Method for manufacturing steel materials and apparatus for manufacturing steel materials

Abstract

This disclosure aims to provide a method for manufacturing steel materials that allows for easy coating with metal while suppressing a decrease in strength and thermal deformation of the steel material. [Solution] A method for manufacturing steel according to one aspect of the present disclosure is a method for manufacturing steel by heat treatment of hot-rolled steel, comprising: a quenching step of heating the rolled steel; an injection step of injecting a metal with a melting point lower than the heating temperature immediately preceding the quenching step into the rolled steel; and a cooling step of cooling the rolled steel after the injection step, wherein the rolled steel after the cooling step is kept at a temperature below the melting point of the metal.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing steel materials and a steel material manufacturing apparatus.

Background Art

[0002] For maintaining the strength of buildings and the like, reinforcing bars such as deformed bars and hoop bars are used. If the above-mentioned reinforcing bars are used as they are, for example, they may corrode and lose thickness (so-called aging deterioration) due to the carbonation of concrete, and the strength of the concrete may easily decrease. Also, in elevated sections such as the Shinkansen and expressways, if the reinforcing bars corrode, there is a risk that the concrete may peel off and fall due to the volume expansion caused by the corrosion products (rust).

[0003] As a method for preventing the corrosion of the above-mentioned reinforcing bars (steel materials), a method of depositing a metal on the surface by thermal spraying after the manufacture of the steel material is known (see, for example, Japanese Patent Application Laid-Open No. 2024-54930). Thermal spraying forms a coating on the surface of the steel material by melting thermal spray powder or wire with plasma (about 20,000°C) or arc (5000°C or higher) and spraying it at high speed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Although the above-mentioned thermal spraying is performed after manufacture, since the reinforcing bars are long wire rods and are wound up, it is not easy to perform thermal spraying on the entire surface of the reinforcing bars after manufacture. Also, since high-temperature particles collide with the reinforcing bars, the reinforcing bars are also heated, and if the temperature exceeds the quenching or tempering temperature, there is a risk of strength reduction, thermal deformation, change in metal structure, etc. of the reinforcing bars themselves.

[0006] This disclosure is made in view of these circumstances and aims to provide a method for manufacturing steel materials and a steel material manufacturing apparatus that can easily coat steel materials with metal while suppressing a decrease in strength, thermal deformation, and changes in the metal structure of the steel materials. [Means for solving the problem]

[0007] A method for manufacturing steel according to one aspect of the present disclosure is a method for manufacturing steel by heat treatment of hot-rolled steel, comprising: a quenching step of heating the rolled steel; an injection step of injecting a metal with a melting point lower than the heating temperature immediately preceding the quenching step into the rolled steel; and a cooling step of cooling the rolled steel after the injection step, wherein the rolled steel after the cooling step is kept at a temperature below the melting point of the metal.

[0008] A steel manufacturing apparatus according to another aspect of the present disclosure is a steel manufacturing apparatus for heat-treating hot-rolled rolled steel, comprising: a quenching section for heating the rolled steel; an injection section for injecting a metal having a lower melting point than the heating temperature immediately preceding the quenching section onto the rolled steel after it has been treated in the quenching section; and a cooling section for cooling the rolled steel after it has been treated in the injection section. [Effects of the Invention]

[0009] The steel manufacturing method and steel manufacturing apparatus of this disclosure enable easy coating of steel with metal while suppressing reduction in strength, thermal deformation, and changes in the metal structure. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a flowchart showing the procedure for a method of manufacturing steel according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the steel manufacturing apparatus used in the steel manufacturing method shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing the procedure for a steel manufacturing method according to a different embodiment than that shown in Figure 1. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the steel manufacturing apparatus used in the steel manufacturing method shown in Figure 3. [Modes for carrying out the invention]

[0011] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0012] (1) A method for manufacturing steel according to one aspect of the present disclosure is a method for manufacturing steel by heat treatment of hot-rolled steel, comprising: a quenching step of heating the rolled steel; an injection step of injecting a metal with a melting point lower than the heating temperature immediately preceding the quenching step into the rolled steel; and a cooling step of cooling the rolled steel after the injection step, wherein the rolled steel after the cooling step is kept at a temperature below the melting point of the metal.

