KR102020387B1 - High-carbon hot-rolled steel sheet having excellent surface quality and method for manufacturing same - Google Patents

Abstract

The present invention relates to a hot rolled steel sheet suitable for construction, tools, automobile parts, and the like, and more particularly, to a high carbon hot rolled steel sheet having excellent surface quality and a method of manufacturing the same.

Description

High carbon hot rolled steel sheet with excellent surface quality and manufacturing method thereof {HIGH-CARBON HOT-ROLLED STEEL SHEET HAVING EXCELLENT SURFACE QUALITY AND METHOD FOR MANUFACTURING SAME}

The present invention relates to a hot rolled steel sheet suitable for construction, tools, automobile parts, and the like, and more particularly, to a high carbon hot rolled steel sheet having excellent surface quality and a method of manufacturing the same.

High-carbon hot-rolled steel sheets, which can be used in a variety of applications such as construction, tools, and automobile parts, are pickled and cold rolled by secondary customers, and then formed into parts for heat treatment and purpose by end customers.

However, if decarburization occurs on the surface of the hot rolled steel sheet during processing as described above, it is difficult to obtain a desired hardness after heat treatment. In addition, when grain boundary oxidation is present on the surface of the hot rolled steel sheet, there is a problem in that cracks are easily generated during use of the product.

Therefore, it is required to minimize surface decarburization and grain boundary oxidation in high carbon steel products.

However, in the case of high carbon steel, transformation heat is generated after winding, and the coil temperature rapidly rises. Such high carbon steel has higher oxygen affinity than Cr, Mn, Al, Si, etc. to improve the hardenability. Since it contains a large amount, there is a problem that decarburization and grain boundary oxidation easily occur.

Therefore, when manufacturing a high carbon hot rolled steel sheet, it is necessary to set the operating conditions in detail so that decarburization and grain boundary oxidation are minimized.

On the other hand, Patent Document 1 proposes a method of adding elements such as Sb or strengthening the cooling process in order to prevent decarburization or grain boundary oxidation of high carbon steel. However, if Sb is not used properly, there is a risk of weakening the grain boundary and impairing the durability of the product. In addition, there is a problem that when the cooling is enhanced, the shape is bad, the workability of the customer during pickling and re-rolling very inferior. In addition, in order to enhance the cooling, the amount of cooling water increases, so that the edge portion of the hot rolled sheet may be overcooled, and when low temperature tissue is formed at the edge portion, there is a fear of causing a crack.

Korean Unexamined Patent Publication No. 2007-0138536

One aspect of the present invention is to provide a high carbon hot rolled steel sheet having excellent surface quality and a method of manufacturing the same by optimizing the alloy composition and manufacturing conditions to minimize decarburization and grain boundary oxidation of the high carbon hot rolled steel sheet.

The problem to be solved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

One aspect of the present invention, by weight, C: 0.8-1.3%, Si: 0.01-0.5%, Mn: 0.3-2.0%, Al: 0.1% or less (excluding 0%), Cr: 2.0% or less ( P: 0.03% or less, S: 0.02% or less, N: 0.01% or less, Ni: 2.0% or less, Mo: 2.0% or less, Cu: 2.0% or less, and V: 1.0% or less It provides a high-carbon hot-rolled steel sheet comprising at least one member selected from the group consisting of, high balance of Fe and other unavoidable impurities, and excellent surface quality including pearlite and grain boundary cementite as a microstructure.

Another aspect of the invention, the step of reheating the steel slab that satisfies the above-described alloy composition in a temperature range of 1100 ~ 1300 ℃; Manufacturing a hot rolled steel sheet by roughly and preliminarily rolling the reheated steel slab; First cooling the hot-rolled steel sheet to 720 to 750 ° C. at a cooling rate of 30 ° C./s or more; And after the first cooling, second cooling to 670-710 ° C at a cooling rate of 10 ° C / s or less, and then winding up, wherein the finish rolling is performed at a temperature higher than a value derived from Equation (1) below. Provided is a method for producing a high carbon hot rolled steel sheet having excellent surface quality.

Equation (1) = 464 + 368C + 6.2Mn + 25.1Si-0.2Ni + 54.8Cr-49.8Mo-64.6Cu + 9.3V

(Wherein C, Mn, Si, Ni, Cr, Mo, Cu, and V each represent a weight content.)

According to the present invention, it is possible to provide a high carbon hot rolled steel sheet having excellent surface quality with minimized surface decarburization and grain boundary oxidation.

