A continuous billet rolling method for rolling small billets of different sizes from large billets using a common pass.

Abstract

This invention provides a continuous billet-making method for rolling small billets of different sizes using a common pass pattern from a large billet. The continuous billet-making method includes the following steps: (1) sequentially heating and descaling the large billet to obtain a large billet blank; (2) continuously rolling the billet using a continuous rolling mill with alternating vertical and horizontal sections to obtain a first billet or a second billet. The continuous rolling mill used in this invention has a pass pattern system and guide spare parts. By adjusting the number of billets rolled in the continuous rolling mill and the size of the rolling pass pattern, the rolling of small billets of different sizes can be achieved. The continuous billet-making process can achieve rapid switching of billet specifications without changing the rolling mill, resulting in high operating efficiency, low cost, and good billet-making quality, which can meet the production needs of high-end cold heading steel, spring steel, high carbon steel, and other products.

Description

Technical Field

[0001] This invention belongs to the field of billet rolling technology, specifically relating to a continuous billet rolling method for rolling large square billets into small square billets of different sizes using a common die. Background Technology

[0002] Currently, bar and wire rod are classified according to the continuously cast billets used in rolling, mainly into small square billets, medium square billets, and large square billets. Among them, small square billets refer to continuously cast billets with a cross-section ≤180mm×180mm; large square billets refer to continuously cast billets with a cross-section ≥220mm×220mm (including rectangular billets and round billets); continuously cast billets with a cross-section between small square billets and large square billets are called medium square billets.

[0003] In the steel metallurgy industry, the process of rolling large billets into small billets is a crucial upstream step in the production of key steel products such as alloy spring steel, alloy cold heading steel, and high-carbon steel. Its product quality and production efficiency directly affect the stability of downstream processes. Currently, the mainstream methods for rolling large billets into small billets in the industry are mainly divided into two categories: one is single-machine multi-pass rolling on a billet mill, and the other is continuous rolling on a continuous rolling mill. Among them, continuous rolling mills have become the main choice for large-scale production of small billets due to their advantages of continuous production and high overall efficiency (e.g., CN 115069765A).

[0004] In the existing continuous billet rolling process, the cross-sectional dimensions of the large square billets used are typically 300–320 mm × 380–400 mm. The mill layout adopts a 9-pass alternating vertical and horizontal twist-free rolling mode, with each pass's pass type referred to as pass 1 to pass 9. Because the rolling requirements of two types of small square billets need to be met simultaneously, the existing process requires the design of two independent pass systems for the two specifications. Pass 8 (the penultimate pass) and pass 9 (the final finished product pass) are the differentiated core pass types, requiring two dedicated rolling mills and matching guide devices to enable switching between different specifications.

[0005] However, existing technical solutions have significant drawbacks, which severely restrict production efficiency and product quality:

[0006] Firstly, the product quality is unstable. Taking a 300mm×390mm large square billet as the raw material, the average elongation coefficient is 1.184 when rolling a 160mm small square billet, and 1.220 when rolling a 140mm small square billet. Because the average elongation coefficient of the 160mm small square billet is even smaller, the corners of the rolled piece are prone to microcracks due to excessive undercooling during the rolling process. Especially when rolling materials that are sensitive to the rolling process, such as alloy spring steel, alloy cold heading steel, and high carbon steel, these microcracks will persist into subsequent processes, ultimately leading to an increased defect rate in the finished product.

[0007] Secondly, production efficiency is low and costs are high. When switching between 160mm and 140mm small square billet specifications, the current specification's hole 8 and hole 9 rolling mills must be dismantled first, and then the corresponding target specification's hole 8 and hole 9 rolling mills must be installed. This dismantling and assembly process alone takes 3 to 4 hours. At the same time, the roll gaps of hole 4 to hole 7 rolling mills, the guide devices of hole 5 and hole 7, and the rolling speed of all stands of rolling mills must be readjusted. Long-term downtime not only leads to production interruption, but also requires the additional stockpiling of two sets of rolling mills, guides, and other process spare parts, significantly increasing spare parts costs. Moreover, after each restart, the speed of each stand of rolling mills needs to be repeatedly adjusted to confirm the finished product dimensions and surface quality, which can easily lead to process accidents and further reduce production stability.

