Steel slab processing device and steel slab processing method

Abstract

To provide a steel slab processing device and a steel slab processing method that can obtain high-quality steel slabs without reducing yield of the steel slabs.SOLUTION: A slab processing device 18 includes: a plurality of laser irradiation devices 24 that irradiate a scale-removed surface 112 of a slab 100 from which a scale 102 has been removed with laser; and a control device 26 that controls the plurality of laser irradiation devices 24 so as to melt a copper-enriched layer 106 remaining on the scale-removed surface 112 and a copper infiltration layer 110 which consists of a portion of a base material of the slab 100 including a copper infiltration part 108 in which copper contained in the copper-enriched layer 106 has infiltrated into grain boundaries of the base material 104 of the slab 100 by irradiating the scale-removed surface 112 with the laser, and mix the melted copper-enriched layer 106 with copper infiltration layer 110.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a steel strip processing apparatus and a steel strip processing method. [Background technology]

[0002] Generally, billets, slabs, and blooms are used as steel billets that are rolled to produce products. During the process of producing billets, cracks may occur on the surface of the billets due to external forces, thermal strain, etc. Such cracks are defects, and in order to maintain the quality of products produced from the billets, it is desirable that the billets have no defects on their surfaces.

[0003] Therefore, techniques for removing the defects have been proposed. For example, in the partial surface machining method described in Patent Document 1, a laser is irradiated onto the defects occurring on the surface of the billet, and oxygen gas or a mixed gas containing oxygen is sprayed onto the laser irradiation point to machine the defects. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-274892 Summary of the Invention [Problem to be solved by the invention]

[0005] Meanwhile, the use of electric furnaces is being considered as a method for producing iron sources with the aim of decarbonizing. In the production method using electric furnaces, a large amount of scrap is fed into the electric furnace, and it is expected that the scrap will be mixed with motors and other materials that contain a lot of copper. Copper is a so-called tramp element, which is an element that cannot be removed by the blowing process, and is contained in the steel slab as it is.

[0006] 8 shows a longitudinal cross section of a slab 100. When the copper content in the slab 100 increases, a problem called red embrittlement occurs. Red embrittlement is a phenomenon that occurs when scale 102 is generated on the surface of the slab 100 in a high-temperature oxygen atmosphere in a heating furnace, copper dissolved in the slab 100 is discharged from the scale 102, and the copper discharged from the scale 102 is concentrated in a liquid state at the interface between the scale 102 and the base material 104.

[0007] Specifically, copper infiltrates into the grain boundaries of the base material 104 from a layer where copper is concentrated in a liquid state (hereinafter referred to as the copper-infiltrated layer 106), and the infiltrated copper (hereinafter referred to as the copper-infiltrated portion 108) embrittles the surface layer of the base material 104 including the copper-infiltrated portion 108 (hereinafter referred to as the copper-infiltrated layer 110). The copper-infiltrated portion 108 is a portion that extends from the copper-infiltrated layer 106 to the opposite side of the scale 102. When the slab 100 is rolled in a state in which the copper-infiltrated layer 110 consisting of a part of the base material 104 including the copper-infiltrated portion 108 is generated on the surface layer of the base material 104, cracks originating from the copper-infiltrated portion 108 frequently occur, which causes a quality problem.

[0008] Here, it is possible to remove the copper-infiltrated layer 110, for example, by using the partial surface machining method described in Patent Document 1. However, in this case, the yield of the slab 100 will decrease by the amount of the copper-infiltrated layer 110 that is removed.

[0009] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a steel slab processing apparatus and a steel slab processing method that are capable of obtaining high-quality steel slabs without reducing the yield of steel slabs. [Means for solving the problem]

[0010] A first aspect of the present invention is a steel piece processing apparatus comprising: a laser irradiation unit that irradiates a laser onto a scale-removed surface of a steel piece from which scale has been removed; and a control unit that controls the laser irradiation unit so that, by irradiating the laser onto the scale-removed surface, a copper-concentrated layer remaining on the scale-removed surface and a copper-infiltrated layer consisting of a part of the base material of the steel piece including a copper-infiltrated portion in which copper contained in the copper-concentrated layer has infiltrated into grain boundaries of the base material of the steel piece are melted and the molten copper-concentrated layer and the copper-infiltrated layer are mixed together.

