A method for controlling the wrinkle defects of high-carbon chromium bearing steel for small bar

Abstract

A method for controlling the wrinkle defects of high-carbon chromium bearing steel for small bar stock, comprising the following steps: S1. Control the heating temperature and heating time to ensure uniform burning through of the steel and a relatively high rolling start temperature; S2. Control the descaling effect of the high-pressure water descaling machine to fully remove the loose scale on the surface of the billet; S3. Install a compressed air scale removal facility between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling; S4. Optimize the design of the roughing pass to improve the uniformity of the transverse deformation of the billet surface during rolling, increase the fitting degree between the billet corner and the pass, and rationally feed and discharge materials; S5. Install a drainage groove at the exit guide of the roughing mill to prevent cooling water from spraying onto the rolled piece; S6. Set requirements for limiting the steel passing amount of the roll to ensure good surface quality of the roll. The present invention can completely eliminate the through-length wrinkle defects and control the short and small amount of wrinkle defects within 0.1 mm.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, and particularly relates to a method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bars. Background Art

[0002] Wrinkling is a surface defect of steel, which is a surface bend formed under the action of pressure processing such as rolling. The low-magnification morphology of the wrinkling defect of hot-rolled bars is similar to that of cracks or scratches. The defect width is narrow, the length is long, and it is distributed in dense multiple strips. Some are through-length defects, and the through-length defects are particularly harmful. For example Figure 1 and Figure 2 As shown, the high-magnification morphology is characterized by a smooth tip without a sharp tip at the defect top, similar to a scratch, but with decarburization. The formation reason of the wrinkling defect is relatively complex. The defect morphology is similar to that of cracks or scratches, and misjudgment is likely to occur when judging the defect type and cause, and it is difficult to control. The wrinkling defect has a great impact on the downstream processing of steel, especially pressure processing such as drawing, forging, and pipe piercing, which will cause the defect to extend, resulting in unqualified products or even waste products, causing losses.

[0003] Due to the characteristics of the steel grade, high-carbon chromium bearing steel is one of the steel grades that are extremely prone to wrinkling defects. High-carbon chromium bearing steel is a large category of bearing steel, which is the most widely used one in various countries at present and has the longest usage history. It is the most commonly used steel grade for manufacturing bearing rolling elements and rings. The most commonly used grade of high-carbon chromium bearing steel is GCr15, with a carbon content of 0.95%-1.05%, belonging to hypereutectoid steel. The relatively high carbon content is to ensure that the steel has high hardness, elastic limit and fatigue strength after quenching and low-temperature tempering. However, due to the high carbon content, its plasticity is good at high temperatures, but it rapidly deteriorates as the temperature decreases, and wrinkling defects are extremely likely to occur on the surface. Chromium is added to high-carbon chromium bearing steel, with a chromium content of 1.4%-1.65%. The purpose is to increase the hardenability of the steel and make the excess carbides increase and become finer, so as to increase the wear resistance of the steel. However, chromium will increase the viscosity of the scale on the surface of the steel billet, enhance the adhesion, and it is not easy to remove. As Figure 3 shown, the scale is pressed into the surface of the steel billet to form pits, and wrinkling defects are formed after subsequent rolling.

[0004] Therefore, developing a method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bars not only has urgent research value, but also has good economic benefits and industrial application potential, which is the motivation and basis for the completion of the present invention. Summary of the Invention

[0005] In order to overcome the defects of the prior art pointed out above, the inventor of the present invention has conducted in-depth research and completed the present invention after a large amount of creative labor.

[0006] Specifically, the technical problem to be solved by the present invention is to provide a method for controlling the wrinkling defects of small-sized high-carbon chromium bearing steel bars, so as to solve the technical problem that the wrinkling defects are difficult to control or eliminate.

[0007] A method for controlling the wrinkling defects of small-sized high-carbon chromium bearing steel bars includes the following steps:

[0008] S1. Control the heating temperature and heating time to ensure uniform burning-through of the steel, ensure a relatively high rolling start temperature, and take effective measures to control and monitor the furnace pressure and the furnace atmosphere to reduce the generation of scale.

[0009] S2. Control the descaling effect of the high-pressure water descaling machine to fully remove the loose scale on the surface of the billet and prevent the loose scale from being pressed in to form wrinkles.

[0010] S3. Install a compressed air scale removal facility between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling, and prevent the loose scale from being pressed in to form wrinkles.

