JP7397318B2 - Steel plate manufacturing method, steel pipe manufacturing method, steel plate manufacturing equipment and program - Google Patents

Description

The present invention relates to a steel plate manufacturing method, a steel pipe manufacturing method, a steel plate manufacturing apparatus, and a program.

In recent years, sulfide stress cracking (SSC) has become a problem in steel plates and steel products manufactured from steel plates that are exposed to a hydrogen sulfide environment. It has become clear that SSC occurs in the surface layer of a steel sheet that is exposed to sulfides such as hydrogen sulfide, starting from a hardened surface area that has a hardness higher than a predetermined hardness upper limit. Furthermore, if the strength of the steel plate is insufficient, the steel plate may break at a softened surface layer whose hardness is lower than a predetermined lower limit of hardness in the surface layer of the steel plate. Therefore, during the manufacturing stage, such surface hardened parts and surface softened parts (hereinafter, the surface hardened parts and surface softened parts are collectively referred to as surface hardness change parts) are detected by hardness measurement, and the surface hardness changed parts are detected. There is a need to manufacture steel plates that do not have the above-mentioned properties, as well as steel products using steel plates.

As a method of measuring the hardness of the surface layer of a steel plate, for example, a method of measuring the electromagnetic characteristics of the surface layer of the steel plate is known. For example, in the technology described in Patent Document 1, while such electromagnetic characteristics show a correspondence relationship with the hardness of the steel plate, they vary in a manner that makes a simple analytical solution impossible. A method has been proposed to roughly estimate the hardness of a steel plate based on its properties. Specifically, the technology described in Patent Document 1 measures the hardness and electromagnetic properties of multiple steel samples having similar chemical compositions with respect to each electromagnetic property, and stores these measured values in a data bank. The hardness is stored in multiple quantized groupings for the electromagnetic properties. Then, multiple electromagnetic properties of the steel whose hardness is to be approximated are measured and compared with the quantized groupings stored in the data bank to determine the quantized grouping into which the measured electromagnetic properties fall. After that, the hardness is roughly estimated by comparing the results grouped by each electromagnetic property.

Special Publication No. 9-507570

However, the technique described in Patent Document 1 is limited to determining the grouping for each electromagnetic characteristic value, and only approximates the likely hardness from the grouping obtained from a plurality of electromagnetic characteristic values. There was only so much I could do. For this reason, it is not always possible to exclude cases where electromagnetic property values change due to influences other than hardness, but it is necessary to detect areas where hardness has changed by definitely deducting influences other than hardness, and to determine whether hardness is a quality problem. There was a need for a technology to manufacture steel plates that do not have any other parts.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and includes a method for producing a steel plate that can produce a steel plate that suppresses areas where hardness poses a quality problem on the target surface, and a method for producing a steel plate. It provides a manufacturing method, a steel plate manufacturing device, and a program.

The inventors measured parameters that change depending on the properties of the surface layer of steel materials of various steel types under various conditions. As a result, the inventors found that the measured parameters depended not only on the hardness of the surface layer but also on the stress state of the surface layer. It was also found that residual stress exists in the surface layer of steel sheets manufactured by controlled rolling and controlled cooling, and the stress state is non-uniform depending on the location. In other words, it was discovered that in order to accurately measure hardness and accurately identify and deal with areas where hardness poses quality problems, it is necessary to resolve the unevenness of the stress state in the surface layer of the steel sheet. Ta.

Based on this knowledge, in order to solve the above problems, the present invention employs the following means. That is, the method for manufacturing a steel plate according to one aspect of the present invention includes a rolling process of controllingly rolling a slab, a cooling process of controllingly cooling the steel plate that has been controlled and rolled in the rolling process, and a process of controllingly cooling the steel plate that has been controlled and cooled in the cooling process. a shot blasting step of adjusting the stress state of the surface layer of the steel sheet including the surface by impinging a blasting material on at least a part of the surface of the steel sheet; and a shot blasting step of adjusting the stress state of the surface layer of the steel sheet including the surface; and a hardness measurement step of measuring hardness; a hardness determination step of determining a region whose hardness exceeds a preset threshold as a hardness defective region based on the measurement result of the hardness measurement step; and a removal step of removing the hardness defective region. and a process.

According to this method, a blasting material is made to collide with the target surface of a steel plate that has been subjected to a rolling process and a cooling process in a shot blasting process. Thereby, even if the surface layer of the steel plate including the target surface is in a stress non-uniform state where the residual stress differs depending on the location after the cooling process, the stress non-uniform state can be resolved. Then, in the hardness measurement process, by measuring the hardness of the target surface after eliminating the non-uniformity of the stress state in the shot blasting process, it is possible to suppress the influence of stress and accurately measure hardness. I can do it. Therefore, in the hardness determination step, the defective hardness portion can be accurately determined based on the accurately measured hardness, and in the removal step, the defective hardness portion can be reliably removed.

Furthermore, in the method for manufacturing a steel plate described above, in the hardness measuring step, the hardness of the surface may be measured by measuring electromagnetic characteristics of the surface.

According to this method, the hardness can be accurately measured in the hardness measurement step without damaging the surface of the steel plate and without being affected by the state of stress.

Further, in the above method for manufacturing a steel plate, in the shot blasting step, a collision energy density given from the blasting material to the surface of the steel plate is 40 MJ/(m ² ·min) or more, and a cumulative collision energy is 1100 MJ/m. It may be ² or more.

According to this method, by setting the collision energy density and cumulative collision energy within the above numerical ranges, the stress state of the surface layer of the steel plate including the target surface can be made more uniform.

Further, in the above method for manufacturing a steel plate, the stress state of the surface layer of the steel plate including the surface of the steel plate is adjusted by repeatedly plastically deforming the steel plate, which is carried out between the cooling step and the hardness measuring step. It may also include a plastic deformation step.

According to this method, by performing the plastic deformation step between the cooling step and the hardness measurement step, the stress state of the surface layer of the steel plate including the target surface can be made more uniform.

Further, in the above method for manufacturing a steel plate, the steel plate is used as a material for a steel pipe, and the shot blasting step, the hardness measurement step, the hardness determination step, and the removal step are performed on a portion that becomes the inner surface of the steel pipe. Good as a thing.

According to this method, it is possible to manufacture a steel pipe in which poor hardness that is susceptible to corrosion is suppressed in the inner surface of the steel pipe where corrosion due to fluid flowing inside the pipe is likely to occur.

Further, in the above steel pipe manufacturing method, a first pressing step of pressing a steel plate manufactured by the steel sheet manufacturing method into a U-shape, and a step of pressing the steel plate processed in the first pressing step into an O-shape. The steel plate may include a second pressing step in which the steel plate is pressed, and a welding step in which the ends of the steel plate processed in the second pressing step are welded together.

According to this method, it is possible to manufacture a steel pipe in which poor hardness that is susceptible to corrosion is suppressed in the inner surface of the steel pipe where corrosion due to fluid flowing inside the pipe is likely to occur.

Further, the steel sheet manufacturing apparatus according to one aspect of the present invention includes a rolling section that performs controlled rolling of a slab, a cooling section that cools the steel sheet that has been controlled and rolled in the rolling section, and a steel sheet that is controlled and cooled in the cooling section. a shot blasting section that impacts the surface of at least a portion of the steel plate with a blasting material to adjust the stress state of the surface layer of the steel plate including the surface; and a shot blasting section that adjusts the stress state of the surface layer of the steel plate including the surface; and The hardness measurement unit includes a hardness measurement unit that measures hardness, and a hardness determination unit that determines a site whose hardness exceeds a preset threshold as a hardness defective site based on the measurement result of the hardness measurement unit.

According to this configuration, the shot blasting section collides the blasting material onto the target surface of the steel plate that has been rolled and cooled by the rolling section and the cooling section. Thereby, even if the surface layer of the steel plate including the target surface is in a stress non-uniform state where the residual stress varies depending on the location after cooling by the cooling unit, the stress non-uniform state can be resolved. Then, the hardness measuring section measures the hardness of the target surface after the unevenness of the stress state has been eliminated by the shot blasting section, suppressing the effects of stress and accurately measuring the hardness. be done. Therefore, the hardness determining section can accurately determine the poor hardness portion based on the accurately measured hardness, and the poor hardness portion can be reliably removed.

