KR101184141B1 - Process for producing hot rolled steel - Google Patents

Abstract

Some or all of one or more surface layers of the surface, back, and side surfaces of the slab in a hot state, which are manufactured by a continuous casting machine and cut into a predetermined length, are driven by an electric rotary cutting tool having a plurality of cutting edges. By using the milled surface cutting device configured, a smooth surface can be obtained by the surface layer treatment method of the hot slab, which cuts a thickness range of 1 mm or more from the slab skin as it is, while providing a smooth surface for the hot slab. The defects under the surface and the skin of the hot slab can be removed with high efficiency without causing deterioration of the quality of the surface and the surface layer portion.

Rotary cutting tools, cutting edges, holders, thermal spraying layers, slabs, coolant furnaces, coolant spray nozzles

Description

Production method of hot rolled steel {PROCESS FOR PRODUCING HOT ROLLED STEEL}

The present invention relates to a method for treating the surface layer portion of a slab in a hot state cast by a continuous casting machine, and more particularly, the present invention relates to a method for producing a hot rolled steel using the slab that has been trimmed by the surface layer portion treatment method.

In continuous casting facilities, slabs of about 10 m length are manufactured from molten steel and sent to the hot rolling line of the next step as raw materials for rolling. Usually, in a hot rolling line, this slab is heated by a heating furnace and then hot rolled with a thin steel plate. In this case, when the slab manufactured in the continuous casting line is charged into the heating furnace of the hot rolling line at a temperature of about 700 ° C. or higher, the heating amount in the heating furnace is reduced, and the fuel raw unit can be reduced. do. This operation method is called hot charge rolling (HCR), and has been widely attempted.

However, the slab contains inclusion defects occurring in the casting step, and in particular, inclusion defects inherent up to several millimeters under the slab skin generate linear scratches on the surface of the steel sheet during the rolling process or the plating process following the next process. Let's do it. This inclusion defect originates in deoxidation products such as mold powder and alumina used in continuous casting, and it is said that inclusions on the order of several hundred microns cause scratches.

Therefore, conventionally, the slab manufactured in a casting facility is hot-pressed or cold-washed after being cooled, and then the entire surface of the slab surface is processed by hot scarf or cold scarfer (scarf). In general, grinding or grinding by a grinder has been generally performed.

However, in the method of cleaning by hot scarper, the slab surface layer portion is melted by high heat, and the slab surface layer portion is locally heated by being blown off while blowing the melt. As a result, there is a phenomenon that the quality of the surface portion of the slab is deteriorated because it causes the concentration of a specific element such as phosphorus (P) or nickel (Ni) in the surface portion of the slab or decarburization of the surface layer.

In the method of cleaning by cold scarpers for cold-laminated slabs, the heating of the slab surface layer where the depth of cut does not change because the slab temperature does not change, so the concentration of the specific element is increased. There are many advantages, such as hard to occur, and the energy loss by coldening the slab is very severe.

In addition, regardless of the hot scarper and the cold scarper, when the slab surface layer is subjected to the entire surface treatment by the scarper, the unevenness having the relief of the height of about 2 mm is generated on the cutting surface of the slab. a lot of works. This occurs because the flammable gas ejection port from the scarper nozzle is divided, and the pitch of the undulation generated on the cutting surface after the scraping by the scarper coincides with the nozzle split pitch. This undulation may cause new surface defects in hot rolled steel in the hot rolling process.

The cleaning by the grinder is remarkably small in efficiency compared to the scarper because the grinder has a low surface removal ability (repair ability). In addition, there is also the removal and adhesion of grindstones that cause surface scratches in steel products, and the use of hot slabs is such that they are used to remove gas-cutting slags at the slab ends.

As described above, any conventional method of cleaning has a risk of causing defects that cause new surface scratches on the skin or surface layer of the slab after the treatment. Therefore, in order to solve this problem, In the treatment of the slab surface layer part, there have been some proposals for a slab treatment method for obtaining a slab without defects on the skin and the surface layer with high productivity.

