Method and apparatus for sintering steel billets

Abstract

To provide a method and a device for scarfing a steel billet, which can stably scarf the surface of a steel material with a shallow depth uniformly.SOLUTION: The method and the device for scarfing a steel billet, which scarf the surface of the steel billet at a hot scarfer, satisfy the following expressions. Y≤-X+53.5 t+43.8 ...(1), X>20 ...(2), and Y>20 ...(3). In the expressions, X(mm) denotes a distance between the tip surface of a lower block of the hot scarfer and the surface of the steel billet, Y(mm) denotes a distance between the nozzle surface of an upper block of the hot scarfer and the surface of the steel billet, and t(mm) denotes a scarfing depth.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method and an apparatus for laser cutting a billet of steel, which laser cuts the surface of a steel material such as a billet of steel. [Background technology]

[0002] For example, surface defects may occur on the surface of a steel billet produced by continuous casting due to inclusion entrapment, surface flaws, etc. To remove such surface defects of a steel billet, for example, a scarifying device (hereinafter referred to as a hot scarfer) disclosed in Patent Documents 1-3 is used. These hot scarfers locally heat and melt the surface of the steel billet to remove the surface defects. In this hot scarfer, a scarfer unit is disposed so as to face the surface of the steel billet.

[0003] In a hot scarfer having such a configuration, first, in a preheating step, combustible gas and preheating oxygen are sprayed onto the surface of the steel piece to combust the combustible gas, and the resulting combustion heat locally melts the surface of the steel piece to form a pool. Next, in a spatula cutting step, spatula cutting oxygen is supplied to the surface of the steel piece while the steel piece is transported, and the spatula cuts the iron and the spatula cuts into an oxidation reaction with each other, and the heat of the oxidation reaction melts the surface of the steel piece and removes surface defects. The area where the spatula cutting oxygen is supplied and the oxidation reaction with the iron of the steel piece occurs is called a hot spot.

[0004] Recently, in order to improve the productivity of scavenging and the yield rate during scavenging, it is required to scavenge shallowly and uniformly. Conventionally, when scavenging the surface of a steel piece using the above-mentioned hot scarfer, the scavenging depth was controlled by adjusting the amount of oxygen (oxygen pressure) of the oxygen for scavenging and the conveying speed of the steel piece. In other words, since the scavenging depth is roughly rate-limited by the supply of oxygen, in order to make the scavenging depth shallow, the amount of oxygen is reduced or the conveying speed of the steel material is increased.

[0005] Here, if the amount of oxygen is reduced or the steel piece transport speed is increased in order to make the slag cutting depth shallower, the supply of oxygen to the hot point becomes unstable, making it impossible to perform stable slag cutting, resulting in fluctuations in the slag cutting depth in the width direction, large irregularities being formed on the surface of the steel piece after slag cutting, and continuous slag cutting being interrupted, resulting in unslag cut areas and poorly slag cut areas. This is commonly known as 'tiger cutting'. Figure 1 shows an example of 'tiger cutting' occurring in a test device.

[0006] When tiger cut occurs, the billet is cooled and turned into a cold slab, then hand-treated, and the treated billet is then fed into a heating furnace for hot rolling, etc., but because the billet has already been cooled, this leads to a worsening of the heating furnace consumption rate and an increase in labor costs. Tiger cuts tend to occur when thinly shave the billet surface, and one method of preventing this is to slow down the table movement speed (shave speed) during shave, but slowing the shave speed means that a thicker amount is shave than is necessary to ensure quality, significantly worsening the yield.