[0011] S4. Optimize the design of the roughing pass, especially the box square pass and the transitional oval pass connected to the box square pass. Ensure the uniformity of the surface temperature of the billet during the rolling process, especially the temperature drop at the corners should not be too large, and it should be ≤150°C. Because the heat dissipation area at the corners is large, too low temperature at the corners is extremely likely to produce deep and continuous wrinkling defects. Improve the uniformity of the transverse deformation of the billet surface during the rolling process through the optimized design of the pass. Improve the ability of the pass to remove loose scale. Improve the fit between the billet corners and the pass through the optimized design of the pass. In addition, by reasonably distributing the rolling reduction system, reasonably feeding and discharging materials, the filling degree of the pass for the box-shaped pass is 0.85 - 0.95 (filling ratio), the oval pass is 0.8 - 0.9 (filling ratio); the round pass is 0.9 - 1.0 (filling ratio), to avoid overfilling or underfilling in a certain pass.

[0012] S5. Install a drainage groove at the outlet guide of the roughing mill to avoid cooling water spraying onto the rolled piece and causing too low temperature at the corners.

[0013] S6. Set requirements for limiting the steel passing amount of the rolling rolls to ensure good surface quality of the rolling rolls. Avoid serious depressions and protrusions due to the spalling of the rolling roll surface. After rolling, depressions and protrusions will also occur on the surface of the steel, and dense wrinkling defects will occur after subsequent multi-pass rolling.

[0014] As an improved technical solution, the small-sized high-carbon chromium bearing steel bars refer to rectangular billets with a cross-section of 260×300mm, which are heated, descaled by high-pressure water, and then rolled into round steel with a specification of φ16 - φ80mm using a continuous rolling mill.

[0015] As an improved technical solution, in step S1, the quality of the billet heating directly affects the generation of wrinkles. A more uniform billet temperature, a higher rolling temperature, and less scale can effectively reduce the generation of wrinkles. The billet is heated in a walking beam reheating furnace, and the loading and unloading method is side-in and side-out with cantilever rollers. Control the surface temperature difference along the length direction ≤ 15°C, the temperature difference between the billet center and the surface ≤ 15°C, and the billet black mark temperature difference ≤ 30°C. The reheating furnace has a total of 4 heating sections, the preheating temperature < 950°C, the temperature of the first heating section is 1120 - 1220°C, and the temperatures of the second heating section and the soaking section are 1220 - 1260°C. Control the time in the high-temperature soaking section (≥ 1220°C) ≥ 2.5 hours, and control the total heating time ≥ 5 hours. Ensure the starting rolling temperature ≥ 1000°C. Control the furnace pressure by controlling the speed of the exhaust fan, and control the furnace atmosphere by controlling the gas and air flow rates. Control the furnace pressure to be 5 - 45 Pa, and control the residual oxygen in the furnace ≤ 0.1%. Ensure that the oxidation loss rate of the billet in the furnace ≤ 1%.

[0016] As an improved technical solution, in step S2, a high-pressure water descaling device with self-cleaning function is used to remove the scale from the billet. The speed of the descaling roller table is 0.5 - 1.5 m / s, and 4 (3 in use and 1 spare) high-pressure pumps are adopted, with a total flow rate of 72 m 3 / h and a rated pressure of 30 Mpa. The number of nozzles is 18, the nozzle aperture is φ2.2 cm, the injection inclination angle is 12°, the injection deflection angle is 15°, and the injection angle is 30°. The temperature drop △T of the billet surface after descaling ≤ 20°C. The scale removal rate after descaling ≥ 98%.

[0017] As an improved technical solution, in step S3, a compressed air purging device is added between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling. The compressed air pressure is 0.4 - 0.6 MPa, and flat-mouth single nozzles are adopted to ensure the purging effect.