[0013] In this steel manufacturing method, during the injection step, a metal with a melting point lower than the heating temperature immediately preceding the injection is injected onto the rolled steel. The metal absorbs heat from the rolled steel, melts, and deposits on the surface of the rolled steel. In this steel manufacturing method, the injection step is performed between the quenching step and the cooling step. In other words, since the injection step can be performed as one of the continuous processes in the manufacturing of the steel, it is possible to easily manufacture steel coated with metal. Furthermore, in this steel manufacturing method, since the metal melts by absorbing heat from the rolled steel, the temperature does not exceed the heating temperature immediately preceding the injection, thus suppressing a decrease in the strength of the steel, thermal deformation, and changes in the metal structure. Moreover, since the rolled steel after the cooling step is kept at a temperature below the melting point of the metal, deterioration and deformation of the metal film deposited on the surface of the rolled steel can be suppressed.

[0014] (2) In the steel manufacturing method described in (1) above, a quenching cooling step for cooling the rolled steel after the quenching step and a tempering step for heating the rolled steel after the quenching cooling step are provided between the quenching step and the injection step, and the heating temperature in the injection step is preferably the same as the heating temperature in the tempering step. In some cases, a tempering step is performed at a low temperature after a quenching step at a high temperature. In such cases, if the melting point of the metal is lower than the heating temperature of the tempering step, corrosion and thinning of the rolled steel can be suppressed by depositing the metal using the heat of the tempering step.

[0015] (3) In the method for manufacturing the steel material according to (1) or (2) above, the metal may be zinc, tin, or a mixture thereof. Zinc and tin adhere easily to the steel material and can be expected to have a high corrosion prevention effect.

[0016] (4) In the method for manufacturing the steel material according to any one of (1) to (3) above, the spraying step may be performed at room temperature using air pressure. By performing the spraying step at room temperature using air pressure in this way, it is possible to more reliably suppress a decrease in the strength of the steel material, thermal deformation, and changes in the metal structure.

[0017] (5) In the method for manufacturing the steel material according to any one of (1) to (4) above, the heating temperature is preferably 650°C or lower. By setting the heating temperature to the upper limit or lower in this way, gasification of the metal can be suppressed, and deposition of the metal on the surface of the hot-rolled steel can be efficiently performed.

[0018] (6) In the method for manufacturing the steel material according to any one of (1) to (5) above, the steel material may be a wire rod. The method for manufacturing the steel material functions effectively particularly when the steel material is a wire rod.

[0019] (7) A steel material manufacturing apparatus according to another aspect of the present disclosure is a steel material manufacturing apparatus for heat-treating hot-rolled steel, comprising a quenching section for heating the hot-rolled steel, a spraying section for spraying a metal having a melting point lower than the immediately preceding heating temperature onto the hot-rolled steel after being treated in the quenching section, and a cooling section for cooling the hot-rolled steel after being treated in the spraying section.

[0020] In the steel manufacturing apparatus, in the injection section, a metal having a melting point lower than the heating temperature immediately before is injected onto the hot-rolled steel. Thus, the metal takes heat from the hot-rolled steel and melts, and is deposited on the surface of the hot-rolled steel. In the steel manufacturing apparatus, the injection section is located between the quenching section and the cooling section. That is, since the injection section can be performed as one of the continuous processes for manufacturing the steel, a steel coated with metal can be easily manufactured. Further, in the steel manufacturing apparatus, since the metal is melted by taking heat from the hot-rolled steel, its temperature does not exceed the heating temperature immediately before, and a decrease in the strength of the steel, thermal deformation, and change in the metal structure can be suppressed. Furthermore, the steel manufacturing apparatus can be realized simply by providing an injection nozzle for injecting metal between the tempering section and the tempering cooling section, for example, in a steel manufacturing apparatus for heat-treating existing hot-rolled steel, and thus can be easily configured.