For example, Patent Document 1: Japanese Patent Laid-Open No. 2004-181561 uses a rotatable cutting edge having a circular cutting edge before cutting a continuously cast slab into a predetermined length by a gas cutter at the base of a continuous casting machine. Then, a trimming method is proposed in which the surface layer portion of the slab in the hot state is cut and removed beyond the oxide film to the steel portion while the cutting edge is rotated by the cutting reaction force from the slab which is a non-cutting body.

The care method proposed by patent document 1 is a method of cutting a plane by the cutting device of a single blade called a shaper. In order to prolong the life of the cutting edge, it is equipped with a free rotating circular cutting edge that rotates by cutting reaction force. It is designed not to catch and to avoid wear of the blade tip.

Here, the rotating circular cutting edge satisfies the function only by having a rotatable structure, but a mechanism for transferring the rotating circular cutting edge along the cutting surface of the slab is required separately. In patent document 1, it is supposed that the slab drive force by the pinch roll of a continuous casting machine or the slab conveyance force of the slab conveyance roller table is suitable for the driving force of the cutting feed of a rotating circular cutting edge.

As removal amount of the defect part in the slab surface layer part immediately after casting, it is empirically about 2-4 mm thickness from the skin. When the overall reaction force of the slab is cut at a thickness of 4 mm and a temperature of 800 ° C., the cutting reaction force is estimated. When the slab width is 1500 mm, the reaction force is 120 to 250 tons. As proposed in Patent Literature 1, it is difficult to obtain a driving force corresponding to such cutting reaction force from the slab driving force by the pinch roll or the slab conveying force of the slab conveying roller table.

For example, a cutting method of reciprocating a plurality of blades with a cutting amount of 100 mm per blade, not the entire width of the slab, may be considered. The cutting reaction takes about 18 tons and the cutting speed is 1 m / sec. Even if the margin of the cutting pitch is taken into consideration, a large number of reciprocating motions of the circular cutting edge are required, and the cutting time is long, which is not realistic.

It is an object of the present invention to obtain a smooth trimmed surface and at the same time eliminate defects in the skin and surface layers of hot slabs cast with a continuous casting machine without causing deterioration in the quality of the skin and surface layers of the hot slab. The present invention provides a method for cleaning the surface layer portion of a hot slab, and at the same time provides a method for producing a hot rolled steel having excellent surface properties using the slab treated by the surface layer treatment method.

Hot-rolled steel manufacturing method according to the first invention for achieving the above object is made of a continuous casting machine, the surface layer portion of any one or two or more of the surface, back surface, side surface of the slab in the hot state cut to a predetermined length. Part or all of the surface layer portion is injected as it is, using a milled surface cutting device composed of a rotary cutting tool having a plurality of cutting edges and rotating with a driving force of an electric motor, in a state where the temperature of the surface layer portion is 600 ° C. or higher and less than 800 ° C. The slab trimmed by the surface layer part method of the hot slab cutting a range of thickness of 1 mm or more from the slab skin is charged into a heating furnace as it is in a hot state, and subsequently hot rolled. The milled surface cutting device is the rotary cutting machine. A cutting chip cooling device that cools the cutting chips cut by the tool by spraying with high pressure water, and air-cools the cutting blades of the rotary cutting tool. Or a cutting edge cooling device for mist cooling, and a cutting chip recovery device for recovering cutting chips.

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The manufacturing method of the hot rolled steel material which concerns on 3rd invention is a 1st invention WHEREIN: The blade edge of the cutting edge of the said rotary cutting tool is comprised by the thermal spray layer of a nickel base alloy.

In the method for producing a hot rolled steel according to the fourth invention, in the first invention, the rotary cutting tool is an internal water cooling structure.

The manufacturing method of the hot rolled steel material which concerns on 5th invention is a 1st invention WHEREIN: The blade end of the said rotary cutting tool is comprised from the heat insulating material or the heat-resistant alloy, It is characterized by the above-mentioned.

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1 is a flow chart showing the flow of the slab from the continuous casting line to the heating furnace of the hot rolling line in the present invention.

2 is a diagram showing a simulation result of slab temperature change analyzed using a general-purpose electrothermal analysis code.

FIG. 3 is a diagram showing a simulation result of the temperature distribution in the slab cross section when about 30 minutes have elapsed from the continuous casting machine.

It is a figure which shows the shear stress in each temperature of steel materials.