[0018] As an improved technical solution, in step S4, the rough rolling pass is reasonably optimized, especially the box square pass and the transitional oval pass connected to the box square pass. The sidewall slope of the box square pass is appropriately increased, the fillet radius at the bottom of the groove is appropriately increased, and the roll gap value is appropriately increased. Among them, the sidewall slope of the V1 side of the box square pass is increased to 9°, and the roll gap is increased to 35 mm. The sidewall slope of the H2 side of the box square pass is increased to 19°, the fillet radius at the bottom of the groove is increased to 30 mm, and the roll gap is increased to 35 mm. The sidewall slope of the V3 side of the box square pass is increased to 14°, the fillet radius at the bottom of the groove is increased to 40 mm, and the roll gap is increased to 30 mm. The transitional oval pass H4 is changed from a tangent ellipse to a double-arc ellipse. Among them, V1, H2, V3, and H4 are the abbreviations of the rolling mills. According to the production line sequence, the first rolling mill V1, the second rolling mill H2, the third rolling mill V3, the fourth rolling mill H4... Through the above optimization, the uniformity of the surface temperature of the billet during the rolling process is ensured, especially the corner temperature drop should be ≤150°C. The uniformity of the transverse deformation of the billet surface during the rolling process is improved. The fitting degree between the billet corner and the pass is improved. The ability of the box square pass to remove loose scale is improved.

[0019] As an improved technical solution, in step S5, the cooling water of the rolling mill is used to cool the surface of the roll to prevent the surface of the roll from cracking. Most of the cooling water will flow directly to the surface of the billet along the exit guide after cooling the roll, resulting in a large temperature drop on the surface of the billet, especially serious at the corners. By adopting the method of adding a drainage groove at the exit guide position, a large amount of cooling water can be effectively prevented from directly impacting the surface of the billet, and the excessive temperature drop at the corners of the billet can be avoided.

[0020] As an improved technical solution, in step S6, the requirement for the steel passing amount of the roll is formulated to ensure good surface quality of the roll. Under the action of the alternating load of heat and cold of the roll, cracks and spalling will occur on the surface, forming depressions and protrusions. Depressions and protrusions will also occur on the surface of the rolled steel, and dense wrinkle defects will occur after subsequent multi-pass rolling.

[0021] After adopting the above technical solutions, the beneficial effects of the present invention are:

[0022] The inventor found in long-term practice that the generation of wrinkles is directly related to the rolling temperature, and the low rolling temperature is the direct cause of wrinkles. When the rolling temperature > 900°C, the surface is relatively smooth, and when the rolling temperature > 950°C, no wrinkle defects will occur. Therefore, controlling the high starting rolling temperature and controlling the local surface temperature drop during the rolling process are the keys to controlling wrinkle defects. At the same time, the present invention creatively adds a compressed air scale removal facility between the rough rolling mills to further remove the loose residual scale and secondary scale after rolling, and prevent the loose scale from being pressed in to form wrinkles.

[0023] In addition, through long-term production summary and practice, it is found that unreasonable design of the square pass in rough rolling and the transition oval pass connecting the square passes will cause the defect of continuous wrinkles. The present invention increases the fillet radius at the bottom of the square pass groove, increases the side wall slope, and increases the roll gap. Ensure the uniformity of the surface temperature of the billet during rolling, especially the temperature drop at the corners should not be too large, and it should be ≤150°C. In addition, the transition oval pass connecting the square passes is changed from a tangent oval to a double-arc oval. It can effectively improve the uniformity of the transverse deformation of the billet surface during rolling. Improve the fit degree between the corner of the billet and the pass. Improve the ability of the square pass to remove loose scale.

[0024] The present invention finds that underfilling of the oval pass will thicken the blunt edge of the stock shape, and wrinkles are likely to form on the roll gap surface and the four corners during rolling in the round pass in the next pass. A continuous wrinkle defect is formed during subsequent rolling. Therefore, reasonable feeding and discharging is the key to controlling continuous wrinkles.

[0025] The present invention creatively adds a drainage groove to the exit guide guard in rough rolling to prevent cooling water from spraying onto the rolled piece, resulting in too low temperature at the corners.

[0026] Set requirements for limiting the steel passing amount of the roll to ensure good surface quality of the roll. Avoid the formation of serious depressions and protrusions due to the spalling of the roll surface. After rolling, depressions and protrusions will also be generated on the surface of the steel, and dense wrinkle defects will be generated after subsequent multi-pass rolling.

[0027] In summary, the present invention systematically controls and eliminates the wrinkle defects of high-carbon chromium bearing steel for small bar. Creatively, it is proposed to control or eliminate wrinkle defects through aspects such as heating quality control, rolling temperature control, descaling effect control, reduction schedule optimization, and pass form optimization.

[0028] The present invention can completely eliminate the continuous wrinkle defects and control the shorter and less wrinkles within 0.1 mm. It is much higher than the requirements in the national standard GB / T18254 for high-carbon chromium bearing steel regarding the allowable removal depth of harmful defects in steel for pressure processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 . High and low magnification pictures of typical wrinkle defects.

