KR101646545B1 - Medium carbon pearlite steel and the method of preparing the same - Google Patents

Abstract

One embodiment of the present invention is a steel sheet comprising, by weight percent, 0.3 to 0.418 weight% of C, 0.2 to 0.5 weight% Si, 1.0 to 3.0 weight% of Mn, 1.5 to 2.5 weight% of Al, 0.5 to 1.5 weight% of Cr, , Co: 1.5 to 2.5 wt%, the balance Fe and other unavoidable impurities.

Description

Technical Field [0001] The present invention relates to a carbonaceous pearlite steel and a method for manufacturing the same. BACKGROUND ART [0002]

One embodiment of the present invention relates to heavy carbon perlite steel and a method of manufacturing the same.

One embodiment of the present invention relates to heavy carbon perlite steel and a method of making the same. Perlite structure is a typical microstructure found in most steels. Such a pearlite structure contains about 0.8% by weight of carbon, and has a high hardness and strength, but is fragile.

In the case of pearlite steel, it is known that the structure of wire after drawing is the most improved structure. In the case of pearlite steel, it has superior work hardenability and high strength compared with other steels, and has a moderate level of ductility. Therefore, the structure is widely used for tire cords, springs, wire ropes, leg cables, and rail rails.

However, since the cementite structure is increased due to the inclusion of a high content of carbon, there is a problem of low ductility and toughness although the strength is high.

Thus, the ductility of pearlite steels depends mainly on the carbon content, so that the development of low carbon content pearlite steels can satisfy the appropriate strength and elongation combination for the mechanical properties of the steel grade.

However, although low carbon content pearlitic steels can be produced through rapid cooling, such rapid cooling is difficult to achieve in thick sheet form steels. In addition, heat treatment is required to maintain the temperature at a low temperature so that the cooling structure does not appear.

Accordingly, there is a demand for the development of heavy carbon pearlite steel which can be produced by a conventional steel manufacturing method such as casting, melting, and rolling while having excellent economical efficiency by using Fe as a main component and minimizing the addition of expensive alloying elements.

Carbon perlite steel and a method for producing the same.

The heavy carbon perlite steel according to one embodiment of the present invention comprises 0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 3.0 wt% of Al, 2.5 to 2.5 wt.%, Cr: 0.5 to 1.5 wt.%, Co: 1.5 to 2.5 wt.%, Balance Fe and other unavoidable impurities.

The heavy carbon pearlite steel may provide a heavy carbon pearlite steel having a pearlite structure of 80 to 100% and a remainder of a ferrite structure.

And the intermediate interfacial spacing of the heavy carbon perlite steel is 100 to 115 nm.

Wherein the heavy carbon perlite steel has a tensile strength of 850 to 950 MPa.

The heavy carbon perlite steel may have an elongation of 10-15%.

0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 2.5 wt% of Al, 0.5 to 1.5 wt% of Cr, Co: 1.5 to 2.5% by weight, the balance Fe and other unavoidable impurities; Hot rolling the melt; Annealing the hot-rolled steel sheet; And cooling the annealed steel sheet; To provide a method for producing carbon mid-pearlite steel.

Hot rolling the melt; , The molten steel is hot-rolled in a temperature range of 950 to 1100 占 폚.

Hot rolling the melt; , The molten metal is hot-rolled at a reduction ratio of 60 to 70%.

Annealing the hot-rolled steel sheet; , The hot-rolled steel sheet is annealed in a temperature range of 900 to 1300 ° C.

Annealing the hot-rolled steel sheet; , The hot-rolled steel sheet is maintained in the annealing temperature range for 30 minutes to 2 hours.

Cooling the annealed steel sheet; , The annealed steel sheet is cooled at a speed range of 50 to 150 DEG C / h.

The heavy carbon pearlite steel may have a pearlite structure of 80 to 100% and the remainder may include a ferrite structure.

And the interfacial distance in the texture of the heavy carbon perlite steel is 100 to 115 nm.

Wherein the heavy carbon perlite steel has a tensile strength of 850 to 950 MPa.

And the medium carbon pearlite steel has an elongation of 10 to 15%.

According to one embodiment of the present invention, it is an object of the present invention to secure ductility by adding aluminum, manganese, and cobalt while maintaining the strength of pearlite steel containing about 0.8 wt% of carbon.

In other words, by transferring the vacancy composition through the addition of aluminum, manganese, and cobalt to the medium carbon, low-pore content pearlite steels can be developed. This can secure not only the strength and hardness of pearlite steel as a vacancy composition but also the ductility by lowering the carbon content. Accordingly, the heavy carbon perlite steel disclosed in the present invention can be used as a structural steel.