FIG. 5 is a diagram comparing cutting resistances of carbon steel, cast iron, and aluminum alloys. FIG.

FIG. 6 is a view showing an example in which a milling type surface cutting apparatus provided with one rotary cutting tool is applied as a device for treating a slab surface layer portion. FIG.

7A and 7B are diagrams showing an example in which a milling surface cutting device having a plurality of rotary cutting tools is applied as a device for treating a slab surface layer.

8 is a view showing an example of a milling type surface cutting apparatus for cutting and trimming the entire surface of the slab.

9 is a view showing an example of the configuration of a milling type surface cutting apparatus for cutting and trimming the front and back surfaces of a slab online.

10 is a view showing the positional relationship between the rotary cutting tool and the hot slab during cutting.

It is a figure which shows the blade edge structure of a cutting edge.

12 is a schematic cross-sectional view of a holder of internal cooling type.

13 is a view showing the installation position of the coolant jet nozzle for cooling the cutting edge and the coolant jet nozzle for cooling the cutting chip.

Fig. 14 is a view showing a state in which the cutting chips are discharged along the cutting edge inclined plane, and at the same time, an installation position of a coolant jet nozzle for cooling the cutting chips.

Reference numerals used in the drawings will be described below.

1: Milling type surface cutting device 2: Rotary cutting tool

2a: rotary cutting tool for surface cutting 2b: rotary cutting tool for backside cutting

2c: Rotary cutting tool for side cutting 3: cutting edge

3a: slope 4: holder

5: thermal spraying layer 6: ceramic plate

7: Coolant 8: Coolant injection nozzle

9: coolant jet nozzle 10: slab inverter

11: roller table 12: slab

13: cutting chip

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail. 1 is a flow chart showing the flow of the slab from the continuous casting line to the heating furnace of the hot rolling line in the present invention.

As shown in FIG. 1, the slab manufactured by the continuous casting line is conveyed to the heating furnace of the hot rolling line which is a next process, in a hot state. During this conveyance process, at a suitable place, such as on a conveyance roller table or in a dedicated surface layer trimming place, at least a defective portion of the surface, the back surface and the side surface of the slab in the hot state is rotated by the driving force of the electric motor. Using a surface cutting device composed of a rotary cutting tool having a plurality of cutting edges, a range of thickness of 1 mm or more is cut from the slab skin in the state of being injected. Prior to cutting processing by the surface cutting device, information on the surface of the slab surface layer is determined by defect detection devices such as an optical surface flaw detection device, a magnetic particle detection device, an ultrasonic flaw detection device, an eddy current sensor, or a mold. The determination is made based on casting performance information such as the amount of fluctuations in the inner surface of the water, and based on the determination result, the defective portion of the skin or the surface layer is partially cut or the entire surface of the surface where the defect is present is cut. In addition, in the case where excellent surface properties are required in the product, the entire surface of the slab surface, the back surface, and the surface layer portions on both sides may be cut without determining whether the slab surface layer portion is trimmed or not. The slab heated at a predetermined temperature and for a predetermined time in the heating furnace of the hot rolling line is hot rolled to produce a hot rolled steel.

Usually, when the slab of the hot state carried out from the casting line is high, it is about 1200 degreeC, and the temperature of the slab charged into a heating furnace as hot charge rolling through a refining process is about 700 degreeC in slab internal temperature. The slab is air-cooled in the air for a period of time from the time it is taken out from the casting line to the next step, and the temperature of the slab skin surface decreases. In FIG. 2, the simulation result of the slab temperature change analyzed by using the general-purpose electrothermal analysis code whose initial temperature is 1200 degreeC as the temperature of the surface and center of a slab is shown. 3 shows the simulation result of the temperature distribution in the slab cross section when the slab was driven out of the continuous casting machine and passed for about 30 minutes.

When the surface layer part of the hot slab is cleaned, it is usually trimmed within 30 minutes after being removed from the continuous casting machine, and the temperature of the slab skin surface at the time of slab surface layer part trimming is also inferred from FIGS. 2 and 3. As it turns out, it becomes temperature of about 800 degreeC (slab internal temperature is about 1000 degreeC). However, the slab corners, etc. are thought to be further lowered to 600 ~ 700 ℃. Therefore, although the slab surface temperature is about 600-800 degreeC, when cutting, a hot layer will come out and slab surface temperature will be 600-1000 degreeC.

