JP5768415B2 - Method for preventing warpage in hot rolling line of high Si steel - Google Patents

Description

  The present invention relates to a method for preventing warping when a high-Si steel material heated in a heating furnace is rolled with a rolling mill in a hot rolling line.

  In hot rolling of steel, the steel material is charged into a heating furnace and heated prior to rolling. Since the inside of the heating furnace is in an oxidizing atmosphere, the surface layer of the steel material is oxidized during heating to generate scale. When rolling is performed with this scale attached to the surface layer of the steel material, the scale bites into the surface of the rolled material and remains as scale soot. In order to prevent the generation of scale flaws, a method for removing the scale of the steel material by performing a descaling process in which high-pressure water is sprayed on the surface layer of the steel material before rolling has been conventionally known (for example, patents). Reference 1).

By the way, the ease of peeling of the scale varies depending on the components of the steel, and in particular, the scale generated in a steel material having a Si content of 0.6% by weight or more (hereinafter referred to as a high Si steel material) It is known that it is difficult to peel off. This is because firelite (2FeO.SiO ₂ ) is formed in a wedge shape at the grain boundary between the scale and the high-Si steel material during scale generation.
For this reason, in the hot rolling line of high Si steel material, the scale is not sufficiently removed only by the injection of high-pressure water in the descaling process.

JP 2010-99725 A

By the way, the scale of the high-Si steel material has a higher heat transfer coefficient than that of the ground iron, and the high-Si steel material with the scale remaining on the surface layer after the descaling process tends to cool down on the surface side where water is accumulated. .
When a high Si steel material with a large temperature difference between the front and back surfaces (high back surface temperature and low surface temperature) is rolled with a rolling mill, the rolled material is likely to warp, There is a risk of quality degradation, operational troubles and damage to production equipment.

  Therefore, the present invention has been made paying attention to the unsolved problems of the above conventional example, removing the scale generated during heating, and rolling the surface of the material and the back surface with a precise temperature difference with a rolling mill. An object of the present invention is to provide a method of preventing warpage in a hot rolling line of high Si steel that can surely prevent warping.

In order to achieve the above object, a method for preventing warpage in a hot rolling line for high Si steel according to claim 1 of the present application is a hot rolling line for rolling a high Si steel material heated in a heating furnace with a rolling mill. In the heating furnace, the high Si steel material is heated so that the temperature of the surface, which is an accurate temperature difference between the front surface and the back surface, is a temperature difference in the range of 10 ° C to 20 ° C higher than the temperature of the back surface , The line between the heating furnace and the rolling mill is provided with a hot scale breaker and a scale removing unit disposed downstream of the hot scale breaker, and the high Si steel heated in the heating furnace in the hot scale breaker. by injecting high pressure water to the surface and the back surface of the material, to remove the portion of scale formed on the surface of the high Si steel material, in the descaling unit, before Symbol high Si Causing cracks in scale formed on the surface of the material, and the scale is divided into a plurality of boundary the crack so as to remove from the surface layer.

Further, the invention according to claim 2 is the sizing press in which the scale removing portion is arranged downstream of the hot scale breaker in the method of preventing warping in the hot rolling line of the high Si steel according to claim 1. Consists of a descaling device arranged between the sizing press and the rolling mill, and the scale is obtained by rolling the high Si steel material that has passed through the hot scale breaker by 30 mm or more in the width direction with the sizing press. The scale is divided into a plurality of portions with the crack as a boundary by injecting high-pressure water onto the front and back surfaces of the high-Si steel material that has been cracked by the sizing press. Was removed from the surface layer.

According to the method for preventing warpage in the hot rolling line of high Si steel according to the present invention, it is generated on the surface layer of the high Si steel material by heating in the heating furnace, and it bites into the ground iron in a wedge shape including the firelight. The scale is cracked by the scale removing portion, and is divided into a plurality of parts and scattered from the surface layer of the high Si steel material to the outside.
Therefore, according to the present invention, the high Si steel material heated so that the temperature difference between the front surface and the back surface becomes an accurate temperature difference in a heating furnace has a high heat transfer coefficient immediately before being rolled by a rolling mill, and has a thermal effect. Easy-to-scale scales are completely removed from the surface layer, and a precise temperature difference between the front and back surfaces is maintained in the heating furnace, so that the warping of the rolled material formed by rolling with a rolling mill is ensured. Can be prevented.

It is the schematic which shows the hot rolling line which concerns on this invention. It is a figure which shows the structure of the furnace temperature control apparatus arrange | positioned at the hot rolling line which concerns on this invention. It is the figure which showed typically the state from which the scale produced | generated to the high Si steel material was removed in the hot rolling line which concerns on this invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
FIG. 1 shows a part of a hot rolling line according to the present invention, and a heating furnace 1 is arranged upstream of the line, and an HSB (hot scale breaker) extends from the heating furnace 1 toward the downstream side of the line. 2), sizing press 3, descaling device 4, edger 5 and roughing mill 6 are arranged in this order.