Further, the program according to one aspect of the present invention may cause a computer to apply a blast material to a surface of a steel plate produced by controlled rolling and controlled cooling, on which the stress state of the surface layer has been adjusted. Hardness calculating means for calculating the hardness of the surface from the measured electromagnetic characteristics; hardness determining means for determining a portion whose hardness exceeds a preset threshold value as having poor hardness based on the hardness calculated by the hardness calculating means; function as

According to the present invention, it is possible to manufacture steel plates and steel pipes with suppressed portions where hardness poses a quality problem on the target surface.

FIG. 1 is a side view schematically showing the steel plate manufacturing apparatus of the first embodiment. FIG. 2 is a cross-sectional view schematically showing a shot blasting section in the steel sheet manufacturing apparatus of the first embodiment, viewed in the conveyance direction. FIG. 2 is a block diagram schematically showing a hardness measuring section in the steel plate manufacturing apparatus of the first embodiment. It is a graph schematically showing an example of the correlation between electromagnetic property values, stress, and hardness. FIG. 2 is a block diagram showing the hardware configuration of a hardness calculation section and a hardness determination section according to the first embodiment. FIG. 2 is a flow diagram showing a method for manufacturing a steel plate according to the first embodiment. FIG. 2 is a flow diagram showing a method for manufacturing a steel pipe according to the first embodiment. FIG. 2 is a block diagram schematically showing a hardness measuring section in a steel sheet manufacturing apparatus according to a modification of the first embodiment. It is a schematic diagram of the waveform obtained by the hardness measurement part of the steel plate manufacturing apparatus of the modification of 1st Embodiment. FIG. 2 is a side view schematically showing a steel sheet manufacturing apparatus according to a second embodiment. FIG. 7 is a side view schematically showing plastic deformation imparting equipment in the steel plate manufacturing apparatus of the second embodiment. FIG. 2 is an explanatory diagram showing the dimensional relationship in the plastic deformation imparting equipment of the steel sheet manufacturing apparatus of the embodiment. It is a graph showing the relationship between the plate thickness and the depth from the surface of the range of plastic deformation at each working degree. FIG. 2 is a flow diagram showing a method for manufacturing a steel plate according to a second embodiment. FIG. 2 is a frequency distribution diagram showing the residual stress distribution on the surface of a steel plate, in Example 1, (a) immediately before the shot blasting process and (b) immediately after the shot blasting process. FIG. FIG. 2 is a contour diagram showing the stress state of the surface of the steel plate of Example 1 using electromagnetic characteristic values, showing (a) immediately before the shot blasting process, and (b) immediately after the shot blasting process. 3 is a graph showing the relationship between the collision energy density and cumulative collision energy applied to a steel plate in the shot blasting process in Example 2.

(First embodiment)
Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 shows a steel plate manufacturing apparatus 1 used in the steel plate manufacturing method of this embodiment.

As shown in FIG. 1, the steel sheet manufacturing apparatus 1 of this embodiment includes a continuous casting facility 10 that continuously casts slabs S, a reheating furnace 20 that reheats the slabs S, and a steel sheet P that performs controlled rolling of the slabs S. A rolling equipment 30 (rolling section), a hot straightening facility 40 for hot straightening the steel sheet P, and a cooling facility 50 (cooling section) for controlling and cooling the steel sheet P are provided. Further, the steel plate manufacturing apparatus 1 includes a shot blasting facility 60 (shot blasting section) that performs shot blasting on the controlled cooled steel plate P, and a hardness measuring section 70 that measures the hardness of the surface P1 of the shot blasted steel plate P. and a hardness determining section 90 that determines a site W with poor hardness based on the measurement result by the hardness measuring section 70. Details will be explained below.

The continuous casting equipment 10 has a mold 11 into which molten steel M is poured, and continuously produces slabs S from the mold 11. The reheating furnace 20 reheats the slab S produced by the continuous casting equipment 10 to a temperature at which it can be rolled by the rolling equipment 30 . Note that the steel plate manufacturing apparatus 1 may not include the continuous casting equipment 10, and may instead heat a pre-manufactured slab piece in the reheating furnace 20 and then roll it in the rolling equipment 30.

The rolling equipment 30 performs controlled rolling on the slab S. The rolling equipment 30 has a rough rolling section 31 and a finish rolling section 32. The rough rolling section 31 performs rough rolling on the slab S reheated by the reheating furnace 20 . Further, the finish rolling section 32 performs finish rolling on the slab S that has been rough rolled in the rough rolling section 31 to produce a steel plate P. The rough rolling section 31 has a plurality of upper and lower rough rolling rollers 31a and 31b. Further, the finish rolling section 32 has a plurality of upper and lower finish rolling rollers 32a and 32b. Both the rough rolling section 31 and the finish rolling section 32 control the rolling reduction rate etc. by the rough rolling rollers 31a, 31b and the finishing rolling rollers 32a, 32b based on information such as the temperature of the steel plate P measured in advance. Then, controlled rolling is performed to produce a desired steel plate P by setting the temperature, rolling reduction, etc. within a preset range. The hot straightening equipment 40 hot straightens the steel plate P produced by the rolling equipment 30. The hot straightening equipment 40 has a plurality of upper and lower straightening rollers 40a, 40b, and corrects the flatness of the steel plate P by adjusting the vertical distance between the straightening rollers 40a, 40b.

The cooling equipment 50 performs controlled cooling on the steel plate P produced by the rolling equipment 30. Here, controlled cooling means controlling the structure of the steel plate P by cooling at a cooling start temperature, a cooling stop temperature, and a cooling rate within a preset range. Specifically, controlled cooling is a process that includes water cooling, which has a faster cooling rate than natural cooling, accelerated cooling using air cooling, natural cooling, and gradual cooling, which has a slower cooling rate than natural cooling, and heating may be performed in the middle. . Controlled cooling also includes multi-stage cooling, in which the cooling rate of accelerated cooling is changed midway through, and intermittent cooling, in which accelerated cooling is stopped midway, natural cooling is performed, and accelerated cooling is restarted.

In this embodiment, the cooling equipment 50 includes a plurality of upper and lower transport rollers 51a, 51b that transport the steel plate P, and a water cooling section 52 that water cools the steel plate P transported by the transport rollers 51a, 51b. The water cooling section 52 injects cooling water onto the steel plate P. A plurality of water cooling units 52 are provided along the conveyance direction above the upper surface P1a which is the surface P1 of the steel plate P conveyed by the conveyance rollers 51a and 51b, and below the lower surface P1b which is the surface P1 as well. A plurality of them are provided along the direction. The water cooling unit 52 cools the steel plate P by injecting cooling water onto the upper surface P1a and the lower surface P1b of the steel plate P.

The shot blasting equipment 60 performs shot blasting on the steel plate P. In this embodiment, the shot blasting equipment 60 performs shot blasting on only the upper surface P1a of the surface P1 of the steel plate P, which will become the inner surface Q1 (see FIG. 7) of the steel pipe Q by subsequent processing as described later, and performs shot blasting on the lower surface P1b. Not implemented. The shot blasting equipment 60 is provided above the steel plate P, and includes an injection section 61 that injects the blasting material A, and a conveyance roller 62 that conveys the steel plate P. In this embodiment, the injection parts 61 are provided at a plurality of different locations in the conveyance direction P (two locations in FIG. 1). In addition, the injection unit 61 is configured such that the injection ranges to the surface P1 of each steel plate P overlap each other in the width direction perpendicular to the conveyance direction at each location, and is capable of spraying over the entire width direction of the surface P1 of the steel plate P. A plurality of them are provided at intervals such that As shown in FIG. 2, each injection section 61 includes a supply section (not shown) that supplies blast material A, injection blades 61a that are arranged radially and rotate and accelerate the supplied blast material A, and It has a jetting port 61b that jets the blasting material A toward the steel plate P.