[0007] Thus, when a steel billet is subjected to thermal cutting, it has been quite difficult to stably make the thermal cutting depth shallow. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Utility Model Application Publication No. 03-070856 [Patent Document 2] Japanese Patent Application Publication No. 09-168862 [Patent Document 3] Japanese Patent Application Publication No. 10-272561 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a method for sintering steel material, and an apparatus for sintering steel material, which are capable of stably sintering the surface of steel material and capable of sintering the surface of steel material to a shallow and uniform depth. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors of the present invention have conducted extensive research and have found that stable scarification without scarification can be achieved by maintaining a certain relationship between the face-to-face distance X (mm) between the tip face of the lower block of the hot scarfer and the surface of the billet, the face-to-face distance Y (mm) between the nozzle face of the upper block of the hot scarfer and the surface of the billet, and the scarification depth t (mm). The present invention has been made based on the above findings, (I) A method for thermally cutting a slab of steel in which the surface of the slab is thermally cut with a hot scarfer, characterized in that, when the inter-face distance (X) (mm) between the tip face of a lower block of the hot scarfer and the surface of the slab is taken as the inter-face distance (Y) (mm) between the nozzle face of an upper block of the hot scarfer and the surface of the slab, and the thermal cutting depth (t) (mm), the following formulas (1), (2), and (3) are satisfied: Y≦-X+53.5t+43.8 (1) X>20 (2) Y>20 (3) (II) A method for hot cutting a steel billet as described in (I), characterized in that the hot cutting depth is 2.0 mm or less and satisfies the above formulas (1) to (3). (III) The method for hot cutting a steel billet according to (I), further characterized in that the hot cutting depth is 1.8 mm or less and satisfies the above formulas (1) to (3). (IV) The method for hot cutting a steel billet according to (I), further characterized in that the hot cutting depth is 1.6 mm or less and satisfies the above formulas (1) to (3). (V) A steel slab scavenging device for scavenging the surface of the steel slab to a scavenging depth t (mm) with a hot scarfer, This is an apparatus for thermally scarifying a billet of steel, characterized in that when the face-to-face distance between the tip face of the lower block of the hot scarfer and the surface of the billet of steel is X (mm) and the face-to-face distance between the nozzle face of the upper block of the hot scarfer and the surface of the billet of steel is Y (mm), the following formulas (1), (2), and (3) are satisfied: Y≦-X+53.5t+43.8 (1) X>20 (2) Y>20 (3) (VI) The apparatus for laser cutting a steel billet as described in (V) is further characterized in that the laser cutting depth is 2.0 mm or less and the above formulas (1) to (3) are satisfied. (VII) The apparatus for laser cutting a steel billet as described in (V) is further characterized in that the laser cutting depth is 1.8 mm or less and the above formulas (1) to (3) are satisfied. (VIII) The apparatus for laser cutting a steel billet as described in (V) is further characterized in that the laser cutting depth is 1.6 mm or less and the above formulas (1) to (3) are satisfied. Effect of the Invention

[0011] As described above, according to the present invention, it is possible to provide a method and an apparatus for laser cutting a steel piece, which are capable of stably laser cutting the surface of a steel piece and capable of laser cutting to a shallow and uniform depth. [Brief description of the drawings]

[0012] [Figure 1] FIG. 13 is a diagram showing an example of a tiger cut being generated by a test device. [Diagram 2] FIG. 2 is a diagram showing an outline of a hot scarfer and the face-to-face distance X (mm) between the tip face of the lower block and the surface of the steel piece, and the face-to-face distance Y (mm) between the nozzle face of the upper block of the hot scarfer and the surface of the steel piece. [Diagram 3] This figure shows the conditions of the surface-to-surface distance X (mm) between the tip face of the lower block and the surface of the steel piece, and the surface-to-surface distance Y (mm) between the nozzle face of the upper block of the hot scarfer and the surface of the steel piece, for investigating the limiting scarification-free shave depth t just before scarification occurs when the steel piece conveying speed is increased and the limiting conveying speed V (mpm) without scarification at that time. [Figure 4] This is a diagram showing the limit cutting depth t without trimming at each X and Y at a cutting oxygen pressure of 0.18 MPa, and the limit cutting depth t without trimming at each X and Y at a cutting oxygen pressure of 0.30 MPa. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, a method and an apparatus for laser cutting a steel billet according to an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the embodiment described below.