Therefore, it is possible to reduce the additional process cost in the secondary customer, it has the effect of greatly improving the durability of the final product.

1 shows the results of observing whether or not surface decarburization occurs in the hot-rolled steel sheet of Comparative Example 4 and Inventive Example 3 according to the embodiment of the present invention.
Figure 2 shows the results of observing whether the grain boundary oxidation of the hot rolled steel sheet of Comparative Example 4 and Inventive Example 3 according to an embodiment of the present invention.
Figure 3 shows the structure of the Comparative Example 8 and Example 3 according to an embodiment of the present invention observed by electron microscopy (in this case, the structure of each steel is 1 / 4t thickness direction (where t is the thickness of the steel (mm) From the point of view).

The present inventors have identified the above-mentioned problems in providing a high carbon hot rolled steel sheet, and have studied in depth a method for minimizing surface decarburization and grain boundary oxidation.

As a result, by optimizing the alloy composition and manufacturing conditions of the hot-rolled steel sheet, it was confirmed that the occurrence of surface decarburization and grain boundary oxidation of the hot-rolled steel sheet can be suppressed to provide a hot-rolled steel sheet with excellent surface quality. .

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

High-carbon hot-rolled steel sheet having excellent surface quality according to an aspect of the present invention by weight%, C: 0.8 ~ 1.3%, Si: 0.01 ~ 0.5%, Mn: 0.3 ~ 2.0%, Al: 0.1% or less (0% Cr: 2.0% or less (excluding 0%), P: 0.03% or less, S: 0.02% or less, and N: 0.01% or less.

Hereinafter, the reason for controlling the alloy composition of the high carbon hot rolled steel sheet according to the present invention will be described in detail.

At this time, unless otherwise specified, the content of each alloy element means weight%.

C: 0.8-1.3%

Carbon (C) is the most effective element for securing strength. In order to obtain excellent hardness in the present invention, it is preferable to add more than 0.8%, but if the content exceeds 1.3%, the steel sheet is too hard during hot rolling, which may cause defects in the process.

Therefore, in the present invention, it is preferable to control the content of C to 0.8 ~ 1.3%.

Si: 0.01 ~ 0.5%

Silicon (Si) is an effective element for the deoxidation effect, and for this purpose, it is preferable to contain at least 0.01%. However, if the content is more than 0.5%, the possibility of causing grain boundary oxidation on the surface of the hot rolled steel sheet is not preferable.

Therefore, in the present invention, it is preferable to control the content of Si to 0.01 to 0.5%.

Mn: 0.3 ~ 2.0%

Manganese (Mn) together with C is an element effective for securing the strength of steel. If the Mn content is less than 0.3%, FeS may be formed to cause grain boundary brittleness at a high temperature. On the other hand, if the content exceeds 2.0%, there is a concern that the quality of the hot rolled steel sheet is inferior due to the central segregation and inclusion formation and grain boundary oxidation.

Therefore, in the present invention, it is preferable to control the content of Mn to 0.3 to 2.0%.

Al: 0.1% or less (except 0%)

Aluminum (Al) is an element added for the deoxidation effect as well as the solid solution strengthening effect. However, when the content of Al exceeds 0.1%, not only causes cracks in slabs during playing, but may cause grain boundary oxidation in the final product.

Therefore, in the present invention, it is preferable to control the content of Al to 0.1% or less, and 0% is excluded.

Cr: 2.0% or less (except 0%)

Chromium (Cr) is an element added to increase the hardenability of steel, and has an effect of suppressing iron rust generation by forming a passivation film in the atmosphere. However, if excessively added, it is difficult to scale off during the hot rolling process and may cause edge cracks of the hot rolled sheet during cooling.

In consideration of this, in the present invention, it is preferable to control the content of Cr to 2.0% or less, and 0% is excluded.

P: 0.03% or less

Phosphorus (P) is an element that is inevitably added during the steel manufacturing process, and segregation in the steel may cause brittleness, so it is preferable to control the content thereof as low as possible.

However, in order to control the content of P as low as possible takes a lot of costs, it is preferable to manage the upper limit, it is preferable to control to a maximum of 0.03% in the present invention.

S: 0.02% or less

Sulfur (S) is an element inevitably added during the steel manufacturing process, and may form inclusions or form FeS sulfide having a low melting point, causing grain boundary brittleness during hot rolling.

Therefore, it is preferable to control the content of S as low as possible, and in the present invention, it is preferable to control the upper limit to a maximum of 0.02%.

