Control method for reducing residual rate of scale in mechanical descaling of 90-grade tire cord steel wire rod

Abstract

The invention relates to a control method for reducing the residual rate of a 90-grade tire cord steel wire rod mechanical descaling oxide scale, which adopts the technological process of steel billet, coping, heating, controlled rolling and controlled cooling, and comprises the following steps of: coping to remove surface defects, heating burning loss to remove and oxidize microdefects, rolling after descaling, optimizing the replacement frequency of a rolling groove and a guide, improving the spinning temperature, and reducing the residual rate of the 90-grade tire cord steel wire rod mechanical descaling oxide scale. After entering the air cooling line, the wire rod is air-cooled to 850-890 DEG C, and then enters the heat preservation cover after being air-cooled until the temperature of the wire rod is reduced to 550 DEG C or below, so that the performance of the wire rod can be considered, the thickness of the oxide scale is 14-18 microns, the proportion of FeO is 80% or above, the oxide scale removal effect is effectively improved when the wire rod is mechanically descaled, and the service life of the wire rod is prolonged. The residual rate of the oxide scale on the surface of the 90-grade tire cord steel wire rod is reduced to below 3%, the surface defect and oxide scale press-in depth is smaller than or equal to 0.02 mm, the wet tensile wire fracture rate of the produced extra-high-strength steel cord with the diameter phi being 0.35 mm is lower than 1.0 time / ton, and the stranding wire fracture rate is lower than 2 times / ton.

Description

Technical Field

[0001] The invention belongs to the technical field of high-speed wire production, and in particular relates to a control method for reducing the residual rate of iron oxide scale in mechanical descaling of a grade 90 cord steel wire rod. Background Art

[0002] Cord steel is widely used in the production of steel cords for automobiles, engineering machinery, and aircraft tires. Its production process is complex. During the processing, it needs to go through a series of drawing, heat treatment, electroplating, and stranding processes, of which the drawing can reach more than 40 times. The quality requirements for the raw wire rod are extremely high. In addition to the quality indicators such as wire rod segregation, network cementite, inclusions, surface quality, and troostite content, it is also necessary to control the iron scale on the wire rod surface. When the steel cord processing process adopts the method of mechanical descaling, the thickness, structure, and adhesion of the iron scale on the wire rod surface to the wire rod matrix directly affect the removal effect of the iron scale, that is, the residual rate of the iron scale on the wire rod. When there is a lot of iron scale on the wire rod surface, it will be brought into the subsequent drawing process, resulting in increased mold wear and poor lubrication effect, and then problems such as bright wire and broken wire will occur during drawing, which will have a great impact on production and quality. With the improvement of the strength grade of cord steel, its harm will gradually increase. Grade 90 cord steel wire rod is used as the base material for producing ultra-high strength steel cord. It is necessary to reduce the residual rate of iron oxide scale on the wire rod surface under mechanical descaling conditions in order to improve the wire rod drawing quality and increase the yield rate of steel cord. Therefore, it is necessary to develop a production control method that takes into account the quality of grade 90 cord steel wire rod and reduces the residual rate of iron oxide scale after mechanical descaling.

[0003] At present, the methods in the industry to reduce the residual rate of scale on the surface of wire rods under mechanical descaling mainly involve increasing the scale thickness or improving the scale structure. For example, a control method for improving the mechanical stripping rate of scale on 80-grade cord steel disclosed in Patent CN113414236B removes the primary scale through hot rolling and high-pressure water descaling, and obtains an ideal scale thickness and structure of the wire rod by means of an appropriate spinning temperature, roller table speed, fan air volume, and the opening of the heat preservation cover, without affecting the microstructure and properties of the wire rod. However, for 90-grade cord steel wire rods, on the one hand, the influence of the surface quality of the wire rod on the adhesion of the scale is not considered, and the adhesion seriously restricts its peelability. As a result, even though the scale thickness increases, due to the influence of the surface quality and micro-defects of the wire rod, the scale is firmly adhered to the surface of the wire rod and is not easily peeled off, resulting in a large fluctuation in the scale stripping rate and the appearance of dot-like or linear scale residues on the surface of the wire rod. On the other hand, the 90-grade cord steel wire rod has a higher strengthening level in its composition system, with higher carbon and alloy component contents. The existing methods have an insignificant improvement effect on the scale quality on the surface of 90-grade cord steel wire rods. The proportion of FeO in the scale structure is not high, and components such as ferric oxide and magnetite in the scale are relatively more, making the scale structure relatively compact, with a greater bonding force between the scale and the wire rod substrate, increasing the removal difficulty, and it is also difficult to take into account the mechanical properties of the wire rod. Summary of the Invention

[0004] The present invention aims to solve at least one of the above technical problems to some extent. The present invention provides a control method for reducing the residual rate of scale on 90-grade cord steel wire rods during mechanical descaling, which can take into account the properties of the wire rod, improve the scale removal effect during mechanical descaling of the wire rod, and effectively reduce the residual rate of scale on the surface of 90-grade cord steel wire rods.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A control method for reducing the residual rate of scale on 90-grade cord steel wire rods during mechanical descaling, the control method comprising:

[0007] (1) Billet grinding: Perform full grinding on the surface of the billet;

[0008] (2) Heating: Heat the ground billet, and control the total heating time of the second heating section and the soaking section to be not less than 120 min;

[0009] (3) Controlled rolling: After heating, the billet is rolled into wire rods through high-pressure water descaling and the rolling line;

[0010] (4) Controlled cooling: The wire rod is spun into a wire coil, control the spinning temperature of the wire coil to be 920°C to 950°C, after the wire coil enters the air-cooling line, it is first air-cooled to 860 - 880°C, and then air-cooled until the temperature of the wire coil drops below 550°C and then enters the heat preservation cover.