Figure 4 shows the shear stress at each temperature of the steel (JIS SS400). Shear stress is proportional to the cutting resistance of the steel, and it can be seen that the cutting resistance of the steel decreases at a high temperature. Regarding the cutting resistance of the cold slab, the cutting resistance in the cleaning of the slab having a temperature of 600 to 800 ° C decreases to 1/2 to 2/3.

FIG. 5 is a diagram showing respective cutting resistances to cutting conditions when milling carbon steel, cast iron and aluminum alloys at room temperature. FIG. As is apparent from Fig. 5, when the cutting resistance of the carbon steel becomes 1/2 or less by increasing the temperature at the time of cutting, the cutting resistance of the carbon steel is almost equal to the cutting resistance of the aluminum alloy, which is equivalent to that of the aluminum alloy. Efficient cutting is possible.

That is, in the present invention, the steel slab at a high temperature of about 800 ° C. is cut by using a milling type surface cutting device composed of a rotary cutting tool having a plurality of cutting edges that rotate with the driving force of the electric motor. The slab surface layer portion can be cut at a cutting speed more than twice that of the machining, and even a milled surface layer cutting device can sufficiently clean the steel slab.

The example which applied the milling type surface cutting apparatus as a trimming device of a slab surface layer part is shown in FIG. Fig. 6 is an example of a milling type surface cutting apparatus having one rotary cutting tool 2, the rotary cutting tool 2 being a disk-shaped holder 4 and a plurality of holders mounted around the holder 4; It consists of the cutting edge 3 of. In this case, the rotary cutting tool 2 has a size equal to or greater than the width of the slab 12, and the entire width of the slab 12 is cut and trimmed by one rotary cutting tool 2. 6, the whole structure of the milling type surface cutting apparatus, such as an electric motor, for rotating the rotary cutting tool 2 is abbreviate | omitted.

The number of installation of the rotary cutting tool 2 which comprises a milling type surface cutting apparatus is not limited to one, It can install in the width direction of the slab 12 in multiple numbers. FIG. 7 is a view showing an example in which a milling type surface cutting device having a plurality of rotary cutting tools 2 is applied as a device for treating a slab surface layer, and FIG. 7 (A) shows two rotary cutting tools 2. It is an example of the milling surface cutting apparatus comprised, FIG. 7 (B) is an example of the milling surface cutting apparatus comprised of three rotary cutting tools 2. As shown in FIG. In the case of providing two rotary cutting tools 2, the size of each rotary cutting tool 2 may be about 1/2 of the slab width, and in the case of n pieces of each of the rotary cutting tools 2 The size can be about 1 / n of the slab width.

The slab 12 carried out from the continuous casting machine is relatively less deformed and is often supported by a milling type surface cutting apparatus equipped with one rotary cutting tool 2 as shown in FIG. When the secondary cooling water distribution becomes nonuniform in the width direction, and the deformation in the width direction of the slab becomes large, or the slab width is large, the deformation in the width direction causes at least the difference in the cutting value to occur. It is preferable to provide the milling type surface cutting apparatus provided with the some rotary cutting tool 2 like A) and FIG. 7 (B). By cutting the slab 12 in the width direction and providing the rotary cutting tool 2, it is possible to prevent cutting unevenness.

FIG. 8 is a diagram showing an example of a milling type surface cutting apparatus for cutting and trimming the entire surface of the slab 12. As shown in FIG. 8, this milling type surface cutting apparatus 1 is provided above the roller table 11 for slab conveyance, and is for two surface cuttings for cutting the surface of the slab 12. As shown in FIG. The rotary cutting tool 2a and the two side cutting rotary cutting tools 2c for cutting the side surface of the slab 12 are provided. The milling surface cutting device 1 is equipped with an electric motor for driving the surface cutting rotary cutting tool 2a and the side cutting rotary cutting tool 2c, or a mount for holding them. Omitted.

