JP2011530659A - High carbon hot rolled steel sheet and manufacturing method thereof - Google Patents

Abstract

  In the present invention, i)% by weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.10 to 0.80%, P: greater than 0 and 0 0.03% or less, and S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), and Cr: 0.30% or less (including 0), Cu: 0 Including any one or more of 25% or less (including 0), the balance including Fe and other inevitable impurities, and ii) the width of cementite is greater than 0 and 0.2 μm or less, and the cementite and cementite A high carbon hot-rolled steel sheet having a fine pearlite structure in which the distance between and is greater than 0 and 0.5 μm or less is provided.

Description

  The present invention relates to a high carbon hot rolled steel sheet. More specifically, the present invention relates to a high carbon hot-rolled steel sheet having a fine pearlite structure and a method for producing the same.

  A high carbon steel plate refers to a steel plate containing 0.3% by weight or more of carbon and having a pearlite crystal phase in its crystal structure. The high carbon steel sheet has high strength and high hardness after the final process. Thus, since the high carbon steel sheet has high strength and high hardness, it is used as tool steel or machine structural steel that requires high strength and hardness.

  As an example of the high carbon steel plate used as the tool steel, there is JS-SK85 steel classified by Japanese Industrial Standard. JS-SK85 steel is used as parts for automobiles, needles for making needles, razor blades or blades for stationery cutters.

  A high carbon steel plate is usually manufactured into an intermediate product called a hot rolled steel plate by performing a continuous hot rolling process on a slab. In order to perform hot rolling, a hot-rolled steel sheet is rolled to a predetermined thickness through rough rolling and finish rolling, and then cooled to an appropriate temperature with a run-out table (ROT). And it is manufactured by being wound around a coil of coil.

  Such a hot-rolled steel sheet is subjected to pickling and spheroidizing steps and then cold-rolled to produce a cold-rolled steel sheet. A cold-rolled steel sheet produces a cold-rolled steel sheet having a desired thickness by repeatedly performing an annealing process and a cold rolling process again in order. Such a cold-rolled steel sheet is processed into a desired product by a process such as blanking or burring, and then processed into a final product by QT heat treatment (quenching and tempering).

  An object of the present invention is to provide a high-carbon hot-rolled steel sheet having a fine pearlite structure while being thin in order to minimize the number of repetitions of spheroidizing annealing and cold rolling in subsequent processes.

  Another object of the present invention is to provide a method for producing a high carbon hot-rolled steel sheet that has a fine pearlite structure and improves the phase transformation rate at the run-out table so that the coil is not crushed.

  According to one embodiment of the present invention for achieving the above object, i) by weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.00. 10 to 0.80%, P: greater than 0 and 0.03% or less, and S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0 .30% or less (including 0) and Cu: 0.25% or less (including 0) and the balance consisting of Fe and other inevitable impurities, and ii) cementite ) Has a fine pearlite structure in which the distance between cementite and cementite is greater than 0 and 0.5 μm or less.

  In addition, according to one embodiment of the present invention, the high carbon hot rolled steel sheet has a fine pearlite structure fraction of 90% or more.

  Such a high carbon hot-rolled steel sheet has a thickness of 1.8 mm or less, preferably 1.6 mm or less.

  According to one embodiment of the present invention to achieve another object, i) by weight, C: 0.60-1.20%, Si: 0.10-0.35%, Mn: 0.00. 10 to 0.80%, P: greater than 0 and 0.03% or less, and S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0 A slab for producing a high carbon slab containing at least one of 30% or less (including 0) and Cu: 0.25% or less (including 0), and the balance being Fe and other inevitable impurities A manufacturing step, ii) a reheating step in which the slab is reheated at 1200 ° C. or higher, and iii) rough rolling the slab and then performing finish rolling in an austenite region at 830 ° C. or higher to obtain a thickness. Produces a thin plate of 1.8 mm or less A cold rolling step, iv) a cooling step in which the thin plate is cooled by shear-controlled cooling at a run-out table, and v) a cooling stop step in which the cooling temperature is maintained for a time required to perform the pearlite phase transformation in the cooling step; Vi) A method for producing a high carbon hot-rolled steel sheet, comprising the step of winding the thin sheet at 650 ° C. or lower.