[0011] A second aspect of the present invention is a steel piece processing apparatus according to the first aspect, wherein the control unit controls the laser irradiation unit so that the copper infiltration layer melts to a depth that includes the entire copper infiltration portion.

[0012] A third aspect of the present invention is the steel piece processing apparatus according to the first or second aspect, wherein the laser irradiation unit irradiates the entire scale removal surface with the laser.

[0013] A fourth aspect of the present invention is a steel piece processing method comprising: a laser irradiation step of irradiating a laser onto a scale-removed surface of a steel piece from which scale has been removed, using a laser irradiation unit; and a control step of controlling the laser irradiation unit using a control unit so as to irradiate the laser onto the scale-removed surface, thereby melting a copper-concentrated layer remaining on the scale-removed surface and a copper-infiltrated layer made of a part of the base material of the steel piece including a copper-infiltrated portion in which copper contained in the copper-concentrated layer has infiltrated into grain boundaries of the base material of the steel piece, and mixing the molten copper-concentrated layer and the copper-infiltrated layer.

[0014] A fifth aspect of the present invention is a steel piece processing method according to the fourth aspect, wherein the control unit controls the laser irradiation unit so that the copper infiltration layer melts to a depth that includes the entire copper infiltration portion.

[0015] A sixth aspect of the present invention is the steel piece processing method according to the fourth or fifth aspect, wherein the laser irradiation unit irradiates the laser onto the entire scale removal surface. Effect of the Invention

[0016] According to the present invention, there are provided a steel slab processing apparatus and a steel slab processing method capable of obtaining high quality steel slabs without reducing the yield of steel slabs. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram showing a slab manufacturing facility according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of a process in which a descaling treatment and a modification treatment are sequentially performed on a slab. [Diagram 3] FIG. 1 is a perspective view showing a slab processing apparatus according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing an optical microscope photograph of a cross section of a slab after heating according to the present embodiment. [Diagram 5] FIG. 2 is a diagram showing an observation image of a cross section of a slab before the scale removal treatment according to the present embodiment. [Figure 6] FIG. 2 is a diagram showing an observation image of a cross section of a slab after the modification treatment according to the present embodiment. [Figure 7] 1A and 1B are diagrams showing optical microscope photographs of the cross section of a slab before and after the modification treatment according to the present embodiment. [Figure 8] FIG. 2 is a vertical cross-sectional view showing an example of a slab. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of a steel piece processing apparatus and a steel piece processing method according to the present invention will be described with reference to the drawings. In the following description, a slab is taken as an example of a steel piece, but the present invention is also applicable to steel pieces other than slabs (for example, billets or blooms).

[0019] (Outline of slab manufacturing equipment 10) 1 shows a slab production facility 10 according to this embodiment. The slab production facility 10 is a facility for producing a slab 100, and includes a continuous casting facility 12, a heating furnace 14, a scale removing device 16, and a slab processing device 18. The slab processing device 18 is an example of a steel slab processing device according to the present invention.

[0020] The continuous casting equipment 12 casts the molten steel sent from the electric furnace to form a slab 100. The heating furnace 14 performs a heat treatment on the slab 100 extracted from the continuous casting equipment 12. In the following description, it is assumed that the slab 100 is heated in the heating furnace 14, thereby generating scale 102, a copper-concentrated layer 106, and a copper-infiltrated portion 108 in the slab 100. The copper content of the slab 100 on which the copper-concentrated layer 106 and the copper-infiltrated portion 108 are generated is, for example, 0.15 wt% or more (particularly, 0.2 wt% or more).

[0021] The scale removing device 16 performs a scale removing process on the slab 100 extracted from the heating furnace 14. The slab processing device 18 performs a modification process on the slab 100 from which the scale 102 has been removed. The scale removing process and the modification process will be described later. The slab 100 that has been modified by the slab processing device 18 is transported to a rolling facility.

