KR102010052B1 - Medium carbon free cutting steel having excellent hot workability and method for manufacturing the same - Google Patents

Abstract

Preferred aspects of the present invention are by weight, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 to 1.5%, P: 0.015% or less (excluding 0%), S: Less than 0.008% (except 0%), B: 0.005 ~ 0.015%, N: 0.010 ~ 0.020%, Al: 0.05% or less (excluding 0%), remaining Fe and other unavoidable impurities, The weight ratio is 1.3 to 2.8, the area fraction of MnS in the cross section of the wire rod is less than 0.1%, the number of fine BN inclusions having a diameter of 5 μm or less is 100 or more per 1 mm ² area, and the average aspect ratio of BN is 2.0. It provides a medium-carbon free-cutting steel excellent in the following hot rolling properties and a manufacturing method thereof.

Description

MEDIUM CARBON FREE CUTTING STEEL HAVING EXCELLENT HOT WORKABILITY AND METHOD FOR MANUFACTURING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free-cutting steel used as materials for automobile hydraulic parts, fasteners for home appliances, shafts of office automation equipment, general cutting parts, and mechanical structures, and more particularly, hot rolling and cutting properties. An excellent medium carbon free cutting steel and a method of manufacturing the same.

In general, free-cutting steel is a steel with high machinability, and is widely used as a material for automobile hydraulic parts, fasteners for home appliances, shafts of office automation equipment, and general cutting parts. There is a trend.

Free-cutting steels with good machinability and dimensional accuracy and similar strengths to that of ordinary medium-carbon carbon steels are also widely used for mechanical construction.

In order to manufacture free-cutting steel with excellent machinability, a small amount of low melting point lead (Pb) or the like may be added or the MnS inclusion may be removed to increase the tool life and chip segmentation of the free-cutting steel and to improve the surface quality and dimensional accuracy of the product. However, with the recent tightening of environmental regulations, the use of lead, an element harmful to the human body, has gradually been avoided. In the manufacture of free cutting steel, the quality of free cutting steel can be improved by adding relatively environmentally friendly bismuth (Bi) or tin (Sn) instead of Pb. A method of improving is proposed.

However, in general, low melting point elements added for improving machinability may lower the hot rolling property of free cutting steel. In addition, even in sulfur-based free-cutting steels in which MnS is formed by adding a large amount of sulfur (S), a large amount of MnS is formed in a long direction in the hot rolling direction, causing anisotropy in mechanical properties and deteriorating toughness. Let's go. Due to this, the ends of the wire rod are cracked, and to compensate for this, operations such as sharpening the billet end of the wire rod before cutting the wire rod, such as the tip shape of the pencil, are greatly reduced, thereby greatly reducing productivity.

Graphite free cutting steel has been studied to solve this problem, but 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

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

Another preferred aspect of the present invention is to provide a method for producing medium-carbon free-cutting steel excellent in hot rolling and cutting properties.

Another preferred aspect of the present invention is by weight, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 to 1.5%, P: 0.015% or less (excluding 0%), S: 0.008% or less (except 0%), B: 0.005% to 0.015%, N: 0.010% to 0.020%, Al: 0.05% or less (except 0%), including remaining Fe and other unavoidable impurities, The weight ratio of B is 1.3 to 2.8, the area fraction of MnS in the rolling direction cross section of the wire rod is less than 0.1%, and there are 100 or more fine BN inclusions having a diameter of 5 μm or less per 1 mm ² area, and the average aspect ratio of BN. It provides a medium-carbon free-cutting steel excellent in hot rolling property of 2.0 or less.

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

Another preferred aspect of the present invention is by weight, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 to 1.5%, P: 0.015% or less (excluding 0%), S: 0.008% or less (except 0%), B: 0.005% to 0.015%, N: 0.010% to 0.020%, Al: 0.05% or less (except 0%), including remaining Fe and other unavoidable impurities, N / A continuous casting step of casting molten steel having a weight ratio of B of 1.3 to 2.8 in bloom;

Rolling the bloom to obtain billets; And

It provides a method for producing a medium-carbon free-cutting steel excellent in hot rolling properties, including the wire rolling step of heating the billet in a heating furnace to roll the wire.

In the continuous casting step, the molten steel may be continuously cast by simultaneously driving an electronic mold stirrer (EMS) and a low pressure device.

