Production method for improving surface quality of high-alloy hot-rolled strip steel

Abstract

The invention discloses a production method for improving the surface quality of high-alloy hot-rolled strip steel, which comprises the steps of heating a plate blank, roughly dephosphorizing, roughly rolling, secondarily descaling, coiling in a hot coiling box, finely descaling and finely rolling, specifically, the speed of roughly dephosphorizing is controlled to be 1.2 m / s-1. 3 m / s, the finish rolling temperature of roughly rolling is controlled to be 1000-1100 DEG C, the secondary descaling is four-pass descaling, and the surface quality of the high-alloy hot-rolled strip steel is improved. The advanced rate of a lower bending roller of the hot coil box is 2.5%-3.5%, the rolling force of the finish rolling tail of the strip steel can be controlled within a proper range while it is guaranteed that oxide on the surface of the strip steel is completely removed, and drifting roller marks are avoided.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, and particularly to a production method for improving the surface quality of high-alloy hot-rolled strip steel. Background Art

[0002] High-alloy steel contains a relatively high content of alloy components, such as metal elements like nickel (Ni), chromium (Cr), molybdenum (Mo), etc. These alloy components not only cause the steel to exhibit significant deformation resistance at high temperatures but also promote the formation of a very strong adhesion force between the oxides on the steel surface and the base material. Using conventional hot-rolling processes to produce high-alloy steel cannot effectively guarantee the surface quality of the steel. Summary of the Invention

[0003] The embodiments of this application provide a production method for improving the surface quality of high-alloy hot-rolled strip steel, which can reduce the oxides on the strip surface while avoiding the generation of tailing roll marks.

[0004] In a first aspect, this application provides a production method for improving the surface quality of high-alloy hot-rolled strip steel, including heating and rough descaling of the slab to obtain a slab after rough descaling, where the descaling speed of the rough descaling is 1.2 m / s - 1.3 m / s; performing rough rolling and secondary descaling on the slab after rough descaling to obtain an intermediate billet, where the final rolling temperature of the rough rolling is 1000°C - 1100°C, and the secondary descaling is four-pass descaling; putting the intermediate billet into a hot coil box for coiling and finish descaling to obtain an intermediate billet after finish descaling, where the forward rate of the lower bending roll of the hot coil box is 2.5% - 3.5%; performing finish rolling on the intermediate billet after finish descaling to obtain high-alloy hot-rolled strip steel.

[0005] In any embodiment of this application, the rough rolling is seven-pass rough rolling.

[0006] In any embodiment of this application, the four-pass descaling is descaling in the first, third, fifth, and seventh passes.

[0007] In any embodiment of this application, the high-alloy hot-rolled strip steel is coiled to obtain a high-alloy hot-rolled steel coil, where the coiling temperature is 500°C - 600°C.

[0008] In any embodiment of this application, the descaling water at the head is delayed by 1 - 2 s during the finish descaling process.

[0009] In any embodiment of this application, the finish rolling is continuous rolling using 7 stands; and / or, the finish rolling is speed-up rolling; and / or, the acceleration of the finish rolling is 0.04 - 0.08 m / s 2 ; and / or, the final rolling temperature of the finish rolling is 900°C - 1000°C.

[0010] In any embodiment of the present application, the cooling water volume between the stands of the 6th and 7th finishing mill groups during the finishing rolling process is turned on by 10%.

[0011] In any embodiment of the present application, the slab is heated by means of hot charging.

[0012] In any embodiment of the present application, during the heating process of the slab, the slab's furnace inlet temperature is ≥300°C; and / or, the slab's furnace outlet temperature is 1150°C - 1250°C; and / or, the total time of the slab in the furnace is 150 min - 250 min.

[0013] In a second aspect, the present application provides a high-alloy hot-rolled strip steel, which is prepared according to the production method described in the first aspect.

