KR101726074B1

KR101726074B1 - High carbon rolled steel sheet with excellent temper embrittlement resistance properties, and method for producing the same

Info

Publication number: KR101726074B1
Application number: KR1020150151336A
Authority: KR
Inventors: 김용우; 장제욱
Original assignee: 주식회사 포스코
Priority date: 2014-10-30
Filing date: 2015-10-29
Publication date: 2017-04-12
Also published as: CN105568149A; KR20160053790A; CN105568149B

Abstract

One aspect of the present invention provides a high carbon hot-rolled steel sheet excellent in resistance to embrittlement in tempering and a method of manufacturing the same.
According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.2 to 0.6% of C; 0.5% or less of Si (excluding 0%); 0.2 to 1.5% of Mn; (Excluding 0%), Al: not more than 0.05% (excluding 0%), N: not more than 0.01% (excluding 0%), and further additionally selected from the group consisting of Sn, B, Mo, Ni and Cr There is provided a high carbon hot-rolled steel sheet comprising at least one component in a total amount of 0.0001 to 0.35% and having the remainder Fe and other unavoidable impurities, and satisfying the following relational expression (1) do.
[Relation 1]
-3.1 [Si] -10 [P] -50 [N] +172.4 [Sn] +150 [B] +0.4 [Mo] +0.3 [Ni] +0.1 [Cr] +0.9?
(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]
According to an aspect of the present invention, a high carbon hot-rolled steel sheet having excellent material uniformity and excellent resistance to brittle embrittlement can be provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high carbon hot-rolled steel sheet having excellent tempering resistance, and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 >

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high carbon hot-rolled steel sheet which can be used for machine parts, tools and automobile parts, and more particularly to a high carbon hot-rolled steel sheet having excellent tempering resistance.

High carbon steel hot rolled steel sheets using high carbon steel have been used for various purposes, for example, in mechanical parts, tools and automobile parts.

When manufacturing high-carbon hot-rolled steel sheets, such as machine parts, tools and automobile parts, a hot-rolled steel sheet having a desired thickness is prepared, and then a desired shape is obtained through blanking, bending, The high hardness is given through the heat treatment.

One of the characteristics required of a high carbon hot-rolled steel sheet used for mechanical parts, tools, and automobile parts as described above is excellent moldability.

One of the means for securing excellent moldability is to ensure excellent material uniformity.

If the material deviation in the high carbon hot-rolled steel sheet is large, not only the dimensional accuracy of the parts is lowered during the molding process, but also causes defects during processing and causes uneven distribution of the structure in the final heat treatment process.

On the other hand, in the prior art for improving the moldability of a high carbon steel sheet, it is general to control the size and distribution of carbide in a microstructure in cold rolling and annealing.

As an example of the prior art for manufacturing the high carbon hot-rolled steel sheet, the average size and distribution of the carbides in the high carbon annealed steel sheet are controlled by controlling the annealing conditions to improve the moldability (Patent Document 1, Patent Document 2) A method of improving the formability such as fine blanking workability and stretch flangeability by controlling the fraction of pearlite, cementite and ferrite and the grain size of ferrite (Patent Document 3, Patent Document 4, Patent Document 5), and the like are known.

However, the above-mentioned conventional techniques are only for improving the formability of the high carbon annealed steel sheet subjected to cold rolling and annealing, and are not related to the formability in the hot rolled steel sheet state. Further, in the case of the high carbon hot-rolled steel sheet manufactured by the conventional techniques, when the heat treatment for imparting the final high hardness after the machining to the desired part type is performed, the temper embrittlement due to P-grain segregation or cementite coarsening So that desired tensile strength and toughness can not be obtained.

Japanese Laid-Open Patent Application No. 2005-344194 Japanese Patent Application Laid-Open No. 2005-344196 Japanese Patent Laid-Open No. 2001-140037 Japanese Patent Laid-Open No. 2006-063394 Korea Patent Publication No. 2007-0068289

An aspect of the present invention is to provide a high carbon hot-rolled steel sheet excellent in resistance to tempering and a method of manufacturing the same.