[0021] Here, the "room temperature" means a temperature at which heating or cooling is not performed, and refers to a temperature of 10°C or higher and 50°C or lower, preferably 20°C or higher and 40°C or lower.

[0022] [Details of Embodiments of the Present Disclosure] Hereinafter, a method for manufacturing a steel material and a steel manufacturing apparatus according to an embodiment of the present disclosure will be described with appropriate reference to the drawings.

[0023] [First Embodiment] A method for manufacturing a steel material according to an embodiment of the present disclosure is a method for manufacturing a steel material by heat-treating hot-rolled steel. As shown in FIG. 1, the method for manufacturing the steel material includes a quenching step S1, a quenching cooling step S2, a tempering step S3, an injection step S4, and a tempering cooling step S5.

[0024] The method for manufacturing the steel material can be performed using a steel manufacturing apparatus 1 according to another aspect of the present disclosure for heat-treating the hot-rolled steel X shown in FIG. 2. The steel manufacturing apparatus 1 includes a quenching section 10, a quenching cooling section 20, a tempering section 30, an injection section 40, and a tempering cooling section 50.

[0025] In the steel manufacturing apparatus 1, the rolled steel X is fed in the direction of the arrows in Figure 2, passing through the quenching section 10, the quenching and cooling section 20, the tempering section 30, the injection section 40, and the tempering and cooling section 50 in that order, and is recovered as steel material Y.

[0026] The steel material Y is preferably in the form of a wire. The manufacturing method for the steel material is particularly effective when the steel material Y is in the form of a wire. The lower limit of the diameter of the wire is preferably 0.5 mm, and more preferably 1 mm, from the viewpoint of the maximum thickness of the metal film that can be obtained. On the other hand, the upper limit of the diameter of the wire is preferably 20 mm, and more preferably 18 mm, so that it can be hardened.

[0027] The quenching section 10, quenching and cooling section 20, tempering section 30, injection section 40, and tempering and cooling section 50 of the steel manufacturing apparatus 1 perform processes corresponding to the quenching process S1, quenching and cooling process S2, tempering process S3, injection process S4, and tempering and cooling process S5 of the steel manufacturing method, respectively. Therefore, the configuration of each part of the steel manufacturing apparatus 1 will be described in accordance with the description of each process in the steel manufacturing method.

[0028] <Heat treatment process> In the quenching process S1, the rolled steel X is heated. The quenching process S1 is performed in the quenching section 10 where the rolled steel X is heated.

[0029] The hardening section 10 includes, for example, a high-frequency power supply 11 and an induction heating coil 12. The induction heating coil 12 may consist of a preheating coil 12a for preheating the rolled steel X and a main heating coil 12b for main heating the preheated rolled steel X. The preheating coil 12a and the main heating coil 12b are connected in parallel to the high-frequency power supply 11 and can be controlled independently. A predetermined gap is provided between the preheating coil 12a and the main heating coil 12b.

[0030] When the induction heating coil 12 is composed of a preheating coil 12a and a main heating coil 12b, in the quenching process S1, the rolled steel X is first preheated by the preheating coil 12a, at which point the surface temperature is raised to, for example, 850°C to 900°C and the core temperature to 100°C to 150°C. As the preheated rolled steel X passes through a predetermined gap between the preheating coil 12a and the main heating coil 12b, the surface temperature decreases, but the core temperature rises further due to heat conduction towards the center, and the steel is then introduced into the main heating coil 12b. In the main heating coil 12b, the rolled steel X undergoes main heating, and at its outlet, for example, the surface temperature is raised to 900°C to 950°C and the core temperature to 600°C to 650°C. This makes it possible to quench the entire cross-section uniformly.

[0031] <Quenching and Cooling Process> In the quenching and cooling process S2, the rolled steel X after the quenching process S1 is cooled. The quenching and cooling process S2 is performed in the quenching and cooling section 20, which cools the rolled steel X after it has been processed in the quenching section 10.