[0014] The production method for improving the surface quality of the high-alloy hot-rolled strip steel in the embodiments of the present application includes steps of heating the slab, rough descaling, rough rolling, secondary descaling, coiling in a hot coil box, finish descaling, and finish rolling. Among them, by controlling the speed of rough descaling to be 1.2 m / s - 1.3 m / s, the final rolling temperature of rough rolling to be 1000°C - 1100°C, secondary descaling to be four-pass descaling, and the lead ratio of the lower bending roll of the hot coil box to be 2.5% - 3.5%, it is possible to ensure that the oxides on the strip steel surface are removed cleanly while controlling the rolling force at the tail of the strip steel finishing rolling within a suitable range and avoiding the generation of tailing roll marks. Brief Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a schematic diagram of the strip steel surface oxides in Comparative Example 2 of the present application;

[0017] Figure 2 It is a schematic diagram of the strip steel surface oxides in Comparative Example 4 of the present application;

[0018] Figure 3 It is a schematic diagram of the strip steel surface impact roll marks in Comparative Example 11 of the present application;

[0019] Figure 4 It is a schematic diagram of the strip steel surface layer structure in Comparative Example 4 of the present application;

[0020] Figure 5 It is a schematic diagram of the strip steel surface layer structure in Embodiment 1 of the present application;

[0021] Figure 6 It is a schematic diagram of the change in the slab finish rolling force in Comparative Example 10 of the present application;

[0022] Figure 7 It is a schematic diagram showing the change of the slab finishing rolling force in Embodiment 2 of the present application. Detailed implementation manners

[0023] In order to make the application purpose, technical solutions and beneficial technical effects of the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and are not intended to limit the present application.

[0024] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recorded.

[0025] It should be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "including..." do not exclude the existence of additional identical elements in the process, method, article or device including the said elements.

[0026] Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application). Unless otherwise specified, the test temperature of the various parameters mentioned in the present application is 25°C and the test pressure is standard atmospheric pressure.

[0027] The above application content of the present application does not intend to describe each disclosed embodiment or each implementation manner in the present application. The following description more specifically gives examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, and these embodiments can be used in various combinations. In each instance, the enumeration is only a representative group and should not be construed as exhaustive.

[0028] A bimetal saw blade is a saw blade made by compounding two metals, with excellent properties such as high wear resistance, high hot hardness, and saw teeth that are not easily broken and have a long service life. Its structure mainly consists of two parts: the back material and the tooth material. The tooth tip part usually uses high-speed steel or cemented carbide to ensure cutting performance. The back material is mostly processed from cold-rolled alloy strip steel, and the most commonly used material grade is X32CrMoV4-1 steel (abbreviated as X32 in China). Since the alloy content of the X32 steel used for the back material of the bimetal saw blade is relatively high, its deformation resistance at high temperatures is relatively large, resulting in a significant increase in the rolling force required during rolling on a conventional hot rolling production line and prone to various roll mark defects. In addition, the X32 steel contains alloying elements such as Ni, Cr, and Mo. These elements will cause the surface oxides to be tightly combined with the matrix during the hot rolling process, resulting in poor descaling effect and prone to surface quality defects such as oxide pressing-in.

[0029] In view of the above problems, the inventor has improved the hot rolling process of high-alloy steel, especially X32 steel, effectively improving the surface quality of high-alloy hot-rolled strip steel.

[0030] The first aspect of the embodiment of the present application provides a production method for improving the surface quality of high-alloy hot-rolled strip steel, including heating and rough descaling of the slab to obtain a slab after rough descaling, wherein the descaling speed of the rough descaling is 1.2 m / s - 1.3 m / s; performing rough rolling and secondary descaling on the slab after rough descaling to obtain an intermediate billet, wherein the final rolling temperature of the rough rolling is 1000 °C - 1100 °C, and the secondary descaling is four-pass descaling; putting the intermediate billet into a hot coil box for coiling and finish descaling to obtain an intermediate billet after finish descaling, wherein the lead ratio of the lower bending roll of the hot coil box is 2.5% - 3.5%; performing finish rolling on the intermediate billet after finish descaling to obtain high-alloy hot-rolled strip steel.