[0008] In summary, the existing technical solutions for rolling small square billets of different sizes in continuous rolling mills have insurmountable shortcomings in terms of quality control, production efficiency, and cost control. There is an urgent need for an innovative process that can adapt one roll pass system to two specifications and balance quality and efficiency. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a continuous billet rolling method using a common die for rolling small billets of different sizes from large billets. The continuous billet rolling method provided by this invention employs a single die system and a set of guide components, enabling the rolling of small billets of different sizes. It features high efficiency, low cost, and good billet quality, and can meet the production needs of high-end cold heading steel, spring steel, high carbon steel, and other products.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] This invention provides a continuous billet rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The continuous billet rolling method includes the following steps:

[0012] (1) The large square billet is subjected to heat treatment and surface descaling treatment in sequence to obtain the large square billet material;

[0013] (2) A continuous rolling mill with alternating vertical and horizontal sections is used to continuously roll the billet to obtain a first square billet or a second square billet;

[0014] The continuous rolling mill includes a first rolling mill, a second rolling mill, a third rolling mill, a fourth rolling mill, a fifth rolling mill, a sixth rolling mill, a seventh rolling mill, and a detachable rolling mill, all installed sequentially.

[0015] The detachable rolling mill includes an eighth rolling mill and a ninth rolling mill connected in sequence;

[0016] The rolling pass pattern of the continuous rolling mill is square-box-square-box-square-box-square-box-square-box-square;

[0017] The rolling of the first or second square billet is achieved by unloading or installing a detachable rolling mill and adjusting the rolling pass dimensions of the sixth, seventh, eighth, and ninth rolling mills.

[0018] The continuous rolling mill used in this invention has a set of pass system and guide spare parts. By adjusting the number of rolls and the size of the rolling pass in the continuous rolling mill, the rolling of small square billets of different sizes can be achieved. The continuous billet opening process can realize the rapid switching of billet specifications without changing the rolling mill. It has high operating efficiency, low cost, and good billet opening quality, which can meet the production needs of high-end cold heading steel, spring steel, high carbon steel and other products.

[0019] As a preferred technical solution of the present invention, the size of the first square billet is 160~170×160~170mm, for example, it can be 160×160mm, 165×165mm or 170×170mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The preferred size is 160×160mm.

[0020] Preferably, the size of the second billet is 140~150×140~150mm, for example, it can be 140×140mm, 145×145mm or 150×150mm, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The preferred size is 140×140mm.

[0021] In this invention, the size of the first square billet is larger than that of the second square billet.

[0022] As a preferred technical solution of the present invention, when rolling the first square billet, the eighth and ninth rolling mills are unloaded and an empty guide groove is installed.

[0023] Preferably, when rolling the second square billet, the empty guide groove is unloaded and the eighth and ninth rolling mills are installed.

[0024] In this invention, the guide groove is equipped with rollers to prevent it from being suspended in mid-air after the eighth and ninth rolling mills are dismantled.

[0025] More specifically, the method provided by this invention enables rapid switching between rolling a first square billet and a second square billet. During the rolling process of switching from the first square billet to the second square billet, the eighth and ninth rolling mills are installed, while the rolling pass gaps and elongation coefficients of the first to fifth rolling mills remain unchanged, and the opening degree of the inlet guides of the rolling pass of the sixth and seventh rolling mills is finely adjusted. During the rolling process of switching from the second square billet to the first square billet, the eighth and ninth rolling mills are removed (adjusted from nine-pass rolling to seven-pass rolling compared to the prior art), while the rolling pass gaps and elongation coefficients of the first to fifth rolling mills remain unchanged, and the opening degree of the inlet guides of the rolling pass of the sixth and seventh rolling mills is finely adjusted.

[0026] As a preferred embodiment of the present invention, the heights of the rolling passes of the first to the fifth rolling mills are 340~350mm, 225~235mm, 250~260mm, 190~200mm, and 200~210mm, respectively.