[0022] (Explanation of scale removal treatment and modification treatment) 2 shows how a scale removal process and a modification process are sequentially performed on the slab 100. The scale removal process is a process for removing the scale 102 formed on the surface of the slab 100. By removing the scale 102, a scale removal surface 112 is generated on the slab 100. As a method for removing the scale 102, for example, a method for spraying high-pressure water onto the surface of the slab 100 to which the scale 102 is attached is used. By removing the scale 102, it becomes possible to directly irradiate a laser onto the scale removal surface 112 in the modification process described below.

[0023] The modification process is a process in which the copper-rich layer 106 remaining on the scale-removed surface 112 and the copper-infiltrated layer 110 consisting of a part of the base material 104 including the copper-infiltrated portion 108 in which the copper contained in the copper-rich layer 106 has infiltrated into the grain boundaries of the base material 104 of the slab 100 are melted by irradiating the scale-removed surface 112 with a laser, and the melted copper-rich layer 106 and the copper-infiltrated layer 110 are mixed. The copper-infiltrated layer 110 is a layer including the copper-infiltrated portion 108 of the base material 104. More specifically, the copper of the copper-rich layer 106 infiltrates into the grain boundaries of the base material 104 to form the copper-infiltrated portion 108, and the range (layer) in the thickness direction of the base material 104 in which the copper-infiltrated portion 108 is included (exists) is referred to as the copper-infiltrated layer 110. Therefore, the copper components of the molten copper-concentrated layer 106 and the copper-infiltrated layer 110 are diffused into the base material 104, which makes up the majority of the volume of the copper-concentrated layer 106 and the copper-infiltrated layer 110, thereby reducing the copper concentration per volume and making it possible to prevent the copper components from becoming the starting point of cracks (to render them harmless).

[0024] The molten copper-enriched layer 106 and the copper-infiltrated layer 110 are mixed together to form an alloy, and the copper-enriched layer 106 and the copper-infiltrated portion 108 disappear, forming a harmless modified layer 114 in the slab 100. In other words, the modified layer 114 that does not crack even when the slab 100 is rolled is formed in the slab 100. In this embodiment, "disappearance" refers to a state in which the volumes of the copper-enriched layer 106 and the copper-infiltrated portion 108 are reduced to such an extent that quality problems such as cracks do not occur during rolling, in addition to complete disappearance.

[0025] In order to completely eliminate the copper infiltrated portion 108, the copper infiltrated layer 110 may be melted to a depth including the entire copper infiltrated portion 108 (i.e., the entire length), or may be melted to a depth beyond the copper infiltrated portion 108. In addition, in order to eliminate the copper-enriched layer 106 and the copper infiltrated portion 108 over the entire surface of the scale removal surface 112, the entire surface of the scale removal surface 112 may be irradiated with a laser. In this embodiment, the term "entire surface" refers to the entire surface including an error that is generally acceptable in the technical field to which the present invention belongs, as well as the complete entire surface, and does not violate the spirit of the present invention. In this embodiment, the term "entire surface" refers to the entire surface including an error that is generally acceptable in the technical field to which the present invention belongs, as well as the complete entire surface.

[0026] The above-described scale removal treatment and modification treatment are performed on both the front and back surfaces of the slab 100. The slab treatment method realized by performing the modification treatment is one example of a steel slab treatment method according to the present invention.

[0027] (Specific configuration of slab processing device 18) 3 shows a slab processing apparatus 18 according to this embodiment. The slab processing apparatus 18 includes a transport mechanism 22, a plurality of laser irradiation devices 24, and a control device 26. The transport mechanism 22 includes a plurality of transport rollers 28, and a drive device (not shown). With a slab 100 placed on the plurality of transport rollers 28, the drive device rotates the plurality of transport rollers 28 to transport the slab 100.

[0028] The multiple laser irradiation devices 24 are arranged side by side in the width direction of the slab 100. The multiple laser irradiation devices 24 are arranged opposite the scale removal surface 112 and are configured to irradiate the scale removal surface 112 with a laser beam L. Each laser irradiation device 24 has a scanning optical head (not shown) and is configured to be able to move the focused spot of the laser beam L back and forth in the width direction of the slab 100. In the example shown in FIG. 3, adjacent laser irradiation devices 24 are arranged with a shift in the transport direction of the slab 100.