[0031] The production method for improving the surface quality of high-alloy hot-rolled strip steel in the embodiment of the present application includes the steps of heating, rough descaling, rough rolling, secondary descaling, hot coil box coiling, finish descaling, and finish rolling of the slab. Among them, by controlling the descaling speed of the rough descaling to be 1.2 m / s - 1.3 m / s, the final rolling temperature of the rough rolling to be 1000 °C - 1100 °C, the secondary descaling to be four-pass descaling, and the lead ratio of the lower bending roll of the hot coil box to be 2.5% - 3.5%, it is not only possible to avoid oxides being pressed into the surface of the steel during rolling, forming oxide pressing-in defects or pits on the surface, but also to control the rolling force at the tail of the finish rolling of the strip steel within a suitable range, avoid the generation of tail-swing impact roll marks, and improve the surface quality of high-alloy steel, especially X32 steel.

[0032] As an example, the descaling speed of the rough descaling can be 1.2 m / s, 1.22 m / s, 1.24 m / s, 1.26 m / s, 1.28 m / s, or 1.3 m / s.

[0033] Optionally, the descaling speed of rough dephosphorization is 1.2 m / s.

[0034] Optionally, the descaling speed of rough dephosphorization is 1.3 m / s.

[0035] As an example, the finishing rolling temperature of rough rolling can be 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1040 °C, 1050 °C, 1060 °C, 1070 °C, 1075 °C, 1078 °C, 1080 °C, 1082 °C, 1085 °C, 1087 °C, 1088 °C, 1089 °C, 1090 °C or 1100 °C.

[0036] Optionally, the finishing rolling temperature of rough rolling is 1088 °C.

[0037] Optionally, the finishing rolling temperature of rough rolling is 1100 °C.

[0038] As an example, the leading rate of the lower bending roll of the hot coil box is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4% or 3.5%.

[0039] Optionally, the leading rate of the lower bending roll of the hot coil box is 3%.

[0040] Putting the hot coil box into use for rolling the slab, flipping the head and tail of the intermediate billet, so that the tail with large temperature drop is adjusted to the head for prior rolling, can reduce the temperature drop at the tail of finish rolling, reduce the rolling force at the tail of finish rolling, improve the rolling stability, and reduce the tail flick roll marks; reducing the leading rate of the bending roll of the hot coil box to 3% is beneficial to reducing the rubbing between the intermediate billet and the bending roll, and reducing the abrasion oxide on the surface of the bending roll of the hot coil box and the intermediate billet.

[0041] As an example, the thickness of the intermediate billet can be 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, 33 mm, 34 mm or 35 mm.

[0042] By controlling the speed of rough dephosphorization to be 1.2 m / s - 1.3 m / s, the finishing rolling temperature of rough rolling to be 1000 °C - 1100 °C, the secondary descaling to be four-pass descaling, and the leading rate of the lower bending roll of the hot coil box to be 2.5% - 3.5%, the thickness of the intermediate billet can be controlled within the range of ≤ 35 mm. The thinner thickness of the intermediate billet can reduce the overall rolling force of subsequent finish rolling, and further reduce the generation of tail flick impact roll marks.

[0043] In some embodiments, the rough rolling is seven-pass rough rolling.

[0044] In some embodiments, the four-pass descaling is carried out in the first, third, fifth and seventh passes of descaling.

[0045] For rough descaling, a slow descaling mode with a specific speed is adopted, and descaling in the rough rolling body is selected to be carried out at the specific 3rd, 5th, and 7th passes, which can ensure that the surface oxide scale is removed cleanly.

[0046] In some embodiments, the high-alloy hot-rolled strip is coiled to obtain a high-alloy hot-rolled steel coil, wherein the coiling temperature is 500°C - 600°C.

[0047] Optionally, the thickness of the high-alloy hot-rolled steel coil is 2.5 mm - 6.0 mm.

[0048] As an example, the thickness of the high-alloy hot-rolled steel coil can be 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.8 mm, 4.0 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5.0 mm, 5.2 mm, 5.4 mm, 5.6 mm, 5.8 mm, or 6.0 mm.

[0049] As an example, the coiling temperature can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, or 600°C.

[0050] Optionally, the coiling temperature is 580°C.

[0051] A lower coiling temperature is beneficial to grain refinement, and is also beneficial to the surface eutectoid reaction, generating an iron oxide structure that is easy to pickling, while thinning the oxide scale, which is beneficial to subsequent pickling processing.

[0052] In some embodiments, during the finish descaling process, the descaling water at the head is delayed by 1 - 2 s.

