Control method for preventing rough rolling upwarp during low-temperature production of non-oriented silicon steel

Abstract

The invention relates to a control method for preventing rough rolling upwarp during low-temperature production of non-oriented silicon steel, which comprises the following steps: adopting a hot charging and hot delivery process for a non-oriented silicon steel slab, and controlling the temperature difference between the upper surface and the lower surface of the slab within 10 DEG C after the slab enters a second heating section; the total heating time of the second heating section and the soaking section is not less than 70 minutes, and the total time of the second heating section and the soaking section in the furnace is 170-230 minutes; the tapping temperature of the plate blank is 1100-1120 DEG C; the R2 rolling mill working roll is pressed downwards, and the roll diameter difference is 1-2 mm; and the rolling reduction rate of the fourth pass of rough rolling is controlled to be 20%-25%. By controlling the charging temperature of the plate blank, the temperature difference between the upper surface and the lower surface of the plate blank when the plate blank enters the furnace, the heating temperature and time of each section and controlling the reduction rate of the fourth pass of rough rolling and the R2 working roller, the head warping phenomenon after low-temperature heating during rough rolling is effectively controlled, energy is saved, accidents caused by head warping of the plate blank are prevented, and the production efficiency is improved. And the excellent magnetic performance of the low-temperature non-oriented silicon steel product is ensured.

Description

Technical Field

[0001] This invention relates to the field of non-oriented silicon steel production technology, and in particular to a method for controlling the occurrence of warping defects during the rough rolling stage when producing non-oriented silicon steel (Si content of 0.9% to 1.6%) at low temperatures. Background Technology

[0002] Non-oriented silicon steel is generally produced using a low-temperature heating process and is mainly used in air conditioner compressors, refrigerator motors, small and medium-sized industrial motors, water pumps, fans, auxiliary motors for new energy vehicles, and drone motors. The low-temperature heating temperature range is 1100–1160℃, but when the temperature approaches the upper limit, the strip is prone to serrated edge defects after hot rolling. Therefore, in actual production, it is usually necessary to produce near the lower limit. Currently, non-oriented silicon steel with a Si content of 0.9%–1.6% exhibits a curling phenomenon during the roughing stage when produced near the lower limit of the low-temperature heating temperature. This curling phenomenon is exacerbated during low-temperature tapping after heating. Severe curling can affect the bite of the next roughing or finishing rolling pass, and may even damage the descaling box between roughing mill stands or cause steel jamming accidents. To alleviate the severe curling problem in roughing, the heating temperature must be increased, but this directly affects the final silicon steel properties, increases the incidence of serrated edge defects, and increases heating energy consumption.

[0003] Chinese patent application CN202010071651.5 discloses a "method for controlling the head-up of rough-rolled slabs of non-oriented silicon steel". The method involves: 1) setting the furnace temperature for the upper and lower sections of each section of the heating furnace according to the silicon and aluminum content in the silicon steel; the upper heating temperature of each section is T1i = 1200 * Ni * As; the lower heating temperature of each section is T2i = 1200 * Ni * As + ΔTs; 2) controlling the reduction rate of each pass according to the thickness of the raw material entering the roughing mill, with the reduction rate being δi = (0.37 - 0.0012 * Hi) * 100% + G; the thickness of the raw material entering each pass is Hi, where H1 in the first pass is the original slab thickness, ranging from 170 to 230 mm, and the values ​​of Hi in subsequent passes are the rolling exit thickness of the previous pass, ranging from 38 to 230 mm. This method differs significantly from the method described in this invention.

[0004] Chinese patent application CN201810051999.0 discloses a "method for controlling head warping in the roughing mill of hot-rolled steel grades," comprising the following steps: roughing mill preparation, confirming whether rolling conditions are met, and checking the adhesion between the guides and water-cutting plates and the rolls before rolling; slab heating, after the rolling conditions are met, heating the hot-rolled slab with a thickness of 135-150mm to ensure uniform slab temperature, ensuring that the end face of the slab exiting the furnace is free of black marks and obvious watermarks, otherwise it is returned to the furnace; descaling, ensuring that the surface of the slab exiting the furnace is smooth and free of iron oxide scale residue, and slabs with incomplete iron oxide scale removal are returned to the furnace; roughing mill rolling, after descaling, the slab enters the roughing mill for three passes. Its steel grade, slab thickness, and main control methods are significantly different from those of this invention.