[0027] For example, the height of the rolling pass of the first rolling mill is 340~350mm, such as 340mm, 342mm, 344mm, 346mm, 348mm or 350mm, etc., but not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0028] Preferably, the height of the rolling pass of the second rolling mill is 225~235mm, for example, it can be 225mm, 227mm, 229mm, 231mm, 233mm or 235mm, etc., but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0029] Preferably, the height of the rolling pass of the third rolling mill is 250~260mm, for example, it can be 250mm, 252mm, 254mm, 256mm, 258mm or 260mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the height of the rolling pass of the fourth rolling mill is 190~200mm, for example, it can be 190mm, 192mm, 194mm, 196mm, 198mm or 200mm, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0031] Preferably, the height of the rolling pass of the fifth rolling mill is 200~210mm, for example, it can be 200mm, 202mm, 204mm, 206mm, 208mm or 210mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the widths of the rolling passes of the first to fifth rolling mills are 325~330mm, 365~370mm, 275~280mm, 294~298mm, and 232~236mm, respectively.

[0033] For example, the width of the rolling pass of the first rolling mill is 325~330mm, such as 325mm, 326mm, 327mm, 328mm, 329mm or 330mm, but is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0034] Preferably, the width of the rolling pass of the second rolling mill is 365~370mm, for example, it can be 365mm, 366mm, 367mm, 368mm, 369mm or 370mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the width of the rolling pass of the third rolling mill is 275~280mm, for example, it can be 275mm, 276mm, 277mm, 278mm, 279mm or 280mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the width of the rolling pass of the fourth rolling mill is 294~298mm, for example, it can be 294mm, 295mm, 296mm, 297mm or 298mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the width of the rolling pass of the fifth rolling mill is 232~236mm, for example, it can be 232mm, 233mm, 234mm, 235mm or 236mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the inner radius R of the rolling pass of the first to the ninth rolling mill are 28~32mm, 28~32mm, 32~36mm, 28~32mm, 26~30mm, 24~28mm, 18~22mm, 18~22mm, and 18~22mm, respectively.

[0039] In the continuous billet rolling process, in order to meet the rolling requirements of alloy spring steel, alloy cold heading steel and high carbon steel, and to avoid the formation of undercooled structure due to large corner deformation and uneven metal flow, the corners of the workpiece should be protected during rolling, and the inner radius R should be extended sequentially according to the R value of the billet.

[0040] For example, the inner radius R of the rolling pass of the first rolling mill is 28~32mm, such as 28mm, 29mm, 30mm, 31mm or 32mm, but not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0041] Preferably, the inner radius R of the rolling pass of the second rolling mill is 28~32mm, for example, it can be 28mm, 29mm, 30mm, 31mm or 32mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the inner radius R of the rolling pass of the third rolling mill is 32~36mm, for example, it can be 32mm, 33mm, 34mm, 35mm or 36mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the inner radius R of the rolling pass of the fourth rolling mill is 28~32mm, for example, it can be 28mm, 29mm, 30mm, 31mm or 32mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the inner radius R of the rolling pass of the fifth rolling mill is 26~30mm, for example, it can be 26mm, 27mm, 28mm, 29mm or 30mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the inner radius R of the rolling pass of the sixth rolling mill is 24~28mm, for example, it can be 24mm, 25mm, 26mm, 27mm or 28mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the inner radius R of the rolling pass of the seventh rolling mill is 18~22mm, for example, it can be 18mm, 19mm, 20mm, 21mm or 22mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the inner radius R of the rolling pass of the eighth rolling mill is 18~22mm, for example, it can be 18mm, 19mm, 20mm, 21mm or 22mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the inner radius R of the rolling pass of the ninth rolling mill is 18~22mm, for example, it can be 18mm, 19mm, 20mm, 21mm or 22mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the elongation coefficients of the rolling passes of the first to fifth rolling mills are 1.15±0.01, 1.28±0.01, 1.27±0.01, 1.24±0.01, and 1.24±0.01, respectively.