[0053] The slab is subjected to finish descaling treatment before entering the finishing mill, and the head avoidance function of the finish descaling is turned on, that is, the descaling water at the head is delayed, which can increase the temperature of the intermediate slab, facilitate the smooth biting of the rolled piece, and at the same time reduce the impact on the roll.

[0054] In some embodiments, the finish rolling is continuous rolling with 7 stands; and / or, the finish rolling is speed-up rolling; and / or, the acceleration of the finish rolling is 0.04 - 0.08 m / s 2 ; and / or, the final rolling temperature of the finish rolling is 900°C - 1000°C.

[0055] As an example, the acceleration of the finish rolling can be 0.04 m / s 2 、0.05 m / s 2 、0.06 m / s 2 、0.07 m / s2 or 0.08 m / s 2 。

[0056] During the finish rolling process, the rolling speed is increased throughout the coil, and the acceleration of the finish rolling is set to 0.04 - 0.08 m / s 2 , so that the rolling force at the tail of the slab can be lower than 40,000 KN. The reduction of the rolling force at the tail can make the rolling process more stable and reduce the generation of tail flick marks.

[0057] As an example, the finish rolling temperature can be 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C or 1000°C.

[0058] Optionally, the finish rolling temperature is 900°C.

[0059] Optionally, the finish rolling temperature is 1000°C.

[0060] In some embodiments, during the finish rolling process, the cooling water volume between the stands of the 6th and 7th finish rolling mills is turned on by 10%.

[0061] The inter-stand water, roll gap spray water, side spray water, etc. for rolling are all turned on normally, which can ensure that the surface of the strip during rolling is clean, reduce the contact between air and the rolled piece, and reduce the generation of oxides; to prevent the temperature from being too low during the rolling of the last stand and causing impact marks on the head, the water flow between the stands of the last group is manually adjusted to 10% to reduce the impact marks on the head of the rear stand.

[0062] In some embodiments, the slab is heated by means of hot charging.

[0063] In some embodiments, during the heating process of the slab, the slab's furnace inlet temperature is ≥300°C; and / or, the slab's furnace outlet temperature is 1150°C - 1250°C; and / or, the total time of the slab in the furnace is 150 min - 250 min.

[0064] As an example, the slab's furnace inlet temperature can be 300°C, 350°C, 400°C, 450°C, 460°C, 470°C, 475°C, 480°C, 485°C, 490°C, 495°C, 500°C, 550°C or 600°C.

[0065] Optionally, the slab's furnace inlet temperature is 485°C.

[0066] As an example, the slab's furnace outlet temperature can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, 1201°C, 1202°C, 1203°C, 1204°C, 1205°C, 1210°C, 1230°C, 1240°C or 1250°C.

[0067] Optionally, the tapping temperature of the slab is 1203 °C.

[0068] As an example, the total in-furnace time of the slab can be 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 220 min, 240 min or 250 min.

[0069] Optionally, the total in-furnace time of the slab is 180 min.

[0070] By controlling the low tapping temperature and rolling temperature and the high rolling speed, the contact between the strip steel and air can be reduced, and the thickness of the scale generated during the rolling process can be effectively reduced.

[0071] The first aspect of the embodiment of the present application provides a high-alloy hot-rolled strip steel prepared by the production method described in the first aspect.

[0072] As an example, the high-alloy hot-rolled strip steel is X32 high-alloy hot-rolled strip steel.

[0073] As an example, the chemical composition of the slab is as follows: C (%): 0.31, Si (%): 0.24, Mn (%): 1.02, P (%): 0.008, S (%): ≤0.006, Cr (%): 4.12, Mo (%): 1.08, Ni (%): 0.69, V (%): 0.32, Cu (%): 0.02.

[0074] Examples

[0075] The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0076] Example 1

[0077] Example 1 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32.

[0078] The chemical composition of the slab is as follows: C (%): 0.31, Si (%): 0.24, Mn (%): 1.02, P (%): 0.008, S (%): ≤0.006, Cr (%): 4.12, Mo (%): 1.08, Ni (%): 0.69, V (%): 0.32, Cu (%): 0.02.