N: 0.01% or less

Nitrogen (N) has the effect of strengthening the solid solution, but if the content is excessive, there is a concern that the employment element causes yield stretching and inferior the surface quality. In addition, there is a risk of depositing nitride to impair workability.

Therefore, in the present invention, it is preferable to control the content of N to 0.01% or less.

Hot rolled steel sheet of the present invention may further include the following components in addition to the above-described alloy composition for the purpose of improving the physical properties.

Specifically, it is preferable to further include one or more of Ni, Mo, Cu and V.

Ni: 2.0% or less

Nickel (Ni) is an element added to increase strength and improve corrosion resistance, and when added together with Cu to be described later, it has an effect of preventing high temperature grain embrittlement by Cu. However, if the content exceeds 2.0%, there is a problem of degrading the descaling property of the scale at a high temperature by making the interface uneven.

Therefore, in the present invention, it is preferable to control the content of Ni at 2.0% or less.

Mo: 2.0% or less

Molybdenum (Mo) is an effective element for improving the hardenability of the steel, and may be added to impart thermal stability of the precipitation hardening element. However, if Mo is an expensive element and its content exceeds 2.0%, there is a fear that the manufacturing cost will be greatly increased.

Therefore, in the present invention, it is preferable to control the content of the Mo at 2.0% or less.

Cu: 2.0% or less

Copper (Cu) is an element added for increasing strength and improving corrosion resistance. However, when the content of Cu exceeds 2.0%, it is not preferable because it may cause grain boundary embrittlement at a high temperature.

Therefore, in the present invention, it is preferable to control the content of the Cu at 2.0% or less.

V: 1.0% or less

Vanadium (V) is an element added to improve strength. However, if V is an expensive element and its content exceeds 1.0%, there is a fear that the manufacturing cost will be greatly increased.

Therefore, in the present invention, it is preferable to control the content of the V at 1.0% or less.

The remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, not all of them are specifically mentioned in the present specification.

It is preferable that the hot rolled steel sheet of this invention which satisfy | fills the alloy composition mentioned above contains a pearlite and grain boundary cementite as a microstructure.

More specifically, the pearlite is preferably included in an area fraction of 90% or more. If the fraction of pearlite is less than 90%, a film of grain boundary cementite forms a network, and thus, grain embrittlement tends to occur.

The hot rolled steel sheet may include at least 50% of the grain boundary cementite having an aspect ratio (the length of one grain cementite / the maximum thickness of one grain cementite) of the total grain boundary cementite divided by 30 or less.

That is, the hot-rolled steel sheet of the present invention contains a large amount of segmented cementite in grain boundary cementite, and even if grain boundary oxidation occurs from this, it is possible to obtain an effect of suppressing propagation thereof.

Here, the length and maximum thickness of the grain boundary cementite to obtain the aspect ratio are measured in one and the same grain boundary cementite.

In the high carbon hot rolled steel sheet, when the final structure is made of pearlite and grain cementite, it is accompanied by transformation heat after winding, so that decarburization and grain boundary oxidation easily occur as the temperature of the wound coil increases.

However, in the present invention, while controlling the alloy composition as described above, as will be described in detail later, the decarburization and grain boundary oxidation depth of the high carbon hot rolled steel sheet can be formed in the thickness direction of 10 μm or less from the surface by optimizing the process conditions.

In other words, even if the alloy composition that can easily occur decarburization and grain boundary oxidation can be effectively suppressed decarburization and grain boundary oxidation is to provide a hot rolled steel sheet with excellent surface quality.

Hereinafter, a method of manufacturing a high carbon hot rolled steel sheet having excellent surface quality according to another aspect of the present invention will be described in detail.

Briefly, the high-carbon hot-rolled steel sheet of the present invention can be manufactured through a process of [reinforcing steel slab-hot rolling-cooling and winding], and the conditions for each process will be described in detail below.

Reheating Steel Slabs

First, after preparing a steel slab that satisfies the above-described alloy composition, it is preferable to reheat it in the temperature range of 1100 ~ 1300 ℃.

The reheating process is a process for homogenizing the slab. If the temperature is less than 1100 ° C., the rolling load may increase rapidly during the subsequent hot rolling process. On the other hand, if the temperature exceeds 1300 ° C., the surface temperature is high during finishing rolling, and a high-temperature oxidation scale is formed on the surface, causing surface defects, or a defect that causes the scale to fall off when the coil is wound afterwards. have.