[0032] The quenching and cooling section 20 has multiple jackets 21 (four jackets 21 in Figure 2) that can spray air or mist onto the rolled steel X. The rolled steel X passes through these multiple jackets 21 in sequence.

[0033] As the rolled steel X passes through the first jacket 21, it is subjected to a spray of air or mist, which temporarily and rapidly cools the surface of the rolled steel X, which is slightly hotter than the center. As a result, the surface temperature of the rolled steel X drops to about 760°C, while the core temperature rises to about 730°C to 750°C.

[0034] Furthermore, as the rolled steel X passes through the second jacket 21, a portion corresponding to 10% to 25% of its thickness from the surface is rapidly cooled, and this surface layer becomes quenched by the rapid cooling, while the temperature of the surface layer drops to between 40°C and 60°C. The core is still at a temperature of around 650°C, and heat conduction towards the surface due to this temperature gradient promotes the removal of heat from the core. This process is repeated, and the core is rapidly cooled to a temperature of 150°C or lower. The number of jackets 21 is determined so that the temperature of the core can be cooled to the desired temperature.

[0035] <Tempering process> In the tempering process S3, the rolled steel X after the quenching and cooling process S2 is heated. The tempering process S3 is performed in the tempering section 30, which heats the rolled steel X after it has been treated in the quenching and cooling section 20.

[0036] The tempering section 30 includes, for example, a high-frequency power supply 31 and an induction heating coil 32, and can be configured in the same way as the hardening section 10. In the tempering section 30, the surface temperature is raised to, for example, 450°C to 550°C at the outlet of the induction heating coil 12. Since the target temperature is lower than that of the hardening section 10, the induction heating coil 32 may consist only of the main heating coil, omitting the preheating coil.

[0037] <Injection process> In the injection process S4, a metal M with a lower melting point than the heating temperature of the tempering process S3, which is the heating temperature immediately preceding the injection process, is injected into the rolled steel X after the tempering process S3. The tempering process S3 is performed in the injection unit 40, in which a metal M with a lower melting point than the heating temperature of the tempering unit 30 is injected into the rolled steel X after it has been treated in the tempering unit 30.

[0038] The steel manufacturing method includes a quenching and cooling step S2 and a tempering step S3 between the quenching step S1 and the injection step S4. The corresponding steel manufacturing apparatus 1 includes a quenching and cooling section 20 and a tempering section 30 between the quenching section 10 and the injection section 40. During heating in the quenching step S1, as described above, the surface temperature of the rolled steel X is high, at 900°C or higher. In particular, when zinc (boiling point 907°C) is used as the metal M, the heating temperature may exceed the boiling point, and zinc easily gasifies due to its high vapor pressure. Furthermore, in the steel manufacturing apparatus 1, the rolled steel X is always under tension, and low-melting-point metals M such as zinc and tin may diffuse through the grain boundaries of the polycrystalline structure, potentially embrittle the rolled steel X itself. For this reason, in the steel manufacturing method, the injection step S4 is performed immediately after the tempering step S3, not immediately after the quenching step S1.

[0039] The injection unit 40 has one or more injection nozzles 41. The steel manufacturing apparatus 1 can be easily constructed, for example, by simply adding injection nozzles 41 for injecting metal M between the tempering unit 30 and the tempering cooling unit 50 in a steel manufacturing apparatus that heat-treats existing hot-rolled rolled steel X. The number of injection nozzles 41 may be one, but it is preferable to have multiple nozzles, and more preferably two to four, so that metal M can be uniformly injected over the entire surface of the rolled steel X.

[0040] The injection nozzle 41 is preferably configured to inject metal M from the tempering section 30 side toward the tempering cooling section 50 side, as shown in Figure 2. If the injection is directed toward the tempering section 30 side, liquid metal embrittlement may occur.

