A method for eliminating surface wrinkles of bars

Abstract

The present invention relates to the field of steel rolling, and specifically discloses a method for eliminating surface wrinkles of bars. The method comprises the following steps: (1) Select a bearing steel rectangular billet of 250×280. Grind the surface of the billet with a billet grinding machine. After grinding, roll the cast billet. Take a material section on the finished product and conduct multiple surface pickling verifications to confirm that the wrinkle defects occur in the cogging pass system; (2) Model according to the rolling schedule and pass system, take a 1 / 4 rolled piece model, and conduct four-pass continuous rolling simulation according to the rolling schedule; (3) Compare and analyze after intercepting the cross sections of the rolling processes of each pass; (4) Optimize the pass and reduction of the first pass and the second pass; (5) Optimize the reduction of the third pass and the fourth pass, and conduct the subsequent rolling process according to the optimized reduction and pass. The present invention solves the problem that it is difficult to handle the surface wrinkle defects of continuous casting billets in the prior art.

Description

Technical Field

[0001] The present invention belongs to the field of steel rolling, and particularly relates to a method for eliminating surface wrinkles of bars. Background Art

[0002] A continuous casting billet is a product obtained by casting molten steel from a steelmaking furnace through a continuous caster. The application fields of continuous casting billets are becoming wider and wider, and continuous casting billet products have been used in mechanical engineering equipment both at home and abroad. The difference between a continuous casting billet and a forging and rolling billet is that the former is in a casting state, and the defects in it are much more obvious than those in a forging and rolling billet, and there are also regulations on "cracks" that are not allowed in a forging and rolling billet.

[0003] Generally, the defects of continuous casting billets are divided into three categories, namely surface defects, internal defects, and shape defects. After the 250×280 rectangular continuous casting billet is rolled through the cogging pass, surface wrinkle defects in a linear aggregation state are formed on the surface. At present, it is difficult to determine the specific situation of the surface wrinkle defects in a linear aggregation state formed on the surface of the 250×280 rectangular continuous casting billet. The formed surface wrinkle defects are difficult to handle, and there is a problem that the depth of the wrinkle defects is difficult to improve. Summary of the Invention

[0004] In order to solve the problems in the above-mentioned prior art that it is difficult to determine the specific situation of the surface wrinkle defects in a linear aggregation state formed on the surface of the 250×280 rectangular continuous casting billet, the formed surface wrinkle defects are difficult to handle, and the depth of the wrinkle defects is difficult to improve, the present invention provides a method for eliminating surface wrinkles of bars.

[0005] The technical solution of the present invention: A method for eliminating surface wrinkles of bars, the method comprising the following steps:

[0006] (1) Select a 250×280 bearing steel rectangular billet, grind the surface of the billet with a billet grinding machine, roll the billet after grinding, take a sample section on the finished product, and conduct multiple surface pickling verifications to confirm that the wrinkle defects are generated in the cogging pass system;

[0007] (2) Build a model according to the rolling schedule and pass system, take a 1 / 4 rolled piece model, and conduct four-pass continuous rolling simulation according to the rolling schedule;

[0008] (3) After intercepting the cross-sections of each pass rolling process, conduct a comparative analysis;

[0009] (4) Optimize the pass and reduction of the first pass and the second pass;

[0010] (5) Optimize the reduction of the third pass and the fourth pass, and conduct the subsequent rolling process according to the optimized reduction and pass.

[0011] In the step (1), the unilateral grinding amount of the surface of the billet ground by the billet grinding machine is ≥6 mm.

[0012] In step (1), the length of a single billet section taken from the finished product is 300 mm.

[0013] In step (1), the number of pickling times for the billet section is 4 - 5 times.

[0014] In step (4), the reduction of the first optimized pass is 55 - 60 mm.

[0015] In step (4), the reduction of the second optimized pass is 76 - 80 mm.

[0016] In step (4), the R - angle of the pass profile of the first optimized pass is 20° - 25°.

[0017] In step (4), the R - angle of the pass profile of the second optimized pass is 30° - 35°.

[0018] In step (5), the reduction of the third optimized pass is 45 - 50 mm.

[0019] In step (5), the reduction of the fourth optimized pass is 55 - 60 mm.

[0020] Advantages of the present invention:

[0021] In the present invention, through numerical simulation and verification of the deformation of the cogging pass system, and combined with sampling pickling inspection, it is found that the depth of the fold defect ranges from 0.05 - 0.5 mm, and the defects are mainly concentrated in 4 symmetric regions near the roll gap, near the end of the deformation streamline. After determining the defect position, after optimizing the pass profiles and reduction of the first and second passes, and the reduction of the third and fourth passes, the depth of the fold defect is improved significantly.

