KR20220089552A - Steel for tool and manufacturing method for the same - Google Patents

Abstract

According to one aspect of the present invention, it is possible to provide a steel material suitable for a tool and a method for manufacturing the same because the heat treatment property of the spheroidizing annealing is improved while having high hardness characteristics.

Description

Steel for tool and manufacturing method thereof {Steel for tool and manufacturing method for the same}

The present invention relates to a steel material for a tool and a method for manufacturing the same, and more particularly, to a steel material for a tool having improved heat treatment properties and a method for manufacturing the same.

In general, among the physical properties of steel, hardness and workability are widely known as incompatible properties. This is because an increase in the strength of the steel causes an increase in hardness, whereas when the strength of the steel increases, the workability of the steel deteriorates.

In the case of tool steel used for the manufacture of tool parts, excellent workability is required when producing the part shape, whereas the parts after final machining require high hardness in order to secure wear resistance and impact resistance characteristics. In particular, in the case of tool steel used for manufacturing tool parts, steel containing a relatively large amount of carbon (C) is mainly used to secure hardness and strength above a certain level, so it is easy to secure a desired level of workability has not been done.

In the case of steel for tools, a method of securing the hardness by introducing a martensitic structure into the steel through quenching after securing the workability of the steel through spheroidizing annealing is generally used. Spheroidizing annealing is a heat treatment in which plate-shaped cementite in lamellar pearlite is heated at a high temperature to make it spherical, and it takes a long time to secure a desired level of workability. Industrially, a method of maintaining a temperature below A1 for a long time is mainly used, but heat treatment at a high temperature for a long time inevitably entails a decrease in economic efficiency and productivity.

Patent Document 1 proposes a method of accelerating the spheroidization of cementite in a steel sheet having a lamellar pearlite structure through cold rolling without annealing, but the steel sheet of Patent Document 1 has a carbon (C) content of 0.6% by weight or less. Therefore, it is not possible to provide hardness suitable as a steel material for tools. Patent Document 2 proposes a method of performing a secondary annealing heat treatment at a temperature of about 650° C. after performing a primary annealing heat treatment at a temperature directly above A1 in order to control the spheroidized carbide structure, but such a heating condition is a typical heating furnace There are aspects that are difficult to implement in

Therefore, there is a need for research and development of a steel material having a hardness suitable for a tool and having improved heat treatment properties of spheroidizing annealing.

Japanese Laid-Open Patent Publication No. 2005-133199 A (published on May 26, 2005) Japanese Patent Application Laid-Open No. 2006-257449 A (published on September 28, 2006)

According to one aspect of the present invention, a steel material suitable for tools and a method for manufacturing the same can be provided by improving the heat treatment properties of the spheroidizing annealing while securing high hardness characteristics including 0.8% by weight or more of carbon (C).

The subject of the present invention is not limited to the above. A person of ordinary skill in the art will have no difficulty in understanding the further problems of the present invention from the overall content of the present specification.

Steel material for tools according to an aspect of the present invention, by weight, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr) : 0.1~0.3%, phosphorus (P): 0.03% or less, sulfur (S): 0.005% or less, contains the remaining iron (Fe) and unavoidable impurities, contains pearlite as a matrix structure, in the center of the thickness, {100 The average pole density of the }<011> to {223}<110> crystal orientation groups may be 1.8 or more, and the {332}<113> crystal orientation may have a pole density of 2.0 or more. Here, the thickness center means a region within the range of 3/8t to 5/8t with respect to the thickness (t, mm) of the steel material when the cross-section of the steel material is observed.

Steel material for tools according to an aspect of the present invention, by weight, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr) : 0.1~0.3%, phosphorus (P): 0.03% or less, sulfur (S): 0.005% or less, contains the remaining iron (Fe) and unavoidable impurities, contains pearlite as a matrix structure, and a pearlite block in the longitudinal section The average long/short axis ratio of (block) may be 1.41:1 or more.

The method for manufacturing a steel material for a tool according to an aspect of the present invention, by weight, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1 to 0.3%, phosphorus (P): 0.03% or less, sulfur (S): 0.005% or less, reheating the slab containing the remaining iron (Fe) and unavoidable impurities in a temperature range of 1000 to 1300 ℃ step; hot rolling the reheated slab in a temperature range of 850 to 1150 °C; and cold-rolling the hot-rolled steel at a reduction ratio of 30-50% without annealing.