[0079] The production method includes the following steps:

[0080] 1) Slab heating: The thickness of the continuous casting slab is 240 mm. It enters the heating furnace in a hot charging manner. The furnace inlet temperature is 485 °C, the furnace outlet temperature is 1203 °C, and the total residence time in the furnace is 180 min.

[0081] 2) Rough descaling: After the slab leaves the furnace, rough descaling treatment is carried out. The rough descaling adopts a slow descaling mode, and the descaling speed is 1.2 m / s.

[0082] 3) Rough rolling: The slab after rough descaling treatment is rough rolled by a four-high roughing mill. The rough rolling is carried out in 7 passes, and the final rolling temperature of the rough rolling is 1088 °C.

[0083] 4) Secondary descaling: The rough rolling slab is subjected to secondary descaling, specifically, descaling is carried out in the 1st, 3rd, 5th, and 7th passes to obtain an intermediate slab with a thickness of 33 mm.

[0084] 5) Coiling in the hot coil box: The above intermediate slab is rolled using the hot coil box. The head and tail of the intermediate slab are reversed, and the lead rate of the lower bending roll of the hot coil box is 3%.

[0085] 6) Finish descaling: The head avoidance function of the finish descaling is turned on, that is, the descaling water at the head is delayed by 1 s to be turned on.

[0086] 7) Finish rolling: The intermediate slab after finish descaling treatment is rolled by a four-high seven-stand finish rolling mill. The final rolling temperature of the finish rolling is 900 °C. The inter-stand water, roll gap spray water, side spray water, etc. during rolling are all normally turned on. Manually adjust the water flow between the last group of stands (the stands of the 6th and 7th groups of finish rolling mills) to 10%; The whole coil is rolled at an increasing speed, and the acceleration of the finish rolling is 0.04 m / s 2 , the initial speed of the finish rolling is 6.8 m / s, the final speed of the finish rolling is 10.5 m / s, and the rolling force at the tail of the strip is 38000 KN.

[0087] 8) Coiling: The coiling temperature is set at 580 °C.

[0088] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared, and there are no serious quality problems such as roll marks and oxides on the surface after hot rolling. Figure 5 It is a schematic diagram of the surface layer structure of the strip in Example 1 of this application.

[0089] Example 2

[0090] Example 2 of this application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32.

[0091] The chemical composition of the slab is as follows: C (%): 0.31, Si (%): 0.24, Mn (%): 1.02, P (%): 0.008, S (%): ≤0.006, Cr (%): 4.12, Mo (%): 1.08, Ni (%): 0.69, V (%): 0.32, Cu (%): 0.02.

[0092] The production method includes the following steps:

[0093] 1) Slab heating: The thickness of the continuous casting slab is 240 mm. It enters the heating furnace in a hot charging manner, with the furnace inlet temperature of 485 °C, the furnace outlet temperature of 1203 °C, and the total residence time in the furnace of 180 min.

[0094] 2) Rough descaling: After the slab leaves the furnace, rough descaling treatment is carried out. The rough descaling adopts a slow descaling mode, with a descaling speed of 1.3 m / s.

[0095] 3) Rough rolling: The slab after rough descaling treatment is rough rolled using a four-high roughing mill. The rough rolling is carried out in 7 passes, and the final rough rolling temperature is 1100 °C.

[0096] 4) Secondary descaling: The rough rolling slab is subjected to secondary descaling, specifically descaling in the 1st, 3rd, 5th, and 7th passes to obtain an intermediate slab with a thickness of 33 mm.

[0097] 5) Coiling in the hot coil box: The above intermediate slab is rolled using the hot coil box, with the head and tail of the intermediate slab reversed, and the lead rate of the lower bending roll of the hot coil box being 3%.

[0098] 6) Finish descaling: The head avoidance function of the finish descaling is turned on, that is, the finish descaling water is delayed by 2 s to start.

[0099] 7) Finish rolling: The intermediate slab after finish descaling treatment is rolled using a four-high seven-stand finish rolling mill. The final finish rolling temperature is 1000 °C. The inter-stand water, roll gap spray water, side spray water, etc. are all normally turned on. Manually adjust the water flow between the last set of stands (the stands of the 6th and 7th finish rolling mills) to 10%; The whole coil is rolled at an increasing speed, with a finish rolling acceleration of 0.06 m / s 2 , the initial finish rolling speed is 7.2 m / s, the final finish rolling speed is 11.8 m / s, and the rolling force at the tail of the strip is 39000 KN.

