbon steel wire rods suitable for the above-mentioned improvement method are as follows by mass percentage: C: 0.18-0.23%, Si≤0.10%, Mn: 0.70-1.00%, P≤0.03%, S≤0.035%, Al: 0.03-0.05%, Cr: 0.15-0.25%, Ti: 0.025-0.055%, B: 0.0018-0.0030%, Ni, Cu≤0.20%, As, Sn≤0.20%, Pb≤0.005%, and the rest are iron and unavoidable impurities.

[0012] Specifically, in the heating process, a regenerative blast furnace gas heating furnace is used for segmented heating, with the preheating section temperature being 715~785°C, the first section heating temperature being 810~850°C, the second section heating temperature being 920~960°C, and the equalizing section temperature being 1000~1040°C.

[0013] During the heating process, the temperature difference between the head, tail and middle of the billet must be controlled not to exceed 30°C. After leaving the heating furnace, the billet is dephosphorized by 10~15Mpa high-pressure water to remove the surface oxide scale and then bites the steel through the head of the roller. The time it takes for the tail of the billet to reach this position will be longer, resulting in a greater drop in temperature. Therefore, adjustments are made accordingly to control the temperature of the tail of the billet to be 15~30°C higher than that of the head, ensuring that the temperature of the tail of the billet to the biting position of the head is consistent.

[0014] The tail is 15~30℃ higher than the head, because when the head bites into the rolling mill, the tail is exposed to the air and there will be temperature loss, so it is necessary to control the temperature of the tail to be higher than the head during heating. In addition, there is a temperature drop when the billet is water-cooled, and the temperature drop of the head is greater. In actual production, the flying shear cuts off the irregular head shape or the part with too low temperature. If there is no temperature drop and the temperature loss is exposed to the air, the most ideal state is that the temperature of the head, the middle and the tail is uniform. The determination of the temperature value of the tail being higher than the head can be widely described as the temperature loss of the tail of the billet exposed to the air, which varies according to the factors such as the instruments and equipment in the actual production of different factories.

[0015] In the temperature-controlled rolling process, the starting rolling temperature is set at 910~950℃, and the steel billet is successively subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to become wire rod. Specifically, the finishing rolling inlet temperature is set at 865~885℃, and the finishing rolling outlet temperature is ≤1020℃.

[0016] At the same time, a total of four water tanks are provided during the rolling process, namely 1#, 2#, 3#, and 4# water tanks. After passing through the pre-finishing mill, the wire rod is water-cooled in the 1# water tank, and after diameter measurement and flying shearing, it enters the finishing mill for rolling. After exiting the finishing mill, it passes through the 2#, 3#, and 4# water tanks in sequence for water cooling before spinning. In order to prevent the wire rod from vibrating greatly and hitting the steel pile in the guide groove due to the large impact force when entering the water tank, a clamping roller is provided between the water tanks in the embodiment of the present invention. In addition, if the control hotkey signal of the water tank is set at the outlet of the finishing mill, the rolled piece with water or high water vapor may cause signal delay. If it is set at a farther position in front of the finishing mill, there will be too much uncertainty in time control, and the delay setting is difficult. Therefore, in the embodiment of the present invention, the control hotkey signal of the water tank is set at the entrance of the finishing mill.

[0017] In addition, for the front end of the steel billet to be rolled, the high temperature state of the finished product must be maintained to prevent the head of the rolled piece from blooming and piling up steel, so as to ensure that the wire is spun on the loose coil cooling conveyor in the correct shape. However, because the temperature of the first few turns of wire is generally higher than the temperature required for the length of most products (called "hot length"), in order to maintain the "hot length" at high temperature, the water tank valve is closed when the head of the steel billet passes through the water cooling section. The time from the completion of the previous product to the start of the next wire product (that is, the interval time between rolling two steel billets) can be as short as 5 seconds. In order to quickly divert the cooling water from the product, a three-way diverter valve is used in the embodiment of the present invention.

[0018] When the hot length of the rolled piece passes, the three-way diverter valve quickly transfers to the cooling water channel. The hot length distance of the rolled piece is determined by the cross-sectional size of the product and the distance between the control equipment. In the embodiment of the present invention, when the product specification is φ5.5mm~φ8mm, the hot length of the wire is about 30m, the hot length of the wire with a product specification of φ10mm is about 15m, and the hot length of the wire with a product specification of φ12mm~φ24mm is 0~3m.

