A method for producing cold heading steel wire rod and the cold heading steel wire rod obtained therefrom

Abstract

This invention discloses a method for producing cold-heading steel wire rod, including heating, descaling, rough rolling, intermediate rolling, pre-finish rolling, finish rolling, wire drawing, and Stellmore cooling. The method controls specific finish rolling exit speeds, wire drawing machine speeds, and the speed difference between the finish rolling exit speed and the wire drawing machine speed according to the specifications of the produced wire rod. This production method aims to reduce surface scoring defects in cold-heading steel wire rod. The invention also discloses the wire rod produced by the above method. The production method provided by this invention, by controlling parameters such as the finish rolling exit speed, wire drawing machine speed, wire drawing temperature, water volume and distribution in the water tank after finish rolling, finish rolling elongation coefficient, and roller speed, achieves high tension, high temperature, and low water volume, reducing surface scoring defects in the wire rod, improving the surface quality of the product, and effectively improving the cold-heading performance of the cold-heading steel wire rod. It also prevents surface scoring defects from damaging the integrity of the wire rod and causing stress concentration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of steel production, in particular to a production method of cold heading steel wire rod and the cold heading steel wire rod produced thereby. BACKGROUND

[0002] Cold heading steel wire rod is widely used to manufacture bolts, nuts, screws and other types of fasteners. It has the advantages of high production efficiency, low subsequent processing cost, wide application and large market demand. However, cold heading steel wire rod needs to utilize the plasticity of metal to produce standard parts by cold heading forming process, so it is sensitive to surface defects of the wire rod. Therefore, cold heading steel has strict requirements on the surface quality of the wire rod, especially the steel for automobiles, which requires "zero defects" on the surface of the wire rod. Research has found that more than 70% of cold heading cracking is caused by poor surface quality. In addition, with the development of industry, the development of high-end products requires increasingly strict surface quality of the wire rod, which requires steel plants to continuously improve the surface quality of cold heading steel products.

[0003] The surface quality of the wire rod is an important evaluation index of the quality of wire rod products. For cold heading steel, the surface quality of the wire rod directly affects the cold heading performance, so cold heading steel has strict requirements on the surface quality. Common surface defects of the wire rod include scratch, fold and wrinkle: scratch is a defect in which a straight line-shaped groove appears on the surface of the wire rod and the groove bottom is visible, which is continuously or discontinuously distributed on the whole length of the wire rod, usually produced after final rolling, and is caused by improper tension adjustment and rolling temperature change; fold is a thin line on the surface of the wire rod in the rolling direction, which is a defect with a small angle intersection between the cross section and the surface, mainly caused by the size of the previous pass being too large, resulting in the occurrence of ears and then the generation of folds; wrinkle is a cluster of cracks parallel to the rolling direction on the surface of the wire rod, mainly generated in the rough rolling process and often appearing in the corner area of the billet. Surface defects destroy the integrity of the wire rod, causing stress concentration, and in the cold working deformation process, cracking occurs when the deformation is large, which reduces the cold heading performance of the product.

[0004] The existing production method for improving the surface quality of the wire rod mainly focuses on reducing the generation of surface wrinkle cracks, reducing the surface wrinkle cracks of the wire rod and improving the surface quality of the low-carbon cold heading steel wire rod by designing the roughing pass and controlling the process parameters such as the roughing temperature, the cooling water pressure, the water temperature, the rolling speed and the billet corner temperature. However, the surface defects of the wire rod also include scratch lines and folds, which can also cause product cracking and reduce the cold heading performance of the product in the cold working deformation process. According to research, the 0.05mm deep pits on the surface of the finished wire rod can affect the subsequent cold heading. In the cold heading process, there is stress concentration around the scratch lines, and when the deformation amount is large, cracking phenomenon can occur. At present, there is less research on the surface scratch lines of the wire rod, so it is necessary to conduct in-depth research on the scratch lines, reduce the generation of surface scratch lines in the production process, improve the surface quality of the wire rod and reduce the cold heading cracking rate. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is that there is no research on the surface scratch lines of the wire rod in the prior art, so as to provide a production method of cold heading steel wire rod and cold heading steel wire rod prepared by the method.

