KR101657815B1 - Soft magnetic steel and soft magnetic part having excellent electromagnetic properties, and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a soft magnetic steel material and a soft magnetic steel material having excellent electromagnetic properties by controlling the content of Mn to a low level and suppressing abnormal crystal grain growth by adding B, and a method of manufacturing the same. The excellent soft magnetic steel is characterized by containing 0.001 to 0.02% of C, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, 0.02% or less of P, 0.002 to 0.01% of S, 0.001 to 0.004% of B, %, N: 0.002 to 0.005%, balance Fe and other unavoidable impurities, the microstructure is a ferrite single phase, and includes a complex precipitate of MnS and BN, and the complex precipitate is a form in which BN surrounds MnS.

Description

TECHNICAL FIELD [0001] The present invention relates to a soft magnetic steel material, a soft magnetic steel material, and a method of manufacturing the same. More particularly, the present invention relates to a soft magnetic steel material,

TECHNICAL FIELD [0001] The present invention relates to a soft magnetic steel material, a soft magnetic steel material, and a manufacturing method thereof excellent in electromagnetic characteristics that can be used for electric parts such as automobiles.

In order to improve energy efficiency according to environmental regulations, it is required to improve the electromagnetic characteristics of steel materials for electric parts such as automobiles. For example, such electrical components include generators, solenoid valves, pole segments or claw poles of alternator rotors. Electromagnetic properties required for steel parts for electric components are high magnetic permeability, high magnetic flux density and low iron loss. In addition, depending on the application and shape to which the component is applied, a certain level of strength, hot or cold stepping may be required. For this reason, a low carbon steel having a magnetic flux density of a steel which is easy to respond to an external magnetic field and satisfies the strength and the mono-composition is usually used.

In the past, the focus was focused on improving the efficiency of electric parts through the effects of designing and designing parts rather than focusing on improving the material performance of low carbon steel. In recent years, there has been a steady increase in demands for material performance improvement aiming at high performance of electric parts as well as parts design, starting from automobile field.

In order to improve the performance of the steel for electric parts, a method of applying pure iron based soft magnetic steel (JIS-SUYB1, etc.) may be considered. Pure iron-based soft magnetic steel has excellent magnetic properties because it has a ferrite single-phase structure of extremely low carbon steel having a carbon content of 0.02 wt% or less. However, in the case of hot forging products or cold forged products, There is a problem that the electromagnetic characteristics of the forged product due to heat are lost.

In order to prevent abnormal crystal grain growth, Patent Document 1 of the related art steel sheet uses MnS, AlN, MnSe or the like to prevent abnormal crystal growth during annealing after cold rolling.

However, unlike electric steel sheets, in the case of semi-finished products such as wire rod and bar steel, hot forging or cold forging-annealing is performed as a post-process. Accordingly, nonuniform deformation due to forging promotes abnormal crystal grain growth, and the deterioration of electromagnetic characteristics is further exacerbated by such microstructure.

Accordingly, there is a demand for development of soft magnetic steel, soft magnetic steel, and a manufacturing method thereof, which can prevent abnormal crystal grain growth by performing the process of hot forging or cold forging-annealing.

Korean Patent Publication No. 2002-0043690

The object of the present invention is to provide a soft magnetic steel material and a soft magnetic steel material excellent in electromagnetic characteristics by controlling the content of Mn to a low level and inhibiting the growth of abnormal crystal grains by adding B do.

According to one aspect of the present invention, there is provided a soft magnetic steel having excellent electromagnetic properties, comprising 0.001 to 0.02% of C, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, 0.02% or less of P, And the balance Fe and other unavoidable impurities, wherein the microstructure is a ferrite single phase, and comprises a complex precipitate of MnS and BN, the complex precipitate is BN (0.01-0.01%), B is 0.001-0.004%, N is 0.002-0.005% This MnS is wrapped around.

According to another aspect of the present invention, there is provided a method of manufacturing a soft magnetic steel having excellent electromagnetic characteristics, comprising the steps of: heating a steel billet satisfying the above-described composition at 1000 to 1200 占 폚;

Hot-rolling the heated billet to obtain a steel material; And

And cooling the hot-rolled steel at a cooling rate of 0.1 to 10 占 폚 / sec.