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

According to a preferred aspect of the present invention, by adding an appropriate amount of B, N to the free-cutting steel to induce BN precipitation, it has excellent hot rolling and cutting properties, and does not contain low melting point elements such as lead. A free cutting steel having a property can be provided.

Various and advantageous advantages and effects of the present invention is not limited to the above description, it will be more readily understood in the course of describing specific embodiments of the present invention.

1 is an exemplary view showing a method for evaluating the machinability of free cutting steel according to an embodiment of the present invention.

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

Embodiments of the present invention may be modified in various other forms, or various embodiments may be combined, and the scope of the present invention is not limited to the embodiments described below. Moreover, embodiment of this invention is provided in order to demonstrate this invention more completely to the person with average knowledge in the technical field. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity, and the elements denoted by the same reference numerals in the drawings are the same elements.

Free cutting steel is widely used in automobiles, office equipment, home appliances, etc., and particularly has excellent cutting properties and dimensional accuracy. In order to increase the machinability of free cutting steel, a low melting point element may be added in a manufacturing process. An increase in the addition amount of the low melting point element may increase surface defects occurring in the free cutting steel in a wire rod manufacturing process. That is, the hot rolling property may be lowered as the machinability is improved by adding a large amount of low melting point elements to the free cutting steel.

The present invention improves machinability in the medium-carbon free-cutting steel, but eliminates the use of low-melting point elements or MnS that can degrade hot rolling, and instead induces the production of fine BN with uniform distribution to ensure machinability. It is to provide a medium-carbon free-cutting steel and a method of manufacturing the same, which can secure hot rollability and machinability at the same time.

Hereinafter, the medium-carbon free cutting steel excellent in the hot rolling property which concerns on one preferable aspect of this invention is demonstrated.

Another preferred aspect of the present invention is by weight%, C: 0.40 ~ 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 ~ 1.5%, P: 0.015% or less (excluding 0%), S: 0.008% or less (except 0%), B: 0.005% to 0.015%, N: 0.010% to 0.020%, Al: 0.05% or less (except 0%), including remaining Fe and other unavoidable impurities, N / The weight ratio of B is 1.3 to 2.8, the area fraction of MnS in the rolling direction cross section of the wire rod is less than 0.1%, and there are 100 or more fine BN inclusions having a diameter of 5 μm or less per 1 mm ² area, and the average aspect ratio of BN. Is 2.0 or less.

Hereinafter, the steel component and the component range will be described.

Carbon (C): 0.40 to 0.5 wt%

Carbon is an element that increases the strength and hardness of materials by forming carbides. In medium-carbon free cutting steel, carbon is mostly present as pearlite, and thus, it serves to give an appropriate strength to be used for, for example, heavy carbon mechanical structures. can do. If the content of carbon is less than 0.40% by weight, strength and hardenability may decrease. On the other hand, if the carbon content exceeds 0.50% by weight, the hardness of the material is excessively increased, which may shorten the tool life during cutting. Therefore, the content of carbon is preferably limited to 0.40 to 0.50% by weight.

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

When the silicon content exceeds 0.30% by weight, a large amount of hard SiO-based nonmetallic inclusions may be generated, thereby reducing tool life in the cutting process of free cutting steel. Therefore, the Si content is preferably limited to 0.30% by weight or less. More preferred Si content is 0.01% to 0.3% of Si.

Manganese (Mn): 1.0 to 1.5 wt%

Mn improves the strength of the steel and is added to prevent the harmfulness of S present in the steel, thereby forming MnS to prevent the red light brittleness. When the Mn content is more than 1.0% by weight, desired quenchability and strength can be obtained, and the austenite region can be widened to delay the formation of cornerstone ferrite during rolling and to suppress surface defects of the steel sheet during hot rolling. However, when the Mn content is added in excess of 1.5% by weight, the toughness may be lowered and a thick pearlite band may be formed during material cooling, thereby deteriorating surface roughness during cutting. Therefore, the content of the 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. The phosphorus is present as segregation or compound at grain boundaries of the raw material, thereby suppressing a build-up edge that is easily formed at the tip of the cutting tool. However, when too much phosphorus is added, mechanical properties and hot rolling properties of the free cutting steel may be degraded. Therefore, the phosphorus content is preferably limited to 0.015% by weight or less. More preferable phosphorus content is 0.001-0.015%.