The means for solving the above problems do not enumerate all the features of the present invention, and various features of the present invention and its advantages and effects will be understood in more detail with reference to the specific embodiments below.

According to one aspect of the present invention, it is possible to provide a steel material suitable for a tool and a method for manufacturing the same because the heat treatment property of the spheroidizing annealing is improved while having high hardness characteristics.

The effect of the present invention is not limited to the above, and it can be interpreted as including technical effects that those skilled in the art can infer from the matters described below.

1 is a photograph of a cross-section of a non-annealed cold-rolled specimen 1 observed with a scanning electron microscope.
2 is a photograph of a cross-section of Specimen 1 after spheroidizing heat treatment observed with a scanning electron microscope.

The present invention relates to a steel material for a tool and a method for manufacturing the same, and preferred embodiments of the present invention will be described below. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The present embodiments are provided in order to further detailed the present invention to those of ordinary skill in the art to which the present invention pertains.

Hereinafter, a steel material for a tool according to an aspect of the present invention will be described in more detail.

The steel material for tools of the present invention is, by weight, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1 to 0.3 %, phosphorus (P): 0.03% or less, sulfur (S): 0.005% or less, the remaining iron (Fe) and unavoidable impurities, and pearlite as a matrix, in the center of the thickness, {100}<011> to {223}<110> crystal orientation groups may have an average pole density of 1.8 or more, and {332}<113> crystal orientations may have a pole density of 2.5 or more.

Here, the thickness center means a region within the range of 3/8t to 5/8t with respect to the thickness (t, mm) of the steel material when the cross-section of the steel material is observed.

Hereinafter, the alloy composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated, % described in relation to the alloy composition means % by weight.

Carbon (C): 0.8~1.0%

Carbon (C) is a representative hardenability improving element, and in the present invention, it is an element essential to secure hardness after quenching. Therefore, the present invention may contain 0.8% or more of carbon (C) for this effect. A preferred carbon (C) content may be greater than 0.8%, and a more preferred carbon (C) content may be 0.82% or higher. On the other hand, if the carbon (C) content in the steel exceeds a certain range, the cementite fraction in the steel is too high to promote brittle fracture, so the present invention limits the upper limit of the carbon (C) content to 1.0%. can A preferred carbon (C) content may be less than 1.0%, and a more preferred carbon (C) content may be 0.98% or less.

Silicon (Si): 0.1~0.3%

Since silicon (Si) is a component contributing to the improvement of the strength of steel, the present invention may include 0.1% or more of silicon (Si) to achieve such an effect. A preferable lower limit of the silicon (Si) content may be 0.12%, and a more preferable lower limit of the silicon (Si) content may be 0.15%. However, when the silicon (Si) content in the steel exceeds a certain range, not only the cold rolling is inferior, but also the possibility of decarburization during heat treatment increases, and since it may cause an increase in scale defects on the surface of the steel, the present invention provides silicon ( The upper limit of the Si) content may be limited to 0.3%. A preferable upper limit of the silicon (Si) content may be 0.28%, and a more preferable upper limit of the silicon (Si) content may be 0.25%.

Manganese (Mn): 0.3-0.5%

Manganese (Mn) is not only an element contributing to the improvement of hardenability, but also an element that effectively contributes to the improvement of the strength of the material by solid solution strengthening. In addition, since manganese (Mn) is combined with sulfur (S) in steel to precipitate as MnS, it is possible to effectively prevent red heat embrittlement caused by sulfur (S). The present invention may contain 0.3% or more of manganese (Mn) to achieve such an effect. A preferred lower limit of the manganese (Mn) content may be 0.32%, and a more preferred lower limit of the manganese (Mn) content may be 0.35%. However, when the manganese (Mn) content in the steel exceeds a certain range, not only the cold rolling property is inferior, but also the decrease in workability due to central segregation may be a problem, so the present invention sets the upper limit of the manganese (Mn) content It can be limited to 0.5%. The upper limit of the preferable manganese (Mn) content may be 0.48%, and the upper limit of the more preferable manganese (Mn) content may be 0.45%.