The blasting material A is injected onto a predetermined range of the steel plate P by the injection part 61. As a result, the surface layer portion of the surface P1 of the steel plate P, including the upper surface P1a onto which the blasting material A has been sprayed, is plastically deformed by the impact of the blasting material A, and the stress state of the surface layer portion is adjusted and made uniform. I can do it. Here, uniformity of the stress state not only means that the stress is equalized in the target range from a state where the stress varies, but also that the stress is not affected by stress in the hardness measurement process by the hardness measurement unit described later. It also includes adjusting the stress to such a degree that the hardness can be measured. The steel plate P is conveyed by the conveyance roller 62 and is sprayed with the blasting material A by the spraying section 61, thereby uniformly spraying the blasting material A over the entire upper surface P1a, thereby imparting plasticity to the surface layer over the entire upper surface P1a. Deformation is applied.

In this embodiment, the blast material A is a spherical member made of steel. However, as the granular blasting material A used in the shot blasting process, various materials can be used as long as it is possible to plastically deform the surface P1 of the steel plate P. The material is not limited to steel, and may be other metal materials or ceramic materials. Furthermore, the particle shape is not limited to spherical, but may also be ellipsoidal or polygonal. Alternatively, the blasting material A may be a so-called sandblasting material in which the blasting material A is made of sand. In the case of spherical blasting material A, the diameter of the particles is preferably 0.5 mm or more and 3.0 mm or less. When the diameter of the grains is 0.5 mm or more, impact energy can be applied more effectively to the surface P1 of the steel plate P. In addition, since the diameter of the grains is 3.0 mm or less, the roughness of the shot blasted surface can be improved to 100 μm or less in ten-point average roughness (JIS B 0601 Appendix JA) R _ZJIS . can do. Note that the diameter of the particles is more preferably 2.0 mm or less. By setting the diameter of the grains to 2.0 mm or less, the roughness of the shot blasted surface can be further improved to _RZJIS 50 μm or less.

Further, it is preferable that the collision energy density given to the surface P1 of the steel plate P by the blasting material A injected from the injection part 61 is 40 MJ/(m ² ·min) or more. Furthermore, it is more preferable that the collision energy density is 200 MJ/(m ² ·min) or more. Moreover, it is preferable that the cumulative collision energy given to the surface P1 of the steel plate P by the blasting material A injected from the injection part 61 is 1100 MJ/m ² or more. The collision energy density (MJ/(m ² ·min)) is determined by the injection speed (m/sec) of the blasting material, the injection flow rate (kg/min), the injection area (m ² ) that can be injected by the injection unit 61, and the conveyance roller. It can be determined by the threading speed (mpm) of the steel plate P conveyed by the steel plate 62. Further, the cumulative collision energy density (MJ/m ² ) can be determined by dividing the collision energy by the sheet passing speed. Since the collision energy density is 40 MJ/(m ² · min) or more and the cumulative collision energy is 1100 MJ/m ² or more, the stress in the surface layer portion including the surface P1 of the steel plate P on which the blasting material A has been injected is It becomes possible to uniformize the state more suitably. Further, by setting the collision energy density to 200 MJ/(m ² ·min) or more, the stress state of the surface layer portion can be more effectively made uniform.

In addition, in the above, in order to perform shot blasting on the upper surface P1a of the steel plate P, the injection part 61 was provided above the steel plate P, but it is not limited to this. Shot blasting may be performed on both the upper surface P1a and lower surface P1b of the steel plate P, or, if hardness determination of the lower surface P1b is required, shot blasting may be performed only on the lower surface P1b. When performing shot blasting on the lower surface P1b, a configuration may be adopted in which a spraying section 61 is provided below the steel plate P to spray the blasting material A toward the lower surface P1b of the steel plate P.

The hardness measurement unit 70 measures the hardness of the surface P1 of the steel plate P that has been subjected to shot blasting. In this embodiment, since shot blasting was performed on the upper surface P1a of the surface P1 of the steel plate P, the hardness measurement unit 70 measures the hardness of the upper surface P1a.

As shown in FIG. 3, the hardness measurement unit 70 of this embodiment is a device that measures hardness based on parameters that vary depending on the properties of the surface layer of the steel plate P. The parameters of this embodiment include, for example, parameters that are input to generate a magnetic field when a magnetic field is applied to the surface layer of the steel plate P and that change depending on the properties of the surface layer, and parameters that change the magnetic field. It includes parameters whose values are measured according to the properties of the surface layer by multiplying the parameters. Note that when a magnetic field is applied to the surface layer of the steel plate P, parameters that change under the influence of the properties of the surface layer are collectively referred to as electromagnetic characteristics, and the values of the obtained parameters are referred to as electromagnetic characteristic values. Hereinafter, a case will be described in which the parameter that changes depending on the properties of the surface layer of the steel plate P is the electromagnetic property of the surface layer of the steel plate P.

The hardness measurement unit 70 includes a parameter measurement unit 700 that measures electromagnetic property values of the surface layer of the steel plate P, and a hardness calculation unit 720 that calculates the hardness of the surface layer of the steel plate P based on the electromagnetic property values measured by the parameter measurement unit 700. Equipped with Here, the hardness in this embodiment includes hardness determined by various tests. For example, the Vickers hardness is determined by the Vickers hardness test, the Brinell hardness is determined by the Brinell hardness test, the Knoop hardness is determined by the Knoop hardness test, and the Rockwell hardness is determined by the Rockwell hardness test. In addition, these hardnesses do not have to be values measured by the test method that measures each hardness, but if the correlation is known in advance, the measured values can be obtained based on the results measured by a rebound tester. Alternatively, the measured value obtained by the rebound test itself may be used as an index of hardness. In the following description, Vickers hardness will be measured as an example, and will simply be referred to as hardness.

As shown in FIG. 3, in this embodiment, the parameter measurement unit 700 is a device that measures electromagnetic characteristic values obtained from the BH loop of the steel plate P, for example. The BH loop is correlation data showing the relationship between the strength H of the magnetic field periodically applied to the surface layer of the steel plate P and the magnetic flux density B generated in the surface layer of the steel plate P due to the applied magnetic field. The parameter measurement section 700 includes a magnetizer 710, an oscillator 712, an excitation power source 713, a magnetic field calculation section 714, a detection coil 715, a magnetic flux density calculation section 716, a BH loop calculation section 717, and an electromagnetic characteristic value detection section. 718.

The magnetizer 710 is disposed above the upper surface P1a with a gap between the surface layer portion of the steel plate P to be measured, that is, the upper surface P1a of the surface layer portion including the shot blasted upper surface P1a. ing. Magnetizer 710 has a yoke 711A and an exciting coil 711B. The U-shaped yoke 711A has a body portion 711b and a pair of tip portions 711a formed at both ends of the body portion 711b. The pair of tip portions 711a are arranged such that the tip surfaces serving as magnetic poles face the surface P1 of the surface layer of the steel plate P to be measured. The excitation coil 711B is wound around each of the tip portions 711a. With such a configuration, the yoke 711A has an alternating current flowing through the excitation coil 711B, so that a strength H corresponding to the magnitude of the alternating current is applied to the surface layer of the steel plate P disposed at a position facing the tip portion 711a. A magnetic field can be generated.

The oscillator 712 outputs a signal with a frequency corresponding to the frequency of the target alternating current. Excitation power supply 713 outputs an alternating current according to the frequency of the signal received from oscillator 712 to excitation coil 711B. Furthermore, the excitation power source 713 can set the magnitude of the alternating current to be output, that is, the amplitude of the alternating current. The magnetic field calculation unit 714 detects the magnitude of the alternating current output from the excitation power supply 713 to the excitation coil 711B, and based on the magnitude of the detected alternating current, the pre-stored number of turns of the excitation coil 711B, etc. The strength H of the magnetic field generated on the surface layer of is calculated. The magnetic field calculation unit 714 outputs the calculated magnetic field strength H to the BH loop calculation unit 717.

The detection coil 715 is wound around at least one of the pair of tip portions 711a so as to surround the tip surface that becomes a magnetic pole. The magnetic flux Φ generated in the gap between the magnetic pole and the surface P1 of the steel plate P changes depending on the magnetic field generated by the magnetizer 710 and the state of the surface layer of the steel plate P. A voltage is generated in the detection coil 715 by electromagnetic induction in accordance with the time change of this magnetic flux Φ. The magnetic flux density calculation unit 716 detects the voltage generated in the detection coil 715, and calculates the magnetic flux density B from the detected voltage, the predetermined number of turns of the detection coil 715, the cross-sectional area of the detection coil 715, etc. . The magnetic flux density calculation unit 716 outputs the calculated magnetic flux density B to the BH loop calculation unit 717.