In order to clean the slab 12 using this milling type surface cutting apparatus 1, the structural example of the milling type surface cutting apparatus for cutting and trimming the front and back surfaces of the slab 12 is shown, for example in FIG. As described above, the milling type surface cutting apparatus having the above-described configuration can be quickly implemented by arranging in series above the roller table 11 for slab conveyance with two slab inverters 10 interposed therebetween. First, after cutting the surface and side surfaces of the slab 12 with the milling type surface cutting device 1, the slab 12 is inverted with the slab inverter 10, and then the back surface of the slab 12 is milled. It cuts with the surface cutting device 1A. The milling surface cutting device 1A has the same configuration as the milling surface cutting device 1, and is provided with two rotary cutting tools 2b for cutting the back surface from cutting the back surface of the slab 12. . The slab 12 in the hot state is clamped by the roller table 11 to the lower side of the side or the front and the lower side of the slab 12, and the milled surface cutting apparatuses 1 and 1A to the roller table 11 The cutting is performed while traveling in the direction of), or the milling surface cutting apparatuses 1 and 1A are fixed, and the slab 12 is cut while moving on the roller table 11. In addition, since the milling type surface cutting apparatus 1 and the milling type surface cutting apparatus 1A have the same structure, they are collectively represented as "milling type surface cutting apparatus 1" hereafter.

Since the casting speed of the continuous casting machine is about 2 m / min, when the trimming time of the slab 12, i.e., the cutting feed rate of the slab 12 is later than the casting speed, the slab 12 in the milled surface cutting device 1 Will stay. Although 2 m / min is very fast as the feed rate of milling cutting of steel, since the slab 12 is in a hot state, the normal cutting feed of aluminum is obtained as mentioned above, and it is realizable.

Specifically, the cutting speed is 500 to 1000 m / min, the feed per blade is 0.5 to 1.0 mm, and the number of blades of the cutting edge 3 mounted on the rotary cutting tool 2 is 15 to 36 (24 to 10 degrees). By mounting the cutting edge 3 at a pitch), a cutting feed speed of 2 to 3 m / min can be realized even if the slab surface layer portion is cut at full width and full length. The number of the blades of the cutting edge 3 is preferably 20 to 30 pieces. The cutting spindle total required power at that time also becomes less than 500 kW when the cutting resistance is 1000 MPa (100 kgf / mm) or less, which is a practical facility. In the seal line, the slab trimming lines shown in Fig. 9 are arranged in a row so that the trimming of the entire width and the entire length of the slabs of the entire number is possible without retaining the slab carried out from the continuous casting machine.

The big problem when cutting the slab in the hot state with the milling type surface cutting apparatus 1 is that the slab which is the workpiece is in a high temperature state of 800 ° C. and is affected by the heat of the slab. Since the cutting time of one surface of the slab is about 5 to 7 minutes, the whole device of the cutting edge 3, the holder 4 and the milled surface cutting device 1 of the rotary cutting tool 2 is hot It is exposed to contact heat, radiant heat, etc. from the slab. In particular, the cutting edge of the cutting edge 3 is the most severe condition. However, since the cutting resistance is less than half of the cold steel, the temperature rise of the cutting edge 3 by cutting is very small.

Since the cutting speed is high at 500 m / min to 1000 m / min, the time that one cutting edge 3 is in contact with the hot slab for cutting is less than 2 seconds and the idle time is several times the contact time with the hot slab. ), There is originally sufficient air cooling time. However, in the milling type surface cutting apparatus 1, as shown in FIG. 10, the whole rotary cutting tool 2 is in the distance very close to the skin surface of a hot slab, and especially the lower surface of the rotary cutting tool 2 Since the radiant heat continues to be directly received from the slab at 800 ° C, the blade edge of the cutting edge 3 and the lower surface of the holder 4 have a very high heat load. In addition, the present invention utilizes a decrease in cutting resistance due to the high temperature of the hot slab, and the coolant for cooling the cutting edge of the cutting portion causes the temperature of the slab skin and the surface layer portion to decrease, thereby actively cooling the cutting edge during cutting. Can not be used as

From this, it is preferable to perform the following four heat dissipation measures with respect to the cutting edge 3 and the holder 4 of the rotary cutting tool 2. That is, (1) the blade edge of the cutting edge 3 is formed of the thermal spray alloy layer of Ni-based alloy, and (2) the Ni-based alloy of the heat-resistant alloy is sprayed on the lower part of the holder 4, or the holder 4 (3) A cooling water channel is provided inside the holder 4 of the rotary cutting tool 2, and the holder 4 is an internal water cooling structure. Cooling of the blade edge of the cutting edge 3 at the time of idle cooling of the cutting edge 3 is carried out. Hereinafter, the respective heat radiation measures will be described.