Chromium (Cr): 0.1~0.3%

Chromium (Cr) is an element that effectively contributes to improvement of hardenability, like manganese (Mn). Therefore, the present invention may contain 0.1% or more of chromium (Cr) for this effect. A preferable lower limit of the chromium (Cr) content may be 0.13%, and a more preferable lower limit of the chromium (Cr) content may be 0.16%. However, if the chromium (Cr) content in the steel exceeds a certain range, not only the cold rolling ductility may decrease, but also the decomposition of cementite by heat treatment is delayed, so that the spheroidization of the carbide is not completed even by spheroidizing annealing. Possibility exists. Accordingly, the present invention may limit the upper limit of the chromium (Cr) content to 0.3%. A preferable upper limit of the chromium (Cr) content may be 0.28%, and a more preferable upper limit of the chromium (Cr) content may be 0.25%.

Phosphorus (P): 0.03% or less (including 0%)

Phosphorus (P) in steel is a typical impurity element, but it is also the most advantageous element for securing strength without significantly impairing formability. However, when phosphorus (P) is added excessively, the possibility of brittle fracture increases, which may cause plate breakage of the slab during hot rolling, as well as greatly deteriorate the surface properties of the plated steel sheet. Therefore, the present invention may limit the upper limit of the phosphorus (P) content to 0.03%.

Sulfur (S): 0.005% or less (including 0%)

Sulfur (S) is an impurity element that is unavoidably introduced into steel, and it is desirable to manage its content as low as possible. In particular, since sulfur (S) in steel may cause red hot brittleness, the present invention may limit the upper limit of the sulfur (S) content to 0.005%.

The steel material for tools of the present invention may include the remaining Fe and other unavoidable impurities in addition to the above-described components. However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, it cannot be entirely excluded. Since these impurities are known to those of ordinary skill in the art, all contents thereof are not specifically mentioned in the present specification. In addition, additional addition of effective ingredients other than the above-mentioned ingredients is not entirely excluded.

The steel material for a tool according to an aspect of the present invention may have a microstructure including a pearlite matrix and other residual structures. Pearlite is an essential structure for securing the desired physical properties of the present invention, and the preferred fraction of pearlite may be 90% by area or more. Other residual structures may include low-temperature structures such as proeutectoid ferrite and bainite and martensite. When proeutectoid ferrite is excessive, not only hardness is lowered, but also workability may be deteriorated by promoting grain boundary fracture, so the fraction of proeutectoid ferrite may be limited to 10 area% or less (including 0%). Since hard bainite and martensite are not preferable in terms of workability, the fraction of hard structures such as bainite and martensite may be limited to less than 3 area% (including 0%).

In the steel material for tools according to an aspect of the present invention, the average value of the pole density of the {100}<011> to {223} <110> crystal orientation groups measured at the center of the thickness of the steel is 1.8 or more, and it is measured at the center of the thickness of the steel. {332}<113> The pole density of the crystal orientation may be 2.5 or more. Preferably, the pole density average value of the {100}<011> to {223}<110> crystal orientation groups measured at the center of the thickness of the steel may be 1.9 or more, and the {332}<113> crystals measured at the center of the thickness of the steel. The pole density of the orientation may be 2.7 or more. Here, the average values of the pole densities of the {100}<011> to {223}<110> crystal orientation groups are {100}<011>, {116}<110>, {114}<110>, {113}<110>, {112}<110>, {335}<110>, and {223}<110> mean the pole density average value of the crystal orientation, and the thickness center of the steel material is 3/8t to 5/ with respect to the steel material thickness (t, mm) It means an area within the range of 8t. Each crystal orientation pole density can be measured using a backscattered electron diffraction pattern (EBSD) of a scanning electron microscope, and a person skilled in the art can determine the present invention without difficulty without adding special technical means. The azimuth pole density can be measured.

As will be described later, the plate-shaped lamellar pearlite structure is deformed by cold rolling without annealing, and the growth of a specific crystal orientation can be controlled according to the non-annealing reduction method. In the steel material for tools according to an aspect of the present invention, the pole density average value of the {100}<011> to {223}<110> crystal orientation groups of the thickness center of the steel material is controlled to be 1.8 or more, and measured at the thickness center of the steel material. {332}<113> The pole density of the crystal orientation can be controlled to be 2.5 or more. If the average value of the pole density of the crystal orientation group does not satisfy the above conditions, it is insufficient to promote the spheroidization rate of cementite, so that the spheroidization of the carbide is not completed under the targeted spheroidization annealing conditions, and the desired workability can be secured. there will be no