The BH loop calculation unit 717 calculates the difference between the magnetic field strength H and the magnetic flux density B based on the magnetic field strength H output from the magnetic field calculation unit 714 and the magnetic flux density B output from the magnetic flux density calculation unit 716. Compute a BH loop that shows the relationship. FIG. 4 shows an example of a BH loop calculated by the BH loop calculation unit 717. Using the BH loop as shown in FIG. 4, it is possible to obtain electromagnetic characteristic values of the surface layer of the steel plate P to be measured. Specifically, the electromagnetic characteristic values include residual magnetic flux density Br, coercive force Hc, magnetic permeability μ, and the like. The residual magnetic flux density Br is the magnetic flux density B at a point R2 where the magnetic field strength H is reduced to zero from a point R1 where H is maximum in the BH loop. Further, the coercive force Hc indicates the strength of the magnetic field at a point R3 where the direction of the magnetic field is further reversed and the magnetic flux density B becomes zero. Further, the magnetic permeability μ indicates the rate of change of the magnetic flux density B with respect to the magnetic field strength H when the magnetic field strength is varied by ΔH at a given magnetic field strength H. Note that the electromagnetic characteristic values are not limited to the residual magnetic flux density Br, the coercive force Hc, and the magnetic permeability μ, but are not limited to these as long as they are electromagnetic characteristic values detected by changes in the strength of the magnetic field. In this embodiment, the electromagnetic characteristic value detection unit 718 extracts, for example, the coercive force Hc. However, the present invention is not limited to this, and the electromagnetic characteristic value detecting section 718 may detect residual magnetic flux density Br, magnetic permeability μ, etc. instead of coercive force Hc, or may detect a plurality of types of electromagnetic characteristic values. The electromagnetic characteristic value detection section 718 outputs the extracted electromagnetic characteristic value to the hardness calculation section 720.

Next, the hardness calculation section 720 will be explained. As shown in FIG. 5, the hardness calculation unit 720 is a functional unit that is realized by executing a program by a control unit 80 that includes a processor 800 such as a CPU (Central Processing Unit) and a memory 810 that are connected via a bus. It is. The hardness calculating section 720 calculates the hardness based on the correlation between the hardness and the electromagnetic characteristic value stored in advance in the storage section 82 and the electromagnetic characteristic value measured by the hardness measuring section 70.

Note that all or part of each function of the hardness calculation unit 720 may be implemented using an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable GaN). It may be realized using hardware such as TE Array). . The program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, magneto-optical disk, ROM, or CD-ROM, or a storage device such as a hard disk built into a computer system. The program may be transmitted via a telecommunications line.

The output unit 81 outputs various information. The output unit 81 outputs, for example, the hardness measured by the parameter measurement unit 700 and calculated by the hardness calculation unit 720 at an arbitrary position on the surface of the steel plate P. Alternatively, position information may be acquired, and the position information and information regarding hardness may be displayed in association with each other. Further, information regarding the hardness may be visually displayed using numerical values or colors on the plane showing the steel plate P based on the position information and the hardness. The output unit 81 is configured to include a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, and an organic EL (Electro-Luminescence) display. The output unit 81 may be configured as an interface that connects these display devices to its own device.

The hardness determination unit 90 shown in FIG. 1 is a functional unit realized by executing a program in the same way as the hardness calculation unit 720 by the control unit 80 shown in FIG. The hardness determining section 90 determines, based on the hardness measured by the hardness measuring section 70, whether the position where the hardness was measured is a hardness defective region. In this embodiment, a hardened surface portion whose hardness is higher than a predetermined upper limit value of hardness is detected on the target upper surface P1a of the surface P1 of the steel plate P. That is, the hardness determination unit 90 compares the upper limit value stored in advance in the storage unit 82 with the hardness measured by the hardness measurement unit 70, and if the measured hardness exceeds the upper limit value, the hardness determination unit 90 determines the position. It is determined that the part W has poor hardness. In addition, the hardness determination unit 90 may detect a surface softened portion whose hardness is lower than a predetermined lower limit of hardness on the target upper surface P1a of the surface P1 of the steel plate P. The hardness determination unit 90 detects a surface hardness change portion of at least one of a surface hardening portion and a surface softening portion as a hardness defective portion W. The hardness determination section 90 causes the output section 81 to display the region determined as the defective hardness region W together with position information.

In addition, in the steel plate manufacturing apparatus 1 of this embodiment, the hardness measurement unit 70 and the hardness determination unit 90 are connected to the continuous casting equipment 10, the reheating furnace 20, the rolling equipment 30, the hot straightening equipment 40, the cooling equipment 50, and the shot Although the line has been described as being integrated with the blast equipment 60, the line is not limited to this. The steel plate P that has been subjected to shot blasting is transported to another line, and a hardness measurement step S7 and a hardness determination step S8, which will be described later, are carried out by a hardness measurement section 70A and a hardness determination section 90 configured as devices in the other line. You may do so. Furthermore, the shot blasting equipment 60 may also be set as a separate line, and the steel plate P cooled by the cooling equipment 50 may be transported to the separate line, and the shot blasting process S6 described later may be performed by the shot blasting equipment 60 in the separate line. .

Further, an annealing process may be performed on the steel plate P after the controlled cooling is performed. When implementing the annealing process, an annealing facility may be provided between the cooling facility 50 and the shot blasting facility 60. Further, an internal defect detection step may be performed to detect internal defects on the manufactured steel plate P. When performing the internal defect detection process, for example, the internal defect detection equipment is provided after the cooling equipment 50 when the annealing process is not performed, and after the annealing equipment when the annealing process is performed. Examples of the internal defect detection equipment include an ultrasonic flaw detection testing device that detects internal defects by emitting ultrasonic waves to the steel plate P and detecting reflected waves.

Next, a method for manufacturing a steel plate according to the present embodiment will be explained. FIG. 6 shows a flow diagram of the method for manufacturing a steel plate according to this embodiment. As shown in FIG. 6, the method for manufacturing a steel plate according to the present embodiment includes a casting process S1 of continuously casting a slab S, a reheating process S2 of reheating the slab S, and a controlled rolling of the slab S to form a steel plate P. A hot straightening process S4 for hot straightening the steel plate P, and a cooling process S5 for controlling and cooling the steel plate P. Furthermore, the manufacturing method of the steel plate P of this embodiment includes a shot blasting process S6 in which shot blasting is performed on the steel plate P that has been controlled and cooled, and a hardness measuring process S7 in which the hardness of the surface P1 of the shot blasted steel plate P is measured. and a hardness determination step S8 of determining a site W with poor hardness based on the hardness measurement results. Furthermore, the method for manufacturing a steel plate of the present embodiment includes a surface polishing step S9 of polishing the surface of a portion determined to be a defective hardness portion W, and a hardness confirmation step S10 of confirming the hardness of the defective hardness portion W whose surface has been polished. , a removal step S11 in which the defective hardness portion W is removed based on the hardness confirmation result, a hardness reconfirmation step S12 in which the hardness is confirmed again after the removal step S11, and a thickness confirmation step S13 in which the thickness of the steel plate P is measured. S14. Details will be explained below.

In the casting process S1, a slab S is produced by the continuous casting equipment 10. Further, in the reheating step S2, the slab S produced by the continuous casting equipment 10 is reheated by the reheating furnace 20 to a temperature at which it can be rolled by the rolling equipment 30. Note that the casting step S1 may not be performed, and a pre-manufactured slab piece may be heated in the reheating furnace 20 and then rolled in the rolling step S3 described below.

In the rolling process S3, the slab S is controlled-rolled by the rolling equipment 30. In the present embodiment, the rolling process S3 includes a rough rolling process S3a in which the reheated slab S is roughly rolled, and a finish rolling process in which the rough rolled slab S is subjected to finish rolling to produce the steel plate P. Step S3b is performed. In the hot straightening step S4, the hot straightening equipment 40 hotly straightens the flatness of the steel plate P produced by controlled rolling. In the cooling step S5, the cooling equipment 50 performs controlled cooling on the steel plate P that has been subjected to controlled rolling.