Further, the soft magnetic steel part having excellent electromagnetic characteristics, which is another aspect of the present invention, satisfies the above-mentioned composition, wherein the microstructure is a ferrite single phase and includes a complex precipitate of MnS and BN, And has an average size of 35 nm or less and a magnetic flux density B ₁₀ of 1.2 Tesla or more.

According to another aspect of the present invention, there is provided a method of manufacturing a soft magnetic steel part having excellent electromagnetic characteristics, comprising the steps of: heating a steel material at 770 to 1200 ° C; Hot forging the heated steel to obtain a hot forging; Cooling the hot forging at a cooling rate of 0.1 to 10 ° C / second; And cold forging the cooled hot forging.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

According to the present invention, there is an effect of improving the electromagnetic characteristics of a soft magnetic steel material used for electrical parts such as automobiles. As such electromagnetic characteristics are improved, miniaturization and high precision of electric parts can be achieved, and there is an eco-friendly effect such as improvement of fuel economy by weight saving effect.

Fig. 1 shows the average size of the complex precipitates of MnS and BN according to the content of Mn in the steel to which B is added.
2 is a TEM photograph of the precipitate of Inventive Example 3 and a schematic diagram of the composition of the precipitate.
3 is a graph showing the behavior of the precipitate according to Example 3 of the present invention.

Since the soft magnetic steel has a ferrite single phase structure through an extremely low carbon steel having a carbon content of 0.02 wt% or less and has a small amount of carbides that prevent grain boundary growth (pinning effect) The speed is fast.

In addition, when the soft magnetic wire and the steel rod are annealed after hot forging or cold forging, the amount of internal precipitates in the soft magnetic steel is small, resulting in a tissue imbalance due to abnormal crystal grain growth. Due to the unsteady grain growth, the microstructure in which the coarse grains and the fine grains are mixed may cause the difference of the dislocation density in the grains. This difference in dislocation density and high deviation in grain size cause the non-homogeneous magnetic flux in the steel, which causes the electromagnetic properties of the final product to be inferior.

The present inventors have recognized that such a tissue imbalance deteriorates the electromagnetic characteristics of the final part. In order to solve the above problems, the present inventors have found that MnS precipitates are finely adjusted by controlling the amount of Mn added, It is possible to improve the electromagnetic characteristics through the suppression of the abnormal crystal growth of the steel material, leading to the present invention.

Hereinafter, the soft magnetic steel having excellent electromagnetic characteristics according to one aspect of the present invention will be described in detail.

According to one aspect of the present invention, there is provided a soft magnetic steel having excellent electromagnetic properties, comprising 0.001 to 0.02% of C, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, 0.02% or less of P, And the balance Fe and other unavoidable impurities, wherein the microstructure is a ferrite single phase, and comprises a complex precipitate of MnS and BN, the complex precipitate is BN (0.01-0.01%), B is 0.001-0.004%, N is 0.002-0.005% And the average size thereof is 35 nm or less.

Hereinafter, the reason why the alloy composition of the steel is controlled will be described. (Hereinafter, the unit of each element content is% by weight).

Carbon (C): 0.001 to 0.02 wt%

C is dissolved in the steel or forms a carbide or the like. For excellent magnetic properties of the soft magnetic steel, it is preferable to be managed with extremely low carbon. If it is added in an amount exceeding 0.02%, the magnetic properties due to the formation of carbide will be deteriorated. If it is less than 0.001%, the productivity of the steel will be deteriorated. Therefore, the content of C is preferably 0.001 to 0.02% by weight.

Manganese (Mn): 0.05 to 0.1 wt%

Mn is an important component in the present invention and serves to inhibit abnormal crystal growth by forming MnS. However, when the Mn content is excessively higher than 0.1%, it is easy to form coarse MnS. Since MnS acts as a seed in which BN is precipitated, coarse MnS forms a coarse MnS and BN complex precipitate, which causes a problem that the electromagnetic characteristics are weakened. Therefore, the upper limit of the Mn content is preferably 0.1%. More preferably, it is 0.95%. And even more preferably 0.9%.

In addition, when Mn is added in an amount of less than 0.05%, it is difficult to control the manganese content, and MnS is not formed when added in a trace amount, which may cause high temperature deformation cracking due to S. Therefore, the lower limit of the Mn content is preferably 0.05%.

