Production method of Ti-containing microalloyed hot-rolled strip steel

Abstract

The invention provides a production method of Ti-containing microalloyed hot-rolled strip steel, and aims to solve the technical problems that after a steel strip passes through a heating furnace, rough rolling and a hot coiling box, the temperature difference between the two ends and the middle part is large, the temperature at the two ends is difficult to control, and the performance is different from that of the middle part. The method comprises the following steps: step S10, feeding; step S20, heating and discharging; s30, rough rolling is conducted, specifically, rolling is conducted through a rough rolling unit, and an intermediate billet is formed; s40, hot rolling and shearing are conducted, specifically, the end of the intermediate billet is subjected to heat preservation or heating in a hot rolling box, and the irregular end of the intermediate billet is sheared at the flying shear position; s50, finish rolling is conducted, and strip steel is formed; step S60, cooling: cooling the strip steel by adopting a laminar flow sparse cooling method; and S70, coiling is conducted, and finished steel coils are formed. In the cooling process, the strip steel is cooled by adopting a laminar flow sparse cooling method, so that the temperature of the strip steel is accurately controlled, and the physical performance of the strip steel is improved.

Description

Technical Field

[0001] The present invention relates to a production method of strip steel, and particularly to a production method of hot-rolled strip steel with Ti microalloying. Background Art

[0002] In recent years, microalloyed hot-rolled high-strength steel with trace metal elements added to the matrix chemical composition of ordinary C-Mn steel or low-alloy steel has been widely used in fields such as automobiles, construction machinery, containers, bridges, buildings, and railway vehicles. Meeting the product performance standard requirements through microalloying technology has gradually become the mainstream technology in steel production.

[0003] Among microalloying elements, niobium, vanadium, and titanium are generally used for strengthening. Considering the cost, the price of Ti microalloying is relatively the lowest. Therefore, optimizing and reasonably controlling the Ti microalloyed steel process helps to improve the enterprise's ability to develop high-strength steel products and the competitiveness of products in the market. Thus, studying the application and promotion of Ti microalloyed steel is more significant.

[0004] The microalloying element Ti mainly precipitates in the form of titanium carbide (TiC) or titanium carbonitride (Ti(C, N)) in steel, which can improve the strength of the steel and the performance of the steel.

[0005] The current Q355 / Q420 series of hot-rolled strip steel with Ti microalloying is mainly used for producing cold-rolled galvanized and direct galvanized photovoltaic brackets. After the strip steel passes through the heating furnace, rough rolling, and hot coil box, the temperature difference between the head and tail and the body temperature is relatively large, and it is difficult to control the temperature of the head and tail, and there are differences in performance from the body. Summary of the Invention

[0006] Aiming at the technical problem that after the strip steel passes through the heating furnace, rough rolling, and hot coil box, the temperature difference between the two ends and the middle temperature is relatively large, and it is difficult to control the temperature of the two ends and there are differences in performance from the middle, the present invention provides a production method of hot-rolled strip steel with Ti microalloying. During the cooling process, the strip steel is cooled by the laminar flow sparse cooling method to precisely control the temperature of the strip steel and improve the physical properties of the strip steel.

[0007] The technical solution of the present invention is as follows:

[0008] A production method of hot-rolled strip steel with Ti microalloying includes the following steps:

[0009] Step S10, loading materials. The slab is hot-loaded and directly sent into the heating furnace.

[0010] Step S20, heating. According to the set heating program, the slab is heated and soaked in the heating furnace. After reaching a uniform and consistent tapping temperature, it is discharged.

[0011] Step S30: Rough rolling. After removing the scale formed in the furnace and the attached protective slag on the surface of the slab, it is rolled by the rough rolling mill to form an intermediate slab, and the width of the intermediate slab is controlled.

[0012] Step S40: Hot coiling and shearing. The intermediate slab is sent to the hot coil box, where the ends of the intermediate slab are insulated or heated, and the irregular ends of the intermediate slab are sheared at the flying shear.

[0013] Step S50: Finish rolling. After removing the secondary scale from the intermediate slab, finish rolling is carried out to form a strip steel.

[0014] Step S60: Cooling. The strip steel is sent into the laminar cooling device, and the strip steel is cooled by the laminar sparse cooling method.

[0015] Step S70: Coiling. The cooled strip steel is transported to the downcoiler for coiling to form a finished steel coil.

[0016] Optionally, in step S60, cooling the strip steel by the laminar sparse cooling method specifically includes:

[0017] Coarse adjustment: Preset the cooling headers in the coarse adjustment section during cooling according to the target thickness, target coiling temperature, and target finish rolling temperature of the strip steel.

