JP6443411B2 - Steel slab joining method in continuous hot rolling - Google Patents

Description

  The present invention relates to a method of joining a preceding steel slab and a subsequent steel slab on the entry side of a finish rolling mill of a continuous hot rolling line.

  Conventionally, as a method of joining the preceding steel slab and the subsequent steel slab at the entry side of the finish rolling mill of the continuous hot rolling line, for example, The tail end and the tip of the subsequent billet are placed in contact with each other in a non-contact manner, and in this state, the tail end of the preceding billet and the tip of the following billet are rapidly heated by the induction heating device, and then heated. In addition, there is known a method in which the tail end of the preceding steel piece and the tip of the subsequent steel piece are brought into contact with each other and pressed (upset).

  However, when joining in an air atmosphere, an oxide having a melting point higher than the melting point of the steel (1400 to 1600 ° C.) such as Cr, Ti, Mn, Al, Si, etc. in the steel (for example, Cr oxide) : For stainless steels and high-strength steels that contain components that generate a melting point of about 2000 ° C., these oxides generated on the joint surface during induction heating remain in the joint as a solid phase even after upsetting. The strength is remarkably reduced, and problems such as breakage of the joint portion occur in finish rolling in the subsequent process.

  In order to solve this problem, a method has been proposed in which the temperature of each joint surface of the preceding steel slab and the subsequent steel slab is set to be equal to or higher than the liquidus temperature of the steel slab by using an induction heating device in the heating process (Patent Document 1). reference). However, in joining by upset when the temperature of each joint surface is equal to or higher than the liquidus temperature of the steel slab, the oxide is discharged from the joint interface together with the molten steel at the time of upset in order to obtain joint strength. Is important. When the oxide is not discharged from the bonding interface, the bonding between the irons is hindered, the bonding strength is lowered, and the bonded part may break during finish rolling.

  Conventionally, techniques for positively discharging molten steel from the end face of the joint have been studied in order to remove oxide from the joint during upset. For example, Patent Documents 2 to 6 describe techniques for examining the shape of the joint end face. Normally, the joint end faces are almost flat by slitting or end grinding, but with these technologies, the joint end faces are tapered before joining, and the molten steel discharge during welding is reduced by the processed end shape. The purpose is to improve.

  However, the techniques described in Patent Documents 2 to 6 described above require equipment for processing the shape of the joint end face before joining. Therefore, there has been a demand for a method that can prevent breakage of the joint without requiring equipment for processing the shape of the end face of the joint before joining.

JP 2000-271605 A JP 2009-119483 A JP 2009-119484 A JP 2011-25311 A JP 2013-6207 A JP 2009-119482 A

  The present invention was made in order to solve the above-mentioned problems, without requiring equipment for processing the shape of the end face of the joint, and can easily prevent breakage of the joint by finish rolling. It aims at providing the joining method of the steel slab in hot rolling.

  As a result of investigating the influence of the heating frequency on the bonding strength in view of the above problems, the inventors have clarified that the oxide can be sufficiently discharged by setting the induction heating frequency to 1.2 kHz or more. .

Based on such knowledge, the gist of the present invention completed as a result of intensive studies by the present inventors is as follows.
[1] The tail end of the preceding steel slab and the tip of the succeeding steel slab are arranged so as to face each other in a non-contact manner on the entry side of the finish rolling mill of the continuous hot rolling line. A heating step of induction heating the tip of the steel piece;
A joining step of pressing and joining the tail end of the preceding steel slab heated in the heating step and the tip of the succeeding steel slab,
In the heating step, the heating frequency f is set to 1.2 to 500 kHz, and the tail end of the preceding steel slab and the tip of the succeeding steel slab are melted. Method.
[2] In the continuous hot rolling according to [1], in the heating step, the heating frequency f (kHz) and a heating time t (sec) satisfy the following formula (1): Method of joining billets.
{30 / (f + 10)} + 0.2 ≦ t ≦ {1400 / (f + 100)} + 4.0 (1)
[3] In the heating step, heating is performed until the temperature in the range of 50 to 100% of the total width of each joining surface of the preceding steel slab and the subsequent steel slab becomes equal to or higher than the liquidus temperature of the steel slab,
The upset amount in the joining step is 1.1 to 7.0 times the sum of the maximum melting depth of the preceding steel slab and the maximum melting depth of the succeeding steel slab, The method for joining steel slabs in continuous hot rolling according to [1] or [2].