  In such a method for producing a high carbon hot-rolled steel sheet, in the cooling step, the cooling rate for cooling the thin sheet is set to 50 to 300 ° C./sec.

  And in the manufacturing process of the thin plate by hot rolling, a thin plate manufactures a hot-rolled steel plate as 1.6 mm or less.

  Further, in the cooling step, the shear control cooling for cooling the thin plate is performed so as to be 650 ° C. or less, and such cooling is completed within at least 3 seconds.

  In the cooling stop step of the method for producing a high carbon hot-rolled steel sheet, the pearlite phase transformation is completed by 90% or more, and such a phase transformation completion time is at least 6 seconds or more. Further, such a cooling stop step maintains the temperature at 550 to 660 ° C.

  The method for producing a high carbon hot-rolled steel sheet according to an embodiment of the present invention provides a technique capable of producing a large number of thin plates having a thickness of 1.8 mm or less, preferably 1.6 mm or less. There is.

  The method for manufacturing a high carbon hot-rolled steel sheet according to an embodiment of the present invention can be manufactured in a thin plate state having a thickness of 1.8 mm or less, preferably 1.6 mm or less. There is a technical effect that the number of spheroidizing annealing and cold rolling can be reduced at least once.

  In this way, by making it possible to omit subsequent manufacturing process steps, it is possible to reduce processing costs during product production and to shorten the manufacturing process time.

  Since the high carbon hot-rolled steel sheet manufactured according to one embodiment of the present invention has a fine pearlite structure, there is a technical effect that durability and strength can be imparted to the final product.

FIG. 3 is a micrograph showing a 1.6 mm thick hot-rolled steel sheet that is gradually cooled and wound up after finish hot rolling according to a comparative example of the present invention, the crystal structure of which is a rough pearlite structure. FIG. 2 is a micrograph showing a crystal structure in a state in which the hot-rolled steel sheet of FIG. 1 is spheroidized and annealed, and black striped undissolved cementite remains. According to an embodiment of the present invention, a hot-rolled steel sheet having a thickness of 1.6 mm, which is wound after finishing hot rolling and then completing rapid pearlite transformation by 90% or more, and its crystal structure shows a fine pearlite structure. It is a photomicrograph. It is a microscope picture which shows the crystal structure of the state which carried out the spheroidizing annealing of the hot-rolled steel plate of FIG. 2, and an undissolved cementite is not observed.

  Hereinafter, although the Example with respect to the high carbon hot rolled sheet steel by this invention and its manufacturing method is described in detail, this invention is not limited to the following Example. Accordingly, those skilled in the art can implement the present invention in various other forms without departing from the technical idea of the present invention.

  In the present invention, the content of the component elements means all by weight unless otherwise specified.

  Hereinafter, the high carbon hot-rolled steel sheet according to the embodiment of the present invention will be described in detail.

  The high carbon hot-rolled steel sheet according to an embodiment of the present invention is, by weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.10 to 0.80%. P: greater than 0 and 0.03% or less, S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0.30% or less (including 0), and Cu: 0.25% or less (including 0) and the balance Fe and other inevitable impurities.

  In the high carbon hot-rolled steel sheet according to one embodiment of the present invention, the reason why the components are limited in this way will be described.

[C: 0.60 to 1.20%]
Carbon (C) is a component that affects the hardenability when the final product is heat-treated (QT). When C is contained at 0.6% or less, the hardenability is lowered, the strength of the product is lowered, and the wear resistance may be deteriorated. And when C contains exceeding 1.20%, the workability of a final product may deteriorate and impact toughness may fall. Therefore, the preferable range of carbon (C) content is 0.60 to 1.20%.