On the other hand, the average long-short axis ratio of the pearlite block in the longitudinal section of the steel is also a factor affecting the spheroidization rate of cementite. Since the longitudinal elongation of pearlite occurs by non-annealing cold rolling, the average long-short axis ratio of the pearlite block in the longitudinal section of the steel is also a factor controlled by non-annealing cold rolling. In the steel for tools according to an aspect of the present invention, the average long-short axis ratio of the pearlite block observed in the longitudinal section of the steel can be controlled to 1.41:1 or more in order to promote a sufficient rate of spheroidization of cementite. . More preferably, the average long-short axis ratio of the pearlite block may be 1.43:1 or more.

The steel material for a tool according to an aspect of the present invention may have a surface hardness of HRB 104 to HRB 115. A more preferable surface hardness may be HRB 108 or more or HRB 112 or less.

The spheroidization speed of the steel material for tools according to an aspect of the present invention is accelerated, so that spheroidization of carbides can be effectively completed even when the spheroidization annealing is performed in a temperature range of 650 to 700°C. A preferred spheroidizing annealing time may be 10 hours to 30 hours. Here, the spheroidization completion condition of the carbide means that the number of spherical carbides having a long/short axis ratio of 1.2 or less of the carbide is 90% or more of the total number of carbides, and more preferably 95% or more. If the spheroidization ratio is less than 90%, the workability may be significantly reduced by the needle-shaped carbide that has not been spheroidized. When the spheroidization annealing temperature is less than 650° C., it is not easy to spheroidize the carbide due to the low temperature, and it may take an excessively long time for the spheroidization of the carbide. On the other hand, when the spheroidizing annealing temperature exceeds 700 ℃, the size of the carbide becomes coarse and cracks easily occur at the interphase boundary, so that the workability may be poor.

Hereinafter, a method for manufacturing a steel material for a tool according to an aspect of the present invention will be described in more detail.

The method of manufacturing a steel material for a tool according to an aspect of the present invention, by weight, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1~0.3%, phosphorus (P): 0.03% or less, sulfur (S): 0.005% or less, reheating the slab containing the remaining iron (Fe) and unavoidable impurities and then hot rolling to provide hot-rolled steel sheet to do; and mechanically segmenting pearlite cementite included in the hot-rolled steel sheet by cold-rolling the hot-rolled steel sheet without annealing at a reduction ratio of 30-50%.

Slab reheating and hot rolling

After preparing a slab having a predetermined alloy composition content, reheating of the slab may be performed. Since the slab alloy composition of the present invention corresponds to the alloy composition of the above-described steel, the description of the slab alloy composition of the present invention is replaced with a description of the alloy composition of the above-described steel. In addition, the slab reheating temperature of the present invention may be applied to the conditions applied to normal slab reheating, as a non-limiting example, the slab reheating temperature of the present invention may be in the range of 1000 to 1300 ℃.

It is possible to provide hot-rolled steel by performing hot rolling in a temperature range of 850 to 1150° C. for the reheated slab. When the hot rolling temperature is excessively high, there is a problem that the desired physical properties cannot be secured due to the coarsening of the microstructure, so the present invention can limit the upper limit of the hot rolling temperature range to 1150°C. On the other hand, when the hot rolling temperature is less than a certain level, excessive rolling load may be a problem, so the present invention may limit the lower limit of the hot rolling temperature to 850 °C.

Hot-rolled steel can be wound in the temperature range of 600 ~ 650 ℃. When the coiling temperature is excessively high, not only the thickness of the cementite in the pearlite structure becomes thick, but also shape defects may occur due to the phase transformation after winding, the present invention can limit the upper limit of the coiling temperature to 650 °C. On the other hand, when the coiling temperature is less than a certain level, since the strength is too high and there is concern about plate breakage in the process after winding, the present invention may limit the lower limit of the coiling temperature to 600°C. In addition, in order to prevent the occurrence of plate breakage due to material deviation in the carbide segmentation step to be described later, the temperature deviation in the longitudinal direction of the hot-rolled coil may be controlled to 20° C. or less.