  Here, the melting depth refers to the length in the rolling direction in the range where each steel slab shown in FIG. 6 is heated to the liquidus temperature or higher and melted, and the maximum melting depth is an example in FIG. It shows the maximum value of the melting depth in the entire joining surface (full width and full thickness).

  Further, the amount of upset is the amount of pushing of the steel slab in the rolling direction in the joining process (the state in which the distance between the joint surface at the tail end of the preceding steel slab and the joint surface at the tip of the succeeding steel slab is zero (2 The amount of push-in from when the two surfaces fit together. The amount of upset depends on the relative distance between the preceding steel slab and the succeeding steel slab, and is therefore the sum of the pushing amounts of the preceding steel slab and the subsequent steel slab. If it is the conditions which become the value within the range of the upset amount, each pushing amount of a preceding steel slab and a succeeding steel slab can be determined arbitrarily. For example, only the subsequent billet may be pushed in a desired upset amount without pushing (moving) the preceding billet.

  According to this invention, it can prevent that a junction part fractures | ruptures by finish rolling of a post process.

It is the schematic which shows the equipment arrangement | sequence from the coil box of a continuous hot rolling line to the 1st stand of a finishing mill. It is a schematic sectional drawing of a joining apparatus. It is the schematic of an induction heating apparatus. It is explanatory drawing for demonstrating the flow of an alternating magnetic field and an induced current. It is a figure which shows the plate | board thickness direction distribution of the width center of the longitudinal direction length (melting depth) from the joining end surface of a melting range in case a heating frequency is 1.0 kHz, 1.2 kHz, or 5.0 kHz. It is a figure for demonstrating the definition of a melting depth. It is a figure for demonstrating the definition of the maximum melting depth.

  Hereinafter, the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

  FIG. 1 is a schematic diagram showing an equipment arrangement from a coil box of a continuous hot rolling line to a first stand of a finishing mill. In FIG. 1, reference numeral 1 is a coil box that winds a plate material from a rough rolling mill, and reference numeral 2 is a crop that cuts the tail end of a preceding steel slab S1 and the tip of a subsequent steel slab S2 that are unwound from the coil box 1. Shear, code 3 is a joining device for joining the cut surfaces (joint surfaces) of the preceding steel piece S1 and the succeeding steel piece S2, reference numeral 4 is a leveler, reference numerals 5a to 5c are pinch rolls, reference numeral 6 is a descaling device, reference numeral Reference numeral 7 denotes a first stand of a finishing mill.

  FIG. 2 is a schematic cross-sectional view of the bonding apparatus 3. As shown in FIG. 2, the joining device 3 has the joining surfaces of the cutting ends of the preceding steel piece S <b> 1 in which the rear end crop is cut off by the crop shear 2 and the succeeding steel piece S <b> 2 in which the front end crop is cut off. Induction heating that heats the left and right clamping devices 8 and 9 that are gripped so as to face each other in a non-contact manner, and the cutting ends of the preceding steel piece S1 and the subsequent steel piece S2 that are held by the clamping devices 8 and 9 The apparatus 10 and the clamping device 8 are pressed and moved to the clamping device 9 side, and the joining surfaces of the cutting ends of the preceding steel piece S1 and the succeeding steel piece S2 heated by the induction heating device 10 are brought into contact with each other and upset joined. And a press cylinder 11 that forms a joint portion α, and a mistake prevention plate 20 that prevents the preceding steel piece S1 and the subsequent steel piece S2 from shifting in the vertical direction during the upset joining.