And the material hot-rolled by this hot rolling line is the steel material 7 whose Si content is 0.6 weight% or more (hereinafter, referred to as high-Si steel material 7), and the width dimension is about 1400 mm. It has a rectangular parallelepiped shape and moves in the longitudinal direction toward the transport direction.
As shown in FIG. 2, the heating furnace 1 is a heating furnace having eight zones 1 a to 1 h for heating the high Si steel material 7 from the front surface and the back surface, 1 a being a pre-tropical upper zone, and 1 b being a pre-tropical lower zone. 1c is the first heating zone upper zone, 1d is the first heating zone lower zone, 1e is the second heating zone upper zone, 1f is the second heating lower zone, 1g is the soaking zone upper zone, 1h is the soaking zone lower zone is there.

Reference numeral 10 in FIG. 2 is a furnace temperature control device that performs furnace temperature control of each of the eight zones 1 a to 1 h constituting the heating furnace 1. The furnace temperature control is to control the heating of the high Si steel material 7 by adjusting the flow rate of the fuel to be supplied to the burner based on the furnace atmosphere temperature in each zone.
The furnace temperature control device 10 includes a temperature regulator (TIC) 11, a gas flow rate regulator (FIC) 12, and a combustion air flow rate regulator (FIC) 13.
The temperature regulator 11 receives an in-furnace temperature signal of the soaking zone 1h from a temperature sensor 14 that detects the in-furnace temperature. And the temperature regulator 11 calculates the setting value of the gas flow regulator 12 with respect to the soaking zone 1h based on the furnace temperature signal input from the temperature sensor 14.

Further, the gas flow rate regulator 12 calculates valve opening control based on the set value input from the temperature regulator 11 and the flow rate signal input from the flow rate sensor 15a on the gas pipe, and the gas flow rate adjustment valve 16 Adjust the valve opening. Thereby, the gas supply amount to the gas burner 17 which adjusts the furnace temperature of the soaking zone 1h is controlled.
Further, the combustion air flow rate regulator 13 receives a set value obtained by multiplying the set value inputted from the temperature regulator 11 by the air ratio M, and this flow rate signal inputted from the flow rate sensor 15b on the combustion air piping. And the valve opening of the combustion air flow rate adjustment valve 18 is continuously adjusted.
The furnace temperature control device 10 including the temperature regulator 11, the gas flow rate regulator 12, and the combustion air flow rate regulator 13 includes a temperature sensor 14 and a gas burner 16 in each zone 1a to 1h, and a furnace in each zone 1a to 1h. The internal temperature is measured by the temperature sensor 14, and furnace temperature control is performed to adjust the flow rate of fuel and air to be supplied to the gas burner 16 based on the measured value.

The HSB 2 is a device that performs descaling of the hot high-Si steel material 7 extracted from the heating furnace 1, and by injecting high-pressure water toward the front and back surfaces of the high-Si steel material 7, The scale produced in the surface layer of the high Si steel material 7 is removed.
The sizing press 3 is a device that performs the width reduction of the high Si steel material 7.
The descaling device 4 is a device that performs descaling by injecting high-pressure water onto the front and back surfaces of the high-Si steel material 7 that has been width-reduced by the sizing press 3.

The edger 5 is an apparatus that performs rolling in the width direction of the high Si steel material 7 that has passed through the descaling apparatus 4.
The rough rolling mill 6 is an apparatus that forms a rolled material 20 by rolling a high Si steel material 7 subjected to widthwise rolling to a predetermined thickness.
Here, the rolling mill according to the present invention corresponds to the rough rolling mill 6.

Next, hot rolling of the high Si steel material 7 of the present embodiment will be described with reference to FIGS.
First, as shown in FIG. 1, the high Si steel material 7 is charged into the heating furnace 1. As shown in FIG. 2, the furnace temperature control device 10 arranged in each zone 1 a to 1 h of the heating furnace 1 has a gas supply amount and a combustion air amount to the gas burner 17 based on the furnace temperature detected by the temperature sensor 14. Is controlled so that the front and back surfaces of the high-Si steel material 7 have an accurate temperature difference.
Said exact temperature difference means the case where there exists a temperature difference of the range whose surface temperature of the high Si steel material 7 is 10-20 degreeC higher than the temperature of a back surface.
Here, since the high Si steel material 7 charged in the heating furnace 1 has an oxidizing atmosphere inside the furnace, a scale 21 is generated by oxidation of the surface layer (see FIG. 3A). The scale 21 includes a firelight, and the scale is in a state of being wedged into the ground iron.