Silicon (Si): 0.1 to 0.7 wt%

Si is a widely used element for improving electromagnetic characteristics because it acts as an element that effectively reduces iron loss due to eddy currents. Also, it acts as a deoxidizing agent and has an effect of suppressing the magnetic property deterioration due to oxygen in the steel, so that it is preferably added at 0.1% or more. However, when Si is added in excess of 0.7%, the saturation magnetic flux density is lowered. Therefore, the content of Si is preferably 0.1 to 0.7% by weight.

Phosphorus (P): not more than 0.02% by weight

The phosphorus is inevitably contained as an impurity and is preferably controlled as low as possible. Theoretically, it is preferable to limit the phosphorus content to 0%, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the phosphorus content is preferably limited to 0.02 wt%. If the content of P is less than 0.001% by weight, the production cost of the refining process is greatly increased. Therefore, it is more preferable to control the P content to 0.001% to 0.02%.

Sulfur (S): 0.002 to 0.01%

S is inevitably contained in the manufacturing process. It is important to manage the upper limit. It is particularly important to control the upper limit of the S content of the steel to which 0.05 to 0.1% by weight of Mn of the present invention is added. When S is added in excess of 0.01%, all of MnS is not consumed and high temperature cracking due to S may occur. In order to suppress the abnormal crystal grain growth through MnS, which is contemplated in the present invention, it is preferable to add Mn in an amount of 0.002% or more. Therefore, the content of S is preferably 0.002 to 0.01% by weight.

Boron (B): 0.001 to 0.004 wt%

B forms BN and fixes N to prevent electromagnetic property embrittlement by N. And also plays a role of inhibiting abnormal crystal grain growth by forming BN. It is preferably added in an amount of 0.001% or more for the purpose of forming BN and N, and when the content exceeds 0.004%, the effect tends to saturate. Therefore, the content of B is preferably 0.001 to 0.004%.

Nitrogen (N): 0.002 to 0.005 wt%

N is preferably contained as little as possible because it embrits the electromagnetic characteristics, but it is inevitably contained inevitably in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the nitrogen content is preferably limited to 0.005%. If the content of N is less than 0.002% by weight, the manufacturing cost of the refining process is greatly increased and the effect of suppressing abnormal grain growth due to the formation of BN is insufficient. Therefore, the N content is preferably 0.002% to 0.005% Is more preferable.

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 microstructure of the steel material is a ferrite single phase. Since pearlite, carbide, or the like hinders electromagnetic characteristics, carbon added to the steel is preferably present in a solid state to form a ferrite single phase.

Further, the steel material includes a composite precipitate of MnS and BN, and the composite precipitate is a shape in which BN surrounds MnS.

The reason for the precipitation in the above-described form is that the precipitation temperature of MnS is high and precipitates first, and BN precipitates immediately after MnS precipitation.

The average size of the complex precipitates of MnS and BN is preferably 35 nm or less.

When the average size of the complex precipitates is more than 35 nm, there is a problem that the electromagnetic characteristics are weakened. If the composite precipitates are formed in a large amount exceeding 35 nm, the abnormal crystal growth can not be suppressed during hot forging or cold forging-annealing, which is a component manufacturing process, and electromagnetic characteristics are weakened. Therefore, the average size of the complex precipitates of MnS and BN is preferably 35 nm or less.

In order for the precipitates to prevent abnormal grain growth, the precipitates should be distributed evenly in a sufficient amount and at an appropriate size under operating conditions. And that the precipitates in the final product are not coarsened and do not degrade the electromagnetic properties.

The phase fraction of the MnS and BN complex precipitates is preferably 0.01 to 0.05% by area.

If the phase fraction of the complex precipitate is less than 0.01% by area, the amount of precipitate may be insufficient and it may not be effective in suppressing abnormal crystal growth. On the other hand, when it exceeds 0.05% by area, it is not preferable because it can act as a nonmetallic inclusion which causes deterioration of electromagnetic characteristics. Therefore, the phase fraction of the MnS and BN complex precipitates is preferably 0.01 to 0.05% by area.

The steel material is preferably in the form of a wire rod or a bar.

Unlike electrical steel sheets, semi-finished products such as wire and bar steel are subjected to hot forging or cold forging and annealing as post-processes. Accordingly, nonuniform deformation due to forging promotes abnormal crystal grain growth, and the deterioration of electromagnetic characteristics is further exacerbated by such microstructure. Therefore, the effect of suppressing the abnormal crystal grain growth according to the present invention can be more clearly shown in the case of the wire or bar shape.