  The joining device 3 is installed on a carriage 17 that can travel on a rail 19 (see also FIG. 1) that extends a predetermined length along the line direction. Further, the billet transfer table roller 18 installed in the travelable range of the carriage 17 is a liftable table roller, and the carriage table roller 18 corresponding to the position of the joining device 3 is pushed down by the carriage 17. It has become. By setting the joining apparatus 3 to such a configuration, the preceding steel piece S1 and the succeeding steel piece S2 can be joined without stopping the conveyance of the steel piece.

  FIG. 3 is a schematic diagram of the induction heating apparatus 10. The induction heating device (high frequency induction heating device) 10 is for penetrating an alternating magnetic field in the plate thickness direction of each cutting end of the preceding steel piece S1 and the subsequent steel piece S2. As shown in FIG. 3, the induction heating device 10 includes a pair of magnetic pole cores 13 disposed above and below the cutting ends of the preceding steel piece S1 and the succeeding steel piece S2, and the magnetic pole cores 13 in the vertical direction. A coil 14 continuously wound and a power source 15 are provided.

  FIG. 4 is an explanatory diagram for explaining the flow of the alternating magnetic field and the induced current. By using the induction heating device 10 having the above-described configuration, as shown in FIG. 4, by passing an alternating magnetic field in the thickness direction of each cutting end of the preceding steel piece S1 and the succeeding steel piece S2, each cutting end An eddy current is generated to preferentially heat the joint surfaces. In the present embodiment, the so-called transverse joining device 3 that synchronizes the heating / joining process with the travel of the steel slab is adopted, but when performing the heating / joining process with the joining device 3 stopped, A looper 16 indicated by a broken line in FIG. 1 is used.

  Here, in the present invention, the steel types of the preceding steel slab S1 and the succeeding steel slab S2 are not particularly limited. For example, at least one of the preceding steel slab S1 and the succeeding steel slab S2 has a melting point of steel (1400 to 1400). 1600 ° C.), a steel type containing 1% by mass or more of an element that generates an oxide having a melting point higher than 1600 ° C. An oxide having a melting point higher than that of steel refers to an oxide such as Cr, Ti, Mn, Al, Si, or the like (for example, Cr oxide: melting point about 2000 ° C.).

  In the joining method in continuous hot rolling according to the present invention, the tail end of the preceding steel slab S1 and the tip of the succeeding steel slab S2 are opposed to each other on the entry side of the finishing mill of the continuous hot rolling line described above. Then, the heating step of heating the tail end of the preceding steel slab S1 and the tip of the succeeding steel slab S2, and the heated tail end of the preceding steel slab S1 and the tip of the succeeding steel slab S2 are brought into contact with each other and pressed. Joining process.

  In the heating step, the heating frequency f is set to 1.2 to 500 kHz, and the tail end of the preceding steel slab S1 and the tip of the succeeding steel slab S2 are melted.

  Hereinafter, these features of the joining method in continuous hot rolling of the present invention will be described in detail.

  First, the heating process will be described.

  As a result of investigating the influence of the heating frequency f on the bonding strength, the present inventors have clarified that the oxide can be sufficiently discharged by setting the induction heating frequency to 1.2 kHz or more.

  Here, an example in which the influence of the heating frequency f on the bonding strength is investigated with reference to FIG.

  FIG. 5 shows the thickness direction distribution at the center of the length in the longitudinal direction (melting depth) from the joining end face in the melting range when the heating frequency is 1.0 kHz, 1.2 kHz, or 5.0 kHz. FIG. More specifically, in FIG. 5, the melting range from the joining end face in the melting range in the heating time in which the ratio of the melting range in the plate width direction is 90% of the total width calculated by the electromagnetic-thermal conduction coupled finite element analysis. The distribution in the plate thickness direction at the center of the width in the longitudinal direction (melting depth) is shown. The dimensions of the preceding steel slab S1 and the succeeding steel slab S2 are a sheet bar (1.5% by mass Si steel) having a width of 1200 mm and a thickness of 30 mm, respectively, and the interval between each joining surface of the preceding sheet bar and the succeeding sheet bar is 5 mm. It is said. Other heating conditions are not particularly limited in the present invention, but the input power is 1000 kW.

