EP3395958A1

EP3395958A1 - Apparatus and method for steel sheet thermal treatment

Info

Publication number: EP3395958A1
Application number: EP16879246.3A
Authority: EP
Inventors: Yeong Seob Kueon
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2015-12-23
Filing date: 2016-12-13
Publication date: 2018-10-31
Also published as: JP6692431B2; KR20170075231A; WO2017111379A1; JP2019506524A; KR101758517B1; CN108603238B; CN108603238A; EP3395958A4

Abstract

A steel sheet thermal treatment apparatus according to an embodiment of the present invention may comprise: a body unit which is provided on a movement path of steel sheets which are continuously being produced; and an irradiation unit which is provided on the body unit and comprises a plurality of line irradiation units for irradiating laser, on the surface of the steel sheets, in the form of a line with respect to the width direction of the steel sheets so as to thermally treat the steel sheets, wherein each line irradiation unit irradiates energy which is different from that of at least one other line irradiation unit.

Description

[Technical Field]

The present disclosure relates to an apparatus and a method for steel sheet thermal treatment, and more particularly, to a thermal treatment of a steel sheet, a blank material, by laser.

[Background Art]

In general, a steel sheet which is continuously produced passes through an annealing furnace and a cooling apparatus as a thermal treatment, which results in a change in characteristics of the steel sheet. However, the above-mentioned process may take an excessively long time to perform heating, maintenance, and cooling, and also affects the inside of the steel sheet, which are problems, in that it requires a lot of productivity and high costs.
In recent years, in order to solve the above-mentioned problems, an attempt has been made to irradiate a surface of the steel sheet with energy having high energy density, and various methods have been proposed.
Since the above-mentioned method merely relates to a method and a technology of scanning collected energy, that is, point energy on the surface of the steel sheet and the steel sheet, a target to be processed, is processed in a stationary state, there is a problem in that productivity is low.
In other words, the above-mentioned conventional methods have a technical difficulty to process a large area at a high speed. For example, in processing a surface on which the steel sheet of the blank material having a width of about 1,200mm continuously moves at 50m per minute, there is a limitation in processing a large area with a narrow point laser beam.
In addition, in recent years, for the purpose of lightening automobiles due to the global warming problem, for steel sheets used in automobiles, a tailor welded blanket in which a thick steel sheet is used where strength is required and a relative thin steel sheet is welded and used where strength is not required, or a tailor welded coil in which steel sheets having different thicknesses or strengths are continuously welded and used are used.
According to the conventional methods, the strength of the welded part is different from that of the basic material due to the welded part, and as a result, it has an adverse effect on a design of a metal mold during processing, and there is a problem in that the welded part is broken at the time of molding using a mold.
In addition, there is a problem in that it takes a lot of cost to transport the steel sheets for processing due to different thicknesses of the steel sheets, and since the blank material is produced with a batch processing rather than the continuous processing, it is not only low in productivity but also has a disadvantage that a manufacturing cost is increased.
Therefore, it is necessary to study an apparatus and a method for steel sheet thermal treatment for solving the above-mentioned problems.

[Disclosure]

[Technical Problem]

An aspect of the present disclosure is to provide an apparatus and a method for a steel sheet thermal treatment capable of forming and providing different strengths in at least one portion in a width direction of steel sheet formed of a blank material, which is continuously produced.

[Technical Solution]