[Si: 0.10 to 0.35%]
Silicon (Si) is an element added for deoxidation. When Si is contained at 0.10% or less, deoxidation is incomplete and oxidative inclusions remain in the product. Therefore, when the hot-rolled steel sheet is cold-rolled to an extremely thin thickness, the surface is broken and the fatigue strength of the final product is reduced. And when Si is contained exceeding 0.35%, when reheating the slab for the hot rolling process, the hot-rolled steel sheet manufactured by promoting the generation of a substance that induces red scale is used. A red scale is generated on the surface, causing the surface quality of the product to deteriorate. Therefore, the preferable range of Si content is 0.10 to 0.35%.

[Mn: 0.10 to 0.80%]
Manganese (Mn) improves hardenability when the final product is heat treated (QT). Moreover, it plays the role which suppresses that the impact transition temperature which generate | occur | produces with the increase in C rises. When Mn is contained at 0.10% or less, the impact transition temperature rises and the workability decreases. When Mn is contained in excess of 0.80%, the product is thermally deformed during heat treatment (QT) of the final product. Therefore, the preferable range of Mn content is 0.10 to 0.80%.

[P: 0.03% or less]
Phosphorus (P) induces precipitation of Fe ₃ P and the like at the fine austenite grain boundaries of the hot-rolled steel sheet during the manufacturing process. When such precipitates are generated inside the hot-rolled steel sheet, the impact toughness of the product deteriorates. Therefore, the P content is preferably larger than 0 but limited to 0.03% by weight or less.

[S: 0.03% or less]
Sulfur (S) forms MnS and CuS, which are fine precipitates, during the manufacturing process. When such precipitates are formed inside the hot-rolled steel sheet, the growth of crystal grains is suppressed and the hardenability of the final product is deteriorated. Therefore, it is preferable to manage S as low as possible, and its content is larger than 0 but limited to 0.03% by weight or less.

  The high carbon hot-rolled steel sheet according to one embodiment of the present invention contains the balance of Fe and other inevitable impurities in addition to the above elemental components.

  One embodiment of the present invention may include any one or more of Ni, Cr, and Cu in addition to the above component elements. Although these elements may be mixed as impurities, these elements are added in order to improve the hardenability in the final heat treatment step. However, when these elements contain Ni at 0.25% or more, Cr at 0.30% or more, and Cu at 0.25% or more, the content effect is saturated and the cost increases. It is preferable to make it contain below these ranges. And when Cr reheats a slab at a hot rolling process, it has the effect which suppresses surface layer oxidation and decarburization by forming a Cr oxide layer on the surface of a slab. Considering the points described above, the contents of these elements are Ni: 0.25% or less (including 0), Cr: 0.30% or less (including 0), and Cu: 0.0. Control to 25% or less (including 0).

  Hereinafter, a method for producing the high carbon hot-rolled steel sheet according to the above-described embodiment will be described.

  First, by weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.10 to 0.80%, P: greater than 0 and 0.03% or less, S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0.30% or less (including 0), and Cu: 0.25% or less (including 0) And a high carbon steel slab composed of the balance Fe and other inevitable impurities.

  After the manufactured steel slab is reheated at a temperature of 1200 ° C. or lower, hot rolling is performed in an austenite region of 830 ° C. or higher.

  In the hot rolling, the heated slab is rolled in a thin plate state so that the thickness is 1.8 mm or less, preferably 1.6 mm or less, after the rough rolling and finish rolling are completed.

  The reason why the slab is hot-rolled to a thin plate in this way is as follows.

  In order to produce a final product with a hot-rolled steel sheet, first, it is produced into a cold-rolled steel sheet in an intermediate state. However, in order to manufacture such a cold-rolled steel sheet, the hot-rolled steel sheet is subjected to a spheroidizing annealing process and a cold-rolling process several times to thereby obtain a cold sheet having a desired thickness (for example, 0.6 mm or less). Production of rolled steel sheets. Therefore, the thicker the hot-rolled steel sheet that is provided, the more the spheroidizing annealing process and the cold rolling process must be repeated.

  The high carbon steel according to one embodiment of the present invention has a carbon content of 0.60 to 1.20% by weight. High carbon steel is characterized by high strength but low impact toughness due to high carbon content. Therefore, the hot-rolled eutectoid steel is subjected to spheroidizing annealing before cold rolling. And eutectoid steel performs cold rolling after spheroidizing annealing. When the eutectoid steel is cold-rolled by cold rolling at this time so that the reduction ratio is 70% or more, the spheroidized cementite is separated from the base, and fine voids are formed in the product. The Such voids cause a decrease in durability and strength of the final product. Therefore, in the case of eutectoid steel, when the cold rolling is performed once, the rolling reduction is limited to 60 to 70%.