[0030] Figure 2 . The extension of wrinkle defects after cold heading.

[0031] Figure 3 . Generation mechanism of wrinkle defects during hot rolling.

[0032] Figure 4 . Difference in corner wrinkle defects at different deformation temperatures.

[0033] Figure 5 . Wrinkle defects formed by roll surface spalling and scale pressing-in.

[0034] Figure 6 . Schematic diagram of the temperature field and corner defects at the square hole of the box.

[0035] Figure 7 . Optimization design of rough rolling pass (taking H2 and H4 as examples).

[0036] Figure 8 Water avoidance device for exit guide.

[0037] Among them, Figure 5 indicates that after rolling through 5 passes, the defect does not disappear, but becomes narrower and deeper, gradually forming a wrinkling defect; Figure 7 indicates that the fillet radius at the bottom of the H2 groove is increased from R26mm to R30mm, the side wall slope is increased from 9° to 19°, the roll gap is increased from 30mm to 35mm, and for H4, it is changed from a tangent ellipse to a double-arc ellipse. Figure 8 indicates that before improvement (left figure): the fillet at the corner of the rolled piece is small, the temperature drop is fast, and the cooling water directly flows to the corner; after improvement (right figure): the fillet at the corner of the rolled piece is increased, the temperature drop is slow, a water avoidance groove is added, and the cooling water flows down from both sides. Specific implementation manners

[0038] The present invention will be further described below in conjunction with specific embodiments. However, the uses and purposes of these exemplary embodiments are only used to illustrate the present invention, and do not constitute any form of limitation to the actual protection scope of the present invention, nor will the protection scope of the present invention be limited thereto.

[0039] A method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar, comprising the following steps:

[0040] S1. Control the heating temperature and heating time to ensure uniform burning through of the steel, ensure a relatively high rolling start temperature, take effective measures to control and monitor the furnace pressure and furnace atmosphere (control the furnace pressure by controlling the speed of the exhaust fan, and control the furnace atmosphere by controlling the gas and air flow rates), and reduce the generation of scale; as Figure 4 shown, for the difference in corner wrinkling defects at different deformation temperatures studied by the inventor, therefore, the heating temperature is executed according to the following table.

[0041]

[0042] The heating time is executed according to the following table.

[0043]

[0044] Control the surface temperature difference along the length direction ≤ 15°C, the temperature difference between the center and the surface of the billet ≤ 15°C, the black mark temperature difference of the billet ≤ 30°C, take effective measures to control and monitor the furnace pressure and furnace atmosphere, control the furnace pressure to be 5 - 45 Pa, control the residual oxygen in the furnace ≤ 0.1%, and ensure that the oxidation and burning loss rate of the billet in the furnace ≤ 1%.

[0045] S2. For the removal of scale from the billet, a high-pressure water descaling device with self-cleaning function is used to control the descaling effect of the high-pressure water descaling machine, so as to fully remove the loose scale on the surface of the billet and prevent the loose scale from being pressed in to form wrinkles.

[0046] Control the outlet water pressure of the descaling machine to 25 MPa, observe the descaling effect. If the descaling effect is not good, the outlet water pressure can be increased until the upper limit. It is required that the scale removal rate after descaling is ≥98%.

[0047] S3. Install a compressed air scale removal facility between the roughing mills to further remove the loose residual scale and secondary scale that become loose after rolling, and prevent the loose scale from being pressed in to form wrinkles.

[0048] Turn on the compressed air blowing device installed between the roughing mills to further remove the loose residual scale and secondary scale that become loose after rolling. The compressed air pressure is 0.4 - 0.6 MPa. A flat single nozzle is used, and the distance and angle between the nozzle and the surface of the billet are controlled to ensure the blowing effect.

[0049] S4. Optimize the design of the roughing pass, especially the box square pass and the transition elliptical pass connected to the box square pass. Ensure the uniformity of the surface temperature of the billet during the rolling process, especially the temperature drop at the corners should not be too large, and it should be ≤150°C. Because the heat dissipation area at the corners is large, too low temperature at the corners is very likely to produce deep and continuous wrinkle defects. Improve the uniformity of the transverse deformation of the billet surface during the rolling process through the optimized design of the pass. Improve the ability of the pass to remove loose scale. Improve the fit degree between the corners of the billet and the pass through the optimized design of the pass. In addition, by reasonably distributing the rolling reduction schedule, reasonably feeding and discharging, the filling degree of the rolled piece in the box pass is 0.85 - 0.95 (filling ratio), the elliptical pass is 0.8 - 0.9 (filling ratio); the round pass is 0.9 - 1.0 (filling ratio), to avoid overfilling or underfilling in a certain pass.