Annealed cold rolling

After uncoiling the wound steel, the pickling process can be selectively applied according to the surface quality of the uncoiled steel, and then the carbide (plate-like cementite) can be mechanically segmented by applying a mechanical external force to the steel. . The method of applying a mechanical external force to the steel material may be any method as long as it is a method capable of segmenting plate-shaped cementite, but preferably cold rolling may be applied. In the present invention, cold rolling for mechanical segmentation of carbides is referred to as non-annealing cold rolling in order to distinguish it from conventional cold rolling for manufacturing a cold rolled steel sheet. During cold rolling without annealing, it is possible to limit the cold rolling reduction in the range of 30 to 50% in terms of effective elongation of cementite and effective elongation of pearlite.

In the case of the present invention, since the plate-shaped cementite is segmented by applying a mechanical external force to the hot-rolled steel, it is possible to effectively improve the spheroidizing efficiency in the spheroidizing annealing performed later. That is, in the present invention, since the spheroidizing annealing is initiated in a state in which a large amount of finely segmented carbide is distributed, the carbide can be effectively spheroidized within a relatively short time.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the examples described below are for illustrative purposes only and not for limiting the scope of the present invention.

(Example)

After preparing a slab having the alloy composition of Table 1, it was heated in a temperature range of 1200 ° C., hot-rolled in a temperature range of 950 ° C., and finished hot rolling at 850 ° C. or higher to prepare each hot-rolled steel sheet.

steel grade Chemical composition (wt%) hot-rolled thickness
(mm) C Si Mn Cr P S Invention lecture 1 0.84 0.23 0.37 0.22 0.0126 0.0023 2.0 Invention lecture 2 0.96 0.23 0.39 0.21 0.0118 0.0020 1.9 Comparative lecture 1 0.60 0.21 0.37 0.21 0.0129 0.0022 1.9 Comparative lecture 2 1.17 0.17 0.36 0.19 0.0121 0.0022 2.0

Thereafter, the final specimen was prepared by performing cold rolling without annealing under the conditions of Table 2, and the rolling properties during cold rolling without annealing were evaluated according to the following criteria and described together in Table 2. The polar density of the crystal azimuth group in the thickness center (3/8t to 5/8t region) of each non-annealed cold-rolled specimen was measured using a scanning electron microscope, and the values are also described in Table 2. In Table 2, pole density 1 means the average pole density of the {100}<011> to {223}<110> crystal orientation groups, and pole density 2 means the pole density of the {332}<113> crystal orientations. In addition, the pearlite block was observed in the longitudinal section of each specimen using a scanning electron microscope, and the average long-short axis ratio of the pearlite block calculated through this was also described in Table 2. In addition, the surface hardness of each specimen was measured according to ISO6508, and the Rockwell hardness (HRB) measured using this was also described in Table 2.

<Rollability evaluation method>

OK: When there is no plate breakage or cracks in the edge part during cold rolling, or cracks in the edge part occur, but rolling is possible to the final target thickness within the edge crack length having a size of less than 10 mm

NG: When plate breakage or cracks in the edge part occur during cold rolling, and edge cracks of 10 mm or more occur, or 5 or more edge cracks of less than 10 mm occur

Psalter
No. steel grade cold rolled extremely dense perlite
block
short/long ratio surface hardness
(HRB) final thickness
(mm) cold
reduction rate
(%) rollability ultra-dense 1 extreme density 2 One Invention lecture 1 1.3 35 OK 2.0 2.7 1.45 108 2 Invention lecture 1 1.0 50 OK 2.0 2.8 1.68 112 3 Invention lecture 2 1.3 32 OK 1.9 3.0 1.43 110 4 Invention lecture 2 1.0 47 OK 2.1 2.9 1.56 115 5 Invention lecture 1 1.6 20 OK 1.4 1.8 1.32 103 6 Invention lecture 1 0.8 60 NG - - - - 7 Invention lecture 2 1.6 16 OK 1.3 1.7 1.29 105 8 Invention lecture 2 0.8 58 NG - - - - 9 Comparative lecture 1 1.3 32 OK 1.7 2.6 1.39 102 10 Comparative lecture 2 1.3 35 NG - - - -

Spheroidizing annealing was performed under the conditions of Table 3 for each specimen. At this time, the spheroidization annealing time was commonly applied to 15 hours. After completion of the spheroidization annealing, carbides were observed in the cross section of each specimen using a scanning electron microscope, and the spheroidization rate was determined using the number ratio of carbides having a long/short axis ratio of 1.2 or less to the total number of carbides. Vickers hardness was measured by pressing the surface of the specimen with a load of 1 kg and a holding time of 10 seconds for the specimen after spheroidization annealing, and the values are described together in Table 3.