According to an aspect of the present disclosure, an apparatus for a steel sheet thermal treatment includes a body unit provided on a movement path of a steel sheet which is continuously produced; and an irradiation unit provided on the body unit and including a plurality of line irradiation parts irradiating a laser onto a surface of the steel sheet in a line shape for a width direction of the steel sheet to thermally treat the steel sheet, wherein each of the line irradiation parts irradiates an energy different from the energy irradiated by at least the other line irradiation part.
The irradiation unit may include at least one high output line irradiation part provided in a portion in the width direction of the steel sheet; and at least one low output line irradiation part irradiating a laser with an energy lower than the high output line irradiation part and provided to be in parallel to the high output line irradiation part.
The apparatus may include a cooling unit provided in the body unit to be positioned downstream of a movement direction of the steel sheet as compared to the irradiation unit.
The apparatus may include a tension unit positioned in at least one of an upstream portion and a downstream portion in a movement direction of the steel sheet with respect to the irradiation unit and provided in the body unit to form tension in the steel sheet.
The tension unit may include an upstream guide roll provided in the body unit to guide a movement of the steel sheet; a downstream guide roll provided in the body unit to be spaced apart from the upstream guide roll by a predetermined interval in the movement direction of the steel sheet; and a movement roll provided between the upstream guide roll and the downstream guide roll and forming tension by pushing the steel sheet to one side.
The line irradiation part may include an irradiating supporting part coupled to the body unit; a plurality of point irradiation parts provided to the irradiating supporting part to be in parallel to each other and discharging the laser; and a line lens part provided to be coupled to end portions of the plurality of point irradiation parts irradiating the laser.
The line irradiation part may include a condensing lens part provided to the irradiating supporting part and adjusting a distance with an end portion of the line lens part to collect the laser irradiated onto the steel sheet.
The plurality of point irradiation parts may be disposed to be parallel to each other in a line shape to irradiate the laser in one line shape, or may be disposed to be parallel to each other in a surface shape to irradiate the laser in a plurality of line shapes.
According to another aspect of the present disclosure, a method for a steel sheet thermal treatment includes disposing an irradiation unit irradiating a laser of a line shape on a movement path of a steel sheet, on the steel sheet; and irradiating at least one region in a width direction of the steel sheet which is continuously moved with the laser having energy different from the other region.
The method may include, after the irradiating of the laser, cooling the steel sheet.
The method may include imparting tension in which flatness of the steel sheet is sensed after the disposing of the irradiation unit, and the flatness of the steel sheet is increased by the tension before the irradiating of the laser.

[Advantageous Effects]

As set forth above, according to an exemplary embodiment in the present disclosure, the apparatus and the method for a steel sheet thermal treatment may form different strengths in at least one portion in a width direction of the steel sheet formed of the blank material, which is continuously produced.
Thereby, the existing tailor welded blanket or the tailor welded coil in which the steel sheets having different thicknesses or strengths is continuously welded and used may be replaced.
In addition, since the strength may be continuously modified for the steel sheet which is continuously produced, a rate of production of the steel sheet may be increased and productivity of the steel sheet may be improved.

[Description of Drawings]

FIG. 1 is a front view showing an apparatus for a steel sheet thermal treatment according to the present disclosure.
FIGS. 2 and 3 show a state in which different strengths are continuously formed in at least one portion in a width direction of the steel sheet by the apparatus for a steel sheet thermal treatment according to the present disclosure.
FIG. 4 is a front view and a perspective view showing a line irradiation part in the apparatus for a steel sheet thermal treatment according to the present disclosure.
FIG. 5 is a side view showing an apparatus for a steel sheet thermal treatment according to the present disclosure.
FIG. 6 is a front view showing an arrangement of a point irradiation part in the apparatus for a steel sheet thermal treatment according to the present disclosure.
FIG. 7 is a flowchart showing a method for a steel sheet thermal treatment according to the present disclosure.