[0011] In the above method, in order to reduce the influence of continuous casting defects on the surface quality of the wire rod, the surface of the billet is completely ground, which can effectively remove various longitudinal cracks, transverse cracks, corner cracks and other defects on the surface of the continuous casting billet, avoid defect inheritance to the wire rod, and provide high-quality billet raw materials for subsequent rolling and finished wire rod; when heating the ground billet, by extending the time of the billet at high temperature heating, the residual burrs and micro-defects after grinding the billet can be fully burned and oxidized, further improving the surface quality of the billet. Then, high-pressure water descaling is used to remove the surface scale formed by heating the billet, which is beneficial to improving the surface finish of the wire rod after controlled rolling, and further reducing the adhesion between the scale and the wire rod matrix, providing favorable conditions for better peeling and removing the scale during mechanical descaling of the wire rod. On this basis, a controlled cooling process of high-temperature spinning followed by air cooling + air cooling + slow cooling with a heat preservation cover is adopted:

[0012] By increasing the spinning temperature of the wire rod, the spun wire rod is not directly air-cooled but the fan is turned off, so that the wire rod is cooled in a natural air-cooling state to 860 - 880 °C, which is beneficial to extending the residence time of the wire rod in the high-temperature section. At high temperatures, the reaction rate between the surface of the wire rod and oxygen is faster, which can increase the thickness of the scale formed, and FeO is relatively stable at high temperatures. The scale formed in this stage is mainly FeO, and it is above the precipitation temperature range of proeutectoid cementite at 780 - 820 °C, avoiding affecting subsequent network carbon control. After air cooling, the wire rod can be quickly cooled by air cooling, thereby reducing the precipitation of network carbon in the center of the wire rod and improving the drawing stability. The wire rod enters the heat preservation cover below 550 °C, which can reduce the air-cooling speed and increase the residence time in the high-temperature section, being beneficial to the release of internal stress in the wire rod, shortening the natural aging period, and at the same time allowing sufficient time for the scale to thicken. Slow cooling is beneficial to the retention of FeO, increasing the proportion of FeO in the scale structure, making the scale structure relatively loose, and the bonding force between the scale and the wire rod matrix relatively weak, achieving the effects of taking into account the performance of the wire rod, increasing the thickness of the scale, improving the surface quality of the wire rod, and reducing the adhesion between the scale and the wire rod matrix, promoting the surface scale of the wire rod to peel off quickly in large flakes during subsequent mechanical descaling, thus improving the mechanical descaling effect of the scale on the surface of grade cord steel wire rod and reducing the scale residue rate.

[0013] In the preferred technical solution, the chemical composition of the billet by mass percentage includes: C: 0.88% - 0.93%, Si: 0.15% - 0.30%, Mn: 0.20% - 0.45%, Cr: 0.15% - 0.45%, S ≤ 0.020%, P ≤ 0.025%, Al ≤ 0.010%, Ti ≤ 0.005%, O ≤ 0.0015%, N ≤ 0.0030%, and the rest are Fe and inevitable impurity elements.

[0014] In order to more thoroughly remove the surface cracks of the billet formed during the continuous casting process of the billet due to factors such as mold powder, liquid level fluctuations, and casting speed fluctuations, and further reduce the impact of continuous casting defects on the surface quality of the wire rod. In the preferred technical solution, when grinding the billet, the grinding depth of the four sides of the billet is controlled to be 1.0 - 2.0 mm respectively, the radius of the R corner after grinding the billet corners is ≥ 30 mm. After grinding, shot blasting is carried out to remove the burrs generated during grinding.

[0015] In the heating process, relatively high temperatures in the second heating section and soaking section and a relatively long heating time are adopted. In order to form a certain thickness of scale on the surface of the billet under the condition of controllable furnace atmosphere, and fully remove the processing micro-cracks on the billet surface caused by grinding by burning, so as to further improve the surface quality of the billet. In the preferred technical solution, when heating, the temperature of the second heating section is controlled to be 1000℃ - 1100℃, the soaking section temperature is 1080℃ - 1180℃, the furnace pressure is not less than 10 Pa, and the residual oxygen content is 1.0% - 3.0%.

[0016] In the controlled rolling process, ultra-high pressure water descaling is adopted, which can further completely remove the surface scale formed by heating the billet. In the preferred technical solution, when performing controlled rolling, the descaling pressure of the high-pressure water descaling is controlled to be ≥ 24 MPa.

[0017] In the controlled rolling process, selecting an appropriate rolling temperature can reduce the deformation resistance of the rolled piece, obtain higher dimensional accuracy and a relatively fine and uniform microstructure, meet the requirements of the laying head temperature, and maintain a continuous and stable rolling rhythm. In the preferred technical solution, when performing controlled rolling, the starting rolling temperature is 1080℃ - 1110℃, the temperature entering the finishing mill is 910℃ - 940℃, and the temperature entering the sizing mill is 920 - 950℃.