Another aspect of the present invention is to provide a high carbon hot-rolled steel sheet excellent in material uniformity and temper embrittlement resistance and a method of manufacturing the same.

According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.2 to 0.6% of C; 0.5% or less of Si (excluding 0%); 0.2 to 1.5% of Mn; (Excluding 0%), Al: not more than 0.05% (excluding 0%), N: not more than 0.01% (excluding 0%), and further additionally selected from the group consisting of Sn, B, Mo, Ni and Cr There is provided a high carbon hot-rolled steel sheet excellent in tempering resistance against tempering which contains at least one component in a total amount of 0.0001 to 0.35% and contains the remainder Fe and other unavoidable impurities and satisfies the following relational expression (1).

[Relation 1]

-3.1 [Si] -10 [P] -50 [N] +172.4 [Sn] +150 [B] +0.4 [Mo] +0.3 [Ni] +0.1 [Cr] +0.9?

(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]

The grain size of P in the high carbon hot-rolled steel sheet is preferably at most 16.5 atomic%.

The high-carbon hot-rolled steel sheet preferably has an area fraction of 90% or more of pearlite and 10% or less of the second phase. The more preferable microstructure is that the pearlite is 95% or more and the second phase is 5% or less.

Preferably, the pearlite phase has an average size of a pearlite colony divided by a tilt angle of 15 degrees or more in an orientation direction of 20 m or less.

The minimum and maximum hardness of the high carbon hot-rolled steel sheet is preferably 50 HV or less. The more preferable hardness deviation is 30 HV or less.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.2 to 0.6% of C, 0.5% or less of Si (excluding 0%), 0.2 to 1.5% of Mn, (Excluding 0%), Al: not more than 0.05% (excluding 0%), N: not more than 0.01% (excluding 0%), and further additionally selected from the group consisting of Sn, B, Mo, Ni and Cr Preparing a slab containing at least one component in a total amount of 0.0001 to 0.35% and containing the balance iron (Fe) and other unavoidable impurities and satisfying the following relational expression (1);

Reheating the slab to 1100 to 1300 占 폚;

Hot-rolling the reheated slab to a hot finish rolling temperature of 850 to 1000 占 폚 to obtain a hot-rolled steel sheet;

Cooling the hot-rolled steel sheet to a cooling end temperature of 500 to 750 ° C at a cooling rate CR satisfying the following relational expression (2); And

There is provided a method of manufacturing a high carbon hot-rolled steel sheet excellent in resistance to embrittlement of the brittle embrittlement, which comprises winding the cooled steel sheet.

[Relation 1]

(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]

[Relation 2]

Cond? CR (占 폚 / sec)? 100 占 폚 / sec

C, Si, Mn, Cr, Al and Mo satisfy the following equations: Cond = 60-56.1 [C] +2.1 [Si] -19.2 [Mn] -8.9 [Cr] +8.0 Represents the content (weight%) of the corresponding element.

According to the present invention, it is possible to provide a high carbon hot-rolled steel sheet excellent in resistance to tempering embrittlement, as well as a high carbon hot-rolled steel sheet excellent in material uniformity and temper embrittlement resistance.

Fig. 1 is a graph showing the values derived from the relational expression (1) representing the hardness deviation and the temper embrittlement resistance of the inventive and comparative examples.
Fig. 2 shows a wavefront photograph after the tensile test of Comparative Example (2) and Inventive Example (1).

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a high carbon hot-rolled steel sheet and a method of manufacturing the same will be described in detail. However, the present invention is not limited to the following embodiments.

Accordingly, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

The present inventors have conducted studies and experiments on a method for securing excellent tempering resistance, preferably excellent moldability, superior material uniformity and resistance to embrittlement in tempering at the same time, and have completed the present invention based on the results .

In the present invention, the grain boundary is strengthened in view of the control of the microstructure in terms of ensuring excellent formability, that is, securing excellent homogeneity of the material, And the toughness of the steel sheet itself is improved.

