KR20160082363A - Soft magnetic steel having excellent free cutting characteristics and method of manufacturing therof - Google Patents

Abstract

The present invention relates to a soft magnetic steel material and a manufacturing method thereof. The soft magnetic steel material has enhanced electromagnetic characteristics by adding Sn to develop a crystal texture seen in (100) and has enhanced free machining properties in accordance with the grain boundary segregation of Sn. According to an embodiment of the present invention, the soft magnetic steel material with excellent free machining properties includes: 0.001 to 0.01 wt% of C; 0.1 to 1.0 wt% of Mn; 0.03 to 1.0 wt% of Si; 0.02 to 0.1 wt% of Sn; 0.025% or less of P; 0.025 or less wt% of S; residual Fe; and other inevitable impurities. The microstructure of the soft magnetic steel material is in a ferrite phase.

Description

TECHNICAL FIELD [0001] The present invention relates to a soft magnetic steel material having excellent free cutting properties and a method of manufacturing the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

TECHNICAL FIELD The present invention relates to a soft magnetic steel having excellent free cutting and electromagnetic characteristics, and a method of manufacturing the same.

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. Electromagnetic properties required for steel materials to be used as electrical components are high permeability, high magnetic flux density, and low iron loss. In addition, in order to be produced in a complicated shape in accordance with demands for miniaturization and high precision, high free-cutting workability or monoaxiality is required.

Solenoid valves used in automotive anti-lock breaking systems (ABS), automatic fuel injectors, and active suspensions are required to improve the electromagnetic characteristics of component parts in order to achieve miniaturization and high precision. The wire rod used as the core of the solenoid valve and the iron core is utilized free cutting steel for the processing of conventional precision parts. General free-machining steel has an advantage in machining and machinability, but its magnetic properties are poor due to limited movement of magnetic domains by inclusions such as carbide and MnS. Despite the electromagnetic characteristics, the reason for using free cutting steel was to manufacture precision parts by minimizing machining error limit through cutting.

There has been an invention for improving the electromagnetic characteristics of the free cutting steel in order to solve the problem of opening the electromagnetic characteristics. The present invention has been made to commercialize a soft magnetic material having excellent free-cutting properties by adding Pb to a pure iron-based soft magnetic material, but has a problem of environmental pollution due to the addition of Pb.

Since Pb-free free cutting steel is required to be developed due to environmental pollution problems, Patent Document 1 discloses a sulfur soft-magnetic steel material using MnS by adding S to the soft magnetic steel. However, the sulfur soft magnetic steel has improved free cutting characteristics, but has a problem that the electromagnetic characteristics are heated by the MnS inclusions.

Accordingly, there is a demand for development of a soft magnetic steel material excellent in electromagnetic characteristics and free-cutting properties and a manufacturing method thereof without environmental pollution problems.

U.S. Published Patent Application No. 2007-0034300

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a Sn-Sn alloy having improved electromagnetic characteristics and improved free-cutting characteristics It is an object of the present invention to provide a soft magnetic steel and a manufacturing method thereof.

According to one aspect of the present invention, there is provided a soft magnetic steel having excellent free-cutting properties, comprising 0.001 to 0.01% of C, 0.1 to 1.0% of Mn, 0.03 to 1.0% of Si, 0.02 to 0.1% of Sn, 0.025% or less, S: 0.025% or less, the balance Fe and other unavoidable impurities, and the microstructure is a ferrite single phase.

The present invention also provides a method for producing a soft magnetic steel having excellent free-cutting properties, comprising the steps of: adding 0.001 to 0.01% of C, 0.1 to 1.0% of Mn, 0.03 to 1.0% of Si, 0.1%, P: not more than 0.025%, S: not more than 0.025%, the balance Fe and other unavoidable impurities at 1000 to 1200 占 폚; Hot-rolling the heated billet to obtain a steel material; And cooling the steel material at a cooling rate of 0.1 to 10 占 폚 / second.

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, by adding Sn to soft magnetic steel, it is possible to simultaneously improve the electromagnetic characteristics and free cutting ability, and there is no environmental pollution problem due to Pb, and Sn having a low melting point forms a thin film on the tool surface, There is an effect that improvement can be achieved. Therefore, it is possible to utilize the soft magnetic steel having excellent free cutting characteristics of the present invention as a component material such as a core and an iron core of a solenoid valve which requires precision parts machining.