[0018] In the controlled rolling process, shortening the replacement cycle of the guide guard and roll ring can reduce the impact of their excessive wear on the surface quality of the wire rod, reduce the risk of surface defects of the rolled piece caused by excessive wear, improve the surface finish of the wire rod, avoid micro-defects such as wrinkles, pitted surfaces, and pits, and further effectively reduce the adhesion between the scale and the wire rod matrix, which is beneficial to the peeling of the scale during mechanical descaling. In the preferred technical solution, when performing controlled rolling, the replacement cycle of the guide guard of the finishing mill is controlled to be ≤ 7 h, and the replacement cycle of the roll ring is ≤ 700 tons of rolled material; the replacement cycle of the guide guard of the sizing mill is ≤ 4 h, and the replacement cycle of the roll ring is ≤ 400 tons of rolled material.

[0019] To further control production costs, the cycle time for replacing the guide guards and roll rings in the finishing mill and the sizing mill can be further optimized. Preferably, the cycle time for replacing the guide guards in the finishing mill is 6 - 7 hours, and the cycle time for replacing the roll rings is 600 - 700 tons of rolled products; the cycle time for replacing the guide guards in the sizing mill is 3 - 4 hours, and the cycle time for replacing the roll rings is 300 - 400 tons of rolled products.

[0020] To extend the residence time of the wire rod in the high - temperature section, further increase the thickness of the scale formed, and take into account production efficiency, in the preferred technical solution, during controlled cooling, the cooling rate of the wire rod during air cooling is controlled at 6 - 8 °C / s.

[0021] To further control the precipitation of network carbon in the center of the wire rod and improve drawing stability, when the temperature of the wire rod drops below the precipitation temperature range of pro - eutectoid cementite at 780 - 820 °C, a larger air volume is selected to increase the cooling rate of the wire rod. In the preferred technical solution, during controlled cooling, the temperature of the wire rod during air cooling is controlled to drop below the precipitation temperature range of pro - eutectoid cementite, and during this period, the cooling rate of the wire rod is 20 - 26 °C / s.

[0022] In the preferred technical solution, during controlled cooling, the rated air volume of the fans on the air - cooling line is 280000 m 3 / h, and 3 - 9 fans are turned on at 40% - 75% of the rated air volume of the fans. Starting from the 4th fan, the air volume of the fans decreases in sequence, and the remaining fans are turned off. When the temperature of the wire rod drops below 550 °C, a heat - insulating cover is added.

[0023] On the premise of a large air volume of the fans, the first two fans on the air - cooling line, i.e., the 1st - 2nd fans, are turned off, which can extend the residence time of the wire rod in the high - temperature section and control the cooling rate of the wire rod at 6 - 8 °C / s; under the condition of the 3rd - 5th fans, a large air volume can be used to quickly cool the wire rod through the precipitation temperature range of pro - eutectoid cementite, control the cooling rate of the wire rod up to 20 - 26 °C / s, and drop below the precipitation temperature range of pro - eutectoid cementite. As the cooling process progresses, the temperature difference between the surface and the interior of the wire rod gradually decreases. Starting from the 4th fan, the air volume of the fans decreases in sequence, which can reduce the cooling rate of the wire rod, make the cooling rates of the surface and the interior of the wire rod tend to be uniform, and avoid defects such as cracks caused by large thermal stresses inside the wire rod. By reducing the air volume, the wire rod completes the sorbite phase transformation at a relatively low air - cooling rate, promoting the uniformity and stability of the organizational structure and performance. The fans after the 9th fan are turned off, and a heat - insulating cover is added, so that the wire rod enters the heat - insulating cover below 550 °C, which can reduce the air - cooling speed and is beneficial to the release of internal stress in the wire rod and the optimization of the thickness and structure of the scale on the wire rod.

[0024] During controlled cooling, the air - cooling link can extend the residence time of the wire rod in the high - temperature section by increasing the wire - rod spinning temperature and reducing the roller - way speed. In the preferred technical solution, during controlled cooling, the initial speed of the roller way on the air - cooling line ≤ 0.90 m / s.

[0025] A 90-grade cord steel wire rod is produced by any one of the above-mentioned control methods for reducing the residual rate of oxidized iron scale in mechanical descaling of a 90-grade cord steel wire rod.

[0026] Compared with the prior art, the beneficial effects of the present invention are at least:

[0027] (1) The present invention adopts steel billet grinding to reduce the influence of continuous casting defects on the surface quality of wire rod. During heating, the heating time is extended to burn and oxidize the micro defects on the surface of the steel billet caused by grinding, thereby improving the surface quality of the steel billet and reducing the adhesion between the oxidized iron scale and the wire rod matrix. A controlled cooling process of air cooling + wind cooling + slow cooling with a heat preservation cover after high-temperature spinning is adopted. Air cooling is used to extend the residence time of the wire rod in the high temperature section to increase the thickness of the oxidized iron scale. Wind cooling is used to reduce the precipitation of carbon in the center network of the wire rod and improve the drawing stability. The heat preservation cover is used to slow cool and reduce the cooling rate, thereby releasing the internal stress of the wire rod and allowing the oxidized iron scale to have sufficient time to thicken. The oxidized iron scale structure and the surface quality of the wire rod are optimized, making the oxidized iron scale structure relatively loose, further reducing the bonding force between the oxidized iron scale and the wire rod matrix, and thus being able to take into account the performance of the wire rod and achieve The thickness of the iron oxide scale of the grade cord steel wire rod is 14-18μm, and the FeO ratio is more than 80%. It can improve the iron oxide scale removal effect during the mechanical descaling of the wire rod, ensure that the iron oxide scale is peeled off in large flakes during mechanical descaling, reduce the fluctuation of the iron oxide scale peeling rate, and effectively reduce the residual iron oxide scale rate on the surface of the 90 grade cord steel wire rod. The residual rate of the iron oxide scale after mechanical descaling is 0-3% after testing; the surface defects and the depth of the iron oxide scale are ≤0.02mm; after customer production The ultra-high strength steel cord has a wet wire breakage rate of less than 1.0 times / ton and a twisted wire breakage rate of less than 2 times / ton, which can effectively improve the wire rod drawing quality and increase the yield rate of steel cord.

[0028] (2) The present invention can further reduce the risk of surface defects of rolled parts caused by excessive wear by optimizing the cycle time of replacing guides and roller rings in the finishing mill and the sizing mill, ensure that the surface of the finished wire rod is smooth and free of micro-defects such as wrinkles, pits, and pits, further reduce the adhesion between the iron oxide scale and the wire rod substrate, and facilitate the peeling of the iron oxide scale during mechanical descaling.

[0029] (3) The present invention can further improve the surface quality of the steel billet and the wire rod by optimizing the steel billet grinding parameters, the heating furnace atmosphere, the ultra-high pressure water descaling and the controlled rolling temperature. The present invention can further optimize the control of the air cooling line, increase the spinning temperature, reduce the roller speed, optimize the fan on and off and the opening amount, further optimize the production control and reduce the fluctuation of the iron oxide peeling rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, where:

[0031] Figure 1 is the micrograph of the scale thickness of Embodiment 2 of the present invention;

[0032] Figure 2 is the micrograph of the scale thickness of Comparative Example 3 of the present invention. Detailed Description of the Invention

[0033] The embodiments of the present invention will be described in detail below. The embodiments described by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention; the tensile strength and average reduction of area of the wire rod are tested according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; the scale thickness and structure of the wire rod are tested according to the standard GB / T6462-2005 "Metallic and oxide coatings - Measurement of coating thickness - Microscopical method".

[0034] Embodiment 1:

[0035] A preferred embodiment of the control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rod of the present invention, the control method includes:

[0036] (1) Billet grinding: The surface of a 90-grade cord steel rectangular billet with a specification of 200mm×240mm is fully ground to remove surface defects. The chemical composition of the billet by mass percentage includes: C: 0.89%, Si: 0.22%, Mn: 0.30%, Cr: 0.24%, S: 0.007%, P: 0.013%, Al: 0.004%, Ti: 0.002%, O: 0.0009%, N: 0.0021%, and the rest are Fe and inevitable impurity elements. The grinding depth of the four sides of the billet is controlled to be 1.6mm respectively, and the R corner radius after grinding the billet corners is ≥30mm. After grinding, shot blasting is carried out to remove the burrs generated during grinding.

[0037] (2) Heating: The ground billet is heated by a walking beam reheating furnace. The heating program is in sequence of the first heating section, the second heating section and the soaking section. The temperature of the second heating section of the walking beam reheating furnace is controlled to be 1084°C, the soaking section temperature is 1142°C, the total heating time of the second heating section and the soaking section is 126min, the furnace pressure is 13 - 21Pa, and the residual oxygen content is 1.4 - 2.8%. The micro-defects generated on the billet surface due to grinding are burned out and oxidized.

[0038] (3) Controlled rolling: After heating, the billet is descaled by ultra-high pressure water to remove the primary scale on the billet surface. The descaling pressure of the ultra-high pressure water descaling is controlled at 25 MPa to obtain good billet surface quality. The billet enters the rolling line and is rolled into wire rods with a diameter of , controlling the starting rolling temperature at 1095 °C, the finishing rolling temperature at 923 °C, and the sizing temperature at 934 °C. The replacement frequency of the rolling grooves and guides is controlled to improve the surface quality of the wire rods. Specifically: the guide replacement cycle of the finishing mill unit is 6.3 h, and the roll ring replacement cycle is 620 tons of rolled products; the guide replacement cycle of the sizing mill unit is 3.5 hours, and the roll ring replacement cycle is 340 tons of rolled products.

[0039] (4) Controlled cooling: The wire rod is coiled into coils by a laying head, controlling the laying head temperature of the coil at 937 °C. The coil is transported by roller table into the air cooling line. The initial speed of the roller table is 0.90 m / s. The rated air volume of the fans in the air cooling line is 280,000 m 3 / h. The air volumes of the 1st - 9th fans are set at 0% / 0% / 75% / 75% / 70% / 65% / 60% / 50% / 40% of the rated air volume of the fans, and the rest of the fans are turned off. Control the coil to pass through the closed 1st and 2nd fans and be in a natural air cooling state. The cooling rate of the coil during air cooling is 6 - 8 °C / s. Air cool the coil until its temperature reaches 869 °C, and then through air cooling, the 3rd - 5th fans use a large air volume to quickly cool the coil below the precipitation temperature range of proeutectoid cementite. During this period, the cooling rate of the coil is 20 - 26 °C / s, and then complete the transformation of sorbite under the relatively low air cooling rate of the 6th - 9th fans. When the coil temperature cools to 541 °C, it enters the heat preservation hood to obtain a suitable thickness and structure of the scale. After the coil exits the hood, is coiled and taken offline, the finished coil product is obtained.