  This electromagnetic-heat conduction coupled finite element method analysis uses general-purpose calculation software JMAG to model the target sheet bar, coil, and magnetic pole core, and the dimensions of the sheet bar, the gap between the joint surfaces, the electrical resistance of the steel, and the specific heat. , Thermal conductivity, density and relative permeability, coil / pole core dimensions and relative positional relationship with the sheet bar, and heating conditions (heating time, input power and frequency) can be set as appropriate.

As shown in FIG. 5 (a), when the heating frequency is 1.0 kHz, the closer to the center of the plate thickness, the larger the melting depth, but as shown in FIG. 5 (b) and FIG. At 2 kHz or higher, the closer to the upper and lower surfaces, the larger the melting depth, and the pseudo shape is similar to the taper shape applied to the upper and lower surfaces. Therefore, by setting the heating frequency to 1.2 kHz or more, it is possible to obtain the same oxide discharging effect as when the upper and lower surfaces of the end portions to be joined are tapered.
The sheet bar dimension range to which this method can be applied is about 200 mm to 2400 mm in width and about 10 mm to 60 mm in thickness. The range of the heating frequency is 500 kHz in consideration of the heating efficiency for obtaining a molten metal sufficient to discharge the oxide. The above examination is performed, and in the present invention, the heating frequency f is set to 1.2 to 500 kHz. Preferably, the heating frequency f is 1.5 to 500 kHz, and more preferably 5 to 100 kHz.

In the heating step, it is preferable that the heating frequency f (kHz) and the heating time t (sec) satisfy the following formula (1) while the heating frequency f is set to 1.2 to 500 kHz as described above.
{30 / (f + 10)} + 0.2 ≦ t ≦ {1400 / (f + 100)} + 4.0 (1)
When the heating time t (sec) is less than [{30 / (f + 10)} + 0.2], the ratio in the width direction of the portion heated to the liquidus temperature or higher is small, and there is a possibility of breaking during rolling. There is. On the other hand, if the heating time t (sec) exceeds [{1400 / (f + 100)} + 4.0], the melting depth becomes large and it may be difficult to perform the upset.

  Therefore, the heating time t (sec) is preferably set to [{30 / (f + 10)} + 0.2] or more and [{1400 / (f + 100)} + 4.0] or less. More preferably, the heating time t (sec) is [{50 / (f + 10)} + 0.4] or more and [{1100 / (f + 100)} + 3.2] or less.

  Moreover, in order to continue rolling stably at any heating frequency, heating is performed until the temperature in the range of 50 to 100% of the entire width of each joint surface is equal to or higher than the liquidus temperature of the steel slab. It is preferable to do. This is because when the ratio of the unjoined portion at the width end portion to the plate width is large, tension is concentrated on the joined portion in finish rolling in the subsequent process, and the joined portion may be separated. As mentioned above, in this invention, it is preferable to heat until the temperature of the range of 50-100% of the width direction becomes more than the liquidus temperature of a steel piece in a heating process, More preferably, the said width direction is 70-100. %, More preferably 85 to 100%. In order to make the temperature in the range of 50 to 100% in the width direction equal to or higher than the liquidus temperature of the steel slab, it can be adjusted by the heating time, the input power during heating, the heating frequency f, and the like.

  Next, the joining process will be described.