[0041] Examples of metals M to be sprayed include zinc (melting point 419°C), tin (melting point 232°C), and bismuth (melting point 272°C), with metal M being preferably zinc, tin, or a mixture thereof. Zinc is a metal that acts as a sacrificial anode for iron, and its oxide has a lower standard free energy of formation than iron oxide. Therefore, even without prior descaling treatment such as shot blasting, the reduction reaction of high-temperature scale, which is iron oxide, removes oxygen from the iron, allowing for adhesion. In addition, tin has an erosive effect on iron, and because it has a lower ionization tendency than iron, it is easy to adhere to and a high corrosion protection effect can be expected.

[0042] The above heating temperature is at least below the boiling point of metal M. If metal M is zinc, the boiling point is 907°C, and if it is tin, the boiling point is 2602°C. Furthermore, the upper limit of the above heating temperature is preferably 650°C, more preferably 600°C, and even more preferably 500°C. By keeping the above heating temperature below the above upper limit, the gasification of metal M can be suppressed, and the deposition of metal M on the surface of rolled steel X can be efficiently carried out.

[0043] The heating temperature mentioned above is above the melting point of metal M. The lower limit of the difference between the heating temperature and the melting point of metal M is preferably 50°C, and more preferably 100°C. By setting the heating temperature above the lower limit, metal M is heated in a short time, allowing for efficient deposition on the surface of rolled steel X. On the other hand, the upper limit of the difference is preferably 200°C, and more preferably 150°C. If the difference exceeds the upper limit, metal M becomes more likely to gasify, which may hinder the deposition of metal M on the surface of rolled steel X.

[0044] The spraying process S4 is preferably carried out at room temperature using pneumatic pressure. Since the melting point of metal M is lower than the heating temperature of the tempering process S3, even when metal M is sprayed at room temperature, it absorbs heat from the rolled steel X, which is the material to be coated, melts, and deposits on the surface of the rolled steel X. By carrying out the spraying process S4 at room temperature using pneumatic pressure in this way, the reduction in strength, thermal deformation, and changes in the metal structure of the manufactured steel Y can be suppressed more reliably.

[0045] <Tempering cooling process> In the tempering and cooling process S5, the rolled steel X after the injection process S4 is cooled. The tempering and cooling process S5 is performed in the tempering and cooling section 50, which cools the rolled steel X after it has been processed in the injection section 40.

[0046] The tempering cooling section 50 can be configured in the same way as the quenching cooling section 20, so a detailed explanation is omitted. The number of jackets is determined so that the temperature of the central part can be cooled to a desired temperature, and therefore may differ from the number of jackets 21 in the quenching cooling section 20. Generally, the number of jackets in the tempering cooling section 50 is less than the number of jackets 21 in the quenching cooling section 20.

[0047] In this steel manufacturing method, steel material Y is obtained after a tempering and cooling process S5. No heat treatment for the production of steel material Y is performed after the tempering and cooling process S5. In other words, the rolled steel X after the cooling process (tempering and cooling process S5) is kept at a temperature below the melting point of metal M.

[0048] <Advantages> In this steel manufacturing method, during the injection step S4, a metal M with a lower melting point than the heating temperature of the preceding tempering step S3 is injected onto the rolled steel X. As a result, the metal M absorbs heat from the rolled steel X, melts, and deposits on the surface of the rolled steel X. In this steel manufacturing method, the injection step S4 is performed between the tempering step S3 and the tempering cooling step S5. In other words, since the injection step S4 can be performed as one of the continuous processes in the manufacturing of the steel Y, it is possible to easily manufacture steel Y coated with metal M. Furthermore, in this steel manufacturing method, since the metal melts by absorbing heat from the rolled steel X, its temperature does not exceed the heating temperature immediately preceding it, thus suppressing a decrease in strength and thermal deformation of the steel Y. Moreover, since the rolled steel X after the tempering cooling step S5 is kept at a temperature below the melting point of metal M, deterioration and deformation of the metal film deposited on the surface of the rolled steel X can be suppressed.