In addition, after the blanking test for each specimen, the height of the bur on the punching surface is measured through a stereoscopic optical microscope, and the specimen of thickness t is rotated at 90 degrees in the vertical direction of the rolling direction using a jig having a radius of curvature R. After bending, the occurrence of cracks on the surface was judged, and the minimum radius of curvature at which cracks did not occur was measured to evaluate bending at 90 degrees, and the values are also listed in Table 3.

In addition, quenching was performed after heating to the quenching temperature of Table 3 for each specimen, and the surface hardness of each specimen was measured according to the C-scale evaluation method of the Rockwell hardness test of ISO6508 and described together in Table 3.

Psalter
No. linen
No. spheroidization annealing machinability quenching Annealing
temperature
(℃) conception
harmony
(%) carbide
size
(μm) surface
Hardness
(HV) friend
Height
(um) 90 degrees
bending
(R/t) quenching
temperature
(℃) surface
Hardness
(HRC) One One 650 96 0.52 252 12 0 812 57.0 2-1 2 660 100 0.58 243 14 0 809 57.1 2-2 2 690 100 0.71 232 12 0 817 56.5 3 3 650 95 0.58 262 8 0 811 59.1 4-1 4 660 99 0.62 250 8 0 807 59.6 4-2 4 690 99 0.68 236 15 0 806 59.4 5 5 660 87 0.53 263 12 3.8 814 55.3 7 7 660 85 0.47 275 8 2.5 808 58.4 9 9 660 98 0.74 198 21 0.8 807 52.6

As shown in Tables 1 to 3, the specimens satisfying the alloy composition and process conditions of the present invention have excellent hardness properties and workability at the same time, whereas the specimens that do not satisfy any one of the alloy composition or process conditions of the present invention are It can be seen that both excellent hardness properties and workability are not compatible at the same time.

Although the present invention has been described in detail through examples above, other types of embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (8)

By weight%, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1 to 0.3%, phosphorus (P): 0.03 % or less, sulfur (S): 0.005% or less, including the remaining iron (Fe) and unavoidable impurities,
Perlite is included as a matrix,
In the central thickness, the average value of the pole density of the {100}<011> to {223}<110> crystal orientation groups is 1.8 or more, and the {332}<113> pole density of the crystal orientation is 2.5 or more, a tool steel.
Here, the thickness center means a region within the range of 3/8t to 5/8t with respect to the thickness (t, mm) of the steel material when the cross-section of the steel material is observed.
By weight%, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1 to 0.3%, phosphorus (P): 0.03 % or less, sulfur (S): 0.005% or less, including the remaining iron (Fe) and unavoidable impurities,
Perlite is included as a matrix,
Steel for tools, wherein the average long-short axis ratio of the pearlite block in the longitudinal section is 1.41:1 or more.
3. The method of claim 1 or 2,
The fraction of the pearlite is 90 area% or more, steel for tools.
4. The method of claim 3,
The steel is 10 area% or less (including 0%) of proeutectoid ferrite as other structures and further comprising a hard structure of less than 3 area% (including 0%), steel for tools.
3. The method of claim 1 or 2,
When the spheroidizing annealing of the steel for 10 to 30 hours in a temperature range of 650 to 700 ℃, the spheroidizing annealing rate of the steel is 90% or more, steel for tools.
3. The method of claim 1 or 2,
The surface hardness of the steel is 104 HRB or more, steel for tools.
By weight%, carbon (C): 0.8 to 1.0%, silicon (Si): 0.1 to 0.3%, manganese (Mn): 0.3 to 0.5%, chromium (Cr): 0.1 to 0.3%, phosphorus (P): 0.03 % or less, sulfur (S): 0.005% or less, reheating the slab containing the remaining iron (Fe) and unavoidable impurities in a temperature range of 1000 to 1300 ℃;
hot rolling the reheated slab in a temperature range of 850 to 1150 °C; and
A method of manufacturing steel for tools, comprising the step of cold-rolling the hot-rolled steel at a reduction ratio of 30-50% without annealing.
8. The method of claim 7,
After the hot rolling, the method of manufacturing a steel for a tool further comprising the step of winding the hot rolled steel in a temperature range of 600 ~ 650 ℃.

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