[0019] In addition, when the water pressure in the cooling nozzle in the water tank is less than the minimum value, the water cannot penetrate the steam film to exchange heat between the cooling water and the surface of the high-temperature rolled piece when the high-temperature wire is cooled by water. When the cooling water pressure is too high, the surface of the wire product will be overcooled and may form an undesirable allotrope of steel, martensite structure. Therefore, according to the wire rod spinning temperature and the uniformity of the wire structure, the water pressure of the four water tanks is set to 2.8~3.5bar in production.

[0020] In the embodiment of the present invention, the setting height of the side looper is also optimized and adjusted. The adjustment of the side looper's starting height is the main adjustment method for adjusting the tension between the pre-finishing mill and the finishing mill. Whether the starting height is reasonable is mainly reflected in the coefficient value of the looper after the looper is started. When the starting height is set unreasonably, rolling instability will occur during rolling, thereby affecting the wire size smoothness, that is, the uniformity of the structure. The starting height of the side looper is set according to the specifications of the wire. Specifically, in the present invention, when the wire specifications are φ5.5mm~φ10mm, the starting height of the side looper is 26%~30% of the maximum adjustable height, and the side looper is most stable when adjusted to 28%; when the wire specifications are φ10mm~φ24mm, the starting height of the side looper is 30%~35% of the maximum adjustable height, and the side looper is most stable when adjusted to 32%. Through experiments, the optimal starting height of the side looper between the pre-finishing mill and the finishing mill during the rolling process of wires of different specifications was obtained, so that the wire can be stably tension-free rolled during the high-speed rolling process with a smaller cross-section, ensuring its dimensional uniformity.

[0021] In addition, in order to ensure that no phase change occurs during the rolling process and the rolling is performed completely in the single-phase austenite region, the final rolling temperature of the hypoeutectoid steel should be higher than the final temperature of 841°C at which all ferrite is integrated into austenite. After the final rolling, the wire rod is water-cooled in 2#, 3#, and 4# water tanks. Therefore, in the actual production process, the final rolling temperature of the embodiment of the present invention is controlled at 890~910°C.

[0022] In the corresponding spinning and coiling process, the spinning temperature is set at 840~860℃. In order to improve the stability of the spinning ring shape, the curing dynamic adjustment advance coefficient is 1.012~1.020, and the spinning machine speed adjustment range is less than 2%. Then the wire is coiled at 780~850℃.

[0023] In the slow cooling and heat preservation process, the heat preservation cover and fan of the Stellmore line are all closed during the slow cooling period, and the entrance roller speed is controlled at 0.15~0.335m / s according to the wire specifications of φ5.5mm~24mm, and the exit roller speed is controlled at 0.3~0.5m / s. The entrance and exit roller speeds of the slow cooling line corresponding to each specification can have an error of ±5%. The appropriate entrance roller speed can ensure that the wire rod enters the slow cooling line smoothly, avoiding deformation or damage of the wire rod caused by too fast or too slow speed. At the same time, a reasonable entrance speed also helps to control the temperature distribution of the wire rod entering the slow cooling line, laying the foundation for the subsequent cooling process.

[0024] The slow cooling rate of the product is controlled at 0.2~1℃ / s to ensure that the critical temperatures of ferrite and pearlite precipitation of the wire rod are around 783℃ and 718℃ respectively. The coiled wire rod is put into the insulation corridor for slow cooling at 740~770℃, during which the cooling rates of the overlap points and non-overlap points of the wire rod tend to be consistent.

[0025] The cooling rate of the wire from spinning to coiling to entering the insulation corridor is 0.2℃ / s~2℃ / s. Most of the decomposition process of austenite can be carried out in the insulation corridor and fully decomposed to obtain a uniform structure, thereby obtaining cold heading steel wire rod with good mechanical properties in the same circle. Finally, after slow cooling in the insulation corridor for 75~150 minutes, it leaves the corridor for finished product inspection, weighing and labeling, and storage.

[0026] In addition, the insulation time of the wire in the insulation corridor is related to the size of the wire. The insulation time of the wire with small specifications is longer than that of the wire with large specifications. The slow cooling speed of the wire in the insulation corridor is fast at first and then slow, and 0℃ / s<slow cooling speed in the insulation corridor≤1℃ / s.

[0027] The present invention will be further described in detail below in conjunction with specific embodiments.