[0040] Example 2:

[0041] A preferred implementation manner of the control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rod coils of the present invention, the control method includes:

[0042] (1) Billet grinding: The surface of a 90-grade cord steel rectangular billet with a specification of 200 mm×240 mm is fully ground to remove surface defects. The chemical composition of the billet by mass percentage includes: C: 0.92%, Si: 0.24%, Mn: 0.33%, Cr: 0.22%, S: 0.005%, P: 0.012%, Al: 0.003%, Ti: 0.004%, O: 0.0006%, N: 0.0019%, and the rest are Fe and unavoidable impurity elements. Control the grinding depth of the four sides of the billet to be 1.9 mm respectively. After grinding the corners of the billet, the radius of the R corner is ≥30 mm. After grinding, shot blasting is carried out to remove the burrs generated during grinding.

[0043] (2) Heating: The ground billets are heated in a walking beam reheating furnace. The heating process includes a first heating zone, a second heating zone, and a soaking zone. The temperature of the second heating zone of the walking beam reheating furnace is controlled at 1076 °C, and the temperature of the soaking zone is 1135 °C. The total heating time of the second heating zone and the soaking zone is 122 min. The furnace pressure is 15 - 20 Pa, and the residual oxygen content is 1.2 - 2.5%. The microdefects generated on the billet surface due to grinding are burned off and oxidized.

[0044] (3) Controlled rolling: After heating, the primary scale of the billets is removed by ultra-high pressure water descaling. The descaling pressure of the ultra-high pressure water descaling is controlled at 25 MPa to obtain good surface quality of the billets. The billets enter the rolling line and are rolled into wire rods with a diameter of . The rolling start temperature is controlled at 1087 °C, the finishing rolling temperature is 919 °C, and the sizing temperature is 937 °C. The replacement frequency of the rolling grooves and guides is controlled to improve the surface quality of the wire rods. Specifically: the guide replacement cycle of the finishing mill unit is 6.7 h, and the roll ring replacement cycle is 664 tons of rolled products; the guide replacement cycle of the sizing mill unit is 3.4 h, and the roll ring replacement cycle is 328 tons of rolled products.

[0045] (4) Controlled cooling: The wire rods are coiled into coils by a laying head. The laying head temperature of the coils is controlled at 931 °C. The coils are transported by roller tables into the air cooling line. The initial speed of the roller tables is 0.90 m / s. The rated air volume of the fans in the air cooling line is 280,000 m 3 / h. The air volumes of fans 1 - 9 are set at 0% / 0% / 75% / 75% / 70% / 65% / 60% / 50% / 40% of the rated air volume of the fans, and the remaining fans are turned off. The coils are controlled to pass through the closed fans 1 and 2 and are in a natural air cooling state. The cooling rate of the coils during air cooling is 6 - 8 °C / s. The coils are air cooled to a temperature of 864 °C, and then air cooled. Fans 3 - 5 use a large air volume to quickly cool the coils below the precipitation temperature range of proeutectoid cementite. The cooling rate of the coils during this period is 20 - 26 °C / s. Then, the pearlite transformation is completed at a relatively low air cooling rate of fans 6 - 9. When the coil temperature cools to 538 °C, the coils enter the insulation hood to obtain a suitable scale thickness and structure. After the coils leave the hood and are coiled and discharged from the line, the coil products are obtained.

[0046] Example 3:

[0047] A preferred embodiment of the control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rod coils of the present invention. The control method includes:

[0048] (1) Slab grinding: The surface of a 200mm×240mm rectangular slab of grade 90 cord steel is fully ground to remove surface defects. The chemical composition of the slab by mass percentage includes: C: 0.92%, Si: 0.21%, Mn: 0.34%, Cr: 0.20%, S: 0.006%, P: 0.014%, Al: 0.003%, Ti: 0.002%, O: 0.0010%, N: 0.0023%, and the rest are Fe and inevitable impurity elements. The grinding depth of the four sides of the slab is controlled to be 1.5mm respectively, and the radius of the R corner after grinding the slab corners is ≥30mm. After grinding, shot blasting is carried out to remove the burrs generated during grinding.

[0049] (2) Heating: The ground slab is heated by a walking beam reheating furnace. The heating process is in sequence of the first heating section, the second heating section and the soaking section. The temperature of the second heating section of the walking beam reheating furnace is controlled to be 1068°C, the temperature of the soaking section is 1127°C, the total heating time of the second heating section and the soaking section is 131min, the furnace pressure is 11 - 24Pa, and the residual oxygen content is 1.2 - 2.9%. The micro-defects generated on the slab surface due to grinding are burned out and oxidized.