[Best Mode for Invention]

Hereinafter, exemplary embodiments in the present disclosure will be described in detail with reference to the accompanying drawings. However, it should be noted that the spirit of the present disclosure is not limited to the exemplary embodiments set forth herein and those skilled in the art and understanding the present disclosure can easily accomplish retrogressive disclosures or other exemplary embodiments included in the spirit of the present disclosure by the addition, modification, and removal of components within the same spirit, but those are construed as being included in the spirit of the present disclosure.
Further, like reference numerals will be used to designate like components having similar functions throughout the drawings within the scope of the present disclosure.
An apparatus and a method for a steel sheet thermal treatment according to the present disclosure relates to a thermal treatment of a steel sheet S formed of a blank material by laser, and since strength of the steel sheet S which is continuously produced may be continuously modified by forming different strengths in at least one portion in a width direction of the steel sheet S formed of the blank material, which is continuously produced, a rate of production of the steel sheet S may be increased and productivity thereof may be improved.
In addition, the existing tailor welded blanket or the tailor welded coil in which the steel sheets S having different thicknesses or strengths are continuously welded and used may be replaced.
In other words, in the apparatus and the method for a steel sheet thermal treatment according to the present disclosure, by irradiating laser having a line beam (sheet beam) shape at different energies on a surface of the steel sheet S which is continuously produced in such a manner that the surface is divided into two or more parts in a width direction x, a different degree of grain refining layer may be formed in the width direction x on the surface of the blank steel sheet S or a different degree of amorphous layer may be formed in the width direction x on the surface of the blank steel sheet S, or a continuous process that imparts the same characteristics as the different surface cured layers may be performed in the width direction x.
Referring to the drawings, FIG. 1 is a front view showing an apparatus for a steel sheet thermal treatment according to the present disclosure. Referring to FIG. 1, the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include a body unit 100 provided on a movement path of steel sheet S which is continuously produced, and an irradiation unit 200 provided on the body unit 100 and including a plurality of line irradiation parts 210 irradiating a laser onto a surface of the steel sheet S in a line shape for a width direction of the steel sheet S to thermally treat the steel sheet S, wherein each of the line irradiation parts 210 irradiates an energy different from the energy irradiated by at least the other line irradiation part 210.
The body unit 100 may serve as a body including an irradiation unit 200, and the like to be described below, and may be provided on the movement path of the steel sheet S which is continuously produced such that the irradiation unit 200 may perform a thermal treatment for the steel sheet S in a continuous process.
In addition, the body unit 100 may include a base member and an alignment roll AR so that a position of the steel sheet S in the width direction thereof is not changed.
That is, the body unit 100 may include the base member to which the irradiation unit 200 or the like is coupled, and the alignment roll AR coupled to the base member and provided to be in contact with a side end portion of the steel sheet S so as to guide a movement of the steel sheet S.
This is to improve the quality of the thermal treatment for the steel sheet S by keeping a portion of the steel sheet S which is thermally treated constant, when the irradiation unit 200 irradiates the steel sheet S with a laser to perform the thermal treatment.
To this end, the alignment roll AR may be provided to be coupled to the base member, and may be formed to be in contact with the side end surface of the steel sheet S. In addition, in order to reduce friction force when the alignment roll AR is in contact with the side end surface of the steel sheet S, the alignment roll AR may be rotatably coupled to the base member.
In addition, the body unit 100 may also include a seating roll SR for supporting the moved steel sheet S and moving the steel sheet S.
The irradiation unit 200 may serve to thermally treat the blank steel sheet S which is continuously produced by irradiating the steel sheet S with the laser. As an example, a grain refining layer, an amorphous layer, a surface cured layer, and the like may be continuously formed on the steel sheet S by irradiating the steel sheet S with the laser.
In particular, the irradiation unit 200 according to the present disclosure may continuously perform the thermal treatment in a width direction x of the steel sheet S by irradiating the laser irradiated on the steel sheet S in the width direction x of the steel sheet S in a line shape, and at least a portion of the steel sheet S in the width direction may be irradiated with the laser at an output different from other portions thereof.
This may allow the steel sheet S formed of the blank material, which is continuously produced, to have different properties (strength distribution, and the like) in the width direction x. A description thereof will be provided below with reference to FIGS. 2 and 3.