[0014] The inventors conducted a study on factors that affect the scalding depth and the occurrence of scalding, and found that the face-to-face distance X (mm) between the tip face of the lower block 2 and the surface 10 of the billet, and the face-to-face distance Y (mm) between the nozzle face of the upper block 3 and the surface 10 of the billet, as shown in Fig. 2, are related to the scalding depth t (mm) and the occurrence of scalding, and that if these are set within a predetermined range, a stable scalding depth t can be secured without the occurrence of scalding. This will be explained in detail below. The reason why X is set as the face-to-face distance between the tip face of the lower block 2 and the surface 10 of the billet, rather than the face-to-face distance between the nozzle face of the lower block 2 and the surface 10 of the billet, is that the step of the nozzle face of the lower block 2 is small, usually about 5 mm, and this step is considered to be filled with a shielding gas, which will be described later, and it is considered that the entrainment of air that reduces the scalding performance occurs from the tip of the lower block 2.

[0015] First, an overview of the scarification of the surface of a steel piece by the hot scarfer 1 will be given. The hot scarfer 1 is arranged on the surface 10 of the steel piece in the order of the shoe 4, the lower block 2, and the upper block 3, and a shielding gas 5 (flammable gas, which may contain oxygen) is sprayed from the nozzle of the lower block 2, a preheating gas 6 (oxygen + flammable gas) is sprayed from the nozzle of the upper block 3, and oxygen for scarification 7 is sprayed from between the lower block 2 and the upper block 3. Here, the preheating gas 6, the shielding gas 5, and a small amount of oxygen for scarification 7 are sprayed first to melt part of the surface and form a pool of molten metal (preheating process), and then a large amount of oxygen for scarification 7 is sprayed, and the shielding gas 5 and preheating gas 6 are also sprayed to protect the oxygen for scarification 7. The oxygen for cutting 7 passes through the pool of water, and using the pool of water as a heat source, an oxidation reaction occurs between the oxygen for cutting 7 and the iron on the surface 10 of the steel piece. As the steel piece is transported in the opposite direction to the gas injection direction, the surface 10 of the steel piece is cut (cutting process).

[0016] Normally, the cutting depth is stabilized by adjusting the pressure of the oxygen for cutting 7 or the conveying speed of the steel piece. However, in order to improve productivity and the yield rate during cutting, it is not easy to achieve a shallow and uniform cutting depth, and there is a limit to what can be achieved by simply adjusting the pressure of the oxygen for cutting 7 and the conveying speed of the steel piece.

[0017] Therefore, the inventors assumed a vertical plane relative to the center line of the slit between the lower block 2 and the upper block 3, through which the oxygen for cutting 7 is sprayed, at the position where the center line intersects with the surface 10 of the slab, and defined the distance from the tip surface of the lower block 2 to the vertical plane as "the inter-face distance X (mm) between the tip surface of the lower block 2 and the surface 10 of the slab." That is, it is the distance between the tip surface of the lower block 2 in FIG. 2 and 101 in FIG. 2. Similarly, the distance from the nozzle surface of the upper block 3 to the vertical plane as "the inter-face distance Y (mm) between the nozzle surface of the upper block 3 and the surface 10 of the slab." That is, it is the distance between the nozzle surface of the upper block 3 in FIG. 2 and 102 in FIG. 2. X and Y in the claims and this specification of the present invention are based on this definition.

[0018] Regarding these X, Y and slag cutting depth t (mm), the steel piece conveying speed was gradually increased under the conditions of X and Y shown in Figure 3 to investigate the limit slag cutting depth t without slag cutting just before slag cutting occurred, and the limit conveying speed V (mpm) without slag cutting at that time. The pressure of the slag cutting oxygen 7 (hereinafter referred to as slag cutting oxygen pressure) was also investigated by changing the conditions. The results are shown in Tables 1 and 2 and Figure 4. Regarding the occurrence of slag cutting, if slag cutting was interrupted midway, it was deemed to have occurred, and the test was immediately rejected. In addition, if the gas holes of each block were clogged with rebounded slag, the test was rejected even if slag cutting did not occur.