In addition, the pearlite steel according to an embodiment of the present invention has Fe as a main component and minimizes the addition of expensive alloying elements, thereby providing excellent economic efficiency. In addition, a separate manufacturing method is not required, and can be manufactured by a conventional steel manufacturing method such as casting, melting, and rolling.

Fig. 1 shows microstructure of Invention Material 1 observed.
2 shows the microstructure of the comparative material 1 observed.

The heavy carbon perlite steel according to one embodiment of the present invention comprises 0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 3.0 wt% of Al, 2.5 to 2.5 wt.%, Cr: 0.5 to 1.5 wt.%, Co: 1.5 to 2.5 wt.%, Balance Fe and other unavoidable impurities.

The reasons for limiting the composition will be described below.

C: 0.3 to 0.418 wt%

Carbon is an essential element added to ensure strength of the steel.

In order to obtain such an effect in the present invention, it is preferable that the content is 0.3 wt% or more. On the other hand, when it exceeds 0.418% by weight, carbides in pearlite are formed to reduce the phase-to-phase compatibility with the precipitate, and the hot rolling property and the room temperature ductility may be lowered. In addition, there is a problem of drastically increasing the strength in the mouth to reduce the ductility. Therefore, the carbon content is preferably 0.418 wt% or less.

More specifically, the content of carbon may be 0.4 to 0.418% by weight.

Si: 0.2 to 0.5 wt%

Si plays a role of stabilizing the layered structure in the pearlite structure and suppressing the strength reduction, in addition to the effect of strengthening the solid solution. However, the elongation can be lowered when added in a large amount.

Therefore, in one embodiment of the present invention, silicon may be contained in an amount of 0.2 to 0.5% by weight. When the content of silicon is less than 0.2% by weight, the desired strength can not be secured, while when it is more than 0.5% by weight, the elongation can be lowered. More specifically, silicon may comprise from 0.24 to 0.4% by weight.

Mn: 1.0 to 3.0 wt%

Manganese, like the aluminum described below, serves to transfer the vacancy composition to the medium carbon. In other words, it serves to suppress the generation of pro-eutectoid ferrite.

However, if the content of manganese is less than 1.0 wt%, the generation of pro-eutectoid ferrite can not be inhibited and the strength may be lowered. If the content is more than 3.0 wt%, low temperature structure may be caused during cooling. More specifically, manganese may comprise 2.0 to 3.0 wt%.

Al: 1.5 to 2.5 wt%

Aluminum, like manganese, is an element for transferring the vacancy composition to the medium carbon.

Thus, if the aluminum content is less than 1.5% by weight, it may be difficult to transfer the vacancy composition toward the medium carbon. On the other hand, if it exceeds 2.5% by weight, delta-ferrite can be included because heat treatment at a high temperature suppresses austenite transformation. More specifically, the content of aluminum may include 1.8 to 2.5% by weight. More specifically, the aluminum content may comprise from 2.0 to 2.5% by weight.

Cr: 0.5 to 1.0 wt%

In the case of Cr, the interfacial distance between the carbides inside the pearlite structure is reduced to improve the strength.

Therefore, when the content of carbon is less than 0.5% by weight, desired strength may not be obtained, and when it is more than 1.0% by weight, low-temperature structure may be caused.

Co: 1.5 to 2.5 wt%

In the case of Co, it lowers the vacancy composition of carbon to increase the driving force for the formation of pearlite structure and to accelerate the pearlite structure formation rate.

Therefore, when it is less than 1.5% by weight, 80% or more of pearlite structure may not be produced, and when it is added by more than 2.5% by weight, the cost of the steel may be greatly increased and it may be economically disadvantageous. More specifically, the content of cobalt may include 1.8 to 2.3% by weight.

In addition, the heavy carbon pearlite steel can provide heavy carbon pearlite steel in which the pearlite structure of 80 to 100% of the whole structure and the remainder are composed of ferrite.

In addition, the heavy carbon perlite steel may have a interfacial spacing of 100 to 115 nm in the texture.

The interface refers to the interface between the carbides in the present specification, and the meaning of the interface referred to in this specification will be omitted herein.

The pearlite structure of the heavy carbon pearlite steel is 80 to 100%, and the pearlite structure enhances the strength. However, brittleness can be increased due to high strength.