[0018] Correction: Correct the opened cooling headers according to the measured thickness, actual running speed, and actual finish rolling temperature.

[0019] Fine adjustment: Open the cooling headers in the fine adjustment section according to the difference between the measured coiling temperature and the target coiling temperature.

[0020] Optionally, the laminar sparse cooling method further includes:

[0021] Obtain the strip steel grade data, thickness data, finish rolling temperature data, target temperature data required during coiling, and measured coiling temperature data of the strip steel, and judge the number of cooling headers to be opened, the opening sequence, and the cooling treatment method for the strip steel ends based on the obtained data.

[0022] Optionally, the opening sequence of the cooling headers includes forward opening and reverse opening;

[0023] The number of opened groups of cooling headers includes opening one group, two groups, three groups, and four groups. When opening two groups, the first group and the third group are opened in the direction of the opening sequence;

[0024] The cooling treatment methods for the strip steel ends include normal cooling, only tail cooling, only head cooling, neither end cooling, and both ends slightly cooling.

[0025] Optionally, in the laminar sparse cooling method, the coiling temperature of the strip steel in summer is lower than that in winter.

[0026] Optionally, the slab discharging temperature in step S20 is 1200°C - 1280°C. During the discharging process, scale is removed from the slab, and then it enters step S30.

[0027] Optionally, during the rough rolling process in step S30, the width of the intermediate billet is controlled by a width gauge and a vertical roll mill;

[0028] The shape of both ends of the intermediate billet is improved by an SSC short stroke control system.

[0029] Optionally, in step S40, for an intermediate billet with a thickness of 24 - 32 mm and less than or equal to 28 mm, it is coiled without a core and transferred with a core in a hot coil box, and heat preservation is carried out;

[0030] When both ends of the intermediate billet with a thickness greater than 28 mm are regular, it can directly pass through the hot coil box, and the ends of the intermediate billet are sheared at the flying shear in the hot coil box.

[0031] Optionally, in step S50, a cooling device is provided in finish rolling, and the finish rolling final rolling temperature is 820 - 900950°C.

[0032] Optionally, in step S60, the strip steel is cooled to 590°C - 680°C in a laminar flow cooling device. The number of opened groups of cooling headers includes opening one group, two groups, three groups, and four groups. When opening two groups

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] The strip steel is cooled by the laminar flow sparse cooling method, which can improve the accuracy of strip steel temperature control. The improvement of temperature control accuracy has a great promotion on the physical properties such as the processing performance and mechanical properties of the strip steel, and can also optimize the metallographic structure inside the strip steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a schematic diagram of the production line of the present invention;

[0037] Figure 2 It is a process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the accompanying drawings and the description are considered to be exemplary in nature rather than restrictive.

[0039] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0040] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] Embodiment:

[0042] See Figure 1 and Figure 2 This embodiment discloses a production method of a Ti microalloyed hot-rolled strip steel, including the following steps:

[0043] Step S10, loading: The slab is hot-loaded and directly fed into the heating furnace 10.

[0044] The continuously cast slab is hot-loaded, that is, the continuously cast slab is directly fed into the heating furnace 10 in a state without cooling down.

[0045] The qualified slab is positioned by the continuous casting hot charging roller table 20, the elevator, the post-elevator hot charging roller table 20, the rotary roller table 20, the charging roller table 20 in front of the furnace, and the charging roller table 20 into the furnace, and then loaded into the heating furnace 10 by the steel charging machine.

[0046] Step S20, heating: According to the set heating program, the slab is heated and soaked in the heating furnace 10. After reaching a uniform tapping temperature, it is discharged.

[0047] According to the different slab grades, the slab tapping temperature is controlled at 1200 - 1280 °C.

[0048] Step S30, rough rolling: After removing the scale formed on the surface of the slab and the attached protective slag, it is rolled by the rough rolling mill group 30 to form an intermediate slab, and the width of the intermediate slab is controlled.

[0049] The slab output from the heating furnace 10 is descaled (scale is the iron oxide scale on the surface of the slab, named because the high-temperature iron oxide scale on the slab after heating resembles fish scales), the furnace-generated iron oxide scale and attached protective slag are removed, and then it is sent to the rough rolling mill 30 group by the roller 20 for rough rolling, and rolled to form an intermediate slab.

[0050] Through the cooperation of the width gauge at the exit of the roughing mill 30, the vertical roller mill adopts the hydraulic AWC automatic control system to control the width of the intermediate billet, and adopts the SSC short stroke control system to improve the shape of both ends of the intermediate billet.

