JP2011161504A - Device and method for surface conditioning of continuously cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for the surface conditioning of a continuously cast slab, which can eliminate defects on the surface of the continuously cast slab before the hot rolling of a steel product and can prevent a deep crack from being caused at a part where scarfing is commenced. <P>SOLUTION: A solenoid type induction coil 5 is placed on the upstream of a scarfer 1 which scarfs the longitudinal ends of the slab 3 with gas to preheat the longitudinal ends of the slab 3 by electromagnetic induction heating before scarfing. Scarfing by the scarfer 1 is commenced after the surface layer of the longitudinal ends of the slab 3 is preheated by the induction coil 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a continuous casting slab surface care apparatus and method for removing defects on the surface of a continuous casting slab before hot rolling of steel products, and in particular, it is possible to prevent deep digging at the start of welding. The present invention relates to a surface care apparatus and method for a continuous cast slab.

Surface defects such as surface cracks and oscillation marks often occur on the surface of a slab (steel piece) produced by continuous casting of steel. In addition, non-metallic inclusions and gas bubbles (Ar gas, N ₂ gas, etc.) mainly composed of alumina and mold powder are easily collected on the surface layer of the continuous casting slab, and when the steel material is produced by rolling the continuous casting slab as it is, A slab surface caused by slab surface defects and a slab surface caused by inclusions on the steel slab surface layer are generated.

  In order to deal with the above problems, surface care is currently generally performed in which the surface layer (depth 2 mm to 4 mm) of the slab is cut by gas scarfing with oxygen gas before hot rolling. An apparatus for performing gas scarfing is called a scarf or scarf unit. In gas scarfing, the pre-heating gas (combustion gas) is pre-injected to preheat the portion to be cut and then the oxygen and oxidative combustion reaction of oxygen and oxygen generated by blowing oxygen gas is used. In general, the welded start portion is set at a position of about 50 mm from the end portion in the slab longitudinal direction in order to prevent the slab end portion from sagging. However, this preheating method inevitably has a problem that an uncut portion (slab endmost portion) is generated. Further, as shown in FIG. 2, since preheating is performed with a preheating flame with an inclination angle (about 32 °) with respect to the slab horizontal direction as shown in FIG. 2, temperature control in the slab thickness direction is difficult, and depending on the preheating time and preheating gas pressure, Deep digging of the preheated part occurs. It is known that many oxides resulting from the oxidation reaction of iron are generated on the surface of the preheated portion where deep digging has occurred, which causes surface defects after rolling. For this reason, it is necessary to grind the uncut and deep slab end of the slab after grinding with a scarf with a grinder, which not only increases the work load, but directly reheats the high-temperature slab without reheating. There is a problem in that the HDR and slab to be rolled are disturbed by DHCR which is charged into the heating furnace at a high temperature, and the fuel intensity of hot rolling is deteriorated.

In order to solve the above problems, Patent Document 1 proposes a surface care method in which a slab surface layer is preheated by a plasma flame and then is cut by oxygen gas.
Patent Document 2 proposes a method for removing scale after heating the surface of a slab with a solenoid induction heating device.

JP 59-163076 A JP 2003-170201 A

  In the method described in Patent Document 1, the preheating time can be shortened as compared with the conventional gas scarfing preheated with oxygen gas, but the plasma flame has a high energy density and is not suitable for heating only the surface layer. There is a problem that deep digging remains. Moreover, in the method described in Patent Document 2, since it is necessary to reciprocate the slab a plurality of times in order to scale off the surface layer of 2 mm or more, there is a problem that the work time becomes long and the productivity is lowered.

  As mentioned above, surface care is usually performed by gas scarfing for surface treatment of continuous cast slabs, but deep digging due to preheating at the start of welding and unmachined parts at the end of the slab are surface defects after rolling. For this reason, the surface is ground by a grinder after the scarfing and the work load is increased and the DHCR is lowered. This is an unsolved problem.