[0050] The adjustment of the mill roll gap can be reduced during continuous billet preparation, and the elongation coefficient can be redistributed. The rolling pass of the first mill should meet the requirement of smooth bite of the workpiece, and a smaller elongation coefficient should be used. The average elongation coefficient of the second to seventh mills is increased (from 1.184 to 1.242).

[0051] For example, the elongation coefficient of the rolling pass of the first rolling mill is 1.15±0.01, such as 1.14, 1.144, 1.148, 1.152, 1.156 or 1.16, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the elongation coefficient of the rolling pass of the second rolling mill is 1.28±0.01, for example, it can be 1.27, 1.274, 1.278, 1.282, 1.286 or 1.29, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, the elongation coefficient of the rolling pass of the third rolling mill is 1.27±0.01, for example, it can be 1.26, 1.264, 1.268, 1.272, 1.276 or 1.28, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the elongation coefficient of the rolling pass of the fourth rolling mill is 1.24±0.01, for example, it can be 1.23, 1.234, 1.238, 1.242, 1.246 or 1.25, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the elongation coefficient of the rolling pass of the fifth rolling mill is 1.24±0.01, for example, it can be 1.23, 1.234, 1.238, 1.242, 1.246 or 1.25, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] Preferably, the bite angles of the rolling pass of the first to the fifth rolling mill are 21±1°, 25±1°, 29±1°, 22±1°, and 25±1°, respectively.

[0057] For example, the bite angle of the rolling pass of the first rolling mill is 21±1°, such as 20°, 20.4°, 20.8°, 21.2°, 21.6° or 22°, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the bite angle of the rolling pass of the second rolling mill is 25±1°, for example, it can be 24°, 24.4°, 24.8°, 25.2°, 25.6° or 26°, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, the bite angle of the rolling pass of the third rolling mill is 29±1°, for example, it can be 28°, 28.4°, 28.8°, 29.2°, 29.6° or 30°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, the bite angle of the rolling pass of the fourth rolling mill is 22±1°, for example, it can be 21°, 21.4°, 21.8°, 22.2°, 22.6° or 23°, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Preferably, the bite angle of the rolling pass of the fifth rolling mill is 25±1°, for example, it can be 24°, 24.4°, 24.8°, 25.2°, 25.6° or 26°, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] As a preferred technical solution of the present invention, when rolling the first square billet, the height of the rolling pass of the sixth rolling mill is 145~150mm, for example, it can be 145mm, 146mm, 147mm, 148mm, 149mm or 150mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] The width is 243~247mm, for example, it can be 243mm, 244mm, 245mm, 246mm or 247mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] The extension factor is 1.29±0.01, and can be, for example, 1.28, 1.284, 1.288, 1.292, 1.296 or 1.30, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] The bite angle is 24±1°, for example, it can be 23°, 23.4°, 23.8°, 24.2°, 24.6° or 25°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] Preferably, when rolling the first square billet, the height of the rolling pass of the seventh rolling mill is 162~163mm, for example, it can be 162mm, 162.2mm, 162.4mm, 162.6mm, 162.8mm or 163mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] The width is 174~175mm, for example, it can be 174mm, 174.2mm, 174.4mm, 174.6mm, 174.8mm or 175mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] The extension factor is 1.24 ± 0.01, and can be, for example, 1.23, 1.234, 1.238, 1.242, 1.246 or 1.25, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] The bite angle is 24±1°, for example, it can be 23°, 23.4°, 23.8°, 24.2°, 24.6° or 25°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] As a preferred technical solution of the present invention, when rolling the second square billet, the height of the rolling pass of the sixth rolling mill is 151~153mm, for example, it can be 151mm, 151.4mm, 151.8mm, 152.2mm, 152.6mm or 153mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] The width is 243~247mm, for example, it can be 243mm, 244mm, 245mm, 246mm or 247mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] The extension factor is 1.27±0.01, and can be, for example, 1.26, 1.264, 1.268, 1.272, 1.276 or 1.28, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] The bite angle is 23±1°, for example, it can be 22°, 22.4°, 22.8°, 23.2°, 23.6° or 24°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] Preferably, when rolling the second square billet, the height of the rolling pass of the seventh rolling mill is 173~175mm, for example, it can be 173mm, 173.4mm, 173.8mm, 174.2mm, 174.6mm or 175mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] The width is 174~175mm, for example, it can be 174mm, 174.2mm, 174.4mm, 174.6mm, 174.8mm or 175mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] The extension factor is 1.18±0.01, and can be, for example, 1.17, 1.174, 1.178, 1.182, 1.186 or 1.19, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] The bite angle is 22±1°, for example, it can be 21°, 21.4°, 21.8°, 22.2°, 22.6° or 23°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] Preferably, when rolling the second square billet, the height of the rolling pass of the eighth rolling mill is 128~132mm, for example, it can be 128mm, 129mm, 130mm, 131mm or 132mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0079] The width is 195~199mm, for example, it can be 195mm, 196mm, 197mm, 198mm or 199mm, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] The extension factor is 1.19±0.01, and can be, for example, 1.18, 1.184, 1.188, 1.192, 1.196 or 1.20, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] The bite angle is 18±1°, for example, it can be 17°, 17.4°, 17.8°, 18.2°, 18.6° or 19°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] Preferably, when rolling the second square billet, the height of the rolling pass of the ninth rolling mill is 141~142mm, for example, it can be 141mm, 141.2mm, 141.4mm, 141.6mm, 141.8mm or 142mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0083] The width is 152~153mm, for example, it can be 152mm, 152.2mm, 152.4mm, 152.6mm, 152.8mm or 153mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0084] The extension factor is 1.19±0.01, and can be, for example, 1.18, 1.184, 1.188, 1.192, 1.196 or 1.20, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0085] The bite angle is 21±1°, for example, it can be 20°, 20.4°, 20.8°, 21.2°, 21.6° or 22°, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0086] As a preferred embodiment of the present invention, the rolling speed of the continuous rolling mill is:

[0087] V n-1 =V n / R n

[0088] Among them, V n-1 R is the rolling speed of the previous rolling mill. n V is the elongation coefficient of the rolling mill. n =V 成品 Set the rolling speed for the finished product.

[0089] As a preferred technical solution of the present invention, the cross-sectional dimensions of the large square billet in step (1) are 300~320mm×380~400mm, for example, it can be 300mm×390mm, 320mm×400mm or 300mm×380mm, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0090] Preferably, the corner radius of the large square billet is 17~23mm, for example, it can be 17mm, 18mm, 19mm, 20mm, 21mm, 22mm or 23mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0091] Preferably, the carbon content of the large billet is 0.05~0.92wt%, for example, it can be 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt% or 0.92wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0092] Preferably, the temperature of the heating treatment in step (1) is 1150~1250℃, for example, it can be 1150℃, 1180℃, 1200℃, 1220℃, 1240℃ or 1250℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0093] Preferably, the pressure of the high-pressure water used in the surface descaling treatment in step (1) is 15~20MPa, for example, it can be 15MPa, 16MPa, 17MPa, 18MPa, 19MPa or 20MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0094] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0095] Compared with the prior art, the present invention has the following beneficial effects:

[0096] (1) The method provided by the present invention is to continuously roll out two types of small square billets using the same set of roll passes, which has the characteristics of sharing the rolling mill and guides, low spare parts cost, simple and efficient specification change;

[0097] (2) The method provided by the present invention saves the workload of disassembling and assembling the rolling mill. Compared with the traditional method, it can save about 2 hours of downtime each time the rolling small square billet specification is changed, thereby improving work efficiency, reducing the labor intensity of workers and spare parts costs.

[0098] (3) By using the method provided by the present invention, the adjustment of the workpiece height setting and the mill speed setting is minimal during the continuous rolling billet opening process. The first to fifth mills remain unchanged each time the rolling small square billet specification is switched. Only the workpiece height and rolling speed of the sixth to ninth mills need to be reset. The adjustment range is narrow and the specification change is simple, which can effectively prevent process and quality accidents.

[0099] (4) This invention uses continuous rolling to produce large square billets and uses corner protection rolling to prevent the formation of undercooled structures. This can avoid microcracks when rolling alloy spring steel, alloy cold heading steel and high carbon steel, and can meet the quality requirements of high-end bar and wire products. Detailed Implementation

[0100] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0101] The dimensions of the large square blank used in the following embodiments and comparative examples are 300mm × 390mm.