[0051] The two-roll roughing mill 30 uses an electric APC control system to ensure that the intermediate billet can still maintain the dimensional accuracy at a large reduction rate, while preventing the slab size from deviating. A high-pressure water descaling system is set at the entrance of the E1 vertical mill to remove the iron oxide produced during rolling.

[0052] Step S40, hot coiling and shearing, the intermediate billet is sent to the hot coil box 40, and the end of the intermediate billet is kept warm in the hot coil box 40 to prevent the temperature drop of the end of the intermediate billet from reaching 100°C, thereby avoiding a significant impact on subsequent production control and product quality. The irregular end of the intermediate billet is sheared at the flying shear 80.

[0053] After the rough rolling, the intermediate billet is transported to the hot coil box 40 and the flying shear area. According to different temperature control requirements and different slab grades, the intermediate billet with a thickness of 22mm-32mm can enter the hot coil box 40 for coreless coiling or core transfer, and keep the temperature in the hot coil box 40 to keep the temperature at both ends of the intermediate billet consistent. Under the condition that the quality of the two ends of the intermediate billet is not affected, it can enter the hot coil box 40 in a straight-through mode. The intermediate billet passes through the hot coil box 40 and the irregular two ends are cut off at the flying shear 80.

[0054] Step S50, finish rolling, after removing the secondary iron oxide scale from the intermediate billet, performing finished rolling to form a steel strip.

[0055] Finishing rolling is also called finished product rolling. The temperature of the intermediate billet coming out of the hot coil box 40 is 960-1050℃. After that, the secondary iron oxide scale is removed by the fine descaling box and then enters the E2 vertical roller mill and the F1-F7 four-roll finishing mill 50 group to roll the intermediate billet into finished product.

[0056] The four-roller finishing mill 50 is a four-roller irreversible rolling mill under full hydraulic pressure. A hydraulic looper is arranged between the frames of the finishing mill 50, and the rolling mill is automatically adjusted in speed through the loop height adjustment system, and the strip is rolled under micro-tension and constant tension through the tension adjustment system.

[0057] The finishing mill 50 is servo-hydraulic pressure reduction, with AGC control. The mill is equipped with a work roll bending device, and the work roll bending force is adjusted to control the strip shape. By setting a reasonable exit speed and the inter-stand spray cooling system, the final rolling temperature is ensured (the final rolling temperature is 820 - 950 °C). Behind the finishing mill 50 group, thickness gauges, width gauges, surface quality detectors and other detection instruments are provided to conduct online closed-loop control and quality inspection on strip production.

[0058] Step S60, cooling: Feed the strip into the laminar cooling device 60, and adopt the laminar sparse cooling method to cool the strip.

[0059] The strip rolled out from the finishing mill enters the laminar cooling device 60 via the output roller table 20. The cooling water headers of the laminar cooling device 60 can control the number of opened spray groups and adjust the water volume according to the strip thickness, steel grade and rolling speed, and cool the strip from the final rolling temperature to the required coiling temperature: 590 - 680 °C.

[0060] Step S70, coiling: Transport the cooled strip to the downcoiler 70 underground for coiling to form a finished steel coil.

[0061] The strip is transported to the downcoiler 70 underground via the hot output roller table 20 for coiling.

[0062] The coiler 70 adopts a fully hydraulic three-auxiliary coiling roll downcoiler 70. Under the action of the auxiliary coiling rolls, the strip is coiled and formed on the mandrel. The auxiliary coiling rolls of the coiler 70 have an automatic stepping control (AJC) function to ensure that the inner layer of the steel coil is not indented by the head of the strip under a large pressure.

[0063] A hydraulic side guide is provided in front of the coiler 70 to strictly center the strip. A pinch roll is provided in front of the coiler 70 to form the head of the strip and create a certain tension between the tail of the strip coming out of the last finishing mill stand and the coiler 70.

[0064] During the cooling process of this embodiment, the laminar sparse cooling method is adopted to cool the strip, which can improve the accuracy of strip temperature control. The improvement of temperature control accuracy has a great promotion on the physical properties such as the processing performance and mechanical properties of the strip, and can also optimize the metallographic structure inside the strip.

[0065] In one specific embodiment:

[0066] Since there is a relatively long roller table 20 (with a length of more than 50 meters) between the heating furnace 10 and the roughing mill, when the slab is output from the heating furnace 10, descaling operation is carried out on the slab to ensure that no pitting or pits are formed on the surface of the slab during the subsequent roughing process, thereby ensuring the surface quality of the steel plate.

[0067] Before the slab enters the rough rolling, descaling operation is carried out again, aiming to remove the secondary scale formed when the slab is exposed to air on the roller table 20 from the heating furnace 10 to the rough rolling.