[0019] [Table 1]

[0020] [Table 2]

[0021] The results of Tables 1 and 2 are plotted in Figure 4. Although there are some differences depending on the cutting oxygen pressure, in either case, for X and Y, the limit of cutting depth t without a certain amount of trimming seems to be distributed with a certain gradient, which is explained in detail below. In Figure 4, the cutting oxygen pressure of 0.18 MPa is shown in standard font with a rough dashed line, and the cutting oxygen pressure of 0.30 MPa is shown in italic font with a fine dashed line.

[0022] In Figure 4, for the limit cutting depth t without the occurrence of tiger clipping, when the cutting oxygen pressure was 0.18 MPa and the cutting depth was 0.77 to 0.79 mm, the limit cutting condition was set to 0.8 mm. Similarly, when the cutting depth was 0.95 to 0.97 mm, the limit cutting condition was set to 1.0 mm, when the cutting depth was 1.38 to 1.50 mm, the limit cutting condition was set to 1.5 mm, when the cutting depth was 1.76 to 1.80 mm, the limit cutting condition was set to 1.8 mm, when the cutting depth was 2.35 to 2.40 mm, the limit cutting condition was set to 2.4 mm, and when the cutting depth was 3.15 to 3.18 mm, the limit cutting condition was set to 3.2 mm. The result was a linear distribution like a roughly dotted line, and the slope was almost the same in each case.

[0023] In addition, when the cutting oxygen pressure was 0.30 MPa, the limit cutting condition was set to 0.75 mm for 0.72 to 0.75 mm, the limit cutting condition was set to 0.9 mm for 0.86 to 0.87 mm, the limit cutting condition was set to 1.3 mm for 1.23 to 1.30 mm, the limit cutting condition was set to 1.3 mm for 1.50 to 1.60 mm, the limit cutting condition was set to 1.6 mm for 2.03 to 2.10 mm, and the limit cutting condition was set to 2.1 mm for 2.87 to 2.90 mm. Similarly, a linear distribution like a fine dotted line was obtained, and the slope was almost the same in each case.

[0024] The dotted line in Figure 4 will be explained. For example, in Figure 4, the rough dotted line of "1.5 mm" is the limit cutting condition for a cutting depth of 1.5 mm when the cutting oxygen pressure is 0.18 MPa. The limit conveying speed V without slitting is 16.0 to 16.5 mpm, and if the conveying speed V is increased any further, slitting will occur. In addition, under the X and Y conditions in the upper right of the dotted line, slitting will occur at values ​​greater than the cutting depth of 1.5 mm, so a cutting depth of 1.5 mm cannot be achieved. In the lower left of the dotted line, slitting will occur at values ​​smaller than the cutting depth of 1.5 mm, but the conveying speed at that time is greater than that of 1.5 mm, so if the conveying speed is reduced and cutting is performed slowly, deeper cutting can be achieved, and it is also possible to achieve a cutting depth of 1.5 mm.

[0025] In this way, it was found that in order to achieve the cutting depth of each dotted line, it is preferable to operate under the conditions below the dotted line at a certain cutting oxygen pressure. Furthermore, regardless of the cutting oxygen pressure, the gas holes in each block begin to become clogged with rebounded slag when X and Y are 20 mm.

[0026] From these results, it can be seen that in order to keep the swarf depth to within 2 mm, for example, without the occurrence of tiger cutting, stably, and to avoid loss of steel billet yield as much as possible, operation should be performed under conditions of a swarf depth of 2.0 mm, at the lower left below the dashed line in Figure 4. Similarly, if it is desired to keep the swarf depth to within 1.8 mm, operation should be performed under conditions of a swarf depth of 1.8 mm, at the lower left below the dashed line, at the lower right, if it is desired to keep the swarf depth to within 1.6 mm, operation should be performed under conditions of a swarf depth of 1.6 mm, and operation should be performed under conditions of a swarf depth of 1.4 mm, at the lower left below the dashed line, at the lower right.