The proportion of the pearlite structure in the pearlite structure can be obtained in the case of the vacancy composition, but the heavy carbon perlite steel according to one embodiment of the present invention is a medium carbon steel through the addition of aluminum and manganese, Lt; / RTI >

Thus, through the pearlite structure and interfacial spacing of the above ratio, a tensile strength of 850 to 950 MPa can be obtained and an elongation of a medium carbon steel size can be obtained.

Thus, the medium carbon pearlite steel can obtain an elongation of 10 to 15%. The elongation means the rate at which the material is stretched during the tensile test. In other words, assuming that the length of the rod is L when a force is applied to both ends of a steel sheet having an initial length L ₀ , the increased length is L- L ₀ , And the elongation means that (L-L ₀ ) / L ₀ is expressed as a percentage.

In addition, the elongation described in this specification means the elongation of the specimen corresponding to ASTM No. 4, and the elongation was performed at a rate of 3 mm per minute.

By having an elongation in the above range, it is possible to maintain the strength at the time of vacancy formation and to have an elongation as large as that of the medium carbon steel.

Further, it can be used as a structural steel through the above range of tensile strength and elongation.

Hereinafter, a method for producing heavy carbon perlite steel according to an embodiment of the present invention will be described.

0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 2.5 wt% of Al, 0.5 to 1.5 wt% of Cr, Co: 1.5 to 2.5% by weight, the balance Fe and other unavoidable impurities; Hot rolling the melt; Annealing the hot-rolled steel sheet; And cooling the annealed steel sheet; To provide a method for producing carbon mid-pearlite steel.

The description of the composition is the same as that of the heavy carbon perlite steel according to the embodiment of the present invention described above, and its explanation is omitted.

Also, there is provided a method of manufacturing a hot rolled steel sheet, in,

The melt can be hot rolled at a reduction rate of 60 to 70% at a temperature range of 950 to 1100 占 폚.

The temperature range of the molten metal is 950 to 1100 占 폚, which is a temperature for heating carbon steel containing 0.3 to 0.5% by weight to the austenite region.

Further, cracks can be prevented from occurring when the molten metal is rolled at a reduction ratio of 60 to 70%.

Annealing the hot-rolled steel sheet; By this,

The hot-rolled steel sheet can be maintained in the temperature range of 900 to 1300 DEG C for 30 minutes to 2 hours.

When maintained in the above-mentioned temperature range, the crystal grains are not coarsened and may have the effect of relieving the stress.

Cooling the annealed steel sheet; By this,

The annealed steel sheet can be cooled in the range of 50 to 150 DEG C / h.

Other microstructures such as bainite can be precipitated when the cooling rate is cooled above a 150 ° C / h rate, and when cools below 50 ° C / h, coarse pearlite textures .

Wherein the heavy carbon pearlite steel has a pearlite structure of 80 to 100% of the entire structure and the remainder is composed of a ferrite structure.

Also, the interfacial spacing of the heavy carbon perlite steel may be 100 to 115 nm.

The intermediate carbon perlite steel having a tensile strength of 850 to 950 MPa through the microstructure and intra-structure interfacial spacing of the heavy carbon perlite steel.

Further, the heavy carbon pearlite steel has an elongation of 10 to 15%.

The structural fraction of the steel sheet, the interfacial spacing between carbides, and the test results of the mechanical properties test are the same as those of the heavy carbon perlite steel according to one embodiment of the present invention, and the description thereof is omitted.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid an undesirable interpretation of the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. Also, singular forms include plural forms unless the context clearly dictates otherwise.

Hereinafter, the embodiment will be described in detail. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 2.5 wt% of Al, 0.5 to 1.5 wt% of Cr, 1.5 to 2.5 wt% of Co, %, The balance Fe, and other unavoidable impurities.

The melt was hot-rolled at a temperature of 1050 占 폚 at a reduction ratio of 70%.

The hot-rolled steel sheet was annealed at 1000 ° C for 1 hour.

The annealed steel sheet was cooled at a rate of 110 ° C / h.

The composition ranges of the steel sheets produced under the above conditions are shown in Table 1. Table 2 shows the test results of the structural fraction of the steel sheet having the composition range shown in Table 1, the interfacial distance between the carbides, and the mechanical property test results.

