KR20190043790A - Medium carbon free cutting steel having excellent hot workability and method for manufacturing the same - Google Patents

Abstract

The present invention provides a medium carbon free-cutting steel having excellent hot rolling performance and a manufacturing method for the same. According to a desirable aspect of the present invention, the medium carbon free-cutting steel includes: 0.40-0.50 wt% of C; 0.3 wt% or less (except for 0 wt%) of Si; 1.0-1.5 wt% of Mn; 0.015 wt% or less (except for 0 wt%) of P; 0.008 wt% or less (except for 0 wt%) of S; 0.005-0.015 wt% of B; 0.010-0.020 wt% of N; 0.05 wt% or less (except for 0 wt%) of Al; and residues composed of Fe and inevitable impurities. A weight ratio of N/B is 1.3-2.8, and an area ratio of MnS on a cross-section in a rolling direction of a wire rod is less than 0.1%. A number of inclusions with the diameter of 5μm or less is 100 or greater in an area per 1 mm^2. An average aspect ratio of BN is equal to or less than 2.0.

Description

TECHNICAL FIELD The present invention relates to a medium carbon free cutting steel having excellent hot rolling property and a method of manufacturing the same.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free cutting steel used as a material for a hydraulic part of an automobile, a fastening part of an electric appliance, a shaft of an office automation machine, a general cutting part, To an excellent medium carbon free cutting steel and a manufacturing method thereof.

Generally, free cutting steels are widely used as materials for hydraulic parts of automobiles, fastening parts for home appliances, shafts for office automation equipment, and general cutting parts, and they are increasingly used and demanded There is a trend.

Free cutting steels with good machinability, dimensional accuracy and similar strengths to carbon-carbon steels in common use are also widely used for mechanical construction.

In order to produce free cutting steel with excellent cutting performance, a small amount of lead (Pb) or the like as a low melting point element can be added or the MnS inclusions can be crystallized to improve the tool life and chip segmentability of the free cutting steel and improve the surface quality and dimensional accuracy of the product. In recent years, however, as environment regulations have been strengthened, the use of lead, which is a harmful element to the human body, has been gradually reduced. In the production of free-cutting steel, instead of Pb, relatively eco- friendly bismuth (Bi) or tin Is proposed.

However, in general, the low melting point elements added for improving the cutting performance can lower the hot rolling property of the free cutting steel. In addition, even in the case of the sulfur free cutting steel in which a large amount of sulfur (S) is added to induce the formation of MnS, a large amount of MnS stretched in the hot rolling direction is formed in a large amount to cause anisotropy in mechanical properties, . In order to compensate for this, the ends of the billets before the rolling of the wire are finely cut, such as the tip of the pencil, to reduce the productivity.

In order to solve this problem, graphite free cutting steels and the like have been studied. However, there is still a problem of productivity and cost due to the long heat treatment time required for graphitizing the initial pearlite structure.

Japanese Laid-Open Patent Publication No. 2011-052299

A preferred aspect of the present invention is to provide a medium carbon free cutting steel excellent in hot rolling property and cutting property.

Another aspect of the present invention is to provide a method for producing heavy carbon free cutting steel excellent in hot rolling property and cutting property.

In another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.40 to 0.50% of C, 0.3% or less of Si (excluding 0%), 1.0 to 1.5% of Mn, 0.015% S: 0.008% or less (excluding 0%), B: 0.005 to 0.015%, N: 0.010 to 0.020%, Al: 0.05% or less (excluding 0%), remaining Fe and other unavoidable impurities, B weight ratio of the two is 1.3 to 2.8, less than 0.1% area fraction of the MnS in the rolling direction cross-section of the wire, fine BN inclusions having a diameter of 5μm or less and 1mm ² per unit area more than 100 and an average aspect ratio (aspect ratio) of the BN Of not more than 2.0, which is excellent in hot-rolling property.

The fine BN inclusions having a diameter of 5 탆 or less may be, for example, 100 to 200 per 1 mm ² area.