[0005] Chinese patent application CN201510010543.6 discloses a "method for controlling head warping in the roughing of hot-rolled strip steel." This method determines the speed difference ΔV between the upper and lower work rolls of the rolling mill during the roughing process, corresponding to different temperature differences ΔT between the upper and lower slabs at the time of exiting the furnace during the heating stage of continuous rolling. Then, based on the actual production process, the rotational speeds of the upper and lower work rolls are set, thereby preventing head warping of the slab during rolling. However, its steel grades and main control methods differ significantly from those of this invention. Summary of the Invention

[0006] This invention provides a method for controlling the warping phenomenon during rough rolling of non-oriented silicon steel at low temperatures. By controlling the slab loading temperature, the temperature difference between the upper and lower surfaces of the slab when it enters the furnace, the heating temperature and time of each section, and controlling the reduction rate of the fourth rough rolling pass and the R2 work roll, the warping phenomenon during rough rolling after low-temperature heating is effectively controlled, saving energy, preventing accidents caused by slab warping, and ensuring the excellent magnetic properties of non-oriented silicon steel products.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for controlling rough rolling head warping during low-temperature production of non-oriented silicon steel, comprising controlling the following production process:

[0009] 1) Slab charging: Non-oriented silicon steel slabs are charged using a hot charging and hot delivery process, with the slab temperature ≥300℃ during charging.

[0010] 2) Slab heating: The walking beam furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section; when the non-oriented silicon steel slab enters the second heating section, the temperature difference between the upper and lower surfaces of the non-oriented silicon steel slab is controlled within 10℃; the total heating time of the second heating section and the soaking section is not less than 70 minutes, and the total time in the furnace is 170 to 230 minutes; the furnace exit temperature of the non-oriented silicon steel slab is 1100 to 1120℃;

[0011] 3) Roughing: The working rolls of the R2 mill are pressed down, and the roll diameter difference is 1-2mm; the rolling reduction rate of the fourth pass of roughing is controlled to be 20%-25%.

[0012] The chemical composition of non-oriented silicon steel, by mass percentage, is C≤0.004%, Si: 0.9%~1.6%, Mn: 0.2%~0.65%, P≤0.1%, S≤0.006%, Als: 0.15%~0.45%, with the remainder being Fe and unavoidable impurities.

[0013] In the production process 1), if the non-oriented silicon steel slab cannot be immediately loaded into the furnace, the non-oriented silicon steel slab is first placed in a heat preservation pit for heat preservation, and the temperature in the heat preservation pit is ≥400℃.

[0014] The thickness of the non-oriented silicon steel slab is 200-250 mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] By controlling the slab loading temperature, the temperature difference between the upper and lower surfaces of the slab when it enters the furnace, the heating temperature and time of each section, and controlling the reduction rate of the fourth pass of rough rolling and the R2 work roll, the phenomenon of slab head warping during rough rolling after low-temperature heating is effectively controlled, saving energy, preventing accidents caused by slab head warping, and ensuring the excellent magnetic properties of non-oriented silicon steel products. Attached Figure Description

[0017] Figure 1 This is a deformation resistance diagram for non-oriented silicon steel with grade 50AW600.

[0018] Figure 2 This is a deformation resistance diagram for non-oriented silicon steel with grade 50AW800. Detailed Implementation

[0019] This invention discloses a method for controlling head warping during rough rolling in the low-temperature production of non-oriented silicon steel. The chemical composition of the non-oriented silicon steel, by mass percentage, is: C ≤ 0.004%, Si: 0.9%–1.6%, Mn: 0.2%–0.65%, P ≤ 0.1%, S ≤ 0.006%, Als: 0.15%–0.45%, with the remainder being Fe and unavoidable impurities. The thickness of the non-oriented silicon steel slab (hereinafter referred to as the slab) is 220–240 mm. Head warping mainly occurs during the rough rolling stage of the rolled product.

[0020] The present invention discloses a method for controlling rough rolling head warping during low-temperature production of non-oriented silicon steel, which controls the following production process:

[0021] 1) Slab loading: Non-oriented silicon steel slabs are loaded into the furnace using a hot loading and hot delivery process. The slab temperature is ≥300℃ during loading. If non-oriented silicon steel slabs cannot be loaded into the furnace immediately, they are first placed in an insulation pit for insulation. The temperature in the insulation pit is ≥400℃.

[0022] 2) Slab heating: The walking beam furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section; when the non-oriented silicon steel slab enters the second heating section, the temperature difference between the upper and lower surfaces of the non-oriented silicon steel slab is controlled within 10℃; the total heating time of the second heating section and the soaking section is not less than 70 minutes, and the total time in the furnace is 170 to 230 minutes; the furnace exit temperature of the non-oriented silicon steel slab is 1100 to 1120℃;

[0023] This invention reduces the furnace exit temperature of slabs from the conventional 1150℃ to about 1110℃, saving energy and preventing rough rolling accidents caused by the tip of the rolled piece, thus improving production line efficiency. Lowering the furnace exit temperature also helps the finished product to have better magnetic properties.