[0028] The chemical composition of the steel billets used in the low carbon cold heading steel wire rods corresponding to Examples 1-3 and Comparative Examples 1-3 is shown in Table 1: Table 1: Composition of steel billets used in various embodiments and comparative examples (wt / %) C Si Mn P S Al Cr Ti B Ni+Cu As+ Sn Pb Example 1 0.18 0.1 0.7 0.03 0.035 0.03 0.15 0.025 0.0018 0.2 0.2 0.005 Example 2 0.20 0.08 0.85 0.02 0.02 0.04 0.2 0.045 0.0024 0.15 0.15 0.003 Example 3 0.23 0.05 1 0.01 0.01 0.05 0.25 0.055 0.0030 0.1 0.1 0.001 Comparative Example 1 0.12 0.2 0.5 0.05 0.05 0.02 0.1 0.02 0.0005 0.3 0.25 0.007 Comparative Example 2 0.28 0.15 1.2 0.08 0.07 0.07 0.4 0.07 0.005 0.4 0.3 0.006 Comparative Example 3 0.25 0.12 1.15 0.04 0.03 0.06 0.3 0.020 0.015 0.35 0.3 0.006 Example 1 The steel billet corresponding to Example 1 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 910°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 28% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 890°C. After being cooled to 840℃ through water, the wire is spun; after spinning, it is first subjected to Stelmor slow cooling with a cooling rate of 0.20~1℃ / s, and then hot-rolled through a certain number of rollers with a hot-rolling temperature of 780℃, and then slowly cooled in a heat preservation corridor at 740℃ for 150min, and then the temperature reaches 400℃ to obtain the φ5.5mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤10MPa, the yield strength fluctuation is ≤7MPa, the cross-sectional shrinkage rate is 65%≤≤66%, the elongation after fracture is 34%≤≤35%, the wire rod has excellent wire-pass property, uniform metallographic structure, and no abnormal structure.

[0029] Example 2 The steel billet corresponding to Example 2 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 950°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 32% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 910°C. After being cooled to 860℃ through water, the wire is spun; after spun, it is first subjected to Stelmor slow cooling at a cooling rate of 0.2~1℃ / s, and then hot-rolled through a certain number of rollers at a hot rolling temperature of 850℃, and then slowly cooled in a heat preservation corridor at 770℃ for 75 minutes, and then the temperature reaches 386℃ to obtain the φ24mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤7MPa, the yield strength fluctuation is ≤5MPa, the cross-sectional shrinkage rate is 67%≤≤68%, the elongation after fracture is 37%≤≤38%, the wire rod has excellent wire-pass properties, uniform metallographic structure, and no abnormal structure.

[0030] Example 3 The steel billet corresponding to Example 3 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 930°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 26% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 903°C. After being cooled to 846℃ through water, the wire is spun; after spun, it is first subjected to Stelmor slow cooling with a cooling rate of 0.2~1℃ / s, and then hot-rolled through a certain number of rollers with a hot-rolling temperature of 818℃, and then slowly cooled in a heat preservation corridor at 756℃ for 90min, and then the temperature reaches 388℃ to obtain the φ10mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤9MPa, the yield strength fluctuation is ≤8MPa, the cross-sectional shrinkage rate is 65%≤≤66%, the elongation after fracture is 36%≤≤37%, the wire rod has good wire-pass property, uniform metallographic structure, and no abnormal structure.

[0031] Comparative Example 1 The steel billet corresponding to Example 1 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 930°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 30% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 903°C. After being cooled to 855℃ through water, the wire is spun; after spun, it is first subjected to Stelmor slow cooling at a cooling rate of 5-15℃ / s, and then hot-rolled through a certain number of rollers at a hot rolling temperature of 711℃, and then slowly cooled in a heat preservation corridor at 698℃ for 83min, and the temperature reaches 389℃ to obtain the φ8mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤38MPa, the yield strength fluctuation is ≤33MPa, the cross-sectional shrinkage rate is 59%≤≤64%, the elongation after fracture is 30%≤≤34%, the wire rod has good wire passing property, the metallographic structure is unevenly distributed, and abnormal structures such as bainite are present.

[0032] Comparative Example 2 The steel billet corresponding to Example 2 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 933°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 35% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 898°C. After being cooled to 855℃ through water, the wire is spun; after spinning, Stelmor slow cooling is carried out, and the cooling rate is 5-15℃ / s. When the temperature reaches 377℃, the wire is rolled out of the Stelmor slow cooling line to obtain the φ16mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤81MPa, the yield strength fluctuation is ≤72MPa, the cross-sectional shrinkage rate is 56%≤≤64%, the elongation after fracture is 27%≤≤34%, the wire rod has good wire-pass property, the metallographic structure is unevenly distributed in many places, the mechanical properties at the overlap point and the non-overlap point are greatly different, and there are abnormal structures such as bainite.