In another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.40 to 0.50% of C, 0.3% or less of Si (excluding 0%), 1.0 to 1.5% of Mn, 0.015% S: 0.008% or less (excluding 0%), B: 0.005 to 0.015%, N: 0.010 to 0.020%, Al: 0.05% or less (excluding 0%), remaining Fe and other unavoidable impurities, A continuous casting step of casting molten steel having a weight ratio of B to 1.3 to 2.8 into blooms;

Rolling the bloom to obtain billets; And

And a wire rod rolling step of heating the billet in a heating furnace and rolling the wire rod into a wire rod. The present invention also provides a method for manufacturing a medium carbon free cutting steel excellent in hot rolling property.

In the continuous casting step, the molten steel may be continuously cast by simultaneously driving a mold electromagnetic stirrer (EMS) and a light-weight reduction device.

During the rolling of the billet, the bloom can be maintained at a temperature of 1100 ° C or more for 3 to 5 hours in the heating furnace, and the billet can be maintained in the range of 1100 to 1200 ° C for 2 to 5 hours in the heating furnace.

According to a preferred aspect of the present invention, an appropriate amount of B and N is added to free cutting steel to induce precipitation of BN, thereby providing excellent hot rolling property and cutting property and at the same time not containing a low melting point element such as lead, A free cutting steel having good properties can be provided.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

FIG. 1 is a view illustrating an example of a method of evaluating cutting performance of free cutting steel according to an embodiment of the present invention. Referring to FIG.

Hereinafter, preferred embodiments of the present invention will be described.

The embodiments of the present invention may be modified into various other forms or various embodiments may be combined, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. Accordingly, the shapes and sizes of the elements in the drawings may be exaggerated for clarity of description, and the elements denoted by the same reference numerals in the drawings are the same elements.

Free cutting steels are widely used in automobiles, office equipment, household appliances, and especially, they have excellent machinability and dimensional accuracy. In order to improve cutting performance of free cutting steel, low melting point elements can be added in the manufacturing process. If the amount of low melting point elements is increased, surface defects occurring in free cutting steels in the wire manufacturing process may increase. That is, as the cutting ability is improved by adding a large amount of low melting point element to the free cutting steel, the hot rolling property may be deteriorated.

INDUSTRIAL APPLICABILITY The present invention aims at eliminating the use of a low-melting point element or MnS which can improve the cutting property in heavy carbon free cutting steel but can lower the hot rolling property and induces generation of fine BN having a uniform distribution in order to secure machinability Hot-rolled and machinable at the same time, and a method for producing the same.

Hereinafter, a medium carbon free cutting steel having excellent hot rolling property according to a preferred aspect of the present invention will be described.

In another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.40 to 0.50% of C, 0.3% or less of Si (excluding 0%), 1.0 to 1.5% of Mn, 0.015% S: 0.008% or less (excluding 0%), B: 0.005 to 0.015%, N: 0.010 to 0.020%, Al: 0.05% or less (excluding 0%), remaining Fe and other unavoidable impurities, B weight ratio of the two is 1.3 to 2.8, less than 0.1% area fraction of the MnS in the rolling direction cross-section of the wire, fine BN inclusions having a diameter of 5μm or less and 1mm ² per unit area more than 100 and an average aspect ratio (aspect ratio) of the BN Is 2.0 or less.

Hereinafter, the steel components and the component ranges will be described.

Carbon (C): 0.40 to 0.5 wt%

Carbon is an element that increases the strength and hardness of a material by forming carbide. Most of the carbon free cutting steel exists as pearlite. It plays a role of giving proper strength to be used for heavy carbon machine structure, for example can do. If the content of carbon is less than 0.40% by weight, the strength and the incombustibility may be reduced. On the other hand, when the content of carbon is more than 0.50 wt%, the hardness of the material is excessively increased, which may shorten the tool life at the time of cutting. Therefore, the carbon content is preferably limited to 0.40-0.50 wt%.

Silicon (Si): 0.3% or less (excluding 0%)

If the silicon content exceeds 0.30 wt%, hard SiO 2 -based metal inclusions can be generated in a large amount, which can reduce tool life in the cutting process of free cutting steel. Therefore, the Si content is preferably limited to 0.30 wt% or less. A more preferable Si content is Si: 0.01 to 0.3%.