In the present invention, the components affecting the tempering resistance of a high carbon hot-rolled steel sheet, for example, grain boundary strengthening, grain boundary segregation of P, and toughness of the steel sheet itself are investigated and the interaction between these components is studied and experimented (1), and the components constituting the relational expression (1) must satisfy the condition of the relational expression (1).

In the present invention, as a result of research and experiment on the correlation between the tempering property and the grain boundary segregation amount of P, it has been recognized that controlling the grain segregation amount of P to a predetermined amount or less improves the temper embrittlement resistance, Can be set to a predetermined value or less.

In the present invention, the phases constituting the microstructure and the grain size of the microstructure can be controlled in order to ensure excellent moldability, that is, to ensure excellent homogeneity of the material.

The phase and grain size of the microstructure of the hot-rolled steel sheet of the present invention can be obtained, for example, by controlling the cooling rate up to the coiling temperature after the finish hot rolling in accordance with the relationship (2).

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

The hot-rolled steel sheet according to the present invention has 0.2 to 0.6% of C, 0.5% or less of Si (excluding 0%), 0.2 to 1.5% of Mn, 0.03% or less of P (0% (Excluding 0%), N: 0.01% or less (excluding 0%), the balance iron (Fe) and other unavoidable impurities.

The reasons for limiting the content and the content of the high carbon hot-rolled steel sheet of the present invention will be described below.

Carbon (C): 0.2 to 0.6 wt%

Carbon (C) is the most economical and effective element in ensuring hardenability during heat treatment and hardness after heat treatment.

In order to exhibit such an effect, the carbon (C) is preferably contained in an amount of 0.2 wt% or more, more preferably 0.3 wt% or more, and still more preferably 0.32 wt% or more.

On the other hand, when the content is excessive, there is a problem that the strength is excessively increased, and the moldability is deteriorated. Therefore, the upper limit of the carbon content is preferably 0.6% by weight.

Silicon (Si): 0.5% by weight or less (excluding 0%)

Silicon (Si) is an element that deoxidizes molten steel and has a solid solution strengthening effect .

In order to exhibit such an effect, the silicon (Si) is preferably contained in an amount of 0.01 wt% or more, more preferably 0.1 wt% or more.

On the other hand, if the content is excessive, a red scale is formed on the surface of the steel sheet, which not only deteriorates the surface quality of the steel sheet, but also excessively increases the strength and deteriorates impact toughness in the final product, There is a risk. Therefore, the upper limit of the Si content is preferably limited to 0.5 wt%.

Manganese (Mn): 0.2 to 1.5 wt%

Manganese (Mn) is an element contributing to hardenability after heat treatment by increasing hardenability.

On the other hand, when the content of manganese in the steel is too low, coarse FeS is formed and the impact toughness of the steel may be deteriorated. Therefore, the lower limit of the manganese content is preferably 0.2 wt%, more preferably 0.3 wt%, and still more preferably 0.35 wt%. However, when the content is excessive, the thickness central segregation portion is greatly developed during casting of the steel slab in the casting process, thereby forming retained austenite around the segregation portion, and the formability is deteriorated. Therefore, the upper limit of the content of manganese is preferably 1.5 wt%, more preferably 1.0 wt%, and even more preferably 0.8 wt%.

Phosphorus (P): 0.03% by weight or less (excluding 0%)

Phosphorus (P) is an impurity inevitably contained. It is an element which is a major cause of deteriorating the weldability of steel and segregating in grain boundaries to increase the temper embrittlement. Therefore, it is desirable to control the content as low as possible. Theoretically, it is preferable to limit the content of phosphorus to 0 wt%, but it is inevitably contained inevitably in the manufacturing process. Therefore, the upper limit is preferably limited to 0.03% by weight, more preferably 0.02% by weight.

Sulfur (S): 0.015% by weight or less (excluding 0%)

Sulfur (S) is an impurity inevitably contained in the phosphorus (P), and forms a nonmetallic inclusion by binding with Mn or the like, thereby significantly reducing the toughness of the steel. The theoretical sulfur content is advantageous to be limited to 0 wt%, but it is inevitably contained in the manufacturing process inevitably. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur content is preferably limited to 0.015 wt%.