Hot rolled

It is preferable to hot-roll the steel slab reheated according to the above to produce a hot-rolled steel sheet, and it is preferable to be carried out in the rough rolling and finish rolling process.

Since the rough rolling can be carried out under ordinary conditions, the present invention is not particularly limited to the conditions.

It is preferable that the said finish rolling is performed at temperature higher than the value derived from following formula (1). More preferably, it is preferable to control the entrance temperature at the time of finishing rolling to 950-1100 degreeC, and to control the exit temperature higher than the value of following formula (1).

The hot rolled steel sheet of the present invention is a high carbon steel containing 0.8% or more of carbon (C), and the cementite cementite is precipitated at the austenite grain boundary during rolling. If the finish rolling exit temperature is lower than the value derived from Equation (1), precipitation of the cementite cementite at the austenite grain boundary is promoted and brittleness is increased. There is a high risk of cracking.

Therefore, in the present invention, by controlling the finish rolling temperature during hot rolling higher than the value derived from Equation (1), it is preferable to prevent the surface cracks of the hot rolled steel sheet and to minimize decarburization and grain boundary oxidation.

Equation (1) = 464 + 368C + 6.2Mn + 25.1Si-0.2Ni + 54.8Cr-49.8Mo-64.6Cu + 9.3V

(Wherein C, Mn, Si, Ni, Cr, Mo, Cu, and V each represent a weight content.)

The elements of the above formula (1) are elements that affect the Acm temperature (the temperature at which the cementite cementite precipitates at the grain boundary from austenite). In the present invention, since the above-mentioned elements are contained in a certain content, by completing rolling and starting cooling within the temperature range satisfying the above formula (1), sementite is excessively precipitated at the austenite grain boundary to prevent the brittleness from increasing. can do.

Cooling and Winding

It is preferable to wind up after cooling the hot rolled steel sheet manufactured as described above.

The cooling may cool the hot rolled steel sheet by water cooling on a cooling table such as a run-out table (ROT).

In particular, the cooling is preferably started to cool within 3 seconds immediately after the finish rolling, if the time from the finish rolling to the start of cooling exceeds 3 seconds, the time that the hot-rolled steel sheet is exposed at high temperature is long This is because grain boundary oxidation may worsen.

On the other hand, in the present invention, after performing the primary cooling to cool at an average cooling rate of 30 ℃ / s or more up to a temperature range of 720 ~ 750 ℃ during the cooling, 10 ℃ / s or less (excluding 0 ℃ / s) to the winding temperature range It is preferable to perform secondary cooling at an average cooling rate of.

As described above, the stepwise cooling is to suppress surface decarburization and grain boundary oxidation of the high carbon hot rolled steel sheet.

If the average cooling rate during the primary cooling is less than 30 ℃ / s there is a fear that grain boundary oxidation occurs during cooling.

The upper limit of the average cooling rate during the primary cooling is not particularly limited and may be appropriately selected according to the cooling equipment.

If the cooling end temperature at the cooling rate described above is less than 720 ℃ or more than 750 ℃ the shape is poor, there is a problem that the surface decarburization and grain boundary oxidation exceeds 10㎛.

The secondary cooling is preferably carried out at an average cooling rate of 10 ℃ / s or less (except 0 ℃ / s) in order to minimize the cooling deviation to obtain a uniform material, more preferably after cooling to the range of 670 ~ 710 ℃ It is preferable to wind up in the temperature range.

If the coiling temperature is less than 670 ℃ may cause a problem that the temperature of the coil is increased by the transformation heat after winding, the decarburization and grain boundary oxidation exceeds 10㎛. On the other hand, if the coiling temperature exceeds 710 ℃, the initial coiling temperature itself is high, there may be a problem that the decarburization and grain boundary oxidation depth exceeds 10㎛ even a slight transformation heat, surface quality is inferior due to scale peeling It is not desirable because there is a possibility.

In the case of the existing high-carbon hot-rolled steel sheet, there is a problem that surface decarburization and grain boundary oxidation are easily generated by transformation heat when winding is performed in the above temperature range. However, in the present invention, while controlling the alloy composition contained in the high-carbon hot-rolled steel sheet, by controlling the rolling and cooling process during manufacturing, the amount of transformation heat generated during winding in the above temperature range is reduced, which can effectively suppress surface decarburization and grain boundary oxidation. will be.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

( Example )

The steel slab having the alloy composition shown in Table 1 below was reheated at a temperature range of 1100 to 1300 ° C., and then hot rolled steel sheets were manufactured through a finish rolling-cooling-winding process under the conditions shown in Table 2 below.