In addition, to this end, the irradiation unit 200 may include a plurality of line irradiation parts 210 irradiating lasers having different outputs.
In other words, the line irradiation parts 210 may serve to irradiate a line laser in the width direction x of the steel sheet S, and the plurality of line irradiation parts 210 may be formed in the width direction x of the steel sheet S.
The line irradiation parts 210 may include an irradiating supporting part 211, a point irradiation part 212, a line lens part 213, a condensing lens part 214, and the like to irradiate the line laser. A description thereof will be provided below with reference to FIG. 4.
In addition, the irradiation unit 200 is not limited to perform the thermal treatment by irradiating only an upper surface of the steel sheet S with the laser, but may perform the thermal treatment for the steel sheet S by irradiating a lower surface of the steel sheet S or both the upper and lower surfaces of the steel sheet S.
In other words, the irradiation unit 200 may be included in at least one of an upper member of the body unit 100 which is adjacent to the upper surface of the steel sheet S and a lower member of the body unit 100 which is adjacent to the lower surface of the steel sheet S.
FIGS. 2 and 3 show a state in which different strengths are continuously formed in at least one portion in a width direction x of the steel sheet S by the apparatus for a steel sheet thermal treatment according to the present disclosure. Here, FIG. 2 shows an irradiation sate of a case in which two line irradiation parts 210 are formed and FIG. 3 shows an irradiation state of a case in which three line irradiation parts 210 are formed.
Referring to FIGS. 2 and 3, the irradiation unit 200 of the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include at least one high output line irradiation part 210a provided in a portion in the width direction x of the steel sheet S, and a low output line irradiation part 210b irradiating a laser with an energy lower than the high output line irradiation part 210 and provided to be in parallel to the high output line irradiation part 210.
In other words, the irradiation unit 200 may include a configuration irradiating a high output laser HL and a configuration irradiating a low output laser LL, on the surface of the steel sheet S formed of the blank material, which is continuously produced.
Thereby, at least a portion S1 of the steel sheet S in the width direction x of the steel sheet S may be thermally treated to be different from the other portion S2, such that portions in which properties such as strength and the like are different from each other in the width direction x of the steel sheet S.
As an example, in FIG. 2, one high output line irradiation part 210a and one low output line irradiation part 210b may be provided to be in parallel to each other in the width direction x of the steel sheet S, respectively. Thereby, the thermal treatment for two portions in the width direction x of the steel sheet S may be differently performed.
In addition, in FIG. 3, the high output line irradiation part 210a is provided to a middle portion in the width direction x of the steel sheet S and the low output line irradiation parts 210b are provided to both sides of the high output line irradiation part 210a, such that the thermal treatment may be differently performed for three portions.
FIG. 4 is a front view and a perspective view showing a line irradiation part 210 in the apparatus for a steel sheet thermal treatment according to the present disclosure and FIG. 6 is a front view showing an arrangement of a point irradiation part 212 in the apparatus for a steel sheet thermal treatment according to the present disclosure.
Referring to FIGS. 4 and 6, the line irradiation part 210 of the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include an irradiating supporting part 211 coupled to the body unit 100, a plurality of point irradiation parts 212 provided to be in parallel to each other on the irradiating supporting part 211 and discharging a laser, and a line lens part 213 provided to be connected to end portions of the plurality of point irradiation parts 212 discharging the laser.
In addition, the line irradiation part 210 of the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include a condensing lens part 214 provided to the irradiating supporting part 211 and adjusting a distance with an end portion of the line lens part 213 to collect the laser irradiated onto the steel sheet S.
The irradiating supporting part 211, which is a member on which the point irradiation parts 212 are disposed, may dispose the point irradiation parts 212 in a line shape to allow a line laser to be irradiated by the line lens part 213. In addition, the irradiating supporting part 211 may include a plurality of point irradiation parts which are disposed in the line shape and may dispose it in a surface shape.
In other words, the plurality of point irradiation parts 212 of the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may be disposed to be parallel to each other in the line shape to irradiate the laser in one line shape, or may be disposed to be parallel to each other in the surface shape to irradiate the laser in a plurality of line shapes.