[0050] Such as Figure 6 shown, the temperature field and corner defects at the corners of the box square pass. Therefore, the optimized roughing pass design of the present invention is used. As Figure 7 shown, the optimized design of the roughing pass. The slope of the V1 side wall of the box square pass is increased to 9°, and the roll gap is increased to 35 mm. The slope of the H2 side wall of the box square pass is increased to 19°, the radius of the bottom corner of the groove is increased to 30 mm, and the roll gap is increased to 35 mm. The slope of the V3 side wall of the box square pass is increased to 14°, the radius of the bottom corner of the groove is increased to 40 mm, and the roll gap is increased to 30 mm. The transition elliptical pass H4 is changed from a tangent ellipse to a double-arc ellipse..

[0051] S5. Install a drainage groove at the outlet guide of the roughing mill (that is, set an outlet guide water avoidance device, such as Figure 8As shown in the figure, prevent the cooling water from spraying onto the rolled piece, which may cause the corner temperature to be too low;

[0052] S6. Set the requirement for the steel passing amount of the roll to ensure good roll surface quality. Set the requirement for the steel passing amount of the roll to avoid severe depressions and protrusions formed due to the spalling of the roll surface. As Figure 5 shown in the figure, there are wrinkling defects formed by the spalling of the roll surface and the pressing-in of scale. This is because depressions and protrusions will also be generated on the surface of the steel after rolling, and dense wrinkling defects will be generated after subsequent multi-pass rolling.

[0053] The following are examples in actual work.

[0054] Example 1

[0055] A certain steel plant uses a rectangular billet of high-carbon chromium bearing steel GCr15 with a cross-section of 260×300mm. After heating and high-pressure water descaling, it is rolled into round steel with a specification of φ16 80mm using a continuous rolling mill.

[0056] Basically consistent with the above steps, in this example,

[0057] Control the preheating section at 900°C, the first heating section at 1120°C, and the second heating section and soaking section at 1220°C. Control the surface temperature difference along the length direction ≤15°C, the temperature difference between the billet center and the surface ≤15°C, and the billet black mark temperature difference ≤30°C. Control the time at 1220°C in the high-temperature soaking section for 2.5 hours, and control the total heating time for 5 hours. Ensure the rolling start temperature at 1000°C and the steel discharging rhythm at 20 pieces / hour. Take effective measures to control and monitor the furnace pressure and the furnace atmosphere. Control the furnace pressure at 5Pa, control the residual oxygen in the furnace ≤0.1%, and ensure the oxidation loss rate of the steel billet in the furnace ≤1%. The steel billet is descaled using a high-pressure water descaling device with self-cleaning function. The descaling roller table speed of the descaling device is 0.5m / s, and 4 (3 in use and 1 standby) high-pressure pumps are used, with a total flow rate of 72m 3 / h, rated pressure 30 Mpa. The number of nozzles is 18, the nozzle aperture is φ2.2 cm, the injection inclination angle is 12°, the injection deflection angle is 15°, and the injection angle is 30°. The temperature drop △T of the billet surface after descaling is 20 °C. Control the water outlet pressure of the descaling machine to 25 MPa and observe the descaling effect. If the descaling effect is not good, the water outlet pressure can be increased until the upper limit. It is required that the scale removal rate after descaling ≥ 98%. Open the compressed air purging device added between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling. The compressed air pressure is 0.4 MPa, a flat-mouth single nozzle is used, and the distance and angle between the nozzle and the billet surface are controlled to ensure the purging effect. Use the optimized roughing pass. The slope of the V1 side wall of the box square pass is 9°, the roll gap is 35 mm; the slope of the H2 side wall of the box square pass is 19°, the radius of the bottom corner of the groove is 30 mm, and the roll gap is 35 mm; the slope of the V3 side wall of the box square pass is 14°, the radius of the bottom corner of the groove is 40 mm, and the roll gap is 30 mm; the transition oval pass H4 uses a double-arc ellipse. Reasonably feed and discharge materials. The filling degree of the rolled piece in the box pass is 0.85 - 0.95 (filling ratio), the oval pass is 0.8 - 0.9 (filling ratio); the round pass is 0.9 - 1.0 (filling ratio) to avoid overfilling or underfilling in a certain pass. Add a drainage trough at the exit guard of the roughing mill to prevent the cooling water from directly impacting the surface of the steel. Control the amount of steel passing through the roll to ensure good surface quality of the roll. In this embodiment, the requirements for the amount of steel passing through are as follows:

[0058] Flight V1 - V5 H6 - V11 H12 V13 H14 V15 H16 V17 H18 V19 H20 V21 Steel Passing Quantity (t) 10000 8000 8000 8000 8000 8000 5000 5000 2000 2000 2000 2000

[0059] Check that there are no long wrinkles on the surface of the finished product, and there are individual small and short wrinkle defects with a depth < 0.1 mm.

[0060] Example 2

[0061] A certain steel plant uses a rectangular billet of high-carbon chromium bearing steel GCr15 with a cross-section of 260×300 mm, which is heated, descaled by high-pressure water, and then rolled into round steel with a φ60 mm specification by a continuous rolling mill.

[0062] Basically the same as the above steps, in this embodiment,

[0063] The preheating section is controlled at 940°C, the first heating section at 1170°C, and the second heating section and soaking section at 1240°C. The surface temperature difference along the length direction is controlled to be ≤15°C, the temperature difference between the billet center and the surface is ≤15°C, and the billet black mark temperature difference is ≤30°C. The time at 1240°C in the high-temperature soaking section is controlled for 3 hours, and the total heating time is controlled for 6 hours. Ensure the rolling start temperature is 1100°C, and the steel discharging rhythm is 15 pieces per hour. Take effective measures to control and monitor the furnace pressure and the furnace atmosphere. Control the furnace pressure at 30 Pa, control the residual oxygen in the furnace to be ≤0.1%, and ensure the oxidation loss rate of the steel billets in the furnace is ≤1%. The scale removal of the steel billets uses a high-pressure water descaling device with self-cleaning function. The descaling roller table speed of the descaling device is 1.0 m / s. Four (3 in use and 1 standby) high-pressure pumps are used, with a total flow rate of 72 m 3 / h and a rated pressure of 30 Mpa. The number of nozzles is 18, the nozzle aperture is φ2.2 cm, the injection angle is 12°, the injection deflection angle is 15°, and the injection angle is 30°. The surface temperature drop △T of the steel billets after descaling is 18°C. Control the water outlet pressure of the descaling machine at 25 MPa, observe the descaling effect. If the descaling effect is not good, the water outlet pressure can be increased until the upper limit. It is required that the scale removal rate after descaling is ≥98%. Open a compressed air purging device added between the rough rolling mills to further remove the residual loose scale and secondary scale after rolling. The compressed air pressure is 0.5 MPa, a flat-mouth single nozzle is used, and the distance and angle between the nozzle and the steel billet surface are controlled to ensure the purging effect. Use the optimized rough rolling pass. The side wall slope of the box square pass V1 is 9°, the roll gap is 35 mm; the side wall slope of the box square pass H2 is 19°, the bottom radius of the groove is 30 mm, and the roll gap is 35 mm; the side wall slope of the box square pass V3 is 14°, the bottom radius of the groove is 40 mm, and the roll gap is 30 mm; the transition oval pass H4 uses a double-arc ellipse. Reasonably load and unload materials. The filling degree of the rolled piece in the box pass is taken as 0.85 - 0.95 (filling ratio), the oval pass is taken as 0.8 - 0.9 (filling ratio); the round pass is taken as 0.9 - 1.0 (filling ratio) to avoid overfilling or underfilling in a certain pass. Add a drainage trough at the outlet guard of the rough rolling to prevent the cooling water from directly impacting the steel surface. Control the steel passing amount of the rolls to ensure good roll surface quality. In this embodiment, the requirements for the steel passing amount limit are as follows:

[0064] Flight V1 - V5 H6 - V11 H12 V13 H14 V15 H16 V17 H18 V19 H20 V21 Steel Passing Quantity (t) 10000 8000 8000 8000 8000 8000 5000 5000 2000 2000 2000 2000

[0065] Check that there are no through-length wrinkling defects on the finished product surface, and there are individual small and short wrinkling defects with a depth <0.1 mm.