For each hot rolled steel sheet produced, the surface decarburization and grain boundary oxidation depth from the surface to the thickness direction were observed, and the results are shown in Table 3 below. At this time, the decarburization and grain boundary oxidation depth was measured by SEM (Scanning Electron Microscopy), and then measured through a photograph and image analysis of the oxide.

In addition, the structure of the rolling direction was observed by SEM at the 1 / 4t thickness direction of each hot rolled steel sheet, and the fraction of grain boundary cementite was measured and shown in Table 3 below. In this case, the fraction of grain boundary cementite measured the fraction of grain boundary cementite having an aspect ratio (length of one grain cementite / maximum thickness of one grain cementite) divided into 30 or less.

Then, it was visually confirmed whether cracks occurred on the surface of each of the wound hot rolled coils when uncoiling. In addition, by measuring the high and low difference of the edge wave (wave), the shape irregularity of the hot-rolled steel sheet was observed, and at this time, it was determined that the difference is more than 10mm.

Steel grade Alloy composition (% by weight) Formula (1)
C Si Mn Al Cr P S N Ni Mo Cu V One 0.80 0.2 0.40 0.015 0.25 0.01 0.003 0.004 1.8 0 0 0 779 2 0.85 0.2 0.55 0.015 0.15 0.01 0.003 0.004 0 0.2 0 0 783 3 0.90 0.3 0.90 0.015 1.10 0.01 0.003 0.004 0 0 0 0.1 870 4 1.10 0.2 0.70 0.015 0.50 0.01 0.003 0.004 0 0 0.1 0.1 900 5 1.22 0.2 0.40 0.015 0.55 0.01 0.003 0.004 0 0 0.3 0 931

Steel grade Wrap-up
Rolling (℃) Start of cooling
Time in seconds Primary cooling
Speed (℃ / s) Primary cooling
End temperature (℃) Secondary cooling
Speed (℃ / s) Winding temperature
(℃) Remarks One 881 2 80 730 5 690 Inventive Example 1 2 883 3 80 730 5 692 Inventive Example 2 3 890 2 80 730 5 691 Inventive Example 3 4 912 3 80 730 5 688 Inventive Example 4 5 938 2 30 730 4 699 Inventive Example 5 3 887 3 50 740 4 706 Inventive Example 6 3 884 2 100 720 4 689 Inventive Example 7 3 886 3 80 730 4 700 Inventive Example 8 3 886 3 200 750 9 677 Inventive Example 9 3 885 2 200 720 5 678 Inventive Example 10 3 884 3 10 740 4 707 Comparative Example 1 3 881 4 200 750 8 683 Comparative Example 2 3 889 2 50 760 10 681 Comparative Example 3 3 888 3 100 670 9 602 Comparative Example 4 3 883 3 100 650 8 584 Comparative Example 5 3 887 3 50 750 4 721 Comparative Example 6 5 879 3 30 730 6 680 Comparative Example 7 3 859 3 50 730 6 683 Comparative Example 8

division aspect ratio
Fraction of grain boundary cementite less than 30 Decarburization depth
(Μm) Grain boundary depth
(Μm) Crack
The presence or absence shape Inventive Example 1 59 2 5 Not Occurred Good Inventive Example 2 77 2 3 Not Occurred Good Inventive Example 3 100 3 3 Not Occurred Good Inventive Example 4 100 3 8 Not Occurred Good Inventive Example 5 100 6 8 Not Occurred Good Inventive Example 6 90 8 10 Not Occurred Good Inventive Example 7 85 2 6 Not Occurred Good Inventive Example 8 89 5 9 Not Occurred Good Inventive Example 9 88 7 9 Not Occurred Good Inventive Example 10 86 One 4 Not Occurred Good Comparative Example 1 83 14 15 Not Occurred Good Comparative Example 2 56 11 12 Not Occurred Good Comparative Example 3 100 13 11 Not Occurred Good Comparative Example 4 100 12 13 Not Occurred Bad Comparative Example 5 78 12 12 Not Occurred Bad Comparative Example 6 91 19 21 Not Occurred Good Comparative Example 7 48 7 8 Occur Good Comparative Example 8 13 4 7 Occur Good

As shown in Tables 1 to 3, Inventive Examples 1 to 10 satisfying all of the alloy composition and manufacturing process conditions proposed by the present invention have a total depth of decarburization and grain boundary oxidation produced in the thickness direction from the surface of the hot-rolled steel sheet. It was formed to have a μm or less, it can be confirmed that no cracks or the like occurred when the hot rolled coil is loosened.