[0027] Summarizing the above, it has been found that if X and Y are within a range with a nearly constant slope, that is, in the case of the cutting depth of 2.0 mm shown by the dashed line in Figure 4, the occurrence of tiger cutting can be avoided and cutting can be performed if they are in the lower left of the following formula (1). In addition, in order to perform stable cutting without gas hole blockage, formulas (2) and (3) must also be satisfied. Y≦―X+150 (1) X>20 (2) Y>20 (3)

[0028] In addition, in the case of a cutting depth of 1.8 mm (dotted line), formula (1) becomes the lower left of formula (4) below. In the case of a cutting depth of 1.6 mm (dotted line), it becomes the lower left of formula (5) below. In the case of a cutting depth of 1.4 mm (dotted line), it becomes the lower left of formula (6) below. Y≦―X+141 (4) Y≦―X+130 (5) Y≦―X+118 (6) Here, when the intercepts of the formulas (1) and (4) to (6) are expressed as a function of the cutting depth t, the formulas (1) and (4) to (6) are expressed as the following formula (7). Y≦―X+53.5t+43.8 (7)

[0029] If the above formulas (2) and (3) are satisfied and the range is within the lower left range of the above formula (7), stable slag cutting can be performed without any slag cutting or gas hole blockage. The above formula was calculated from the actual slag cutting depth t in Figure 4, but it goes without saying that even if this is used as the target slag cutting depth, it will be in the same range where stable slag cutting can be performed. When using a slag cutting device, appropriate slag cutting can be performed stably by controlling it with a control device so that the above formula is satisfied. [Explanation of symbols]

[0030] 1. Hot Scarfer 2 Lower block 3 Upper block 4. Shoe 5. Shielding gas 6 Preheating gas 7. Oxygen for cutting 10 Billet surface

Claims

1. A method for thermally scarifying a steel billet by using a hot scarfer to thermally scarify the surface of the steel billet, comprising the steps of:

1. A method for scarifying a slab, characterized in that, when the face-to-face distance X (mm) between the tip face of a lower block of a hot scarfer and the surface of the slab, the face-to-face distance Y (mm) between the nozzle face of an upper block of the hot scarfer and the surface of the slab, and the scarifying depth t (mm), the scarifying depth is 2.0 mm or less and the following formulas (1), (2), and (3) are satisfied: Y≦-X+53.5t+43.8 (1) X>20 (2) Y>20 (3)

2. 2. The method for laser cutting a steel billet according to claim 1, wherein the laser cutting depth is 1.8 mm or less and the above formulas (1) to (3) are satisfied.

3. 2. The method for laser cutting a steel billet according to claim 1, wherein the laser cutting depth is 1.6 mm or less and the above formulas (1) to (3) are satisfied.

4. A steel slab scarifying apparatus for scarifying a steel slab surface to a scarifying depth t (mm) using a hot scarfer, 1. An apparatus for scarifying a slab, characterized in that, when a face-to-face distance X (mm) is between a tip face of a lower block of a hot scarfer and a surface of the slab, and a face-to-face distance Y (mm) is between a nozzle face of an upper block of the hot scarfer and the surface of the slab, the scarifying depth is 2.0 mm or less, and the following formulas (1), (2), and (3) are satisfied: Y≦-X+53.5t+43.8 (1) X>20 (2) Y>20 (3)

5. 5. The apparatus for laser cutting a steel slab according to claim 4, wherein the laser cutting depth is 1.8 mm or less and the above formulas (1) to (3) are satisfied.

6. 5. The apparatus for laser cutting a steel slab according to claim 4, wherein the laser cutting depth is 1.6 mm or less and the above formulas (1) to (3) are satisfied.

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