Aluminum (Al): 0.05 wt% or less (excluding 0%)

Aluminum (Al) is an element added for deoxidation of molten steel. In the present invention, the lower limit of the aluminum content is not particularly limited, but may be preferably 0.005% by weight, and more preferably 0.01% by weight. However, when the content thereof is excessive, not only the effect is saturated but also there is a problem that clogging of the nozzle is caused at the performance. Therefore, the upper limit of the aluminum content is preferably 0.05 wt%, more preferably 0.03 wt%.

Nitrogen (N): 0.01 wt% or less (excluding 0%)

Nitrogen (N) contributes to the hardness of the steel but is difficult to control and segregates in the grain boundary as well as phosphorus, thereby enhancing the embrittlement of the tempering of the steel. In theory, limiting the content of nitrogen to 0% by weight is advantageous to the resistance to temper embrittlement, but it is inevitably contained in the manufacturing process inevitably. Therefore, it is preferable to limit the upper limit to 0.01 wt%, more preferably 0.007 wt%.

In addition to 0.0001-0.35 wt% of at least one element selected from the group consisting of tin (Sn), boron (B), molybdenum (Mo), nickel (Ni) and chromium (Cr) Lt; / RTI >

The content of these components should satisfy the following relationship (1) in order to improve the temper embrittlement resistance.

[Relation 1]

(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]

Tin (Sn) is an element that segregates preferentially to phosphorus (P) at grain boundaries and reduces the segregation position of phosphorus by inhibiting occurrence of temper embrittlement due to segregation by phosphorus, thereby contributing to improvement of the impact resistance of steel.

In order to exhibit such an effect, the content of tin (Sn) is preferably 0.0005 wt% or more, more preferably 0.001 wt% or more. However, when the content is excessive, the toughness deteriorates due to tin segregation at grain boundaries. Therefore, the upper limit of the tin content is preferably 0.002 wt%, more preferably 0.0015 wt%.

Boron (B) is an element that segregates preferentially to phosphorus (P) at grain boundaries and reduces phosphorus segregation, thereby suppressing occurrence of temper embrittlement due to segregation of phosphorus and contributing to improvement of the impact resistance of steel.

In order to exhibit such an effect, the boron (B) is preferably contained in an amount of 0.0005% by weight or more, more preferably 0.0009% by weight or more. However, when the content is excessive, there is a fear that the toughness deteriorates due to the B precipitates precipitated in the grain boundaries. Therefore, the upper limit of the boron content is preferably 0.002 wt%, more preferably 0.0015 wt%.

Molybdenum (Mo) is an intergranular strengthening element. By strengthening the grain boundaries, molybdenum (Mo) plays a role of preventing the occurrence of temper brittleness even if a relatively large amount of P segregates in the grain boundary, thereby contributing to improvement of the brittle fracture resistance of the steel.

In order to exhibit such an effect, the molybdenum (Mo) content is preferably 0.05 wt% or more, more preferably 0.1 wt% or more. However, if the content is excessive, the effect is not only saturated but also there is a fear that the economic efficiency is lowered due to an increase in slab production cost. Accordingly, the upper limit of the molybdenum content is preferably 0.35% by weight, more preferably 0.3% by weight.

Nickel (Ni) is an intergranular strengthening element. By strengthening the grain boundaries, it plays a role to prevent the occurrence of the temper embrittlement even if a relatively large amount of P segregates in the grain boundary, thereby contributing to improvement of the brittle fracture resistance of the steel.

In order to exhibit such an effect, the content of nickel (Ni) is preferably 0.005% by weight or more, more preferably 0.01% by weight or more. However, if the content is excessive, the effect is not only saturated but also there is a fear that the economic efficiency is lowered due to an increase in slab production cost. Therefore, the upper limit of the nickel content is preferably 0.35% by weight, more preferably 0.3% by weight.