Figure 1 is an inverse pole figure measured using EBSD. (a) is an inverse pole diagram of Inventive Example 2 in which Sn is added, and (b) is an inverse pole diagram of Comparative Example 1 in which Sn is not added.

The present inventors have recognized that the electromagnetic characteristics of the free cutting steel are in need of heat. In addition, soft magnetic materials with excellent electromagnetic properties have been found to be susceptible to free radicals. In order to simultaneously improve these conflicting characteristics, the inventors of the present invention have confirmed that, when the soft magnetic material is properly added with Sn, the above-mentioned conflicting characteristics can be improved at the same time, and the present invention has been achieved.

Specifically, Sn is an element segregating in grain boundaries, suppressing the diffusion of nitrogen through the grain boundaries, suppressing the <111> direction aggregate structure inhibiting the electromagnetic characteristics, and increasing the <100> direction aggregate structure Thereby improving the electromagnetic characteristics.

In addition, Sn improves free cutting. Generally, excellent free cutting characteristics means that a minimum production cost or a maximum production rate can be realized in machining. That is, it means that the tool life is long, the cutting force is low, and the surface roughness is excellent. Sn is segregated in grain boundaries to induce brittleness of the grain boundaries and can be processed with low cutting power. Especially, Sn is formed by forming a thin film on the tool surface by melting low melting point of Sn due to temperature rise due to cutting, Thereby contributing to improvement in tool life.

Hereinafter, a soft magnetic steel having excellent free-cutting properties 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 free-cutting properties, comprising 0.001 to 0.01% of C, 0.1 to 1.0% of Mn, 0.03 to 1.0% of Si, 0.02 to 0.1% of Sn, 0.025% or less, S: 0.025% or less, the balance Fe and other unavoidable impurities, and the microstructure is a ferrite single phase.

Hereinafter, the reason why the alloy composition of the steel is controlled will be described.

Carbon (C): 0.001 to 0.01 wt%

C is dissolved in the steel or forms carbides and the like. For excellent magnetic properties of the soft magnetic steel, it is preferable to be managed with extremely low carbon. However, if it is added in an amount exceeding 0.01%, the magnetic properties due to formation of carbides will be deteriorated. When the amount is less than 0.001%, the productivity of the steel is lowered because RH (Rheinstahl Hüttenwerke & Heraus) . Therefore, the content of C is preferably 0.001 to 0.01% by weight.

Manganese (Mn): 0.1 to 1.0 wt%

Mn not only acts as a deoxidizer but also has an effect of lowering the iron loss by increasing the resistivity. However, since the resistivity is lower than that of Si, it is generally added for the purpose of preserving the strength of the material. When a large amount of Mn is added, the iron loss tends to increase again. Therefore, it is preferable to control the iron loss to 1.0% or less. Also, when manganese is controlled to less than 0.1%, the productivity is lowered. Therefore, the content of Mn is preferably 0.1 to 1.0% by weight.

Silicon (Si): 0.03 to 1.0 wt%

Si is a widely used element for improving electromagnetic characteristics because it effectively reduces iron loss due to eddy currents. In addition, it also acts as a deoxidizing agent and has an effect of suppressing magnetic property deterioration due to oxygen in the steel, so that it is preferably added in an amount of 0.03% or more. However, since the saturation magnetic flux density is lowered by adding Si, it is preferable to limit the density to 1.0% or less for the magnetic flux density. Therefore, the content of Si is preferably 0.03 to 1.0% by weight.

Tin (Sn): 0.02 to 0.1 wt%

Sn is an important element in the present invention. As an element segregating in grain boundaries, it suppresses the diffusion of nitrogen through grain boundaries, suppresses the <111> directional texture which inhibits the electromagnetic characteristics, and the <100> To improve the electromagnetic characteristics.

In addition, Sn improves free cutting. Generally, excellent free cutting characteristics means that a minimum production cost or a maximum production rate can be realized in machining. That is, it means that the tool life is long, the cutting force is low, and the surface roughness is excellent. Sn is segregated in grain boundaries to induce brittleness of the grain boundaries and can be processed with low cutting power. Especially, Sn is formed by forming a thin film on the tool surface by melting low melting point of Sn due to temperature rise due to cutting, Thereby contributing to improvement in tool life.