[0066] Example 3

[0067] A certain steel plant uses a rectangular billet of high-carbon chromium bearing steel GCr15 with a cross-section of 260×300 mm. After heating and high-pressure water descaling, it is rolled into round steel with a φ80 mm specification by a continuous rolling mill.

[0068] Basically the same as the above steps, in this embodiment,

[0069] The preheating section is controlled at 920 °C, the first heating section is at 1220 °C, and the temperatures of the second heating section and the soaking section are 1260 °C. The surface temperature difference along the length direction is controlled to be ≤15 °C, the temperature difference between the billet center and the surface is ≤15 °C, and the billet black mark temperature difference is ≤30 °C. The time at 1260 °C in the high-temperature soaking section is controlled for 3 hours, and the total heating time is controlled for 6 hours. Ensure the rolling start temperature is 1050 °C, and the steel discharging rhythm is 20 pieces per hour. Take effective measures to control and monitor the furnace pressure and the furnace atmosphere. Control the furnace pressure to be 45 Pa, control the residual oxygen in the furnace to be ≤0.1%, and ensure that the oxidation loss rate of the steel billets in the furnace is ≤1%. The scale removal of the steel billets uses a high-pressure water descaling device with self-cleaning function. The descaling roller table speed of the descaling device is 1.5 m / s. Four (3 in use and 1 standby) high-pressure pumps are used, with a total flow rate of 72 m 3 / h and a rated pressure of 30 Mpa. The number of nozzles is 18, the nozzle aperture is φ2.2 cm, the injection inclination angle is 12°, the injection deflection angle is 15°, and the injection angle is 30°. The surface temperature drop △T of the steel billets after descaling is 20 °C. Control the outlet water pressure of the descaling machine to be 25 MPa, observe the descaling effect. If the descaling effect is not good, the outlet water pressure can be increased until the upper limit. It is required that the scale removal rate after descaling is ≥98%. Open the compressed air purging device added between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling. The compressed air pressure is 0.6 MPa, and a flat-mouth single nozzle is used. Control the distance and angle between the nozzle and the steel billet surface to ensure the purging effect. Use the optimized roughing pass design. The sidewall slope of the box square pass V1 is 9°, the roll gap is 35 mm; the sidewall slope of the box square pass H2 is 19°, the bottom radius of the groove is 30 mm, and the roll gap is 35 mm; the sidewall slope of the box square pass V3 is 14°, the bottom radius of the groove is 40 mm, and the roll gap is 30 mm; the transition elliptical pass H4 uses a double-arc ellipse. Reasonably load and unload materials. The filling degree of the rolled piece in the box pass is taken as 0.85 - 0.95 (filling ratio), the elliptical pass is taken as 0.8 - 0.9 (filling ratio); the round pass is taken as 0.9 - 1.0 (filling ratio) to avoid overfilling or underfilling in a certain pass. Add a drainage trough at the outlet guard of the roughing mill to prevent the cooling water from directly impacting the surface of the steel. Control the steel passing amount of the rolling rolls to ensure good surface quality of the rolling rolls. In this embodiment, the requirements for the steel passing amount limit are as follows:

[0070] Flight V1 - V5 H6 - V11 H12 V13 H14 V15 H16 V17 H18 V19 H20 V21 Steel Passing Quantity (t) 10000 8000 8000 8000 8000 8000 5000 5000 2000 2000 2000 2000

[0071] Check that there are no through-length wrinkling defects on the surface of the finished product, and the depth of individual small and short wrinkling defects is <0.1 mm.

[0072] Comparative Example 1

[0073] A certain steel mill uses a rectangular billet of high-carbon chromium bearing steel GCr15 with a cross-section of 260×300 mm. After heating and descaling with high-pressure water, it is rolled into round steel with a diameter of φ60 mm using a continuous rolling mill. The temperature of the second heating section and the soaking section is controlled at 1060 - 1100 °C. The time in the high-temperature section (≥1080 °C) is controlled to be ≥2.5 hours, and the total heating time is controlled to be ≥5 hours. Ensure that the starting rolling temperature is ≥900 °C. There is no in-furnace residual oxygen control device, and the oxidation loss rate of the steel billet in the furnace is 2%. The water outlet pressure of the descaling machine is 20 MPa, and the removal rate of scale after descaling is 70%. There is no compressed air purging device between the rough rolling mills. The slope of the side wall of the square pass V1 in the rough rolling box is 6°, and the roll gap is 30 mm. The slope of the side wall of the square pass H2 is 9°, the radius of the bottom corner of the groove is 26 mm, and the roll gap is 30 mm. The slope of the side wall of the square pass V3 is 10°, the radius of the bottom corner of the groove is 30 mm, and the roll gap is increased to 25 mm. The transition oval pass H4 is a tangent oval. There is no water avoidance device for the exit guide, and the cooling water directly impacts the surface of the steel. The surface quality of the roll is poor, with serious cracks and spalling. Through rolling inspection, there are defects of continuous wrinkles on the surface of the finished product, and at the same time, there are a large number of dense and short wrinkles. The depth of the wrinkle defects is generally >0.2 mm.