[0029] The multiple laser irradiating devices 24 are arranged such that the ends of the movement trajectories of the focused spots of adjacent laser irradiating devices 24 overlap in the width direction of the slab 100. The multiple laser irradiating devices 24 irradiate the laser L over the entire width direction of the slab 100. While the slab 100 is transported relative to the multiple laser irradiating devices 24, the multiple laser irradiating devices 24 irradiate the laser L over the entire width direction of the slab 100, so that the entire scale removal surface 112 is irradiated with the laser L.

[0030] 3, the number of the laser irradiation devices 24 is four, but any number of the laser irradiation devices 24 may be used. The laser irradiation device 24 is an example of a laser irradiation unit according to the present invention. The laser irradiation device 24 executes a laser irradiation step of irradiating the scale removal surface 112 with a laser L.

[0031] The control device 26 is a device that controls the multiple laser irradiation devices 24, and is configured by an electronic circuit having, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control device 26 may have an electronic circuit such as a PLD (Programmable Logic Device) or an ASIC (Application Specific Integrated Circuit) instead of or in addition to the CPU. The control device 26 is an example of a control unit according to the present invention. The control device 26 executes a control step for controlling the multiple laser irradiation devices 24.

[0032] The control device 26 controls each laser irradiation device 24 so that the laser L is irradiated from each laser irradiation device 24 and the focused spot of the laser L moves back and forth. The control device 26 also controls the moving speed of the focused spot or the output of the laser so that the depth to which the slab 100 is melted is uniform over the entire surface of the scale removal surface 112. For example, the control device 26 controls to increase the moving speed of the focused spot or decrease the output of the laser L at the timing when the ends of the movement trajectories of adjacent laser irradiation devices 24 overlap.

[0033] The control device 26 also controls the movement speed of the focused spot or the output of the laser so that the copper infiltration layer 110 is melted to a depth including the entire copper infiltration portion 108. By melting the copper infiltration layer 110 to a depth including the entire copper infiltration portion 108, the copper infiltration portion 108 completely disappears.

[0034] The depth to which the copper infiltrated layer 110 is melted is, for example, about 0.1 to 1.0 mm. The depth to which the copper infiltrated layer 110 is melted is set based on a database that is created in advance based on conditions such as the type of steel, the copper content, and the heating temperature in the heating furnace 14. The laser input energy density per unit area of ​​the slab required to melt the copper infiltrated layer 110 to a depth that includes the entire copper infiltrated portion 108 is, for example, 0.1 kJ to 2.0 kJ / cm. 2 That's about it.

[0035] Each laser irradiation device 24 may be a device having a linear focusing type optical head that focuses a laser beam into a line instead of a scanning type optical head.

[0036] (Difference between this embodiment and the prior art) For example, in the conventional technology described in Patent Document 1, the target of repair using a laser is a crack that occurs on the surface of a slab due to stress during casting, or a hole that occurs on the surface of a slab due to the entrapment of foreign matter or gas. The size of the opening of the crack or hole is about 1.0 mm. The conventional technology uses a repair method called "scalding" in which the crack or hole is identified with a flaw inspection device, and the identified area is melted by a laser and simultaneously blown away by spraying oxygen, air, or high-pressure water.

[0037] On the other hand, in this embodiment, the target of repair using the laser L is a copper-infiltrated portion 108 that has infiltrated into the grain boundary of the base material 104. The copper-infiltrated portion 108 is generated due to a copper-concentrated layer 106 that is liquefied and concentrated at the interface between the scale 102 and the base material 104 when copper that has been dissolved in the slab 100 is discharged from the scale 102 while the slab 100 is being heated in the heating furnace 14.

[0038] The width of the copper infiltrated portion 108 is about several μm, and the depth of the copper infiltrated portion 108 is about several hundred μm, so it is difficult to detect the copper infiltrated portion 108 by surface defect inspection. The copper infiltrated portion 108 itself is not a crack or a hole, and when the slab 100 having the copper infiltrated portion 108 is rolled, cracks are generated starting from the copper infiltrated portion 108, and these cracks become flaws on the surface of the product. Since many copper infiltrated portions 108 are generated in the slab 100, it is difficult to improve the situation by partial repair.