However, when the content of Sn is more than 0.1%, there is a problem that crystal grain growth is suppressed and the electromagnetic characteristics are lowered and the rolling property is deteriorated. Therefore, the upper limit of the Sn content is preferably 0.1 wt%. More preferably 0.08% by weight.

On the other hand, when the content of Sn is less than 0.02%, the effect of improving magnetic properties and free cutting properties is not sufficient. Therefore, the lower limit of the content of Sn is preferably 0.02% by weight. More preferably 0.04% by weight.

Phosphorus (P): 0.025% by weight or less

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 0.025 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 0.025%.

Sulfur (S): 0.025% by weight or less

The sulfur is inevitably contained and is preferably controlled as low as possible. Theoretically, it is advantageous to limit the content of sulfur 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 sulfur content is preferably limited to 0.025 wt%. If the content of S is less than 0.001% by weight, the production cost of the refining process is greatly increased. Therefore, the content of S is more preferably controlled to 0.001% to 0.02%.

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.

In addition, Sb may be further included within a range that the sum of Sn and Sb contents is 0.02 to 0.1% by weight or less.

Sb is an element segregated in grain boundaries as well as Sn, suppressing the diffusion of nitrogen through grain boundaries, suppressing <111> aggregate structure detrimental to magnetism, enhancing magnetic properties by increasing <100> Free cutting ability can be improved.

However, when the sum of the content of Sn and the content of Sb exceeds 0.1%, the grain growth is inhibited and the electromagnetic characteristics are deteriorated and the rolling property is deteriorated. Therefore, the upper limit of the sum of Sn and Sb content is preferably 0.1 wt%. More preferably 0.08% by weight.

On the other hand, when the sum of Sn and Sb contents is less than 0.02%, the effect of improving magnetic properties and free-cutting properties is not sufficient. Therefore, the lower limit of the sum of the contents of Sn and Sb is preferably 0.02% by weight. More preferably 0.04% by weight.

It is preferable that the microstructure of the steel material is a ferrite single phase. Ferrite and other non-ferrite pearlite are present, the electromagnetic characteristics are inferior. When C above the solubility in Fe is added to form pearlite or carbide, the electromagnetic characteristics are poor.

In addition, it is preferable that the steel has an aggregate structure in which the <100> aggregate fraction is higher than the <111> aggregate fraction in the rolling direction. The orientation in the < 100 > direction, which is the direction of easy magnetization, can be improved to simultaneously improve iron loss and magnetic flux density.

In addition, the steel material according to the present invention may have a magnetic flux density B ₅₀ of 1.65 Tesla or more when the magnetic field H = 5,000 A / m is applied.

In addition, the steel material according to the present invention may have a number of free-machining sites represented by the following relational formula 1: 104% or more.

[Relation 1]

(Where A denotes the steel material, B denotes a steel material having an alloy composition excluding Sn and Sb alloy components in A steel, CF denotes a cutting force, SR denotes surface roughness, (A ₁ = 0.6, a ₂ = 0.2, and a ₃ = 0.2).

As shown in the above-mentioned relational expression 1, the free cutting tool index can express the machinability of the workpiece B, which is the object to be evaluated, with respect to the workpiece A by relative comparison.

A ₁ , a ₂ , and a ₃ are factors indicating the relative importance of cutting force, surface roughness, Generally, consumers can weight according to the purpose of use. In the present invention, a ₁ , a ₂ , and a ₃ are set to 0.6, 0.2, and 0.2, respectively.

Further, the steel material according to the present invention is preferably in the form of a wire rod or a bar.

This is because, in the case of the wire rod or the bar-shaped form, the work requiring the free cutting is accompanied.

Hereinafter, a method of manufacturing a soft magnetic steel having excellent free-cutting 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 for manufacturing a soft magnetic steel having excellent free cutting characteristics, comprising the steps of: heating a 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 steel strip exceeds 1200 캜, the austenite grains are coarsened and the fraction of the grain boundaries becomes small, so that the grain boundary of Sn or Sb is deepened and the hot rolling property can be inhibited. 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 steel as described above. At this time, when the cooling rate is less than 0.1 ° C / second, the mechanical properties of the wire rod and the steel rod due to grain growth are deteriorated. On the other hand, if it exceeds 10 DEG C / second, internal cracking due to generation of low-temperature structure and grain boundary brittleness may occur. Therefore, the cooling rate is preferably in the range of 0.1 to 10 DEG C / sec. The cooling step may further include a step of winding after cooling to facilitate storage and movement of the cooled steel.