[0102] Example 1

[0103] This embodiment provides a continuous billet rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The continuous billet rolling method includes the following steps:

[0104] (1) The large square billet is subjected to heat treatment and surface descaling treatment in sequence to obtain the large square billet material;

[0105] The corner radius of the large square billet is 20mm, and the carbon content is 0.52wt%; the heat treatment temperature is 1225℃, and the pressure of the high-pressure water used for surface descaling is 18MPa;

[0106] (2) A continuous rolling mill with alternating vertical and horizontal sections is used to continuously roll the billet to obtain a first square billet with dimensions of 160×160mm;

[0107] The continuous rolling mill includes a first rolling mill, a second rolling mill, a third rolling mill, a fourth rolling mill, a fifth rolling mill, a sixth rolling mill, and a seventh rolling mill arranged in succession, with a rolling pass pattern of square-box-square-box-square-box-square;

[0108] The rolling pass parameters of the continuous rolling mill are shown in Table 1:

[0109] Table 1

[0110]

[0111] Example 2

[0112] This embodiment provides a continuous billet rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The continuous billet rolling method includes the following steps:

[0113] (1) The large square billet is subjected to heat treatment and surface descaling treatment in sequence to obtain the large square billet material;

[0114] The large square billet has a corner radius of 19mm and a carbon content of 0.82wt%; the heat treatment temperature is 1250℃ and the pressure of the high-pressure water used for surface descaling is 20MPa.

[0115] (2) A continuous rolling mill with alternating vertical and horizontal sections is used to continuously roll the billet to obtain a second square billet with dimensions of 140×140mm;

[0116] The continuous rolling mill includes a first rolling mill, a second rolling mill, a third rolling mill, a fourth rolling mill, a fifth rolling mill, a sixth rolling mill, a seventh rolling mill, an eighth rolling mill, and a ninth rolling mill arranged in succession, with a rolling pass pattern of square-box-square-box-square-box-square-box-square-box-square;

[0117] The continuous rolling mill described in this embodiment is: an eighth rolling mill and a ninth rolling mill installed on the basis of the continuous rolling mill provided in Embodiment 1;

[0118] The rolling pass parameters of the continuous rolling mill are shown in Table 2:

[0119] Table 2

[0120]

[0121] Example 3

[0122] This embodiment provides a continuous billet rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The continuous billet rolling method includes the following steps:

[0123] (1) The large square billet is subjected to heat treatment and surface descaling treatment in sequence to obtain the large square billet material;

[0124] The corner radius of the large square billet is 23mm, and the carbon content is 0.92wt%; the heat treatment temperature is 1200℃, and the pressure of the high-pressure water used for surface descaling is 15MPa.

[0125] (2) A continuous rolling mill with alternating vertical and horizontal sections is used to continuously roll the billet to obtain a second square billet with dimensions of 160×160mm;

[0126] The continuous rolling mill includes a first rolling mill, a second rolling mill, a third rolling mill, a fourth rolling mill, a fifth rolling mill, a sixth rolling mill, and a seventh rolling mill arranged in succession, with a rolling pass pattern of square-box-square-box-square-box-square;

[0127] The continuous rolling mill described in this embodiment is: based on the continuous rolling mill provided in Embodiment 2, the eighth and ninth rolling mills are unloaded, and an empty guide groove is installed;

[0128] The rolling pass parameters of the continuous rolling mill are shown in Table 3:

[0129] Table 3

[0130]

[0131] Comparative Example 4

[0132] This comparative example provides a continuous billet-rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The only difference between this continuous billet-rolling method and Example 1 is that:

[0133] This comparative example adjusts the rolling pass patterns of the sixth and seventh rolling mills described in step (2) to be the same as those in Example 2.

[0134] Comparative Example 5

[0135] This comparative example provides a continuous billet-rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The only difference between this continuous billet-rolling method and Example 2 is that:

[0136] This comparative example adjusts the rolling pass patterns of the sixth and seventh rolling mills in step (2) to be the same as those in Example 1.