[0039] Here, for example, it is conceivable to remove the copper-infiltrated layer 110 from the entire surface of the slab 100, but in this case, the yield of the slab 100 will decrease by the amount of the copper-infiltrated layer 110 that is removed.

[0040] Depending on the type of steel, hot rolling is performed under conditions exceeding the melting point of copper in the hot rolling process. Therefore, if the copper-rich layer 106 remains, it will not solidify and will become the source of new copper infiltrated parts 108. Therefore, it is desirable that the copper-rich layer 106 disappears in the hot rolling process.

[0041] Therefore, in this embodiment, first, the scale 102 is removed from the slab 100 extracted from the heating furnace 14, and then the scale removal surface 112 of the slab 100 is irradiated with a laser L to melt the copper-rich layer 106 remaining on the scale removal surface 112 and the copper-infiltrated layer 110 consisting of a part of the base material 104 including the copper-infiltrated portion 108 in which the copper contained in the copper-infiltrated layer 106 has infiltrated into the grain boundaries of the base material 104 of the slab 100, and a modification process is performed in which the molten copper-infiltrated layer 106 and the copper-infiltrated layer 110 are mixed. As a result, a modified layer 114 in which the copper-infiltrated layer 106 and the copper-infiltrated portion 108 have disappeared is generated in the slab 100 without removing the copper-infiltrated layer 110.

[0042] In this way, the object to be repaired and the repair method are different between this embodiment and the prior art.

[0043] (effect) As described above in detail, in this embodiment, the scale removal process is performed on the slab 100 by the scale removal device 16, and the scale 102 generated on the surface of the slab 100 is removed. Then, the slab treatment device 18 performs a modification process on the slab 100 from which the scale 102 has been removed. Specifically, the laser L is irradiated onto the scale removal surface 112 of the slab 100 by the multiple laser irradiation devices 24, whereby the copper-enriched layer 106 remaining on the scale removal surface 112 and the copper infiltrated layer 110 consisting of a part of the base material 104 including the copper infiltrated portion 108 in which the copper contained in the copper-enriched layer 106 has infiltrated into the grain boundaries of the base material 104 of the slab 100 are melted, and the molten copper-enriched layer 106 and the copper infiltrated layer 110 are mixed. As a result, a modified layer 114 in which the copper-enriched layer 106 and the copper infiltrated layer 110 have disappeared is generated in the slab 100.

[0044] Therefore, since the copper infiltrated layer 110 is not removed, it is possible to avoid a decrease in the yield of the slab 100. In addition, since the copper-enriched layer 106 and the copper-infiltrated portion 108 disappear due to the generation of the modified layer 114, it is possible to obtain a high-quality slab 100 in which the copper-enriched layer 106 and the copper-infiltrated portion 108 have disappeared.

[0045] In addition, the laser L is irradiated onto the scale removal surface 112 by the multiple laser irradiation devices 24, thereby melting the copper infiltrated layer 110 to a depth including the entire copper infiltrated portion 108. This allows the copper infiltrated portion 108 to completely disappear.

[0046] In addition, the laser L is irradiated onto the entire surface of the scale removal surface 112 by the multiple laser irradiation devices 24. This makes it possible to obtain a high-quality slab 100 in which the copper-enriched layer 106 and the copper infiltrated portion 108 have disappeared over the entire surface of the scale removal surface 112.

[0047] (Modification) In the above embodiment, the copper infiltrated layer 110 is melted to a depth including the entire copper infiltrated portion 108. However, for example, if the copper infiltrated layer 110 is melted to a depth including a part of the copper infiltrated portion 108 and the other part remaining, the copper infiltrated layer 110 may be melted to a depth including a part of the copper infiltrated portion 108 and the other part remaining, as long as the copper infiltrated layer 110 does not cause cracks to occur starting from the copper infiltrated portion 108 when the slab 100 is rolled.

[0048] In addition, in the above embodiment, the laser L is irradiated onto the entire surface of the scale removal surface 112, but for example, there may be areas on the scale removal surface 112 where the laser L is not irradiated, as long as the quality of the slab 100 is ensured.