Manganese (Mn): 1.0 to 1.5 wt%

Mn improves the strength of steel and is added to prevent the harmfulness of S present in the steel to form MnS, thereby preventing red-hot brittleness. When the Mn content is more than 1.0% by weight, the desired ingot strength and strength can be obtained and the austenite region can be widened, so that the generation of erosion ferrite during rolling can be delayed and the surface defects of the steel strip during hot rolling can be suppressed. However, when Mn is added in an amount exceeding 1.5% by weight, the toughness is lowered and a thick pearlite band may be formed during cooling of the material, so that the surface roughness can be deteriorated during cutting. Therefore, the content of manganese is preferably limited to 1.0 to 1.5% by weight.

Phosphorus (P): 0.015% or less (excluding 0%)

Phosphorus is an element added to improve machinability. It can inhibit a build-up edge that is present as a segregation or a compound in a crystal grain boundary of the material and is likely to be formed at the tip of a cutting tool. However, if phosphorus is added excessively, the mechanical properties of the free cutting steel and the hot rolling property may be deteriorated. Therefore, the phosphorus content is preferably limited to 0.015 wt% or less. More preferred phosphorus content is 0.001 to 0.015%.

Sulfur (S): 0.008% or less (excluding 0%)

S combines with Mn in the steel to form MnS. In the present invention, cutting performance can be improved by forming MnS, but machinability can be ensured without the effect of improving the machinability by MnS. If excess amount of S is added, net-like FeS precipitation can be promoted in grain boundaries. Such FeS is very weak and has a low melting point, so that the hot rolling property can be largely lowered. In addition, when MnS is produced by adding a large amount of S, not only the hot rolled property like FeS is lowered but also the coarse BN is formed using MnS as nuclei or the BN is unevenly distributed around the drawn MnS in rolling And the homogeneity can be lowered. Therefore, the content of S is preferably limited to 0.008 wt% or less. The more preferable content of S is 0.001 to 0.008% by weight.

Boron (B): 0.005 to 0.015 wt%

B bonds with N at the time of solidification of the steel to form BN inclusions, thereby contributing to improvement of cutting performance. When the content of B is less than 0.0050 wt%, the effect of BN is too small to exhibit the above effect. If the content of B is more than 0.0150 wt%, the BN may deteriorate the hot rolling property. Therefore, the content of B is preferably limited to 0.005 to 0.015% by weight

Nitrogen (N): 0.010-0.020 wt%

Nitrogen (N) combines with B during solidification of steel to form BN inclusions, which contributes to cutting performance. However, when the N content is less than 0.010 wt%, the above effects are difficult to be expected. If the N content is more than 0.020 wt%, steelmaking is difficult and the surface quality may be deteriorated due to pin holes and cracks have. Therefore, the content of N is preferably limited to 0.010 to 0.020% by weight.

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

As described above, the free cutting steel according to the embodiment of the present invention can be manufactured, for example, by casting molten steel on a teaming ladle in an Al-Si composite deoxidized state. When the aluminum content exceeds 0.05% by weight, hard Al ₂ O ₃ -based non-metallic inclusions can be generated in a large amount, which can significantly reduce the tool life in the cutting process of free cutting steel. Therefore, the Al content is preferably limited to 0.05 wt% or less. A more preferable Al content is 0.01 to 0.05% by weight.

N / B weight ratio: 1.3 to 2.8

The weight ratio of N / B in the BN formation and the residual amount of N is very important. When the weight ratio of N / B is less than 1.3, N is too small to form a sufficient amount of BN inclusions. Conversely, if the weight ratio of N / B exceeds 2.8, the hardness increases due to excess N after BN formation, The workability and workability are adversely affected by the work hardening effect. Therefore, the N / B weight ratio is preferably limited to 1.3 to 2.8.

And the balance Fe and inevitable impurities. 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 referred to in this specification, as they are known to one of ordinary skill in the art. In addition, addition of an effective component other than the above-mentioned composition is not excluded.

According to a preferred aspect of the present invention, the medium carbon free cutting steel excellent in hot rolling property is characterized in that the area fraction of MnS in the rolling direction section of the wire is less than 0.1%, the fine BN inclusions having a diameter of 5 탆 or less are 100 or more per 1 mm ² area, (Aspect ratio) of 2.0 or less.