[0100] 8) Coiling: The coiling temperature is set at 580 °C.

[0101] Finally, a hot-rolled steel coil of X32 with a thickness of 3.0 mm is prepared, and there are no quality problems such as serious roll marks and oxides on the surface after hot rolling.Figure 7 It is a schematic diagram of the change in the finishing rolling force during the finishing rolling of the slab in Embodiment 2 of the present application.

[0102] Comparative Example 1

[0103] Comparative Example 1 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different rough descaling speeds.

[0104] Specifically, the rough descaling speed in Comparative Example 1 is 1.1 m / s.

[0105] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. After rough rolling, the RDT is only about 1060 °C, the finishing rolling is unstable, the tail rolling force is 42000 KN, the deviation is serious, the roll is damaged after rolling, and there are serious roll mark defects on the strip surface.

[0106] Comparative Example 2

[0107] Comparative Example 2 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different rough descaling speeds.

[0108] Specifically, the rough descaling speed in Comparative Example 2 is 1.4 m / s.

[0109] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. There are serious oxide defects on the surface of the hot-rolled steel coil, the surface scale is thick, and there are many oxide indentation defects. Figure 1 It is a schematic diagram of the strip surface oxide in Comparative Example 2 of the present application.

[0110] Comparative Example 3

[0111] Comparative Example 3 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different rough rolling passes and secondary descaling processes.

[0112] Specifically, in Comparative Example 3, the rough rolling is carried out in 5 passes; the secondary descaling is to descale the rough rolling body in the 1st, 3rd, and 5th passes.

[0113] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. The thickness of the intermediate billet in 5 passes is 36 mm, the finishing rolling force is large, the tail rolling force is 43000 KN, the strip deviation is serious, and there are serious tail flick impact roll marks and surface scale defects on the surface of the hot-rolled steel coil.

[0114] Comparative Example 4

[0115] Comparative Example 4 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different lead ratios of the lower bending rolls of the hot coil box.

[0116] Specifically, the lead ratio of the lower bending roll of the hot coil box in Comparative Example 4 is 6%.

[0117] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared, and there are oxide-pressed pit defects on the surface of the hot-rolled steel coil. Figure 2 It is a schematic diagram of the strip surface oxide in Comparative Example 5 of the present application. Figure 4 It is a schematic diagram of the strip surface layer structure in Comparative Example 4 of the present application.

[0118] Comparative Example 5

[0119] Comparative Example 5 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different lead ratios of the lower bending rolls of the hot coil box.

[0120] Specifically, the lead ratio of the lower bending roll of the hot coil box in Comparative Example 5 is 2.5%. The coiling shape of the hot coil box is poor, the strip runs off during uncoiling seriously, and the finish rolling is unstable.

[0121] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared, and there are slightly oxide-scale-pressed pit defects on the surface of the hot-rolled steel coil.

[0122] Comparative Example 6

[0123] Comparative Example 6 of the present application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different roughing finishing temperatures.

[0124] Specifically, the roughing finishing temperature in Comparative Example 6 is 995 °C. At this roughing finishing temperature, the slab cannot be rolled, and forced threading will cause a scrap steel accident.

[0125] Comparative Example 7

[0126] Comparative Example 7 of the application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 is only the different roughing finishing temperatures.

[0127] Specifically, the roughing finishing temperature in Comparative Example 7 is 1120 °C.

[0128] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared, and there are serious oxide-pressed pit defects on the surface of the hot-rolled steel coil.

[0129] Comparative Example 8

[0130] Comparative Example 8 of the application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 lies only in the secondary descaling process.

[0131] Specifically, in Comparative Example 8, descaling is carried out at the 1st, 3rd, 5th, 6th, and 7th passes.

[0132] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. The number of descaling times is too large, the outlet temperature of rough rolling is lower than 1050 °C, the finish rolling is unstable, the rolling force at the tail is 43000 KN, the deviation is serious, the rolls are damaged after rolling, and there are serious roll mark defects on the strip surface.