[0024] Once the slab enters the second heating section of the furnace, the temperature difference between the upper and lower surfaces of the slab must be controlled within 10°C to significantly reduce the extension of the lower surface of the rolled piece relative to the upper surface. Figure 1 , Figure 2 The diagrams show the deformation resistance of two different grades of non-oriented silicon steel (Si content 0.9% and 1.6%, respectively). It can be seen that for non-oriented silicon steel with a Si content of 0.9%–1.6%, the phase transformation point temperature is generally high (typically in the range of 950–1100℃). In the austenite and ferrite regions, the deformation resistance increases with decreasing deformation temperature. During rough rolling, the temperature falls within this two-phase region. As the slab temperature decreases, the ferrite content gradually increases while the austenite content gradually decreases. In the high-temperature region, the flow stress of ferrite is lower than that of austenite. Therefore, during rough rolling, the deformation resistance gradually decreases with decreasing slab temperature, making deformation more likely. This invention controls the temperature difference between the upper and lower surfaces of the slab to within 10℃, effectively reducing the elongation of the lower surface during rolling and preventing warping.

[0025] In addition, the total furnace time of the slab should be moderate (required to be 170-230 min). Not less than 170 min is to ensure that the temperature of the slab is uniform and to prevent large temperature differences between the surface and core of the slab. Not more than 230 min is to prevent abnormal grain growth, which would lead to deterioration of the magnetic properties of the finished product. The heating time of the second heating section and the soaking section should be sufficient (the sum of the two should not be less than 70 min).

[0026] 3) Roughing: The working rolls of the R2 mill are pressed down, and the roll diameter difference is 1-2mm; the rolling reduction rate of the fourth pass of roughing is controlled to be 20%-25%.

[0027] The roughing of non-oriented silicon steel generally adopts the "3+3" rolling mode. When the rolling reaches the fourth pass, it is easy for the head to rise. The reduction rate of the fourth pass should not be too high. Therefore, this invention controls the reduction rate of the fourth pass of roughing to be within the range of 20% to 25%.

[0028] The occurrence of slab warping is generally due to the lower surface of the slab extending more than the upper surface. Warping is more likely to occur during the R2 rolling stage. Therefore, in this invention, the R2 work roll adopts a downward pressing mode, and the roll diameter difference is controlled at 1 to 2 mm, in order to reduce the extension of the lower surface of the slab.

[0029] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0030] Example:

[0031] The chemical composition of the non-oriented silicon steel in each embodiment is shown in Table 1, and the key control parameters are shown in Table 2.

[0032] Table 1 Chemical composition of non-oriented silicon steel (wt%)

[0033]

[0034] Table 2 Key Control Process Parameters

[0035]

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling rough rolling head warping during low-temperature production of non-oriented silicon steel, characterized in that, Control the following production processes: 1) Slab charging: Non-oriented silicon steel slabs are charged using a hot charging and hot delivery process, with the slab temperature ≥300℃ during charging. 2) Slab heating: The walking beam furnace is divided into a preheating section, a first heating section, a second heating section, and a soaking section; when the non-oriented silicon steel slab enters the second heating section, the temperature difference between the upper and lower surfaces of the non-oriented silicon steel slab is controlled within 10℃; the total heating time of the second heating section and the soaking section is not less than 70 minutes, and the total time in the furnace is 170 to 230 minutes; the furnace exit temperature of the non-oriented silicon steel slab is 1100 to 1120℃; 3) Roughing: The R2 mill work rolls are pressed down, and the roll diameter difference is 1-2 mm; the rolling reduction rate of the fourth pass of roughing is controlled to be 20%-25%.

2. The method for controlling rough rolling head warping during low-temperature production of non-oriented silicon steel according to claim 1, characterized in that, The chemical composition of non-oriented silicon steel, by mass percentage, is C≤0.004%, Si: 0.9%~1.6%, Mn: 0.2%~0.65%, P≤0.1%, S≤0.006%, Als: 0.15%~0.45%, with the remainder being Fe and unavoidable impurities.

3. The method for controlling rough rolling head warping during low-temperature production of non-oriented silicon steel according to claim 1, characterized in that, In the production process 1), if the non-oriented silicon steel slab cannot be immediately loaded into the furnace, the non-oriented silicon steel slab is first placed in a heat preservation pit for heat preservation, and the temperature in the heat preservation pit is ≥400℃.

4. A method for controlling roughing head warping during low-temperature production of non-oriented silicon steel according to claim 1 or 3, characterized in that, The thickness of the non-oriented silicon steel slab is 200-250 mm.

Images