Cr (Cr) serves to lower the grain boundary segregation density by increasing the area fraction of the grain boundaries by finely pulverizing the pearlite colony, thereby contributing to improvement of the brittle fracture resistance of the steel.

In order to exhibit such an effect, the chromium (Cr) content is preferably 0.01 wt% or more, more preferably 0.05 wt% or more. However, if the content is excessive, the effect is not only saturated but also there is a fear that the economic efficiency is lowered due to an increase in slab production cost. Therefore, the upper limit of the chromium content is preferably 0.35% by weight, more preferably 0.3% by weight.

On the other hand, when the value of the above-mentioned relational expression (1) is less than 0, the resistance to temper embrittlement is weakened.

The value of the relational expression (1) is preferably 0.2 or less, and more preferably 0.08 to 0.12.

It is preferable to set the grain size of P to 16.5 atomic% or less in order to secure a superior tempering resistance. If the grain size of the P exceeds 16.5 atomic%, there is a possibility that the temper embrittlement occurs. More preferably, the grain size of P is not more than 16.0 atomic%.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

It is preferable that the high carbon hot rolled steel sheet of the present invention satisfies the above-described composition conditions and that its microstructure has a pearlite content of 90% by area or more and a second phase such as pro-eutectoid ferrite, bainite and martensite is 10% By ensuring the same microstructure, a homogeneous material having a hardness deviation of 50 HV or less can be obtained.

It is more preferable that the microstructure has a pearlite of 95% or more by area and more preferably 5% or less of a second phase such as pro-eutectoid ferrite, bainite and martensite. By ensuring the microstructure as described above, Can be obtained.

In order to ensure better material uniformity, the average size of the pearlite colony is preferably set to 20 탆 or less, more preferably 15 탆 or less.

The second phase may include at least one of pro-eutectoid ferrite, bainite and martensite.

Hereinafter, a method for producing a high carbon hot-rolled steel sheet excellent in tempering resistance of the present invention will be described in detail. The following production method shows a preferable example of producing the high carbon hot rolled steel sheet of the present invention, but is not limited thereto.

In order to produce the high carbon hot-rolled steel sheet of the present invention having excellent material uniformity and temper embrittlement resistance as described above, a slab having a composition satisfying the relational expression (1) and the alloy composition range of the present invention is first prepared.

Thereafter, the slab is heated at a temperature of 1100 to 1300 ° C, and the heated slab is hot-rolled at a finishing rolling temperature of 850 to 1000 ° C to obtain a hot-rolled steel sheet. The hot-rolled steel sheet is cooled at a cooling rate ( CR) to a cooling end temperature of 500 to 750 DEG C, and the cooled hot-rolled steel sheet is wound.

Hereinafter, each process (step) will be described in detail.

Slab reheat step

In the present invention, the reheating temperature of the slab is preferably 1100 to 1300 ° C, and more preferably 1120 to 1200 ° C.

If the slab reheating temperature is less than 1100 ° C, there is a fear that the rolling load will increase sharply during the subsequent hot rolling process. In particular, since the alloy component is not uniformly dispersed in the slab, Mn stagnation occurs at the center, The phase fraction of the superficial layer structure is changed, resulting in a material deviation.

On the other hand, when the slab reheating temperature exceeds 1300 ° C, the austenite is partially coarsened through abnormal grain growth, and the final structure may be coarsened or unevenly obtained.

Hot rolling step

Thereafter, the reheated slab is finely rolled to obtain a hot-rolled steel sheet.

At this time, the finishing rolling temperature is preferably 850 to 1000 占 폚, and more preferably 855 to 920 占 폚.

If the finish rolling temperature is less than 850 ° C, there is a possibility that the rolling load will increase significantly. In particular, in the case of the edge portion of the steel sheet with a severe temperature drop, have.

On the other hand, when the finish rolling temperature exceeds 1000 캜, the structure of the steel sheet becomes coarse, the steel becomes fragile, the scale becomes thick, and the surface quality such as high-temperature rolling-ability scale defects may be remarkably deteriorated.

Cooling step

The hot rolled steel sheet thus cooled is cooled.