  For these reasons, when the hot-rolled steel sheet is cold-rolled, if the hot-rolled steel sheet becomes thick, it must be rolled thinly to the target thickness by repeatedly performing cold rolling several times.

  Therefore, when the thickness of the hot-rolled steel sheet is manufactured to be 1.8 mm or less, preferably 1.6 mm or less as in the embodiment of the present invention, at least one spheroidizing annealing process is performed in the subsequent cold rolling process. And cold rolling can be omitted.

  Providing a hot-rolled steel sheet in a thin plate state in this way makes it possible to omit manufacturing process steps in subsequent processes, so that processing costs can be reduced during product production and manufacturing process time can be shortened.

  The thin plate that has been subjected to finish hot rolling to the thickness as described above is cooled to an appropriate temperature by a run-out table, and then wound on a coil of a coil.

  The thin plate cooled by the runout table is made to have a pearlite phase transformation rate of 90% or more before being wound by the winder.

  When the degree of pearlite phase transformation is 90% or less before the thin plate cooled by the run-out table is wound, the hot rolled steel plate is transformed into pearlite while being wound. Then, the temperature of the winding coil rises due to transformation heat generation, and when the temperature rises, the formed pearlite structure becomes coarse. When the subsequent process is performed in a state where the pearlite structure is coarse, residual cementite is present in the product after annealing. When residual cementite exists in this way, stress concentrates on the cementite structure in the product processing step, and the product is broken or heat treatment is not smoothly performed. In addition, if the thin plate cooled by the runout table is not wound into the pearlite before being wound, if the phase is transformed into the pearlite in the wound state, the volume fraction of the crystal structure changes, and the coil state The shape of the hot-rolled steel sheet wound up at is collapsed up and down and changes to an elliptical shape. Such a collapsed coil is referred to as a “talent-like coil”. When such a talent-like coil is generated in this way, it is difficult to operate in the subsequent refining process, pickling process, and the like, which causes a decrease in productivity and actual yield.

  The reason why transformation heat is generated during the hot rolling process of the high carbon hot rolled steel sheet according to one embodiment of the present invention will be described.

  In the case of high carbon steel, as the C content increases, the curve nose of the CCT curve moves to the right side. Therefore, the time for starting the phase transformation from austenite to pearlite is delayed, and the end time thereof is also delayed. Further, as the C content increases, the transformation heat generation due to the difference in heat capacity increases.

  Therefore, for the reasons as described above, it is preferable that the thin plate that has been subjected to finish hot rolling completes 90% or more of the phase transformation from austenite to pearlite before being wound in a coil state.

  For this reason, it is preferable that the thin plate that has been subjected to finish hot rolling is rapidly cooled when it begins to enter the run-out table. The cooling rate at this time is preferably 50 to 300 ° C./sec.

  Therefore, it is preferable that the thin plate entering the run-out table is rapidly cooled to a cooling stop temperature of 650 ° C. or lower. The thin plate cooled to 650 ° C. or lower by the runout table is wound at 650 ° C. or lower after completing the pearlite phase transformation by 90% or more while maintaining the cooling temperature while passing through the runout table.

  A time of 9 seconds or more is required for high carbon steel to complete the phase transformation at the run-out table. However, as the thickness is reduced by hot rolling, the sheet passing speed increases, and when rolling to a thickness of 1.8 mm or less, it is easy to ensure sufficient time for completing the phase transformation. Not. Accordingly, in one embodiment of the present invention, in order to minimize the time required for the hot-rolled steel sheet to complete the phase transformation, the steel sheet is rapidly cooled to 50 to 300 ° C./sec at the initial stage of entering the runout table. Then, it is cooled to the cooling stop temperature. The required time at this time is preferably controlled within 3 seconds. The hot-rolled steel sheet cooled while moving on the run-out table completes the phase transformation while reducing the amount of heat generated by annealing at a cooling stop temperature in the temperature range of 550 to 660 ° C. The required time at this time is preferably maintained for 6 seconds or more.