[0006] Therefore, the technical problem to be solved by the present application is that there is no research on the surface scratch lines of the wire rod in the prior art, so as to provide a production method of cold heading steel wire rod and cold heading steel wire rod prepared by the method.

[0007] The present application provides a production method of cold heading steel wire rod, which comprises heating, dephosphorization, rough rolling, intermediate rolling, pre-precision rolling, precision rolling, wire laying and Stelmor cooling.

[0008] When the prepared wire rod specification is 5-7mm, the precision rolling outlet speed is 100-106m / s, the wire laying machine speed is 105-110m / s, and the difference between the precision rolling outlet speed and the wire laying machine speed is 4-5m / s;

[0009] When the prepared wire rod specification is 8-9mm, the precision rolling outlet speed is 70-90m / s, the wire laying machine speed is 73-94m / s, and the difference between the precision rolling outlet speed and the wire laying machine speed is 3-4m / s;

[0010] When the prepared wire rod specification is 10-12.5mm, the precision rolling outlet speed is 35-55m / s, the wire laying machine speed is 37-58m / s, and the difference between the precision rolling outlet speed and the wire laying machine speed is 2-3m / s;

[0011] When the prepared wire rod specification is 13-14mm, the precision rolling outlet speed is 25-35m / s, the wire laying machine speed is 27-37m / s, and the difference between the precision rolling outlet speed and the wire laying machine speed is 2-3m / s;

[0012] The production method is used for reducing the surface scratch lines of the cold heading steel wire rod.

[0013] The wire rod specifications are 5, 5.5, 6, 7, 8, 9, 10, 11, 12, 12.5, 13, 14 mm.

[0014] Further, the wire drawing temperature is 940±20℃, and the total water quantity of the water tanks in the last three sections of the finishing mill is 2000-2500L / min.

[0015] In the third section water tank, the water quantity of the 1#, 2# and 3# water tanks is 1050±100L / min, 750±100L / min and 400±100L / min respectively.

[0016] When the wire rod specifications are 5-7mm, the extension coefficients of the 10 rolling mills in the rolling direction are 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, 1.29-1.31, 1.19-1.22, 1.28-1.31 and 1.18-1.21 respectively.

[0017] When the wire rod specifications are 8-9mm, the extension coefficients of the 10 rolling mills in the rolling direction are empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, 1.29-1.31 and 1.19-1.22 respectively.

[0018] When the wire rod specifications are 10-11mm, the extension coefficients of the 10 rolling mills in the rolling direction are empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, empty and empty respectively.

[0019] When the wire rod specifications are 12-14mm, the extension coefficients of the 10 rolling mills in the rolling direction are empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, empty, empty, empty and empty respectively.

[0020] The speed of the Stelmor entrance section roller is 0.20-0.4m / s, and the fan and the heat preservation cover are all closed.

[0021] The entrance temperature of the finishing mill is 910±30℃, and the exit temperature of the finishing mill is ≤1020℃.

[0022] The application further provides a cold heading steel wire rod prepared by the production method, and the specifications of the wire rod are 5.0-14mm.

[0023] Further, the content of C in the wire rod is ≤0.45wt%.

[0024] The technical scheme of the present application has the following advantages:

[0025] (1) The production method provided by the present application realizes large tension, high temperature and small water quantity by controlling the parameters such as the finishing outlet speed, the wire drawing machine speed, the wire drawing temperature, the water quantity and distribution of the water tank after finishing, the finishing elongation coefficient, and the roller speed, reduces the wire drawing surface scratch defect, improves the product surface quality, and effectively improves the cold heading performance of the cold heading steel wire rod.