[0022] By optimizing the pass profiles and reduction of the first and second passes in the present invention, the pass profiles of the first and second passes are increased, and the contact R - angles of the pass profiles are increased from 17 / 25 to 20° - 25° / 30° - 35° respectively; the reduction of the third and fourth passes is increased from 36 mm / 45 mm to 45 - 50 mm / 55 - 60 mm respectively. The present invention achieves the purpose of improving the depth of the fold defect, and finally achieves the effect that the depth of the fold defect is basically below 0.1 mm, and the width of the fold zone is significantly reduced. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the first pass of the rolling pass system of the present invention;

[0024] Figure 2 It is a schematic diagram of the second pass of the rolling pass system of the present invention;

[0025] Figure 3 Schematic diagram of the third pass rolling of the rolling pass system of the present invention;

[0026] Figure 4 Schematic diagram of the fourth pass rolling of the rolling pass system of the present invention;

[0027] Figure 5 Hydrostatic pressure distribution diagram of the first pass of tandem rolling;

[0028] Figure 6 Hydrostatic pressure distribution diagram of the second pass of tandem rolling;

[0029] Figure 7 Hydrostatic pressure distribution diagram of the third pass of tandem rolling;

[0030] Figure 8 Hydrostatic pressure distribution diagram of the fourth pass of tandem rolling;

[0031] Figure 9 Schematic diagram of the cross-sectional shape of the workpiece before the first pass of tandem rolling;

[0032] Figure 10 Schematic diagram of the cross-sectional shape of the workpiece before the second pass of tandem rolling;

[0033] Figure 11 Schematic diagram of the cross-sectional shape of the workpiece before the third pass of tandem rolling;

[0034] Figure 12 Schematic diagram of the cross-sectional shape of the workpiece before the fourth pass of tandem rolling;

[0035] Figure 13 Schematic diagram of the actual shape of the workpiece before tandem rolling;

[0036] Figure 14 Simulation result diagram of the pass shape and the cross-sectional shape of the bar after the first pass of blooming rolling;

[0037] Figure 15 Simulation result diagram of the pass shape and the cross-sectional shape of the bar after the second pass of blooming rolling;

[0038] Figure 16 Simulation result diagram of the pass shape and the cross-sectional shape of the bar after the third pass of blooming rolling;

[0039] Figure 17 Simulation result diagram of the pass shape and the cross-sectional shape of the bar after the fourth pass of blooming rolling;

[0040] Figure 18 Cross-sectional diagram after the first pass of rolling;

[0041] Figure 19 Cross-sectional diagram after the second pass of rolling;

[0042] Figure 20It is the cross-sectional view after three-pass rolling;

[0043] Figure 21 It is the cross-sectional view after four-pass rolling;

[0044] Figure 22 It is the schematic diagram of the hydrostatic pressure during the rolling process. Specific embodiments

[0045] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described below with specific embodiments. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0046] The present invention provides a method for eliminating surface wrinkles of bars. Select a 250×280 bearing steel rectangular billet, grind the surface with a billet grinding machine, with a unilateral grinding amount ≥6 mm. After grinding, the surface of the cast billet is manually inspected and qualified for rolling. A 300-mm long section is taken from the finished product for surface pickling verification. Such verification operations have been carried out 4 times repeatedly. Finally, it is confirmed that the wrinkle defect occurs in the cogging pass system. Modeling is carried out according to the rolling schedule and pass system given on site. A 1 / 4 model of the rolled piece is taken, and four-pass continuous rolling simulation is carried out according to the rolling schedule in Table 1.

[0047] Table 1 Rolling process table

[0048]

[0049] The cross-sectional shapes intercepted during the simulation of each pass rolling process are as Figure 9 shown and compared with the Figure 10 CAD shape of the cross-section after rolling. It can be seen that the appearance of the platform area is mainly due to the existence of a tangent area near the roll gap edge during the design of the second-pass pass.

[0050] The cross-section after four-pass rolling simulation and the equivalent strain results are compared and analyzed, and there is a good position correspondence between the actual defect position and the high-strain area. In order to eliminate or reduce the severe deformation in this area, the pass and reduction of the first pass and the second pass should be considered for optimization.

[0051] Optimize the cogging pass parameters to reduce the stress state of the billet corner in the pass. As shown in Table 2, there is no obvious change in the reduction of the first stand of the first pass and the second stand of the first pass, and they are basically the same, which does not affect the normal operation of production, while changing the R angle size of the first stand and the second stand of the rolling mill.