  When hot rolling is performed under the shear-controlled cooling conditions on the runout table as described above, the structure of the manufactured hot-rolled steel sheet has fine pearlite.

  The manufactured hot-rolled steel sheet preferably has a cementite width of 0.2 μm or less, and an interval between cementite and cementite of 0.5 μm or less. Such a crystal structure eventually has a fine pearlite structure, and the final hot-rolled steel sheet has a fine pearlite phase fraction of 90% or more.

  The manufactured hot-rolled steel sheet is subjected to pickling and spheroidizing annealing, and then cold-rolled to produce a cold-rolled steel sheet. A cold-rolled steel sheet produces a cold-rolled steel sheet having a desired thickness by repeatedly performing an annealing process and a cold rolling process again in order. Such a cold-rolled steel sheet is processed into a desired product by a process such as blanking or burring, and then processed into a final product by QT heat treatment.

  Only when the structure of the hot-rolled steel sheet is controlled to fine pearlite when processing into the final product, it is possible to suppress the cementite residue in the final product, increase the strength of the final product, and wear resistance. And fatigue resistance can be imparted.

  Table 1 shows the composition of the steel plate used in the experiment.

  After manufacturing the slab which has a composition of Table 1, this slab was reheated at 1200 degreeC and hot-rolled.

  The thickness of the hot-rolled steel sheet by hot rolling was set to 1.8 to 1.4 mm in both the comparative example and the example.

  All of the comparative examples in Table 1 were subjected to finish hot rolling, and then no shear control cooling was performed on the runout table, and all the examples were subjected to shear control cooling.

  And it wound up at the winding temperature shown in Table 2. Table 2 shows both the values obtained by performing the HrC hardness test on the hot-rolled steel sheets that have been subjected to hot rolling and winding, and the results of microscopic observation.

  As shown in Table 2, in the comparative examples in which the shear control cooling was not performed on the run-out table, the HrC hardness values were all lower than those in the examples, and all the structures showed coarse pearlite. In the case of the example to be compared with this, the HrC hardness value was higher than that of the comparative example, and all of the structures showed fine pearlite.

  Next, FIGS. 1-4 show the crystal structure photograph after performing hot rolling on the test pieces of Comparative Example 1 and Example 1 and the crystal structure photograph after performing spheroidizing annealing.

  In Comparative Example 1 shown in FIG. 1, after finishing hot rolling, the sample was wound after passing through the run-out table without shear control cooling.

  The manufacturing process conditions of Comparative Example 1 were that slow cooling was performed without shear control cooling in the run-out table section, so that sufficient time for phase transformation could not be secured in the run-out table section. In this case, the phase transformation rate before winding is 50% or less, and the crystal structure shows a rough pearlite structure at a level observable with an optical microscope (× 500). In this case, the winding temperature is in the range of 600 to 650 ° C., but the temperature rises as high as 650 ° C. or more due to transformation heat generation after winding, and the shape of the coil wound becomes a talented head shape.

  The hot-rolled steel sheet of Comparative Example 1 thus manufactured was subjected to pickling and spheroidizing annealing. FIG. 2 shows a micrograph of the product that has been subjected to spheroidizing annealing.

  The comparative example 1 shown in FIG. 2 performed the pickling process with respect to the hot rolled steel plate of 1.6 mm thickness, and performed spheroidizing annealing, maintaining for 30 hours or more in the range of 650-720 degreeC. And after cold rolling once, after manufacturing to a 0.8 mm-thick cold-rolled steel plate, it is the structure | tissue observed with the microscope after recrystallization annealing. As shown in FIG. 2, the point expressed in black is undissolved cementite, which adversely affects the heat treatment failure and fatigue characteristics of the final product.