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, the laminate was heated at 1100 DEG C by a conventional method, and the hot-rolled 10 mm wire at a temperature of 1000 DEG C was cooled at a rate of 2 DEG C / sec and wound.

The magnetic flux density, iron loss, free cutting ability index, and fraction of <100> texture and <111> texture of the wire were compared with each other in Table 2 below.

The specimens were measured by electrospinning of specimens of 5 mm x 5 mm x 1 mm in thickness perpendicular to the rolling direction. The magnetic flux density B ₅₀ is a magnetic flux density induced when a magnetic field was applied in the 5000 A / m, the iron loss W _10/50 is the average of the iron loss when the induced magnetic flux density of 1.0 Tesla at 50Hz frequency.

For the free-cutting evaluation, 8 mm CD-bar was manufactured and evaluated for free-cutting. The free cutting edge index can be obtained by the following relational expression 1, and the machinability of the workpiece B to be evaluated with respect to the workpiece A can be expressed by relative comparison. In Table 2, the reference material 1 is referred to as A, and the values calculated based on the respective inventive and comparative examples are shown.

[Relation 1]

Where CF is the cutting force, SR is the surface roughness, and TL is the tool life. a ₁ , a ₂ , and a ₃ are factors indicating the relative importance of machinability evaluation criteria, surface roughness, and tool life, respectively. Generally, consumers can assign weights according to the purpose of use. In this embodiment, a ₁ , a ₂ , and a ₃ are given as 0.6, 0.2, and 0.2, respectively.

The texture of the texture was compared with the intensity of the <100> and <111> directional texture through the inverse pole figure using electron backscatter diffraction (EBSD).

division Alloy composition (% by weight) C Mn Si P S Sn Sb Inventory 1 0.004 0.30 0.10 0.005 0.004 0.04 - Inventory 2 0.004 0.28 0.62 0.005 0.004 0.04 - Inventory 3 0.004 0.28 0.89 0.005 0.004 0.04 - Honorable 4 0.004 0.31 0.09 0.005 0.004 0.06 - Inventory 5 0.004 0.31 0.57 0.005 0.004 0.06 - Inventory 6 0.004 0.29 0.90 0.005 0.004 0.06 - Honorable 7 0.004 0.30 0.10 0.005 0.004 0.08 - Honors 8 0.004 0.30 0.56 0.005 0.004 0.08 - Proposition 9 0.004 0.30 0.90 0.005 0.004 0.08 - Inventory 10 0.004 0.28 0.59 0.005 0.004 0.02 - Exhibit 11 0.004 0.30 0.59 0.005 0.004 0.10 - Inventory 12 0.004 0.29 0.60 0.005 0.004 0.04 0.04 Comparative Example 1 0.004 0.28 0.56 0.005 0.004 - - Comparative Example 2 0.004 0.30 0.87 0.005 0.004 - - Comparative Example 3 0.004 0.28 0.57 0.005 0.004 0.12 - Comparative Example 4 0.004 0.28 0.58 0.005 0.004 0.015 - Comparative Example 5 0.004 0.30 0.61 0.005 0.004 0.01 0.005 Comparative Example 6 0.004 0.30 0.60 0.005 0.004 0.06 0.06

division Magnetic flux density B ₅₀
(Tesla) Iron loss W _10/50
(W / kg) Free-spawning index
(%) Organized organization
Fraction comparison Inventory 1 1.71 6.0 110 V ₁₀₀ > V ₁₁₁ Inventory 2 1.68 5.4 106 V ₁₀₀ > V ₁₁₁ Inventory 3 1.65 5.1 105 V ₁₀₀ > V ₁₁₁ Honorable 4 1.73 5.7 114 V ₁₀₀ > V ₁₁₁ Inventory 5 1.70 5.4 110 V ₁₀₀ > V ₁₁₁ Inventory 6 1.68 4.8 109 V ₁₀₀ > V ₁₁₁ Honorable 7 1.74 5.7 116 V ₁₀₀ > V ₁₁₁ Honors 8 1.71 5.2 113 V ₁₀₀ > V ₁₁₁ Proposition 9 1.69 4.8 111 V ₁₀₀ > V ₁₁₁ Inventory 10 1.66 5.4 104 V ₁₀₀ > V ₁₁₁ Exhibit 11 1.70 5.2 118 V ₁₀₀ > V ₁₁₁ Inventory 12 1.69 5.2 113 V ₁₀₀ > V ₁₁₁ Comparative Example 1 1.61 6.1 100 V ₁₀₀ < V ₁₁₁ Comparative Example 2 1.60 5.4 96 V ₁₀₀ < V ₁₁₁ Comparative Example 3 * Rolling defect
Occur - -  - Comparative Example 4 1.63 6.1 100 V ₁₀₀ < V ₁₁₁ Comparative Example 5 1.63 6.1 99 V ₁₀₀ < V ₁₁₁ Comparative Example 6 * Rolling defect
Occur