[0052] Table 2 Process parameters before and after pass optimization

[0053]

[0054] After the pass shapes of the first pass and the second pass rolling mills are optimized, the occurrence ratio of wrinkles changes little compared with that before optimization, but the depth of the wrinkle defects is improved significantly. After optimization, the defect depth is basically below 0.1 mm, and the width of the wrinkle zone is significantly reduced after optimization.

[0055] Observe the stress state at the core of the rolled material during the rolling process. The observation positions are as Figure 22 shown. Observe the contour map of the hydrostatic pressure distribution after the fourth pass rolling. The results are as Figures 5 - 8 shown. From the hydrostatic pressure distribution, during the deformation process of the fourth pass, the core is basically under a relatively small compressive stress. Statistically analyze the stress values at the core of the rolled material for different passes. The first four passes before rough rolling are basically under compressive stress, with a range of -15 - 0 MPa.

[0056] The cross-sectional shapes intercepted during the simulation of each pass rolling process are as Figures 9 - 12 shown and compared with the Figure 13 actual CAD shape of the cross-section after rolling. After the second pass, a flat zone appears in the rolled material, located between the roll gap and the billet corner. This flat zone is finally retained until the fourth pass of rolling. The appearance of this flat zone is consistent with the tangent position of the transition zone at the roll gap edge corresponding to the actual bar after the fourth pass of rolling, indicating that the simulation results are in good agreement with the actual situation. Figures 14 - 17 For the simulation result diagrams of the pass shapes and the bar cross-sectional shapes of each pass, the appearance of the flat zone is mainly due to the existence of a tangent zone near the roll gap edge during the design of the second pass shape.

[0057] Compare and analyze the cross-section and equivalent strain results after the fourth pass of rolling simulation. After the first pass of rolling of the billet, obvious protrusions appear at the corners, as Figure 18 shown. After the second pass of deformation, the protrusions deform significantly and a high-strain zone is generated. Track and analyze the position where the high-strain zone appears. The results are as Figure 19 shown. From the equivalent strain distribution at the core and the surface after the fourth pass of rolling, it can be seen that the strain distribution at the core after the fourth pass of rolling is uniform and has a certain penetration effect, while the equivalent strain in the 45° oblique direction on the surface of the rolled material is relatively high, leaving a high-strain zone on the rolling surface. The position where the actual defect appears has a good positional correspondence with the high-strain area. Optimize the pass shapes and reduction amounts of the first pass and the second pass to eliminate or reduce the severe deformation in this area.

[0058] Through numerical simulation and verification of the deformation of the cogging pass system in the present invention, and combined with sampling pickling inspection, it is found that the depth of the fold defect ranges from 0.05 to 0.5 mm, and the defects are mainly concentrated in 4 symmetric regions near the roll gap, near the end of the deformation streamline. After optimizing the pass and reduction of the first pass and the second pass, the proportion of folds changes little compared with that before optimization, but the depth of the fold defect is improved significantly. After optimization, the defect depth is basically below 0.1 mm, and the width of the fold zone is significantly reduced after optimization.

[0059] Blooms of 250×280 rectangular cross-section are rolled through different types of continuous rolling pass systems to obtain round steel products of different diameter specifications. However, when the rectangular blooms are deformed into oval-round in the cogging pass with large reduction, there is corner equivalent strain with strain concentration. After rolling, four symmetric fold crack bands appear on the surface. The defects are mainly concentrated in 4 symmetric regions near the roll gap, near the end of the deformation streamline, and the defect depth ranges from 0.05 to 0.5 mm. The varieties are most prominent in low-carbon steel and bearing steel. The present invention solves the above problems, overcomes the above technical resistance, and obtains products with a defect depth basically below 0.1 mm by finely adjusting the pass and reduction of the first pass and the second pass.