[0033] Comparative Example 3 The steel billet corresponding to Example 3 in Table 1 is placed in a regenerative blast furnace gas heating furnace with a soaking section temperature of 1000-1040°C for heating, and the start rolling temperature is 930°C. The heated steel billet is descaled by high-pressure water and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling. The side looper between the pre-finishing mill and the finishing mill is set to a starting height of 26% of the maximum adjustable starting height of the side looper, and the final rolling temperature is controlled to be 891°C. After being cooled to 846℃ through water, the wire is spun; after spun, it is first subjected to Stelmor slow cooling at a cooling rate of 0.2~1℃ / s, and then hot-rolled through a certain number of rollers at a hot rolling temperature of 811℃, and then slowly cooled in a heat preservation corridor at 768℃ for 120min, and then the temperature reaches 390℃ to obtain the φ18mm low-carbon cold heading steel wire rod, the tensile strength fluctuation in the same circle is ≤46MPa, the yield strength fluctuation is ≤38MPa, the cross-sectional shrinkage rate is 58%≤≤64%, the elongation after fracture is 29%≤≤34%, the wire rod size is poor, the metallographic structure is unevenly distributed, and there is no abnormal structure.

[0034] In summary, the present invention obtains wire rods with good size uniformity and good organizational uniformity from the aspects of heating, temperature-controlled rolling, and spinning. On the other hand, the wire rods with good organizational structure are obtained by controlling the spinning temperature and slow cooling speed of the wire rods and adding a heat preservation corridor for further slow cooling, thereby solving the problem of large organizational differences at the overlap points and non-overlap points of the wire rods or the generation of abnormal bainite or martensite organizations at two places due to too fast cooling, so that the mechanical properties of the wire rods in the same circle can reach tensile strength fluctuations ≤10MPa, cross-sectional shrinkage fluctuations ≤2%, elongation fluctuations ≤2%, and yield strength fluctuations ≤8MPa. At the same time, it has wide applicability, good practicality, and flexible control methods.

[0035] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rod in the same circle, characterized in that: The steps include: S1: Heating, heating the steel billet in sections, wherein the preheating section temperature is 715-785°C, the first section heating temperature is 810-850°C, the second section heating temperature is 920-960°C, and the soaking section temperature is 1000-1040°C; S2: temperature-controlled rolling, rolling the steel billet obtained in step S1 into wire rod, wherein the starting rolling temperature is 910-950° C., the finishing rolling inlet temperature is 865-885° C., the finishing rolling outlet temperature is ≤1020° C., and the final rolling temperature is 890-910° C.; S3: spinning and coiling, cooling the wire obtained in step S2 to 840-860° C., spinning, and then coiling into wire rods at 780-850° C.; S4: Slow cooling and heat preservation, placing the wire rod prepared in step S3 on a Stelmor slow cooling line for heat preservation and slow cooling, the Stelmor slow cooling rate is 0.2~1℃ / s, the temperature entering the heat preservation corridor is 740~770℃, the heat preservation time in the heat preservation corridor is 75~150min, and the temperature out of the heat preservation corridor is ≤400℃.

2. A method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rod in the same coil according to claim 1, characterized in that: The chemical elements of suitable low carbon steel wire rod are calculated in mass percentage as follows: C: 0.18~0.23%, Si≤0.10%, Mn: 0.70~1.00%, P≤0.03%, S≤0.035%, Al: 0.03~0.05%, Cr: 0.15~0.25%, Ti: 0.025~0.055%, B: 0.0018~0.0030%, Ni, Cu≤0.20%, As, Sn≤0.20%, Pb≤0.005%, and the rest are iron and unavoidable impurities.

3. The method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rod in the same coil according to claim 1, characterized in that: In step S1, during heating, the temperature difference between the head, middle and tail of the billet is controlled to be less than 30°C, and the temperature of the tail is 15-30°C higher than that of the head.

4. The method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rod in the same coil according to claim 1, characterized in that: In the step S2, the rolling process includes pre-finishing rolling and finishing rolling, a side looper is arranged between the pre-finishing rolling and the finishing rolling, and the starting height of the side looper is set according to the specification of the wire rod.

5. A method for improving the uniformity of mechanical properties of low-carbon cold heading steel wire rod in the same coil according to claim 4, characterized in that: When the wire specification is 5.5mm≤φ≤10mm, the side looper starting height between the pre-finishing rolling and the finishing rolling is 26%~30% of the adjustable maximum height; when the wire specification is 10mm<φ≤24mm, the side looper starting height between the pre-finishing rolling and the finishing rolling is 30%~35% of the adjustable maximum height.