At this time, the hot-rolled steel sheet is cooled to a cooling end temperature of 500 to 750 ° C at a cooling rate (CR) satisfying the following relational expression (2).

[Relation 2]

Cond? CR (占 폚 / sec)? 100 占 폚 / sec

When the cooling rate is less than Cond, the pearlite structure becomes coarse or the ferrite fraction exceeds 10%, and the hardness deviation becomes larger than 50 HV. On the other hand, when it exceeds 100 ° C / sec, the fraction of bainite or martensite exceeds 10%, and the hardness deviation increases to 50 HV or more, and the plate shape also deteriorates greatly.

The upper limit of the cooling rate is preferably limited to 100 DEG C / sec.

The cooling termination temperature during cooling of the steel sheet is preferably limited to 500 to 750 ° C.

If the cooling termination temperature exceeds 750 캜, the ferrite phase may be formed in an amount of 10% or more in the post-winding holding step even if the production conditions such as the above-mentioned cooling conditions are satisfied. On the other hand, when the temperature at which the cooling is terminated is less than 500 DEG C, most of the microstructure in the steel has bainite or martensite, so that the microstructure to be secured by the present invention can not be secured.

Winding step

The hot rolled steel sheet thus cooled is wound.

The hot-rolled steel sheet produced by the manufacturing method according to the present invention can be used as it is without any additional process. Alternatively, a pickling steel sheet can be produced by further pickling the surface layer scale and raising the steel sheet. And may be used after further annealing and the like.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

The steel slabs satisfying the component systems described in the following Table 1 were heated to the heating temperatures shown in Table 2 below and subjected to hot rolling at a hot finishing rolling temperature (FDT) to obtain hot-rolled steel sheets. Thereafter, the hot-rolled steel sheet was cooled to the coiling temperature (CT) (cooling termination temperature) described in the following Table 2 at the cooling rate shown in Table 2, and then wound.

The pellet fraction (area%), the collar size of the pelletite, the Vickers hardness deviation, the tempering resistance and the grain boundary segregation were measured for the thus prepared steel sheet, and the results are shown in Table 2 below.

In this case, the hardness was measured by Vickers hardness at a load of 500 g, and the hardness difference was defined as the difference between the 95% level and the 5% hardness level when the maximum value was set at 100% and the minimum value was set at 0%.

The tempering resistance was evaluated by taking samples at 90 ^° relative to the rolling direction of the rolled steel sheet, heat-treating at 860 ° C for 50 minutes, oiling at 60 ° C and tempering at 320 ° C for 2 hours to prepare tensile specimens After the tensile test was repeated 10 times, any one of them was evaluated as heat for the case of occurrence of the tempering brittleness .

Grade Nr. C Si Mn Al P S N Relation
(One) Additional ingredient Inventive Steel 1 0.2 0.14 0.7 0.025 0.015 0.005 0.0037 0.63 Sn: 0.002, B: 0.001 Comparative River 1 0.2 0.19 One 0.025 0.018 0.005 0.0045 -0.05 Mo: 0.1 Comparative River 2 0.35 0.2 0.7 0.025 0.016 0.005 0.005 -0.10 Ni: 0.1 Invention river 2 0.35 0.15 One 0.025 0.014 0.005 0.0038 0.41 B: 0.0015, Mo: 0.2 Invention steel 3 0.35 0.1 0.7 0.025 0.01 0.005 0.0043 0.46 Sn: 0.001, Cr: 0.1 Comparative Steel 3 0.45 0.34 One 0.025 0.015 0.005 0.0045 -0.45 Mo: 0.2 Comparative Steel 4 0.45 0.2 0.7 0.025 0.015 0.005 0.0059 -0.11 Ni: 0.2 Inventive Steel 4 0.35 0.19 0.5 0.025 0.018 0.005 0.004 0.05 Sn: 0.0005, Ni: 0.1 Invention steel 5 0.4 0.19 0.4 0.025 0.019 0.005 0.005 0.08 B: 0.001, Mo: 0.15 Invention steel 6 0.45 0.19 0.4 0.025 0.018 0.005 0.005 0.05 Sn: 0.001 Invention steel 7 0.5 0.16 0.4 0.025 0.019 0.005 0.005 0.05 Mo: 0.2, Cr: 0.05 Inventive Steel 8 0.55 0.16 0.7 0.025 0.01 0.005 0.005 0.06 Ni: 0.01, Cr: 0.05 Invention river 9 0.58 0.17 0.4 0.025 0.015 0.005 0.005 0.12 B: 0.001 Invented Steel 10 0.51 0.15 0.5 0.025 0.011 0.003 0.005 0.09 Cr: 0.13 Invention steel 11 0.54 0.14 0.6 0.025 0.012 0.004 0.005 0.11 Cr: 0.13