  In the present invention, although not particularly limited, preferably, the sum of the maximum melting depth of the preceding steel slab S1 and the maximum melting depth of the succeeding steel slab S2 in order to sufficiently upset the entire width and thickness of the joining surface. 1.1 to 7.0 times, and more preferably 1.3 to 7.0 times. In order to appropriately set the upset amount, it is necessary to know in advance the thickness direction distribution of the longitudinal direction length (melting depth) from the joining end face of the melting range. It can be obtained by calculating by heat conduction coupled finite element analysis.

  Here, the melting depth refers to the length in the rolling direction in the range where each steel slab shown in FIG. 6 is heated to the liquidus temperature or higher and melted, and the maximum melting depth is an example in FIG. It shows the maximum value of the melting depth in the entire joining surface (full width and full thickness).

  Further, the amount of upset is the amount of pushing of the steel slab in the rolling direction in the joining process (the state in which the distance between the joint surface at the tail end of the preceding steel slab and the joint surface at the tip of the succeeding steel slab is zero (2 The amount of push-in from when the two surfaces fit together. Since the amount of upset depends on the relative distance between the preceding steel slab and the succeeding steel slab, the amount of upset is the sum of the pushing amounts of the preceding steel slab and the subsequent steel slab. The pushing amount of each of the preceding steel slab and the succeeding steel slab can be arbitrarily determined under the condition of the upset amount. For example, the following steel slab may be pushed in a desired upset amount without pushing (moving) the preceding steel slab.

  In addition, when the time from the end of heating to the completion of upset is 2.0 sec or more, the viscosity decreases due to a decrease in the temperature of the joint surface. In this case as well, the discharge promotion effect due to the tapered shape is significant.

  In the present embodiment, the pressing force in the joining process is not particularly limited.

  As described above, in the present invention, the heating frequency f in the heating step is set to 1.2 to 500 kHz, so that no equipment for processing the end surface is required, and the joining portion can be easily formed by finish rolling in the subsequent step. Breakage can be prevented. In the present invention, the heating time can also be shortened, and the time required for joining can be shortened to improve productivity. Moreover, in this invention, the molten steel which generate | occur | produces can be decreased and the possibility that the molten steel which remain | survived will be bitten by a joining surface can be reduced in the case of the joining of the next steel piece.

  Moreover, when manufacturing a hot-rolled steel strip using the joining method in the continuous hot rolling of the present invention, for production conditions other than the above-described joining method conditions, conventionally known conditions are adopted, and the steel type and the shape of the steel It can be set appropriately depending on the situation.

  In the above description, only 1.5% Si steel is taken as an example, but the steel composition is 1.2 mass% at maximum in the case of C, 4.0 mass% in the case of Si, and 6. max in the case of Mn. 2% by mass, Cr: 35.0% by mass, Ti: 0.5% by mass, Al: 0.5% by mass, P: 0.5% by mass, S: 0. 4 mass%, Ni 25.0 mass% maximum, Mo Mo maximum 1.0 mass%, V 0.5 mass% maximum Good continuous rolling can be continued up to a finished sheet thickness of 2 mm.

  Hereinafter, the present invention will be described based on examples.

  A sheet bar (3.0 mass% Mn steel) having a width of 1250 mm and a thickness of 30 mm as a preceding steel piece and a subsequent steel piece was subjected to the continuous hot rolling line shown in FIG. As the preceding steel slab and the subsequent steel slab, in mass%, Si: 1.5%, C: 0.12%, Mn: 3.0%, Cr: 0.3%, the balance being Fe and What has the steel composition which consists of an unavoidable impurity was used.

  In addition, after the joining surfaces of the preceding sheet bar and the succeeding sheet bar are arranged to face each other with a gap of 5 mm in the joining device 3, each is heated by the induction heating device 10 (size in the width direction is 1300 mm, dimension in the longitudinal direction is 240 mm). The joining surface was heated. The heating conditions at this time were an input power of 1000 kW, and the heating frequency f and heating time were as shown in Table 1.