[0050] (3) Controlled rolling: After heating, the slab is descaled by ultra-high pressure water to remove the primary scale of the slab. The descaling pressure of the ultra-high pressure water descaling is controlled to be 25MPa to obtain good surface quality of the slab. The slab enters the rolling line and is rolled into wire rods with a diameter of . The starting rolling temperature is controlled to be 1083°C, the entry temperature of the finishing mill is 917°C, and the entry temperature of the sizing mill is 931°C. The replacement frequency of the rolling grooves and guides is controlled to improve the surface quality of the wire rods. Specifically: the guide replacement cycle of the finishing mill is 6.2h, and the roll ring replacement cycle is 617 tons of rolled products; the guide replacement cycle of the sizing mill is 3.2 hours, and the roll ring replacement cycle is 313 tons of rolled products.

[0051] (4) Controlled cooling: The wire rods are coiled into coils by a laying head. The laying head temperature of the coils is controlled to be 930°C. The coils are transported by roller table into the air cooling line. The initial speed of the roller table is 0.90m / s, and the rated air volume of the fans in the air cooling line is 280000m 3 / h, the air volume of the 1st - 9th fans is set to 0% / 0% / 75% / 75% / 70% / 65% / 60% / 50% / 40% of the rated air volume of the fans, and the rest of the fans are closed. The control rod passes through the closed 1st and 2nd fans and is in the natural air - cooling state. The cooling rate of the rod during air - cooling is 6 - 8 °C / s. The rod is air - cooled until the temperature reaches 874 °C, and then through air - blast cooling. The 3rd - 5th fans use a large air volume to quickly cool the rod below the precipitation temperature range of pro - eutectoid cementite. During this period, the cooling rate of the rod is 20 - 26 °C / s. Then, the sorbite phase transformation is completed at a relatively low air - blast cooling rate of the 6th - 9th fans. When the rod temperature cools to 539 °C, it enters the heat - preservation hood to obtain a suitable thickness and structure of the scale. After the rod exits the hood and is coiled and unloaded, the finished rod product is obtained.

[0052] Comparative Example 1:

[0053] A production method of 90 - grade cord steel rod, the method includes:

[0054] (1) Heating: The steel billet is heated by a walking - beam reheating furnace. The chemical composition of the steel billet by mass percentage includes: C: 0.91%, Si: 0.22%, Mn: 0.31%, Cr: 0.22%, S: 0.004%, P: 0.011%, Al: 0.002%, Ti: 0.002%, O: 0.0009%, N: 0.0020%, and the rest are Fe and inevitable impurity elements. The heating process is in turn the first heating section, the second heating section, and the soaking section. Control the temperature of the second heating section of the walking - beam reheating furnace to be 1012 °C, the soaking section temperature to be 1067 °C. The total heating time of the second heating section and the soaking section is 97 min, the furnace pressure is 6 - 32 Pa, and the residual oxygen content is 4.9 - 6.7%.

[0055] (2) Controlled rolling: After heating, the steel billet is descaled by high - pressure water to remove the primary scale of the steel billet. Control the descaling pressure of the high - pressure water descaling to be 15 MPa. The steel billet enters the rolling line and is rolled into wire rods with a diameter of, control the starting rolling temperature to be 1004 °C, the temperature entering the finishing mill to be 912 °C, the temperature entering the sizing mill to be 923 °C. The guide - guard replacement cycle of the finishing mill unit is 9.8 h, and the roll - ring replacement cycle is 940 tons of rolled products; the guide - guard replacement cycle of the sizing mill unit is 6.3 h, and the roll - ring replacement cycle is 648 tons of rolled products.

[0056] (3) Controlled cooling: The wire rod is spun into a rod by a spinner. Control the spinning temperature of the rod to be 912 °C. The rod is conveyed by a roller table and enters the air - blast cooling line. The initial speed of the roller table is 1.10 m / s. The rated air volume of the fans in the air - blast cooling line is 280000 m 3 / h, the air volume of fans 1 - 9 is set to 75% / 75% / 75% / 70% / 65% / 60% / 60% / 50% / 40% of the rated air volume of the fans, the other fans are turned off, all the heat preservation covers are opened, and wire rod products are obtained after the wire rods are coiled and taken off the production line.

[0057] Comparative Example 2:

[0058] A production method of 90-grade cord steel wire rod, the method includes:

[0059] (1) Heating: The steel billet is heated by a walking beam reheating furnace. The chemical composition of the steel billet by mass percentage includes: C: 0.90%, Si: 0.21%, Mn: 0.35%, Cr: 0.21%, S: 0.006%, P: 0.017%, Al: 0.004%, Ti: 0.003%, O: 0.0010%, N: 0.0025%, and the rest are Fe and inevitable impurity elements. The heating procedures are the first heating section, the second heating section and the soaking section in sequence. Control the temperature of the second heating section of the walking beam reheating furnace to be 998 °C, the soaking section temperature to be 1059 °C, the total heating time of the second heating section and the soaking section to be 102 min, the furnace pressure to be 3 - 41 Pa, and the residual oxygen content to be 3.7 - 8.6%.