  In Example 1 shown in FIG. 3, after finishing hot rolling at a temperature of 880 ° C. or higher, cooling is started at a rate of 50 ° C./sec or higher by shearing at a run-out table, and cooling is stopped at 580 ° C. Quenched to temperature. Then, after passing through the run-out table, the temperature was maintained so as to complete 90% or more of the pearlite transformation, and then wound at 650 ° C. or less.

  The hot-rolled steel sheet of Example 1 manufactured in this way was hot-rolled to a thickness of 1.6 mm. The pickling process and the spheroidizing annealing process that maintains a temperature of 650 to 720 ° C. for 30 hours or more. Went. The test piece was subjected to cold rolling once, then cold rolled to a thickness of 0.8 mm, and then recrystallized and annealed.

  FIG. 4 is a photomicrograph of Example 1 after such recrystallization annealing. As shown in FIG. 4, in the case of the embodiment in which the shear control cooling is performed by the run-out table, the cementite is uniformly dispersed, so that the heat treatment of the final product is improved and the fatigue characteristics are improved.

  Although the crystal structure photographs of Comparative Example 1 and Example 1 have been described above, the test pieces manufactured according to other Comparative Examples and other Examples also showed a structure having a similar form.

  Summarizing these experimental results, the hot-rolled steel sheet manufactured according to the example has a fine pearlite structure as shown in FIG. 3, whereas the hot-rolled steel sheet manufactured according to the comparative example is rough as shown in FIG. Has a pearlite structure.

  Thus, when a hot-rolled steel sheet is directly rolled in a thin plate state having a thickness of 1.8 mm or less, the comparative example manufactured by a normal hot rolling method has a coarse pearlite structure. In the state, twist due to thermal deformation appears.

  However, even if the hot-rolled steel sheet is directly rolled in a thin plate state having a thickness of 1.8 mm or less, when the shear control cooling is performed on the run-out table as in the example, the crystal structure shows a fine pearlite structure. Thus, the coil was wound in a state where the transformation was 90% or more, so that no twisting phenomenon of the coil appeared.

  Further, the results of spheroidizing annealing of the hot rolled steel sheets of the comparative example and the example manufactured as described above by the subsequent process are all similar to the structures shown in FIGS. 2 and 4.

  As shown in FIG. 2, in the product according to the comparative example, a plurality of undissolved cementite was found, whereas in the product according to the example, such undissolved cementite was not found.

  Therefore, the product according to the example did not break due to stress concentration in the processing process of the final product, and no defective product was generated by the heat treatment.

  As described above, the high carbon hot-rolled steel sheet and the method for producing the same have been described with reference to the preferred embodiments of the present invention. However, those skilled in the art will be described in the following claims. It should be understood that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention.

According to one embodiment of the present invention to achieve another object, i) by weight, C: 0.60-1.20%, Si: 0.10-0.35%, Mn: 0.00. 10 to 0.80%, P: greater than 0 and 0.03% or less, and S: greater than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0 A slab manufacturing step of manufacturing a high carbon slab containing at least one of 30% or less (including 0) and Cu: 0.25% or less (including 0) and the balance including Fe and other inevitable impurities And ii) a reheating step in which the slab is reheated at 1200 ° C. or lower , and iii) rough rolling the slab, and then performing finish rolling in an austenite region at 830 ° C. or higher to obtain a thickness of 1 . Hot rolling to produce thin plates of 8 mm or less Iv) a cooling step for cooling the thin plate by shear-controlled cooling at a run-out table; v) a cooling stop step for maintaining a cooling temperature for a time required for performing the pearlite phase transformation in the cooling step; vi And a step of winding the thin plate at 650 ° C. or lower.

In the cooling stop step of the method for producing a high carbon hot-rolled steel sheet, the pearlite phase transformation is completed by 90% or more, and such a phase transformation completion time is at least 6 seconds or more. In addition, such a cooling stop step maintains the temperature at 550 to 650 ° C.