[0026] (2) In the present application, the tension control is mainly achieved by increasing the wire drawing machine speed, increasing the speed difference between the finishing mill outlet speed and the wire drawing machine speed, increasing the rolling piece tension, improving the rolling piece stability, avoiding the rolling piece from shaking and colliding with the guide groove, and reducing the scratch. In addition, the wire drawing temperature is appropriately increased, the total water quantity of the water tank after the finishing mill is reduced, and the water quantity distribution is reasonably matched, so as to reduce the impact of the cooling water on the rolling piece, avoid the rolling piece from shaking and colliding with the guide groove, and cause the surface scratch. By controlling the finishing elongation coefficient, the deformation amount is reasonably matched, and the surface quality is further improved. The roller speed is controlled, and the heat preservation cover is added, so that the higher temperature can further burn off the surface scratch, further reduce the surface scratch, and improve the surface quality of the product. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present application or the technical scheme in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0028] Figure 1 is the wire rod photo obtained in Example 1 in the present application;

[0029] Figure 2 is the wire rod photo obtained in Comparative Example 1 in the present application. DETAILED DESCRIPTION

[0030] The following examples are provided in order to better further understand the present application, and do not limit the best embodiments, and do not constitute a limitation on the content and protection scope of the present application. Any person under the inspiration of the present application or the combination of the present application with other prior art features can obtain any product which is the same or similar to the present application, and falls within the protection scope of the present application.

[0031] The specific experimental steps or conditions are not indicated in the examples, and the operation or conditions can be performed according to the conventional experimental steps described in the literature in the art. The reagents or instruments used are not indicated by the manufacturer, and are conventional reagent products that can be obtained by purchase.

[0032] Embodiment

[0033] The embodiment provides a production method of cold upsetting steel wire rod, and comprises the following steps:

[0034] Heating-phosphorus removal-rough rolling-medium rolling-pre-precision rolling-precision rolling-wire drawing-Stelmor cooling.

[0035] Specific rolling process parameters are shown in Table 1, the precision rolling extension coefficient is shown in Table 2, the wire drawing temperature and the water tank water amount are shown in Table 3, and the rest of the process is completely the same as the examples and the comparative examples.

[0036] Table 1 Rolling process parameters

[0037]

[0038] Table 2 Precision rolling extension coefficient

[0039]

[0040] Table 3 Wire drawing temperature and water tank water amount

[0041] Grade Temper Temper Temper Temper Temper Temper Temper 940℃ 2010 1010 700 300 Temper Temper 890℃ 2680 1000 680 1000 Temper 10B21 940℃ 2120 1023 757 340 Temper 10B21 890℃ 2795 1120 580 1095 Temper Temper 940℃ 2200 1136 734 330 Temper Temper 890℃ 2850 1158 642 1050 Temper Temper 920℃ 2410 1150 760 500 Temper Temper 880℃ 3000 1255 570 1175

[0042] Test example

[0043] (1) The wire rods of the examples 1 and the comparative example 1 are taken, and the appearances are respectively shown in Figs. Temper and Temper It can be seen that the surface of the wire rod obtained by the example 1 is smooth and has no scribe line, and the surface of the wire rod in the comparative example 1 has obvious scribe line.

[0044] (2) The wire rods obtained by rolling of the examples and the comparative example are subjected to 1 / 3 cold upsetting, and the specific cold upsetting method is as follows:

[0045] The sample with a length of 2 times of the diameter is taken, and the 1 / 3 cold upsetting is performed by using a cold upsetting testing machine, that is, the diameter before the cold upsetting is 1 / 3 of the diameter after the cold upsetting.

[0046] The cold upsetting cracking rate is counted, and is shown in Table 4.