If the area fraction of MnS in the section in the rolling direction of the wire rod is 0.1% or more, the hot rolling property may be lowered to cause surface flaws.

Nitride boron (BN), a nonmetallic inclusion, is also called white graphite because it has almost the same crystal structure and physical properties as graphite, which improves cutting performance in graphite free cutting steels.

In the present invention, by producing a proper amount of such BN, BN acts as a stress concentration source at the time of cutting, thereby facilitating crack generation and crack growth, thereby improving cutting performance without a significant reduction in hot rolling property. In addition, BN as a solid lubricant So that the cutting force can be lowered by reducing the frictional force between the workpiece and the cutting tool.

As in the present invention, when B and N necessary for BN formation are added in an appropriate amount and finely uniformly distributed in the steel, the machinability can be improved without deteriorating the hot rolling property.

When the number of fine BN inclusions having a diameter of 5 탆 or less is less than 100 per 1 mm ² area, it may be difficult to ensure a sufficient cutting property improving effect.

The fine BN inclusions having a diameter of 5 탆 or less may be, for example, 100 to 200 per 1 mm ² area.

When the average aspect ratio of BN is more than 2.0, anisotropy may occur in mechanical properties, which may lower the roughness of the surface to be cut.

Hereinafter, a method for producing a medium carbon free cutting steel having excellent hot rolling property according to another preferred embodiment of the present invention will be described.

According to another preferred embodiment of the present invention, there is provided a method for producing a medium carbon free cutting steel having excellent hot rolling properties, comprising: 0.40 to 0.50% of C; 0.3% or less (excluding 0%) of Si; , P: 0.015% or less (excluding 0%), S: 0.008% or less (excluding 0%), B: 0.005 to 0.015%, N: 0.010 to 0.020% , Remaining Fe and other unavoidable impurities, and casting molten steel having a weight ratio of N / B of 1.3 to 2.8 into blooms;

Rolling the bloom to obtain billets; And

And a wire rolling step of heating the billet in a heating furnace and rolling it into a wire rod.

In the continuous casting step, for example, the molten steel may be continuously cast by simultaneously driving a mold electromagnetic stirring apparatus (EMS) and a light-weight reducing apparatus.

In producing carbon steel free-cutting steel, excellent cast steel can be obtained by continuously casting molten steel using a mold electromagnetic stirrer (EMS) and a light-weight reduction device in a continuous casting process. It is possible to obtain a uniformly distributed nonmetallic inclusions by using the mold electromagnetic stirring apparatus. By using a device under competition, it is possible to reduce center segregation of the cast steel and to reduce surface defects such as pinhole blowholes on the surface of the cast steel.

During the rolling of the billet, the bloom can be maintained at a temperature of 1100 ° C or more for 3 to 5 hours in the heating furnace, and the billet can be maintained in the range of 1100 to 1200 ° C for 2 to 5 hours in the heating furnace.

If the temperature of the bloom is less than 1100 占 폚 or the holding time is less than 3 hours, rolling flaws may occur. If the bloom temperature exceeds 5 hours, the production efficiency may be lowered.

On the other hand, when the temperature of the billet is lower than 1100 ° C, it may be difficult to obtain good wire surface quality because corner portions are blown or surface defects are generated.

The free cutting steel produced by the above-described production method can have excellent hot rolling property and cutting property.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only illustrative of the present invention in more detail and do not limit the scope of the present invention.

(Example)

A bloom having a cross section of 500 mm x 600 mm was produced through a continuous casting process using molten steel having the composition shown in the following Table 1 and then a billet having a cross section of 160 mm x 160 mm was produced through a rolling process of a steel billet, And finally rolled to produce a CD Bar (Cold-Drawn) having a diameter of 25 mm.

In the following Table 1, the test materials prepared for the 'invented material' and the comparative material are shown as 'comparative material' when the chemical composition as shown in the present invention is satisfied.

The BN density (g / mm ² ), the MnS area fraction (%), the aspect ratio, the BN average diameter (占 퐉), the tool wear depth (占 퐉) ), Hot rolling property and machinability were examined. The results are shown in Table 2 below.