[0068] Before the above-mentioned finish rolling, descaling operation is also required, aiming to remove the scale generated between the rough rolling and the finish rolling.

[0069] In another specific embodiment:

[0070] The above step S60, cooling the strip by laminar flow sparse cooling method includes:

[0071] Step S61, coarse adjustment, preset the cooling headers in the coarse adjustment section when cooling according to the target thickness of the strip, the target finish rolling final temperature and the target coiling temperature.

[0072] Step S62, correction, correct the opened cooling headers according to the measured thickness, the actual running speed and the actual finish rolling final temperature.

[0073] Step S63, fine adjustment, according to the difference between the measured coiling temperature and the target coiling temperature, open the cooling headers in the fine adjustment section (wherein, when the adjustment in the fine adjustment section is insufficient, open the coarse adjustment section, and when the detected temperature is higher than the target temperature, close the coarse adjustment section).

[0074] Specifically, temperature measuring instruments are respectively arranged after the finish rolling and before the coiling, and the actual finish rolling final temperature required in step S62 is obtained through the temperature measuring instrument after the finish rolling, and the measured coiling temperature required in step S63 is obtained through the temperature measuring instrument before the coiling.

[0075] In another specific embodiment:

[0076] Step S60, the laminar flow sparse cooling method during cooling further includes:

[0077] Obtain the strip grade data, thickness data, finish rolling final temperature data and the temperature data required during coiling, and judge the number of cooling headers to be opened, the opening sequence and the cooling treatment method for the strip ends through the obtained data.

[0078] Specifically, the laminar flow cooling 60 device is a low-pressure tube laminar flow cooling 60, inertia-free siphon, including a plurality of upper headers and a plurality of lower headers. All upper headers are arranged above the output roller table 20, and all lower headers are arranged below the output roller table 20.

[0079] There are a total of 12 zones in the laminar flow cooling 60 device, divided into 10 coarse adjustment zones and 2 fine adjustment zones. Each coarse adjustment zone has 4 upper headers, 12 lower headers, 1 upper header corresponding to 3 lower headers, forming 4 coarse cooling units in total. Each fine adjustment zone has 8 upper headers and 8 lower headers, corresponding one by one, and forming 8 fine cooling units.

[0080] Each cooling unit is controlled by a pneumatic butterfly valve. The upper and lower headers of the coarse adjustment area and the fine adjustment area are corresponding, and can be controlled together or separately. Since the strip runs on the hot output roller 20 for a short time, each header of the laminar cooling 60 must have low pressure and large water volume, and the water volume is uniform.

[0081] The opening sequence of the cooling header includes forward opening and reverse opening. The number of opening groups of the cooling header includes opening one group, two groups, three groups and four groups, wherein when opening two groups, the first group and the third group are opened in the direction of the opening sequence. The cooling treatment methods of the strip ends include normal cooling, tail cooling only, head cooling only, no cooling at both ends and slight cooling at both ends.

[0082] The forward opening sequence refers to opening the cooling headers in sequence along the forward direction of the intermediate billet, while the reverse opening sequence refers to opening the cooling headers in sequence against the forward direction of the intermediate billet.

[0083] Preferably, in the laminar sparse cooling method, the coiling temperature of the steel strip in summer is lower than the coiling temperature of the steel strip in winter.

[0084] Specifically, the relationship between the strip steel grade data, thickness data, finishing rolling temperature data, coiling temperature data and seasons, and the corresponding cooling method are shown in Table 1. In Table 1, the rough rolling start temperature is 1080℃±30℃, wherein the error range of the finishing rolling temperature and the error range of the coiling temperature are both ±15℃.

[0085] Table 1. Temperature control scheme

[0086]

[0087] The meaning of the numerical values ​​in the cooling method is as follows in Table 2:

[0088] Table 2. Cooling method numerical meaning table

[0089]

[0090] In the meaning corresponding to the tens digit in Table 2, the value 1 indicates that the coarse cooling unit at the corresponding position is turned on, and 0 indicates that it is turned off. For example, 1010 indicates that the first coarse cooling unit and the third coarse cooling unit are turned on, and the second coarse cooling unit and the fourth coarse cooling unit are turned off.

[0091] In this embodiment, by optimizing the layer cooling amount, the strip is quickly cooled to a temperature close to the ferrite transformation temperature, and relaxation cooling is performed by utilizing the long laminar cooling length of the hot rolling production line. By optimizing the layer cooling temperature, the TiC precipitated in the ferrite phase reaches a peak value, and the precipitation of TiC induced by the ferrite phase transformation is beneficial to improving the strength of the steel.