Hereinafter, a method of manufacturing a soft magnetic steel material having excellent magnetic characteristics, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a soft magnetic steel having excellent electromagnetic characteristics, comprising the steps of: heating a steel billet satisfying the above composition at 1000 to 1200 캜;

Hot-rolling the heated billet to obtain a steel material; And

And cooling the hot-rolled steel at a cooling rate of 0.1 to 10 占 폚 / sec.

Heating step

And the billet satisfying the above-mentioned component system is heated to 1000 to 1200 占 폚. By heating the steel strip in the temperature range described above, the remaining segregation, carbides and inclusions can be effectively dissolved. When the heating temperature of the above-mentioned steel strip exceeds 1200 캜, the production operation is inefficient. On the other hand, if it is less than 1000 ° C, the above-mentioned effect due to heating may not be sufficient. Here, the term "steel" means all semifinished products such as blooms and billets, which can be produced from a wire rod or a bar.

Step of hot rolling to obtain steel

The hot-rolled steel strip as described above can be subjected to hot rolling. When the rolling temperature is lower than 800 ° C, the electromagnetic characteristics may be deteriorated due to the fine ferrite crystal grains. On the other hand, when the rolling temperature exceeds 1100 ° C, the mechanical properties of the wire rod and the steel rod are impaired due to the coarsening of the austenite grains. Therefore, the hot rolling is preferably performed at 800 to 1100 占 폚.

Cooling step

It is preferable to cool the hot-rolled wire as described above. At this time, when the cooling rate is less than 0.1 ° C / second, abnormal crystal growth during cooling can be promoted and the surface properties are lowered by scale formation. On the other hand, if it exceeds 10 ° C / second, crystal grain growth is suppressed, and the electromagnetic characteristics can be lowered. Therefore, the cooling rate is preferably in the range of 0.1 to 10 DEG C / sec. After the cooling step, the step of winding may be further included to facilitate the storage and movement of the cooled wire rod.

Hereinafter, a soft magnetic steel part having excellent magnetic properties, which is another aspect of the present invention, will be described in detail.

The soft magnetic steel part according to another aspect of the present invention satisfies the above-mentioned composition, the microstructure is a ferrite single phase, and the BN surrounds MnS.

The soft magnetic steel parts satisfying the above alloy composition and microstructure exhibit an excellent electromagnetic property with a magnetic flux density B ₁₀ of 1.2 Tesla or more.

The average size of the composite precipitates of MnS and BN in the soft magnetic steel component is preferably 35 nm or less. When the average size of the complex precipitates is more than 35 nm, there is a problem that the electromagnetic characteristics are weakened.

Hereinafter, a method for manufacturing a soft magnetic steel part, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a soft magnetic steel part having excellent electromagnetic characteristics, comprising the steps of: heating a steel material according to the present invention at 770 to 1200 ° C; Hot forging the heated steel to obtain a hot forging; Cooling the hot forging at a cooling rate of 0.1 to 10 ° C / second; And cold forging the cooled hot forging.

At this time, the heating and hot forging are preferably performed at 770 to 1200 ° C. When the heating temperature is less than 770 ° C, the effect of hot forging is small. Therefore, when the heating temperature exceeds 1200 ° C, MnS and BN are reused, and MnS and BN precipitation The effect of inhibiting abnormal crystal grain growth is low.

At this time, the cooling is preferably performed at a rate of 0.1 to 10 ° C / second. If it is less than 0.1 ° C / second, abnormal crystal grain growth during cooling can be promoted and the surface properties are lowered by scale formation. If it exceeds 10 DEG C / second, crystal grain growth is suppressed and the electromagnetic characteristics can be lowered.

Thereafter, the cooled hot forging is cold-forged to produce a soft magnetic steel part having excellent electromagnetic characteristics.

Meanwhile, after the step of cold forging, the step of heat-treating the cold-forged steel at 560 to 790 ° C may be further performed to manufacture a soft-magnetic steel part having excellent electromagnetic characteristics.

At this time, the heat treatment after the cold forging is preferably heat-treated at 560 to 790 ° C. If the heat treatment temperature is less than 560 캜, the internal stress disappearing rate is slow and the effect of improving the electromagnetic characteristics after the heat treatment is small. If the temperature exceeds 790 캜, recrystallization may occur due to the phase transformation.