FIG. 5 shows the result of calculating the region where the temperature is higher than the liquidus temperature of steel by the electromagnetic-thermal conduction coupled finite element analysis. In this electromagnetic-heat conduction coupled finite element method analysis, general-purpose calculation software JMAG is used to model a sheet bar, a coil, and a magnetic pole core. In this model, the dimensions of the seat bar and the gap between the joint surfaces are the same as those in the previous example, and the physical properties are the same as in this example (characteristic values of electrical resistance, specific heat, thermal conductivity, density).・ Relative permeability) was used. Specifically, electric resistance: 120 μΩ · cm, specific heat: 350 J / kg / degC, thermal conductivity: 28 W / m / degC, density: 7850 kg / m ³ , and relative magnetic permeability: 8. The dimensions of the coil and magnetic pole core and the relative positional relationship with the seat bar are the same as those of the joining machine used in this embodiment, and the heating conditions (input power and frequency) are the same as in this embodiment.

Subsequently, the joining surfaces were brought into contact with each other and pressed by the pressing cylinder 11 with a pressing force of 5.2 kg / mm ² to complete the joining. The amount of upset is as shown in Table 1.

  Tensile test specimens were collected from the joints and subjected to joint hot tensile strength (test temperature 1000 ° C.) using JIS No. 14A tensile test specimens. Partial strength was obtained.

In addition, after completion of joining, 20 times of joining / rolling up to a plate thickness of 2 mm were performed by 7 stand mills of a finish rolling mill, and the probability that the joint was broken at that time (breaking probability (%)) is shown in the table. In the example of the present invention, the fracture probability could be reduced to 35% or less by setting the frequency to 1.2 kHz or more. Also, among the examples of the present invention, as a heating condition, the formula (1) was satisfied, Heat the temperature in the range of 50-100% in the width direction of each joining surface of the succeeding steel slab until it reaches the liquidus temperature of the steel slab, and as a joining condition, set the upset amount as the maximum melting depth of the preceding steel slab. No. and 1.1 to 7.0 times the sum of the maximum melting depth of the succeeding steel slab. In 3, 4, 5, 6, 7, 10, 12, 13, and 14, the fracture strength could be 0% while the joint strength was 80% or more.

DESCRIPTION OF SYMBOLS 1 Coil box 2 Crop shear 3 Joining device 4 Leveler 5 Pinch roll 6 Descaling device 7 First stand of finishing mill 8, 9 Clamp device 10 Induction heating device 11 Pressing cylinder 13 Magnetic pole core 14 Coil 15 Power source 16 Looper 17 Carriage 18 Steel slab conveying table roller 19 Rail 20 Misalignment prevention plate S1 Leading steel slab S2 Backing steel slab

Claims (3)

The leading edge of the preceding steel slab and the leading edge of the following steel slab are placed in contact with each other in a non-contact manner on the entry side of the finish rolling mill of the continuous hot rolling line, and the tail edge of the preceding steel slab and the following steel slab A heating process for induction heating the tip;
A joining step of pressing and joining the tail end of the preceding steel slab heated in the heating step and the tip of the succeeding steel slab,
In the heating step, the heating frequency f is set to 1.2 to 500 kHz, and the tail end of the preceding steel slab and the tip of the succeeding steel slab are melted. Method. In the said heating process, the said heating frequency f (kHz) and heating time t (sec) satisfy | fill the following formula | equation (1), The joining of the steel slab in the continuous hot rolling of Claim 1 characterized by the above-mentioned. Method.
{30 / (f + 10)} + 0.2 ≦ t ≦ {1400 / (f + 100)} + 4.0 (1) In the heating step, heating is performed until the temperature in the range of 50 to 100% of the total width of each joining surface of the preceding steel slab and the subsequent steel slab becomes equal to or higher than the liquidus temperature of the steel slab,
The upset amount in the joining step is 1.1 to 7.0 times the sum of the maximum melting depth of the preceding steel slab and the maximum melting depth of the succeeding steel slab, Item 3. A method for joining steel pieces in continuous hot rolling according to item 1 or 2.

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