On the other hand, in the comparative examples in which any one or more conditions of the alloy composition and manufacturing process deviate from the present invention, surface decarburization and grain boundary oxidation are not effectively suppressed and the depth is formed to exceed 10 μm, or cracks are generated when the hot rolled coil is loosened. You can see that.

In particular, Comparative Example 1 having a slow cooling rate in the first cooling after finishing hot rolling, and Comparative Example 2 in which the primary cooling was not performed within three seconds after finishing hot rolling were performed. Decarburization and grain boundary oxidation occurred excessively.

In addition, in Comparative Examples 4 and 5, when the coiling temperature was too low or too high, not only surface decarburization and grain boundary oxidation occurred excessively, but also the shape was poor.

And in the case of Comparative Examples 7 and 8 in which the temperature at the time of finish hot rolling is lower than Formula (1), a crack generate | occur | produced on the surface when loosening a wound coil. This is because grain boundary cementite having an aspect ratio of grain boundary cementite of 30 or less is formed to have an area fraction of less than 50% of the total grain cementite, and thus, grain boundary becomes weak and crack propagation is facilitated along grain boundary. (See FIG. 3).

Claims (8)

In weight percent, C: 0.8-1.3%, Si: 0.01-0.5%, Mn: 0.3-2.0%, Al: 0.1% or less (except 0%), Cr: 2.0% or less (except 0%), P : 0.03% or less, S: 0.02% or less, N: 0.01% or less, Ni: 2.0% or less, Mo: 2.0% or less, Cu: 2.0% or less, and V: 1.0% or less selected from the group consisting of Including the above, it contains the balance Fe and other unavoidable impurities,
Its microstructure includes pearlite and grain boundary cementite,
High-carbon hot-rolled steel sheet with excellent surface quality including segmental grained cementite having an aspect ratio (length of one grained cementite / maximum thickness of one grained cementite) of 30 or less in total grain boundary cementite with an area fraction of 50% or more.
The method of claim 1,
The hot rolled steel sheet is a high carbon hot rolled steel sheet having an excellent surface quality including pearlite in an area fraction of more than 90%.
delete The method of claim 1,
The hot rolled steel sheet is a high carbon hot rolled steel sheet having excellent surface quality of the decarburization and grain boundary oxidation depth of 10㎛ or less from the surface.
In weight percent, C: 0.8-1.3%, Si: 0.01-0.5%, Mn: 0.3-2.0%, Al: 0.1% or less (except 0%), Cr: 2.0% or less (except 0%), P : 0.03% or less, S: 0.02% or less, N: 0.01% or less, Ni: 2.0% or less, Mo: 2.0% or less, Cu: 2.0% or less, and V: 1.0% or less selected from the group consisting of Reheating the steel slab further comprising the above, including the remaining Fe and other unavoidable impurities in the temperature range of 1100 ~ 1300 ℃;
Manufacturing a hot rolled steel sheet by roughly and preliminarily rolling the reheated steel slab;
First cooling the hot-rolled steel sheet to 720 to 750 ° C. at a cooling rate of 30 ° C./s or more; And
After the first cooling to secondary cooling to 670 ~ 710 ℃ at a cooling rate of 10 ℃ / s or less, and then winding up,
The finish rolling is a method of producing a high carbon hot rolled steel sheet having a good surface quality that is performed at a temperature higher than the value derived from the following formula (1).

Equation (1) = 464 + 368C + 6.2Mn + 25.1Si-0.2Ni + 54.8Cr-49.8Mo-64.6Cu + 9.3V
(Wherein C, Mn, Si, Ni, Cr, Mo, Cu, and V each represent a weight content.)
The method of claim 5,
The primary cooling is a method for producing a high carbon hot rolled steel sheet having excellent surface quality that is performed within 3 seconds immediately after the finish rolling.
The method of claim 5,
The finish rolling is a method of producing a high carbon hot rolled steel sheet having excellent surface quality that is performed in the temperature range of the entrance temperature of 950 ~ 1100 ℃.
The method of claim 5,
Method of producing a high carbon hot rolled steel sheet having excellent surface quality that the decarburization and grain boundary oxidation depth of the hot rolled steel sheet after the winding is formed in the thickness direction 10㎛ or less from the surface.

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