In addition, here, the point irradiation part 212 may be a configuration that irradiates the laser at point, the irradiating supporting part 211 may include the plurality of point irradiation parts 212 which are in parallel to each other in the line shape in the width direction x of the steel sheet S, and may thus perform the irradiation of the laser in the width direction x of the steel sheet S at the same time.
In other words, the thermal treatment in the width direction x of the steel sheet S may be performed at the same time by performing the irradiation of the laser in the width direction x of the steel sheet S, such that the steel sheet S which are continuously produced may be thermally treated in a continuous process.
In addition, the point irradiation part 212 may set irradiation energy density of the laser to about 10⁴ to 10⁸ W/cm² and set an irradiation time of the laser to about the range of 10^-8 to 10°, so that the grain refining layer, the amorphous layer, the surface cured layer, and the like are formed.
However, in addition to disposing the point irradiation part 212 to be in parallel in the width direction x of the steel sheet S, the line lens part 213 may be provided as an intermediate medium to absorb the laser radiated from the point irradiation part 212 and to irradiate a laser of a line shape to the steel sheet S.
Thereby, since the steel sheet S which is continuously moved may be continuously and thermally treated, the thermal treatment for the surface of the steel sheet S may be continuously performed without stopping the steel sheet S, thereby quickly producing the steel sheet S.
In addition, a shape of the line lens part 213 is an example, and in order to distribute the point laser radiated from the point irradiation part 212 in the line shape, a portion facing the point irradiation part 212 may be formed in a flat shape and an opposite portion radiating the laser distributed in the line shape may be formed in a convex lens shape.
Further, in order to focus the line laser on the surface of the steel sheet S with respect to the line laser radiated from the line lens part 213, the apparatus for a steel sheet thermal treatment may further include a condensing lens part 214.
In other words, the condensing lens part 214 may focus the radiated line laser by adjusting an interval with the line lens part 213.
Such an adjustment of the interval may be performed by providing the condensing lens part 214 coupled to the driving cylinder coupled to the irradiating supporting part 211. However, a configuration of an actuator for adjusting the interval between the line lens part 213 and the condensing lens part 214 is not limited to the driving cylinder, and may also include a configuration such as a coupling between a driving motor and a gear, or the like.
In addition, the condensing lens part 214 may have, for example, opposite surfaces which are convex to concentrate the line laser radiated from the line irradiation part at a shorter distance.
Further, such a condensing lens part 214 is provided such that the line irradiation part 210 may be provided to be spaced apart from the steel sheet S by a predetermine distance. As a result, a contamination of the line irradiation part 210 by fume generated by the line laser irradiated on the steel sheet S may be prevented. As an example, a focal distance for achieving the above-mentioned effect may be about 100 to 300mm.
In addition, a width of the condensing lens part 214 may be set to about 50 to 70mm so that a thermal lens effect in which the condensing lens part 214 is deformed by heat does not occur.
FIG. 5 is a side view showing an apparatus for a steel sheet thermal treatment according to the present disclosure. Referring to FIG. 5, the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include a cooling unit 300 provided in the body unit 100 to be positioned downstream of a movement direction y of the steel sheet S as compared to the irradiation unit 200.
In other words, the cooling unit 300 may cool the steel sheet S which is thermally treated by the irradiation unit 200 to thereby shorten a thermal treatment time or adjust property of the steel sheet S.
To this end, the cooling unit 300 may be provided downstream in the movement direction y of the steel sheet S as compared to the irradiation unit 200 so as to cool the steel sheet S after the irradiation unit 200 irradiates the line laser.
In addition, in order to cool the steel sheet S, the cooling unit 300 may include a nozzle capable of spraying a cooling fluid onto the surface of the steel sheet S, or may include a cooling roll which is in contact with the steel sheet S and performs the cooling by conduction.
In addition, the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include a tension unit 400 positioned in at least one of an upstream portion and a downstream portion in the movement direction y of the steel sheet S with respect to the irradiation unit 200, and provided in the body unit 100 to form tension in the steel sheet S.
In other words, the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include the tension unit 400 capable of improving flatness of the steel sheet S by imparting tension to the steel sheet S so that the steel sheet S is produced in the continuous process and is thermally treated and an uniform thermal treatment may be performed on the surface of the steel sheet S .
To this end, the tension unit 400 may include an upstream guide roll 410, a downstream guide roll 420, a movement roll 430, and the like.