Next, the high Si steel material 7 in the hot state heated in the heating furnace 1 was charged into the HSB 2 and generated on the surface layer by injecting high pressure water toward the front and back surfaces of the high Si steel material 7. Part of the scale is removed.
Next, the high Si steel material 7 unloaded from the HSB 2 is carried into the sizing press 3, and the sizing press 3 performs a width reduction of 30 mm or more on the high Si steel material 7 having a width dimension of about 1400 mm. .
When the sizing press 3 reduces the width of the high-Si steel material 7 by 30 mm or more, as shown in FIG. 3B, the rolling of the scale 21 that includes the firelight and bites into the ground iron in a wedge shape. Cracks 22 occur in the direction. The formation of the crack 22 makes it easy to remove the scale 21.

Next, the high Si steel material 7 in which the cracks 22 are generated in the scale 21 is carried into the descaling device 4, and high pressure water is sprayed on the front and back surfaces of the descaling device 4.
At this time, as shown in FIG. 3 (c), when high-pressure water is injected from the nozzle 4a of the descaling device 4 toward the scale 21, the scale 21 in which the crack 22 is generated is divided into small lumps. It is scattered outside from the surface layer of the Si steel material 7 and is completely removed from the surface layer of the high Si steel material 7.

Next, the high Si steel material 7 from which the scale has been completely removed from the surface layer is loaded into the edger 5 and subjected to width direction rolling.
Next, the high Si steel material 7 that has been subjected to the widthwise rolling by the edger 5 is press-fitted by the roughing mill 6 to form a rolled material 20.
According to the hot rolling of the high Si steel material 7 of the present embodiment, the scale 21 is generated in the surface layer of the high Si steel material 7 by heating of the heating furnace 1 and includes a firelight and bites into the ground iron in a wedge shape. In the sizing press 3, the high Si steel material 7 is subjected to a width reduction of 30 mm or more so that a crack 22 is generated, which can be easily removed from the surface layer of the high Si steel material 7. Then, it is divided into small lumps and scattered from the surface layer of the high Si steel material 7 to the outside.

Therefore, the high Si steel material 7 heated so that the temperature difference between the front surface and the back surface becomes an accurate temperature difference in the heating furnace 1 passes through the sizing press 3 and the descaling device 4 immediately before being rolled by the rough rolling mill 6. Therefore, the scale 21 having a high heat transfer coefficient and easily affecting the heat is completely removed from the surface layer, and the heating furnace 1 maintains a state with an accurate temperature difference between the front surface and the back surface. The warpage of the rolled material 20 formed by rolling with the rough rolling mill 6 can be reliably prevented.
In addition, although the heating furnace 1 of this embodiment was made into the heating furnace which has the eight zones 1a-1h which heat the material 3 from the surface and a back surface, the summary of this invention is not limited to this.

DESCRIPTION OF SYMBOLS 1 ... Heating furnace, 1a-1h ... Zone, 2 ... HSB, 3 ... Sizing press, 4 ... Descaling apparatus, 5 ... Edger, 6 ... Rough rolling mill, 7 ... High Si steel material, 10 ... Furnace temperature control apparatus, DESCRIPTION OF SYMBOLS 11 ... Temperature controller, 12 ... Gas flow controller, 13 ... Combustion air flow controller, 14 ... Temperature sensor, 15a, 15b ... Flow sensor, 16 ... Gas flow control valve, 17 ... Gas burner, 18 ... Combustion air flow control Valve, 20 ... Rolled material, 21 ... Scale, 22 ... Crack

Claims (2)

In a hot rolling line that rolls high-Si steel material heated in a heating furnace with a rolling mill,
In the heating furnace, the high-Si steel material is heated so that the temperature of the surface, which is an accurate temperature difference between the front surface and the back surface, is a temperature difference in the range of 10 ° C. to 20 ° C. higher than the temperature of the back surface ,
The line between the heating furnace and the rolling mill is provided with a hot scale breaker and a scale removing unit disposed downstream of the hot scale breaker, and the high Si steel heated in the heating furnace in the hot scale breaker. by injecting high pressure water to the surface and the back surface of the material, to remove the portion of scale formed on the surface of the high Si steel material, in the descaling unit, generating the surface layer of the prior SL high Si steel material A method of preventing warping in a hot rolling line of high-Si steel, wherein a crack is generated in the scale, and the scale divided into a plurality at the crack is removed from the surface layer. The scale removing unit is composed of a sizing press disposed downstream of the hot scale breaker , and a descaling device disposed between the sizing press and the rolling mill,
The high Si steel material that has passed through the hot scale breaker is caused to crack in the scale by being reduced by 30 mm or more in the width direction with the sizing press,
The descaling device injects high-pressure water onto the front and back surfaces of the high-Si steel material that has been width-reduced by the sizing press, thereby removing the scale divided into a plurality of borders from the cracks. The method of preventing warpage in a hot rolling line for high-Si steel according to claim 1.

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