[0137] Comparative Example 6

[0138] This comparative example provides a continuous billet-rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The only difference between this continuous billet-rolling method and Example 1 is that:

[0139] In this comparative example, the elongation coefficient of the rolling pass of the continuous rolling mill used in the continuous rolling process described in step (2) is adjusted to: 1.05, 1.26, 1.23, 1.21, 1.21, 1.27 and 1.20.

[0140] Comparative Example 7

[0141] This comparative example provides a continuous billet-rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The only difference between this continuous billet-rolling method and Example 1 is that:

[0142] In this comparative example, the elongation coefficient of the rolling pass of the first rolling mill used in the continuous rolling process described in step (2) is adjusted to 1.25.

[0143] Comparative Example 8

[0144] This comparative example provides a continuous billet-rolling method for rolling small billets of different sizes from a large billet using a common roll pass. The only difference between this continuous billet-rolling method and Example 1 is that:

[0145] In this comparative example, the rolling pass of the continuous rolling mill described in step (2) is adjusted to a box-shaped pass.

[0146] Performance testing:

[0147] The small square billets provided in the above embodiments and comparative examples were shot peened and then subjected to magnetic particle testing to test the corner crack ratio and grinding ratio of the small square billets. The results are shown in Table 4.

[0148] Table 4

[0149]

[0150] According to Table 4, the following points can be observed:

[0151] (1) According to the comprehensive analysis of Examples 1-3, the method provided by the present invention uses a continuous rolling mill with a set of pass system and guide spare parts. By adjusting the number of rolls in the continuous rolling mill and the rolling pass size of the rolling mill, the rolling of small square billets of different sizes can be realized.

[0152] In addition, the continuous billet-making process can achieve rapid switching of billet specifications without changing the rolling mill, resulting in high operating efficiency, low cost, and good billet quality, which can meet the production needs of high-end cold heading steel, spring steel, high carbon steel and other products.

[0153] (2) A comprehensive analysis of Examples 1-2 and Comparative Examples 1-2 shows that the adjustment of the rolling pass of the sixth and seventh rolling mills will affect the rapid switching of the billet specifications;

[0154] During the rolling of the first square billet, if the rolling pass of the sixth and seventh rolling mills is the same as that of the rolling pass of the second square billet, the size of the first square billet cannot be obtained. If no additional rolling mill is added, the switching of the billet specifications cannot be achieved.

[0155] Conversely, if the rolling pass of the sixth and seventh rolling mills is the same as that used for rolling the first billet during the rolling process of the second billet, it will lead to a decrease in the elongation coefficient and an increase in cracks in the eighth and ninth rolling mills.

[0156] (3) According to the comprehensive analysis of Example 1 and Comparative Example 3, if the elongation coefficient of the rolling pass of the continuous rolling mill used in the rolling process of the first square billet is too low, it will lead to an increase in the elongation coefficient of the seventh rolling mill, resulting in a larger billet size and an increase in cracks.

[0157] A comprehensive analysis of Example 1 and Comparative Example 4 shows that, during the rolling of the first square billet, if the elongation coefficient of the rolling pass of the first rolling mill used in the continuous rolling process is too high, it will lead to a decrease in the elongation coefficient of the second to seventh rolling mills, resulting in a smaller billet size and an increase in cracks.

[0158] (4) A comprehensive analysis of Example 1 and Comparative Example 5 shows that if the pass system of the continuous rolling mill is adjusted to the same box-shaped pass, it will lead to a rapid increase in cracks.

[0159] The continuous rolling mill used in this invention has a set of pass system and guide spare parts. By adjusting the number of rolls and the size of the rolling pass in the continuous rolling mill, the rolling of small square billets of different sizes can be achieved. The continuous billet opening process can realize the rapid switching of billet specifications without changing the rolling mill. It has high operating efficiency, low cost, and good billet opening quality, which can meet the production needs of high-end cold heading steel, spring steel, high carbon steel and other products.