[0133] Comparative Example 9

[0134] Comparative Example 9 of the application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 lies only in the secondary descaling process.

[0135] Specifically, in Comparative Example 9, descaling is carried out at the 1st and 3rd passes. After reducing the number of descaling passes, more oxides are generated in the rough rolling area, the descaling effect of fine descaling is limited, and some oxides are carried into the finishing mill to cause oxide pressing-in defects.

[0136] Comparative Example 10

[0137] Comparative Example 10 of the application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 lies only in the finish rolling final temperature.

[0138] Specifically, the finish rolling final temperature in Comparative Example 10 is 1005 °C.

[0139] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. The scale on the surface of the hot-rolled steel coil is relatively thick, and there are oxide pressing-in pits at some positions. Figure 6 It is a schematic diagram of the change in the finish rolling force during the finish rolling process of the slab in Comparative Example 10 of this application.

[0140] Comparative Example 11

[0141] Comparative Example 11 of the application provides a production method for improving the surface quality of high-alloy hot-rolled steel X32, and the difference from Example 1 lies only in the acceleration of finish rolling.

[0142] Specifically, the acceleration of finish rolling in Comparative Example 11 is 0.03 m / s 2 . The initial speed of finish rolling is 7.2 m / s, the final speed of finish rolling is 10 m / s, and the rolling force at the tail of the strip is 43000 KN.

[0143] Finally, an X32 hot-rolled steel coil with a thickness of 3.5 mm is prepared. The finish rolling is unstable, the rolling force at the tail is 43000 KN, the deviation is serious, the roll is damaged after rolling, and there are serious roll mark defects on the strip surface. Figure 3 It is a schematic diagram of the impact roll mark on the strip surface in Comparative Example 11 of the present application.

[0144] As mentioned above, it is only the specific implementation manner of the present application. Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working process described above can refer to the corresponding process in the foregoing method embodiment and will not be repeated here. It should be understood that the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application.

Claims

1. A production method for improving the surface quality of high alloy hot rolled strip steel, characterized in that: include, Heating and roughly dephosphorizing the slab to obtain a roughly dephosphorized slab, wherein the descaling speed of the roughly dephosphorization is 1.2 m / s-1.3 m / s; The slab after rough dephosphorization is subjected to rough rolling and secondary descaling to obtain an intermediate slab, wherein the final rolling temperature of the rough rolling is 1000° C.-1100° C., and the secondary descaling is performed in four steps; Putting the intermediate billet into a hot coil box for coiling and fine descaling to obtain a finely descaled intermediate billet, wherein the leading rate of the lower bending roll of the hot coil box is 2.5%-3.5%; The descaled intermediate billet is subjected to finish rolling to obtain a high-alloy hot-rolled steel strip.

2. The production method according to claim 1, characterized in that The rough rolling is performed in seven passes.

3. The production method according to claim 1, characterized in that The four descaling passes are descaling at the first, third, fifth and seventh passes.

4. The production method according to claim 1, characterized in that The high alloy hot rolled steel strip is coiled to obtain a high alloy hot rolled steel coil, wherein the coiling temperature is 500°C-600°C.

5. The production method according to claim 1, characterized in that: During the fine descaling process, the head descaling water is delayed to open for 1 to 2 seconds.

6. The production method according to claim 1, characterized in that: The finishing rolling is carried out by continuous rolling using 7 stands; and / or, The finishing rolling is accelerated rolling; and / or, The acceleration of the finishing rolling is 0.04-0.08 m / s 2 ; And / or, the final rolling temperature of the finish rolling is 900°C-1000°C.

7. The production method according to claim 6, characterized in that: During the finishing process, the cooling water volume between the stands of the 6th and 7th finishing mill groups was opened by 10%.

8. The production method according to claim 1, characterized in that: The slab is heated by hot charging.

9. The production method according to claim 1, characterized in that: During the heating of the slab, the temperature of the slab entering the furnace is ≥ 300°C; and / or, The slab has a furnace discharge temperature of 1150° C. to 1250° C.; and / or, The total furnace time of the slab is 150 min-250 min.

10. A high alloy hot rolled steel strip, characterized in that: Prepared according to the production method according to any one of claims 1 to 9.

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