In the shot blasting process S6, the shot blasting equipment 60 performs shot blasting on the controlled cooled steel plate P. In this embodiment, shot blasting is performed on the upper surface P1a of the surface P1 of the steel plate P. Various blasting materials A can be used for shot blasting as long as they can plastically deform the surface P1 of the steel plate P. Further, the preferable degree of energy given to the steel plate P by the blasting material A is as described above, and the collision energy density is preferably 40 MJ/(m ² ·min) or more, and 200 MJ/(m ² ·min) or more. More preferably, the cumulative collision energy is 1100 MJ/m ² or more.

In the hardness measurement step S7, the hardness measurement unit 70 measures the hardness of the surface P1 of the steel plate P that has been subjected to shot blasting. In the hardness measurement step S7 of the present embodiment, since shot blasting was performed on the upper surface P1a of the surface P1 of the steel plate P, hardness measurement is performed on the upper surface P1a. In the hardness measurement step S7 of this embodiment, hardness is measured based on parameters that vary depending on the properties of the surface layer of the steel plate P. Parameters in this embodiment include electrical characteristic values such as the residual magnetic flux density Br, coercive force Hc, and magnetic permeability μ as described above. The method of measuring hardness is not limited to the method of measuring hardness based on parameters that change depending on the properties of the surface layer of the steel plate P, as described above, but also the method of measuring hardness directly, such as the rebound hardness test. It may also be used as a test method.

In the hardness determination step S8, the hardness determination unit 90 determines whether or not there is a poor hardness region W on the measured upper surface P1a based on the measured hardness. The algorithm for determining the portion W with poor hardness is as described above. Note that if the presence of the poor hardness site W is not confirmed, the steel plate manufacturing method of this embodiment is completed, and the steel plate P is taken out as a product.

In the surface polishing step S9, in order to directly measure the hardness and confirm the hardness in the hardness confirmation step S10, which will be described later, the surface of the portion determined to be the poor hardness portion W is polished to remove scale on the surface. Examples of the polishing method include a method of polishing the surface with a grinder. When the surface is polished with a grinder, the particle size of the abrasive powder used as the abrasive is, for example, P100 to 180 (JIS R6001). By performing the surface polishing step S9, scale existing on the surface P1 of the steel plate P is removed, for example, within a depth range of about 0.01 to 0.1 mm.

In the hardness confirmation step S10, the hardness is confirmed again at the position where the scale is removed on the surface P1 of the steel plate P, which is determined to be a site W with poor hardness (step S10a). In this embodiment, a test method that directly measures hardness, such as a rebound hardness test, is used. Thereby, hardness can be measured more accurately in a narrower range than when hardness is measured indirectly. Note that, similarly to the hardness measuring step S7, the hardness may be measured indirectly. Furthermore, when measuring the hardness indirectly, the surface polishing step S9 may be omitted. If the poor hardness portion W is not confirmed by the measurement result in the hardness confirmation step S10 (step S10b: NO), the steel plate manufacturing method is completed and the steel plate P is taken out as a product. On the other hand, if the defective hardness site W is confirmed (step S10b: YES), the process moves to the removal step S11.

In the removal step S11, the poor hardness portion W confirmed in the hardness confirmation step S10 is removed. Specifically, a grinding device performs grinding on the position where the defective hardness region W exists. Examples of the grinding method include a method of grinding the surface with a grinder. When grinding the surface with a grinder, the particle size of the grinding powder used as the abrasive material is, for example, P36 to 60 (JIS R 6010). Thereby, the steel material causing poor hardness can be removed from the surface P1 of the steel plate P, for example, within a depth range of about 0.1 to 0.5 mm. Since poor hardness may occur at least within a range of about 0.25 mm from the surface, it is preferable to grind at least within a range exceeding 0.25 mm from the surface. After removal, a hardness reconfirmation step S12 is performed.

In the hardness reconfirmation step S12, the hardness is confirmed again at the position where the steel material on the surface P1 was removed because it was determined to be a site W with poor hardness (step S12a). In this embodiment, a test method that directly measures hardness, such as a rebound hardness test, is used. Note that, similarly to the hardness confirmation step S10, the hardness may be carried out using a measurement method that indirectly measures the hardness, similarly to the hardness measurement step S7. If the hardness defective portion W is not confirmed by the measurement result in the hardness reconfirmation step S12 (step S12b: NO), the process moves to the thickness confirmation step S13. On the other hand, if the defective hardness site W is confirmed (step S12b: YES), the process moves to the thickness confirmation step S14.

In the thickness confirmation step S13, the thickness of the steel plate P from which it has been confirmed that the defective hardness portion W has been removed is measured (step S13a). The range for measuring the thickness may be the entire steel plate P, or may be only the position where the poor hardness portion W has been removed in the removal step S11. As a measurement method, for example, an ultrasonic flaw detection test is used. The thickness of the steel plate P at the measurement position can be measured by transmitting ultrasonic waves from one surface using an ultrasonic testing machine and measuring the reflected waves reflected from the opposite surface. As a result of the measurement, if the thickness of the steel plate P is equal to or greater than a preset reference value (step S13b: YES), the steel plate manufacturing method is completed and the steel plate P is taken out as a product. On the other hand, as a result of the measurement, if the thickness of the steel plate P is less than a preset reference value (step S13b: NO), it is determined that the product is defective.

Further, in the thickness confirmation step S14, the thickness of the steel plate P for which it has been confirmed that the defective hardness portion W remains is measured (step S14a). The range for measuring the thickness may be the entire steel plate P, or may be only the position where the hardness defective portion W is ground in the removal step S11. The measurement method is the same as the thickness confirmation step S13. As a result of the measurement, if the thickness of the steel plate P is equal to or greater than a preset reference value (step S14b: YES), the removal step S11 is performed again. On the other hand, as a result of the measurement, if the thickness of the steel plate P is less than a preset reference value (step S14b: NO), it is determined that the product is defective.

In addition, in the manufacturing method of the said steel plate, you may implement the annealing process which anneals the steel plate P after cooling process S5. Further, an internal defect detection step may be performed to detect internal defects on the manufactured steel plate P. If the internal defect detection step is to be performed, it is performed after the cooling step S5 if the annealing step is not performed, and after the annealing step if the annealing step is to be performed. Examples of the inspection method carried out in the internal defect detection step include the ultrasonic flaw detection test as described above.

Moreover, although the above method for manufacturing a steel plate includes a surface polishing step S9, a hardness confirmation step S10, a hardness reconfirmation step S12, and thickness confirmation steps S13 and S14, the present invention is not limited thereto. For example, after carrying out up to the hardness determination step S8, if the existence of the poor hardness region W is not confirmed, the manufacturing method of the steel plate P is completed, and even if the existence of the poor hardness region W is confirmed, the method for manufacturing the steel plate P is completed. The method for manufacturing the steel plate P may be completed by performing the removal step S11.

As described above, in the steel plate manufacturing method and steel plate manufacturing apparatus 1 of the present embodiment, blasting material is applied to the target surface P1 in the shot blasting process S6 for the steel plate P that has been subjected to the rolling process S3 and the cooling process S5. Collide A. As a result, even if the steel plate P after the cooling step S5 is in a state where the stress is uneven and the residual stress varies depending on the location, the stress is uneven in the surface layer portion of the steel plate P including the upper surface P1a which is the target surface P1. The uniform state can be resolved. Then, in the hardness measurement step S7, the hardness of the target surface P1 is measured with the non-uniformity of the stress state eliminated in the shot blasting step S6, thereby suppressing the influence of stress and accurately measuring the hardness. can be measured. Therefore, in the hardness determination step S8, the defective hardness region W can be accurately determined based on the accurately measured hardness, and the defective hardness region W can be reliably removed in the removal step S11. Therefore, on the target surface P1, it is possible to manufacture a steel plate P in which portions where hardness poses a quality problem are suppressed.

In addition, in the hardness measurement step S7, by measuring the electromagnetic characteristics of the surface P1 of the steel plate P, the surface P1 of the steel plate P whose hardness is to be measured is not damaged and is not affected by the state of stress. Hardness can be measured accurately. Furthermore, by setting the collision energy density to 40 MJ/(m ² ·min) or more and the cumulative collision energy to 1100 MJ/m ² or more, the stress state of the surface layer of the steel plate P including the target surface P1 is made more uniform. be able to.