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

S combines with Mn in steel to form MnS. In the present invention, it is possible to improve the machinability by forming MnS, but the machinability is secured without the machinability improvement effect by MnS, and when an excessively large amount of S is added, it is possible to promote the precipitation of mesh-like FeS at grain boundaries. Since FeS is very fragile and its melting point is low, hot rolling can be greatly reduced. In addition, even when MnS is formed by the addition of a large amount of S, not only the hot rolling property is lowered like FeS, but also coarse BN is produced using MnS as a nucleus or BN is unevenly distributed around the stretched MnS during rolling. While reducing the homogeneity. Therefore, the content of S is preferably limited to 0.008% by weight or less. More preferable content of S is 0.001 to 0.008% by weight.

Boron (B): 0.005 to 0.015% by weight

B combines with N to solidify the steel to form BN inclusions, contributing to improved machinability. When the content of B is less than 0.0050% by weight, the amount of BN formed is too small to exhibit the above effect, and when added in excess of 0.0150% by weight, the hot rolling property may be lowered by excessive BN. Therefore, the content of B is preferably limited to 0.005 to 0.015% by weight.

Nitrogen (N): 0.010-0.020 weight%

Nitrogen (N) combines with B when the steel solidifies to form BN inclusions, contributing to improved machinability. However, when the N content is less than 0.010% by weight, it is difficult to expect the above effect. When the N content is more than 0.020% by weight, steelmaking is difficult, and the surface quality may be degraded by the production of pin holes and cracks during performance. have. Therefore, the content of N is preferably limited to 0.010 to 0.020% by weight.

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

As described above, the free cutting steel according to the embodiment of the present invention, for example, can be manufactured by tapping the teaming ladle in the state of Al-Si composite deoxidation. When the aluminum content exceeds 0.05% by weight, a large amount of hard Al ₂ O ₃ nonmetallic inclusions may be generated, which may significantly reduce the tool life in the cutting process of free cutting steel. Therefore, the Al content is preferably limited to 0.05% by weight or less. More preferable Al content is 0.01 to 0.05 weight%.

Weight ratio of N / B: 1.3 ~ 2.8

The weight ratio of N / B is a very important variable for BN formation and the high capacity of residual N. If 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 surplus N after BN formation and is excessive during deformation. The work hardening effect adversely affects machinability and workability. Therefore, it is preferable to limit the said N / B weight ratio to 1.3-2.8.

In addition to the balance Fe and unavoidable impurities. However, in the conventional manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, not all of them are specifically mentioned in the present specification. In addition, addition of an effective component other than the said composition is not excluded.

The medium-carbon free-cutting steel having excellent hot rolling property according to the preferred aspect of the present invention has an area fraction of MnS of less than 0.1% in the rolling direction cross section of the wire rod, fine BN inclusions having a diameter of 5 μm or less, and 100 or more per 1 mm ² area, and BN The average aspect ratio of is 2.0 or less.

If the area fraction of MnS in the rolling direction cross section of the wire rod is 0.1% or more, there is a fear that the hot rolling property is lowered to cause surface defects.

Boron nitride (BN), a non-metallic inclusion, is also called white graphite because it has a crystal structure and physical properties similar to that of graphite, which improves machinability in graphite free-cutting steel.

In the present invention, by generating an appropriate amount of BN, BN acts as a stress concentration source during cutting, thereby facilitating crack formation and growth of cracks, thereby improving machinability without significantly reducing hot rolling property, and during cutting, BN serves as a solid lubricant. By reducing the friction between the material and the cutting tool.

As in the present invention, by adding an appropriate amount of B and N necessary for forming BN and finely distributing it in the steel, it is possible to improve the machinability without reducing the hot rolling property.

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

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

When the average aspect ratio of BN exceeds 2.0, there is a concern that anisotropy occurs in the mechanical properties and the roughness of the cut surface is lowered.

Hereinafter, the manufacturing method of the medium-carbon free cutting steel excellent in the hot rolling property which concerns on another preferable aspect of this invention is demonstrated.

According to another preferred aspect of the present invention, the method for producing a medium-carbon free-cutting steel having excellent hot rolling property is weight%, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), and Mn: 1.0 to 1.5%. , 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%, Al: 0.05% or less (excluding 0%) A continuous casting step of casting molten steel having a remaining Fe and other unavoidable impurities and having a weight ratio of N / B of 1.3 to 2.8 in bloom;

Rolling the bloom to obtain billets; And

And a wire rod rolling step of heating the billet in a furnace to roll the wire.