In the following Table 2, hot rolling property and cutting property were measured as follows.

In order to investigate the effect of chemical composition and BN formation on the hot rolling property, the on - site hot rolling property evaluation was performed by visually inspecting the surface condition during the wire rolling or after the wire rolling, It was conducted according to acceptance criteria. The final judgment of the hot rolling property was made by observation through a thermal imaging camera during rolling and observing the surface of the final wire finished product.

In Table 2, O indicates a material having a good rolling property and no scratches of 100 m (micrometer) or more in thickness, X indicates poor local rolling property due to poor rolling property, Indicates the material where the blemish was found.

The machinability evaluation was evaluated by machining using a CNC lathe, and an example of a cutting tool and tool is shown in Fig. Cutting was done by turning method. CD Bar (100) with an initial diameter (d1) of 25 mm was machined to have a diameter (d2) of 23 mm after cutting and the feed distance (T) 20 mm. The amount of cutting per one specimen was 11.9 grams, and 300 parts were cut to remove a total of 5,950 grams. The cutting tool 200 has a diamond shape, a corner angle of 55 degrees, an allowance angle of 7 degrees, a nose radius (R) of 0.4 mm, and a cermet as a tool grade. Cutting conditions with a cutting speed of 200 m / min, a feed rate of 0.075 mm / rev, and an infeed depth of 0.5 mm were applied and the maximum depth of the flankwear of the tool after the final 300 parts machining was measured .

In Table 2, the depth of abrasion is expressed as " 0 " in machinability, and " X " in machinability, based on the maximum side wear depth 200 μm (micrometer) of the tool after 300 parts machining.

Example No. 2. C Si Mn P S B N Al N / B weight ratio Inventory 1 0.43 0.22 1.11 0.012 0.008 0.0059 0.0125 0.021 2.12 Inventory 2 0.42 0.15 1.06 0.014 0.004 0.0060 0.0140 0.024 2.33 Inventory 3 0.46 0.24 1.13 0.011 0.006 0.0065 0.0135 0.025 2.08 Invention 4 0.49 0.28 1.22 0.013 0.005 0.0060 0.0110 0.028 1.83 Invention Article 5 0.41 0.12 1.01 0.011 0.006 0.0075 0.0190 0.019 2.53 Comparison 1 0.75 0.23 1.01 0.012 0.007 0.0057 0.0119 0.021 2.09 Comparative material 2 0.45 0.61 1.45 0.014 0.008 0.0055 0.0118 0.028 2.15 Comparative material 3 0.42 0.27 1.45 0.011 0.011 0.0060 0.0110 0.029 1.83 Comparison 4 0.48 0.17 1.48 0.012 0.006 0.0038 0.0148 0.019 3.89 Comparative material 5 0.44 0.24 1.45 0.010 0.007 0.0077 0.0087 0.020 1.13 Comparative material 6 0.42 0.24 1.23 0.010 0.030 0.0077 0.0170 0.020 2.21

Example No. 2. BN density
(Pieces / mm ² ) MnS area fraction
(%) Aspect ratio
(Aspect ratio) BN average diameter (占 퐉) Tool wear depth
(탆) Hot rolling property Machinability Inventory 1 120 0.03 1.7 3.1 167 O O Inventory 2 165 0.01 1.7 2.9 187 O O Inventory 3 143 0.02 1.6 3.2 123 O O Invention 4 112 0.02 1.4 3.3 165 O O Invention Article 5 172 0.02 1.7 2.8 156 O O Comparison 1 123 0.02 1.4 3.1 332 O X Comparative material 2 125 0.03 1.4 3.5 297 O X Comparative material 3 123 0.04 2.2 4.7 187 X O Comparison 4 78 0.02 1.1 2.2 321 O X Comparative material 5 67 0.02 1.7 2.1 253 O X Comparative material 6 102 0.11 1.9 5.5 273 X X

As shown in Tables 1 and 2, the comparative material 1 had a carbon content of 0.75% by weight, which was more than 0.5% by weight, which is the carbon content upper limit of the present invention. Therefore, it can be understood that the hot-rolling property satisfies the reference value, but the tool wear after cutting due to excessive hardness increase causes the cutting property to fail to satisfy the reference value.