[0049] In the steel manufacturing apparatus 1, the injection unit 40 injects metal M, which has a lower melting point than the heating temperature of the tempering unit 30 immediately preceding it, onto the rolled steel X. As a result, metal M absorbs heat from the rolled steel X, melts, and deposits on the surface of the rolled steel X. In the steel manufacturing apparatus 1, the injection unit 40 is located between the tempering unit 30 and the tempering cooling unit 50. In other words, the injection unit 40 can be operated as one of the continuous processes in the manufacturing of steel Y, so steel Y coated with metal M can be easily manufactured. Furthermore, in the steel manufacturing apparatus 1, since metal M melts by absorbing heat from the rolled steel X, its temperature does not exceed the heating temperature immediately preceding it, thus suppressing a decrease in strength and thermal deformation of the steel Y.

[0050] [Second Embodiment] A method for manufacturing steel according to one embodiment different from the first embodiment of the present disclosure, as shown in Figure 3, is a method for manufacturing steel by heat treatment of hot-rolled rolled steel X, comprising: a quenching step S21 for heating the rolled steel X; an injection step S24 for injecting metal M having a lower melting point than the heating temperature of the preceding quenching step S21 into the rolled steel X after the quenching step S21; and a quenching and cooling step S25 for cooling the rolled steel X after the injection step S24, wherein the rolled steel X after the quenching and cooling step S25 is kept at a temperature below the melting point of metal M.

[0051] A steel manufacturing apparatus 2 according to one embodiment different from the first embodiment of the present disclosure, as shown in Figure 4, is a steel manufacturing apparatus for heat-treating hot-rolled rolled steel X, and comprises a quenching section 10 for heating the rolled steel X, an injection section 42 for injecting a metal M having a lower melting point than the heating temperature of the quenching section 10 immediately preceding the quenching section 10 onto the rolled steel X after it has been treated in the quenching section 10, and a quenching cooling section 20 for cooling the rolled steel X after it has been treated in the injection section 42.

[0052] In the steel manufacturing apparatus 2, the rolled steel X is fed in the direction of the arrows in Figure 4, passing through the quenching section 10, the injection section 42, and the quenching and cooling section 20 in that order, and is recovered as steel material Y.

[0053] The steel material Y is preferably a wire rod. The method for manufacturing the steel material is particularly effective when the steel material Y is a wire rod. The diameter of the wire rod is the same as that of the wire rod in the first embodiment.

[0054] The quenching section 10, the injection section 42, and the quenching and cooling section 20 of the steel manufacturing apparatus 2 perform processes corresponding to the quenching process S21, the injection process S24, and the quenching and cooling process S25 of the steel manufacturing method, respectively. Therefore, the configuration of each part of the steel manufacturing apparatus 2 corresponds to each process of the steel manufacturing method.

[0055] <Heat treatment process> The quenching process S21 is carried out under conditions that the surface temperature of the rolled steel X is 650°C or lower. This is so-called low-temperature quenching. Except for this point, the quenching process S21 can be carried out in the same manner as the quenching process S1 of the first embodiment. Furthermore, the quenching section 10 of the steel manufacturing apparatus 2 can also be configured in the same manner as the quenching section 10 of the first embodiment, so the same reference numerals are used and detailed explanation is omitted.

[0056] <Injection process> The injection process S24 is performed immediately after the quenching process S21. Therefore, the heating temperature immediately preceding it corresponds to the heating temperature of the quenching process S21. Except for the points mentioned above, the injection process S24 is the same as the injection process S4 of the first embodiment, so a detailed explanation is omitted.

[0057] The injection unit 42 can have the same configuration as the injection unit 40 of the first embodiment, except that it is positioned between the hardening unit 10 and the hardening and cooling unit 20, so the same reference numerals are used and a detailed explanation is omitted.

[0058] <Quenching and Cooling Process> In the steel manufacturing method, the quenching and cooling step S25 is a cooling step performed after the injection step S24. The quenching and cooling step S25 can be performed in the same manner as the quenching and cooling step S25 of the first embodiment, except that it is performed after the injection step S24 and the rolled steel X after the quenching and cooling step S25 is kept at a temperature below the melting point of the metal M. Furthermore, the quenching and cooling section 20 can have the same configuration as the quenching and cooling section 20 of the first embodiment, so the same reference numerals are used and a detailed explanation is omitted.