A time of 9 seconds or more is required for high carbon steel to complete the phase transformation at the run-out table. However, as the thickness is reduced by hot rolling, the sheet passing speed increases, and when rolling to a thickness of 1.8 mm or less, it is easy to ensure sufficient time for completing the phase transformation. Not. Accordingly, in one embodiment of the present invention, in order to minimize the time required for the hot-rolled steel sheet to complete the phase transformation, the steel sheet is rapidly cooled to 50 to 300 ° C./sec at the initial stage of entering the runout table. Then, it is cooled to the cooling stop temperature. The required time at this time is preferably controlled within 3 seconds. The hot-rolled steel sheet cooled while moving on the run-out table completes the phase transformation while reducing the amount of heat generated by annealing at a cooling stop temperature in the temperature range of 550 to 650 ° C. The required time at this time is preferably maintained for 6 seconds or more.

Claims (13)

% By weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.10 to 0.80%, greater than P: 0 to 0.03% or less, and S: more than 0 and 0.03% or less,
Any one or more of Ni: 0.25% or less (including 0), Cr: 0.30% or less (including 0), and Cu: 0.25% or less (including 0),
It has a fine pearlite structure consisting of the balance Fe and other inevitable impurities, and having a width of cementite of more than 0 and 0.2 μm or less, and a distance between the cementite and cementite of more than 0 and 0.5 μm or less. A high-carbon hot-rolled steel sheet.   The high carbon hot rolled steel sheet according to claim 1, wherein the high carbon hot rolled steel sheet has a fine pearlite structure fraction of 90% or more.   The high carbon hot rolled steel sheet according to claim 1 or 2, wherein the high carbon hot rolled steel sheet has a thickness of 1.8 mm or less.   The high carbon hot rolled steel sheet according to claim 1 or 2, wherein the high carbon hot rolled steel sheet has a thickness of 1.6 mm or less. % By weight, C: 0.60 to 1.20%, Si: 0.10 to 0.35%, Mn: 0.10 to 0.80%, greater than P: 0 to 0.03% or less, and S: more than 0 and 0.03% or less, Ni: 0.25% or less (including 0), Cr: 0.30% or less (including 0), and Cu: 0.25% or less (0 A slab manufacturing step of manufacturing a high carbon slab including the balance Fe and other inevitable impurities,
A reheating step of reheating the slab at 1200 ° C. or higher;
After roughly rolling the slab, a hot rolling step for producing a thin plate having a thickness of 1.8 mm or less by performing a finish hot rolling in an austenite region of 830 ° C. or higher;
A cooling step of cooling the thin plate with a run-out table by shear control cooling;
A cooling stop step for maintaining the cooling temperature for a time necessary for performing the pearlite phase transformation in the cooling step;
And a winding step of winding the thin plate at 650 ° C. or less.   The method for producing a high carbon hot-rolled steel sheet according to claim 5, wherein in the cooling step, the cooling control cooling for cooling the thin plate has a cooling rate of 50 to 300 ° C / sec.   The method for manufacturing a high carbon hot-rolled steel sheet according to claim 6, wherein the thin plate is 1.6 mm or less in the step of manufacturing the thin plate by hot rolling.   In the said cooling step, the shear control cooling which cools a thin plate is cooled so that it may become 650 degrees C or less, The manufacturing method of the high carbon hot rolled sheet steel of Claim 7 characterized by the above-mentioned.   The method for producing a high carbon hot-rolled steel sheet according to claim 8, wherein in the cooling step, cooling to 650 ° C or lower is within at least 3 seconds.   The method for producing a high carbon hot-rolled steel sheet according to any one of claims 5 to 9, wherein in the cooling stop step, the pearlite phase transformation is completed by 90% or more.   The method for producing a high carbon hot-rolled steel sheet according to claim 10, wherein the cooling stop step maintains the temperature at 550 to 660 ° C.   The method for producing a high carbon hot-rolled steel sheet according to claim 11, wherein in the cooling stop step, a time period required to complete 90% or more of the pearlite phase transformation is at least 6 seconds.   The hot-rolled steel sheet produced by the method for producing a high carbon hot-rolled steel sheet has a cementite width of more than 0 and not more than 0.2 μm, and a gap between cementite and cementite is more than 0 and not more than 0.5 μm. It has a pearlite structure | tissue, The manufacturing method of the high carbon hot rolled sheet steel of Claim 10 characterized by the above-mentioned.

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