[0092] According to the data in actual production (as shown in Table 3), among the temperature anomaly and performance anomaly coil data from September to November in the statistical year 2024, through this production method, the number of temperature anomaly coils has decreased significantly, and the proportion has reached a new low for the year. At the same time, the performance uniformity of the hot-rolled strip steel with Ti microalloying has tended to be stable, and the number of performance anomalies has decreased by 76.38% year-on-year. The anomaly proportion in November is only 0.3%.

[0093] Table 3. Actual production data

[0094]

[0095] The above-described embodiments only represent the specific implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A production method of a Ti-containing microalloyed hot-rolled strip steel, characterized in that, It includes the following steps: Step S10: Loading. The slab is hot-loaded and directly fed into the heating furnace. Step S20: Heating. According to the set heating program, the slab is heated and soaked in the heating furnace. After reaching a uniform tapping temperature, it is discharged. Step S30: Rough rolling. After removing the scale formed in the furnace and the adhering protective slag on the slab surface, it is rolled by the roughing mill to form an intermediate slab, and the width of the intermediate slab is controlled. Step S40: Hot coiling and shearing. The intermediate slab is sent to the hot coil box, where the ends of the intermediate slab are heat-insulated or heated, and the irregular ends of the intermediate slab are sheared at the flying shear. Step S50: Finish rolling. After removing the secondary scale from the intermediate slab, it is rolled into a strip steel. Step S60: Cooling. The strip steel is sent into the laminar cooling device, and the strip steel is cooled by the laminar sparse cooling method. Step S70: Coiling. The cooled strip steel is transported to the downcoiler for coiling to form a finished steel coil.

2. The production method of the Ti microalloyed hot-rolled strip steel according to claim 1, characterized in that, In step S60, the specific steps of cooling the strip steel by the laminar sparse cooling method include: Coarse adjustment. According to the target thickness, target coiling temperature, and target finish rolling temperature of the strip steel, the cooling headers in the coarse adjustment section are preset to be opened during cooling. Correction. The opened cooling headers are corrected according to the measured thickness, actual running speed, and actual finish rolling temperature. Fine adjustment. According to the difference between the measured coiling temperature and the target coiling temperature, the cooling headers in the fine adjustment section are opened.

3. The production method of the Ti microalloyed hot rolled strip steel according to claim 2, characterized in that, The laminar sparse cooling method further includes: Obtaining the strip steel grade data, thickness data, finish rolling temperature data, coiling target temperature data, and measured coiling temperature data of the strip steel. Based on the obtained data, judge the number of cooling headers to be opened, the opening sequence, and the cooling treatment method for the strip steel ends.

4. The production method of the Ti-containing microalloyed hot-rolled strip steel according to claim 2, characterized in that: The opening sequence of the cooling headers includes forward opening and reverse opening; The number of opened groups of cooling headers includes opening one group, two groups, three groups, and four groups. When opening two groups, the first group and the third group are opened in the direction of the opening sequence; The cooling treatment methods for the strip steel ends include normal cooling, only tail cooling, only head cooling, neither end cooling, and both ends slightly cooling.

5. The production method of the Ti microalloyed hot-rolled strip steel according to claim 2, characterized in that, In the laminar sparse cooling method, the coiling temperature of the strip steel in summer is lower than that in winter.

6. The production method of the Ti microalloyed hot-rolled strip steel according to claim 1, characterized in that, The tapping temperature of the slab in step S20 is 1200°C - 1280°C. During the discharging process, the slab is descaled and then enters step S30.

7. The production method of the Ti-containing microalloyed hot-rolled strip steel according to claim 1, characterized in that: During the rough rolling process in step S30, the width of the intermediate slab is controlled by a width gauge and a vertical roll mill; The shape of both ends of the intermediate slab is improved by the SSC short stroke control system.

8. The production method of the Ti-containing microalloyed hot-rolled strip steel according to claim 1, characterized in that: In step S40, for an intermediate slab with a thickness of 24 - 32 mm, it is coiled without a core and transferred with a core in the hot coil box and heat-insulated; When both ends of the intermediate slab are regular, it can directly pass through the hot coil box, and the ends of the intermediate slab are sheared inside the flying shear.

9. The production method of the Ti microalloyed hot rolled strip steel according to claim 1, characterized in that, In the step S50, a cooling device is provided in the finish rolling process, and the finish rolling temperature is 820 - 950 °C.

10. The production method of the Ti microalloyed hot-rolled strip steel according to claim 1, characterized in that, In the step S60, the strip steel is cooled to 590 °C - 680 °C in the laminar cooling device.

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