Example No. 2. Steel grade Heating temperature (℃) FDT
(° C) CT
(° C) Cooling rate (° C / sec) Cond
(° C / sec) Perlite fraction (area%) Colony Size
(탆) Hardness
Deviation Temper embrittlement resistance P grain boundary
Segregation
(atomic%) Comparative Example 1 Inventive Steel 1 1150 870 480 65 36 55 28 89 ○ 5.2 Comparative Example 2 Comparative River 1 1140 860 610 41 27 98 14 22 X 17.0 Comparative Example 3 Comparative River 2 1160 860 610 41 28 95 16 23 X 17.8 Comparative Example 4 Invention river 2 1050 860 630 38 16 84 21 56 ○ 9.0 Comparative Example 5 Invention steel 3 1180 830 610 36 26 78 23 65 ○ 8.1 Comparative Example 6 Comparative Steel 3 1150 860 560 50 11 99 14 11 X 23.8 Comparative Example 7 Comparative Steel 4 1130 870 580 48 22 98 14 13 X 17.8 Inventory 1 Inventive Steel 4 1150 870 620 41 31 97 15 15 ○ 15.2 Inventory 2 Invention steel 5 1140 860 580 46 26 98 14 16 ○ 14.6 Inventory 3 Invention steel 6 1170 870 550 53 28 90 18 32 ○ 15.1 Honorable 4 Invention steel 7 1160 860 560 50 19 99 14 9 ○ 15.2 Inventory 5 Inventive Steel 8 1150 860 580 46 16 97 15 18 ○ 15.0 Inventory 6 Invention river 9 1150 890 610 46 20 99 14 10 ○ 13.9 Honorable 7 Invented Steel 10 1150 860 570 48 21 97 15 17 ○ 14.5 Honors 8 Invention steel 11 1160 880 600 46 18 98 14 15 ○ 14.2

As shown in Table 2, in Comparative Example 1, the coiling temperature (CT) was out of the range of the present invention, the pearlite fraction was 55%, and the hardness deviation was 89 HV. In Comparative Examples 2, 7 did not satisfy the relational expression (1), and the grain boundary segregation amount exceeded 16.5 atomic%.

In Comparative Example 4, the slab reheating temperature is out of the range of the present invention, and the hardness variation is 56 HV due to the microstructure unevenness due to the central Mn segregation zone.

In Comparative Example 5, it is found that the FDT is out of the range of the present invention, the pearlite fraction is 78%, and the hardness deviation is 65HV.

On the other hand, all of Examples 1 to 8 in accordance with the present invention satisfy the criteria of the resistance to temper embrittlement, and the hardness deviation is 50HV or less, confirming that the material uniformity is excellent.

FIG. 1 is a graph showing the hardness deviations of Comparative Examples and Inventive Examples and the values derived from the relational expression (1). The portions indicated by the square dots are comparative examples, and the portions indicated by the circular dots are examples.

2 shows a wavefront photograph after the tensile test of the comparative example (2) and the inventive example (1), FIG. 2 (a) shows the comparative example (2), and FIG. 2 (b) 1).

In the case of Comparative Example 2 in which the brittleness of the tempering occurred, as shown in Fig. 2 (a), in the case of the inventive example 1 in which the brittle wavefront ratio is 100% As can be seen from b), it can be seen that the ductile wavefront ratio is remarkably high.