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)

Steels of the component system described in Table 1 below were cast. Thereafter, it was heated at 1150 ° C by a conventional method, and hot-rolled to produce bars each having a diameter of 50 mm. Thereafter, the hot-rolled 50 mm bar was cooled at a temperature of 1050 DEG C at a rate of 5 DEG C / sec.

A pole segment (or claw pole) of the automotive alternator rotor was fabricated using the bar. A 50 mm bar was cut to a weight of 1.2 kg and heated to 1200 캜, which was subjected to hot forging in four steps. After hot forging, the coating was applied and cold forging was performed in three steps.

The average size of the complex precipitates of MnS and BN with respect to the bar steel, the electromagnetic characteristics of the forged workpiece and the occurrence of blast texture were observed, and the results are shown in Table 1 below.

The electromagnetic characteristics were obtained from ring solenoid specimens with an outer diameter of 45 mm, an inner diameter of 35 mm, and a thickness of 10 mm. The copper wire was observed for 20 times from the primary 100 times and the magnetic flux density - magnetic field strength curve from HH = 1000 A / m The magnetic flux density is defined as B ₁₀ and is shown in Table 1.

In the following Table 1, occurrence of coarse gravel texture was evaluated as occurrence of coarse grains in the case where the number of grains having a difference of 4 or more in ASTM standard relative to the average grain size was 20% or more of the total grain number at the magnification x50 optical microscope observation, , And when it is less than 20%, it is represented by X.

Fig. 1 shows the average size of composite precipitates of MnS and BN depending on the content of Mn in the B-added steel. Fig. 2 shows the precipitates in the steel extracted by using the Replica method by transmission electron microscopy And FIG. 3 shows the behavior of the precipitate depending on the temperature of the steel having the component of Inventive Example 3.

division C Mn Si P S B N Forged steel parts Steel Magnetic flux density
B ₁₀
(Tesla) Complexity
Occur Precipitate
Average size
(nm) Inventory 1 0.004 0.05 0.35 0.005 0.004 0.0020 0.0041 1.24 X 22.5 Inventory 2 0.004 0.08 0.42 0.005 0.004 0.0019 0.0038 1.22 X 26.4 Inventory 3 0.004 0.10 0.37 0.005 0.004 0.0020 0.0040 1.22 X 31.3 Comparative Example 1 0.004 0.01 0.34 0.005 0.004 0.0019 0.0041 1.11 O - Comparative Example 2 0.004 0.10 0.37 0.005 0.001 0.0021 0.0037 1.09 O - Comparative Example 3 0.004 0.14 0.38 0.005 0.004 0.0020 0.0040 1.14 O 58.5 Comparative Example 4 0.004 0.21 0.40 0.005 0.004 0.0021 0.0040 1.07 O 70.1 Comparative Example 5 0.004 0.40 0.40 0.005 0.004 0.0020 0.0042 1.04 O 81.6 Comparative Example 6 0.004 0.05 0.35 0.005 0.004 - 0.0039 0.98 O - Comparative Example 7 0.004 0.09 0.43 0.005 0.004 - 0.0041 0.97 O -

In Table 1, the unit of each element content is% by weight.

As can be seen from Table 1, the inventive inventions 1 to 3 have a magnetic flux density B ₁₀ of 1.22 to 1.24, and the magnetic flux density B ₁₀ of the comparative examples 1 to 7 have excellent electromagnetic characteristics as compared with 0.97 to 1.11. Inventive Example 1 to Inventive Example 3 satisfied the alloy composition of the present invention, so that the Mn content was low and B was added. Thereby effectively suppressing the abnormal crystal growth and ensuring excellent electromagnetic characteristics.

The average sizes of the MnS and BN complex precipitates according to the amount of Mn added are shown in FIG. 1 and Table 1 above. In the case of Inventive Examples 1 to 3 in which the Mn content was 0.05 to 0.1% or less, the mean size of the MnS and BN complex precipitates was 22.5 to 31.3 nm, and these fine precipitates prevent the abnormal crystal growth and improve the electromagnetic characteristics Able to know.