Moreover, the steel plate P manufactured by such a manufacturing method of the steel plate P is used as a material for the steel pipe Q, and the shot blasting process S6, the hardness measurement process S7, the hardness determination process S8, and the removal process S11 are performed on the inner surface Q1 of the steel pipe Q. (See Fig. 7 and below), that is, the upper surface P1a of the above-mentioned steel plate P is carried out, so that the influence of corrosion on the inner surface Q1 of the steel pipe Q, where corrosion due to the fluid flowing inside is concerned, is carried out. It is possible to manufacture a steel pipe Q in which hardness defects W that are susceptible to damage are suppressed.

The method for manufacturing the steel plate P described above may be implemented as a step in the method for manufacturing a steel pipe to manufacture the steel pipe Q. That is, as shown in FIG. 7, the method for manufacturing the steel pipe Q of the present embodiment includes a steel plate manufacturing process S20 in which the steel plate P is manufactured by the above-described method for manufacturing the steel plate P, a first press process S21, and a second press. It includes a step S22 and a welding step S23. In the first pressing step S21, the steel plate P produced by the steel plate production method described above is pressed into a U-shape to form a U-shaped intermediate material P'. At that time, the upper surface P1a of the steel plate P on which the shot blasting step S6, the hardness measurement step S7, the hardness determination step S8, and the removal step S11 were performed becomes the inner surface Q1 when the steel pipe Q is formed, in other words, it is a concave curved surface. The steel plate P is processed into a U-shape. In the second pressing step S22, the U-shaped intermediate material P' processed in the first pressing step S21 is pressed into an O-shape to form an O-shaped intermediate material P''. Furthermore, in the welding step S23, the portions of the O-shaped intermediate material P'' processed in the second pressing step S22, which are the ends of the steel plate P, are welded together along the welding line Q2.

According to such a method of manufacturing a steel pipe, it is possible to manufacture a steel pipe Q in which poor hardness areas W that are susceptible to corrosion are suppressed in the inner surface Q1 of the steel pipe Q where corrosion due to fluid flowing inside is a concern. I can do it. Furthermore, in the method for manufacturing a steel pipe described above, a UOE steel pipe can also be manufactured by performing a diameter expansion process of expanding the diameter of the steel pipe Q after the welding process S23.

In addition, in the hardness measurement step S7, the BH loop is measured for the steel plate P to be inspected, and the hardness is calculated by obtaining the electromagnetic characteristic value obtained from the BH loop, but the method is not limited to this. do not have. FIGS. 8 and 9 show a hardness measuring section 70A in a modified steel sheet manufacturing apparatus 1A used in the hardness measuring step S7.

As shown in FIG. 8, the hardness measuring section 70A of the steel plate manufacturing apparatus 1A of this modification is an eddy current flaw detection device. That is, the hardness measurement section 70A includes an inspection probe 851, an oscillator 852, a bridge 853, a phase shifter 854, an amplifier 855, a synchronous detector 856, a waveform generation section 857, and an electromagnetic characteristic value detection section 858. has. The inspection probe 851 has a measurement coil 851a. Oscillator 852 generates a reference signal having a predetermined frequency and outputs it to bridge 853 and phase shifter 854. Bridge 853 converts minute impedance changes of measurement coil 851a into voltage and outputs it to amplifier 855. Amplifier 855 amplifies the signal output from bridge 853 and outputs it to synchronous detector 856. The phase shifter 854 generates a signal whose phase is shifted while maintaining the frequency of the reference signal, and outputs it to the synchronous detector 856. The synchronous detector 856 synchronously detects the signal output from the amplifier 855 using the signal output from the phase shifter 854, extracts a DC component, and outputs it to the waveform generator 857. The waveform generator 857 generates a waveform as shown in FIG. 9 based on the signal output from the synchronous detector 856. The electromagnetic characteristic value detection unit 858 detects, for example, the eddy current phase δ from the waveform generated by the synchronous detector 856 as the electromagnetic characteristic value. Then, the electromagnetic characteristic value detection section 858 outputs the eddy current phase δ, which is the electromagnetic characteristic value, to the hardness calculation section 720. The hardness calculation unit 720 calculates the correlation between the hardness stored in advance in the storage unit 82 (see FIG. 5) and the eddy current phase δ, which is an electromagnetic characteristic value, and the eddy current phase δ, which is measured by the hardness measurement unit 70A. Calculate hardness based on

As described above, the device for measuring electromagnetic characteristic values is not limited to a device for detecting a BH loop, but may be an eddy current flaw detection test device as in this embodiment, and the electromagnetic characteristic values obtained thereby may be used. Further, a device for detecting a BH loop and an eddy current flaw detection test device may be combined, or a device other than a device for detecting a BH loop and an eddy current flaw detection test device may be used. Any device that can generate a magnetic field at least on the surface layer of the steel plate P and measure electromagnetic characteristic values that provide different responses depending on the difference in hardness can be applied.

(Second embodiment)
Next, a second embodiment of the present invention will be described. 10 to 12 show a second embodiment of the present invention. In this embodiment, members common to those used in the above-described embodiments are given the same reference numerals, and their explanations will be omitted.

As shown in FIG. 10, the steel plate manufacturing apparatus 1B of the present embodiment includes a flatness measurement section 900 and a plastic deformation imparting facility 910 (plastic deformation imparting section) between the cooling facility 50 and the shot blasting facility 60. Equipped with The flatness measurement unit 900 measures the flatness of the upper surface P1a, which is the target surface P1 of the steel plate P. The flatness measurement unit 900 includes a conveyance roller 901 that conveys the steel plate P, and a laser distance meter 902 that is arranged at a position spaced apart above the upper surface P1a that measures the flatness of the steel plate P conveyed by the conveyance roller 901. have The laser distance meter 902 measures the distance to the irradiation position by irradiating a laser onto the upper surface P1a of the steel plate P conveyed by the conveyance roller 901 and receiving the reflected light. A plurality of laser distance meters 902 are provided in the width direction (that is, the depth direction of the sheet) perpendicular to the conveyance direction, and can measure distances over the entire width of the steel plate P. Therefore, while the steel plate P is being conveyed by the conveyance roller 901, the distance can be measured over the entire upper surface P1a, and the flatness of the upper surface P1a can be measured from the distance measurement result.

In this embodiment, the plastic deformation imparting equipment 910 is a flatness correction unit that repeatedly plastically deforms the steel plate P by correcting the flatness of the steel plate P. As shown in FIG. 11, the plastic deformation imparting equipment 910 includes a plurality of lower rollers 911 disposed below the steel plate P being transported, and a plurality of upper rollers 912 disposed above the steel plate P. The lower roller 911 and the upper roller 912 are arranged so as to be shifted in position in the conveying direction. Further, at least one of the lower roller 911 and the upper roller 912 is provided to be movable up and down, so that the distance between the lower roller 911 and the upper roller 912 can be adjusted. Then, the distance between the upper end of the lower roller 911 and the lower end of the upper roller 912 is set to be less than or equal to the thickness of the steel plate P, or the upper end of the lower roller 911 is set above the lower end of the upper roller 912 (if the distance dimension is negative). By making the steel plate P meander between the upper ends of the plurality of lower rollers 911 and the lower ends of the plurality of upper rollers 912 according to the interval, the steel plate P undergoes tensile deformation and compressive deformation. is repeated. Then, on the surface side, the tensile stress associated with tensile deformation and the compressive stress associated with compressive deformation exceed the yield stress depending on the size of the above-mentioned interval, and as a result, tensile plastic deformation and compressive plastic deformation occur in the surface layer of the steel plate P. That is, by the plastic deformation imparting equipment 910, tensile plastic deformation and compressive plastic deformation are alternately and repeatedly performed on the surface layer portion including the surface of the steel plate P. Thereby, the residual compressive stress occurring in the surface layer portion including the surface P1 of the steel plate P after controlled cooling is alleviated.

As mentioned above, the thickness of the plastic deformation region generated in the surface layer portion can be expressed by the working degree K. The working degree K is the ratio of the total thickness of the steel plate P to the thickness of the plastic deformation region. The degree of machining caused by meandering between the upper ends of the plurality of lower rollers 911 and the lower ends of the plurality of upper rollers 912 as described above is shown as follows.