In the continuous casting step, for example, the molten steel may be continuously cast by simultaneously driving an electronic mold stirrer (EMS) and a low pressure device.

In manufacturing medium-carbon free-cutting steel, an excellent cast can be obtained by continuously casting molten steel using a mold electrostirrer (EMS) and a low pressure device in a continuous casting process. The use of a mold electronic stirrer can be used to obtain a uniform distribution of nonmetallic inclusions, and the use of a contention apparatus can reduce the center segregation of the cast and reduce surface defects such as pinhole blowholes on the surface of the caster.

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

If the temperature of the bloom is less than 1100 ° C. or the holding time is less than 3 hours, there may be a rolling flaw, and if it exceeds 5 hours, the manufacturing efficiency may be lowered.

On the other hand, when the temperature of the billet is lower than 1100 ℃, it may be difficult to obtain a good wire surface quality because the corner portion is broken or surface defects occur.

The free cutting steel produced by the above-described manufacturing method may have excellent hot rolling property and machinability.

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

(Example)

The molten steel having the composition shown in Table 1 was used to produce a bloom having a cross section of 500 mm X 600 mm through a continuous casting process, and then a billet having a cross section of 160 mm X 160 mm through a steel sheet rolling process, followed by a wire rod having a diameter of 27 mm. Finally, a CD bar (Cold-Drawn) having a diameter of 25 mm was manufactured by rolling.

In Table 1, when the chemical composition presented in the present invention is satisfied, the test material manufactured for the invention and the comparative material for the purpose of comparison are shown as 'comparative material'.

BN density (pieces / mm ² ), MnS area fraction (%), aspect ratio, BN average diameter (µm), and tool wear depth (µm) for the CD Bar (inventive and comparative materials) prepared as described above. ), Hot rollability and machinability were investigated, and the results are shown in Table 2 below.

In Table 2 below, hot rolling property and machinability were measured as follows.

For the purpose of evaluating the effect of chemical composition and the formation of BN on hot rolling property, on-site hot rolling property evaluation was conducted by visually inspecting the surface condition during wire rolling or after wire rolling. It was carried out according to the acceptance criteria. Final determination of hot rolling was made through observation through a thermal imaging camera during rolling and observation of the surface of the final wire rod finished product.

In Table 2 below, O represents a material having good rolling property and no blemishes of 100 μm (micrometer) or more are found, and X represents poor rolling property and causes local bursting or a surface of 100 μm (micrometer) or more. Indicates the material from which the flaw was found.

Machinability evaluation was evaluated by machining using a CNC lathe, an example of the cutting specimen and the tool is shown in FIG. The cutting process was performed by turning method. The CD bar 100 having an initial diameter (d1) of 25 mm was processed to have a diameter (d2) of 23 mm after cutting, and the feed distance (T) per specimen was 20 mm. The cutting volume per 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 and has a corner angle of 55 degrees, a clearance angle of 7 degrees, and a nose radius R of 0.4 mm. The tool grade used cermet. Cutting conditions with a cutting speed of 200 m / min, a feed rate of 0.075 mm / rev, and a cutting depth of 0.5 mm were applied, and the maximum depth of flankwear of the tool was measured after the final 300 parts were machined. .

In Table 2 below, the wear depth below the maximum side wear depth of 200 μm (micrometer) of the tool after machining 300 parts was expressed as “O” in machinability, and more than “X”.

Example No. C Si Mn P S B N Al Weight ratio of N / B Invention 1 0.43 0.22 1.11 0.012 0.008 0.0059 0.0125 0.021 2.12 Invention 2 0.42 0.15 1.06 0.014 0.004 0.0060 0.0140 0.024 2.33 Invention 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 5 0.41 0.12 1.01 0.011 0.006 0.0075 0.0190 0.019 2.53 Comparative Material 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 Comparative Material 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. BN density
(Pcs / mm ² ) MnS area fraction
(%) Aspect ratio
(Aspect ratio) BN Average Diameter (㎛) Tool wear depth
(Μm) Hot rollability Machinability Invention 1 120 0.03 1.7 3.1 167 O O Invention 2 165 0.01 1.7 2.9 187 O O Invention 3 143 0.02 1.6 3.2 123 O O Invention 4 112 0.02 1.4 3.3 165 O O Invention 5 172 0.02 1.7 2.8 156 O O Comparative Material 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 Comparative Material 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 Table 1 and Table 2, Comparative Material 1 is 0.75% by weight of carbon content exceeds the upper limit of 0.5% by weight based on the content of carbon presented in the present invention. Accordingly, it can be seen that the hot rolling property satisfies the reference value while the tool wear increases after cutting due to excessive hardness increase, and thus the machinability does not satisfy the reference value.