[0060] (2) Controlled rolling: After heating, the primary scale of the steel billet is removed by high-pressure water descaling. Control the descaling pressure of the high-pressure water descaling to be 15 MPa. The steel billet enters the rolling line and is rolled into wire rods with a diameter of The wire rods are controlled with a starting rolling temperature of 1009 °C, an entrance finishing rolling temperature of 907 °C, an entrance sizing temperature of 918 °C. The guide and guard replacement cycle of the finishing mill unit is 9.1 h, and the roll ring replacement cycle is 887 tons of rolled products; the guide and guard replacement cycle of the sizing mill unit is 6.8 hours, and the roll ring replacement cycle is 674 tons of rolled products.

[0061] (3) Controlled cooling: The wire rods are spun into wire rods by a laying head. Control the laying head temperature of the wire rods to be 907 °C. The wire rods are transported by roller table and enter the air cooling line. The initial speed of the roller table is 1.10 m / s. The rated air volume of the fans in the air cooling line is 280000 m 3 / h, the air volume of fans 1 - 9 is set to 75% / 75% / 75% / 70% / 65% / 60% / 60% / 50% / 40% of the rated air volume of the fans, the other fans are turned off, all the heat preservation covers are opened, and wire rod products are obtained after the wire rods are coiled and taken off the production line.

[0062] Comparative Example 3:

[0063] A production method of 90-grade cord steel wire rod, the method includes:

[0064] (1) Heating: The steel billet is heated by a walking beam reheating furnace. The chemical composition of the steel billet by mass percentage includes: C: 0.91%, Si: 0.23%, Mn: 0.33%, Cr: 0.24%, S: 0.005%, P: 0.014%, Al: 0.003%, Ti: 0.003%, O: 0.0012%, N: 0.0027%, and the rest is Fe and inevitable impurity elements. The heating process is successively the first heating section, the second heating section, and the soaking section. Control the temperature of the second heating section of the walking beam reheating furnace to be 974 °C, the soaking section temperature to be 1069 °C. The total heating time of the second heating section and the soaking section is 98 min, the furnace pressure is 5 - 45 Pa, and the residual oxygen content is 2.7 - 7.6%.

[0065] (2) Controlled rolling: After heating, the primary scale of the steel billet is removed by high-pressure water descaling. Control the descaling pressure of high-pressure water descaling to be 15 MPa. The steel billet is rolled into wire rods with a diameter of . Control the starting rolling temperature to be 1018 °C, the finishing rolling temperature to be 917 °C, the entry temperature of the sizing mill to be 914 °C. The guide and guard replacement cycle of the finishing mill is 9.3 h, and the roll ring replacement cycle is 928 tons of rolled products; the guide and guard replacement cycle of the sizing mill is 6.7 hours, and the roll ring replacement cycle is 636 tons of rolled products.

[0066] (3) Controlled cooling: The wire rod is coiled into coils by a laying head. Control the laying head temperature of the coil to be 911 °C. The coil is transported by roller table into the air cooling line. The initial speed of the roller table is 1.10 m / s. The rated air volume of the fans in the air cooling line is 280000 m 3 / h. The air volumes of fans 1 - 9 are set to 75% / 75% / 75% / 70% / 65% / 60% / 60% / 50% / 40% of the rated air volume of the fan, and the rest of the fans are turned off. All the heat insulation covers are opened. After the coil is coiled and taken off the production line, the coil finished product is obtained.

[0067] Perform performance testing, scale thickness and structure testing on the coils obtained in Examples 1 - 3 and Comparative Examples 1 - 3. After the customer produces extra-high strength steel cord, mechanical descaling is used to remove the scale on the surface of the coil during the production process, and the results of scale residue rate, surface defects, scale penetration depth, wet drawing breakage rate, and strand twisting breakage rate are obtained. The comparison results are shown in Table 1 below:

[0068] Table 1. Comparison results of the test items of the coils obtained in the examples and comparative examples

[0069] Test items Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Tensile strength (MPa) 1243 1263 1254 1251 1268 1249 Reduction of area (%) 41.3 44.9 42.6 43.2 42.5 44.6 Thickness of mill scale (μm) 15.4 16.1 16.8 8.8 10.2 9.4 Proportion of FeO in mill scale (%) 82.9 83.8 83.7 68.7 64.9 72.9 Residual rate of mill scale (%) 1.8 2.2 2.7 7.9 5.7 4.8 Surface defects and pressing depth of mill scale (mm) ≤0.01 ≤0.02 ≤0.01 ≤0.03 ≤0.04 ≤0.03 Wet drawing breakage rate (times / ton) 0.87 0.69 0.94 1.42 1.72 1.63 Stranding breakage rate (times / ton) 1.45 1.73 1.82 2.91 3.26 2.94

[0070] As can be seen from the results of Examples 1 to 3, for the 90-grade cord steel rectangular billets of the present invention, the surface defects are removed by grinding, and then the total heating time of the second heating section and the soaking section is controlled to be not less than 120 min, so that the micro-defects generated on the billet surface due to grinding are burned out and oxidized. After descaling with high-pressure water to remove the primary scale on the billet, good billet surface quality can be obtained. The surface quality of the wire rod can be further improved by optimizing the replacement frequency of the rolling groove and the guide guard. By increasing the laying head temperature, reducing the roller table speed, and optimizing the blower opening amount, the laying head temperature of the wire rod is controlled to be 920 °C to 950 °C. After the wire rod enters the air cooling line, it is first air-cooled to 860 - 880 °C, and then air-cooled until the wire rod temperature drops below 550 °C and then enters the heat preservation cover, good mechanical properties can be obtained, the thickness of the scale and the proportion of FeO in the structure are increased appropriately, the surface quality of the wire rod is improved, and the adhesion between the scale and the wire rod matrix is reduced. The thickness of the scale of the 90-grade cord steel wire rod is 14 - 18 μm, the proportion of FeO is 80% - 85%, and the residual rate of the scale by mechanical descaling is 0 - 3%; the surface defect and the depth of the scale pressed in ≤ 0.02 mm; when the customer produces the φ0.35 mm extra-high strength steel cord, the wet drawing breakage rate is lower than 1.0 times / ton, and the stranding breakage rate is lower than 2 times / ton.