Comparative Material 2 The Si depth was 0.61 wt%, and the depth of the tool wear was greatly increased as compared with that of the invention due to over production of SiO ₂ oxide and hardness increase due to solid solution strengthening.

In the case of the comparative material 3, it was found that the addition of sulfur (S) over the range proposed in the present invention resulted in an improvement in cutting performance due to the formation of MnS, but a decrease in hot rolling resistance.

The comparative material 4 contains a smaller amount of boron (B) than the criteria set forth in the present invention, and thus the number of BN per unit area is 78 / mm ² , which is 100 / mm ² , Can be confirmed. As the N / B ratio increases and the solvency N, which can not be bonded with BN, increases, the hardness also increases and the machinability decreases. In addition, there was surface scratches due to pinholes and the like when playing with excessive use of N.

The comparative material 5, on the contrary, contains N in a smaller amount than the standard, and the N / B ratio is lower than the reference value, and the excess B which does not bond with N causes sticking due to viscosity at the time of cutting, It will have an adverse effect. In addition, the amount of N is small and the number of BN produced is as small as 67 pieces / mm < ² >

The comparative material 6 was added in excess of the S content standard as proposed in the present invention. As a result, the elongated MnS fraction was increased, and coarse BN produced as a nucleus thereof was unevenly distributed, resulting in remarkable reduction in both hot rolling and machinability .

On the other hand, in the case of the inventive material (1-5) according to the present invention, it can be seen that the tool wear depth (tool life), hot rolling property and machinability are both excellent.

The present invention is not limited to the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

100: CD Bar (Cold-Drawn)
200: Cutting tool

Claims (8)

(Excluding 0%), Mn: 1.0 to 1.5%, P: not more than 0.015% (excluding 0%), S: not more than 0.008% (0% (Excluding 0%), other Fe and other unavoidable impurities, and the weight ratio of N / B is 1.3 to 2.8 (inclusive), B: 0.005 to 0.015%, N: 0.010 to 0.020% direction, and an area fraction of the MnS in the rolling direction cross-section of the wire is less than 0.1%, fine BN inclusions having a diameter of 5μm or less 1mm ² per unit area is more than 100, is 2.0 or lower the hot rolling property is excellent average aspect ratio of BN (aspect ratio) Medium carbon free cutting steel.
The steel according to claim 1, characterized in that the content of Si in the steel is 0.01 to 0.3%, the content of P is 0.001 to 0.015%, the content of S is 0.001 to 0.008% and the content of Al is 0.01 to 0.05% Which is excellent in hot-rolling property.
The medium carbon free cutting steel according to claim 1, wherein the fine BN inclusions having a diameter of 5 탆 or less are 100 to 200 per 1 mm ² area.
(Excluding 0%), Mn: 1.0 to 1.5%, P: not more than 0.015% (excluding 0%), S: not more than 0.008% (0% (Excluding 0%), other Fe and other unavoidable impurities, and the weight ratio of N / B is 1.3 to 2.8 (inclusive), B: 0.005 to 0.015%, N: 0.010 to 0.020% A continuous casting step of casting molten steel into a bloom;
Rolling the bloom to obtain billets; And
And a wire rod rolling step of heating the billet in a heating furnace and rolling the wire rod into a wire rod.
The steel according to claim 4, wherein the molten steel has a Si content of 0.01 to 0.3%, a P content of 0.001 to 0.015%, a S content of 0.001 to 0.008% and an Al content of 0.01 to 0.05% Wherein the hot rolled steel sheet has an excellent hot rolling property.
5. The method of claim 4, wherein the continuous casting step is a step of simultaneously casting the molten steel by simultaneously driving the mold electromagnetic stirring device (EMS) and the light-weight reducing device.
The method of claim 4, wherein the bloom is maintained at a temperature of 1100 캜 or higher for 3 to 5 hours in the heating furnace at the time of rolling the billet.
5. The method for producing heavy carbon free cutting steel according to claim 4, wherein the billet is maintained in a temperature range of 1100 to 1200 占 폚 for 2 to 5 hours in the heating furnace at the time of the wire rolling.

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