[0059] <Advantages> In this steel manufacturing method, since the quenching step S21 is low-temperature quenching, the tempering step S3 and tempering cooling step S5 in the steel manufacturing method of the first embodiment can be omitted. Even in this case, by performing the injection step S24 between the quenching step S21 and the quenching cooling step S25, the steel Y can be easily coated with metal M while suppressing a decrease in strength, thermal deformation, and changes in the metal structure.

[0060] In the steel manufacturing apparatus 2, since the quenching section 10 is low-temperature quenching, the tempering section 30 and tempering cooling section 50 in the steel manufacturing apparatus 1 of the first embodiment can be omitted. Even in this case, by providing an injection section 42 between the quenching section 10 and the quenching cooling section 20, the steel material Y can be easily coated with metal M while suppressing a decrease in strength and thermal deformation.

[0061] [Other embodiments] This disclosure is not limited to the embodiments described above, and can be implemented in various modified and improved forms in addition to those described above.

[0062] In the above embodiment, the quenching section and tempering section are described as being composed of induction heaters, and the quenching cooling section and tempering cooling section are composed of jackets. However, the configuration is not limited to these, as long as the necessary heating and cooling can be performed. Furthermore, the quenching section and tempering section may have different configurations, and the quenching cooling section and tempering cooling section may have different configurations. For example, the quenching cooling section and tempering cooling section can be composed of immersion cooling devices. [Industrial applicability]

[0063] The steel manufacturing method and steel manufacturing apparatus of this disclosure can easily coat the steel with metal while suppressing a decrease in strength and thermal deformation. [Explanation of Symbols]

[0064] 1, 2 Steel manufacturing equipment 10 Hardened section 11 High frequency power supply 12 Induction heating coil 12a Preheating coil 12b Main heating coil 20. Quenching and cooling section 21 Jacket 30 Tempered section 31 High frequency power supply 32 Induction heating coil 40, 42 Injection part 41 Spray nozzle 50 Tempering Cooling Section M Metal X Rolled Steel Y Steel material

Claims

1. A method for manufacturing steel materials by heat treatment of hot-rolled steel, The above-mentioned quenching process involves heating the rolled steel, The process involves injecting a metal with a lower melting point than the heating temperature immediately preceding the quenching process into the rolled steel, The system includes a cooling step for cooling the rolled steel after the injection step described above. A method for manufacturing steel, wherein the rolled steel after the above cooling process is kept at a temperature below the melting point of the above metal.

2. Between the above quenching process and the above injection process, A quenching and cooling process is performed to cool the rolled steel after the above quenching process, A tempering process in which the rolled steel is heated after the above quenching and cooling process, Equipped with, The method for manufacturing steel according to claim 1, wherein the heating temperature in the injection step is the heating temperature in the tempering step.

3. A method for producing steel according to claim 1 or claim 2, wherein the above-mentioned metal is zinc, tin, or a mixture thereof.

4. A method for manufacturing steel according to claim 1 or claim 2, wherein the above injection step is performed using air pressure at room temperature.

5. The method for manufacturing steel according to claim 1 or claim 2, wherein the heating temperature is 650°C or lower.

6. The method for manufacturing a steel material according to claim 1 or claim 2, wherein the steel material is a wire rod.

7. A steel manufacturing apparatus for heat-treating hot-rolled rolled steel, The above-mentioned rolled steel is heated in a quenching section, A spray unit that sprays a metal with a lower melting point than the heating temperature immediately preceding the quenching process onto the rolled steel after the quenching process, A steel manufacturing apparatus comprising a cooling section for cooling the rolled steel after it has been processed in the above-mentioned injection section.

8. Between the above-mentioned hardened portion and the above-mentioned injection portion, A quenching and cooling section for cooling the rolled steel after it has been treated in the above quenching section, A tempering section heats the rolled steel after it has been treated in the above quenching and cooling section. Equipped with, The steel manufacturing apparatus according to claim 7, wherein the heating temperature in the injection section is the heating temperature in the tempering section.

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