(1) cutting edge material

When cutting a high temperature material, the heat load of the blade tip is large, abrasion may be accelerated, or chipping of the blade may occur due to thermal shock. In addition, when the cutting chip at the time of cutting is discharged along the inclined surface of the cutting edge 3, it is hot and the surface pressure by the cutting causes the welding phenomenon of the cutting chip (similar to the formation of the constituent edge), but the cutting chip itself May be deposited on the inclined surface of the blade edge).

In order to prevent this welding phenomenon, a planar cutting test with a cutting width of 100 mm and a depth of several mm is performed on a hot steel material of 1000 ° C. for ceramic, cermet (TiC, TiN), super alloy (WC), and gas turbine blade. It carried out using the cutting tool which consists of each material of the super heat-resistant alloy (Fe base alloy, Co base alloy, Ni base alloy) used for the process.

As a result of the experiment, adhesion of the cutting chip did not occur in the cutting tool made of ceramic and the cutting tool made of Ni-based alloy. However, the ceramic cutting tool could not withstand the surface pressure, and cracks immediately occurred and were broken. On the other hand, the cutting tool made of Ni-based alloy withstands the heat load and the cutting load, and no cutting chips are attached. In particular, in the Ni-based alloy, the state of the used state was better than that of the newly produced state in terms of welding the cutting chips. It was found that the Ni-based alloy concentrates specific elements such as Al on the surface layer and forms oxides such as Al on the surface, further preventing the adhesion of cutting chips during cutting.

In other words, it was found that the Ni-based alloy was particularly excellent as the cutting edge material of the cutting edge 3. Since the Ni-based alloy is basically an alloy that can withstand high temperatures of 1000 ° C or higher, there is no problem even if the cutting of the hot slab is performed for a short time without cooling the blade edge of the cutting edge 3.

Components of the Ni-based alloy which are very suitable as the cutting edge material of the cutting edge 3 used in the present invention are C: 0.01 to 0.1% by mass, Cr: 17 to 20% by mass, Mo: 4 to 7% by mass, and Co: 10. 14 mass% and Al: 1-3 mass% are contained, and remainder is made into Ni and a small amount of unavoidable impurities. As shown in FIG. 11, the cutting edge structure of the cutting edge 3 should just form the thermal spraying layer 5 of Ni-based alloy of about 5 mm as a finishing thickness.

(2) the lower structure of the holder

As shown in FIG. 10 mentioned above, the lower part of the holder 4 of the rotary cutting tool 2 continues to receive high temperature radiant heat from the hot slab skin surface at the time of cutting. Due to the structure of the rotary cutting tool 2, the lower part cannot be cooled directly by spraying of cooling water. Therefore, as shown in FIG. 11, the ceramic plate 6, which is a heat insulating material, is mounted on the entire lower surface of the holder 4, or the lower portion of the holder 4 by the thermal spray layer 5 of the Ni-based heat-resistant alloy. In this configuration, the heat resistance of the holder 4 is improved.

(3) internal water cooling of the holder

12 is a heat dissipation countermeasure of the holder 4, in which a cooling water path 7 for cooling is provided inside the holder 4, and the lower part of the holder 4 is cooled. This cooling water passage 7 is solely for preventing the temperature rise of the entirety or the bottom of the holder 4. As shown in FIG. 12, cooling water is sent to the inside of the holder 4 from the upper part of the holder 4, and cooling water flows toward the lower part of the holder 4. As shown in FIG. The coolant is allowed to leak out of the gap between the holder 4 and the ceramic plate 6, which is a heat insulator, or from the water outlet outlet installed at the circumference of the holder 4. If the cooling water is a circulatory system, it becomes complicated, so it is basically an open system. The cooling water passage 7 may be a closed system as a circulating system. Moreover, it is preferable to devise the cooling water path 7 in the holder 4, to cool the whole lower part of the holder 4, and to cool the part of the cutting edge 3 as well.