In order to solve the above-mentioned problems, the present invention reduces the deep digging of the starting portion of the cutting, can omit the grinding process by the grinder, and can continuously perform the cutting of 2 mm or more by one gas scarfing. The object of the present invention is to provide a means for cleaning the surface of the cast slab, and the gist configuration is as follows.
(1) A continuous cast slab care device for removing surface defects of a continuously cast slab before hot rolling, wherein the melted slab longitudinal end is upstream of a scarfer which is cut by gas scarfing. A continuous cast slab care apparatus comprising a solenoid type induction coil for preheating the longitudinal end of a slab before being cut by electromagnetic induction heating.
(2) The continuous cast slab care device according to (1), wherein the scarf is a member that performs a one-time gas scarfing operation on a surface layer of 2 mm or more of the continuous cast slab.
(3) A method for surface care of a continuously cast slab using the surface care device according to (1), wherein the surface layer at the end in the longitudinal direction of the slab is preheated by the solenoid-type induction coil, and then is cut by the scarf A method for surface care of a continuous cast slab, characterized by starting the process.
(4) The continuous casting slab care method according to (3), wherein the melting is performed by gas scarfing a surface layer of 2 mm or more of the slab once.

  According to the present invention, it is possible to perform the cutting of the end of the slab, and it is possible to clean the surface of the continuously cast slab that does not cause deep digging of the preheated portion. Therefore, it is possible to omit the grinder process after the fusing by the scarf, and it is possible to provide a steel piece free from surface defects after the rolling process.

The schematic diagram which shows the outline | summary of the surface care apparatus and method of the continuous casting slab of this invention Schematic diagram showing an overview of conventional continuous casting slab surface care equipment and methods Slab longitudinal cross-sectional schematic diagram showing an example of slab surface properties after maintenance by the surface care apparatus and method for continuous cast slabs of the present invention Slab longitudinal cross-sectional schematic diagram showing an example of slab surface properties after maintenance by a conventional continuous slab surface care apparatus and method A bar graph showing the defect occurrence rate of a coil obtained from a steel piece subjected to a conventional care method and the defect occurrence rate of a coil obtained from a steel piece subjected to a care method according to the present invention

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is an overview of a conventional general slab surface care apparatus and method. The scarfer (scarf unit) 1 for performing gas scarfing has a width of about 250 mm and is arranged in the width direction of the slab 3 (direction perpendicular to the paper surface). The preheating flame 2 shown in FIG. 2 preheats a portion about 50 mm from the end of the slab, and blows oxygen gas to the preheated portion to cause an oxidation combustion reaction of iron. The preheating time is, for example, about 1 minute for an 800 ° C. slab. Iron oxide is melted by reaction heat and blown off by the momentum of oxygen gas to be removed. Once the reaction is started, the vicinity is heated by the reaction heat, so that the cutting is continued by supplying only oxygen gas after the start of the cutting. In this conventional method, not only does the preheating time take long, but also the temperature control in the slab thickness direction is difficult because the preheating of the welding start portion is performed by the injection of the preheating flame, and the deeper than the desired cutting depth is deepened. Occurs (FIG. 4). Since deep slab surface digging and uncut parts will cause surface defects after hot rolling, the slab surface must be ground with a grinder after cutting with a scarf. If the preheating is insufficient, the desired depth of cutting cannot be obtained and it is necessary to carry out scarfing a plurality of times.

  The present invention makes it possible to clean the surface of a continuously cast slab without causing the above problems, and FIG. 1 shows an outline of the surface care apparatus and method for a continuously cast slab of the present invention. In the present invention, an induction coil (solenoid induction coil) 5 for preheating the surface layer of the continuously cast slab by electromagnetic induction heating is disposed upstream of the scarfer 1. The induction coil 5 is disposed so that the slab 3 can pass through the induction coil 5 as shown in FIG. When an alternating current is passed through the induction coil, a high-density eddy current is generated near the surface of the slab, and the surface generates heat due to the Joule heat. This eddy current becomes stronger closer to the surface of the slab and becomes weaker exponentially as it goes inside (skin effect). In general, the current penetration depth δ [cm] used as an index representing the penetration depth of the eddy current into the conductor is expressed by the equation (1).