[0049] (Example) Fig. 4 shows an optical microscope photograph of a cross section of a slab after heating according to the present embodiment. The slab shown in Fig. 4 is after heating. As shown in Fig. 4, in the slab after heating, multiple copper infiltrated areas are present at the grain boundaries of the base material.

[0050] Fig. 5 shows an observation image of a cross section of a slab before the scale removal treatment according to this embodiment. The observation image shown in Fig. 5(A) is an image taken by an electron probe micro analyzer (EPMA), and the observation image shown in Fig. 5(B) is an image taken of the same part as Fig. 5(A) by a scanning electron microscope (SEM). The slab shown in Fig. 5 is before the scale removal treatment. A copper-enriched layer is present at the interface between the scale and the base material, and a copper-infiltrated portion is present at the grain boundary of the base material.

[0051] Fig. 6 shows an observation image of a cross section of a slab after the modification treatment according to this embodiment. The observation image shown in Fig. 6(A) is an image taken by an electron probe microanalyzer, and the observation image shown in Fig. 6(B) is an image taken by a scanning electron microscope of the same part as Fig. 6(A). The slab shown in Fig. 6 is after the modification treatment. In the slab after the modification treatment, the copper-enriched layer and the copper-infiltrated part have disappeared, and a harmless modified layer has been generated.

[0052] FIG. 7 shows optical microscope photographs of the cross section of a slab before and after the modification treatment according to this embodiment. The slab shown in FIG. 7(A) is after the descaling treatment and before the modification treatment, and the slab shown in FIG. 7(B) is after the modification treatment. As shown in FIG. 7(A), in the slab before the modification treatment and after the descaling treatment, multiple copper infiltrated parts are present at the grain boundaries of the base material. On the other hand, as shown in FIG. 7(B), in the slab after the modification treatment, all the copper infiltrated parts have disappeared, and a harmless modified layer is generated in the slab.

[0053] While one embodiment of the present invention has been described above, the present invention is not limited to the above, and it goes without saying that the present invention can be implemented in various modified forms without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0054] 10 Slab manufacturing equipment 12 Continuous casting equipment 14 Furnace 16 Scale removal device 18 Slab Processing Equipment 22 Transport mechanism 24 Laser irradiation device 26 Control device 28 Transport roller 100 Slabs 102 Scale 104 Base material 106 Copper enriched layer 108 Copper infiltration area 110 Copper infiltration layer 112 Scale removal surface 114 Modified layer

Claims

1. a laser irradiation unit that irradiates a laser onto a scale-removed surface of the steel piece from which the scales have been removed; A control unit that controls the laser irradiation unit so that the copper-rich layer remaining on the scale removal surface and the copper-infiltrated layer made of a part of the base material of the steel piece including a copper infiltrated portion in which copper contained in the copper-rich layer infiltrates into the grain boundaries of the base material of the steel piece are melted by irradiating the laser on the scale removal surface, and the melted copper-rich layer and the copper infiltrated layer are mixed. The steel strip processing device comprises:

2. The steel piece processing apparatus according to claim 1 , wherein the control unit controls the laser irradiation unit so that the copper infiltrated layer is melted to a depth including the entire copper infiltrated portion.

3. The steel piece processing apparatus according to claim 1 or 2, wherein the laser irradiation unit irradiates the entire scale removal surface with the laser.

4. a laser irradiation step of irradiating a laser onto a scale-removed surface of the steel piece from which the scales have been removed, using a laser irradiation unit; A control step of controlling the laser irradiation unit by using a control unit to irradiate the laser onto the scale removal surface to melt the copper-rich layer remaining on the scale removal surface and the copper-infiltrated layer made of a part of the base material of the steel piece including a copper infiltrated portion in which the copper contained in the copper-rich layer has infiltrated into the grain boundaries of the base material of the steel piece, and to mix the molten copper-rich layer and the copper infiltrated layer; A steel strip processing method comprising:

5. The steel piece processing method according to claim 4 , wherein the control unit controls the laser irradiation unit so that the copper infiltrated layer is melted to a depth including the entire copper infiltrated portion.

6. The steel slab processing method according to claim 4 or 5, wherein the laser irradiation unit irradiates the entire scale removal surface with the laser.

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