(4) cooling of cutting edge

If rapid temperature rise due to contact with the hot slab and rapid cooling by direct injection to the blade edge of the cooling water are repeated, the thermal spraying layer of the Ni-based alloy is different from the thermal expansion difference of the Ni-based alloy due to thermal shock or the like. There exists a danger of peeling of (5). Therefore, although the edge of the cutting edge 3 is not actively cooled by the cooling water, it is necessary to suppress the temperature rise at the time of the revolution of the cutting edge due to the radiant heat from the hot slab. The coolant jetting nozzle 8 is provided in the idle range of the cutting edge 3, and cooling is performed by the coolant jetting nozzle 8 when the cutting edge 3 is not thermally shocked. Specifically, the cutting edge 3 is cooled by injecting air or mist of air and water from the coolant injection nozzle 8.

Another problem in the case of cutting a slab in a hot state with the milling type surface cutting apparatus 1 is that it is difficult to process the cutting chip because the cutting chip by cutting is hot.

As shown in FIG. 14, the discharge of the cutting chip 13 in the cutting of the hot slab is basically the same as the normal cold cutting, and the cutting chip 13 is disposed along the inclined surface 3a of the cutting edge 3. Discharged. However, the cutting chip 13 in a high temperature state is weak in strength and easily folds in during discharge, and in the cutting of high temperature materials, the cutting speed of the cutting chip 13 is reduced from the adhesion of the cutting chip 13 and the inclined surface 3a. Tends to be late and the cutting chip compression ratio tends to be large. Therefore, the thickness of the cutting chip becomes larger than the cutting depth thickness. In particular, in the surface layer of the hot slab, the cutting width becomes the slab width, the length of the cutting chip 13 is equal to the cutting width, and the cutting chip 13 having the length equal to the slab width curls. Discharged.

From the above, in the case of hot cutting, the cutting chip 13 is not discharged smoothly, but is blocked between the cutting edges 3 of the rotary cutting tool 2 or rolled up by the rotary cutting tool 2. There is a risk of entering. In order to solve this problem, as shown in Fig. 14, a cooling water jet nozzle 9 is provided as a cutting chip cooling device, and the cutting chip 13 is fitted with high pressure water from the cooling water jet nozzle 9 It is desirable to improve the discharge of 13). In this case, since the temperature decreases, the high pressure water does not directly hit the edge of the cutting edge 3, and the cooling water is sprayed at a predetermined position of the cutting chip 13 discharged along the inclined surface 3a. As shown in FIG. 13, one coolant jet nozzle 9 is provided on each cutting edge 3, and the coolant jet nozzle 9 also rotates in synchronization with the cutting blade 3. do.

Since the injection pressure of cooling water is the cutting chip 13 of high temperature, it is preferable to inject by the water pressure more than tearing a boiling film, Therefore, it injects by the pressure of about 0.2 Mpa or more. In addition, the height position at which the cooling water is injected is discharged to the upper surface of the holder 4 along the inclined surface 3a of the cutting edge 3, and the cooling water at the position where the cutting chip 13 starts to curl. Spray it.

By cooling the cutting chips in this way, the cutting chips are not folded in, the cutting chips curl according to the shape of the inclined surface, and the discharge of the cutting chips is improved. When the cutting chip discharge of the upper part of the blade tip inclined surface is improved by the cooling of the cutting chip, the entire cutting chip is also cooled and indirectly cooled to the cutting chip near the blade tip. This cooling effect improves the discharge speed, improves the cutting chip compression ratio on the blade tip inclined surface, and reduces the thickness of the cutting chip, thereby making it possible to effectively process cutting chips such as chip breakers and the shape of the cutting chips. It becomes easy to become a favorable spiral shape or vortex shape, and also cutting chip collection becomes easy. In addition, the cooling of the cutting chip further prevents oxidation of the surface of the cutting chip, so that the scrap quality of the cutting chip is improved.