That is, the tension unit 400 of the apparatus for a steel sheet thermal treatment according to an exemplary embodiment in the present disclosure may include the upstream guide roll 410 provided in the body unit to guide a movement of the steel sheet S, the downstream guide roll 420 provided in the body unit to be spaced apart from the upstream guide roll 410 by a predetermined interval in the movement direction y of the steel sheet S, and the movement roll 430 provided between the upstream guide roll 410 and the downstream guide roll 420 and forming tension by pushing the steel sheet S to one side.
The upstream guide roll 410 may be provided upstream in the movement direction y of the steel sheet S as compared to the downstream guide roll 420 and the downstream guide roll 420 may be provided downstream in the movement direction y of the steel sheet S as compared to the upstream guide roll 410 to guide the movement of the steel sheet S.
In particular, the movement roll 430 may be provided between the upstream guide roll 410 and the downstream guide roll 420 and may be provided to be moved in a direction different from the movement direction y of the steel sheet S. As an example, when the steel sheet S moves in a horizontal direction with respect to a ground, the movement roll 430 may be provided to be vertically moved in a direction perpendicular to the ground. To this end, the movement roll 430 may be provided to be coupled to a vertical driving cylinder coupled to the body unit 100.
In addition, if the upstream guide roll 410 and the downstream guide roll are provided to support one surface of the steel sheet S, the movement roll 430 may be proved to be in contact with the other surface of the steel sheet S to impart the tension to the steel sheet S during the vertical movement of the movement roll 430.
In other words, the movement roll 430 may be provided to impart the tension to the steel sheet S by pushing a portion of a region of the steel sheet S.
In addition, the tension unit 400 may be provided to both side of the irradiation unit 200. That is, the tension unit 400 may be provided upstream as compared to the irradiation unit 200 and downstream as compared to the irradiation unit 200 with respect to the movement direction y of the steel sheet S, respectively.
In addition, a distance between the upstream tension unit 400 and the downstream tension unit 400 may be two to three times of a diameter of the upstream guide roll 410 or the downstream guide roll 420. This is because it is a preferable interval for forming the steel sheet S to have a constant focus in the width direction x by making the steel sheet S tight.
FIG. 7 is a flowchart showing a method for a steel sheet thermal treatment according to the present disclosure. Referring to FIG. 7, the method for a steel sheet thermal treatment according to another exemplary embodiment in the present disclosure may include disposing an irradiation unit 200 irradiating a laser of a line shape on a movement path of a steel sheet S, on the steel sheet S, and irradiating at least one region in a width direction x of the steel sheet S which is continuously moved with the laser having energy different from the other region.
As described above, in the method for a steel sheet thermal treatment herein, the steel sheet S may be continuously and thermally treated in a process in which the steel sheet S is continuously produced by irradiating the laser of the line shape in the width direction x of the steel sheet S.
In particular, in the thermal treatment of the steel sheet S, by irradiating at least a portion of region of the steel sheet S in the width direction x with the laser having a different output, different properties may be imparted in the width direction x of the steel sheet S.
To this end, in the disposing of the irradiation unit 200, the above-mentioned irradiation unit 200 or the like may be provided on a path in which the steel sheet S is continuously moved.
In addition, in the irradiating of the laser, property such as strength or the like in the width direction x of the steel sheet S may be differently formed in at least one region by irradiating at least one region in the width direction of the steel sheet S with the line laser having a different output. That is, a grain refining layer, an amorphous layer, a surface cured layer, and the like which are different from each other may be continuously formed in the width direction x of the steel sheet S.
In addition, the method for a steel sheet thermal treatment according to another exemplary embodiment in the present disclosure may include, after the irradiating of the laser, cooling the steel sheet S.
The cooling of the steel sheet S is to quickly cool the steel sheet S heated in the irradiating of the laser, or deform the property of the steel sheet S according to a rate of cooling.
The cooling of the steel sheet S may be performed by the cooling unit 300 described above and may be performed after the irradiating of the laser.
In addition, the method for a steel sheet thermal treatment according to another exemplary embodiment in the present disclosure may include imparting tension in which flatness of the steel sheet S is sensed after the disposing of the irradiation unit 200, and the flatness of the steel sheet S is increased by the tension before the irradiating of the laser.
The imparting of the tension is to improve quality of the thermal treatment by laser irradiation, by improving the flatness of the steel sheet S in the irradiating of the laser for the steel sheet S. The imparting of the tension may be performed by the tension unit 400 described above and may be performed before the irradiating of the laser.