Also, by adding B, N dissolved in the steel was fixed to BN to improve the electromagnetic characteristics, and at the same time, the complex precipitates of MnS and BN suppressed the abnormal crystal growth, and the electromagnetic characteristics were improved.

In Comparative Example 1, the Mn content was below the range of the Mn content of the present invention, MnS was not sufficiently formed, blind spots due to abnormal crystal growth were generated, and electromagnetic characteristics were weakened due to S-induced electromagnetic characteristics.

In Comparative Example 2, the S content was less than the S content of the present invention, MnS was not sufficiently formed, and the blend due to the abnormal crystal growth occurred, resulting in the electromagnetic characteristics being deviated.

In Comparative Examples 3 to 5, when the Mn content exceeded the range of the present invention Mn content and the MnS and BN complex precipitates had an average size of 58.5 nm or more, the generation of blisters could not be suppressed and the magnetic flux density was decreased .

When B satisfies the Mn content proposed in the present invention, BN encompasses MnS at the center as shown in Fig. Fig. 2 shows the result of observation of a precipitate in a steel material extracted by the Replica method with a transmission electron microscope. In Fig. 2, the dark and dark color of the center of the precipitate is MnS and the light color of the periphery of the precipitate is BN.

The reason why the precipitate is precipitated as shown in FIG. 2 can be found from the precipitate behavior calculated by Thermocalc, a commercial software program for thermodynamics in FIG. As a result of observation of the precipitate behavior with the temperature of the steel having the component of Inventive Example 3, it was found that the precipitation temperature of MnS was high and precipitated first, and BN precipitated immediately after MnS precipitation. Transmission electron microscopy showed that MnS or BN precipitate alone existed, but the fraction of MnS and BN complex precipitates was high. It can be seen that when MnS is not finely controlled, the coarse precipitates do not play the role of inhibiting the abnormal crystal growth, and the electromagnetic characteristics may be degraded.

In Comparative Examples 6 and 7, it can be seen that not only the BN that inhibits the abnormal crystal growth but also the magnetic flux density dislocation caused by the solid solution N, which is a steel grade to which no B is added, is generated. It can be seen that it is possible to improve the electromagnetic characteristics by precipitating N into BN which can not be avoided as impurities during the forced production process.

It will be understood by 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 in the appended claims. It will be possible.

Claims (12)

0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, %, Balance Fe and other unavoidable impurities,
The microstructure is a ferrite single phase,
A complex precipitate of MnS and BN,
The composite precipitate is in the form of BN surrounding MnS, and the average size of the complex precipitates is 35 nm or less.
The method according to claim 1,
Wherein the phase fraction of the composite precipitates of MnS and BN is 0.01 to 0.05% by area.
delete The method according to claim 1,
Wherein the steel material is in the form of a wire rod or a bar steel.
0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, %, The balance Fe and other unavoidable impurities at 1000 to 1200 캜;
Hot-rolling the heated billet to obtain a steel material; And
And cooling the hot-rolled steel material at a cooling rate of 0.1 to 10 占 폚 / sec.
6. The method of claim 5,
Wherein the steel material is in the form of a wire rod or a bar steel.
0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, %, Balance Fe and other unavoidable impurities,
The microstructure is a ferrite single phase,
A complex precipitate of MnS and BN,
Wherein the composite precipitate is in the form that BN surrounds MnS, the average size of the complex precipitates is 35 nm or less, and the magnetic flux density B ₁₀ is 1.2 Tesla or more.
8. The method of claim 7,
Characterized in that the microstructure of the component has a grain size of less than 20% which is different from the average grain size by ASTM standard 4 or more.
8. The method of claim 7,
Wherein the phase fraction of the composite precipitates of MnS and BN is 0.01 to 0.05% by area.
delete 0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.001 to 0.004% of B, 0.05 to 0.10% of Mn, 0.1 to 0.7% of Si, %, Balance Fe and other unavoidable impurities,
The microstructure is a ferrite single phase,
A complex precipitate of MnS and BN,
Heating the steel material having an average size of the composite precipitate of 35 nm or less at 770 to 1200 ° C;
Hot forging the heated steel to obtain a hot forging;
Cooling the hot forging at a cooling rate of 0.1 to 10 ° C / second; And
And cold forging the cooled hot forging product.
12. The method of claim 11,
Further comprising the step of heat-treating the cold-forged steel material at 560 to 790 캜 after the cold forging.

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