While the illustrative embodiments of the invention have been described above, various modifications and alternative embodiments may be made by those skilled in the art. Such variations and other embodiments will be considered and included in the appended claims, all without departing from the true spirit and scope of the invention.

Claims

(Excluding 0%), Mn: 0.2 to 1.5%, P: not more than 0.03% (excluding 0%), S: not more than 0.015% (excluding 0%), , Al: not more than 0.05% (excluding 0%), N: not more than 0.01% (excluding 0%) and additionally contains at least one component selected from the group consisting of Sn, B, Mo, , 0.0001 to 0.35% in terms of Fe and other inevitable impurities, and satisfies the following relational expression (1), and the microstructure has an area fraction of 90% or more of pearlite and 10% or less of the second phase And the second phase is one or two of bainite and martensite.
[Relation 1]
-3.1 [Si] -10 [P] -50 [N] +172.4 [Sn] +150 [B] +0.4 [Mo] +0.3 [Ni] +0.1 [Cr] +0.9?
(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]

The high carbon hot-rolled steel sheet according to claim 1, wherein the value of the relational expression (1) is 0.08 to 0.12.

The high carbon hot-rolled steel sheet according to claim 1, wherein the grain segregation amount of P is 16.5 atomic% or less.

delete

The high carbon hot-rolled steel sheet according to claim 1, wherein the microstructure of the high carbon hot-rolled steel sheet has an area fraction of 95% or more of pearlite and 5% or less of the second phase.

delete

The high carbon hot-rolled steel sheet according to claim 1 or 5, wherein the pearlite phase has an average size of pearlite colony of 20 mu m or less.

The high carbon hot-rolled steel sheet according to claim 1, wherein the high carbon hot-rolled steel sheet has a minimum and maximum hardness deviation of 50 HV or less and excellent tempering resistance.

The high carbon hot-rolled steel sheet according to claim 5, wherein the high carbon hot-rolled steel sheet has a minimum and maximum hardness deviation of 30 HV or less and excellent resistance to embrittlement in tempering.

(Excluding 0%), Mn: 0.2 to 1.5%, P: not more than 0.03% (excluding 0%), S: not more than 0.015% (excluding 0%), , Al: not more than 0.05% (excluding 0%), N: not more than 0.01% (excluding 0%) and additionally contains at least one component selected from the group consisting of Sn, B, Mo, Of 0.0001 to 0.35%, and the balance Fe and other unavoidable impurities, and satisfying the following relational expression (1): " (1) "
Reheating the slab to 1100 to 1300 占 폚;
Hot-rolling the reheated slab to a hot finish rolling temperature of 850 to 1000 占 폚 to obtain a hot-rolled steel sheet;
Cooling the hot-rolled steel sheet to a cooling end temperature of 500 to 750 ° C at a cooling rate CR satisfying the following relational expression (2); And
Wherein the microstructure comprises at least 90% of pearlite and not more than 10% of the second phase, and the second phase comprises one or two of bainite and martensite, A method for manufacturing a high carbon hot - rolled steel sheet excellent in resistance to brittleness in tempering to manufacture hot - rolled steel sheets.
[Relation 1]
-3.1 [Si] -10 [P] -50 [N] +172.4 [Sn] +150 [B] +0.4 [Mo] +0.3 [Ni] +0.1 [Cr] +0.9?
(Wherein, [Si], [P], [N], [Sn], [B], [Mo], [Ni] and [Cr]
[Relation 2]
Cond? CR (占 폚 / sec)? 100 占 폚 / sec
C, Si, Mn, Cr, Al and Mo satisfy the following equations: Cond = 60-56.1 [C] +2.1 [Si] -19.2 [Mn] -8.9 [Cr] +8.0 Represents the content (weight%) of the corresponding element.

The method of manufacturing a high-carbon hot-rolled steel sheet according to claim 10, further comprising a step of pickling the hot-rolled steel sheet and pickling the hot-rolled steel sheet.