Claims

An apparatus for a steel sheet thermal treatment, the apparatus comprising:
a body unit provided on a movement path of a steel sheet which is continuously produced; and

an irradiation unit provided on the body unit and including a plurality of line irradiation parts irradiating a laser onto a surface of the steel sheet in a line shape for a width direction of the steel sheet to thermally treat the steel sheet, wherein each of the line irradiation parts irradiates an energy different from the energy irradiated by at least the other line irradiation part.
The apparatus of claim 1, wherein the irradiation unit includes:
at least one high output line irradiation part provided in a portion in the width direction of the steel sheet; and

at least one low output line irradiation part irradiating a laser with an energy lower than the high output line irradiation part and provided to be in parallel to the high output line irradiation part.
The apparatus of claim 1, further comprising a cooling unit provided in the body unit to be positioned downstream of a movement direction of the steel sheet as compared to the irradiation unit.
The apparatus of claim 1, further comprising a tension unit positioned in at least one of an upstream portion and a downstream portion in a movement direction of the steel sheet with respect to the irradiation unit and provided in the body unit to form tension in the steel sheet.
The apparatus of claim 4, wherein the tension unit includes:
an upstream guide roll provided in the body unit to guide a movement of the steel sheet;

a downstream guide roll provided in the body unit to be spaced apart from the upstream guide roll by a predetermined interval in the movement direction of the steel sheet; and

a movement roll provided between the upstream guide roll and the downstream guide roll and forming tension by pushing the steel sheet to one side.
The apparatus of claim 1, wherein the line irradiation part includes:
an irradiating supporting part coupled to the body unit;

a plurality of point irradiation parts provided to the irradiating supporting part to be in parallel to each other and discharging the laser; and

a line lens part provided to be coupled to end portions of the plurality of point irradiation parts irradiating the laser.
The apparatus of claim 6, wherein the line irradiation part includes a condensing lens part provided to the irradiating supporting part and adjusting a distance with an end portion of the line lens part to collect the laser irradiated onto the steel sheet.
The apparatus of claim 6, wherein the plurality of point irradiation parts are disposed to be parallel to each other in a line shape to irradiate the laser in one line shape, or are disposed to be parallel to each other in a surface shape to irradiate the laser in a plurality of line shapes.
A method for a steel sheet thermal treatment, the method comprising:
disposing an irradiation unit irradiating a laser of a line shape on a movement path of a steel sheet, on the steel sheet; and

irradiating at least one region in a width direction of the steel sheet which is continuously moved with the laser having energy different from the other region.
The method of claim 9, further comprising, after the irradiating of the laser, cooling the steel sheet.
The method of claim 9, further comprising, imparting tension in which flatness of the steel sheet is sensed after the disposing of the irradiation unit, and the flatness of the steel sheet is increased by the tension before the irradiating of the laser.