That is, the curvature k of the steel plate P meandering between the lower ends of the plurality of upper rollers 912 is determined from Hibino's practical formula (see reference document 1) and FIG. 12 as shown in formula (1).
References 1: Japan Plastic Processing Society, "How to straighten the orthodontic processing -plate, tube, sticks, and lines -STRAIGHTENING OF METAL PRODUCTS -TECHNOLOGY TO STRAIGHTEN SHEET, TUBE AND OTHEET ERS-, Corona Co., Ltd., 1992 January 20, p. 29-89

However, k: curvature m: constant (=6: see reference 1)
d: Intermesh (pushing amount) (mm)
L: Roll half pitch (mm)
It is. The intermesh d is, for example, the value obtained by adding the plate thickness t of the steel plate P to the height of the upper end of the lower roller 911 (vertical position coordinate), and the height of the lower end of the upper roller 912 (vertical position coordinate). ). Further, the roller half pitch L is 1/2 of the distance between the centers of adjacent lower rollers 911 in the conveyance direction, is the distance between the centers of the adjacent lower rollers 911 and upper roller 912 in the conveyance direction, and is a bending beam. corresponds to the length of

Further, in the steel plate P meandering between the lower ends of the adjacent upper rollers 912, the yield curvature ky indicating the plastically deformed portion is similarly calculated as in equation (2).

However, ky: yield curvature sy: yield stress (MPa)
t: Plate thickness (mm)
E: Longitudinal elastic modulus (MPa)

Generally, as mentioned above, poor hardness becomes a problem at least in the range of 0.25 mm from the surface P1, and the range in which the hardness of the surface layer of the steel P can change is from the surface P1 to the thickness of 0.5 mm. range. When measuring the change in hardness in a thickness range of 0.5 mm from the surface P1 based on the measurement of electromagnetic properties described below, the penetration depth of the eddy current generated inside the steel plate P to measure the electromagnetic properties is , it is necessary to set the distance from the surface P1 to at least 0.5 mm. On the other hand, the residual stress may affect not only the range of 0.5 mm from the surface P1, which is the measurement range, but also the state of residual stress in the range adjacent to the range. Therefore, in order to eliminate the influence of residual stress around the surface hardness change portion, it is desirable to relax the residual stress at least in a range of 2.0 mm in thickness from the surface P1.

FIG. 13 and Table 1 show the results of calculating the relationship between the plate thickness t (mm) and the depth h (mm) from the surface plastically deformed by the plastic deformation imparting equipment 910 for each working degree. As shown in FIG. 13 and Table 1, by setting the processing degree to 1.8 or more, in the range of thickness t of 10 mm or more, which includes the thickness range of general thick plates, the thickness from surface P1 to Residual stress can be alleviated by causing plastic deformation in a range of 2.0 mm. For this reason, it is preferable that the processing degree is 1.8 or more. Moreover, in order to relieve residual stress without damaging the steel plate P due to plastic deformation, it is more preferable that the working degree is 5.0 or less. In this way, the target working degree is determined, and based on the thickness of the steel plate P, the yield stress of the material of the steel plate P, the modulus of longitudinal elasticity, and formulas (1) to (3), the intermesh d is What is necessary is to determine the positions of the lower roller 911 and the upper roller 912 in the plastic deformation imparting equipment 910.

The plastic deformation imparting equipment 910 may adjust the distance between the lower roller 911 and the upper roller 912 according to the flatness measurement result by the flatness measuring section 900. The plastic deformation imparting equipment 910 does not include the flatness measuring unit 900 and repeatedly applies plastic deformation to the steel plate P by performing flatness correction on the steel plate P regardless of the measurement result of the flatness measuring unit 900. It may also be given.

Furthermore, in the above description, flatness correction is performed as a means of repeatedly applying plastic deformation to the steel plate P, but the present invention is not limited to this. If the stress state of the surface layer of the steel plate P can be adjusted by repeating compressive plastic deformation and tensile plastic deformation on the steel plate P, it is possible to adjust the stress state of the surface layer of the steel plate P by other means, such as repeatedly performing three-point bending with an oil press machine. It may also be used to realize a plastic deformation imparting section.

As shown in FIG. 14, in the steel plate manufacturing method using such a steel plate manufacturing apparatus 1B, after the cooling step S5 is performed, the steel plate P is repeatedly plastically deformed by the flatness measuring section 900 and the plastic deformation imparting equipment 910. A plastic deformation step S30 is performed. That is, in the plastic deformation step S30, the flatness is first measured on the target upper surface P1a of the surface P1 of the steel plate P (step S30a). Then, based on the measurement results, the steel plate P is repeatedly subjected to plastic deformation by the plastic deformation imparting equipment 910. (Step S30b). In the plastic deformation process S30 of the present embodiment, a flatness correction process is performed in which the flatness of the steel plate P is corrected to repeatedly apply plastic deformation to the steel plate P to adjust the stress state of the surface layer of the steel plate P. Thereby, the steel plate P can be straightened according to its flatness immediately after being cooled by the cooling equipment 50. Therefore, along with the flatness correction, the stress state of the surface layer portion including the surface P1 of the steel plate P can be adjusted and made uniform. After the plastic deformation step S30 is performed, the stress state of the upper surface P1a of the steel plate P is further adjusted by the shot blasting step S6, thereby making the stress state of the surface layer portion including the target upper surface P1a even more uniform. I can do it.

In addition, in this embodiment, the steel plates P are repeatedly subjected to plastic deformation by flatness correction for all the steel plates P, but the present invention is not limited to this. For example, as a result of measuring the flatness of the steel plate P by the flatness measurement unit 900, if the flatness is within a predetermined range and has a predetermined flatness, the flatness correction is performed by the plastic deformation imparting equipment 910. It is not necessary to carry out. That is, a bypass is provided that connects between the flatness measurement unit 900 and the plastic deformation imparting equipment 910 and between the plastic deformation imparting equipment 910 and the shot blasting equipment 60. If the steel plate P has a predetermined flatness, the steel plate P is passed through the bypass and flatness correction by the plastic deformation imparting equipment 910 is omitted, and only if the steel plate P does not have the predetermined flatness, the plastic deformation imparting equipment Flatness correction may be performed by 910. By doing this, it is possible to efficiently manufacture the steel plate P by reducing the need for unnecessary flatness correction, and if the stress state is uneven, the stress state can be reliably maintained in conjunction with shot blasting. The steel plate P can be manufactured with uniformity.

Furthermore, in the above description, flatness correction is performed as a method of repeatedly subjecting the steel plate P to plastic deformation, but the method is not limited to this. As long as the stress state of the surface layer of the steel plate P can be adjusted by repeatedly subjecting the steel plate P to compressive plastic deformation and tensile plastic deformation, the plastic deformation imparting portion may be realized by other methods.

(Example 1)
15 and 16 show Example 1 of the present invention. FIG. 15 shows residual stress on the upper surface P1a of the steel plate P immediately before the shot blasting process S6 is performed by the shot blasting equipment 60 in the case where (a) shows the steel plate P manufactured by the steel plate manufacturing apparatus 1 of the first embodiment. (b) is the result of measuring the residual stress on the upper surface P1a of the steel plate P immediately after performing the shot blasting step S6. For the steel plate P, X65 (yield stress 450 MPa) was used. The blasting material A used in the shot blasting process was a steel ball (material SS400) with a grain diameter of 1.0 mm. Further, the collision energy density during shot blasting was 392 MJ/(m ² ·min), and the cumulative collision energy was 1958 MJ/m ² . Residual stress was measured by X-ray stress measurement. Negative values indicate compressive stress and positive values indicate tensile stress. Further, FIG. 15 is a frequency distribution shown for each stress range, and shows the frequency for each 50 MPa band, such as a band of less than -50 MPa to more than 100 MPa, and a band of less than -100 MPa to more than 150 MPa. As shown in FIG. 15(a), the residual stress before the shot blasting step S6 was -225 MPa on average, and the standard deviation was 77.5 MPa. On the other hand, as shown in FIG. 15(b), by performing the shot blasting process S6, the entire upper surface P1a of the steel plate P is brought into a state of compressive stress with an average of 326 MPa, with a standard deviation of 16.4 MPa, and a standard deviation of 26 MPa. I was able to get it within range. As a result, it was confirmed that the compressive stress state could be made uniform, and that the hardness could be accurately measured without being affected by stress in the subsequent hardness measurement step S7.