Comparative material 2 also had a Si content of 0.61% by weight, which greatly increased the wear depth of the tool due to excessive generation of SiO ₂ oxide and increased hardness due to solid solution strengthening.

In the case of the comparative material 3, although the sulfur content (S) is contained more than the range shown by this invention, and machinability improved by production | generation of MnS, it turns out that the hot rolling property falls.

Comparative material 4 contained less boron (B) than the standard set forth in the present invention, and therefore the number of BNs per unit area was 78 pieces / mm ² , and the lower limit standard proposed by the present invention was 100 pieces / mm ² . You can see that it is underfoot. The machinability decreases because the hardness can also increase as the N / B ratio increases and the number of solid solutions N not bonded to BN increases. In addition, excessive solid solution N caused surface defects due to pinholes and the like.

Comparative material 5, on the contrary, is a case where N contains less than the reference value and the N / B ratio is lower than the reference value. Excessive solid solution B, which cannot be combined with N, causes viscous sintering during cutting, thereby reducing machinability. Will adversely affect. In addition, the number of BNs produced due to the small amount of N is also small at 67 pieces / mm ² , which does not contribute to the improvement of machinability.

Comparative material 6 was added in excess of the S content criterion suggested in the present invention, and as a result, the elongated MnS fraction was increased, and coarse BN produced as a nucleus was distributed unevenly, thereby significantly reducing both hot rolling and machinability. .

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

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

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

Claims (8)

By weight%, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 to 1.5%, P: 0.015% or less (excluding 0%), S: 0.008% or less (0% ), B: 0.005 ~ 0.015%, N: 0.010 ~ 0.020%, Al: 0.05% or less (except 0%), remaining Fe and other unavoidable impurities, and the weight ratio of N / B is 1.3 ~ 2.8 In the rolling direction cross section of the wire rod, the area fraction of MnS is less than 0.1%, and there are 100 or more fine BN inclusions having a diameter of 5 μm or less per 1 mm ² area, and the hot rolling property with an average aspect ratio of BN of 2.0 or less is excellent. Medium carbon free cutting steel.
The method of claim 1, wherein the Si content of the steel is 0.01 to 0.3%, the P content is 0.001 to 0.015%, the S content is 0.001 to 0.008%, and the Al content is 0.01 to 0.05%. A medium-carbon free cutting steel with excellent hot rolling properties.
The medium-carbon free cutting steel having excellent hot rolling property according to claim 1, wherein the fine BN inclusion having a diameter of 5 μm or less is 100 to 200 per 1 mm ² area.
By weight%, C: 0.40 to 0.50%, Si: 0.3% or less (excluding 0%), Mn: 1.0 to 1.5%, P: 0.015% or less (excluding 0%), S: 0.008% or less (0% ), B: 0.005 ~ 0.015%, N: 0.010 ~ 0.020%, Al: 0.05% or less (except 0%), remaining Fe and other unavoidable impurities, and the weight ratio of N / B is 1.3 ~ 2.8 A continuous casting step of casting phosphorus molten steel into bloom;
Rolling the bloom to obtain billets; And
A wire rod rolling step of heating the billet in a heating furnace and rolling the wire bill;
The continuous casting step is a method for producing a medium-carbon free-cutting steel excellent in hot rolling properties to continuously cast the molten steel by simultaneously driving a mold electronic stirring device (EMS) and a low pressure device.
The method of claim 4, wherein the content of Si in the molten 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% A method for producing a medium-carbon free cutting steel having excellent hot rolling property.
delete The method for manufacturing medium-carbon free-cutting steel having excellent hot rolling property according to claim 4, wherein during the rolling of the steel sheet, a bloom is maintained at a temperature of 1100 ° C or more in a heating furnace for 3 to 5 hours.
The method for manufacturing a medium-carbon free cutting steel having excellent hot rolling property according to claim 4, wherein the billet is held for 2 to 5 hours in a heating furnace at the time of rolling the wire rod.

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