C Si Mn Al Cr Co Inventory 1 0.418 0.248 2.51 2.47 1.0 1.9 Inventory 2 0.397 0.252 1.5 2.42 1.0 2.4 Comparison 1 0.421 0.247 2.57 2.43 1.0 - Comparative material 2 0.61 0.243 1.99 2.49 1.0 1.8 Comparative material 3 0.25 0.240 2.48 2.43 1.0 1.9

Table 1 shows the composition range of the steel sheet produced under the conditions of the above examples. The units of the compositions omitted in the above Table 1 are% by weight, and the balance not shown in Table 1 includes Fe and other unavoidable impurities.

Table 2 shows the results of the structural fraction of the steel sheet, the interfacial distance between the carbides, and the mechanical characteristics test results corresponding to the above composition ranges.

Perlite fraction (%) Interfacial spacing (nm) Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Inventory 1 85% 113 nm 914 567 12.1 Inventory 2 83% 108 nm 923 573 11.3 Comparison 1 58% 103 nm 764 385 16.2 Comparative material 2 100% 130nm 920 712 8.8 Comparative material 3 31% 105 nm 511 333 31

As shown in Table 2, it can be seen that the strengths of the inventive material 1 and the inventive material 2 having higher pearlite fractions are higher than those of the comparative material 1 and the comparative material 3. However, in the case of the comparative material 2, as shown in Table 1, since it contains 0.61% of carbon, the pearlite fraction is high, but the ductility is deteriorated by formation of carbide in pearlite.

On the other hand, in the case of Comparative Material 3, as shown in Table 1, it contains 0.25 wt% of carbon. Since the carbon content of the comparative material 3 is lower than the vacancy composition, it contains a large amount of pro-eutectoid ferrite structure. Therefore, as shown in Table 2, it can be seen that the yield strength and tensile strength of Comparative Material 3 are the lowest.

In addition, Inventive material 1 in Table 1 above contains 1.9% by weight of cobalt unlike comparative material 1. Thus, it can be seen that the pearlite fraction is higher than the comparative material 1 and the tensile strength is also increased.

As shown in Table 1, since the Al composition range of the comparative member 1 and the comparative member 3 exceeds 2.0 wt%, the process of reverse-transformation into austenite is suppressed while maintaining at a high temperature of 1000 캜, - It can be seen that the ferrite is left and the strength is lowered.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (15)

0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 2.5 wt% of Al, 0.5 to 1.5 wt% of Cr, Co: 1.5 to 2.5% by weight, the balance being Fe and other unavoidable impurities,
The heavy carbon pearlite steel has a pearlite structure of 80 to 100% and the remainder is composed of a ferrite structure,
Wherein said heavy carbon perlite steel has an interfacial spacing in the range of 100 to 115 nm.
delete delete The method according to claim 1,
Wherein the heavy carbon perlite steel has a tensile strength of 850 to 950 MPa.
5. The method of claim 4,
Said heavy carbon perlite steel having an elongation of 10-15%.
0.3 to 0.418 wt% of C, 0.2 to 0.5 wt% of Si, 1.0 to 3.0 wt% of Mn, 1.5 to 2.5 wt% of Al, 0.5 to 1.5 wt% of Cr, Co: 1.5 to 2.5% by weight, the balance Fe and other unavoidable impurities;
Hot rolling the melt;
Annealing the hot-rolled steel sheet; And
And cooling the annealed steel sheet,
Cooling the annealed steel sheet; in,
The annealed steel sheet is cooled at a speed range of 50 to 150 DEG C / h,
The produced medium carbon pearlite steel has a pearlite structure of 80 to 100% and the remainder is composed of a ferrite structure,
The interfacial spacing in the tissue is between 100 and 115 nm
A method for producing medium carbon perlite steel.
The method according to claim 6,
Hot rolling the melt; in,
Wherein the molten metal is hot-rolled in a temperature range of 950 to 1100 占 폚,
A method for producing medium carbon perlite steel.
8. The method of claim 7,
Hot rolling the melt; in,
Wherein the molten metal is hot-rolled at a reduction ratio of 60 to 70%
A method for producing medium carbon perlite steel.
9. The method of claim 8,
Annealing the hot-rolled steel sheet; in,
Wherein the hot-rolled steel sheet is annealed in a temperature range of 900 to 1300 DEG C,
A method for producing medium carbon perlite steel.
10. The method of claim 9,
Annealing the hot-rolled steel sheet; in,
Wherein the hot-rolled steel sheet is maintained in the annealing temperature range for 30 minutes to 2 hours.
delete delete delete 11. The method of claim 10,
Wherein said heavy carbon perlite steel has a tensile strength of 850 to 950 MPa.
15. The method of claim 14,
Wherein said heavy carbon perlite steel has an elongation of 10-15%.

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