As a cutting chip recovery device for collecting the cutting chips, a suction duct is provided on the upper circumference of the rotary cutting tool 2 of the milling type surface cutting device 1, and a suction blower is sucked through the suction duct. Can be. Further, a cutting chip recovery pit is provided next to the roller table 11 for slab conveyance, and the cutting chip is blown horizontally by the centrifugal force of the rotary cutting tool 2 to drop the cutting chip on the cutting chip recovery pit, or Alternatively, the cutting chips remaining on the surface of the slab may be dropped onto the cutting chip recovery feet next to the conveying line with a mechanical scraper, high pressure air, or high pressure water to recover the cutting chips.

Moreover, heat resistance measures of the whole milling type surface cutting apparatus 1 are also needed. Basically, to prevent radiant heat from the hot slab, a shielding plate or the like is installed on the main movable shaft, and the local cooling of the device is performed by air cooling or mist cooling.

As described above, according to the present invention, since the surface layer part of the hot slab is cleaned using the surface cutting device 1 composed of the rotary cutting tool 2, all surfaces of the surface, the rear surface, and the side surface of the hot slab It is possible to reliably remove the defects in the skin and the surface layer of the slab in the hot state, and if the inclusion defects or the like occur in the skin or the surface layer of the slab during continuous casting, without cooling the cold piece, It is possible to charge the slab without defects in the skin and the surface layer into the heating furnace of the hot rolling line in the hot state, and as a result, it becomes possible to manufacture a steel sheet having excellent surface properties even in hot charge rolling.

In addition, this invention is not limited to the range of the said description, A various change is possible. The above description has been given as an example of a milling surface cutting device 1 having a disk-shaped rotary cutting tool 2, wherein a milling surface layer composed of a cylindrical cutting tool (screw blade for cylindrical milling) having a screw on its surface. The present invention can also be implemented using a cutting device.

According to the present invention, the surface layer part of the slab in the hot state is carried out by using a surface cutting device composed of a rotary cutting tool. It is possible to reliably remove the hot-rolled slab without defects in the skin and the surface layer without cooling the slab to the cold part even if an inclusion defect or the like occurs during the continuous casting. It becomes possible to charge to the heating furnace in the hot state, and can utilize the heat which a slab has effectively. In addition, in the method of cleaning according to the present invention, the smoothness of the surface of the slab after trimming is significantly improved in the conventional cleaning method. It can reliably reduce, and it becomes possible to achieve energy saving and quality improvement of a steel plate.

In addition, in the case of the scraping by the scarf which is conventionally used for the entire surface finish of the slab surface layer part, the layer scraped off by the turning becomes a complete iron oxide and can be reused as an iron source. Accompanied thermal energy was necessary, and manufacturing cost was raised by that much. On the other hand, in the cleaning method of the present invention, since the cutting chips generated by cutting the surface layer portion are recovered as iron oxides with little iron oxide content, the heat energy accompanying the reducing agent and the reduction is not available when reused as an iron source. In comparison, the manufacturing cost can be reduced.

Moreover, when hot-stacking the slab which performed the surface layer part trimming by the trimming method by this invention, a hot rolled steel material with very few surface defects can be obtained.

Claims (7)

Made of a continuous casting machine, the surface layer portion of any one or two or more of the surface, back surface, side surface of the slab in the hot state cut to a predetermined length, the temperature of the surface layer portion is 600 ℃ to less than 800 ℃ in, By using a milling type surface cutting device composed of a rotary cutting tool which has a plurality of cutting edges and rotates with the driving force of an electric motor, the surface layer part of a hot slab is cut by a surface layer of a hot slab that is cut from a slab skin as it is injected. The trimmed slab is charged into a heating furnace as it is in a hot state and subsequently hot rolled; The milling type surface cutting device includes a cutting chip cooling device for cooling the cutting chips cut by the rotary cutting tool by spraying with high pressure water, and a cutting edge cooling device for air cooling or mist cooling the cutting edge of the rotary cutting tool. And a cutting chip recovery device for recovering the cutting chips. delete The method of claim 1, A blade tip of each cutting edge of the rotary cutting tool is a method of manufacturing a hot rolled steel, characterized in that the thermal spraying layer of a nickel-based alloy. The method of claim 1, The rotary cutting tool is a method of manufacturing a hot rolled steel, characterized in that the internal water-cooled structure. The method of claim 1, Blade end of the rotary cutting tool is a method of manufacturing a hot rolled steel, characterized in that consisting of a heat insulating material or a heat-resistant alloy. delete delete

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