FIG. 16 shows the results of measuring the incremental magnetic permeability (Ω) as an electromagnetic characteristic value on the upper surface P1a of the steel plate P by the hardness measurement unit 70A, using contours on the upper surface P1a. The incremental magnetic permeability is a value indicating the rate of change at B=0 in the BH loop shown in FIG. 4 obtained from the measurement results. As long as H=0, it does not matter whether H=+Hc or H=-Hc. FIG. 16(a) shows the measurement results immediately after performing the cooling step S5. Moreover, FIG.16(b) has shown the measurement result immediately after shot blasting process S6 implementation. As shown in FIG. 16(a), immediately after the cooling step S5 is performed, the measurement results of the incremental magnetic permeability on the upper surface P1a of the steel plate P appear as large irregularities. This is because the stress state of the surface layer including the upper surface P1a of the steel plate P is uneven due to the influence of the steps up to the cooling step S5, and the measurement results of the incremental magnetic permeability also vary due to the influence of stress. It depends. On the other hand, as shown in FIG. 16(b), immediately after the shot blasting step S6 is performed, the stress state of the surface layer portion including the upper surface P1a of the steel plate P is made uniform on the compressive stress side by the shot blasting process, and as a result, There is no variation in the measurement results of incremental magnetic permeability because it is not affected by stress. Therefore, it is possible to detect even slight changes in incremental magnetic permeability due to the influence of hardness.

(Example 2)
FIG. 17 shows a second embodiment of the present invention. In Example 2, when the steel plate P is manufactured by the steel plate manufacturing apparatus 1 of the first embodiment, the residual amount on the upper surface P1a of the steel plate P immediately after the shot blasting step S6 is performed by the shot blasting equipment 60 under various conditions. The stress was measured and the degree of uniformity of the stress state was evaluated. Specifically, as shown in Table 2, in Examples 2-1 to 2-6, the blasting material A was spherical and the average particle diameter was 1.0, 2.0, and 3.5 mm. In Example 2-7, the blasting material A was made into polygonal particles and the average particle equivalent diameter was 0.5 mm. The average grain equivalent diameter was determined by determining the volume from the weight and specific gravity, and dividing the volume by the number of blasting materials A. Incidentally, the blasting material A is made of steel material in all embodiments. In addition, in Examples 2-1 to 2-7, by changing the injection speed, injection flow rate, injection area, and threading speed of the steel plate P, the collision energy density and cumulative energy density given to the steel plate P by the blasting material A. were made different. Then, as in Example 1, the residual stress on the upper surface P1a of the steel plate P onto which the blasting material A was sprayed was measured, and the standard deviation was determined. When the standard deviation is 40 MPa or less, it is judged that the stress state has been made uniform and evaluated as ○ or ◎. In particular, when the standard deviation is 26 MPa or less, it is judged that the stress state has been made more uniform and it is given ◎. . Moreover, when the standard deviation exceeds 40 MPa, it is judged that the stress state remains non-uniform and it is marked as ×. Moreover, the roughness of the surface P1 after shot blasting step S6 was measured. The roughness was determined as 10-point average roughness _RZJIS according to JIS B 0601 Appendix JA. When the roughness is 100 μm or less, it is evaluated as ○ or ◎, and especially when the roughness is 50 μm or less, it is evaluated as ◎. In addition, when the roughness exceeds 100 μm, the surface roughness is judged to be inappropriate as a steel material and is marked as ×.

As shown in Examples 2-1 to 2-7, there was no example in which the uniformity of the stress state was judged as poor, and in all cases, the standard deviation was 40 MPa or less, and the stress state was made uniform. Further, in Examples 2-1, 2-2, 2-4, and 2-5, the standard deviation was 26 MPa or less, and the stress state was particularly uniform. Furthermore, as shown in Examples 2-1 to 2-7, there were no examples in which the surface roughness was determined to be poor, and in all cases the roughness was 100 μm or less. Further, especially in Examples 2-1 to 2-4, 2-6, and 2-7, the roughness was 50 μm or less, and the surface roughness was particularly good. In terms of stress uniformity and surface roughness, all Examples 2-1 to 2-7 satisfy the standard value, and especially Examples 2-1, 2-2, and 2-4 have a stress uniformity. Both the uniformity and the surface roughness were within more preferable ranges.

FIG. 17 is a graph plotting the results of Examples 2-1 to 2-7 with the X axis representing the collision energy density and the Y axis representing the cumulative collision energy. Note that the plots of Examples 2-4 to 2-6 overlap the plots of Example 2-1. From this result, the collision energy density is preferably 40 MJ/(m ² ·min) or more, more preferably 200 MJ/(m ² ·min) or more, and the cumulative collision energy is 1100 MJ/m ² or more. It has become clear that it is preferable that

Although the embodiments and examples of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and includes design changes within the scope of the gist of the present invention. It will be done.

1, 1A, 1B Steel plate manufacturing apparatus 30 Rolling section 50 Cooling section 60 Shot blasting section 70, 70A Hardness measuring section 90 Hardness judgment section A Blasting material P Steel plate P1 Surface Q Steel pipe Q1 Inner surface S Slab S3 Rolling process S5 Cooling process S6 Shot blasting Process S7 Hardness measurement process S8 Hardness determination process S11 Removal process S21 First pressing process S22 Second pressing process S23 Welding process S30 Plastic deformation process W Poor hardness area

Claims (8)

A rolling process of controllingly rolling the slab;
a cooling step of controllingly cooling the steel plate subjected to controlled rolling in the rolling step;
A shot blasting step of colliding a blasting material against at least a part of the surface of the steel plate that has been controlled and cooled in the cooling step to adjust the stress state of the surface layer of the steel plate including the surface;
a hardness measuring step of measuring the hardness of the surface of the steel plate that has been subjected to the shot blasting step;
a hardness determination step of determining a region whose hardness exceeds a preset threshold as a hardness defective region based on the measurement results of the hardness measurement step;
and a removing step of removing the portion with poor hardness. 2. The method of manufacturing a steel plate according to claim 1, wherein in the hardness measuring step, the hardness of the surface is measured by measuring electromagnetic characteristics of the surface. In the shot blasting step, the collision energy density imparted from the blasting material to the surface of the steel plate is 40 MJ/(m ² ·min) or more, and the cumulative collision energy is 1100 MJ/m ² or more. 2. The method for manufacturing a steel plate according to 2. From claim 1, comprising a plastic deformation step carried out between the cooling step and the hardness measuring step, the step of repeatedly plastically deforming the steel sheet to adjust the stress state of the surface layer of the steel sheet including the surface of the steel sheet. The method for manufacturing a steel plate according to claim 3. The steel plate is used as a material for steel pipes,
The method for manufacturing a steel plate according to any one of claims 1 to 4, wherein the shot blasting step, the hardness measurement step, the hardness determination step, and the removal step are performed on a portion that becomes the inner surface of the steel pipe. A first pressing step of pressing a steel plate manufactured by the method for manufacturing a steel plate according to any one of claims 1 to 5 into a U-shape;
a second pressing step of pressing the steel plate processed in the first pressing step into an O-shape;
and a welding step of welding together the ends of the steel plates processed in the second pressing step. a rolling section that performs controlled rolling of the slab;
a cooling unit that controls and cools the steel plate subjected to controlled rolling in the rolling unit;
a shot blasting section that adjusts the stress state of the surface layer of the steel plate including the surface by colliding a blasting material with at least a part of the surface of the steel plate that has been controlled and cooled in the cooling section;
a hardness measuring unit that measures the hardness of the surface shot blasted by the shot blasting unit of the steel plate;
A steel plate manufacturing apparatus comprising: a hardness determining section that determines a region whose hardness exceeds a preset threshold value as a hardness defective region based on a measurement result of the hardness measuring section. computer,
Hardness is calculated from the electromagnetic properties measured on the surface of a steel plate produced by controlled rolling and controlled cooling of a slab, on which the stress state of the surface layer has been adjusted by colliding with blasting material. calculation means,
hardness determining means for determining a portion whose hardness exceeds a preset threshold value as having poor hardness based on the hardness calculated by the hardness calculating means;
A program to function as

Images