As shown in Table 2, both the magnetic flux density, the iron loss, and the free cutting index were improved as the amount of Sn + Sb was increased in the same component system. However, in the case of Comparative Example 3, Sn was added in an amount of 0.12%, which exceeded the Sn content range of the present invention and resulted in rolling flaws on the surface. In Comparative Example 6, Sn + Sb was added in an amount of 0.12%, which exceeded the content range of Sn + Sb of the present invention, resulting in rolling flaws on the surface.

According to the embodiment of the present invention, it can be seen that as Si is added in the same component system, the magnetic flux density becomes brittle and the iron loss improves. However, in Inventive Example 3, Inventive Example 6 and Inventive Example 9, it can be seen that both the magnetic flux density and the iron loss were improved in spite of the high Si content as compared with Comparative Example 1. [

As can be seen from FIG. 1 (a), which is the result of XRD comparison of Inventive Example 2, when the content of Sn + Sb of the present invention is satisfied, <100> aggregate structure develops in the rolling direction and magnetic flux density and iron loss are improved will be. On the other hand, FIG. 1- (b) is the XRD analysis result of Comparative Example 1, and it can be confirmed that the <111> aggregate fraction is higher than the <100> aggregate fraction and the magnetic flux density and iron loss are heat-treated.

It is also confirmed that the freeze-drying index is higher in the case of Sn + Sb added than the comparative example. The improvement in the free cutting surface index is due to the fact that Sn + Sb segregated in the grain boundaries lowers the cutting force and increases the tool life.

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 (9)

0.001 to 0.01% of C, 0.1 to 1.0% of Mn, 0.03 to 1.0% of Si, 0.02 to 0.1% of Sn, 0.025% or less of P and 0.025% or less of S, the balance Fe and other unavoidable impurities Characterized in that the microstructure is a ferrite single phase.
The method according to claim 1,
The steel material further comprises Sb, and the sum of Sn and Sb contents is 0.02 to 0.1%.
The method according to claim 1 or 2, wherein
Wherein the steel has an aggregate structure in which the <100> aggregate fraction is higher than the <111> aggregate fraction in the rolling direction.
3. The method according to claim 1 or 2,
Wherein the steel has a magnetic flux density B ₅₀ of 1.65 Tesla or more at a magnetic field H = 5,000 A / m, and has excellent free-cutting characteristics.
3. The method according to claim 1 or 2,
Wherein the steel material has a number of free-machining sites expressed by the following relational expression (1): 104% or more.
[Relation 1]

(Where A denotes the steel material, B denotes a steel material having an alloy composition excluding Sn and Sb alloy components in A steel, CF denotes a cutting force, SR denotes surface roughness, (A ₁ = 0.6, a ₂ = 0.2, and a ₃ = 0.2).
3. The method according to claim 1 or 2,
Wherein the steel material is in the form of a wire rod or a bar steel.
0.001 to 0.01% of C, 0.1 to 1.0% of Mn, 0.03 to 1.0% of Si, 0.02 to 0.1% of Sn, 0.025% or less of P and 0.025% or less of S, the balance Fe and other unavoidable impurities Heating the billet at 1000 to 1200 占 폚;
Hot-rolling the heated billet to obtain a steel material; And
And cooling the steel material at a cooling rate of 0.1 to 10 占 폚 / second.
8. The method of claim 7,
Wherein the steel further comprises Sb, and the sum of Sn and Sb is 0.02 to 0.1%.
9. The method according to claim 7 or 8,
Wherein the steel material is in the form of a wire rod or a bar steel.

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