[0047] Table 4 Cold upsetting results of the examples and the comparative example

[0048] Temper Temper Temper Temper Temper 5.5 0.90％ Temper Temper 5.5 4.3％ Temper Temper 5.5 6.2％ Temper Temper 5.5 4.9％ Temper Temper 5.5 9％ Temper 10B21 8 0.8％ Temper 10B21 8 7.2％ Temper 10B21 8 6.8％ Temper 10B21 8 5..8％ Temper 10B21 8 10％ Temper Temper 10 1％ Temper Temper 10 10％ Temper Temper 14 1.20％ Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper Temper 14 15％

[0049] As can be seen from Table 4, the 1 / 3 cold upsetting cracking rates of Examples 1-4 adopting the technical scheme of the present application are obviously lower than those of each of the comparative examples, the highest being only 1.20%, although different grades of raw materials are adopted; and the 1 / 3 cold upsetting cracking rates of each of the comparative examples changing several parameters in the technical scheme of the present application are all too high, seriously affecting the quality of the products.

[0050] The above examples are merely examples for clearly illustrating but not limiting the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments need not and cannot be exhausted. The changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for producing cold heading steel wire rod, comprising heating, dephosphorization, rough rolling, intermediate rolling, pre-precision rolling, precision rolling, wire drawing, Stelmor cooling, characterized in that, when the produced wire rod specification is 5-7 mm, the precision rolling exit speed is 100-106 m / s, the wire drawing machine speed is 105-110 m / s, the difference between the precision rolling exit speed and the wire drawing machine speed is 4-5 m / s; when the produced wire rod specification is 8-9 mm, the precision rolling exit speed is 70-90 m / s, the wire drawing machine speed is 73-94 m / s, the difference between the precision rolling exit speed and the wire drawing machine speed is 3-4 m / s; when the produced wire rod specification is 10-12.5 mm, the precision rolling exit speed is 35-55 m / s, the wire drawing machine speed is 37-58 m / s, the difference between the precision rolling exit speed and the wire drawing machine speed is 2-3 m / s; when the produced wire rod specification is 13-14 mm, the precision rolling exit speed is 25-35 m / s, the wire drawing machine speed is 27-37 m / s, the difference between the precision rolling exit speed and the wire drawing machine speed is 2-3 m / s; the wire drawing temperature is 940±20℃; the Stelmor entrance section roller speed is 0.20-0.4 m / s, the fan and the heat preservation cover are all closed; the method is used for reducing the surface scratch of the cold heading steel wire rod; when the precision rolling, when the produced wire rod specification is 5-7 mm, the 10-arch rolling mill elongation coefficient is 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, 1.29-1.31, 1.19-1.22, 1.28-1.31, 1.18-1.21 in the rolling direction; when the produced wire rod specification is 8-9 mm, the 10-arch rolling mill elongation coefficient is empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, 1.29-1.31, 1.19-1.22 in the rolling direction; when the produced wire rod specification is 10-11 mm, the 10-arch rolling mill elongation coefficient is empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, 1.32-1.34, 1.17-1.20, empty, empty in the rolling direction; when the produced wire rod specification is 12-14 mm, the 10-arch rolling mill elongation coefficient is empty, empty, 1.30-1.40, 1.18-1.20, 1.28-1.30, 1.17-1.21, empty, empty, empty, empty in the rolling direction. The total water volume of the 3-section water tank after the precision rolling mill is 2000-2500 L / min. In the 3-section water tank, the water volume of the 1#, 2# and 3# water tanks is 1050±100 L / min, 750±100 L / min and 400±100 L / min respectively. The precision rolling entrance temperature is 910±30℃, and the precision rolling exit temperature is ≤1020℃. ​ ​ ​ ​ ​ ​ ​ ​ 2. The production method according to claim 1, characterized by, ​ 3. The production method according to claim 2, characterized by, ​ 4. The production method according to any one of claims 1 to 3, characterized by, ​ 5. A cold heading steel wire rod, characterized in that, The wire rod is produced by the production method of any one of claims 1-4, and has a size of 5.0-14 mm.

6. A cold heading steel wire rod according to claim 5, characterized in that C in the wire rod is ≤0.45 wt%.

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