[0060] Example 1

[0061] A method for eliminating surface folds of bars, the method comprising the following steps:

[0062] (1) Select a bearing steel rectangular bloom of 250×280. Grind the surface of the bloom with a bloom grinding machine. After grinding, roll the cast bloom. Take a billet section on the finished product, with a length of 300 mm, and conduct multiple surface pickling verifications to confirm that the fold defect occurs in the cogging pass system; (2) Build a model according to the rolling schedule and pass system, take a 1 / 4 rolled piece model, and conduct four-pass continuous rolling simulation according to the rolling schedule; (3) After intercepting the cross-sections of each pass rolling process, conduct comparison and analysis; (4) Optimize the pass and reduction of the first pass and the second pass; (5) Optimize the reduction of the third pass and the fourth pass, and conduct the subsequent rolling process according to the optimized reduction and pass. In step (1), the unilateral grinding amount of the bloom surface by the bloom grinding machine is 6 mm. In step (1), the number of pickling times for the billet section is 4-5 times. In step (4), the optimized reduction of the first pass is 55 mm. In step (4), the optimized reduction of the second pass is 76 mm. In step (4), the R angle of the optimized pass of the first pass is 20°. In step (4), the R angle of the optimized pass of the second pass is 30°. In step (5), the optimized reduction of the third pass is 45 mm. The optimized reduction of the fourth pass in step (5) is 55 mm.

[0063] Example 2

[0064] Different from Example 1, in step (4), the reduction of the first pass after optimization is 60 mm. In step (4), the reduction of the second pass after optimization is 80 mm. In step (4), the R angle of the pass profile of the first pass after optimization is 25°. In step (4), the R angle of the pass profile of the second pass after optimization is 35°. In step (5), the reduction of the third pass after optimization is 50 mm. In step (5), the reduction of the fourth pass after optimization is 60 mm.

[0065] Example 3

[0066] Different from Example 1, in step (4), the reduction of the first pass after optimization is 55 mm. In step (4), the reduction of the second pass after optimization is 76 mm. In step (4), the R angle of the pass profile of the first pass after optimization is 22°. In step (4), the R angle of the pass profile of the second pass after optimization is 32°. In step (5), the reduction of the third pass after optimization is 46 mm. In step (5), the reduction of the fourth pass after optimization is 56 mm.

[0067] Example 4

[0068] Different from Example 1, in step (4), the reduction of the first pass after optimization is 55 mm. In step (4), the reduction of the second pass after optimization is 76 mm. In step (4), the R angle of the pass profile of the first pass after optimization is 22°. In step (4), the R angle of the pass profile of the second pass after optimization is 32°. In step (5), the reduction of the third pass after optimization is 46 mm. In step (5), the reduction of the fourth pass after optimization is 55 mm.

[0069] Through numerical simulation and verification of the deformation of the bloom pass system of the present invention, and combined with sampling pickling inspection, it is found that the depth of the fold defect ranges from 0.05 to 0.5 mm, and the defects are mainly concentrated in 4 symmetric regions near the roll gap and near the end of the deformation streamline. After optimizing the pass profiles and reduction of the first and second passes, the proportion of folds does not change much compared with that before optimization, but the depth of the fold defects is improved significantly. After optimization, the defect depth is basically below 0.1 mm, and the width of the fold zone is significantly reduced after optimization.

[0070] The specific protection scope of the present invention is not limited to the above explanations. Any simple substitution or change within the technical idea disclosed by the present invention and according to the technical solution of the present invention should be within the protection scope of the present invention.

Claims

1. A method for eliminating surface wrinkles of bars, characterized in that, The method comprises the following steps: (1) A 250×280 rectangular billet of bearing steel was selected, and the billet surface was ground by a billet grinding machine. After grinding, the billet was rolled. A section of the finished product was taken and surface pickling was performed multiple times to confirm that the wrinkle defect was generated in the initial rolling pass system; (2) Modeling is performed according to the rolling schedule and pass system, taking a 1 / 4 rolled piece model and performing four-pass continuous rolling simulation according to the rolling schedule; (3) Cutting the cross section of each rolling process for comparative analysis; (4) Optimizing the pass profile and the reduction amount of the first and second passes. The reduction amount of the first pass after optimization is 55-60 mm, the reduction amount of the second pass after optimization is 76-80 mm, the R angle of the pass profile of the first pass after optimization is 20°-25°, and the R angle of the pass profile of the second pass after optimization is 30°-35°; (5) Optimize the reduction of the third and fourth passes, and carry out the subsequent rolling process according to the optimized reduction and hole type. The optimized reduction of the third pass is 45-50 mm, and the optimized reduction of the fourth pass is 55-60 mm.

2. The method for eliminating surface wrinkles of bars according to claim 1, characterized in that In the step (1), the single-side grinding amount of the billet surface ground by the billet grinding machine is ≥6 mm.

3. The method for eliminating surface wrinkles of bars according to claim 1, characterized in that, In the step (1), the length of the branch section taken from the finished material is 300 mm.

4. The method for eliminating surface wrinkles of bars according to claim 1, characterized in that, In the step (1), the branch material segment is pickled 4-5 times.

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