[0074] It should be understood that the use of these embodiments is only for illustrating the present invention and is not intended to limit the protection scope of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art can make various changes, modifications, and / or variations to the present invention, and all these equivalent forms also fall within the protection scope defined by the appended claims of this application.

Claims

1. A method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar, characterized in that, Including the following steps: S1. Control the heating temperature and time to ensure uniform burning through of the steel, ensure a relatively high rolling start temperature, control the surface temperature difference along the length of the steel ≤ 15°C, the temperature difference between the center and surface of the billet ≤ 15°C, and the temperature difference of the billet black mark ≤ 30°C; control the temperature of the preheating section of the heating furnace < 950°C, the temperature of the first heating section 1120 - 1220°C, and the temperature of the second heating section and the high-temperature soaking section 1220 - 1260°C; control the heating time of the steel in the high-temperature soaking section ≥ 2.5 hours, and control the total heating time of the steel ≥ 5 hours; ensure the rolling start temperature ≥ 1000°C; control the furnace pressure in the heating furnace to be 5 - 45 Pa, and control the residual oxygen in the furnace ≤ 0.1%; ensure the oxidation loss rate of the steel billet in the furnace ≤ 1%; S2. Control the descaling effect of the high-pressure water descaling machine to fully remove the loose scale on the surface of the steel billet; S3. Install a compressed air scale removal facility between the roughing mills to further remove the residual scale and secondary scale that become loose after rolling; S4. Optimize the design of the roughing pass. The roughing pass refers to the box square pass and the transitional oval pass connected to the box square pass. Among them, the slope of the V1 side wall of the box square pass is 9°, and the roll gap is 35 mm; the slope of the H2 side wall of the box square pass is 19°, the radius of the bottom corner of the groove is 30 mm, and the roll gap is 35 mm; the slope of the V3 side wall of the box square pass is 14°, the radius of the bottom corner of the groove is 40 mm, and the roll gap is 30 mm; the transitional oval pass H4 adopts a double-arc ellipse, thereby improving the uniformity of the transverse deformation of the steel billet surface during rolling and enhancing the fitting degree of the steel billet corner with the pass; reasonably load and unload materials, and control the degree of filling of the rolled piece in the pass. The filling degree of the box square pass is 0.85 - 0.95, the filling degree of the transitional oval pass is 0.8 - 0.9; and the filling degree of the round pass is 0.9 - 1.0; S5. Install a drainage trough at the exit guard of the roughing mill to prevent cooling water from spraying onto the rolled piece; S6. Set requirements for limiting the steel passing amount of the roll to ensure good surface quality of the roll.

2. The method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar according to claim 1, characterized in that, The small-sized bar high-carbon chromium bearing steel refers to round steel with a cross-section of a 260×300 mm rectangular billet, which is heated, descaled by high-pressure water, and then rolled into a φ16 - φ80 mm specification by a continuous rolling mill.

3. The method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar according to claim 2, characterized in that, In step S2, a high-pressure water descaling device with a self-cleaning function is used to remove the scale from the steel billet. The speed of the descaling roller table is 0.5 - 1.5 m / s. A high-pressure pump is used, with a total flow rate of 72 m³ / h, the number of nozzles is 18, the nozzle aperture is φ2.2 cm, the injection angle is 12°, and the injection deflection angle is 15°; the temperature drop △T of the steel billet surface after descaling ≤ 20°C; the scale removal rate after descaling ≥ 98%.

4. The method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar according to claim 2, characterized in that, In step S3, a compressed air blowing device is installed between the roughing mills, and the compressed air pressure is 0.4 - 0.6 MPa.

5. The method for controlling the wrinkling defect of high-carbon chromium bearing steel for small bar according to claim 2, characterized in that, In step S4, the temperature drop at the corner ≤ 150°C.

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