  Here, ρ is a specific resistance [μΩcm], and μ is a relative permeability. According to this equation, the heat input depth can be controlled by the frequency of the alternating current, and it is possible to heat up to a desired depth of cutting. For example, when ρ = 120 and μ = 1, in order to obtain a depth of cutting of 2 mm or more by one gas scarfing, the frequency may be set to about 15000 Hz. In addition, by connecting induction coils in the longitudinal direction, it is possible to perform uniform heating in the longitudinal direction, and compared to conventional preheating with a scarf, it is possible to perform uniform preheating in the longitudinal direction and thickness direction of the slab, There is no deep digging of the preheating part. By performing gas scarfing with oxygen gas after preheating the slab end by induction heating, it is possible to perform cutting without generating deep digging between the uncut portion and the preheated portion as shown in FIG. According to the knowledge of the inventors, the induction coil 5 is installed as shown in FIG. 1, and the preheating portion is set to about 100 mm from the end of the slab, so that it is possible to stably perform the cutting by gas scarfing after preheating. It is.

That is, the present invention provides a scarfer with a solenoid-type induction coil 5 that can electromagnetically control the heating temperature distribution in the slab thickness direction in order to prevent deep digging at the welding start portion and enable the welding from the slab end. It arrange | positions in the upstream of 1, It is characterized by the above-mentioned.
Here, the solenoid induction coil used in the present invention needs to have an output of about 100 kW. With an induction coil with such an output, for example, the time required to preheat the surface of a slab of about 800 ° C. to a temperature sufficient for the next process of cutting (about 900 ° C.) is about 10 seconds, It has sufficient capacity for process production.

  Examples of the present invention are shown below. The output of the induction coil was 100 kW, and the frequency was 15 kHz. Moreover, the target cutting depth was 4 mm, and the cutting speed by the scarf after preheating was 15 mpm. A continuous cast slab (width 1500 mm, length 9000 mm, thickness 230 mm, surface temperature about 800 ° C.), 100 mm in the longitudinal direction, was preheated in the induction coil for 10 seconds and then preheated under the above conditions, and then was cut by a scarf. However, the preheated part is not deeply drilled, the slab edge is not cut or sagging, and both the preheated part and the steady part are cut by the target cutting depth, and the surface of the slab after the cutting is uneven. There was no beauty. In addition, after rolling the surface with a conventional scarf and rolling the slab whose edge was ground by a grinder and the slab whose surface was cleaned by the cleaning method of the present invention (without grinder grinding), the surface defect generation ratio in the cold rolled coil Comparing (coil unit), the coil obtained from the slab that had been cared for by the conventional scarf and the end grounder had a defect occurrence rate of 1.2%, whereas the caring method of the present invention was applied. The coil obtained from the slab was 0.6%, and it was found that the ground grinding in the next step can be omitted in the care method of the present invention. In addition, in the conventional care method using a scarfer, the time taken for the cutting was 90 seconds on average (preheating 60 seconds, actual welding 30 seconds), whereas in the care method of the present invention, the average time was 40 seconds (preheating 10 seconds, It was found that the working time of the present invention can be greatly reduced as compared with the conventional cleaning method.

  As is clear from the above examples, the slab surface care apparatus and method of the present invention can provide a steel slab in which a grinder process after fusing by a scarf can be omitted and no surface defects are generated after the rolling process. I was able to.

1 Scarfer (scarf unit)
2 Preheating flame by conventional gas scarfing
3 Slab (continuous casting slab)
4 Transport roll
5 Induction coil (solenoid type induction coil)
6 Uncut slab
7 Slab after maintenance according to the invention
8 Slab after maintenance by conventional technology

Claims (4)

  A continuous cast slab care device for removing surface defects of a continuous cast slab before hot rolling, wherein the slab longitudinal direction end is cut upstream of a scarfer which is cut by gas scarfing. A continuous cast slab care device comprising a solenoid induction coil for preheating the longitudinal end portion of the previous slab by electromagnetic induction heating.   2. The continuous cast slab care device according to claim 1, wherein the scarf is for scraping a surface layer of 2 mm or more of the continuous cast slab by one gas scarfing.   A surface care method for a continuous cast slab using the surface care apparatus according to claim 1, wherein the surface layer at the end portion in the longitudinal direction of the slab is preheated by the solenoid type induction coil, and then the cutting by the scarf is started. A surface care method for a continuously cast slab characterized by the above.   The method for caring for a continuously cast slab according to claim 3, wherein the overcutting is performed by gas scarfing a surface layer of 2 mm or more of the slab.

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