[0160] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A continuous billet rolling method for rolling small billets of different sizes from a large billet using a shared pass, characterized in that, The continuous billet-making method includes the following steps: (1) The large square billet is subjected to heat treatment and surface descaling treatment in sequence to obtain the large square billet material; (2) A continuous rolling mill with alternating vertical and horizontal sections is used to continuously roll the billet to obtain a first square billet or a second square billet; The continuous rolling mill includes a first rolling mill, a second rolling mill, a third rolling mill, a fourth rolling mill, a fifth rolling mill, a sixth rolling mill, a seventh rolling mill, and a detachable rolling mill, all arranged sequentially; the detachable rolling mill includes an eighth rolling mill and a ninth rolling mill connected in sequence. The rolling pass pattern of the continuous rolling mill is square-box-square-box-square-box-square-box-square-box-square; The rolling of the first or second square billet is achieved by unloading or installing a detachable rolling mill and adjusting the rolling pass size of the sixth, seventh, eighth and ninth rolling mills; When rolling the first square billet, the eighth and ninth rolling mills are unloaded and a blank guide groove is installed; when rolling the second square billet, the blank guide groove is unloaded and the eighth and ninth rolling mills are installed. The heights of the rolling passes of the first to fifth rolling mills are 340-350 mm, 225-235 mm, 250-260 mm, 190-200 mm, and 200-210 mm, respectively; the widths of the rolling passes are 325-330 mm, 365-370 mm, 275-280 mm, 294-298 mm, and 232-236 mm, respectively; and the inner radius R of the rolling passes is 28-32 mm, 28-32 mm, respectively. The elongation coefficients of the rolling pass are 1.15±0.01, 1.28±0.01, 1.27±0.01, 1.24±0.01, and 1.24±0.01, respectively; the bite angles of the rolling pass are 21±1°, 25±1°, 29±1°, 22±1°, and 25±1°, respectively. When rolling the first square billet, the rolling pass of the sixth rolling mill has a height of 145~150mm, a width of 243~247mm, an elongation coefficient of 1.29±0.01, and a bite angle of 24±1°; the rolling pass of the seventh rolling mill has a height of 162~163mm, a width of 174~175mm, an elongation coefficient of 1.24±0.01, and a bite angle of 24±1°. When rolling the second square billet, the rolling pass of the sixth rolling mill has a height of 151~153mm, a width of 243~247mm, an elongation coefficient of 1.27±0.01, and a bite angle of 24±1°; the rolling pass of the seventh rolling mill has a height of 173~175mm, a width of 174~175mm, an elongation coefficient of 1.18±0.01, and a bite angle of 22±1°; the rolling pass of the eighth rolling mill has a height of 128~132mm, a width of 195~199mm, an elongation coefficient of 1.19±0.01, and a bite angle of 18±1°; and the rolling pass of the ninth rolling mill has a height of 141~142mm, a width of 152~153mm, an elongation coefficient of 1.19±0.01, and a bite angle of 21±1°.

2. The continuous billet-making method according to claim 1, characterized in that, The dimensions of the first billet are 160~170×160~170mm.

3. The continuous billet-making method according to claim 1, characterized in that, The dimensions of the second square billet are 140~150×140~150mm.

4. The continuous billet-making method according to claim 1, characterized in that, The rolling speed of the continuous rolling mill is: V n-1 =V n / R n Among them, V n-1 R is the rolling speed of the previous rolling mill. n V is the elongation coefficient of the rolling mill. n =V 成品 Set the rolling speed for the finished product.

5. The continuous billet-making method according to claim 1, characterized in that, The cross-sectional dimensions of the large square billet in step (1) are 300~320mm×380~400mm.

6. The continuous billet-making method according to claim 1, characterized in that, The corner radius of the large square billet is 17~23mm.

7. The continuous billet-making method according to claim 1, characterized in that, The carbon content of the large billet is 0.05~0.92wt%.

8. The continuous billet-making method according to claim 1, characterized in that, The temperature of the heat treatment in step (1) is 1150~1250℃.

9. The continuous billet-making method according to claim 1, characterized in that, The pressure of the high-pressure water used in the surface descaling treatment in step (1) is 15~20MPa.

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