[0071] From the comparison in Figure 1 and the comparison with Figure 2 and the comparison results in Table 1, it can be seen that the tensile strength and the reduction of area of the examples and the comparative examples are comparable. The thickness of the scale in the examples increases by an average of 6.6 μm compared with the comparative examples, the proportion of FeO in the scale increases by 14.6%, the residual rate of the scale decreases by 3.9%, the wet drawing breakage rate of the customer decreases by 0.8 times / ton, and the stranding breakage rate decreases by 1.4 times / ton. The improvement effects are obvious, which can effectively improve the mechanical descaling effect of the scale on the surface of the 90-grade cord steel wire rod, reduce the residual rate of the scale, and is better than the physical quality level of the benchmark supplier.

[0072] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rods, characterized in that, Its control method includes: (1) Slab grinding: Conduct full grinding on the surface of the slab; (2) Heating: Heat the ground slab, and control the total heating time of the second heating section and the soaking section to be not less than 120 min; (3) Controlled rolling: After heating, the slab is descaled by high-pressure water and rolled into wire rods on the rolling line; (4) Controlled cooling: The wire rod is spun into coils, control the spinning temperature of the coil to be 920 °C - 950 °C. After the coil enters the air cooling line, it is first air-cooled to 860 - 880 °C, and then air-cooled until the coil temperature drops below 550 °C and then enters the heat preservation cover.

2. The control method for reducing the residual rate of mechanical descaling scale on the 90-grade cord steel wire rod according to claim 1, characterized in that, The chemical composition of the slab includes by mass percentage: C: 0.88% - 0.93%, Si: 0.15% - 0.30%, Mn: 0.20% - 0.45%, Cr: 0.15% - 0.45%, S ≤ 0.020%, P ≤ 0.025%, Al ≤ 0.010%, Ti ≤ 0.005%, O ≤ 0.0015%, N ≤ 0.0030%, and the rest are Fe and inevitable impurity elements.

3. The control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rod according to claim 1, wherein When grinding the slab, control the grinding depth of the four sides of the slab to be 1.0 - 2.0 mm respectively, and the radius of the R angle after grinding the corners of the slab is ≥ 30 mm. Shot blasting is carried out after grinding.

4. The control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rods according to claim 1, characterized in that, When heating, control the temperature of the second heating section to be 1000 °C - 1100 °C, the temperature of the soaking section to be 1080 °C - 1180 °C, the furnace pressure to be not less than 10 Pa, and the residual oxygen content to be 1.0% - 3.0%.

5. The control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rods according to claim 1, characterized in that, When carrying out controlled rolling, control the descaling pressure of high-pressure water descaling to be ≥ 24 MPa, the starting rolling temperature to be 1080 °C - 1110 °C, the temperature entering the finishing mill to be 910 °C - 940 °C, and the temperature entering the sizing mill to be 920 - 950 °C.

6. The control method for reducing the residual rate of mechanical descaling scale on 90-grade cord steel wire rod according to claim 1, characterized in that, When carrying out controlled rolling, control the guide guard replacement cycle of the finishing mill group to be ≤ 7 h, and the roll ring replacement cycle to be ≤ 700 tons of rolled products; the guide guard replacement cycle of the sizing mill group to be ≤ 4 h, and the roll ring replacement cycle to be ≤ 400 tons of rolled products.

7. The control method for reducing the residual rate of mechanical descaling scale on the 90-grade cord steel wire rod according to claim 1, characterized in that, When carrying out controlled cooling, control the cooling rate of the coil during air cooling to be 6 - 8 °C / s.

8. The control method for reducing the residual rate of mechanical descaling scale on the 90-grade cord steel wire rod according to claim 1, characterized in that, When carrying out controlled cooling, control the coil temperature during air cooling to drop below the precipitation temperature range of proeutectoid cementite, and the cooling rate of the coil during this period to be 20 - 26 °C / s.

9. The control method for reducing the residual rate of mechanical descaling scale on the 90-grade cord steel wire rod according to claim 1, characterized in that, During the controlled cooling, the rated air volume of the fans on the air cooling line is 280,000 m 3 / h. 3 to 9 fans are turned on at 40% to 75% of the rated air volume of the fans. Starting from the 4th fan, the air volume of the fans decreases in turn, and the remaining fans are turned off.

10. A wire rod of 90-grade cord steel, characterized in that, The coil is produced by the control method for reducing the residual rate of mechanical descaling scale of 90-grade cord steel coil as described in any one of claims 1 - 9.

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